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| committer | Roger Frank <rfrank@pglaf.org> | 2025-10-15 01:53:33 -0700 |
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diff --git a/old/22657-8.txt b/old/22657-8.txt new file mode 100644 index 0000000..74d76d1 --- /dev/null +++ b/old/22657-8.txt @@ -0,0 +1,18473 @@ +Project Gutenberg's Steam, Its Generation and Use, by Babcock & Wilcox Co. + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Steam, Its Generation and Use + +Author: Babcock & Wilcox Co. + +Release Date: September 18, 2007 [EBook #22657] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK STEAM, ITS GENERATION AND USE *** + + + + +Produced by Juliet Sutherland, Tony Browne, and the Online +Distributed Proofreading Team at http://www.pgdp.net + + + + + + + + + +STEAM + +ITS GENERATION AND USE + +[Illustration] + +THE BABCOCK & WILCOX CO. +NEW YORK + + + + +Thirty-fifth Edition + +4th Issue + +Copyright, 1919, by The Babcock & Wilcox Co. + + * * * * * + +Bartlett Orr Press + +New York + + + + +THE BABCOCK & WILCOX CO. + +85 LIBERTY STREET, NEW YORK, U. S. A. + +_Works_ + +BAYONNE NEW JERSEY +BARBERTON OHIO + +_Officers_ + +W. D. HOXIE, _President_ +E. H. WELLS, _Chairman of the Board_ +A. G. PRATT, _Vice-President_ + +_Branch Offices_ + +ATLANTA Candler Building +BOSTON 35 Federal Street +CHICAGO Marquette Building +CINCINNATI Traction Building +CLEVELAND New Guardian Building +DENVER 435 Seventeenth Street +HAVANA, CUBA 104 Calle de Aguiar +HOUSTON Southern Pacific Building +LOS ANGELES I. N. Van Nuy's Building +NEW ORLEANS Shubert Arcade +PHILADELPHIA North American Building +PITTSBURGH Farmers' Deposit Bank Building +SALT LAKE CITY Kearns Building +SAN FRANCISCO Sheldon Building +SEATTLE L. C. Smith Building +TUCSON, ARIZ. Santa Rita Hotel Building +SAN JUAN, PORTO RICO Royal Bank Building + +_Export Department, New York: Alberto de Verastegni, Director_ + +TELEGRAPHIC ADDRESS: FOR NEW YORK, "GLOVEBOXES" +FOR HAVANA, "BABCOCK" + +[Illustration: Works of The Babcock & Wilcox Co., at Bayonne, New Jersey] + +[Illustration: Works of The Babcock & Wilcox Co., at Barberton, Ohio] + +[Illustration: Works of Babcock & Wilcox, Limited, Renfrew, SCOTLAND] + + + + +BABCOCK & WILCOX Limited + +ORIEL HOUSE, FARRINGDON STREET, LONDON, E. C. +WORKS: RENFREW, SCOTLAND + +_Directors_ + +JOHN DEWRANCE, _Chairman_ CHARLES A. KNIGHT +ARTHUR T. SIMPSON J. H. R. KEMNAL +WILLIAM D. HOXIE _Managing Director_ +E. H. WELLS WALTER COLLS, _Secretary_ + +_Branch Offices in Great Britain_ + +GLASGOW: 29 St. Vincent Place +BIRMINGHAM: Winchester House +CARDIFF: 129 Bute Street +BELFAST: Ocean Buildings, Donegal Square, E. +MANCHESTER: 30 Cross Street +MIDDLESBROUGH: The Exchange +NEWCASTLE: 42 Westgate Road +SHEFFIELD: 14 Bank Chambers, Fargate + +_Offices Abroad_ + +BOMBAY: Wheeler's Building, Hornby Road, Fort +BRUSSELS: 187 Rue Royal +BILBAO: 1 Plaza de Albia +CALCUTTA: Clive Building +JOHANNESBURG: Consolidated Buildings +LIMA: Peru +LISBON: 84-86 Rua do Commercio +MADRID: Ventura de la Vega +MELBOURNE: 9 William Street +MEXICO: 22-23 Tiburcio +MILAN: 22 Via Principe Umberto +MONTREAL: College Street, St. Henry +NAPLES: 107 Via Santa Lucia +SHANGHAI: 1a Jinkee Road +SYDNEY: 427-429 Sussex Street +TOKYO: Japan +TORONTO: Traders' Bank Building + +_Representatives and Licensees in_ + +ADELAIDE, South Australia +ATHENS, Greece +AUCKLAND, New Zealand +BAHIA, Brazil +BANGKOK, Siam +BARCELONA, Spain +BRUNN, Austria +BUCHAREST, Roumania +BUDAPEST, Hungary +BUENOS AYRES, Argentine Rep. +CAIRO, Egypt +CHILE, Valparaiso, So. America +CHRISTIANIA, Norway +COLOMBO, Ceylon +COPENHAGEN, Denmark +ESKILSTUNA, Sweden +GIJON, Spain +HELSINGFORS, Finland +HENGELO, Holland +KIMBERLEY, South Africa +MOSCOW, Russia +PERTH, Western Australia +POLAND, Berlin +RANGOON, Burma +RIO DE JANEIRO, Brazil +SMYRNA, Asia Minor +SOURABAYA, Java +ST. PETERSBURG, Russia +TAMMERFORS, Finland +THE HAGUE, Holland + +TELEGRAPHIC ADDRESS FOR ALL OFFICES EXCEPT BOMBAY AND CALCUTTA: "BABCOCK" +FOR BOMBAY AND CALCUTTA: "BOILER" + +[Illustration: Fonderies et Ateliers de la Courneuve, Chaudières Babcock +& Wilcox, Paris, France] + + + + +FONDERIES ET ATELIERS DE LA COURNEUVE +CHAUDIÈRES + +BABCOCK & WILCOX + +6 RUE LAFERRIÈRE, PARIS + +WORKS: SEINE--LA COURNEUVE + +_Directors_ + +EDMOND DUPUIS J. H. R. KEMNAL +ETIENNE BESSON IRÉNÉE CHAVANNE +CHARLES A. KNIGHT JULES LEMAIRE + +_Branch Offices_ + +BORDEAUX: 30 Boulevard Antoine Gautier +LILLE: 23 Rue Faidherbe +LYON: 28 Quai de la Guillotier +MARSEILLE: 21 Cours Devilliers +MONTPELLIER: 1 Rue Boussairolles +NANCY: 2 Rue de Lorraine +ST. ETIENNE: 13 Rue de la Bourse + +REPRESENTATIVE FOR SWITZERLAND: SPOERRI & CIE, ZURICH + +TELEGRAPHIC ADDRESS: "BABCOCK-PARIS" + +[Illustration: Wrought-steel Vertical Header Longitudinal Drum +Babcock & Wilcox Boiler, Equipped with Babcock & Wilcox Superheater and +Babcock & Wilcox Chain Grate Stoker] + + + + +THE EARLY HISTORY OF THE GENERATION AND USE OF STEAM + + +While the time of man's first knowledge and use of the expansive force +of the vapor of water is unknown, records show that such knowledge +existed earlier than 150 B. C. In a treatise of about that time entitled +"Pneumatica", Hero, of Alexander, described not only existing devices of +his predecessors and contemporaries but also an invention of his own +which utilized the expansive force of steam for raising water above its +natural level. He clearly describes three methods in which steam might +be used directly as a motive of power; raising water by its elasticity, +elevating a weight by its expansive power and producing a rotary motion +by its reaction on the atmosphere. The third method, which is known as +"Hero's engine", is described as a hollow sphere supported over a +caldron or boiler by two trunnions, one of which was hollow, and +connected the interior of the sphere with the steam space of the +caldron. Two pipes, open at the ends and bent at right angles, were +inserted at opposite poles of the sphere, forming a connection between +the caldron and the atmosphere. Heat being applied to the caldron, the +steam generated passed through the hollow trunnion to the sphere and +thence into the atmosphere through the two pipes. By the reaction +incidental to its escape through these pipes, the sphere was caused to +rotate and here is the primitive steam reaction turbine. + +Hero makes no suggestions as to application of any of the devices he +describes to a useful purpose. From the time of Hero until the late +sixteenth and early seventeenth centuries, there is no record of +progress, though evidence is found that such devices as were described +by Hero were sometimes used for trivial purposes, the blowing of an +organ or the turning of a skillet. + +Mathesius, the German author, in 1571; Besson, a philosopher and +mathematician at Orleans; Ramelli, in 1588; Battista Delia Porta, a +Neapolitan mathematician and philosopher, in 1601; Decause, the French +engineer and architect, in 1615; and Branca, an Italian architect, in +1629, all published treatises bearing on the subject of the generation +of steam. + +To the next contributor, Edward Somerset, second Marquis of Worcester, +is apparently due the credit of proposing, if not of making, the first +useful steam engine. In the "Century of Scantlings and Inventions", +published in London in 1663, he describes devices showing that he had in +mind the raising of water not only by forcing it from two receivers by +direct steam pressure but also for some sort of reciprocating piston +actuating one end of a lever, the other operating a pump. His +descriptions are rather obscure and no drawings are extant so that it is +difficult to say whether there were any distinctly novel features to his +devices aside from the double action. While there is no direct authentic +record that any of the devices he described were actually constructed, +it is claimed by many that he really built and operated a steam engine +containing pistons. + +In 1675, Sir Samuel Moreland was decorated by King Charles II, for a +demonstration of "a certain powerful machine to raise water." Though +there appears to be no record of the design of this machine, the +mathematical dictionary, published in 1822, credits Moreland with the +first account of a steam engine, on which subject he wrote a treatise +that is still preserved in the British Museum. + +[Illustration: 397 Horse-power Babcock & Wilcox Boiler in Course of +Erection at the Plant of the Crocker Wheeler Co., Ampere, N. J.] + +Dr. Denys Papin, an ingenious Frenchman, invented in 1680 "a steam +digester for extracting marrowy, nourishing juices from bones by +enclosing them in a boiler under heavy pressure," and finding danger +from explosion, added a contrivance which is the first safety valve on +record. + +The steam engine first became commercially successful with Thomas +Savery. In 1699, Savery exhibited before the Royal Society of England +(Sir Isaac Newton was President at the time), a model engine which +consisted of two copper receivers alternately connected by a three-way +hand-operated valve, with a boiler and a source of water supply. When +the water in one receiver had been driven out by the steam, cold water +was poured over its outside surface, creating a vacuum through +condensation and causing it to fill again while the water in the other +reservoir was being forced out. A number of machines were built on this +principle and placed in actual use as mine pumps. + +The serious difficulty encountered in the use of Savery's engine was the +fact that the height to which it could lift water was limited by the +pressure the boiler and vessels could bear. Before Savery's engine was +entirely displaced by its successor, Newcomen's, it was considerably +improved by Desaguliers, who applied the Papin safety valve to the +boiler and substituted condensation by a jet within the vessel for +Savery's surface condensation. + +In 1690, Papin suggested that the condensation of steam should be +employed to make a vacuum beneath a cylinder which had previously been +raised by the expansion of steam. This was the earliest cylinder and +piston steam engine and his plan took practical shape in Newcomen's +atmospheric engine. Papin's first engine was unworkable owing to the +fact that he used the same vessel for both boiler and cylinder. A small +quantity of water was placed in the bottom of the vessel and heat was +applied. When steam formed and raised the piston, the heat was withdrawn +and the piston did work on its down stroke under pressure of the +atmosphere. After hearing of Savery's engine, Papin developed an +improved form. Papin's engine of 1705 consisted of a displacement +chamber in which a floating diaphragm or piston on top of the water kept +the steam and water from direct contact. The water delivered by the +downward movement of the piston under pressure, to a closed tank, flowed +in a continuous stream against the vanes of a water wheel. When the +steam in the displacement chamber had expanded, it was exhausted to the +atmosphere through a valve instead of being condensed. The engine was, +in fact, a non-condensing, single action steam pump with the steam and +pump cylinders in one. A curious feature of this engine was a heater +placed in the diaphragm. This was a mass of heated metal for the purpose +of keeping the steam dry or preventing condensation during expansion. +This device might be called the first superheater. + +Among the various inventions attributed to Papin was a boiler with an +internal fire box, the earliest record of such construction. + +While Papin had neglected his earlier suggestion of a steam and piston +engine to work on Savery's ideas, Thomas Newcomen, with his assistant, +John Cawley, put into practical form Papin's suggestion of 1690. Steam +admitted from the boiler to a cylinder raised a piston by its expansion, +assisted by a counter-weight on the other end of a beam actuated by the +piston. The steam valve was then shut and the steam condensed by a jet +of cold water. The piston was then forced downward by atmospheric +pressure and did work on the pump. The condensed water in the cylinder +was expelled through an escapement valve by the next entry of steam. +This engine used steam having pressure but little, if any, above that of +the atmosphere. + +[Illustration: Two Units of 8128 Horse Power of Babcock & Wilcox Boilers +and Superheaters at the Fisk Street Station of the Commonwealth Edison +Co., Chicago, Ill., 50,400 Horse Power being Installed in this Station. +The Commonwealth Edison Co. Operates in its Various Stations a Total of +86,000 Horse Power of Babcock & Wilcox Boilers, all Fitted with Babcock +& Wilcox Superheaters and Equipped with Babcock & Wilcox Chain Grate +Stokers] + +In 1711, this engine was introduced into mines for pumping purposes. +Whether its action was originally automatic or whether dependent upon +the hand operation of the valves is a question of doubt. The story +commonly believed is that a boy, Humphrey Potter, in 1713, whose duty it +was to open and shut such valves of an engine he attended, by suitable +cords and catches attached to the beam, caused the engine to +automatically manipulate these valves. This device was simplified in +1718 by Henry Beighton, who suspended from the bottom, a rod called the +plug-tree, which actuated the valve by tappets. By 1725, this engine was +in common use in the collieries and was changed but little for a matter +of sixty or seventy years. Compared with Savery's engine, from the +aspect of a pumping engine, Newcomen's was a distinct advance, in that +the pressure in the pumps was in no manner dependent upon the steam +pressure. In common with Savery's engine, the losses from the alternate +heating and cooling of the steam cylinder were enormous. Though +obviously this engine might have been modified to serve many purposes, +its use seems to have been limited almost entirely to the pumping of +water. + +The rivalry between Savery and Papin appears to have stimulated +attention to the question of fuel saving. Dr. John Allen, in 1730, +called attention to the fact that owing to the short length of time of +the contact between the gases and the heating surfaces of the boiler, +nearly half of the heat of the fire was lost. With a view to overcoming +this loss at least partially, he used an internal furnace with a smoke +flue winding through the water in the form of a worm in a still. In +order that the length of passage of the gases might not act as a damper +on the fire, Dr. Allen recommended the use of a pair of bellows for +forcing the sluggish vapor through the flue. This is probably the first +suggested use of forced draft. In forming an estimate of the quantity of +fuel lost up the stack, Dr. Allen probably made the first boiler test. + +Toward the end of the period of use of Newcomen's atmospheric engine, +John Smeaton, who, about 1770, built and installed a number of large +engines of this type, greatly improved the design in its mechanical +details. + +[Illustration: Erie County Electric Co., Erie, Pa., Operating 3082 Horse +Power of Babcock & Wilcox Boilers and Superheaters, Equipped with +Babcock & Wilcox Chain Grate Stokers] + +The improvement in boiler and engine design of Smeaton, Newcomen and +their contemporaries, were followed by those of the great engineer, +James Watt, an instrument maker of Glasgow. In 1763, while repairing a +model of Newcomen's engine, he was impressed by the great waste of steam +to which the alternating cooling and heating of the engine gave rise. +His remedy was the maintaining of the cylinder as hot as the entering +steam and with this in view he added a vessel separate from the +cylinder, into which the steam should pass from the cylinder and be +there condensed either by the application of cold water outside or by a +jet from within. To preserve a vacuum in his condenser, he added an air +pump which should serve to remove the water of condensation and air +brought in with the injection water or due to leakage. As the cylinder +no longer acted as a condenser, he could maintain it at a high +temperature by covering it with non-conducting material and, in +particular, by the use of a steam jacket. Further and with the same +object in view, he covered the top of the cylinder and introduced steam +above the piston to do the work previously accomplished by atmospheric +pressure. After several trials with an experimental apparatus based on +these ideas, Watt patented his improvements in 1769. Aside from their +historical importance, Watt's improvements, as described in his +specification, are to this day a statement of the principles which guide +the scientific development of the steam engine. His words are: + + "My method of lessening the consumption of steam, and + consequently fuel, in fire engines, consists of the following + principles: + + "First, That vessel in which the powers of steam are to be + employed to work the engine, which is called the cylinder in + common fire engines, and which I call the steam vessel, must, + during the whole time the engine is at work, be kept as hot as + the steam that enters it; first, by enclosing it in a case of + wood, or any other materials that transmit heat slowly; + secondly, by surrounding it with steam or other heated bodies; + and, thirdly, by suffering neither water nor any other substance + colder than the steam to enter or touch it during that time. + + "Secondly, In engines that are to be worked wholly or partially + by condensation of steam, the steam is to be condensed in + vessels distinct from the steam vessels or cylinders, although + occasionally communicating with them; these vessels I call + condensers; and, whilst the engines are working, these + condensers ought at least to be kept as cold as the air in the + neighborhood of the engines, by application of water or other + cold bodies. + + "Thirdly, Whatever air or other elastic vapor is not condensed + by the cold of the condenser, and may impede the working of the + engine, is to be drawn out of the steam vessels or condensers by + means of pumps, wrought by the engines themselves, or otherwise. + + "Fourthly, I intend in many cases to employ the expansive force + of steam to press on the pistons, or whatever may be used + instead of them, in the same manner in which the pressure of the + atmosphere is now employed in common fire engines. In cases + where cold water cannot be had in plenty, the engines may be + wrought by this force of steam only, by discharging the steam + into the air after it has done its office.... + + "Sixthly, I intend in some cases to apply a degree of cold not + capable of reducing the steam to water, but of contracting it + considerably, so that the engines shall be worked by the + alternate expansion and contraction of the steam. + + "Lastly, Instead of using water to render the pistons and other + parts of the engine air and steam tight, I employ oils, wax, + resinous bodies, fat of animals, quick-silver and other metals + in their fluid state." + +The fifth claim was for a rotary engine, and need not be quoted here. + +The early efforts of Watt are typical of those of the poor inventor +struggling with insufficient resources to gain recognition and it was +not until he became associated with the wealthy manufacturer, Mattheu +Boulton of Birmingham, that he met with the success upon which his +present fame is based. In partnership with Boulton, the business of the +manufacture and the sale of his engines were highly successful in spite +of vigorous attacks on the validity of his patents. + +Though the fourth claim of Watt's patent describes a non-condensing +engine which would require high pressures, his aversion to such practice +was strong. Notwithstanding his entire knowledge of the advantages +through added expansion under high pressure, he continued to use +pressures not above 7 pounds per square inch above the atmosphere. To +overcome such pressures, his boilers were fed through a stand-pipe of +sufficient height to have the column of water offset the pressure within +the boiler. Watt's attitude toward high pressure made his influence felt +long after his patents had expired. + +[Illustration: Portion of 9600 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain +Grate Stokers at the Blue Island, Ill., Plant of the Public Service Co. +of Northern Illinois. This Company Operates 14,580 Horse Power of +Babcock & Wilcox Boilers and Superheaters in its Various Stations] + +In 1782, Watt patented two other features which he had invented as early +as 1769. These were the double acting engine, that is, the use of steam +on both sides of the piston and the use of steam expansively, that is, +the shutting off of steam from the cylinder when the piston had made but +a portion of its stroke, the power for the completion of the stroke +being supplied by the expansive force of the steam already admitted. + +He further added a throttle valve for the regulation of steam admission, +invented the automatic governor and the steam indicator, a mercury steam +gauge and a glass water column. + +It has been the object of this brief history of the early developments +in the use of steam to cover such developments only through the time of +James Watt. The progress of the steam engine from this time through the +stages of higher pressures, combining of cylinders, the application of +steam vehicles and steamboats, the adding of third and fourth cylinders, +to the invention of the turbine with its development and the +accompanying development of the reciprocating engine to hold its place, +is one long attribute to the inventive genius of man. + +While little is said in the biographies of Watt as to the improvement of +steam boilers, all the evidence indicates that Boulton and Watt +introduced the first "wagon boiler", so called because of its shape. In +1785, Watt took out a number of patents for variations in furnace +construction, many of which contain the basic principles of some of the +modern smoke preventing furnaces. Until the early part of the nineteenth +century, the low steam pressures used caused but little attention to be +given to the form of the boiler operated in connection with the engines +above described. About 1800, Richard Trevithick, in England, and Oliver +Evans, in America, introduced non-condensing, and for that time, high +pressure steam engines. To the initiative of Evans may be attributed the +general use of high pressure steam in the United States, a feature which +for many years distinguished American from European practice. The demand +for light weight and economy of space following the beginning of steam +navigation and the invention of the locomotive required boilers designed +and constructed to withstand heavier pressures and forced the adoption +of the cylindrical form of boiler. There are in use to-day many examples +of every step in the development of steam boilers from the first plain +cylindrical boiler to the most modern type of multi-tubular locomotive +boiler, which stands as the highest type of fire-tube boiler +construction. + +The early attempts to utilize water-tube boilers were few. A brief +history of the development of the boilers, in which this principle was +employed, is given in the following chapter. From this history it will +be clearly indicated that the first commercially successful utilization +of water tubes in a steam generator is properly attributed to George H. +Babcock and Stephen Wilcox. + +[Illustration: Copyright by Underwood & Underwood + +Woolworth Building, New York City, Operating 2454 Horse Power of +Babcock & Wilcox Boilers] + + + + +BRIEF HISTORY OF WATER-TUBE BOILERS[1] + + +As stated in the previous chapter, the first water-tube boiler was built +by John Blakey and was patented by him in 1766. Several tubes +alternately inclined at opposite angles were arranged in the furnaces, +the adjacent tube ends being connected by small pipes. The first +successful user of water-tube boilers, however, was James Rumsey, an +American inventor, celebrated for his early experiments in steam +navigation, and it is he who may be truly classed as the originator of +the water-tube boiler. In 1788 he patented, in England, several forms of +boilers, some of which were of the water-tube type. One had a fire box +with flat top and sides, with horizontal tubes across the fire box +connecting the water spaces. Another had a cylindrical fire box +surrounded by an annular water space and a coiled tube was placed within +the box connecting at its two ends with the water space. This was the +first of the "coil boilers". Another form in the same patent was the +vertical tubular boiler, practically as made at the present time. + +[Illustration: Blakey, 1766] + +The first boiler made of a combination of small tubes, connected at one +end to a reservoir, was the invention of another American, John Stevens, +in 1804. This boiler was actually employed to generate steam for running +a steamboat on the Hudson River, but like all the "porcupine" boilers, +of which type it was the first, it did not have the elements of a +continued success. + +[Illustration: John Stevens, 1804] + +Another form of water tube was patented in 1805 by John Cox Stevens, a +son of John Stevens. This boiler consisted of twenty vertical tubes, 1¼ +inches internal diameter and 40½ inches long, arranged in a circle, the +outside diameter of which was approximately 12 inches, connecting a +water chamber at the bottom with a steam chamber at the top. The steam +and water chambers were annular spaces of small cross section and +contained approximately 33 cubic inches. The illustration shows the cap +of the steam chamber secured by bolts. The steam outlet pipe "A" is a +pipe of one inch diameter, the water entering through a similar aperture +at the bottom. One of these boilers was for a long time at the Stevens +Institute of Technology at Hoboken, and is now in the Smithsonian +Institute at Washington. + +[Illustration: John Cox Stevens, 1805] + +About the same time, Jacob Woolf built a boiler of large horizontal +tubes, extending across the furnace and connected at the ends to a +longitudinal drum above. The first purely sectional water-tube boiler +was built by Julius Griffith, in 1821. In this boiler, a number of +horizontal water tubes were connected to vertical side pipes, the side +pipes were connected to horizontal gathering pipes, and these latter in +turn to a steam drum. + +In 1822, Jacob Perkins constructed a flash boiler for carrying what was +then considered a high pressure. A number of cast-iron bars having 1½ +inches annular holes through them and connected at their outer ends by a +series of bent pipes, outside of the furnace walls, were arranged in +three tiers over the fire. The water was fed slowly to the upper tier by +a force pump and steam in the superheated state was discharged to the +lower tiers into a chamber from which it was taken to the engine. + +[Illustration: Joseph Eve, 1825] + +The first sectional water-tube boiler, with a well-defined circulation, +was built by Joseph Eve, in 1825. The sections were composed of small +tubes with a slight double curve, but being practically vertical, fixed +in horizontal headers, which headers were in turn connected to a steam +space above and a water space below formed of larger pipes. The steam +and water spaces were connected by outside pipes to secure a circulation +of the water up through the sections and down through the external +pipes. In the same year, John M'Curdy of New York, built a "Duplex Steam +Generator" of "tubes of wrought or cast iron or other material" arranged +in several horizontal rows, connected together alternately at the front +and rear by return bends. In the tubes below the water line were placed +interior circular vessels closed at the ends in order to expose a thin +sheet of water to the action of the fire. + +[Illustration: Gurney, 1826] + +In 1826, Goldsworthy Gurney built a number of boilers, which he used on +his steam carriages. A number of small tubes were bent into the shape of +a "U" laid sidewise and the ends were connected with larger horizontal +pipes. These were connected by vertical pipes to permit of circulation +and also to a vertical cylinder which served as a steam and water +reservoir. In 1828, Paul Steenstrup made the first shell boiler with +vertical water tubes in the large flues, similar to the boiler known as +the "Martin" and suggesting the "Galloway". + +The first water-tube boiler having fire tubes within water tubes was +built in 1830, by Summers & Ogle. Horizontal connections at the top and +bottom were connected by a series of vertical water tubes, through which +were fire tubes extending through the horizontal connections, the fire +tubes being held in place by nuts, which also served to make the joint. + +[Illustration: Stephen Wilcox, 1856] + +Stephen Wilcox, in 1856, was the first to use inclined water tubes +connecting water spaces at the front and rear with a steam space above. +The first to make such inclined tubes into a sectional form was Twibill, +in 1865. He used wrought-iron tubes connected at the front and rear with +standpipes through intermediate connections. These standpipes carried +the system to a horizontal cross drum at the top, the entrained water +being carried to the rear. + +Clarke, Moore, McDowell, Alban and others worked on the problem of +constructing water-tube boilers, but because of difficulties of +construction involved, met with no practical success. + +[Illustration: Twibill, 1865] + +It may be asked why water-tube boilers did not come into more general +use at an early date, that is, why the number of water-tube boilers +built was so small in comparison to the number of shell boilers. The +reason for this is found in the difficulties involved in the design and +construction of water-tube boilers, which design and construction +required a high class of engineering and workmanship, while the plain +cylindrical boiler is comparatively easy to build. The greater skill +required to make a water-tube boiler successful is readily shown in the +great number of failures in the attempts to make them. + +[Illustration: Partial View of 7000 Horse-power Installation of Babcock +& Wilcox Boilers at the Philadelphia, Pa., Plant of the Baldwin +Locomotive Works. This Company Operates in its Various Plants a Total of +9280 Horse Power of Babcock & Wilcox Boilers] + + + + +REQUIREMENTS OF STEAM BOILERS + + +Since the first appearance in "Steam" of the following "Requirements of +a Perfect Steam Boiler", the list has been copied many times either word +for word or clothed in different language and applied to some specific +type of boiler design or construction. In most cases, although full +compliance with one or more of the requirements was structurally +impossible, the reader was left to infer that the boiler under +consideration possessed all the desirable features. It is noteworthy +that this list of requirements, as prepared by George H. Babcock and +Stephen Wilcox, in 1875, represents the best practice of to-day. +Moreover, coupled with the boiler itself, which is used in the largest +and most important steam generating plants throughout the world, the +list forms a fitting monument to the foresight and genius of the +inventors. + + + +REQUIREMENTS OF A PERFECT STEAM BOILER + + +1st. Proper workmanship and simple construction, using materials which +experience has shown to be the best, thus avoiding the necessity of +early repairs. + + +2nd. A mud drum to receive all impurities deposited from the water, and +so placed as to be removed from the action of the fire. + + +3rd. A steam and water capacity sufficient to prevent any fluctuation in +steam pressure or water level. + + +4th. A water surface for the disengagement of the steam from the water, +of sufficient extent to prevent foaming. + + +5th. A constant and thorough circulation of water throughout the boiler, +so as to maintain all parts at the same temperature. + + +6th. The water space divided into sections so arranged that, should any +section fail, no general explosion can occur and the destructive effects +will be confined to the escape of the contents. Large and free passages +between the different sections to equalize the water line and pressure +in all. + + +7th. A great excess of strength over any legitimate strain, the boiler +being so constructed as to be free from strains due to unequal +expansion, and, if possible, to avoid joints exposed to the direct +action of the fire. + + +8th. A combustion chamber so arranged that the combustion of the gases +started in the furnace may be completed before the gases escape to the +chimney. + + +9th. The heating surface as nearly as possible at right angles to the +currents of heated gases, so as to break up the currents and extract the +entire available heat from the gases. + + +10th. All parts readily accessible for cleaning and repairs. This is a +point of the greatest importance as regards safety and economy. + + +11th. Proportioned for the work to be done, and capable of working to +its full rated capacity with the highest economy. + + +12th. Equipped with the very best gauges, safety valves and other +fixtures. + + +The exhaustive study made of each one of these requirements is shown by +the following extract from a lecture delivered by Mr. Geo. H. Babcock at +Cornell University in 1890 upon the subject: + + + +THE CIRCULATION OF WATER IN STEAM BOILERS + + +You have all noticed a kettle of water boiling over the fire, the fluid +rising somewhat tumultuously around the edges of the vessel, and +tumbling toward the center, where it descends. Similar currents are in +action while the water is simply being heated, but they are not +perceptible unless there are floating particles in the liquid. These +currents are caused by the joint action of the added temperature and two +or more qualities which the water possesses. + +1st. Water, in common with most other substances, expands when heated; a +statement, however, strictly true only when referred to a temperature +above 39 degrees F. or 4 degrees C., but as in the making of steam we +rarely have to do with temperatures so low as that, we may, for our +present purposes, ignore that exception. + +2nd. Water is practically a non-conductor of heat, though not entirely +so. If ice-cold water was kept boiling at the surface the heat would not +penetrate sufficiently to begin melting ice at a depth of 3 inches in +less than about two hours. As, therefore, the heated water cannot impart +its heat to its neighboring particles, it remains expanded and rises by +its levity, while colder portions come to be heated in turn, thus +setting up currents in the fluid. + +Now, when all the water has been heated to the boiling point +corresponding to the pressure to which it is subjected, each added unit +of heat converts a portion, about 7 grains in weight, into vapor, +greatly increasing its volume; and the mingled steam and water rises +more rapidly still, producing ebullition such as we have noticed in the +kettle. So long as the quantity of heat added to the contents of the +kettle continues practically constant, the conditions remain similar to +those we noticed at first, a tumultuous lifting of the water around the +edges, flowing toward the center and thence downward; if, however, the +fire be quickened, the upward currents interfere with the downward and +the kettle boils over (Fig. 1). + +[Illustration: Fig. 1] + +If now we put in the kettle a vessel somewhat smaller (Fig. 2) with a +hole in the bottom and supported at a proper distance from the side so +as to separate the upward from the downward currents, we can force the +fires to a very much greater extent without causing the kettle to boil +over, and when we place a deflecting plate so as to guide the rising +column toward the center it will be almost impossible to produce that +effect. This is the invention of Perkins in 1831 and forms the basis of +very many of the arrangements for producing free circulation of the +water in boilers which have been made since that time. It consists in +dividing the currents so that they will not interfere each with the +other. + +[Illustration: Fig. 2] + +But what is the object of facilitating the circulation of water in +boilers? Why may we not safely leave this to the unassisted action of +nature as we do in culinary operations? We may, if we do not care for +the three most important aims in steam-boiler construction, namely, +efficiency, durability, and safety, each of which is more or less +dependent upon a proper circulation of the water. As for efficiency, we +have seen one proof in our kettle. When we provided means to preserve +the circulation, we found that we could carry a hotter fire and boil +away the water much more rapidly than before. It is the same in a steam +boiler. And we also noticed that when there was nothing but the +unassisted circulation, the rising steam carried away so much water in +the form of foam that the kettle boiled over, but when the currents were +separated and an unimpeded circuit was established, this ceased, and a +much larger supply of steam was delivered in a comparatively dry state. +Thus, circulation increases the efficiency in two ways: it adds to the +ability to take up the heat, and decreases the liability to waste that +heat by what is technically known as priming. There is yet another way +in which, incidentally, circulation increases efficiency of surface, and +that is by preventing in a greater or less degree the formation of +deposits thereon. Most waters contain some impurity which, when the +water is evaporated, remains to incrust the surface of the vessel. This +incrustation becomes very serious sometimes, so much so as to almost +entirely prevent the transmission of heat from the metal to the water. +It is said that an incrustation of only one-eighth inch will cause a +loss of 25 per cent in efficiency, and this is probably within the truth +in many cases. Circulation of water will not prevent incrustation +altogether, but it lessens the amount in all waters, and almost entirely +so in some, thus adding greatly to the efficiency of the surface. + +[Illustration: Fig. 3] + +A second advantage to be obtained through circulation is durability of +the boiler. This it secures mainly by keeping all parts at a nearly +uniform temperature. The way to secure the greatest freedom from unequal +strains in a boiler is to provide for such a circulation of the water as +will insure the same temperature in all parts. + +3rd. Safety follows in the wake of durability, because a boiler which is +not subject to unequal strains of expansion and contraction is not only +less liable to ordinary repairs, but also to rupture and disastrous +explosion. By far the most prolific cause of explosions is this same +strain from unequal expansions. + +[Illustration: Fig. 4] + +[Illustration: 386 Horse-power Installation of Babcock & Wilcox Boilers +at B. F. Keith's Theatre, Boston, Mass.] + +Having thus briefly looked at the advantages of circulation of water in +steam boilers, let us see what are the best means of securing it under +the most efficient conditions We have seen in our kettle that one +essential point was that the currents should be kept from interfering +with each other. If we could look into an ordinary return tubular boiler +when steaming, we should see a curious commotion of currents rushing +hither and thither, and shifting continually as one or the other +contending force gained a momentary mastery. The principal upward +currents would be found at the two ends, one over the fire and the other +over the first foot or so of the tubes. Between these, the downward +currents struggle against the rising currents of steam and water. At a +sudden demand for steam, or on the lifting of the safety valve, the +pressure being slightly reduced, the water jumps up in jets at every +portion of the surface, being lifted by the sudden generation of steam +throughout the body of water. You have seen the effect of this sudden +generation of steam in the well-known experiment with a Florence flask, +to which a cold application is made while boiling water under pressure +is within. You have also witnessed the geyser-like action when water is +boiled in a test tube held vertically over a lamp (Fig. 3). + +[Illustration: Fig. 5] + +If now we take a U-tube depending from a vessel of water (Fig. 4) and +apply the lamp to one leg a circulation is at once set up within it, and +no such spasmodic action can be produced. Thus U-tube is the +representative of the true method of circulation within a water-tube +boiler properly constructed. We can, for the purpose of securing more +heating surface, extend the heated leg into a long incline (Fig. 5), +when we have the well-known inclined-tube generator. Now, by adding +other tubes, we may further increase the heating surface (Fig. 6), while +it will still be the U-tube in effect and action. In such a construction +the circulation is a function of the difference in density of the two +columns. Its velocity is measured by the well-known Torricellian +formula, V = (2gh)^{½}, or, approximately V = 8(h)^{½}, h being measured +in terms of the lighter fluid. This velocity will increase until the +rising column becomes all steam, but the quantity or weight circulated +will attain a maximum when the density of the mingled steam and water in +the rising column becomes one-half that of the solid water in the +descending column which is nearly coincident with the condition of half +steam and half water, the weight of the steam being very slight compared +to that of the water. + +[Illustration: Fig. 6] + +It becomes easy by this rule to determine the circulation in any given +boiler built on this principle, provided the construction is such as to +permit a free flow of the water. Of course, every bend detracts a little +and something is lost in getting up the velocity, but when the boiler is +well arranged and proportioned these retardations are slight. + +Let us take for example one of the 240 horse-power Babcock & Wilcox +boilers here in the University. The height of the columns may be taken +as 4½ feet, measuring from the surface of the water to about the center +of the bundle of tubes over the fire, and the head would be equal to +this height at the maximum of circulation. We should, therefore, have a +velocity of 8(4½)^{½} = 16.97, say 17 feet per second. There are in this +boiler fourteen sections, each having a 4-inch tube opening into the +drum, the area of which (inside) is 11 square inches, the fourteen +aggregating 154 square inches, or 1.07 square feet. This multiplied by +the velocity, 16.97 feet, gives 18.16 cubic feet mingled steam and water +discharged per second, one-half of which, or 9.08 cubic feet, is steam. +Assuming this steam to be at 100 pounds gauge pressure, it will weigh +0.258 pound per cubic foot. Hence, 2.34 pounds of steam will be +discharged per second, and 8,433 pounds per hour. Dividing this by 30, +the number of pounds representing a boiler horse power, we get 281.1 +horse power, about 17 per cent, in excess of the rated power of the +boiler. The water at the temperature of steam at 100 pounds pressure +weighs 56 pounds per cubic foot, and the steam 0.258 pound, so that the +steam forms but 1/218 part of the mixture by weight, and consequently +each particle of water will make 218 circuits before being evaporated +when working at this capacity, and circulating the maximum weight of +water through the tubes. + +[Illustration: A Portion of 9600 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters Being Erected at the South Boston, +Mass., Station of the Boston Elevated Railway Co. This Company Operates +in its Various Stations a Total of 46,400 Horse Power of Babcock & +Wilcox Boilers] + +[Illustration: Fig. 7] + +It is evident that at the highest possible velocity of exit from the +generating tubes, nothing but steam will be delivered and there will be +no circulation of water except to supply the place of that evaporated. +Let us see at what rate of steaming this would occur with the boiler +under consideration. We shall have a column of steam, say 4 feet high on +one side and an equal column of water on the other. Assuming, as before, +the steam at 100 pounds and the water at same temperature, we will have +a head of 866 feet of steam and an issuing velocity of 235.5 feet per +second. This multiplied by 1.07 square feet of opening by 3,600 seconds +in an hour, and by 0.258 gives 234,043 pounds of steam, which, though +only one-eighth the weight of mingled steam and water delivered at the +maximum, gives us 7,801 horse power, or 32 times the rated power of the +boiler. Of course, this is far beyond any possibility of attainment, so +that it may be set down as certain that this boiler cannot be forced to +a point where there will not be an efficient circulation of the water. +By the same method of calculation it may be shown that when forced to +double its rated power, a point rarely expected to be reached in +practice, about two-thirds the volume of mixture of steam and water +delivered into the drum will be steam, and that the water will make 110 +circuits while being evaporated. Also that when worked at only about +one-quarter its rated capacity, one-fifth of the volume will be steam +and the water will make the rounds 870 times before it becomes steam. +You will thus see that in the proportions adopted in this boiler there +is provision for perfect circulation under all the possible conditions +of practice. + +[Illustration: Fig. 8 [Developed to show Circulation]] + +In designing boilers of this style it is necessary to guard against +having the uptake at the upper end of the tubes too large, for if +sufficiently large to allow downward currents therein, the whole effect +of the rising column in increasing the circulation in the tubes is +nullified (Fig. 7). This will readily be seen if we consider the uptake +very large when the only head producing circulation in the tubes will be +that due to the inclination of each tube taken by itself. This objection +is only overcome when the uptake is so small as to be entirely filled +with the ascending current of mingled steam and water. It is also +necessary that this uptake should be practically direct, and it should +not be composed of frequent enlargements and contractions. Take, for +instance, a boiler well known in Europe, copied and sold here under +another name. It is made up of inclined tubes secured by pairs into +boxes at the ends, which boxes are made to communicate with each other +by return bends opposite the ends of the tubes. These boxes and return +bends form an irregular uptake, whereby the steam is expected to rise to +a reservoir above. You will notice (Fig. 8) that the upward current of +steam and water in the return bend meets and directly antagonizes the +upward current in the adjoining tube. Only one result can follow. If +their velocities are equal, the momentum of both will be neutralized and +all circulation stopped, or, if one be stronger, it will cause a back +flow in the other by the amount of difference in force, with practically +the same result. + +[Illustration: 4880 Horse-power Installation of Babcock & Wilcox Boilers +at the Open Hearth Plant of the Cambria Steel Co., Johnstown, Pa. This +Company Operates a Total of 52,000 Horse Power of Babcock & Wilcox +Boilers] + +[Illustration: Fig. 9] + +In a well-known boiler, many of which were sold, but of which none are +now made and a very few are still in use, the inventor claimed that the +return bends and small openings against the tubes were for the purpose +of "restricting the circulation" and no doubt they performed well that +office; but excepting for the smallness of the openings they were not as +efficient for that purpose as the arrangement shown in Fig. 8. + +[Illustration: Fig. 10] + +Another form of boiler, first invented by Clarke or Crawford, and lately +revived, has the uptake made of boxes into which a number, generally +from two to four tubes, are expanded, the boxes being connected together +by nipples (Fig. 9). It is a well-known fact that where a fluid flows +through a conduit which enlarges and then contracts, the velocity is +lost to a greater or less extent at the enlargements, and has to be +gotten up again at the contractions each time, with a corresponding loss +of head. The same thing occurs in the construction shown in Fig. 9. The +enlargements and contractions quite destroy the head and practically +overcome the tendency of the water to circulate. + +A horizontal tube stopped at one end, as shown in Fig. 10, can have no +proper circulation within it. If moderately driven, the water may +struggle in against the issuing steam sufficiently to keep the surface +covered, but a slight degree of forcing will cause it to act like the +test tube in Fig. 3, and the more there are of them in a given boiler +the more spasmodic will be its working. + +The experiment with our kettle (Fig. 2) gives the clue to the best means +of promoting circulation in ordinary shell boilers. Steenstrup or +"Martin" and "Galloway" water tubes placed in such boilers also assist +in directing the circulation therein, but it is almost impossible to +produce in shell boilers, by any means the circulation of all the water +in one continuous round, such as marks the well-constructed water-tube +boiler. + +As I have before remarked, provision for a proper circulation of water +has been almost universally ignored in designing steam boilers, +sometimes to the great damage of the owner, but oftener to the jeopardy +of the lives of those who are employed to run them. The noted case of +the Montana and her sister ship, where some $300,000 was thrown away in +trying an experiment which a proper consideration of this subject would +have avoided, is a case in point; but who shall count the cost of life +and treasure not, perhaps, directly traceable to, but, nevertheless, due +entirely to such neglect in design and construction of the thousands of +boilers in which this necessary element has been ignored? + + +In the light of the performance of the exacting conditions of present +day power-plant practice, a review of this lecture and of the foregoing +list of requirements reveals the insight of the inventors of the Babcock +& Wilcox boiler into the fundamental principles of steam generator +design and construction. + +Since the Babcock & Wilcox boiler became thoroughly established as a +durable and efficient steam generator, many types of water-tube boilers +have appeared on the market. Most of them, failing to meet enough of the +requirements of a perfect boiler, have fallen by the wayside, while a +few failing to meet all of the requirements, have only a limited field +of usefulness. None have been superior, and in the most cases the most +ardent admirers of other boilers have been satisfied in looking up to +the Babcock & Wilcox boiler as a standard and in claiming that the newer +boilers were "just as good." + +Records of recent performances under the most severe conditions of +services on land and sea, show that the Babcock & Wilcox boiler can be +run continually and regularly at higher overloads, with higher +efficiency, and lower upkeep cost than any other boiler on the market. +It is especially adapted for power-plant work where it is necessary to +use a boiler in which steam can be raised quickly and the boiler placed +on the line either from a cold state or from a banked fire in the +shortest possible time, and with which the capacity, with clean feed +water, will be largely limited by the amount of coal that can be burned +in the furnace. + +The distribution of the circulation through the separate headers and +sections and the action of the headers in forcing a maximum and +continuous circulation in the lower tubes, permit the operation of the +Babcock & Wilcox boiler without objectionable priming, with a higher +degree of concentration of salts in the water than is possible in any +other type of boiler. + +Repeated daily performances at overloads have demonstrated beyond a +doubt the correctness of Mr. Babcock's computation regarding the +circulating tube and header area required for most efficient +circulation. They also have proved that enlargement of the area of +headers and circulating tubes beyond a certain point diminishes the head +available for causing circulation and consequently limits the ability of +the boiler to respond to demands for overloads. + +In this lecture Mr. Babcock made the prediction that with the +circulating tube area proportioned in accordance with the principles +laid down, the Babcock & Wilcox boiler could be continuously run at +double its nominal rating, which at that time was based on 12 square +feet of heating surface per horse power. This prediction is being +fulfilled daily in all the large and prominent power plants in this +country and abroad, and it has been repeatedly demonstrated that with +clean water and clean tube surfaces it is possible to safely operate at +over 300 per cent of the nominal rating. + +In the development of electrical power stations it becomes more and more +apparent that it is economical to run a boiler at high ratings during +the times of peak loads, as by so doing the lay-over losses are +diminished and the economy of the plant as a whole is increased. + +The number and importance of the large electric lighting and power +stations constructed during the last ten years that are equipped with +Babcock & Wilcox boilers, is a most gratifying demonstration of the +merit of the apparatus, especially in view of their satisfactory +operation under conditions which are perhaps more exacting than those of +any other service. + +Time, the test of all, results with boilers as with other things, in the +survival of the fittest. When judged on this basis the Babcock & Wilcox +boiler stands pre-eminent in its ability to cover the whole field of +steam generation with the highest commercial efficiency obtainable. Year +after year the Babcock & Wilcox boiler has become more firmly +established as the standard of excellence in the boiler making art. + +[Illustration: South Boston Station of the Boston Elevated Ry. Co., +Boston, Mass. 9600 Horse Power of Babcock & Wilcox Boilers and +Superheaters Installed in this Station] + +[Illustration: 3600 Horse-power Installation of Babcock & Wilcox Boilers +at the Phipps Power House of the Duquesne Light Company, Pittsburgh, +Pa.] + + + + +EVOLUTION OF THE BABCOCK & WILCOX WATER-TUBE BOILER + + +Quite as much may be learned from the records of failures as from those +of success. Where a device has been once fairly tried and found to be +imperfect or impracticable, the knowledge of that trial is of advantage +in further investigation. Regardless of the lesson taught by failure, +however, it is an almost every-day occurrence that some device or +construction which has been tried and found wanting, if not worthless, +is again introduced as a great improvement upon a device which has shown +by its survival to be the fittest. + +The success of the Babcock & Wilcox boiler is due to many years of +constant adherence to one line of research, in which an endeavor has +been made to introduce improvements with the view to producing a boiler +which would most effectively meet the demands of the times. During the +periods that this boiler has been built, other companies have placed on +the market more than thirty water-tube or sectional water-tube boilers, +most of which, though they may have attained some distinction and sale, +have now entirely disappeared. The following incomplete list will serve +to recall the names of some of the boilers that have had a vogue at +various times, but which are now practically unknown: Dimpfel, Howard, +Griffith & Wundrum, Dinsmore, Miller "Fire Box", Miller "American", +Miller "Internal Tube", Miller "Inclined Tube", Phleger, Weigant, the +Lady Verner, the Allen, the Kelly, the Anderson, the Rogers & Black, the +Eclipse or Kilgore, the Moore, the Baker & Smith, the Renshaw, the +Shackleton, the "Duplex", the Pond & Bradford, the Whittingham, the +Bee, the Hazleton or "Common Sense", the Reynolds, the Suplee or Luder, +the Babbit, the Reed, the Smith, the Standard, etc., etc. + +It is with the object of protecting our customers and friends from loss +through purchasing discarded ideas that there is given on the following +pages a brief history of the development of the Babcock & Wilcox boiler +as it is built to-day. The illustrations and brief descriptions indicate +clearly the various designs and constructions that have been used and +that have been replaced, as experience has shown in what way improvement +might be made. They serve as a history of the experimental steps in the +development of the present Babcock & Wilcox boiler, the value and +success of which, as a steam generator, is evidenced by the fact that +the largest and most discriminating users continue to purchase them +after years of experience in their operation. + +[Illustration: No. 1] + +No. 1. The original Babcock & Wilcox boiler was patented in 1867. The +main idea in its design was safety, to which all other features were +sacrificed wherever they conflicted. The boiler consisted of a nest of +horizontal tubes, serving as a steam and water reservoir, placed above +and connected at each end by bolted joints to a second nest of inclined +heating tubes filled with water. The tubes were placed one above the +other in vertical rows, each row and its connecting end forming a single +casting. Hand-holes were placed at each end for cleaning. Internal tubes +were placed within the inclined tubes with a view to aiding circulation. + +No. 2. This boiler was the same as No. 1, except that the internal +circulating tubes were omitted as they were found to hinder rather than +help the circulation. + +Nos. 1 and 2 were found to be faulty in both material and design, cast +metal proving unfit for heating surfaces placed directly over the fire, +as it cracked as soon as any scale formed. + +No. 3. Wrought-iron tubes were substituted for the cast-iron heating +tubes, the ends being brightened, laid in moulds, and the headers cast +on. + +The steam and water capacity in this design were insufficient to secure +regularity of action, there being no reserve upon which to draw during +firing or when the water was fed intermittently. The attempt to dry the +steam by superheating it in the nest of tubes forming the steam space +was found to be impracticable. The steam delivered was either wet, dry +or superheated, according to the rate at which it was being drawn from +the boiler. Sediment was found to lodge in the lowermost point of the +boiler at the rear end and the exposed portions cracked off at this +point when subjected to the furnace heat. + +[Illustration: No. 4] + +No. 4. A plain cylinder, carrying the water line at its center and +leaving the upper half for steam space, was substituted for the nest of +tubes forming the steam and water space in Nos. 1, 2 and 3. The sections +were made as in No. 3 and a mud drum added to the rear end of the +sections at the point that was lowest and farthest removed from the +fire. The gases were made to pass off at one side and did not come into +contact with the mud drum. Dry steam was obtained through the increase +of separating surface and steam space and the added water capacity +furnished a storage for heat to tide over irregularities of firing and +feeding. By the addition of the drum, the boiler became a serviceable +and practical design, retaining all of the features of safety. As the +drum was removed from the direct action of the fire, it was not +subjected to excessive strain due to unequal expansion, and its +diameter, if large in comparison with that of the tubes formerly used, +was small when compared with that of cylindrical boilers. Difficulties +were encountered in this boiler in securing reliable joints between the +wrought-iron tubes and the cast-iron headers. + +[Illustration: No. 5] + +No. 5. In this design, wrought-iron water legs were substituted for the +cast-iron headers, the tubes being expanded into the inside sheets and a +large cover placed opposite the front end of the tubes for cleaning. The +tubes were staggered one above the other, an arrangement found to be +more efficient in the absorption of heat than where they were placed in +vertical rows. In other respects, the boiler was similar to No. 4, +except that it had lost the important element of safety through the +introduction of the very objectionable feature of flat stayed surfaces. +The large doors for access to the tubes were also a cause of weakness. + +An installation of these boilers was made at the plant of the Calvert +Sugar Refinery in Baltimore, and while they were satisfactory in their +operation, were never duplicated. + +[Illustration: No. 6] + +No. 6. This was a modification of No. 5 in which longer tubes were used +and over which the gases were caused to make three passes with a view of +better economy. In addition, some of the stayed surfaces were omitted +and handholes substituted for the large access doors. A number of +boilers of this design were built but their excessive first cost, the +lack of adjustability of the structure under varying temperatures, and +the inconvenience of transportation, led to No. 7. + +[Illustration: No. 7] + +No. 7. In this boiler, the headers and water legs were replaced by +T-heads screwed to the ends of the inclined tubes. The faces of these Ts +were milled and the tubes placed one above the other with the milled +faces metal to metal. Long bolts passed through each vertical section of +the T-heads and through connecting boxes on the heads of the drums +holding the whole together. A large number of boilers of this design +were built and many were in successful operation for over twenty years. +In most instances, however, they were altered to later types. + +[Illustration: No. 8] + +[Illustration: No. 9] + +Nos. 8 and 9. These boilers were known as the Griffith & Wundrum type, +the concern which built them being later merged in The Babcock & Wilcox +Co. Experiments were made with this design with four passages of the +gases across the tubes and the downward circulation of the water at the +rear of the boiler was carried to the bottom row of tubes. In No. 9 an +attempt was made to increase the safety and reduce the cost by reducing +the amount of steam and water capacity. A drum at right angles to the +line of tubes was used but as there was no provision made to secure dry +steam, the results were not satisfactory. The next move in the direction +of safety was the employment of several drums of small diameter instead +of a single drum. + +[Illustration: No. 10] + +This is shown in No. 10. A nest of small horizontal drums, 15 inches in +diameter, was used in place of the single drum of larger diameter. A set +of circulation tubes was placed at an intermediate angle between the +main bank of heating tubes and the horizontal drums forming the steam +reservoir. These circulators were to return to the rear end of the +circulating tubes the water carried up by the circulation, and in this +way were to allow only steam to be delivered to the small drums above. +There was no improvement in the action of this boiler over that of No. +9. + +The four passages of the gas over the tubes tried in Nos. 8, 9 and 10 +were not found to add to the economy of the boiler. + +[Illustration: No. 11] + +No. 11. A trial was next made of a box coil system, in which the water +was made to transverse the furnace several times before being delivered +to the drum above. The tendency here, as in all similar boilers, was to +form steam in the middle of the coil and blow the water from each end, +leaving the tubes practically dry until the steam found an outlet and +the water returned. This boiler had, in addition to a defective +circulation, a decidedly geyser-like action and produced wet steam. + +[Illustration: No. 12] + +All of the types mentioned, with the exception of Nos. 5 and 6, had +between their several parts a large number of bolted joints which were +subjected to the action of the fire. When these boilers were placed in +operation it was demonstrated that as soon as any scale formed on the +heating surfaces, leaks were caused due to unequal expansion. + +No. 12. With this boiler, an attempt was made to remove the joints from +the fire and to increase the heating surface in a given space. Water +tubes were expanded into both sides of wrought-iron boxes, openings +being made for the admission of water and the exit of steam. Fire tubes +were placed inside the water tubes to increase the heating surface. This +design was abandoned because of the rapid stopping up of the tubes by +scale and the impossibility of cleaning them. + +[Illustration: No. 13] + +No. 13. Vertical straight line headers of cast iron, each containing two +rows of tubes, were bolted to a connection leading to the steam and +water drum above. + +[Illustration: No. 14] + +No. 14. A wrought-iron box was substituted for the double cast-iron +headers. In this design, stays were necessary and were found, as always, +to be an element to be avoided wherever possible. The boiler was an +improvement on No. 6, however. A slanting bridge wall was introduced +underneath the drum to throw a larger portion of its heating surface +into the combustion chamber under the bank of tubes. + +This bridge wall was found to be difficult to keep in repair and was of +no particular benefit. + +[Illustration: No. 15] + +No. 15. Each row of tubes was expanded at each end into a continuous +header, cast of car wheel metal. The headers had a sinuous form so that +they would lie close together and admit of a staggered position of the +tubes when assembled. While other designs of header form were tried +later, experience with Nos. 14 and 15 showed that the style here adopted +was the best for all purposes and it has not been changed materially +since. The drum in this design was supported by girders resting on the +brickwork. Bolted joints were discarded, with the exception of those +connecting the headers to the front and rear ends of the drums and the +bottom of the rear headers to the mud drum. Even such joints, however, +were found objectionable and were superseded in subsequent construction +by short lengths of tubes expanded into bored holes. + +[Illustration: No. 16] + +No. 16. In this design, headers were tried which were made in the form +of triangular boxes, in each of which there were three tubes expanded. +These boxes were alternately reversed and connected by short lengths of +expanded tubes, being connected to the drum by tubes bent in a manner to +allow them to enter the shell normally. The joints between headers +introduced an element of weakness and the connections to the drum were +insufficient to give adequate circulation. + +[Illustration: No. 17] + +No. 17. Straight horizontal headers were next tried, alternately shifted +right and left to allow a staggering of tubes. These headers were +connected to each other and to the drums by expanded nipples. The +objections to this boiler were almost the same as those to No. 16. + +[Illustration: No. 18] + +[Illustration: No. 19] + +Nos. 18 and 19. These boilers were designed primarily for fire +protection purposes, the requirements demanding a small, compact boiler +with ability to raise steam quickly. These both served the purpose +admirably but, as in No. 9, the only provision made for the securing of +dry steam was the use of the steam dome, shown in the illustration. This +dome was found inadequate and has since been abandoned in nearly all +forms of boiler construction. No other remedy being suggested at the +time, these boilers were not considered as desirable for general use as +Nos. 21 and 22. In Europe, however, where small size units were more in +demand, No. 18 was modified somewhat and used largely with excellent +results. These experiments, as they may now be called, although many +boilers of some of the designs were built, clearly demonstrated that the +best construction and efficiency required adherence to the following +elements of design: + + +1st. Sinuous headers for each vertical row of tubes. + + +2nd. A separate and independent connection with the drum, both front and +rear, for each vertical row of tubes. + +[Illustration: No. 20A] + +[Illustration: No. 20B] + + +3rd. All joints between parts of the boiler proper to be made without +bolts or screw plates. + + +4th. No surfaces to be used which necessitate the use of stays. + + +5th. The boiler supported independently of the brickwork so as to allow +freedom for expansion and contraction as it is heated or cooled. + + +6th. Ample diameter of steam and water drums, these not to be less than +30 inches except for small size units. + + +7th. Every part accessible for cleaning and repairs. + + +With these points having been determined, No. 20 was designed. This +boiler had all the desirable features just enumerated, together with a +number of improvements as to detail of construction. The general form of +No. 15 was adhered to but the bolted connections between sections and +drum and sections and mud drum were discarded in favor of connections +made by short lengths of boiler tubes expanded into the adjacent parts. +This boiler was suspended from girders, like No. 15, but these in turn +were carried on vertical supports, leaving the pressure parts entirely +free from the brickwork, the mutually deteriorating strains present +where one was supported by the other being in this way overcome. +Hundreds of thousands of horse power of this design were built, giving +great satisfaction. The boiler was known as the "C. I. F." (cast-iron +front) style, an ornamental cast-iron front having been usually +furnished. + +[Illustration: No. 21] + +The next step, and the one which connects the boilers as described above +to the boiler as it is built to-day, was the design illustrated in No. +21. These boilers were known as the "W. I. F." style, the fronts +furnished as part of the equipment being constructed largely of wrought +iron. The cast-iron drumheads used in No. 20 were replaced by +wrought-steel flanged and "bumped" heads. The drums were made longer and +the sections connected to wrought-steel cross boxes riveted to the +bottom of the drums. The boilers were supported by girders and columns +as in No. 20. + +[Illustration: No. 22] + +No. 22. This boiler, which is designated as the "Vertical Header" type, +has the same general features of construction as No. 21, except that the +tube sheet side of the headers is "stepped" to allow the headers to be +placed vertically and at right angles to the drum and still maintain the +tubes at the angle used in Nos. 20 and 21. + +[Illustration: No. 23] + +No. 23, or the cross drum design of boiler, is a development of the +Babcock & Wilcox marine boiler, in which the cross drum is used +exclusively. The experience of the Glasgow Works of The Babcock & +Wilcox, Ltd., with No. 18 proved that proper attention to details of +construction would make it a most desirable form of boiler where +headroom was limited. A large number of this design have been +successfully installed and are giving satisfactory results under widely +varying conditions. The cross drum boiler is also built in a vertical +header design. + +Boilers Nos. 21, 22 and 23, with a few modifications, are now the +standard forms. These designs are illustrated, as they are constructed +to-day, on pages 48, 52, 54, 58 and 60. + +The last step in the development of the water-tube boiler, beyond which +it seems almost impossible for science and skill to advance, consists in +the making of all pressure parts of the boiler of wrought steel, +including sinuous headers, cross boxes, nozzles, and the like. This +construction was the result of the demands of certain Continental laws +that are coming into general vogue in this country. The Babcock & Wilcox +Co. have at the present time a plant producing steel forgings that have +been pronounced by the _London Engineer_ to be "a perfect triumph +of the forgers' art". + +The various designs of this all wrought-steel boiler are fully +illustrated in the following pages. + +[Illustration: Wrought-steel Vertical Header Longitudinal Drum Babcock & +Wilcox Boiler, Equipped with Babcock & Wilcox Superheater and Babcock & +Wilcox Chain Grate Stoker] + + + + +THE BABCOCK & WILCOX BOILER + + +The following brief description of the Babcock & Wilcox boiler will +clearly indicate the manner in which it fulfills the requirements of the +perfect steam boiler already enumerated. + +The Babcock & Wilcox boiler is built in two general classes, the +longitudinal drum type and the cross drum type. Either of these designs +may be constructed with vertical or inclined headers, and the headers in +turn may be of wrought steel or cast iron dependent upon the working +pressure for which the boiler is constructed. The headers may be of +different lengths, that is, may connect different numbers of tubes, and +it is by a change in the number of tubes in height per section and the +number of sections in width that the size of the boiler is varied. + +The longitudinal drum boiler is the generally accepted standard of +Babcock & Wilcox construction. The cross drum boiler, though originally +designed to meet certain conditions of headroom, has become popular for +numerous classes of work where low headroom is not a requirement which +must be met. + +LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type of +boiler is made up of a drum or drums, depending upon the width of the +boiler extending longitudinally over the other pressure parts. To the +drum or drums there are connected through cross boxes at either end the +sections, which are made up of headers and tubes. At the lower end of +the sections there is a mud drum extending entirely across the setting +and connected to all sections. The connections between all parts are by +short lengths of tubes expanded into bored seats. + +[Illustration: Forged-steel Drumhead with Manhole Plate in Position] + +The drums are of three sheets, of such thickness as to give the required +factor of safety under the maximum pressure for which the boiler is +constructed. The circular seams are ordinarily single lap riveted though +these may be double lap riveted to meet certain requirements of pressure +or of specifications. The longitudinal seams are properly proportioned +butt and strap or lap riveted joints dependent upon the pressure for +which the boilers are built. Where butt strap joints are used the straps +are bent to the proper radius in an hydraulic press. The courses are +built independently to template and are assembled by an hydraulic +forcing press. All riveted holes are punched one-quarter inch smaller +than the size of rivets as driven and are reamed to full size after the +plates are assembled. All rivets are driven by hydraulic pressure and +held until black. + +[Illustration: Forged-steel Drumhead Interior] + +The drumheads are hydraulic forged at a single heat, the manhole opening +and stiffening ring being forged in position. Flat raised seats for +water column and feed connections are formed in the forging. + +All heads are provided with manholes, the edges of which are turned +true. The manhole plates are of forged steel and turned to fit manhole +opening. These plates are held in position by forged-steel guards and +bolts. + +The drum nozzles are of forged steel, faced, and fitted with taper +thread stud bolts. + +[Illustration: Forged-steel Drum Nozzle] + +Cross boxes by means of which the sections are attached to the drums, +are of forged steel, made from a single sheet. + +Where two or more drums are used in one boiler they are connected by a +cross pipe having a flanged outlet for the steam connection. + +[Illustration: Forged-steel Cross Box] + +The sections are built of 4-inch hot finished seamless open-hearth steel +tubes of No. 10 B. W. G. where the boilers are built for working +pressures up to 210 pounds. Where the working pressure is to be above +this and below 260 pounds, No. 9 B. W. G. tubes are supplied. + +[Illustration: Inside Handhole Fittings Wrought-steel Vertical Header] + +The tubes are expanded into headers of serpentine or sinuous form, which +dispose the tubes in a staggered position when assembled as a complete +boiler. These headers are of wrought steel or of cast iron, the latter +being ordinarily supplied where the working pressure is not to exceed +160 pounds. The headers may be either vertical or inclined as shown in +the various illustrations of assembled boilers. + +[Illustration: Wrought-steel Vertical Header] + +Opposite each tube end in the headers there is placed a handhole of +sufficient size to permit the cleaning, removal or renewal of a tube. +These openings in the wrought steel vertical headers are elliptical in +shape, machine faced, and milled to a true plane back from the edge a +sufficient distance to make a seat. The openings are closed by inside +fitting forged plates, shouldered to center in the opening, their +flanged seats milled to a true plane. These plates are held in position +by studs and forged-steel binders and nuts. The joints between plates +and headers are made with a thin gasket. + +[Illustration: Inside Handhole Fitting Wrought-steel Inclined Header] + +In the wrought-steel inclined headers the handhole openings are either +circular or elliptical, the former being ordinarily supplied. The +circular openings have a raised seat milled to a true plane. The +openings are closed on the outside by forged-steel caps, milled and +ground true, held in position by forged-steel safety clamps and secured +by ball-headed bolts to assure correct alignment. With this style of +fitting, joints are made tight, metal to metal, without packing of any +kind. + +[Illustration: Wrought-steel Inclined Header] + +Where elliptical handholes are furnished they are faced inside, closed +by inside fitting forged-steel plates, held to their seats by studs and +secured by forged-steel binders and nuts. + +The joints between plates and header are made with a thin gasket. + +[Illustration: Cast-iron Vertical Header] + +The vertical cast-iron headers have elliptical handholes with raised +seats milled to a true plane. These are closed on the outside by +cast-iron caps milled true, held in position by forged-steel safety +clamps, which close the openings from the inside and which are secured +by ball-headed bolts to assure proper alignment. All joints are made +tight, metal to metal, without packing of any kind. + +The mud drum to which the sections are attached at the lower end of the +rear headers, is a forged-steel box 7¼ inches square, and of such length +as to be connected to all headers by means of wrought nipples expanded +into counterbored seats. The mud drum is furnished with handholes for +cleaning, these being closed from the inside by forged-steel plates with +studs, and secured on a faced seat in the mud drum by forged-steel +binders and nuts. The joints between the plates and the drum are made +with thin gaskets. The mud drum is tapped for blow-off connection. + +All connections between drums and sections and between sections and mud +drum are of hot finished seamless open-hearth steel tubes of No. 9 +B. W. G. + +Boilers of the longitudinal drum type are suspended front and rear from +wrought-steel supporting frames entirely independent of the brickwork. +This allows for expansion and contraction of the pressure parts without +straining either the boiler or the brickwork, and also allows of +brickwork repair or renewal without in any way disturbing the boiler or +its connections. + +[Illustration: Babcock & Wilcox Wrought-steel Vertical Header Cross Drum +Boiler] + +CROSS DRUM CONSTRUCTION--The cross drum type of boilers differs from the +longitudinal only in drum construction and method of support. The drum +in this type is placed transversely across the rear of the boiler and is +connected to the sections by means of circulating tubes expanded into +bored seats. + +The drums for all pressures are of two sheets of sufficient thickness to +give the required factor of safety. The longitudinal seams are double +riveted butt strapped, the straps being bent to the proper radius in an +hydraulic press. The circulating tubes are expanded into the drums at +the seams, the butt straps serving as tube seats. + +The drumheads, drum fittings and features of riveting are the same in +the cross drum as in the longitudinal types. The sections and mud drum +are also the same for the two types. + +Cross drum boilers are supported at the rear on the mud drum which rests +on cast-iron foundation plates. They are suspended at the front from a +wrought-iron supporting frame, each section being suspended +independently from the cross members by hook suspension bolts. This +method of support is such as to allow for expansion and contraction +without straining either the boiler or the brickwork and permits of +repair or renewal of the latter without in any way disturbing the boiler +or its connections. + +The following features of design and of attachments supplied are the +same for all types. + +FRONTS--Ornamental fronts are fitted to the front supporting frame. +These have large doors for access to the front headers and panels above +the fire fronts. The fire fronts where furnished have independent frames +for fire doors which are bolted on, and ashpit doors fitted with blast +catches. The lugs on door frames and on doors are cast solid. The faces +of doors and of frames are planed and the lugs milled. The doors and +frames are placed in their final relative position, clamped, and the +holes for hinge pins drilled while thus held. A perfect alignment of +door and frame is thus assured and the method is representative of the +care taken in small details of manufacture. + +The front as a whole is so arranged that any stoker may be applied with +but slight modification wherever boilers are set with sufficient furnace +height. + +[Illustration: Cross Drum Boiler Front] + +In the vertical header boilers large wrought-iron doors, which give +access to the rear headers, are attached to the rear supporting frame. + +[Illustration: Wrought-steel Inclined Header Longitudinal Drum Babcock & +Wilcox Boiler, Equipped with Babcock & Wilcox Superheater] + +[Illustration: Automatic Drumhead Stop and Check Valve] + +FITTINGS--Each boiler is provided with the following fittings as part of +the standard equipment: + +Blow-off connections and valves attached to the mud drum. + +Safety valves placed on nozzles on the steam drums. + +A water column connected to the front of the drum. + +A steam gauge attached to the boiler front. + +Feed water connection and valves. A flanged stop and check valve of +heavy pattern is attached directly to each drumhead, closing +automatically in case of a rupture in the feed line. + +All valves and fittings are substantially built and are of designs which +by their successful service for many years have become standard with The +Babcock & Wilcox Co. + +The fixtures that are supplied with the boilers consist of: + +Dead plates and supports, the plates arranged for a fire brick lining. + +A full set of grate bars and bearers, the latter fitted with expansion +sockets for side walls. + +Flame bridge plates with necessary fastenings, and special fire brick +for lining same. + +Bridge wall girder for hanging bridge wall with expansion sockets for +side walls. + +A full set of access and cleaning doors through which all portions of +the pressure parts may be reached. + +A swing damper and frame with damper operating rig. + +There are also supplied with each boiler a wrench for handhole nuts, a +water-driven turbine tube cleaner, a set of fire tools and a metal steam +hose and cleaning pipe equipped with a special nozzle for blowing dust +and soot from the tubes. + +Aside from the details of design and construction as covered in the +foregoing description, a study of the illustrations will make clear the +features of the boiler as a whole which have led to its success. + +The method of supporting the boiler has been described. This allows it +to be hung at any height that may be necessary to properly handle the +fuel to be burned or to accommodate the stoker to be installed. The +height of the nest of tubes which forms the roof of the furnace is thus +the controlling feature in determining the furnace height, or the +distance from the front headers to the floor line. The sides and front +of the furnace are formed by the side and front boiler walls. The rear +wall of the furnace consists of a bridge wall built from the bottom of +the ashpit to the lower row of tubes. The location of this wall may be +adjusted within limits to give the depth of furnace demanded by the fuel +used. Ordinarily the bridge wall is the determining feature in the +locating of the front baffle. Where a great depth of furnace is +necessary, in which case, if the front baffle were placed at the bridge +wall the front pass of the boiler would be relatively too long, a +patented construction is used which maintains the baffle in what may be +considered its normal position, and a connection made between the baffle +and the bridge wall by means of a tile roof. Such furnace construction +is known as a "Webster" furnace. + +[Illustration: Longitudinal Drum Boiler--Front View] + +A consideration of this furnace will clearly indicate its adaptability, +by reason of its flexibility, for any fuel and any design of stoker. The +boiler lends itself readily to installation with an extension or Dutch +oven furnace if this be demanded by the fuel to be used, and in general +it may be stated that a satisfactory furnace arrangement may be made in +connection with a Babcock & Wilcox boiler for burning any fuel, solid, +liquid or gaseous. + +The gases of combustion evolved in the furnace above described are led +over the heating surfaces by two baffles. These are formed of cast-iron +baffle plates lined with special fire brick and held in position by tube +clamps. The front baffle leads the gases through the forward portion of +the tubes to a chamber beneath the drum or drums. It is in this chamber +that a superheater is installed where such an apparatus is desired. The +gases make a turn over the front baffle, are led downward through the +central portion of the tubes, called the second pass, by means of a +hanging bridge wall of brick and the second baffle, around which they +make a second turn upward, pass through the rear portion of the tubes +and are led to the stack or flue through a damper box in the rear wall, +or around the drums to a damper box placed overhead. + +The space beneath the tubes between the bridge wall and the rear boiler +wall forms a pocket into which much of the soot from the gases in their +downward passage through the second pass will be deposited and from +which it may be readily cleaned through doors furnished for the purpose. + +The gas passages are ample and are so proportioned that the resistance +offered to the gases is only such as will assure the proper abstraction +of heat from the gases without causing undue friction, requiring +excessive draft. + +[Illustration: Partial Vertical Section Showing Method of Introducing +Feed Water] + +The method in which the feed water is introduced through the front +drumhead of the boiler is clearly seen by reference to the illustration. +From this point of introduction the water passes to the rear of the +drum, downward through the rear circulating tubes to the sections, +upward through the tubes of the sections to the front headers and +through these headers and front circulating tubes again to the drum +where such water as has not been formed into steam retraces its course. +The steam formed in the passage through the tubes is liberated as the +water reaches the front of the drum. The steam so formed is stored in +the steam space above the water line, from which it is drawn through a +so-called "dry pipe." The dry pipe in the Babcock & Wilcox boiler is +misnamed, as in reality it fulfills none of the functions ordinarily +attributed to such a device. This function is usually to restrict the +flow of steam from a boiler with a view to avoid priming. In the Babcock +& Wilcox boiler its function is simply that of a collecting pipe, and as +the aggregate area of the holes in it is greatly in excess of the area +of the steam outlet from the drum, it is plain that there can be no +restriction through this collecting pipe. It extends nearly the length +of the drum, and draws steam evenly from the whole length of the steam +space. + +[Illustration: Cast-iron Vertical Header Longitudinal Drum Babcock & +Wilcox Boiler] + +[Illustration: + Closed Open + +Patented Side Dusting Doors] + +The large tube doors through which access is had to the front headers +and the doors giving such access to the rear headers in boilers of the +vertical header type have already been described and are shown clearly +by the illustrations on pages 56 and 74. In boilers of the inclined +header type, access to the rear headers is secured through the chamber +formed by the headers and the rear boiler wall. Large doors in the sides +of the setting give full access to all parts for inspection and for +removal of accumulations of soot. Small dusting doors are supplied for +the side walls through which all of the heating surfaces may be cleaned +by means of a steam dusting lance. These side dusting doors are a +patented feature and the shutters are self closing. In wide boilers +additional cleaning doors are supplied at the top of the setting to +insure ease in reaching all portions of the heating surface. + +The drums are accessible for inspection through the manhole openings. +The removal of the handhole plates makes possible the inspection of each +tube for its full length and gives the assurance that no defect can +exist that cannot be actually seen. This is particularly advantageous +when inspecting for the presence of scale. + +The materials entering into the construction of the Babcock & Wilcox +boiler are the best obtainable for the special purpose for which they +are used and are subjected to rigid inspection and tests. + +The boilers are manufactured by means of the most modern shop equipment +and appliances in the hands of an old and well-tried organization of +skilled mechanics under the supervision of experienced engineers. + +[Illustration: Cast-iron Vertical Header Cross Drum Babcock & Wilcox +Boiler] + + + + +ADVANTAGES OF THE BABCOCK & WILCOX BOILER + + +The advantages of the Babcock & Wilcox boiler may perhaps be most +clearly set forth by a consideration, 1st, of water-tube boilers as a +class as compared with shell and fire-tube boilers; and 2nd, of the +Babcock & Wilcox boiler specifically as compared with other designs of +water-tube boilers. + + + +WATER-TUBE _VERSUS_ FIRE-TUBE BOILERS + + +Safety--The most important requirement of a steam boiler is that it +shall be safe in so far as danger from explosion is concerned. If the +energy in a large shell boiler under pressure is considered, the thought +of the destruction possible in the case of an explosion is appalling. +The late Dr. Robert H. Thurston, Dean of Sibley College, Cornell +University, and past president of the American Society of Mechanical +Engineers, estimated that there is sufficient energy stored in a plain +cylinder boiler under 100 pounds steam pressure to project it in case of +an explosion to a height of over 3½ miles; a locomotive boiler at 125 +pounds pressure from one-half to one-third of a mile; and a 60 +horse-power return tubular boiler under 75 pounds pressure somewhat over +a mile. To quote: "A cubic foot of heated water under a pressure of from +60 to 70 pounds per square inch has about the same energy as one pound +of gunpowder." From such a consideration, it may be readily appreciated +how the advent of high pressure steam was one of the strongest factors +in forcing the adoption of water-tube boilers. A consideration of the +thickness of material necessary for cylinders of various diameters under +a steam pressure of 200 pounds and assuming an allowable stress of +12,000 pounds per square inch, will perhaps best illustrate this point. +Table 1 gives such thicknesses for various diameters of cylinders not +taking into consideration the weakening effect of any joints which may +be necessary. The rapidity with which the plate thickness increases with +the diameter is apparent and in practice, due to the fact that riveted +joints must be used, the thicknesses as given in the table, with the +exception of the first, must be increased from 30 to 40 per cent. + +In a water-tube boiler the drums seldom exceed 48 inches in diameter and +the thickness of plate required, therefore, is never excessive. The +thinner metal can be rolled to a more uniform quality, the seams admit +of better proportioning, and the joints can be more easily and perfectly +fitted than is the case where thicker plates are necessary. All of these +points contribute toward making the drums of water-tube boilers better +able to withstand the stress which they will be called upon to endure. + +The essential constructive difference between water-tube and fire-tube +boilers lies in the fact that the former is composed of parts of +relatively small diameter as against the large diameters necessary in +the latter. + +The factor of safety of the boiler parts which come in contact with the +most intense heat in water-tube boilers can be made much higher than +would be practicable in a shell boiler. Under the assumptions considered +above in connection with the thickness of plates required, a number 10 +gauge tube (0.134 inch), which is standard in Babcock & Wilcox boilers +for pressures up to 210 pounds under the same allowable stress as was +used in computing Table 1, the safe working pressure for the tubes is +870 pounds per square inch, indicating the very large margin of safety +of such tubes as compared with that possible with the shell of a boiler. + + TABLE 1 + +PLATE THICKNESS REQUIRED + FOR VARIOUS CYLINDER + DIAMETERS + + ALLOWABLE STRESS, + 12000 POUNDS PER + SQUARE INCH, + 200 POUNDS GAUGE + PRESSURE, NO JOINTS + ++---------+-----------+ +|Diameter | Thickness | +|Inches | Inches | ++---------+-----------+ +| 4 | 0.033 | +| 36 | 0.300 | +| 48 | 0.400 | +| 60 | 0.500 | +| 72 | 0.600 | +| 108 | 0.900 | +| 120 | 1.000 | +| 144 | 1.200 | ++---------+-----------+ + +A further advantage in the water-tube boiler as a class is the +elimination of all compressive stresses. Cylinders subjected to external +pressures, such as fire tubes or the internally fired furnaces of +certain types of boilers, will collapse under a pressure much lower than +that which they could withstand if it were applied internally. This is +due to the fact that if there exists any initial distortion from its +true shape, the external pressure will tend to increase such distortion +and collapse the cylinder, while an internal pressure tends to restore +the cylinder to its original shape. + +Stresses due to unequal expansion have been a fruitful source of trouble +in fire-tube boilers. + +In boilers of the shell type, the riveted joints of the shell, with +their consequent double thickness of metal exposed to the fire, gives +rise to serious difficulties. Upon these points are concentrated all +strains of unequal expansion, giving rise to frequent leaks and +oftentimes to actual ruptures. Moreover, in the case of such rupture, +the whole body of contained water is liberated instantaneously and a +disastrous and usually fatal explosion results. + +Further, unequal strains result in shell or fire-tube boilers due to the +difference in temperature of the various parts. This difference in +temperature results from the lack of positive well defined circulation. +While such a circulation does not necessarily accompany all water-tube +designs, in general, the circulation in water-tube boilers is much more +defined than in fire-tube or shell boilers. + +A positive and efficient circulation assures that all portions of the +pressure parts will be at approximately the same temperature and in this +way strains resulting from unequal temperatures are obviated. + +If a shell or fire-tubular boiler explodes, the apparatus as a whole is +destroyed. In the case of water-tube boilers, the drums are ordinarily +so located that they are protected from intense heat and any rupture is +usually in the case of a tube. Tube failures, resulting from blisters or +burning, are not serious in their nature. Where a tube ruptures because +of a flaw in the metal, the result may be more severe, but there cannot +be the disastrous explosion such as would occur in the case of the +explosion of a shell boiler. + +To quote Dr. Thurston, relative to the greater safety of the water-tube +boiler: "The stored available energy is usually less than that of any of +the other stationary boilers and not very far from the amount stored, +pound for pound, in the plain tubular boiler. It is evident that their +admitted safety from destructive explosion does not come from this +relation, however, but from the division of the contents into small +portions and especially from those details of construction which make it +tolerably certain that any rupture shall be local. A violent explosion +can only come from the general disruption of a boiler and the liberation +at once of large masses of steam and water." + +Economy--The requirement probably next in importance to safety in a +steam boiler is economy in the use of fuel. To fulfill such a +requirement, the three items, of proper grate for the class of fuel to +be burned, a combustion chamber permitting complete combustion of gases +before their escape to the stack, and the heating surface of such a +character and arrangement that the maximum amount of available heat may +be extracted, must be co-ordinated. + +Fire-tube boilers from the nature of their design do not permit the +variety of combinations of grate surface, heating surface, and +combustion space possible in practically any water-tube boiler. + +In securing the best results in fuel economy, the draft area in a boiler +is an important consideration. In fire-tube boilers this area is limited +to the cross sectional area of the fire tubes, a condition further +aggravated in a horizontal boiler by the tendency of the hot gases to +pass through the upper rows of tubes instead of through all of the tubes +alike. In water-tube boilers the draft area is that of the space outside +of the tubes and is hence much greater than the cross sectional area of +the tubes. + +Capacity--Due to the generally more efficient circulation found in +water-tube than in fire-tube boilers, rates of evaporation are possible +with water-tube boilers that cannot be approached where fire-tube +boilers are employed. + +Quick Steaming--Another important result of the better circulation +ordinarily found in water-tube boilers is in their ability to raise +steam rapidly in starting and to meet the sudden demands that may be +thrown on them. + +In a properly designed water-tube boiler steam may be raised from a cold +boiler to 200 pounds pressure in less than one-half hour. + +For the sake of comparison with the figure above, it may be stated that +in the U. S. Government Service the shortest time allowed for getting up +steam in Scotch marine boilers is 6 hours and the time ordinarily +allowed is 12 hours. In large double-ended Scotch boilers, such as are +generally used in Trans-Atlantic service, the fires are usually started +24 hours before the time set for getting under way. This length of time +is necessary for such boilers in order to eliminate as far as possible +excessive strains resulting from the sudden application of heat to the +surfaces. + +Accessibility--In the "Requirements of a Perfect Steam Boiler", as +stated by Mr. Babcock, he demonstrates the necessity for complete +accessibility to all portions of the boiler for cleaning, inspection and +repair. + +Cleaning--When the great difference is realized in performance, both as +to economy and capacity of a clean boiler and one in which the heating +surfaces have been allowed to become fouled, it may be appreciated that +the ability to keep heating surfaces clean internally and externally is +a factor of the highest importance. + +Such results can be accomplished only by the use of a design in boiler +construction which gives complete accessibility to all portions. In +fire-tube boilers the tubes are frequently nested together with a space +between them often less than 1¼ inches and, as a consequence, nearly the +entire tube surface is inaccessible. When scale forms upon such tubes it +is impossible to remove it completely from the inside of the boiler and +if it is removed by a turbine hammer, there is no way of knowing how +thorough a job has been done. With the formation of such scale there is +danger through overheating and frequent tube renewals are necessary. + +[Illustration: Portion of 29,000 Horse-power Installation of Babcock & +Wilcox Boilers in the L Street Station of the Edison Electric +Illuminating Co. of Boston, Mass. This Company Operates in its Various +Stations a Total of 39,000 Horse Power of Babcock & Wilcox Boilers] + +In Scotch marine boilers, even with the engines operating condensing, +complete tube renewals at intervals of six or seven years are required, +while large replacements are often necessary in less than one year. In +return tubular boilers operated with bad feed water, complete tube +renewals annually are not uncommon. In this type of boiler much sediment +falls on the bottom sheets where the intense heat to which they are +subjected bakes it to such an excessive hardness that the only method of +removing it is to chisel it out. This can be done only by omitting tubes +enough to leave a space into which a man can crawl and the discomforts +under which he must work are apparent. Unless such a deposit is removed, +a burned and buckled plate will invariably result, and if neglected too +long an explosion will follow. + +In vertical fire-tube boilers using a water leg construction, a deposit +of mud in such legs is an active agent in causing corrosion and the +difficulty of removing such deposit through handholes is well known. A +complete removal is practically impossible and as a last resort to +obviate corrosion in certain designs, the bottom of the water legs in +some cases have been made of copper. A thick layer of mud and scale is +also liable to accumulate on the crown sheet of such boilers and may +cause the sheet to crack and lead to an explosion. + +The soot and fine coal swept along with the gases by the draft will +settle in fire tubes and unless removed promptly, must be cut out with a +special form of scraper. It is not unusual where soft coal is used to +find tubes half filled with soot, which renders useless a large portion +of the heating surface and so restricts the draft as to make it +difficult to burn sufficient coal to develop the required power from +such heating surface as is not covered by soot. + +Water-tube boilers in general are from the nature of their design more +readily accessible for cleaning than are fire-tube boilers. + +Inspection--The objections given above in the consideration of the +inability to properly clean fire-tube boilers hold as well for the +inspection of such boilers. + +Repairs--The lack of accessibility in fire-tube boilers further leads to +difficulties where repairs are required. + +In fire-tube boilers tube renewals are a serious undertaking. The +accumulation of hard deposit on the exterior of the surfaces so enlarges +the tubes that it is oftentimes difficult, if not impossible, to draw +them through the tube sheets and it is usually necessary to cut out such +tubes as will allow access to the one which has failed and remove them +through the manhole. + +When a tube sheet blisters, the defective part must be cut out by +hand-tapped holes drilled by ratchets and as it is frequently impossible +to get space in which to drive rivets, a "soft patch" is necessary. This +is but a makeshift at best and usually results in either a reduction of +the safe working pressure or in the necessity for a new plate. If the +latter course is followed, the old plate must be cut out, a new one +scribed to place to locate rivet holes and in order to obtain room for +driving rivets, the boiler will have to be re-tubed. + +The setting must, of course, be at least partially torn out and +replaced. + +In case of repairs, of such nature in fire-tube boilers, the working +pressure of such repaired boilers will frequently be lowered by the +insurance companies when the boiler is again placed in service. + +In the case of a rupture in a water-tube boiler, the loss will +ordinarily be limited to one or two tubes which can be readily replaced. +The fire-tube boiler will be so completely demolished that the question +of repairs will be shifted from the boiler to the surrounding property, +the damage to which will usually exceed many times the cost of a boiler +of a type which would have eliminated the possibility of a disastrous +explosion. In considering the proper repair cost of the two types of +boilers, the fact should not be overlooked that it is poor economy to +invest large sums in equipment that, through a possible accident to the +boiler may be wholly destroyed or so damaged that the cost of repairs, +together with the loss of time while such repairs are being made, would +purchase boilers of absolute safety and leave a large margin beside. The +possibility of loss of human life should also be considered, though this +may seem a far cry from the question of repair costs. + +Space Occupied--The space required for the boilers in a plant often +exceeds the requirements for the remainder of the plant equipment. Any +saving of space in a boiler room will be a large factor in reducing the +cost of real estate and of the building. Even when the boiler plant is +comparatively small, the saving in space frequently will amount to a +considerable percentage of the cost of the boilers. Table 2 shows the +difference in floor space occupied by fire-tube boilers and Babcock & +Wilcox boilers of the same capacity, the latter being taken as +representing the water-tube class. This saving in space will increase +with the size of the plant for the reason that large size boiler units +while common in water-tube practice are impracticable in fire-tube +practice. + + TABLE 2 + + COMPARATIVE APPROXIMATE FLOOR + SPACE OCCUPIED BY BABCOCK & WILCOX + AND H. R. T. BOILERS + ++------------+----------------+---------------+ +|Size of unit|Babcock & Wilcox| H. R. T. | +|Horse Power |Feet and Inches |Feet and Inches| ++------------+----------------+---------------+ +| 100 | 7 3 × 19 9 | 10 0 × 20 0 | +| 150 | 7 10 × 19 9 | 10 0 × 22 6 | +| 200 | 9 0 × 19 9 | 11 6 × 23 10 | +| 250 | 9 0 × 19 9 | 11 6 × 23 10 | +| 300 | 10 2 × 19 9 | 12 0 × 25 0 | ++------------+----------------+---------------+ + + + +BABCOCK & WILCOX BOILERS AS COMPARED WITH OTHER WATER-TUBE DESIGNS + + +It must be borne in mind that the simple fact that a boiler is of the +water-tube design does not as a necessity indicate that it is a good or +safe boiler. + +Safety--Many of the water-tube boilers on the +market are as lacking as are fire-tube boilers in the positive +circulation which, as has been demonstrated by Mr. Babcock's lecture, is +so necessary in the requirements of the perfect steam boiler. In boilers +using water-leg construction, there is danger of defective circulation, +leaks are common, and unsuspected corrosion may be going on in portions +of the boiler that cannot be inspected. Stresses due to unequal +expansion of the metal cannot be well avoided but they may be minimized +by maintaining at the same temperature all pressure parts of the boiler. +The result is to be secured only by means of a well defined circulation. + +The main feature to which the Babcock & Wilcox boiler owes its safety is +the construction made possible by the use of headers, by which the water +in each vertical row of tubes is separated from that in the adjacent +rows. This construction results in the very efficient circulation +produced through the breaking up of the steam and water in the front +headers, the effect of these headers in producing such a positive +circulation having been clearly demonstrated in Mr. Babcock's lecture. +The use of a number of sections, thus composed of headers and tubes, has +a distinct advantage over the use of a common chamber at the outlet ends +of the tubes. In the former case the circulation of water in one +vertical row of tubes cannot interfere with that in the other rows, +while in the latter construction there will be downward as well as +upward currents and such downward currents tend to neutralize any good +effect there might be through the diminution of the density of the water +column by the steam. + +Further, the circulation results directly from the design of the boiler +and requires no assistance from "retarders", check valves and the like, +within the boiler. All such mechanical devices in the interior of a +boiler serve only to complicate the design and should not be used. + +This positive and efficient circulation assures that all portions of the +pressure parts of the Babcock & Wilcox boiler will be at approximately +the same temperature and in this way strains resulting from unequal +temperatures are obviated. + +Where the water throughout the boiler is at the temperature of the steam +contained, a condition to be secured only by proper circulation, danger +from internal pitting is minimized, or at least limited only to effects +of the water fed the boiler. Where the water in any portion of the +boiler is lower than the temperature of the steam corresponding to the +pressure carried, whether the fact that such lower temperatures exist as +a result of lack of circulation, or because of intentional design, +internal pitting or corrosion will almost invariably result. + +Dr. Thurston has already been quoted to the effect that the admitted +safety of a water-tube boiler is the result of the division of its +contents into small portions. In boilers using a water-leg construction, +while the danger from explosion will be largely limited to the tubes, +there is the danger, however, that such legs may explode due to the +deterioration of their stays, and such an explosion might be almost as +disastrous as that of a shell boiler. The headers in a Babcock & Wilcox +boiler are practically free from any danger of explosion. Were such an +explosion to occur, it would still be localized to a much larger extent +than in the case of a water-leg boiler and the header construction thus +almost absolutely localizes any danger from such a cause. + +Staybolts are admittedly an undesirable element of construction in any +boiler. They are wholly objectionable and the only reason for the +presence of staybolts in a boiler is to enable a cheaper form of +construction to be used than if they were eliminated. + +In boilers utilizing in their design flat-stayed surfaces, or staybolt +construction under pressure, corrosion and wear and tear in service +tends to weaken some single part subject to continual strain, the result +being an increased strain on other parts greatly in excess of that for +which an allowance can be made by any reasonable factor of safety. Where +the construction is such that the weakening of a single part will +produce a marked decrease in the safety and reliability of the whole, it +follows of necessity, that there will be a corresponding decrease in the +working pressure which may be safely carried. + +In water-leg boilers, the use of such flat-stayed surfaces under +pressure presents difficulties that are practically unsurmountable. Such +surfaces exposed to the heat of the fire are subject to unequal +expansion, distortion, leakage and corrosion, or in general, to many of +the objections that have already been advanced against the fire-tube +boilers in the consideration of water-tube boilers as a class in +comparison with fire-tube boilers. + +[Illustration: McAlpin Hotel, New York City, Operating 2360 Horse Power +of Babcock & Wilcox Boilers] + +Aside from the difficulties that may arise in actual service due to the +failure of staybolts, or in general, due to the use of flat-stayed +surfaces, constructional features are encountered in the actual +manufacture of such boilers that make it difficult if not impossible to +produce a first-class mechanical job. It is practically impossible in +the building of such a boiler to so design and place the staybolts that +all will be under equal strain. Such unequal strains, resulting from +constructional difficulties, will be greatly multiplied when such a +boiler is placed in service. Much of the riveting in boilers of this +design must of necessity be hand work, which is never the equal of +machine riveting. The use of water-leg construction ordinarily requires +the flanging of large plates, which is difficult, and because of the +number of heats necessary and the continual working of the material, may +lead to the weakening of such plates. + +In vertical or semi-vertical water-tube boilers utilizing flat-stayed +surfaces under pressure, these surfaces are ordinarily so located as to +offer a convenient lodging place for flue dust, which fuses into a hard +mass, is difficult of removal and under which corrosion may be going on +with no possibility of detection. + +Where stayed surfaces or water legs are features in the design of a +water-tube boiler, the factor of safety of such parts must be most +carefully considered. In such parts too, is the determination of the +factor most difficult, and because of the "rule-of-thumb" determination +frequently necessary, the factor of safety becomes in reality a factor +of ignorance. As opposed to such indeterminate factors of safety, in the +Babcock & Wilcox boiler, when the factor of safety for the drum or drums +has been determined, and such a factor may be determined accurately, the +factors for all other portions of the pressure parts are greatly in +excess of that of the drum. All Babcock & Wilcox boilers are built with +a factor of safety of at least five, and inasmuch as the factor of the +safety of the tubes and headers is greatly in excess of this figure, it +applies specifically to the drum or drums. This factor represents a +greater degree of safety than a considerably higher factor applied to a +boiler in which the shell or any riveted portion is acted upon directly +by the fire, or the same factor applied to a boiler utilizing +flat-stayed surface construction, where the accurate determination of +the limiting factor of safety is difficult, if not impossible. + +That the factor of safety of stayed surfaces is questionable may perhaps +be best realized from a consideration of the severe requirements as to +such factor called for by the rules and regulations of the Board of +Supervising Inspectors, U. S. Government. + +In view of the above, the absence of any stayed surfaces in the Babcock +& Wilcox boiler is obviously a distinguishing advantage where safety is +a factor. It is of interest to note, in the article on the evolution of +the Babcock & Wilcox boiler, that staybolt construction was used in +several designs, found unsatisfactory and unsafe, and discarded. + +Another feature in the design of the Babcock & Wilcox boiler tending +toward added safety is its manner of suspension. This has been indicated +in the previous chapter and is of such nature that all of the pressure +parts are free to expand or contract under variations of temperature +without in any way interfering with any part of the boiler setting. The +sectional nature of the boiler allows a flexibility under varying +temperature changes that practically obviates internal strain. + +In boilers utilizing water-leg construction, on the other hand, the +construction is rigid, giving rise to serious internal strains and the +method of support ordinarily made necessary by the boiler design is not +only unmechanical but frequently dangerous, due to the fact that proper +provision is not made for expansion and contraction under temperature +variations. + +Boilers utilizing water-leg construction are not ordinarily provided +with mud drums. This is a serious defect in that it allows impurities +and sediment to collect in a portion of the boiler not easily inspected, +and corrosion may result. + +Economy--That the water-tube boiler as a class lends itself more readily +than does the fire-tube boiler to a variation in the relation of grate +surface, heating surface and combustion space has been already pointed +out. In economy again, the construction made possible by the use of +headers in Babcock & Wilcox boilers appears as a distinct advantage. +Because of this construction, there is a flexibility possible, in an +unlimited variety of heights and widths that will satisfactorily meet +the special requirements of the fuel to be burned in individual cases. + +An extended experience in the design of furnaces best suited for a wide +variety of fuels has made The Babcock & Wilcox Co. leaders in the field +of economy. Furnaces have been built and are in successful operation for +burning anthracite and bituminous coals, lignite, crude oil, gas-house +tar, wood, sawdust and shavings, bagasse, tan bark, natural gas, blast +furnace gas, by-product coke oven gas and for the utilization of waste +heat from commercial processes. The great number of Babcock & Wilcox +boilers now in satisfactory operation under such a wide range of fuel +conditions constitutes an unimpeachable testimonial to the ability to +meet all of the many conditions of service. + +The limitations in the draft area of fire-tube boilers as affecting +economy have been pointed out. That a greater draft area is possible in +water-tube boilers does not of necessity indicate that proper advantage +of this fact is taken in all boilers of the water-tube class. In the +Babcock & Wilcox boiler, the large draft area taken in connection with +the effective baffling allows the gases to be brought into intimate +contact with all portions of the heating surfaces and renders such +surfaces highly efficient. + +In certain designs of water-tube boilers the baffling is such as to +render ineffective certain portions of the heating surface, due to the +tendency of soot and dirt to collect on or behind baffles, in this way +causing the interposition of a layer of non-conducting material between +the hot gases and the heating surfaces. + +In Babcock & Wilcox boilers the standard baffle arrangement is such as +to allow the installation of a superheater without in any way altering +the path of the gases from furnace to stack, or requiring a change in +the boiler design. In certain water-tube boilers the baffle arrangement +is such that if a superheater is to be installed a complete change in +the ordinary baffle design is necessary. Frequently to insure +sufficiently hot gas striking the heating surfaces, a portion is +by-passed directly from the furnace to the superheater chamber without +passing over any of the boiler heating surfaces. Any such arrangement +will lead to a decrease in economy and the use of boilers requiring it +should be avoided. + +Capacity--Babcock & Wilcox boilers are run successfully in every-day +practice at higher ratings than any other boilers in practical service. +The capacities thus obtainable are due directly to the efficient +circulation already pointed out. Inasmuch as the construction utilizing +headers has a direct bearing in producing such circulation, it is also +connected with the high capacities obtainable with this apparatus. + +Where intelligently handled and kept properly cleaned, Babcock & Wilcox +boilers are operated in many plants at from 200 to 225 per cent of their +rated evaporative capacity and it is not unusual for them to be operated +at 300 per cent of such rated capacity during periods of peak load. + +Dry Steam--In the list of the requirements of the perfect steam boiler, +the necessity that dry steam be generated has been pointed out. The +Babcock & Wilcox boiler will deliver dry steam under higher capacities +and poorer conditions of feed water than any other boiler now +manufactured. Certain boilers will, when operated at ordinary ratings, +handle poor feed water and deliver steam in which the moisture content +is not objectionable. When these same boilers are driven at high +overloads, there will be a direct tendency to prime and the percentage +of moisture in the steam delivered will be high. This tendency is the +result of the lack of proper circulation and once more there is seen the +advantage of the headers of the Babcock & Wilcox boiler, resulting as it +does in the securing of a positive circulation. + +In the design of the Babcock & Wilcox boiler sufficient space is +provided between the steam outlet and the disengaging point to insure +the steam passing from the boiler in a dry state without entraining or +again picking up any particles of water in its passage even at high +rates of evaporation. Ample time is given for a complete separation of +steam from the water at the disengaging surface before the steam is +carried from the boiler. These two features, which are additional causes +for the ability of the Babcock & Wilcox boiler to deliver dry steam, +result from the proper proportioning of the steam and water space of the +boiler. From the history of the development of the boiler, it is evident +that the cubical capacity per horse power of the steam and water space +has been adopted after numerous experiments. + +That the "dry pipe" serves in no way the generally understood function +of such device has been pointed out. As stated, the function of the "dry +pipe" in a Babcock & Wilcox boiler is simply that of a collecting pipe +and this statement holds true regardless of the rate of operation of the +boiler. + +In certain boilers, "superheating surface" is provided to "dry the +steam," or to remove the moisture due to priming or foaming. Such +surface is invariably a source of trouble unless the steam is initially +dry and a boiler which will deliver dry steam is obviously to be +preferred to one in which surface must be supplied especially for such +purpose. Where superheaters are installed with Babcock & Wilcox boilers, +they are in every sense of the word superheaters and not driers, the +steam being delivered to them in a dry state. + +The question has been raised in connection with the cross drum design of +the Babcock & Wilcox boiler as to its ability to deliver dry steam. +Experience has shown the absolute lack of basis for any such objection. +The Babcock & Wilcox Company at its Bayonne Works some time ago made a +series of experiments to see in what manner the steam generated was +separated from the water either in the drum or in its passage to the +drum. Glass peepholes were installed in each end of a drum in a boiler +of the marine design, at the point midway between that at which the +horizontal circulating tubes entered the drum and the drum baffle plate. +By holding a light at one of these peepholes the action in the drum was +clearly seen through the other. It was found that with the boiler +operated under three-quarter inch ashpit pressure, which, with the fuel +used would be equivalent to approximately 185 per cent of rating for +stationary boiler practice, that each tube was delivering with great +velocity a stream of solid water, which filled the tube for half its +cross sectional area. There was no spray or mist accompanying such +delivery, clearly indicating that the steam had entirely separated from +the water in its passage through the horizontal circulating tubes, which +in the boiler in question were but 50 inches long. + +[Illustration: Northwest Station of the Commonwealth Edison Co., +Chicago, Ill. This Installation Consists of 11,360 Horse Power of +Babcock & Wilcox Boilers and Superheaters, Equipped with Babcock & +Wilcox Chain Grate Stokers] + +These experiments proved conclusively that the size of the steam drums +in the cross drum design has no appreciable effect in determining the +amount of liberating surface, and that sufficient liberating surface is +provided in the circulating tubes alone. If further proof of the ability +of this design of boiler to deliver dry steam is required, such proof is +perhaps best seen in the continued use of the Babcock & Wilcox marine +boiler, in which the cross drum is used exclusively, and with which +rates of evaporation are obtained far in excess of those secured in +ordinary practice. + +Quick Steaming--The advantages of water-tube boilers as a class over +fire-tube boilers in ability to raise steam quickly have been indicated. + +Due to the constant and thorough circulation resulting from the +sectional nature of the Babcock & Wilcox boiler, steam may be raised +more rapidly than in practically any other water-tube design. + +In starting up a cold Babcock & Wilcox boiler with either coal or oil +fuel, where a proper furnace arrangement is supplied, steam may be +raised to a pressure of 200 pounds in less than half an hour. With a +Babcock & Wilcox boiler in a test where forced draft was available, +steam was raised from an initial temperature of the boiler and its +contained water of 72 degrees to a pressure of 200 pounds, in 12½ +minutes after lighting the fire. The boiler also responds quickly in +starting from banked fires, especially where forced draft is available. + +In Babcock & Wilcox boilers the water is divided into many small streams +which circulate without undue frictional resistance in thin envelopes +passing through the hottest part of the furnace, the steam being carried +rapidly to the disengaging surface. There is no part of the boiler +exposed to the heat of the fire that is not in contact with water +internally, and as a result there is no danger of overheating on +starting up quickly nor can leaks occur from unequal expansion such as +might be the case where an attempt is made to raise steam rapidly in +boilers using water leg construction. + +Storage Capacity for Steam and Water--Where sufficient steam and water +capacity are not provided in a boiler, its action will be irregular, the +steam pressure varying over wide limits and the water level being +subject to frequent and rapid fluctuation. + +Owing to the small relative weight of steam, water capacity is of +greater importance in this respect than steam space. With a gauge +pressure of 180 pounds per square inch, 8 cubic feet of steam, which is +equivalent to one-half cubic foot of water space, are required to supply +one boiler horse power for one minute and if no heat be supplied to the +boiler during such an interval, the pressure will drop to 150 pounds per +square inch. The volume of steam space, therefore, may be over rated, +but if this be too small, the steam passing off will carry water with it +in the form of spray. Too great a water space results in slow steaming +and waste of fuel in starting up; while too much steam space adds to the +radiating surface and increases the losses from that cause. + +That the steam and water space of the Babcock & Wilcox boiler are the +result of numerous experiments has previously been pointed out. + +Accessibility--Cleaning. That water-tube boilers are more accessible as +a class than are fire-tube boilers has been indicated. All water-tube +boilers, however, are not equally accessible. In certain designs, due to +the arrangement of baffling used it is practically impossible to remove +all deposits of soot and dirt. Frequently, in order to cheapen the +product, sufficient cleaning and access doors are not supplied as part +of the boiler equipment. The tendency of soot to collect on the crown +sheets of certain vertical water-tube boilers has been noted. Such +deposits are difficult to remove and if corrosion goes on beneath such a +covering the sheet may crack and an explosion result. + +[Illustration: Rear View--Longitudinal Drum Vertical Header Boiler, +Showing Access Doors to Rear Headers] + +It is almost impossible to thoroughly clean water legs internally, and +in such places also is there a tendency to unsuspected corrosion under +deposits that cannot be removed. + +In Babcock & Wilcox boilers every portion of the interior of the heating +surfaces can be reached and kept clean, while any soot deposited on the +exterior surfaces can be blown off while the boiler is under pressure. + +Inspection--The accessibility which makes possible the thorough cleaning +of all portions of the Babcock & Wilcox boiler also provides a means for +a thorough inspection. + +Drums are accessible for internal inspection by the removal of the +manhole plates. Front headers may be inspected through large doors +furnished for the purpose. Rear headers in the inclined header designs +may be inspected from the chamber formed by such headers and the rear +wall of the boiler. In the vertical header designs rear tube doors are +furnished, as has been stated. In certain designs of water-tube boilers +in order to assure accessibility for inspection of the rear ends of the +tubes, the rear portion of the boiler is exposed to the atmosphere with +resulting excessive radiation losses. In other designs the means of +access to the rear ends of the tubes are of a makeshift and +unworkmanlike character. + +By the removal of handhole plates, all tubes in a Babcock & Wilcox +boiler may be inspected for their full length either for the presence of +scale or for suspected corrosion. + +Repairs--In Babcock & Wilcox boilers the possession of great strength, +the elimination of stresses due to uneven temperatures and of the +resulting danger of leaks and corrosion, the protection of the drums +from the intense heat of the fire, and the decreased liability of the +scale forming matter to lodge on the hottest tube surfaces, all tend to +minimize the necessity for repairs. The tubes of the Babcock & Wilcox +boiler are practically the only part which may need renewal and these +only at infrequent intervals When necessary, such renewals may be made +cheaply and quickly. A small stock of tubes, 4 inches in diameter, of +sufficient length for the boiler used, is all that need be carried to +make renewals. + +Repairs in water-leg boilers are difficult at best and frequently +unsatisfactory when completed. When staybolt replacements are necessary, +in order to get at the inner sheet of the water leg, several tubes must +in some cases be cut out. Not infrequently a replacement of an entire +water leg is necessary and this is difficult and requires a lengthy +shutdown. With the Babcock & Wilcox boiler, on the other hand, even if +it is necessary to replace a section, this may be done in a few hours +after the boiler is cool. + +In the case of certain staybolt failures the working pressure of a +repaired boiler utilizing such construction will frequently be lowered +by the insurance companies when the boiler is again placed in service. +The sectional nature of the Babcock & Wilcox boiler enables it to +maintain its original working pressure over long periods of time, almost +regardless of the nature of any repair that may be required. + +[Illustration: 1456 Horse-power Installation of Babcock & Wilcox Boilers +at the Raritan Woolen Mills, Raritan, N. J. The First of These Boilers +were Installed in 1878 and 1881 and are still Operated at 80 Pounds +Pressure] + +Durability--Babcock & Wilcox boilers are being operated in every-day +service with entirely satisfactory results and under the same steam +pressure as that for which they were originally sold that have been +operated from thirty to thirty-five years. It is interesting to note in +considering the life of a boiler that the length of life of a Babcock & +Wilcox boiler must be taken as the criterion of what length of life is +possible. This is due to the fact that there are Babcock & Wilcox +boilers in operation to-day that have been in service from a time that +antedates by a considerable margin that at which the manufacturer of any +other water-tube boiler now on the market was started. + +Probably the very best evidence of the value of the Babcock & Wilcox +boiler as a steam generator and of the reliability of the apparatus, is +seen in the sales of the company. Since the company was formed, there +have been sold throughout the world over 9,900,000 horse power. + +A feature that cannot be overlooked in the consideration of the +advantages of the Babcock & Wilcox boiler is the fact that as a part of +the organization back of the boiler, there is a body of engineers of +recognized ability, ready at all times to assist its customers in every +possible way. + +[Illustration: 2400 Horse-power Installation of Babcock & Wilcox Boilers +in the Union Station Power House of the Pennsylvania Railroad Co., +Pittsburgh, Pa. This Company has a Total of 28,500 Horse Power of +Babcock & Wilcox Boilers Installed] + + + + +HEAT AND ITS MEASUREMENT + + +The usual conception of heat is that it is a form of energy produced by +the vibratory motion of the minute particles or molecules of a body. All +bodies are assumed to be composed of these molecules, which are held +together by mutual cohesion and yet are in a state of continual +vibration. The hotter a body or the more heat added to it, the more +vigorous will be the vibrations of the molecules. + +As is well known, the effect of heat on a body may be to change its +temperature, its volume, or its state, that is, from solid to liquid or +from liquid to gaseous. Where water is melted from ice and evaporated +into steam, the various changes are admirably described in the lecture +by Mr. Babcock on "The Theory of Steam Making", given in the next +chapter. + +The change in temperature of a body is ordinarily measured by +thermometers, though for very high temperatures so-called pyrometers are +used. The latter are dealt with under the heading "High Temperature +Measurements" at the end of this chapter. + +[Illustration: Fig. 11] + +By reason of the uniform expansion of mercury and its great +sensitiveness to heat, it is the fluid most commonly used in the +construction of thermometers. In all thermometers the freezing point and +the boiling point of water, under mean or average atmospheric pressure +at sea level, are assumed as two fixed points, but the division of the +scale between these two points varies in different countries. The +freezing point is determined by the use of melting ice and for this +reason is often called the melting point. There are in use three +thermometer scales known as the Fahrenheit, the Centigrade or Celsius, +and the Réaumur. As shown in Fig. 11, in the Fahrenheit scale, the space +between the two fixed points is divided into 180 parts; the boiling +point is marked 212, and the freezing point is marked 32, and zero is a +temperature which, at the time this thermometer was invented, was +incorrectly imagined to be the lowest temperature attainable. In the +centigrade and the Réaumur scales, the distance between the two fixed +points is divided into 100 and 80 parts, respectively. In each of these +two scales the freezing point is marked zero, and the boiling point is +marked 100 in the centigrade and 80 in the Réaumur. Each of the 180, 100 +or 80 divisions in the respective thermometers is called a degree. + +Table 3 and appended formulae are useful for converting from one scale +to another. + +In the United States the bulbs of high-grade thermometers are usually +made of either Jena 58^{III} borosilicate thermometer glass or Jena +16^{III} glass, the stems being made of ordinary glass. The Jena +16^{III} glass is not suitable for use at temperatures much above 850 +degrees Fahrenheit and the harder Jena 59^{III} should be used in +thermometers for temperatures higher than this. + +Below the boiling point, the hydrogen-gas thermometer is the almost +universal standard with which mercurial thermometers may be compared, +while above this point the nitrogen-gas thermometer is used. In both of +these standards the change in temperature is measured by the change in +pressure of a constant volume of the gas. + +In graduating a mercurial thermometer for the Fahrenheit scale, +ordinarily a degree is represented as 1/180 part of the volume of the +stem between the readings at the melting point of ice and the boiling +point of water. For temperatures above the latter, the scale is extended +in degrees of the same volume. For very accurate work, however, the +thermometer may be graduated to read true-gas-scale temperatures by +comparing it with the gas thermometer and marking the temperatures at 25 +or 50 degree intervals. Each degree is then 1/25 or 1/50 of the volume +of the stem in each interval. + +Every thermometer, especially if intended for use above the boiling +point, should be suitably annealed before it is used. If this is not +done, the true melting point and also the "fundamental interval", that +is, the interval between the melting and the boiling points, may change +considerably. After continued use at the higher temperatures also, the +melting point will change, so that the thermometer must be calibrated +occasionally to insure accurate readings. + + TABLE 3 + + COMPARISON OF THERMOMETER SCALES + ++---------------+----------+----------+----------+ +| |Fahrenheit|Centigrade| Réaumur | ++---------------+----------+----------+----------+ +|Absolute Zero | -459.64 | -273.13 | -218.50 | +| | 0 | -17.78 | -14.22 | +| | 10 | -12.22 | -9.78 | +| | 20 | -6.67 | -5.33 | +| | 30 | -1.11 | -0.89 | +|Freezing Point | 32 | 0 | 0 | +|Maximum Density| | | | +| of Water | 39.1 | 3.94 | 3.15 | +| | 50 | 10 | 8 | +| | 75 | 23.89 | 19.11 | +| | 100 | 37.78 | 30.22 | +| | 200 | 93.33 | 74.67 | +|Boiling Point | 212 | 100 | 80 | +| | 250 | 121.11 | 96.89 | +| | 300 | 148.89 | 119.11 | +| | 350 | 176.67 | 141.33 | ++---------------+----------+----------+----------+ + +F = 9/5C+32° = 9/4R+32° + +C = 5/9(F-32°) = 5/4R + +R = 4/9(F-32°) = 4/5C + +As a general rule thermometers are graduated to read correctly for total +immersion, that is, with bulb and stem of the thermometer at the same +temperature, and they should be used in this way when compared with a +standard thermometer. If the stem emerges into space either hotter or +colder than that in which the bulb is placed, a "stem correction" must +be applied to the observed temperature in addition to any correction +that may be found in the comparison with the standard. For instance, for +a particular thermometer, comparison with the standard with both fully +immersed made necessary the following corrections: + +_Temperature_ _Correction_ + 40°F 0.0 + 100 0.0 + 200 0.0 + 300 +2.5 + 400 -0.5 + 500 -2.5 + +When the sign of the correction is positive (+) it must be added to the +observed reading, and when the sign is a negative (-) the correction +must be subtracted. The formula for the stem correction is as follows: + +Stem correction = 0.000085 × n (T-t) + +in which T is the observed temperature, t is the mean temperature of the +emergent column, n is the number of degrees of mercury column emergent, +and 0.000085 is the difference between the coefficient of expansion of +the mercury and that in the glass in the stem. + +Suppose the observed temperature is 400 degrees and the thermometer is +immersed to the 200 degrees mark, so that 200 degrees of the mercury +column project into the air. The mean temperature of the emergent column +may be found by tying another thermometer on the stem with the bulb at +the middle of the emergent mercury column as in Fig. 12. Suppose this +mean temperature is 85 degrees, then + +Stem correction = 0.000085 × 200 × (400 - 85) = 5.3 degrees. + +As the stem is at a lower temperature than the bulb, the thermometer +will evidently read too low, so that this correction must be added to +the observed reading to find the reading corresponding to total +immersion. The corrected reading will therefore be 405.3 degrees. If +this thermometer is to be corrected in accordance with the calibrated +corrections given above, we note that a further correction of 0.5 must +be applied to the observed reading at this temperature, so that the +correct temperature is 405.3 - 0.5 = 404.8 degrees or 405 degrees. + +[Illustration: Fig. 12] + +[Illustration: Fig. 13] + +Fig. 12 shows how a stem correction can be obtained for the case just +described. + +Fig. 13 affords an opportunity for comparing the scale of a thermometer +correct for total immersion with one which will read correctly when +submerged to the 300 degrees mark, the stem being exposed at a mean +temperature of 110 degrees Fahrenheit, a temperature often prevailing +when thermometers are used for measuring temperatures in steam mains. + +Absolute Zero--Experiments show that at 32 degrees Fahrenheit a perfect +gas expands 1/491.64 part of its volume if its pressure remains constant +and its temperature is increased one degree. Thus if gas at 32 degrees +Fahrenheit occupies 100 cubic feet and its temperature is increased one +degree, its volume will be increased to 100 + 100/491.64 = 100.203 cubic +feet. For a rise of two degrees the volume would be 100 + (100 × 2) / +491.64 = 100.406 cubic feet. If this rate of expansion per one degree +held good at all temperatures, and experiment shows that it does above +the freezing point, the gas, if its pressure remained the same, would +double its volume, if raised to a temperature of 32 + 491.64 = 523.64 +degrees Fahrenheit, while under a diminution of temperature it would +shrink and finally disappear at a temperature of 491.64 - 32 = 459.64 +degrees below zero Fahrenheit. While undoubtedly some change in the law +would take place before the lower temperature could be reached, there is +no reason why the law may not be used within the range of temperature +where it is known to hold good. From this explanation it is evident that +under a constant pressure the volume of a gas will vary as the number of +degrees between its temperature and the temperature of -459.64 degrees +Fahrenheit. To simplify the application of the law, a new thermometric +scale is constructed as follows: the point corresponding to -460 degrees +Fahrenheit, is taken as the zero point on the new scale, and the degrees +are identical in magnitude with those on the Fahrenheit scale. +Temperatures referred to this new scale are called absolute temperatures +and the point -460 degrees Fahrenheit (= -273 degrees centigrade) is +called the absolute zero. To convert any temperature Fahrenheit to +absolute temperature, add 460 degrees to the temperature on the +Fahrenheit scale: thus 54 degrees Fahrenheit will be 54 + 460 = 514 +degrees absolute temperature; 113 degrees Fahrenheit will likewise be +equal to 113 + 460 = 573 degrees absolute temperature. If one pound of +gas is at a temperature of 54 degrees Fahrenheit and another pound is at +a temperature of 114 degrees Fahrenheit the respective volumes at a +given pressure would be in the ratio of 514 to 573. + +[Illustration: Ninety-sixth Street Station of the New York Railways Co., +New York City, Operating 20,000 Horse Power of Babcock & Wilcox Boilers. +This Company and its Allied Companies Operate a Total of 100,000 Horse +Power of Babcock & Wilcox Boilers] + +British Thermal Unit--The quantitative measure of heat is the British +thermal unit, ordinarily written B. t. u. This is the quantity of heat +required to raise the temperature of one pound of pure water one degree +at 62 degrees Fahrenheit; that is, from 62 degrees to 63 degrees. In the +metric system this unit is the _calorie_ and is the heat necessary +to raise the temperature of one kilogram of pure water from 15 degrees +to 16 degrees centigrade. These two definitions lead to a discrepancy of +0.03 of 1 per cent, which is insignificant for engineering purposes, and +in the following the B. t. u. is taken with this discrepancy ignored. +The discrepancy is due to the fact that there is a slight difference in +the specific heat of water at 15 degrees centigrade and 62 degrees +Fahrenheit. The two units may be compared thus: + +1 Calorie = 3.968 B. t. u. 1 B. t. u. = 0.252 Calories. + +_Unit_ _Water_ _Temperature Rise_ +1 B. t. u. 1 Pound 1 Degree Fahrenheit +1 Calorie 1 Kilogram 1 Degree centigrade + +But 1 kilogram = 2.2046 pounds and 1 degree centigrade = 9/5 degree +Fahrenheit. + +Hence 1 calorie = (2.2046 × 9/5) = 3.968 B. t. u. + + +The heat values in B. t. u. are ordinarily given per pound, and the heat +values in calories per kilogram, in which case the B. t. u. per pound +are approximately equivalent to 9/5 the calories per kilogram. + +As determined by Joule, heat energy has a certain definite relation to +work, one British thermal unit being equivalent from his determinations +to 772 foot pounds. Rowland, a later investigator, found that 778 foot +pounds were a more exact equivalent. Still later investigations indicate +that the correct value for a B. t. u. is 777.52 foot pounds or +approximately 778. The relation of heat energy to work as determined is +a demonstration of the first law of thermo-dynamics, namely, that heat +and mechanical energy are mutually convertible in the ratio of 778 foot +pounds for one British thermal unit. This law, algebraically expressed, +is W = JH; W being the work done in foot pounds, H being the heat in +B. t. u., and J being Joules equivalent. Thus 1000 B. t. u.'s would be +capable of doing 1000 × 778 = 778000 foot pounds of work. + +Specific Heat--The specific heat of a substance is the quantity of heat +expressed in thermal units required to raise or lower the temperature of +a unit weight of any substance at a given temperature one degree. This +quantity will vary for different substances For example, it requires +about 16 B. t. u. to raise the temperature of one pound of ice 32 +degrees or 0.5 B. t. u. to raise it one degree, while it requires +approximately 180 B. t. u. to raise the temperature of one pound of +water 180 degrees or one B. t. u. for one degree. + +If then, a pound of water be considered as a standard, the ratio of the +amount of heat required to raise a similar unit of any other substance +one degree, to the amount required to raise a pound of water one degree +is known as the specific heat of that substance. Thus since one pound of +water required one B. t. u. to raise its temperature one degree, and one +pound of ice requires about 0.5 degrees to raise its temperature one +degree, the ratio is 0.5 which is the specific heat of ice. To be exact, +the specific heat of ice is 0.504, hence 32 degrees × 0.504 = 16.128 +B. t. u. would be required to raise the temperature of one pound of ice +from 0 to 32 degrees. For solids, at ordinary temperatures, the specific +heat may be considered a constant for each individual substance, +although it is variable for high temperatures. In the case of gases a +distinction must be made between specific heat at constant volume, and +at constant pressure. + +Where specific heat is stated alone, specific heat at ordinary +temperature is implied, and _mean_ specific heat refers to the average +value of this quantity between the temperatures named. + +The specific heat of a mixture of gases is obtained by multiplying the +specific heat of each constituent gas by the percentage by weight of +that gas in the mixture, and dividing the sum of the products by 100. +The specific heat of a gas whose composition by weight is CO_{2}, 13 per +cent; CO, 0.4 per cent; O, 8 per cent; N, 78.6 per cent, is found as +follows: + +CO_{2} : 13 × 0.217 = 2.821 +CO : 0.4 × 0.2479 = 0.09916 +O : 8 × 0.2175 = 1.74000 +N : 78.6 × 0.2438 = 19.16268 + -------- + 100.0 23.82284 + +and 23.8228 ÷ 100 = 0.238 = specific heat of the gas. + + +The specific heats of various solids, liquids and gases are given in +Table 4. + +Sensible Heat--The heat utilized in raising the temperature of a body, +as that in raising the temperature of water from 32 degrees up to the +boiling point, is termed sensible heat. In the case of water, the +sensible heat required to raise its temperature from the freezing point +to the boiling point corresponding to the pressure under which +ebullition occurs, is termed the heat of the liquid. + +Latent Heat--Latent heat is the heat which apparently disappears in +producing some change in the condition of a body without increasing its +temperature If heat be added to ice at freezing temperature, the ice +will melt but its temperature will not be raised. The heat so utilized +in changing the condition of the ice is the latent heat and in this +particular case is known as the latent heat of fusion. If heat be added +to water at 212 degrees under atmospheric pressure, the water will not +become hotter but will be evaporated into steam, the temperature of +which will also be 212 degrees. The heat so utilized is called the +latent heat of evaporation and is the heat which apparently disappears +in causing the substance to pass from a liquid to a gaseous state. + + TABLE 4 + + SPECIFIC HEATS OF VARIOUS SUBSTANCES ++--------------------------------------------------------------------+ +| SOLIDS | ++-------------------------------+----------------+-------------------+ +| | Temperature[2]| | +| | Degrees | Specific | +| | Fahrenheit | Heat | ++-------------------------------+----------------+-------------------+ +| Copper | 59-460 | .0951 | +| Gold | 32-212 | .0316 | +| Wrought Iron | 59-212 | .1152 | +| Cast Iron | 68-212 | .1189 | +| Steel (soft) | 68-208 | .1175 | +| Steel (hard) | 68-208 | .1165 | +| Zinc | 32-212 | .0935 | +| Brass (yellow) | 32 | .0883 | +| Glass (normal ther. 16^{III}) | 66-212 | .1988 | +| Lead | 59 | .0299 | +| Platinum | 32-212 | .0323 | +| Silver | 32-212 | .0559 | +| Tin | -105-64 | .0518 | +| Ice | | .5040 | +| Sulphur (newly fused) | | .2025 | ++-------------------------------+----------------+-------------------+ +| LIQUIDS | ++-------------------------------+----------------+-------------------+ +| | Temperature[2]| | +| | Degrees | Specific | +| | Fahrenheit | Heat | ++-------------------------------+----------------+-------------------+ +| Water[3] | 59 | 1.0000 | +| Alcohol | 32 | .5475 | +| | 176 | .7694 | +| Mercury | 32 | .03346 | +| Benzol | 50 | .4066 | +| | 122 | .4502 | +| Glycerine | 59-102 | .576 | +| Lead (Melted) | to 360 | .0410 | +| Sulphur (melted) | 246-297 | .2350 | +| Tin (melted) | | .0637 | +| Sea Water (sp. gr. 1.0043) | 64 | .980 | +| Sea Water (sp. gr. 1.0463) | 64 | .903 | +| Oil of Turpentine | 32 | .411 | +| Petroleum | 64-210 | .498 | +| Sulphuric Acid | 68-133 | .3363 | ++-------------------------------+----------------+-------------------+ +| GASES | ++--------------------------+---------------+--------------+----------+ +| | | Specific | Specific | +| | Temperature[2]| Heat at | Heat at | +| | Degrees | Constant | Constant | +| | Fahrenheit | Pressure | Volume | ++--------------------------+---------------+--------------+----------+ +| Air | 32-392 | .2375 | .1693 | +| Oxygen | 44-405 | .2175 | .1553 | +| Nitrogen | 32-392 | .2438 | .1729 | +| Hydrogen | 54-388 | 3.4090 | 2.4141 | +| Superheated Steam | | See table 25 | | +| Carbon Monoxide | 41-208 | .2425 | .1728 | +| Carbon Dioxide | 52-417 | .2169 | .1535 | +| Methane | 64-406 | .5929 | .4505 | +| Blast Fur. Gas (approx.) | ... | .2277 | ... | +| Flue gas (approx.) | ... | .2400 | ... | ++--------------------------+---------------+--------------+----------+ + +Latent heat is not lost, but reappears whenever the substances pass +through a reverse cycle, from a gaseous to a liquid, or from a liquid to +a solid state. It may, therefore, be defined as stated, as the heat +which apparently disappears, or is lost to thermometric measurement, +when the molecular constitution of a body is being changed. Latent heat +is expended in performing the work of overcoming the molecular cohesion +of the particles of the substance and in overcoming the resistance of +external pressure to change of volume of the heated body. Latent heat of +evaporation, therefore, may be said to consist of internal and external +heat, the former being utilized in overcoming the molecular resistance +of the water in changing to steam, while the latter is expended in +overcoming any resistance to the increase of its volume during +formation. In evaporating a pound of water at 212 degrees to steam at +212 degrees, 897.6 B. t. u. are expended as internal latent heat and +72.8 B. t. u. as external latent heat. For a more detailed description +of the changes brought about in water by sensible and latent heat, the +reader is again referred to the chapter on "The Theory of Steam Making". + +Ebullition--The temperature of ebullition of any liquid, or its boiling +point, may be defined as the temperature which exists where the addition +of heat to the liquid no longer increases its temperature, the heat +added being absorbed or utilized in converting the liquid into vapor. +This temperature is dependent upon the pressure under which the liquid +is evaporated, being higher as the pressure is greater. + + TABLE 5 + +BOILING POINTS AT ATMOSPHERIC PRESSURE + ++---------------------+--------------+ +| | Degrees | +| | Fahrenheit | ++---------------------+--------------+ +| Ammonia | 140 | +| Bromine | 145 | +| Alcohol | 173 | +| Benzine | 212 | +| Water | 212 | +| Average Sea Water | 213.2 | +| Saturated Brine | 226 | +| Mercury | 680 | ++---------------------+--------------+ + +Total Heat of Evaporation--The quantity of heat required to raise a unit +of any liquid from the freezing point to any given temperature, and to +entirely evaporate it at that temperature, is the total heat of +evaporation of the liquid for that temperature. It is the sum of the +heat of the liquid and the latent heat of evaporation. + +To recapitulate, the heat added to a body is divided as follows: + +Total heat = Heat to change the temperature + heat to overcome the + molecular cohesion + heat to overcome the external pressure + resisting an increase of volume of the body. + +Where water is converted into steam, this total heat is divided as +follows: + +Total heat = Heat to change the temperature of the water + heat to + separate the molecules of the water + heat to overcome + resistance to increase in volume of the steam, + = Heat of the liquid + internal latent heat + external + latent heat, + = Heat of the liquid + total latent heat of steam, + = Total heat of evaporation. + +The steam tables given on pages 122 to 127 give the heat of the liquid +and the total latent heat through a wide range of temperatures. + +Gases--When heat is added to gases there is no internal work done; hence +the total heat is that required to change the temperature plus that +required to do the external work. If the gas is not allowed to expand +but is preserved at constant volume, the entire heat added is that +required to change the temperature only. + +Linear Expansion of Substances by Heat--To find the increase in the +length of a bar of any material due to an increase of temperature, +multiply the number of degrees of increase in temperature by the +coefficient of expansion for one degree and by the length of the bar. +Where the coefficient of expansion is given for 100 degrees, as in Table +6, the result should be divided by 100. The expansion of metals per one +degree rise of temperature increases slightly as high temperatures are +reached, but for all practical purposes it may be assumed to be constant +for a given metal. + + TABLE 6 + + LINEAL EXPANSION OF SOLIDS AT ORDINARY TEMPERATURES + + (Tabular values represent increase per foot per 100 degrees increase + in temperature, Fahrenheit or centigrade) + ++-------------------+--------------+----------------+----------------+ +| | Temperature | | | +| | Conditions[4]|Coefficient per |Coefficient per | +| Substance | Degrees | 100 Degrees | 100 Degrees | +| | Fahrenheit | Fahrenheit | Centigrade | ++-------------------+--------------+----------------+----------------+ +|Brass (cast) | 32 to 212 | .001042 | .001875 | +|Brass (wire) | 32 to 212 | .001072 | .001930 | +|Copper | 32 to 212 | .000926 | .001666 | +|Glass (English | | | | +|flint) | 32 to 212 | .000451 | .000812 | +|Glass (French | | | | +|flint) | 32 to 212 | .000484 | .000872 | +|Gold | 32 to 212 | .000816 | .001470 | +|Granite (average) | 32 to 212 | .000482 | .000868 | +|Iron (cast) | 104 | .000589 | .001061 | +|Iron (soft forged) | 0 to 212 | .000634 | .001141 | +|Iron (wire) | 32 to 212 | .000800 | .001440 | +|Lead | 32 to 212 | .001505 | .002709 | +|Mercury | 32 to 212 | .009984[5] | .017971 | +|Platinum | 104 | .000499 | .000899 | +|Limestone | 32 to 212 | .000139 | .000251 | +|Silver | 104 | .001067 | .001921 | +|Steel (Bessemer | | | | +|rolled, hard) | 0 to 212 | .00056 | .00101 | +|Steel (Bessemer | | | | +|rolled, soft) | 0 to 212 | .00063 | .00117 | +|Steel (cast, | | | | +|French) | 104 | .000734 | .001322 | +|Steel (cast | | | | +|annealed, English) | 104 | .000608 | .001095 | ++-------------------+--------------+----------------+----------------+ + +High Temperature Measurements--The temperatures to be dealt with in +steam-boiler practice range from those of ordinary air and steam to the +temperatures of burning fuel. The gases of combustion, originally at the +temperature of the furnace, cool as they pass through each successive +bank of tubes in the boiler, to nearly the temperature of the steam, +resulting in a wide range of temperatures through which definite +measurements are sometimes required. + +Of the different methods devised for ascertaining these temperatures, +some of the most important are as follows: + + 1st. Mercurial pyrometers for temperatures up to 1000 degrees + Fahrenheit. + + 2nd. Expansion pyrometers for temperatures up to 1500 degrees + Fahrenheit. + + 3rd. Calorimetry for temperatures up to 2000 degrees Fahrenheit. + + 4th. Thermo-electric pyrometers for temperatures up to 2900 + degrees Fahrenheit. + + 5th. Melting points of metal which flow at various temperatures + up to the melting point of platinum 3227 degrees Fahrenheit. + + 6th. Radiation pyrometers for temperatures up to 3600 degrees + Fahrenheit. + + 7th. Optical pyrometers capable of measuring temperatures up to + 12,600 degrees Fahrenheit.[6] For ordinary boiler practice + however, their range is 1600 to 3600 degrees Fahrenheit. + +[Illustration: 228 Horse-power Babcock & Wilcox Boiler, Installed at the +Wentworth Institute, Boston, Mass.] + +Table 7 gives the degree of accuracy of high temperature measurements. + + TABLE 7 + + ACCURACY OF HIGH TEMPERATURE MEASUREMENTS[7] + ++------------------------+------------------------+ +| Centigrade | Fahrenheit | ++-------------+----------+-------------+----------+ +| | Accuracy | | Accuracy | +| Temperature | Plus or | Temperature | Plus or | +| Range | Minus | Range | Minus | +| | Degrees | | Degrees | ++-------------+----------+-------------+----------+ +| 200- 500 | 0.5 | 392- 932 | 0.9 | +| 500- 800 | 2 | 932-1472 | 3.6 | +| 800-1100 | 3 | 1472-2012 | 5.4 | +| 1100-1600 | 15 | 2012-2912 | 27 | +| 1600-2000 | 25 | 2912-3632 | 45 | ++-------------+----------+-------------+----------+ + + +Mercurial Pyrometers--At atmospheric pressure mercury boils at 676 +degrees Fahrenheit and even at lower temperatures the mercury in +thermometers will be distilled and will collect in the upper part of the +stem. Therefore, for temperatures much above 400 degrees Fahrenheit, +some inert gas, such as nitrogen or carbon dioxide, must be forced under +pressure into the upper part of the thermometer stem. The pressure at +600 degrees Fahrenheit is about 15 pounds, or slightly above that of the +atmosphere, at 850 degrees about 70 pounds, and at 1000 degrees about +300 pounds. + +Flue-gas temperatures are nearly always taken with mercurial +thermometers as they are the most accurate and are easy to read and +manipulate. Care must be taken that the bulb of the instrument projects +into the path of the moving gases in order that the temperature may +truly represent the flue gas temperature. No readings should be +considered until the thermometer has been in place long enough to heat +it up to the full temperature of the gases. + + +Expansion Pyrometers--Brass expands about 50 per cent more than iron and +in both brass and iron the expansion is nearly proportional to the +increase in temperature. This phenomenon is utilized in expansion +pyrometers by enclosing a brass rod in an iron pipe, one end of the rod +being rigidly attached to a cap at the end of the pipe, while the other +is connected by a multiplying gear to a pointer moving around a +graduated dial. The whole length of the expansion piece must be at a +uniform temperature before a correct reading can be obtained. This fact, +together with the lost motion which is likely to exist in the mechanism +connected to the pointer, makes the expansion pyrometer unreliable; it +should be used only when its limitations are thoroughly understood and +it should be carefully calibrated. Unless the brass and iron are known +to be of the same temperature, its action will be anomalous: for +instance, if it be allowed to cool after being exposed to a high +temperature, the needle will rise before it begins to fall. Similarly, a +rise in temperature is first shown by the instrument as a fall. The +explanation is that the iron, being on the outside, heats or cools more +quickly than the brass. + + +Calorimetry--This method derives its name from the fact that the process +is the same as the determination of the specific heat of a substance by +the water calorimeter, except that in one case the temperature is known +and the specific heat is required, while in the other the specific heat +is known and the temperature is required. The temperature is found as +follows: + +A given weight of some substance such as iron, nickel or fire brick, is +heated to the unknown temperature and then plunged into water and the +rise in temperature noted. + +If X = temperature to be measured, w = weight of heated body in pounds, +W = weight of water in pounds, T = final temperature of water, t = +difference between initial and final temperatures of water, s = known +specific heat of body. Then X = T + Wt ÷ ws + +Any temperatures secured by this method are affected by so many sources +of error that the results are very approximate. + +Thermo-electric Pyrometers--When wires of two different metals are +joined at one end and heated, an electromotive force will be set up +between the free ends of the wires. Its amount will depend upon the +composition of the wires and the difference in temperature between the +two. If a delicate galvanometer of high resistance be connected to the +"thermal couple", as it is called, the deflection of the needle, after a +careful calibration, will indicate the temperature very accurately. + +In the thermo-electric pyrometer of Le Chatelier, the wires used are +platinum and a 10 per cent alloy of platinum and rhodium, enclosed in +porcelain tubes to protect them from the oxidizing influence of the +furnace gases. The couple with its protecting tubes is called an +"element". The elements are made in different lengths to suit +conditions. + +It is not necessary for accuracy to expose the whole length of the +element to the temperature to be measured, as the electromotive force +depends only upon the temperature of the juncture at the closed end of +the protecting tube and that of the cold end of the element. The +galvanometer can be located at any convenient point, since the length of +the wires leading to it simply alter the resistance of the circuit, for +which allowance may be made. + +The advantages of the thermo-electric pyrometer are accuracy over a wide +range of temperatures, continuity of readings, and the ease with which +observations can be taken. Its disadvantages are high first cost and, in +some cases, extreme delicacy. + +Melting Points of Metals--The approximate temperature of a furnace or +flue may be determined, if so desired, by introducing certain metals of +which the melting points are known. The more common metals form a series +in which the respective melting points differ by 100 to 200 degrees +Fahrenheit, and by using these in order, the temperature can be fixed +between the melting points of some two of them. This method lacks +accuracy, but it suffices for determinations where approximate readings +are satisfactory. + +The approximate melting points of certain metals that may be used for +determinations of this nature are given in Table 8. + +Radiation Pyrometers--These are similar to thermo-electric pyrometers in +that a thermo-couple is employed. The heat rays given out by the hot +body fall on a concave mirror and are brought to a focus at a point at +which is placed the junction of a thermo-couple. The temperature +readings are obtained from an indicator similar to that used with +thermo-electric pyrometers. + +Optical Pyrometers--Of the optical pyrometers the Wanner is perhaps the +most reliable. The principle on which this instrument is constructed is +that of comparing the quantity of light emanating from the heated body +with a constant source of light, in this case a two-volt osmium lamp. +The lamp is placed at one end of an optical tube, while at the other an +eyepiece is provided and a scale. A battery of cells furnishes the +current for the lamp. On looking through the pyrometer, a circle of red +light appears, divided into distinct halves of different intensities. +Adjustment may be made so that the two halves appear alike and a reading +is then taken from the scale. The temperatures are obtained from a table +of temperatures corresponding to scale readings. For standardizing the +osmium lamp, an amylacetate lamp, is provided with a stand for holding +the optical tube. + + TABLE 8 + +APPROXIMATE MELTING POINTS OF METALS[8] + ++-----------------+------------------+ +| Metal | Temperature | +| |Degrees Fahrenheit| ++-----------------+------------------+ +|Wrought Iron | 2737 | +|Pig Iron (gray) | 2190-2327 | +|Cast Iron (white)| 2075 | +|Steel | 2460-2550 | +|Steel (cast) | 2500 | +|Copper | 1981 | +|Zinc | 786 | +|Antimony | 1166 | +|Lead | 621 | +|Bismuth | 498 | +|Tin | 449 | +|Platinum | 3191 | +|Gold | 1946 | +|Silver | 1762 | +|Aluminum | 1216 | ++-----------------+------------------+ + + +Determination of Temperature from Character of Emitted Light--As a +further means of determining approximately the temperature of a furnace, +Table 9, compiled by Messrs. White & Taylor, may be of service. The +color at a given temperature is approximately the same for all kinds of +combustibles under similar conditions. + + TABLE 9 + + CHARACTER OF EMITTED LIGHT AND CORRESPONDING + APPROXIMATE TEMPERATURE[9] + ++--------------------------------------+-----------+ +| Character of Emitted Light |Temperature| +| | Degrees | +| | Fahrenheit| ++--------------------------------------+-----------+ +|Dark red, blood red, low red | 1050 | +|Dark cherry red | 1175 | +|Cherry, full red | 1375 | +|Light cherry, bright cherry, light red| 1550 | +|Orange | 1650 | +|Light orange | 1725 | +|Yellow | 1825 | +|Light yellow | 1975 | +|White | 2200 | ++--------------------------------------+-----------+ + + + + +THE THEORY OF STEAM MAKING + +[Extracts from a Lecture delivered by George H. Babcock, at Cornell +University, 1887[10]] + + +The chemical compound known as H_{2}O exists in three states or +conditions--ice, water and steam; the only difference between these +states or conditions is in the presence or absence of a quantity of +energy exhibited partly in the form of heat and partly in molecular +activity, which, for want of a better name, we are accustomed to call +"latent heat"; and to transform it from one state to another we have +only to supply or extract heat. For instance, if we take a quantity of +ice, say one pound, at absolute zero[11] and supply heat, the first +effect is to raise its temperature until it arrives at a point 492 +Fahrenheit degrees above the starting point. Here it stops growing +warmer, though we keep on adding heat. It, however, changes from ice to +water, and when we have added sufficient heat to have made it, had it +remained ice, 283 degrees hotter or a temperature of 315 degrees +Fahrenheit's thermometer, it has all become water, at the same +temperature at which it commenced to change, namely, 492 degrees above +absolute zero, or 32 degrees by Fahrenheit's scale. Let us still +continue to add heat, and it will now grow warmer again, though at a +slower rate--that is, it now takes about double the quantity of heat to +raise the pound one degree that it did before--until it reaches a +temperature of 212 degrees Fahrenheit, or 672 degrees absolute (assuming +that we are at the level of the sea). Here we find another critical +point. However much more heat we may apply, the water, as water, at that +pressure, cannot be heated any hotter, but changes on the addition of +heat to steam; and it is not until we have added heat enough to have +raised the temperature of the water 966 degrees, or to 1,178 degrees by +Fahrenheit's thermometer (presuming for the moment that its specific +heat has not changed since it became water), that it has all become +steam, which steam, nevertheless, is at the temperature of 212 degrees, +at which the water began to change. Thus over four-fifths of the heat +which has been added to the water has disappeared, or become insensible +in the steam to any of our instruments. + +It follows that if we could reduce steam at atmospheric pressure to +water, without loss of heat, the heat stored within it would cause the +water to be red hot; and if we could further change it to a solid, like +ice, without loss of heat, the solid would be white hot, or hotter than +melted steel--it being assumed, of course, that the specific heat of the +water and ice remain normal, or the same as they respectively are at the +freezing point. + +After steam has been formed, a further addition of heat increases the +temperature again at a much faster ratio to the quantity of heat added, +which ratio also varies according as we maintain a constant pressure or +a constant volume; and I am not aware that any other critical point +exists where this will cease to be the fact until we arrive at that very +high temperature, known as the point of dissociation, at which it +becomes resolved into its original gases. + +The heat which has been absorbed by one pound of water to convert it +into a pound of steam at atmospheric pressure is sufficient to have +melted 3 pounds of steel or 13 pounds of gold. This has been transformed +into something besides heat; stored up to reappear as heat when the +process is reversed. That condition is what we are pleased to call +latent heat, and in it resides mainly the ability of the steam to do +work. + +[Graph: Temperature in Fahrenheit Degrees (from Absolute Zero) +against Quantity of Heat in British Thermal Units] + +The diagram shows graphically the relation of heat to temperature, the +horizontal scale being quantity of heat in British thermal units, and +the vertical temperature in Fahrenheit degrees, both reckoned from +absolute zero and by the usual scale. The dotted lines for ice and water +show the temperature which would have been obtained if the conditions +had not changed. The lines marked "gold" and "steel" show the relation +to heat and temperature and the melting points of these metals. All the +inclined lines would be slightly curved if attention had been paid to +the changing specific heat, but the curvature would be small. It is +worth noting that, with one or two exceptions, the curves of all +substances lie between the vertical and that for water. That is to say, +that water has a greater capacity for heat than all other substances +except two, hydrogen and bromine. + +In order to generate steam, then, only two steps are required: 1st, +procure the heat, and 2nd, transfer it to the water. Now, you have it +laid down as an axiom that when a body has been transferred or +transformed from one place or state into another, the same work has been +done and the same energy expended, whatever may have been the +intermediate steps or conditions, or whatever the apparatus. Therefore, +when a given quantity of water at a given temperature has been made into +steam at a given temperature, a certain definite work has been done, and +a certain amount of energy expended, from whatever the heat may have +been obtained, or whatever boiler may have been employed for the +purpose. + +A pound of coal or any other fuel has a definite heat producing +capacity, and is capable of evaporating a definite quantity of water +under given conditions. That is the limit beyond which even perfection +cannot go, and yet I have known, and doubtless you have heard of, cases +where inventors have claimed, and so-called engineers have certified to, +much higher results. + +The first step in generating steam is in burning the fuel to the best +advantage. A pound of carbon will generate 14,500 British thermal units, +during combustion into carbonic dioxide, and this will be the same, +whatever the temperature or the rapidity at which the combustion may +take place. If possible, we might oxidize it at as slow a rate as that +with which iron rusts or wood rots in the open air, or we might burn it +with the rapidity of gunpowder, a ton in a second, yet the total heat +generated would be precisely the same. Again, we may keep the +temperature down to the lowest point at which combustion can take place, +by bringing large bodies of air in contact with it, or otherwise, or we +may supply it with just the right quantity of pure oxygen, and burn it +at a temperature approaching that of dissociation, and still the heat +units given off will be neither more nor less. It follows, therefore, +that great latitude in the manner or rapidity of combustion may be taken +without affecting the quantity of heat generated. + +But in practice it is found that other considerations limit this +latitude, and that there are certain conditions necessary in order to +get the most available heat from a pound of coal. There are three ways, +and only three, in which the heat developed by the combustion of coal in +a steam boiler furnace may be expended. + +1st, and principally. It should be conveyed to the water in the boiler, +and be utilized in the production of steam. To be perfect, a boiler +should so utilize all the heat of combustion, but there are no perfect +boilers. + +2nd. A portion of the heat of combustion is conveyed up the chimney in +the waste gases. This is in proportion to the weight of the gases, and +the difference between their temperature and that of the air and coal +before they entered the fire. + +3rd. Another portion is dissipated by radiation from the sides of the +furnace. In a stove the heat is all used in these latter two ways, +either it goes off through the chimney or is radiated into the +surrounding space. It is one of the principal problems of boiler +engineering to render the amount of heat thus lost as small as possible. + +The loss from radiation is in proportion to the amount of surface, its +nature, its temperature, and the time it is exposed. This loss can be +almost entirely eliminated by thick walls and a smooth white or polished +surface, but its amount is ordinarily so small that these extraordinary +precautions do not pay in practice. + +It is evident that the temperature of the escaping gases cannot be +brought below that of the absorbing surfaces, while it may be much +greater even to that of the fire. This is supposing that all of the +escaping gases have passed through the fire. In case air is allowed to +leak into the flues, and mingle with the gases after they have left the +heating surfaces, the temperature may be brought down to almost any +point above that of the atmosphere, but without any reduction in the +amount of heat wasted. It is in this way that those low chimney +temperatures are sometimes attained which pass for proof of economy with +the unobserving. All surplus air admitted to the fire, or to the gases +before they leave the heating surfaces, increases the losses. + +We are now prepared to see why and how the temperature and the rapidity +of combustion in the boiler furnace affect the economy, and that though +the amount of heat developed may be the same, the heat available for the +generation of steam may be much less with one rate or temperature of +combustion than another. + +Assuming that there is no air passing up the chimney other than that +which has passed through the fire, the higher the temperature of the +fire and the lower that of the escaping gases the better the economy, +for the losses by the chimney gases will bear the same proportion to the +heat generated by the combustion as the temperature of those gases bears +to the temperature of the fire. That is to say, if the temperature of +the fire is 2500 degrees and that of the chimney gases 500 degrees above +that of the atmosphere, the loss by the chimney will be 500/2500 = 20 +per cent. Therefore, as the escaping gases cannot be brought below the +temperature of the absorbing surface, which is practically a fixed +quantity, the temperature of the fire must be high in order to secure +good economy. + +The losses by radiation being practically proportioned to the time +occupied, the more coal burned in a given furnace in a given time, the +less will be the proportionate loss from that cause. + +It therefore follows that we should burn our coal rapidly and at a high +temperature to secure the best available economy. + +[Illustration: Portion of 9880 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain +Grate Stokers at the South Side Elevated Ry. Co., Chicago, Ill.] + + + + +PROPERTIES OF WATER + + +Pure water is a chemical compound of one volume of oxygen and two +volumes of hydrogen, its chemical symbol being H_{2}O. + +The weight of water depends upon its temperature. Its weight at four +temperatures, much used in physical calculations, is given in Table 10. + + TABLE 10 + + WEIGHT OF WATER AT TEMPERATURES + USED IN PHYSICAL CALCULATIONS + ++---------------------------+----------+----------+ +| Temperature Degrees |Weight per|Weight per| +| Fahrenheit |Cubic Foot|Cubic Inch| +| | Pounds | Pounds | ++---------------------------+----------+----------+ +|At 32 degrees or freezing | | | +| point at sea level | 62.418 | 0.03612 | +|At 39.2 degrees or point of| | | +| maximum density | 62.427 | 0.03613 | +|At 62 degrees or standard | | | +| temperature | 62.355 | 0.03608 | +|At 212 degrees or boiling | | | +| point at sea level | 59.846 | 0.03469 | ++---------------------------+----------+----------+ + +While authorities differ as to the weight of water, the range of values +given for 62 degrees Fahrenheit (the standard temperature ordinarily +taken) being from 62.291 pounds to 62.360 pounds per cubic foot, the +value 62.355 is generally accepted as the most accurate. + +A United States standard gallon holds 231 cubic inches and weighs, at 62 +degrees Fahrenheit, approximately 8-1/3 pounds. + +A British Imperial gallon holds 277.42 cubic inches and weighs, at 62 +degrees Fahrenheit, 10 pounds. + +The above are the true weights corrected for the effect of the buoyancy +of the air, or the weight in vacuo. If water is weighed in air in the +ordinary way, there is a correction of about one-eighth of one per cent +which is usually negligible. + + TABLE 11 + +VOLUME AND WEIGHT OF DISTILLED WATER AT + VARIOUS TEMPERATURES[12] + ++-----------+---------------+----------+ +|Temperature|Relative Volume|Weight per| +| Degrees | Water at 39.2 |Cubic Foot| +| Fahrenheit| Degrees = 1 | Pounds | ++-----------+---------------+----------+ +| 32 | 1.000176 | 62.42 | +| 39.2 | 1.000000 | 62.43 | +| 40 | 1.000004 | 62.43 | +| 50 | 1.00027 | 62.42 | +| 60 | 1.00096 | 62.37 | +| 70 | 1.00201 | 62.30 | +| 80 | 1.00338 | 62.22 | +| 90 | 1.00504 | 62.11 | +| 100 | 1.00698 | 62.00 | +| 110 | 1.00915 | 61.86 | +| 120 | 1.01157 | 61.71 | +| 130 | 1.01420 | 61.55 | +| 140 | 1.01705 | 61.38 | +| 150 | 1.02011 | 61.20 | +| 160 | 1.02337 | 61.00 | +| 170 | 1.02682 | 60.80 | +| 180 | 1.03047 | 60.58 | +| 190 | 1.03431 | 60.36 | +| 200 | 1.03835 | 60.12 | +| 210 | 1.04256 | 59.88 | +| 212 | 1.04343 | 59.83 | +| 220 | 1.0469 | 59.63 | +| 230 | 1.0515 | 59.37 | +| 240 | 1.0562 | 59.11 | +| 250 | 1.0611 | 58.83 | +| 260 | 1.0662 | 58.55 | +| 270 | 1.0715 | 58.26 | +| 280 | 1.0771 | 57.96 | +| 290 | 1.0830 | 57.65 | +| 300 | 1.0890 | 57.33 | +| 310 | 1.0953 | 57.00 | +| 320 | 1.1019 | 56.66 | +| 330 | 1.1088 | 56.30 | +| 340 | 1.1160 | 55.94 | +| 350 | 1.1235 | 55.57 | +| 360 | 1.1313 | 55.18 | +| 370 | 1.1396 | 54.78 | +| 380 | 1.1483 | 54.36 | +| 390 | 1.1573 | 53.94 | +| 400 | 1.167 | 53.5 | +| 410 | 1.177 | 53.0 | +| 420 | 1.187 | 52.6 | +| 430 | 1.197 | 52.2 | +| 440 | 1.208 | 51.7 | +| 450 | 1.220 | 51.2 | +| 460 | 1.232 | 50.7 | +| 470 | 1.244 | 50.2 | +| 480 | 1.256 | 49.7 | +| 490 | 1.269 | 49.2 | +| 500 | 1.283 | 48.7 | +| 510 | 1.297 | 48.1 | +| 520 | 1.312 | 47.6 | +| 530 | 1.329 | 47.0 | +| 540 | 1.35 | 46.3 | +| 550 | 1.37 | 45.6 | +| 560 | 1.39 | 44.9 | ++-----------+---------------+----------+ + +Water is but slightly compressible and for all practical purposes may be +considered non-compressible. The coefficient of compressibility ranges +from 0.000040 to 0.000051 per atmosphere at ordinary temperatures, this +coefficient decreasing as the temperature increases. + +Table 11 gives the weight in vacuo and the relative volume of a cubic +foot of distilled water at various temperatures. + +The weight of water at the standard temperature being taken as 62.355 +pounds per cubic foot, the pressure exerted by the column of water of +any stated height, and conversely the height of any column required to +produce a stated pressure, may be computed as follows: + +The pressure in pounds per square foot = 62.355 × height of column in +feet. + +The pressure in pounds per square inch = 0.433 × height of column in +feet. + +Height of column in feet = pressure in pounds per square foot ÷ 62.355. + +Height of column in feet = pressure in pounds per square inch ÷ 0.433. + +Height of column in inches = pressure in pounds per square inch × 27.71. + +Height of column in inches = pressure in ounces per square inch × 1.73. + +By a change in the weights given above, the pressure exerted and height +of column may be computed for temperatures other than 62 degrees. + +A pressure of one pound per square inch is exerted by a column of water +2.3093 feet or 27.71 inches high at 62 degrees Fahrenheit. + +Water in its natural state is never found absolutely pure. In solvent +power water has a greater range than any other liquid. For common salt, +this is approximately a constant at all temperatures, while with such +impurities as magnesium and sodium sulphates, this solvent power +increases with an increase in temperature. + + TABLE 12 + + BOILING POINT OF WATER AT VARIOUS ALTITUDES + ++--------------+----------------+-------------+---------------+ +|Boiling Point | Altitude Above | Atmospheric | Barometer | +| Degrees | Sea Level | Pressure | Reduced | +| Fahrenheit | Feet | Pounds per | to 32 Degrees | +| | | Square Inch | Inches | ++--------------+----------------+-------------+---------------+ +| 184 | 15221 | 8.20 | 16.70 | +| 185 | 14649 | 8.38 | 17.06 | +| 186 | 14075 | 8.57 | 17.45 | +| 187 | 13498 | 8.76 | 17.83 | +| 188 | 12934 | 8.95 | 18.22 | +| 189 | 12367 | 9.14 | 18.61 | +| 190 | 11799 | 9.34 | 19.02 | +| 191 | 11243 | 9.54 | 19.43 | +| 192 | 10685 | 9.74 | 19.85 | +| 193 | 10127 | 9.95 | 20.27 | +| 194 | 9579 | 10.17 | 20.71 | +| 195 | 9031 | 10.39 | 21.15 | +| 196 | 8481 | 10.61 | 21.60 | +| 197 | 7932 | 10.83 | 22.05 | +| 198 | 7381 | 11.06 | 22.52 | +| 199 | 6843 | 11.29 | 22.99 | +| 200 | 6304 | 11.52 | 23.47 | +| 201 | 5764 | 11.76 | 23.95 | +| 202 | 5225 | 12.01 | 24.45 | +| 203 | 4697 | 12.26 | 24.96 | +| 204 | 4169 | 12.51 | 25.48 | +| 205 | 3642 | 12.77 | 26.00 | +| 206 | 3115 | 13.03 | 26.53 | +| 207 | 2589 | 13.30 | 27.08 | +| 208 | 2063 | 13.57 | 27.63 | +| 209 | 1539 | 13.85 | 28.19 | +| 210 | 1025 | 14.13 | 28.76 | +| 211 | 512 | 14.41 | 29.33 | +| 212 | Sea Level | 14.70 | 29.92 | ++--------------+----------------+-------------+---------------+ + +Sea water contains on an average approximately 3.125 per cent of its +weight of solid matter or a thirty-second part of the weight of the +water and salt held in solution. The approximate composition of this +solid matter will be: sodium chloride 76 per cent, magnesium chloride 10 +per cent, magnesium sulphate 6 per cent, calcium sulphate 5 per cent, +calcium carbonate 0.5 per cent, other substances 2.5 per cent. + +[Illustration: 7200 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters at the Capital Traction Co., Washington, D. C.] + +The boiling point of water decreases as the altitude above sea level +increases. Table 12 gives the variation in the boiling point with the +altitude. + +Water has a greater specific heat or heat-absorbing capacity than any +other known substance (bromine and hydrogen excepted) and its specific +heat is the basis for measurement of the capacity of heat absorption of +all other substances. From the definition, the specific heat of water is +the number of British thermal units required to raise one pound of water +one degree. This specific heat varies with the temperature of the water. +The generally accepted values are given in Table 13, which indicates the +values as determined by Messrs. Marks and Davis and Mr. Peabody. + + TABLE 13 + + SPECIFIC HEAT OF WATER AT VARIOUS TEMPERATURES + ++----------------------+--------------------------------+ +| MARKS AND DAVIS | PEABODY | +| From Values of | From Values of | +| Barnes and Dieterici | Barnes and Regnault | ++-----------+----------+---------------------+----------+ +|Temperature| Specific | Temperature | Specific | ++-----------+ Heat +----------+----------+ Heat | +| Degrees | | Degrees | Degrees | | +|Fahrenheit | |Centigrade|Fahrenheit| | ++-----------+----------+----------+----------+----------+ +| 30 | 1.0098 | 0 | 32 | 1.0094 | +| 40 | 1.0045 | 5 | 41 | 1.0053 | +| 50 | 1.0012 | 10 | 50 | 1.0023 | +| 55 | 1.0000 | 15 | 59 | 1.0003 | +| 60 | 0.9990 | 16.11 | 61 | 1.0000 | +| 70 | 0.9977 | 20 | 68 | 0.9990 | +| 80 | 0.9970 | 25 | 77 | 0.9981 | +| 90 | 0.9967 | 30 | 86 | 0.9976 | +| 100 | 0.9967 | 35 | 95 | 0.9974 | +| 110 | 0.9970 | 40 | 104 | 0.9974 | +| 120 | 0.9974 | 45 | 113 | 0.9976 | +| 130 | 0.9979 | 50 | 122 | 0.9980 | +| 140 | 0.9986 | 55 | 131 | 0.9985 | +| 150 | 0.9994 | 60 | 140 | 0.9994 | +| 160 | 1.0002 | 65 | 149 | 1.0004 | +| 170 | 1.0010 | 70 | 158 | 1.0015 | +| 180 | 1.0019 | 75 | 167 | 1.0028 | +| 190 | 1.0029 | 80 | 176 | 1.0042 | +| 200 | 1.0039 | 85 | 185 | 1.0056 | +| 210 | 1.0052 | 90 | 194 | 1.0071 | +| 220 | 1.007 | 95 | 203 | 1.0086 | +| 230 | 1.009 | 100 | 212 | 1.0101 | ++-----------+----------+----------+----------+----------+ + +In consequence of this variation in specific heat, the variation in the +heat of the liquid of the water at different temperatures is not a +constant. Table 22[13] gives the heat of the liquid in a pound of water +at temperatures ranging from 32 to 340 degrees Fahrenheit. + +The specific heat of ice at 32 degrees is 0.463. The specific heat of +saturated steam (ice and saturated steam representing the other forms in +which water may exist), is something that is difficult to define in any +way which will not be misleading. When no liquid is present the specific +heat of saturated steam is negative.[14] The use of the value of the +specific heat of steam is practically limited to instances where +superheat is present, and the specific heat of superheated steam is +covered later in the book. + + + + +BOILER FEED WATER + + +All natural waters contain some impurities which, when introduced into a +boiler, may appear as solids. In view of the apparent present-day +tendency toward large size boiler units and high overloads, the +importance of the use of pure water for boiler feed purposes cannot be +over-estimated. + +Ordinarily, when water of sufficient purity for such use is not at hand, +the supply available may be rendered suitable by some process of +treatment. Against the cost of such treatment, there are many factors to +be considered. With water in which there is a marked tendency toward +scale formation, the interest and depreciation on the added boiler units +necessary to allow for the systematic cleaning of certain units must be +taken into consideration. Again there is a considerable loss in taking +boilers off for cleaning and replacing them on the line. On the other +hand, the decrease in capacity and efficiency accompanying an increased +incrustation of boilers in use has been too generally discussed to need +repetition here. Many experiments have been made and actual figures +reported as to this decrease, but in general, such figures apply only to +the particular set of conditions found in the plant where the boiler in +question was tested. So many factors enter into the effect of scale on +capacity and economy that it is impossible to give any accurate figures +on such decrease that will serve all cases, but that it is large has +been thoroughly proven. + +While it is almost invariably true that practically any cost of +treatment will pay a return on the investment of the apparatus, the fact +must not be overlooked that there are certain waters which should never +be used for boiler feed purposes and which no treatment can render +suitable for such purpose. In such cases, the only remedy is the +securing of other feed supply or the employment of evaporators for +distilling the feed water as in marine service. + + TABLE 14 + + APPROXIMATE CLASSIFICATION OF IMPURITIES FOUND IN FEED WATERS + THEIR EFFECT AND ORDINARY METHODS OF RELIEF + ++-----------------------+--------------+-----------------------------+ +| Difficulty Resulting | Nature of | Ordinary Method of | +| from Presence of | Difficulty | Overcoming or Relieving | ++-----------------------+--------------+-----------------------------+ +| Sediment, Mud, etc. | Incrustation | Settling tanks, filtration, | +| | | blowing down. | +| | | | +| Readily Soluble Salts | Incrustation | Blowing down. | +| | | | +| Bicarbonates of Lime, | Incrustation | Heating feed. Treatment by | +| Magnesia, etc. | | addition of lime or of lime | +| | | and soda. Barium carbonate. | +| | | | +| Sulphate of Lime | Incrustation | Treatment by addition of | +| | | soda. Barium carbonate. | +| | | | +| Chloride and Sulphate | Corrosion | Treatment by addition of | +| of Magnesium | | carbonate of soda. | +| | | | +| Acid | Corrosion | Alkali. | +| | | | +| Dissolved Carbonic | Corrosion | Heating feed. Keeping air | +| Acid and Oxygen | | from feed. Addition of | +| | | caustic soda or slacked | +| | | lime. | +| | | | +| Grease | Corrosion | Filter. Iron alum as | +| | | coagulent. Neutralization | +| | | by carbonate of soda. Use | +| | | of best hydrocarbon oils. | +| | | | +| Organic Matter | Corrosion | Filter. Use of coagulent. | +| | | | +| Organic Matter | Priming | Settling tanks. Filter in | +| (Sewage) | | connection with coagulent. | +| | | | +| Carbonate of Soda in | Priming | Barium carbonate. New feed | +| large quantities | | supply. If from treatment, | +| | | change. | ++-----------------------+--------------+-----------------------------+ + +It is evident that the whole subject of boiler feed waters and their +treatment is one for the chemist rather than for the engineer. A brief +outline of the difficulties that may be experienced from the use of poor +feed water and a suggestion as to a method of overcoming certain of +these difficulties is all that will be attempted here. Such a brief +outline of the subject, however, will indicate the necessity for a +chemical analysis of any water before a treatment is tried and the +necessity of adapting the treatment in each case to the nature of the +difficulties that may be experienced. + +Table 14 gives a list of impurities which may be found in boiler feed +water, grouped according to their effect on boiler operation and giving +the customary method used for overcoming difficulty to which they lead. + + +Scale--Scale is formed on boiler heating surfaces by the depositing of +impurities in the feed water in the form of a more or less hard adherent +crust. Such deposits are due to the fact that water loses its soluble +power at high temperatures or because the concentration becomes so high, +due to evaporation, that the impurities crystallize and adhere to the +boiler surfaces. The opportunity for formation of scale in a boiler will +be apparent when it is realized that during a month's operation of a 100 +horse-power boiler, 300 pounds of solid matter may be deposited from +water containing only 7 grains per gallon, while some spring and well +waters contain sufficient to cause a deposit of as high as 2000 pounds. + +The salts usually responsible for such incrustation are the carbonates +and sulphates of lime and magnesia, and boiler feed treatment in general +deals with the getting rid of these salts more or less completely. + + TABLE 15 + + SOLUBILITY OF MINERAL SALTS IN WATER (SPARKS) +IN GRAINS PER U. S. GALLON (58,381 GRAINS), EXCEPT AS NOTED + ++------------------------------+------------+-------------+ +|Temperature Degrees Fahrenheit| 60 Degrees | 212 Degrees | ++------------------------------+------------+-------------+ +|Calcium Carbonate | 2.5 | 1.5 | +|Calcium Sulphate | 140.0 | 125.0 | +|Magnesium Carbonate | 1.0 | 1.8 | +|Magnesium Sulphate | 3.0 pounds | 12.0 pounds | +|Sodium Chloride | 3.5 pounds | 4.0 pounds | +|Sodium Sulphate | 1.1 pounds | 5.0 pounds | ++------------------------------+------------+-------------+ + + CALCIUM SULPHATE AT TEMPERATURE ABOVE + 212 DEGREES (CHRISTIE) + ++------------------------------+----+----+-------+----+---+ +|Temperature degrees Fahrenheit|284 |329 |347-365| 464|482| +|Corresponding gauge pressure | 38 | 87 |115-149| 469|561| +|Grains per gallon |45.5|32.7| 15.7 |10.5|9.3| ++------------------------------+----+----+-------+----+---+ + +Table 15 gives the solubility of these mineral salts in water at various +temperatures in grains per U. S. gallon (58,381 grains). It will be seen +from this table that the carbonates of lime and magnesium are not +soluble above 212 degrees, and calcium sulphate while somewhat insoluble +above 212 degrees becomes more greatly so as the temperature increases. + +Scale is also formed by the settling of mud and sediment carried in +suspension in water. This may bake or be cemented to a hard scale when +mixed with other scale-forming ingredients. + + +Corrosion--Corrosion, or a chemical action leading to the actual +destruction of the boiler metal, is due to the solvent or oxidizing +properties of the feed water. It results from the presence of acid, +either free or developed[15] in the feed, the admixture of air with the +feed water, or as a result of a galvanic action. In boilers it takes +several forms: + +1st. Pitting, which consists of isolated spots of active corrosion which +does not attack the boiler as a whole. + +2nd. General corrosion, produced by naturally acid waters and where the +amount is so even and continuous that no accurate estimate of the metal +eaten away may be made. + +3rd. Grooving, which, while largely a mechanical action which may occur +in neutral waters, is intensified by acidity. + +Foaming--This phenomenon, which ordinarily occurs with waters +contaminated with sewage or organic growths, is due to the fact that the +suspended particles collect on the surface of the water in the boiler +and render difficult the liberation of steam bubbles arising to that +surface. It sometimes occurs with water containing carbonates in +solution in which a light flocculent precipitate will be formed on the +surface of the water. Again, it is the result of an excess of sodium +carbonate used in treatment for some other difficulty where animal or +vegetable oil finds its way into the boiler. + +Priming--Priming, or the passing off of steam from a boiler in belches, +is caused by the concentration of sodium carbonate, sodium sulphate or +sodium chloride in solution. Sodium sulphate is found in many southern +waters and also where calcium or magnesium sulphate is precipitated with +soda ash. + +Treatment of Feed Water--For scale formation. The treatment of feed +water, carrying scale-forming ingredients, is along two main lines: 1st, +by chemical means by which such impurities as are carried by the water +are caused to precipitate; and 2nd, by the means of heat, which results +in the reduction of the power of water to hold certain salts in +solution. The latter method alone is sufficient in the case of certain +temporarily hard waters, but the heat treatment, in general, is used in +connection with a chemical treatment to assist the latter. + +Before going further into detail as to the treatment of water, it may be +well to define certain terms used. + +_Hardness_, which is the most widely known evidence of the presence in +water of scale-forming matter, is that quality, the variation of which +makes it more difficult to obtain a lather or suds from soap in one +water than in another. This action is made use of in the soap test for +hardness described later. Hardness is ordinarily classed as either +temporary or permanent. Temporarily hard waters are those containing +carbonates of lime and magnesium, which may be precipitated by boiling +at 212 degrees and which, if they contain no other scale-forming +ingredients, become "soft" under such treatment. Permanently hard waters +are those containing mainly calcium sulphate, which is only precipitated +at the high temperatures found in the boiler itself, 300 degrees +Fahrenheit or more. The scale of hardness is an arbitrary one, based on +the number of grains of solids per gallon and waters may be classed on +such a basis as follows: 1-10 grain per gallon, soft water; 10-20 grain +per gallon, moderately hard water; above 25 grains per gallon, very hard +water. + +_Alkalinity_ is a general term used for waters containing compounds with +the power of neutralizing acids. + +_Causticity_, as used in water treatment, is a term coined by A. McGill, +indicating the presence of an excess of lime added during treatment. +Though such presence would also indicate alkalinity, the term is +arbitrarily used to apply to those hydrates whose presence is indicated +by phenolphthalein. + +Of the chemical methods of water treatment, there are three general +processes: + +1st. Lime Process. The lime process is used for waters containing +bicarbonates of lime and magnesia. Slacked lime in solution, as lime +water, is the reagent used. This combines with the carbonic acid which +is present, either free or as carbonates, to form an insoluble +monocarbonate of lime. The soluble bicarbonates of lime and magnesia, +losing their carbonic acid, thereby become insoluble and precipitate. + +2nd. Soda Process. The soda process is used for waters containing +sulphates of lime and magnesia. Carbonate of soda and hydrate of soda +(caustic soda) are used either alone or together as the reagents. +Carbonate of soda, added to water containing little or no carbonic acid +or bicarbonates, decomposes the sulphates to form insoluble carbonate of +lime or magnesia which precipitate, the neutral soda remaining in +solution. If free carbonic acid or bicarbonates are present, bicarbonate +of lime is formed and remains in solution, though under the action of +heat, the carbon dioxide will be driven off and insoluble monocarbonates +will be formed. Caustic soda used in this process causes a more +energetic action, it being presumed that the caustic soda absorbs the +carbonic acid, becomes carbonate of soda and acts as above. + +3rd. Lime and Soda Process. This process, which is the combination of +the first two, is by far the most generally used in water purification. +Such a method is used where sulphates of lime and magnesia are contained +in the water, together with such quantity of carbonic acid or +bicarbonates as to impair the action of the soda. Sufficient soda is +used to break down the sulphates of lime and magnesia and as much lime +added as is required to absorb the carbonic acid not taken up in the +soda reaction. + +All of the apparatus for effecting such treatment of feed waters is +approximately the same in its chemical action, the numerous systems +differing in the methods of introduction and handling of the reagents. + +The methods of testing water treated by an apparatus of this description +follow. + +When properly treated, alkalinity, hardness and causticity should be in +the approximate relation of 6, 5 and 4. When too much lime is used in +the treatment, the causticity in the purified water, as indicated by the +acid test, will be nearly equal to the alkalinity. If too little lime is +used, the causticity will fall to approximately half the alkalinity. The +hardness should not be in excess of two points less than the alkalinity. +Where too great a quantity of soda is used, the hardness is lowered and +the alkalinity raised. If too little soda, the hardness is raised and +the alkalinity lowered. + +Alkalinity and causticity are tested with a standard solution of +sulphuric acid. A standard soap solution is used for testing for +hardness and a silver nitrate solution may also be used for determining +whether an excess of lime has been used in the treatment. + +Alkalinity: To 50 cubic centimeters of treated water, to which there has +been added sufficient methylorange to color it, add the acid solution, +drop by drop, until the mixture is on the point of turning red. As the +acid solution is first added, the red color, which shows quickly, +disappears on shaking the mixture, and this color disappears more slowly +as the critical point is approached. One-tenth cubic centimeter of the +standard acid solution corresponds to one degree of alkalinity. + +[Illustration: 2640 Horse-power Installation of Babcock & Wilcox Boilers +at the Botany Worsted Mills, Passaic, N. J.] + +Causticity: To 50 cubic centimeters of treated water, to which there has +been added one drop of phenolphthalein dissolved in alcohol to give the +water a pinkish color, add the acid solution, drop by drop, shaking +after each addition, until the color entirely disappears. One-tenth +cubic centimeter of acid solution corresponds to one degree of +causticity. + +The alkalinity may be determined from the same sample tested for +causticity by the coloring with methylorange and adding the acid until +the sample is on the point of turning red. The total acid added in +determining both causticity and alkalinity in this case is the measure +of the alkalinity. + +Hardness: 100 cubic centimeters of the treated water is used for this +test, one cubic centimeter of the soap solution corresponding to one +degree of hardness. The soap solution is added a very little at a time +and the whole violently shaken. Enough of the solution must be added to +make a permanent lather or foam, that is, the soap bubbles must not +disappear after the shaking is stopped. + +Excess of lime as determined by nitrate of silver: If there is an excess +of lime used in the treatment, a sample will become a dark brown by the +addition of a small quantity of silver nitrate, otherwise a milky white +solution will be formed. + +Combined Heat and Chemical Treatment: Heat is used in many systems of +feed treatment apparatus as an adjunct to the chemical process. Heat +alone will remove temporary hardness by the precipitation of carbonates +of lime and magnesia and, when used in connection with the chemical +process, leaves only the permanent hardness or the sulphates of lime to +be taken care of by chemical treatment. + + TABLE 16 + + REAGENTS REQUIRED IN LIME AND SODA PROCESS + FOR TREATING 1000 U. S. GALLONS OF WATER + PER GRAIN PER GALLON OF CONTAINED IMPURITIES[16] + ++-----------------------+-----------+-----------+ +| | Lime[17] | Soda[18] | +| | Pounds | Pounds | ++-----------------------+-----------+-----------+ +| Calcium Carbonate | 0.098 | ... | +| Calcium Sulphate | ... | 0.124 | +| Calcium Chloride | ... | 0.151 | +| Calcium Nitrate | ... | 0.104 | +| Magnesium Carbonate | 0.234 | ... | +| Magnesium Sulphate | 0.079 | 0.141 | +| Magnesium Chloride | 0.103 | 0.177 | +| Magnesium Nitrate | 0.067 | 0.115 | +| Ferrous Carbonate | 0.169 | ... | +| Ferrous Sulphate | 0.070 | 0.110 | +| Ferric Sulphate | 0.074 | 0.126 | +| Aluminum Sulphate | 0.087 | 0.147 | +| Free Sulphuric Acid | 0.100 | 0.171 | +| Sodium Carbonate | 0.093 | ... | +| Free Carbon Dioxide | 0.223 | ... | +| Hydrogen Sulphite | 0.288 | ... | ++-----------------------+-----------+-----------+ + +The chemicals used in the ordinary lime and soda process of feed water +treatment are common lime and soda. The efficiency of such apparatus +will depend wholly upon the amount and character of the impurities in +the water to be treated. Table 16 gives the amount of lime and soda +required per 1000 gallons for each grain per gallon of the various +impurities found in the water. This table is based on lime containing 90 +per cent calcium oxide and soda containing 58 per cent sodium oxide, +which correspond to the commercial quality ordinarily purchasable. From +this table and the cost of the lime and soda, the cost of treating any +water per 1000 gallons may be readily computed. + +Less Usual Reagents--Barium hydrate is sometimes used to reduce +permanent hardness or the calcium sulphate component. Until recently, +the high cost of barium hydrate has rendered its use prohibitive but at +the present it is obtained as a by-product in cement manufacture and it +may be purchased at a more reasonable figure than heretofore. It acts +directly on the soluble sulphates to form barium sulphate which is +insoluble and may be precipitated. Where this reagent is used, it is +desirable that the reaction be allowed to take place outside of the +boiler, though there are certain cases where its internal use is +permissible. + +Barium carbonate is sometimes used in removing calcium sulphate, the +products of the reaction being barium sulphate and calcium carbonate, +both of which are insoluble and may be precipitated. As barium carbonate +in itself is insoluble, it cannot be added to water as a solution and +its use should, therefore, be confined to treatment outside of the +boiler. + +Silicate of soda will precipitate calcium carbonate with the formation +of a gelatinous silicate of lime and carbonate of soda. If calcium +sulphate is also present, carbonate of soda is formed in the above +reaction, which in turn will break down the sulphate. + +Oxalate of soda is an expensive but efficient reagent which forms a +precipitate of calcium oxalate of a particularly insoluble nature. + +Alum and iron alum will act as efficient coagulents where organic matter +is present in the water. Iron alum has not only this property but also +that of reducing oil discharged from surface condensers to a condition +in which it may be readily removed by filtration. + +Corrosion--Where there is a corrosive action because of the presence of +acid in the water or of oil containing fatty acids which will decompose +and cause pitting wherever the sludge can find a resting place, it may +be overcome by the neutralization of the water by carbonate of soda. +Such neutralization should be carried to the point where the water will +just turn red litmus paper blue. As a preventative of such action +arising from the presence of the oil, only the highest grades of +hydrocarbon oils should be used. + +Acidity will occur where sea water is present in a boiler. There is the +possibility of such an occurrence in marine practice and in stationary +plants using sea water for condensing, due to leaky condenser tubes, +priming in the evaporators, etc. Such acidity is caused through the +dissociation of magnesium chloride into hydrochloride acid and magnesia +under high temperatures. The acid in contact with the metal forms an +iron salt which immediately upon its formation is neutralized by the +free magnesia in the water, thereby precipitating iron oxide and +reforming magnesium chloride. The preventive for corrosion arising from +such acidity is the keeping tight of the condenser. Where it is +unavoidable that some sea water should find its way into a boiler, the +acidity resulting should be neutralized by soda ash. This will convert +the magnesium chloride into magnesium carbonate and sodium chloride, +neither of which is corrosive but both of which are scale-forming. + +The presence of air in the feed water which is sucked in by the feed +pump is a well recognized cause of corrosion. Air bubbles form below the +water line and attack the metal of the boiler, the oxygen of the air +causing oxidization of the boiler metal and the formation of rust. The +particle of rust thus formed is swept away by the circulation or is +dislodged by expansion and the minute pit thus left forms an ideal +resting place for other air bubbles and the continuation of the +oxidization process. The prevention is, of course, the removing of the +air from the feed water. In marine practice, where there has been +experienced the most difficulty from this source, it has been found to +be advantageous to pump the water from the hot well to a filter tank +placed above the feed pump suction valves. In this way the air is +liberated from the surface of the tank and a head is assured for the +suction end of the pump. In this same class of work, the corrosive +action of air is reduced by introducing the feed through a spray nozzle +into the steam space above the water line. + +Galvanic action, resulting in the eating away of the boiler metal +through electrolysis was formerly considered practically the sole cause +of corrosion. But little is known of such action aside from the fact +that it does take place in certain instances. The means adopted as a +remedy is usually the installation of zinc plates within the boiler, +which must have positive metallic contact with the boiler metal. In this +way, local electrolytic effects are overcome by a still greater +electrolytic action at the expense of the more positive zinc. The +positive contact necessary is difficult to maintain and it is +questionable just what efficacy such plates have except for a short +period after their installation when the contact is known to be +positive. Aside from protection from such electrolytic action, however, +the zinc plates have a distinct use where there is the liability of air +in the feed, as they offer a substance much more readily oxidized by +such air than the metal of the boiler. + +Foaming--Where foaming is caused by organic matter in suspension, it may +be largely overcome by filtration or by the use of a coagulent in +connection with filtration, the latter combination having come recently +into considerable favor. Alum, or potash alum, and iron alum, which in +reality contains no alumina and should rather be called potassia-ferric, +are the coagulents generally used in connection with filtration. Such +matter as is not removed by filtration may, under certain conditions, be +handled by surface blowing. In some instances, settling tanks are used +for the removal of matter in suspension, but where large quantities of +water are required, filtration is ordinarily substituted on account of +the time element and the large area necessary in settling tanks. + +Where foaming occurs as the result of overtreatment of the feed water, +the obvious remedy is a change in such treatment. + +Priming--Where priming is caused by excessive concentration of salts +within a boiler, it may be overcome largely by frequent blowing down. +The degree of concentration allowable before priming will take place +varies widely with conditions of operation and may be definitely +determined only by experience with each individual set of conditions. It +is the presence of the salts that cause priming that may result in the +absolute unfitness of water for boiler feed purposes. Where these salts +exist in such quantities that the amount of blowing down necessary to +keep the degree of concentration below the priming point results in +excessive losses, the only remedy is the securing of another supply of +feed, and the results will warrant the change almost regardless of the +expense. In some few instances, the impurities may be taken care of by +some method of water treatment but such water should be submitted to an +authority on the subject before any treatment apparatus is installed. + +[Illustration: 3000 Horse-power Installation of Cross Drum Babcock & +Wilcox Boilers and Superheaters Equipped with Babcock & Wilcox Chain +Grate Stokers at the Washington Terminal Co., Washington, D. C.] + +Boiler Compounds--The method of treatment of feed water by far the most +generally used is by the use of some of the so-called boiler compounds. +There are many reliable concerns handling such compounds who +unquestionably secure the promised results, but there is a great +tendency toward looking on the compound as a "cure all" for any water +difficulties and care should be taken to deal only with reputable +concerns. + +The composition of these compounds is almost invariably based on soda +with certain tannic substances and in some instances a gelatinous +substance which is presumed to encircle scale particles and prevent +their adhering to the boiler surfaces. The action of these compounds is +ordinarily to reduce the calcium sulphate in the water by means of +carbonate of soda and to precipitate it as a muddy form of calcium +carbonate which may be blown off. The tannic compounds are used in +connection with the soda with the idea of introducing organic matter +into any scale already formed. When it has penetrated to the boiler +metal, decomposition of the scale sets in, causing a disruptive effect +which breaks the scale from the metal sometimes in large slabs. It is +this effect of boiler compounds that is to be most carefully guarded +against or inevitable trouble will result from the presence of loose +scale with the consequent danger of tube losses through burning. + +When proper care is taken to suit the compound to the water in use, the +results secured are fairly effective. In general, however, the use of +compounds may only be recommended for the prevention of scale rather +than with the view to removing scale which has already formed, that is, +the compounds should be introduced with the feed water only when the +boiler has been thoroughly cleaned. + + + + +FEED WATER HEATING AND METHODS OF FEEDING + + +Before water fed into a boiler can be converted into steam, it must be +first heated to a temperature corresponding to the pressure within the +boiler. Steam at 160 pounds gauge pressure has a temperature of +approximately 371 degrees Fahrenheit. If water is fed to the boiler at +60 degrees Fahrenheit, each pound must have 311 B. t. u. added to it to +increase its temperature 371 degrees, which increase must take place +before the water can be converted into steam. As it requires 1167.8 +B. t. u. to raise one pound of water from 60 to 371 degrees and to +convert it into steam at 160 pounds gauge pressure, the 311 degrees +required simply to raise the temperature of the water from 60 to 371 +degrees will be approximately 27 per cent of the total. If, therefore, +the temperature of the water can be increased from 60 to 371 degrees +before it is introduced into a boiler by the utilization of heat from +some source that would otherwise be wasted, there will be a saving in +the fuel required of 311 ÷ 1167.8 = 27 per cent, and there will be a net +saving, provided the cost of maintaining and operating the apparatus for +securing this saving is less than the value of the heat thus saved. + +The saving in the fuel due to the heating of feed water by means of heat +that would otherwise be wasted may be computed from the formula: + + 100 (t - t_{i}) +Fuel saving per cent = --------------- (1) + H + 32 - t_{i} + +where, t = temperature of feed water after heating, t_{i} = temperature +of feed water before heating, and H = total heat above 32 degrees per +pound of steam at the boiler pressure. Values of H may be found in Table +23. Table 17 has been computed from this formula to show the fuel saving +under the conditions assumed with the boiler operating at 180 pounds +gauge pressure. + + TABLE 17 + + SAVING IN FUEL, IN PER CENT, BY HEATING FEED WATER + GAUGE PRESSURE 180 POUNDS + ++-----------+-----------------------------------------+ +| Initial | Final Temperature--Degrees Fahrenheit | +|Temperature|-----+-----+-----+-----+-----+-----+-----| +| Fahrenheit| 120 | 140 | 160 | 180 | 200 | 250 | 300 | ++-----------+-----+-----+-----+-----+-----+-----+-----+ +| 32 | 7.35| 9.02|10.69|12.36|14.04|18.20|22.38| +| 35 | 7.12| 8.79|10.46|12.14|13.82|18.00|22.18| +| 40 | 6.72| 8.41|10.09|11.77|13.45|17.65|21.86| +| 45 | 6.33| 8.02| 9.71|11.40|13.08|17.30|21.52| +| 50 | 5.93| 7.63| 9.32|11.02|12.72|16.95|21.19| +| 55 | 5.53| 7.24| 8.94|10.64|12.34|16.60|20.86| +| 60 | 5.13| 6.84| 8.55|10.27|11.97|16.24|20.52| +| 65 | 4.72| 6.44| 8.16| 9.87|11.59|15.88|20.18| +| 70 | 4.31| 6.04| 7.77| 9.48|11.21|15.52|19.83| +| 75 | 3.90| 5.64| 7.36| 9.09|10.82|15.16|19.48| +| 80 | 3.48| 5.22| 6.96| 8.70|10.44|14.79|19.13| +| 85 | 3.06| 4.80| 6.55| 8.30|10.05|14.41|18.78| +| 90 | 2.63| 4.39| 6.14| 7.89| 9.65|14.04|18.43| +| 95 | 2.20| 3.97| 5.73| 7.49| 9.25|13.66|18.07| +| 100 | 1.77| 3.54| 5.31| 7.08| 8.85|13.28|17.70| +| 110 | .89| 2.68| 4.47| 6.25| 8.04|12.50|16.97| +| 120 | .00| 1.80| 3.61| 5.41| 7.21|11.71|16.22| +| 130 | | .91| 2.73| 4.55| 6.37|10.91|15.46| +| 140 | | .00| 1.84| 3.67| 5.51|10.09|14.68| +| 150 | | | .93| 2.78| 4.63| 9.26|13.89| +| 160 | | | .00| 1.87| 3.74| 8.41|13.09| +| 170 | | | | .94| 2.83| 7.55|12.27| +| 180 | | | | .00| 1.91| 6.67|11.43| +| 190 | | | | | .96| 5.77|10.58| +| 200 | | | | | .00| 4.86| 9.71| +| 210 | | | | | | 3.92| 8.82| ++-----------+-----+-----+-----+-----+-----+-----+-----+ + +Besides the saving in fuel effected by the use of feed water heaters, +other advantages are secured. The time required for the conversion of +water into steam is diminished and the steam capacity of the boiler +thereby increased. Further, the feeding of cold water into a boiler has +a tendency toward the setting up of temperature strains, which are +diminished in proportion as the temperature of the feed approaches that +of the steam. An important additional advantage of heating feed water is +that in certain types of heaters a large portion of the scale forming +ingredients are precipitated before entering the boiler, with a +consequent saving in cleaning and losses through decreased efficiency +and capacity. + +In general, feed water heaters may be divided into closed heaters, open +heaters and economizers; the first two depend for their heat upon +exhaust, or in some cases live steam, while the last class utilizes the +heat of the waste flue gases to secure the same result. The question of +the type of apparatus to be installed is dependent upon the conditions +attached to each individual case. + +In closed heaters the feed water and the exhaust steam do not come into +actual contact with each other. Either the steam or the water passes +through tubes surrounded by the other medium, as the heater is of the +steam-tube or water-tube type. A closed heater is best suited for water +free from scale-forming matter, as such matter soon clogs the passages. +Cleaning such heaters is costly and the efficiency drops off rapidly as +scale forms. A closed heater is not advisable where the engines work +intermittently, as is the case with mine hoisting engines. In this class +of work the frequent coolings between operating periods and the sudden +heatings when operation commences will tend to loosen the tubes or even +pull them apart. For this reason, an open heater, or economizer, will +give more satisfactory service with intermittently operating apparatus. + +Open heaters are best suited for waters containing scale-forming matter. +Much of the temporary hardness may be precipitated in the heater and the +sediment easily removed. Such heaters are frequently used with a reagent +for precipitating permanent hardness in the combined heat and chemical +treatment of feed water. The so-called live steam purifiers are open +heaters, the water being raised to the boiling temperature and the +carbonates and a portion of the sulphates being precipitated. The +disadvantage of this class of apparatus is that some of the sulphates +remain in solution to be precipitated as scale when concentrated in the +boiler. Sufficient concentration to have such an effect, however, may +often be prevented by frequent blowing down. + +Economizers find their largest field where the design of the boiler is +such that the maximum possible amount of heat is not extracted from the +gases of combustion. The more wasteful the boiler, the greater the +saving effected by the use of the economizer, and it is sometimes +possible to raise the temperature of the feed water to that of high +pressure steam by the installation of such an apparatus, the saving +amounting in some cases to as much as 20 per cent. The fuel used bears +directly on the question of the advisability of an economizer +installation, for when oil is the fuel a boiler efficiency of 80 per +cent or over is frequently realized, an efficiency which would leave a +small opportunity for a commercial gain through the addition of an +economizer. + +From the standpoint of space requirements, economizers are at a +disadvantage in that they are bulky and require a considerable increase +over space occupied by a heater of the exhaust type. They also require +additional brickwork or a metal casing, which increases the cost. +Sometimes, too, the frictional resistance of the gases through an +economizer make its adaptability questionable because of the draft +conditions. When figuring the net return on economizer investment, all +of these factors must be considered. + +When the feed water is such that scale will quickly encrust the +economizer and throw it out of service for cleaning during an excessive +portion of the time, it will be necessary to purify water before +introducing it into an economizer to make it earn a profit on the +investment. + +From the foregoing, it is clearly indicated that it is impossible to +make a definite statement as to the relative saving by heating feed +water in any of the three types. Each case must be worked out +independently and a decision can be reached only after an exhaustive +study of all the conditions affecting the case, including the time the +plant will be in service and probable growth of the plant. When, as a +result of such study, the possible methods for handling the problem have +been determined, the solution of the best apparatus can be made easily +by the balancing of the saving possible by each method against its first +cost, depreciation, maintenance and cost of operation. + +Feeding of Water--The choice of methods to be used in introducing feed +water into a boiler lies between an injector and a pump. In most plants, +an injector would not be economical, as the water fed by such means must +be cold, a fact which makes impossible the use of a heater before the +water enters the injector. Such a heater might be installed between the +injector and the boiler but as heat is added to the water in the +injector, the heater could not properly fulfill its function. + + TABLE 18 + + COMPARISON OF PUMPS AND INJECTORS + _________________________________________________________________________ +| | | | +| Method of Supplying | | | +| Feed-water to Boiler | Relative amount of | Saving of fuel over| +| Temperature of feed-water as | coal required per | the amount required| +| delivered to the pump or to | unit of time, the | when the boiler is | +| injector, 60 degrees Fahren- | amount for a direct-| fed by a direct- | +| heit. Rate of evaporation of | acting pump, feeding| acting pump without| +| boiler, to pounds of water | water at 60 degrees | heater | +| per pound of coal from and | without a heater, | Per Cent | +| at 212 degrees Fahrenheit | being taken as unity| | +|______________________________|_____________________|____________________| +| | | | +| Direct-acting Pump feeding | | | +| water at 60 degrees without | | | +| a heater | 1.000 | .0 | +| | | | +| Injector feeding water at | | | +| 150 degrees without a heater | .985 | 1.5 | +| Injector feeding through a | | | +| heater in which the water is | | | +| heated from 150 to 200 | | | +| degrees | .938 | 6.2 | +| | | | +| Direct-acting Pump feeding | | | +| water through a heater in | | | +| which it is heated from 60 | | | +| to 200 degrees | .879 | 12.1 | +| | | | +| Geared Pump run from the | | | +| engine, feeding water | | | +| through a heater in which it | | | +| is heated from 60 to 200 | | | +| degrees | .868 | 13.2 | +|______________________________|_____________________|____________________| + +The injector, considered only in the light of a combined heater and +pump, is claimed to have a thermal efficiency of 100 per cent, since all +of the heat in the steam used is returned to the boiler with the water. +This claim leads to an erroneous idea. If a pump is used in feeding the +water to a boiler and the heat in the exhaust from the pump is imparted +to the feed water, the pump has as high a thermal efficiency as the +injector. The pump has the further advantage that it uses so much less +steam for the forcing of a given quantity of water into the boiler that +it makes possible a greater saving through the use of the exhaust from +other auxiliaries for heating the feed, which exhaust, if an injector +were used, would be wasted, as has been pointed out. + +In locomotive practice, injectors are used because there is no exhaust +steam available for heating the feed, this being utilized in producing a +forced draft, and because of space requirements. In power plant work, +however, pumps are universally used for regular operation, though +injectors are sometimes installed as an auxiliary method of feeding. + +Table 18 shows the relative value of injectors, direct-acting steam +pumps and pumps driven from the engine, the data having been obtained +from actual experiment. It will be noted that when feeding cold water +direct to the boilers, the injector has a slightly greater economy but +when feeding through a heater, the pump is by far the more economical. + +Auxiliaries--It is the general impression that auxiliaries will take +less steam if the exhaust is turned into the condensers, in this way +reducing the back pressure. As a matter of fact, vacuum is rarely +registered on an indicator card taken from the cylinders of certain +types of auxiliaries unless the exhaust connection is short and without +bends, as long pipes and many angles offset the effect of the condenser. +On the other hand, if the exhaust steam from the auxiliaries can be used +for heating the feed water, all of the latent heat less only the loss +due to radiation is returned to the boiler and is saved instead of being +lost in the condensing water or wasted with the free exhaust. Taking +into consideration the plant as a whole, it would appear that the +auxiliary machinery, under such conditions, is more efficient than the +main engines. + +[Illustration: Portion of 4160 Horse-power Installation of Babcock & +Wilcox Boilers at the Prudential Life Insurance Co. Building, Newark, +N. J.] + + + + +STEAM + + +When a given weight of a perfect gas is compressed or expanded at a +constant temperature, the product of the pressure and volume is a +constant. Vapors, which are liquids in aeriform condition, on the other +hand, can exist only at a definite pressure corresponding to each +temperature if in the saturated state, that is, the pressure is a +function of the temperature only. Steam is water vapor, and at a +pressure of, say, 150 pounds absolute per square inch saturated steam +can exist only at a temperature 358 degrees Fahrenheit. Hence if the +pressure of saturated steam be fixed, its temperature is also fixed, and +_vice versa_. + +Saturated steam is water vapor in the condition in which it is generated +from water with which it is in contact. Or it is steam which is at the +maximum pressure and density possible at its temperature. If any change +be made in the temperature or pressure of steam, there will be a +corresponding change in its condition. If the pressure be increased or +the temperature decreased, a portion of the steam will be condensed. If +the temperature be increased or the pressure decreased, a portion of the +water with which the steam is in contact will be evaporated into steam. +Steam will remain saturated just so long as it is of the same pressure +and temperature as the water with which it can remain in contact without +a gain or loss of heat. Moreover, saturated steam cannot have its +temperature lowered without a lowering of its pressure, any loss of heat +being made up by the latent heat of such portion as will be condensed. +Nor can the temperature of saturated steam be increased except when +accompanied by a corresponding increase in pressure, any added heat +being expended in the evaporation into steam of a portion of the water +with which it is in contact. + +Dry saturated steam contains no water. In some cases, saturated steam is +accompanied by water which is carried along with it, either in the form +of a spray or is blown along the surface of the piping, and the steam is +then said to be wet. The percentage weight of the steam in a mixture of +steam and water is called the quality of the steam. Thus, if in a +mixture of 100 pounds of steam and water there is three-quarters of a +pound of water, the quality of the steam will be 99.25. + +Heat may be added to steam not in contact with water, such an addition +of heat resulting in an increase of temperature and pressure if the +volume be kept constant, or an increase in temperature and volume if the +pressure remain constant. Steam whose temperature thus exceeds that of +saturated steam at a corresponding pressure is said to be superheated +and its properties approximate those of a perfect gas. + +As pointed out in the chapter on heat, the heat necessary to raise one +pound of water from 32 degrees Fahrenheit to the point of ebullition is +called the _heat of the liquid_. The heat absorbed during ebullition +consists of that necessary to dissociate the molecules, or the _inner +latent heat_, and that necessary to overcome the resistance to the +increase in volume, or the _outer latent heat_. These two make up the +_latent heat of evaporation_ and the sum of this latent heat of +evaporation and the heat of the liquid make the _total heat_ of the +steam. These values for various pressures are given in the steam tables, +pages 122 to 127. + +The specific volume of saturated steam at any pressure is the volume in +cubic feet of one pound of steam at that pressure. + +The density of saturated steam, that is, its weight per cubic foot, is +obviously the reciprocal of the specific volume. This density varies as +the 16/17 power over the ordinary range of pressures used in steam +boiler work and may be found by the formula, D = .003027p^{.941}, which +is correct within 0.15 per cent up to 250 pounds pressure. + +The relative volume of steam is the ratio of the volume of a given +weight to the volume of the same weight of water at 39.2 degrees +Fahrenheit and is equal to the specific volume times 62.427. + +As vapors are liquids in their gaseous form and the boiling point is the +point of change in this condition, it is clear that this point is +dependent upon the pressure under which the liquid exists. This fact is +of great practical importance in steam condenser work and in many +operations involving boiling in an open vessel, since in the latter case +its altitude will have considerable influence. The relation between +altitude and boiling point of water is shown in Table 12. + +The conditions of feed temperature and steam pressure in boiler tests, +fuel performances and the like, will be found to vary widely in +different trials. In order to secure a means for comparison of different +trials, it is necessary to reduce all results to some common basis. The +method which has been adopted for the reduction to a comparable basis is +to transform the evaporation under actual conditions of steam pressure +and feed temperature which exist in the trial to an equivalent +evaporation under a set of standard conditions. These standard +conditions presuppose a feed water temperature of 212 degrees Fahrenheit +and a steam pressure equal to the normal atmospheric pressure at sea +level, 14.7 pounds absolute. Under such conditions steam would be +generated _at_ a temperature of 212 degrees, the temperature +corresponding to atmospheric pressure at sea level, _from_ water at 212 +degrees. The weight of water which _would_ be evaporated under the +assumed standard conditions by exactly the amount of heat absorbed by +the boiler under actual conditions existing in the trial, is, therefore, +called the equivalent evaporation "from and at 212 degrees." + +The factor for reducing the weight of water actually converted into +steam from the temperature of the feed, at the steam pressure existing +in the trial, to the equivalent evaporation under standard conditions is +called the _factor of evaporation._ This factor is the ratio of the +total heat added to one pound of steam under the standard conditions to +the heat added to each pound of steam in heating the water from the +temperature of the feed in the trial to the temperature corresponding to +the pressure existing in the trial. This heat added is obviously the +difference between the total heat of evaporation of the steam at the +pressure existing in the trial and the heat of the liquid in the water +at the temperature at which it was fed in the trial. To illustrate by an +example: + +In a boiler trial the temperature of the feed water is 60 degrees +Fahrenheit and the pressure under which steam is delivered is 160.3 +pounds gauge pressure or 175 pounds absolute pressure. The total heat of +one pound of steam at 175 pounds pressure is 1195.9 B. t. u. measured +above the standard temperature of 32 degrees Fahrenheit. But the water +fed to the boiler contained 28.08 B. t. u. as the heat of the liquid +measured above 32 degrees Fahrenheit. Therefore, to each pound of steam +there has been added 1167.82 B. t. u. To evaporate one pound of water +under standard conditions would, on the other hand, have required but +970.4 B. t. u., which, as described, is the latent heat of evaporation +at 212 degrees Fahrenheit. Expressed differently, the total heat of one +pound of steam at the pressure corresponding to a temperature of 212 +degrees is 1150.4 B. t. u. One pound of water at 212 degrees contains +180 B. t. u. of sensible heat above 32 degrees Fahrenheit. Hence, under +standard conditions, 1150.4 - 180 = 970.4 B. t. u. is added in the +changing of one pound of water into steam at atmospheric pressure and a +temperature of 212 degrees. This is in effect the definition of the +latent heat of evaporation. + +Hence, if conditions of the trial had been standard, only 970.4 B. t. u. +would be required and the ratio of 1167.82 to 970.4 B. t. u. is the +ratio determining the factor of evaporation. The factor in the assumed +case is 1167.82 ÷ 970.4 = 1.2034 and if the same amount of heat had been +absorbed under standard conditions as was absorbed in the trial +condition, 1.2034 times the amount of steam would have been generated. +Expressed as a formula for use with any set of conditions, the factor +is, + + H - h +F = ----- (2) + 970.4 + +Where H = the total heat of steam above 32 degrees Fahrenheit from steam + tables, + h = sensible heat of feed water above 32 degrees Fahrenheit from + Table 22. + +In the form above, the factor may be determined with either saturated or +superheated steam, provided that in the latter case values of H are +available for varying degrees of superheat and pressures. + +Where such values are not available, the form becomes, + + H - h + s(t_{sup} - t_{sat}) +F = ---------------------------- (3) + 970.4 + +Where s = mean specific heat of superheated steam at the + pressure existing in the trial from saturated + steam to the temperature existing in the trial, + t_{sup} = final temperature of steam, + t_{sat} = temperature of saturated steam, corresponding to + pressure existing, +(t_{sup} - t_{sat}) = degrees of superheat. + +The specific heat of superheated steam will be taken up later. + +Table 19 gives factors of evaporation for saturated steam boiler trials +to cover a large range of conditions. Except for the most refined work, +intermediate values may be determined by interpolation. + +Steam gauges indicate the pressure above the atmosphere. As has been +pointed out, the atmospheric pressure changes according to the altitude +and the variation in the barometer. Hence, calculations involving the +properties of steam are based on _absolute_ pressures, which are equal +to the gauge pressure plus the atmospheric pressure in pounds to the +square inch. This latter is generally assumed to be 14.7 pounds per +square inch at sea level, but for other levels it must be determined +from the barometric reading at that place. + +Vacuum gauges indicate the difference, expressed in inches of mercury, +between atmospheric pressure and the pressure within the vessel to which +the gauge is attached. For approximate purposes, 2.04 inches height of +mercury may be considered equal to a pressure of one pound per square +inch at the ordinary temperatures at which mercury gauges are used. +Hence for any reading of the vacuum gauge in inches, G, the absolute +pressure for any barometer reading in inches, B, will be (B - G) ÷ 2.04. +If the barometer is 30 inches measured at ordinary temperatures and not +corrected to 32 degrees Fahrenheit and the vacuum gauge 24 inches, the +absolute pressure will be (30 - 24) ÷ 2.04 = 2.9 pounds per square inch. + + TABLE 19 + + FACTORS OF EVAPORATION + CALCULATED FROM MARKS AND DAVIS TABLES + + ______________________________________________________________________ +| | | +|Feed | | +|Temp- | | +|erature| | +|Degrees| Steam Pressure by Gauge | +|Fahren-| | +|heit | | +|_______|______________________________________________________________| +| | | | | | | | | +| | 50 | 60 | 70 | 80 | 90 | 100 | 110 | +|_______|________|________|________|________|________|________|________| +| | | | | | | | | +| 32 | 1.2143 | 1.2170 | 1.2194 | 1.2215 | 1.2233 | 1.2233 | 1.2265 | +| 40 | 1.2060 | 1.2087 | 1.2111 | 1.2131 | 1.2150 | 1.2168 | 1.2181 | +| 50 | 1.1957 | 1.1984 | 1.2008 | 1.2028 | 1.2047 | 1.2065 | 1.2079 | +| 60 | 1.1854 | 1.1881 | 1.1905 | 1.1925 | 1.1944 | 1.1961 | 1.1976 | +| 70 | 1.1750 | 1.1778 | 1.1802 | 1.1822 | 1.1841 | 1.1859 | 1.1873 | +| 80 | 1.1649 | 1.1675 | 1.1699 | 1.1720 | 1.1738 | 1.1756 | 1.1770 | +| 90 | 1.1545 | 1.1572 | 1.1596 | 1.1617 | 1.1636 | 1.1653 | 1.1668 | +| 100 | 1.1443 | 1.1470 | 1.1493 | 1.1514 | 1.1533 | 1.1550 | 1.1565 | +| 110 | 1.1340 | 1.1367 | 1.1391 | 1.1411 | 1.1430 | 1.1448 | 1.1462 | +| 120 | 1.1237 | 1.1264 | 1.1288 | 1.1309 | 1.1327 | 1.1345 | 1.1359 | +| 130 | 1.1134 | 1.1161 | 1.1185 | 1.1206 | 1.1225 | 1.1242 | 1.1257 | +| 140 | 1.1031 | 1.1058 | 1.1082 | 1.1103 | 1.1122 | 1.1139 | 1.1154 | +| 150 | 1.0928 | 1.0955 | 1.0979 | 1.1000 | 1.1019 | 1.1036 | 1.1051 | +| 160 | 1.0825 | 1.0852 | 1.0876 | 1.0897 | 1.0916 | 1.0933 | 1.0948 | +| 170 | 1.0722 | 1.0749 | 1.0773 | 1.0794 | 1.0813 | 1.0830 | 1.0845 | +| 180 | 1.0619 | 1.0646 | 1.0670 | 1.0691 | 1.0709 | 1.0727 | 1.0741 | +| 190 | 1.0516 | 1.0543 | 1.0567 | 1.0587 | 1.0606 | 1.0624 | 1.0638 | +| 200 | 1.0412 | 1.0439 | 1.0463 | 1.0484 | 1.0503 | 1.0520 | 1.0535 | +| 210 | 1.0309 | 1.0336 | 1.0360 | 1.0380 | 1.0399 | 1.0417 | 1.0432 | +|_______|________|________|________|________|________|________|________| + ______________________________________________________________________ +| | | +|Feed | | +|Temp- | | +|erature| | +|Degrees| Steam Pressure by Gauge | +|Fahren-| | +|heit | | +|_______|______________________________________________________________| +| | | | | | | | | +| | 120 | 130 | 140 | 150 | 160 | 170 | 180 | +|_______|________|________|________|________|________|________|________| +| | | | | | | | | +| 32 | 1.2280 | 1.2292 | 1.2304 | 1.2314 | 1.2323 | 1.2333 | 1.2342 | +| 40 | 1.2196 | 1.2209 | 1.2221 | 1.2231 | 1.2241 | 1.2250 | 1.2259 | +| 50 | 1.2093 | 1.2106 | 1.2117 | 1.2128 | 1.2137 | 1.2147 | 1.2156 | +| 60 | 1.1990 | 1.2003 | 1.2014 | 1.2025 | 1.2034 | 1.2044 | 1.2053 | +| 70 | 1.1887 | 1.1900 | 1.1911 | 1.1922 | 1.1931 | 1.1941 | 1.1950 | +| 80 | 1.1785 | 1.1797 | 1.1809 | 1.1819 | 1.1828 | 1.1838 | 1.1847 | +| 90 | 1.1682 | 1.1695 | 1.1706 | 1.1717 | 1.1725 | 1.1735 | 1.1744 | +| 100 | 1.1579 | 1.1592 | 1.1603 | 1.1614 | 1.1623 | 1.1633 | 1.1642 | +| 110 | 1.1477 | 1.1489 | 1.1500 | 1.1511 | 1.1520 | 1.1530 | 1.1539 | +| 120 | 1.1374 | 1.1386 | 1.1398 | 1.1408 | 1.1418 | 1.1427 | 1.1436 | +| 130 | 1.1271 | 1.1284 | 1.1295 | 1.1305 | 1.1315 | 1.1324 | 1.1333 | +| 140 | 1.1168 | 1.1181 | 1.1192 | 1.1203 | 1.1212 | 1.1221 | 1.1230 | +| 150 | 1.1065 | 1.1078 | 1.1089 | 1.1099 | 1.1109 | 1.1118 | 1.1127 | +| 160 | 1.0962 | 1.0975 | 1.0986 | 1.0997 | 1.1006 | 1.1015 | 1.1024 | +| 170 | 1.0859 | 1.0872 | 1.0883 | 1.0893 | 1.0903 | 1.0912 | 1.0921 | +| 180 | 1.0756 | 1.0768 | 1.0780 | 1.0790 | 1.0800 | 1.0809 | 1.0818 | +| 190 | 1.0653 | 1.0665 | 1.0676 | 1.0687 | 1.0696 | 1.0706 | 1.0715 | +| 200 | 1.0549 | 1.0562 | 1.0573 | 1.0584 | 1.0593 | 1.0602 | 1.0611 | +| 210 | 1.0446 | 1.0458 | 1.0469 | 1.0480 | 1.0489 | 1.0499 | 1.0508 | +|_______|________|________|________|________|________|________|________| + ______________________________________________________________________ +| | | +|Feed | | +|Temp- | | +|erature| | +|Degrees| Steam Pressure by Gauge | +|Fahren-| | +|heit | | +|_______|______________________________________________________________| +| | | | | | | | | +| | 190 | 200 | 210 | 220 | 230 | 240 | 250 | +|_______|________|________|________|________|________|________|________| +| | | | | | | | | +| 32 | 1.2350 | 1.2357 | 1.2364 | 1.2372 | 1.2378 | 1.2384 | 1.2390 | +| 40 | 1.2267 | 1.2274 | 1.2282 | 1.2289 | 1.2295 | 1.2301 | 1.2307 | +| 50 | 1.2164 | 1.2171 | 1.2178 | 1.2186 | 1.2192 | 1.2198 | 1.2204 | +| 60 | 1.2061 | 1.2068 | 1.2075 | 1.2083 | 1.2089 | 1.2095 | 1.2101 | +| 70 | 1.1958 | 1.1965 | 1.1972 | 1.1980 | 1.1986 | 1.1992 | 1.1998 | +| 80 | 1.1855 | 1.1863 | 1.1869 | 1.1877 | 1.1883 | 1.1889 | 1.1895 | +| 90 | 1.1750 | 1.1760 | 1.1766 | 1.1774 | 1.1780 | 1.1786 | 1.1792 | +| 100 | 1.1650 | 1.1657 | 1.1664 | 1.1671 | 1.1678 | 1.1684 | 1.1690 | +| 110 | 1.1547 | 1.1554 | 1.1562 | 1.1569 | 1.1575 | 1.1581 | 1.1587 | +| 120 | 1.1444 | 1.1452 | 1.1459 | 1.1466 | 1.1472 | 1.1478 | 1.1484 | +| 130 | 1.1341 | 1.1349 | 1.1356 | 1.1363 | 1.1369 | 1.1375 | 1.1381 | +| 140 | 1.1239 | 1.1246 | 1.1253 | 1.1260 | 1.1266 | 1.1272 | 1.1278 | +| 150 | 1.1136 | 1.1143 | 1.1150 | 1.1157 | 1.1163 | 1.1169 | 1.1176 | +| 160 | 1.1033 | 1.1040 | 1.1047 | 1.1054 | 1.1060 | 1.1066 | 1.1073 | +| 170 | 1.0930 | 1.0937 | 1.0944 | 1.0951 | 1.0957 | 1.0963 | 1.0969 | +| 180 | 1.0826 | 1.0834 | 1.0841 | 1.0848 | 1.0854 | 1.0860 | 1.0866 | +| 190 | 1.0723 | 1.0730 | 1.0737 | 1.0745 | 1.0751 | 1.0757 | 1.0763 | +| 200 | 1.0620 | 1.0627 | 1.0634 | 1.0641 | 1.0647 | 1.0653 | 1.0660 | +| 210 | 1.0516 | 1.0523 | 1.0530 | 1.0538 | 1.0544 | 1.0550 | 1.0556 | +|_______|________|________|________|________|________|________|________| + +The temperature, pressure and other properties of steam for varying +amounts of vacuum and the pressure above vacuum corresponding to each +inch of reading of the vacuum gauge are given in Table 20. + + TABLE 20 + + PROPERTIES OF SATURATED STEAM FOR VARYING AMOUNTS OF VACUUM + CALCULATED FROM MARKS AND DAVIS TABLES + ______________________________________________________________________ +| | | | | | | | +| | | | Heat of | Latent | Total | | +| | | Temp- | the Liquid| Heat | Heat | | +| | | erature | Above | Above | Above |Density or| +| | Absolute | Degrees | 32 De- | 32 De- | 32 De- |Weight per| +| Vacuum | Pressure | Fahren- | grees | grees | grees |Cubic Foot| +|Ins. Hg.| Pounds | heit | B. t. u. |B. t. u.|B. t. u.| Pounds | +|________|__________|_________|___________|________|________|__________| +| | | | | | | | +| 29.5 | .207 | 54.1 | 22.18 | 1061.0 | 1083.2 | 0.000678 | +| 29 | .452 | 76.6 | 44.64 | 1048.7 | 1093.3 | 0.001415 | +| 28.5 | .698 | 90.1 | 58.09 | 1041.1 | 1099.2 | 0.002137 | +| 28 | .944 | 99.9 | 67.87 | 1035.6 | 1103.5 | 0.002843 | +| 27 | 1.44 | 112.5 | 80.4 | 1028.6 | 1109.0 | 0.00421 | +| 26 | 1.93 | 124.5 | 92.3 | 1022.0 | 1114.3 | 0.00577 | +| 25 | 2.42 | 132.6 | 100.5 | 1017.3 | 1117.8 | 0.00689 | +| 24 | 2.91 | 140.1 | 108.0 | 1013.1 | 1121.1 | 0.00821 | +| 22 | 3.89 | 151.7 | 119.6 | 1006.4 | 1126.0 | 0.01078 | +| 20 | 4.87 | 161.1 | 128.9 | 1001.0 | 1129.9 | 0.01331 | +| 18 | 5.86 | 168.9 | 136.8 | 996.4 | 1133.2 | 0.01581 | +| 16 | 6.84 | 175.8 | 143.6 | 992.4 | 1136.0 | 0.01827 | +| 14 | 7.82 | 181.8 | 149.7 | 988.8 | 1138.5 | 0.02070 | +| 12 | 8.80 | 187.2 | 155.1 | 985.6 | 1140.7 | 0.02312 | +| 10 | 9.79 | 192.2 | 160.1 | 982.6 | 1142.7 | 0.02554 | +| 5 | 12.24 | 202.9 | 170.8 | 976.0 | 1146.8 | 0.03148 | +|________|__________|_________|___________|________|________|__________| + +From the steam tables, the condensed Table 21 of the properties of steam +at different pressures may be constructed. From such a table there may +be drawn the following conclusions. + + TABLE 21 + + VARIATION IN PROPERTIES OF + SATURATED STEAM WITH PRESSURE + ___________________________________________________ +| | | | | | +| Pressure |Temperature | Heat of | Latent | Total | +| Pounds | Degrees | Liquid | Heat | Heat | +| Absolute | Fahrenheit |B. t. u. |B. t. u.|B. t. u.| +|__________|____________|_________|________|________| +| | | | | | +| 14.7 | 212.0 | 180.0 | 970.4 | 1150.4 | +| 20.0 | 228.0 | 196.1 | 960.0 | 1156.2 | +| 100.0 | 327.8 | 298.3 | 888.0 | 1186.3 | +| 300.0 | 417.5 | 392.7 | 811.3 | 1204.1 | +|__________|____________|_________|________|________| + +As the pressure and temperature increase, the latent heat decreases. +This decrease, however, is less rapid than the corresponding increase in +the heat of the liquid and hence the total heat increases with an +increase in the pressure and temperature. The percentage increase in the +total heat is small, being 0.5, 3.1, and 4.7 per cent for 20, 100, and +300 pounds absolute pressure respectively above the total heat in one +pound of steam at 14.7 pounds absolute. The temperatures, on the other +hand, increase at the rates of 7.5, 54.6, and 96.9 per cent. The +efficiency of a perfect steam engine is proportional to the expression +(t - t_{1})/t in which t and t_{1} are the absolute temperatures of the +saturated steam at admission and exhaust respectively. While actual +engines only approximate the ideal engine in efficiency, yet they follow +the same general law. Since the exhaust temperature cannot be lowered +beyond present practice, it follows that the only available method of +increasing the efficiency is by an increase in the temperature of the +steam at admission. How this may be accomplished by an increase of +pressure is clearly shown, for the increase of fuel necessary to +increase the pressure is negligible, as shown by the total heat, while +the increase in economy, due to the higher pressure, will result +directly from the rapid increase of the corresponding temperature. + + TABLE 22 + + HEAT UNITS PER POUND AND + WEIGHT PER CUBIC FOOT OF WATER + BETWEEN 32 DEGREES FAHRENHEIT AND + 340 DEGREES FAHRENHEIT + _________________________________ +| | | | +|Temperature|Heat Units| Weight | +| Degrees | per | per | +| Fahrenheit| Pound |Cubic Foot| +|___________|__________|__________| +| | | | +| 32 | 0.00 | 62.42 | +| 33 | 1.01 | 62.42 | +| 34 | 2.01 | 62.42 | +| 35 | 3.02 | 62.43 | +| 36 | 4.03 | 62.43 | +| 37 | 5.04 | 62.43 | +| 38 | 6.04 | 62.43 | +| 39 | 7.05 | 62.43 | +| 40 | 8.05 | 62.43 | +| 41 | 9.05 | 62.43 | +| 42 | 10.06 | 62.43 | +| 43 | 11.06 | 62.43 | +| 44 | 12.06 | 62.43 | +| 45 | 13.07 | 62.42 | +| 46 | 14.07 | 62.42 | +| 47 | 15.07 | 62.42 | +| 48 | 16.07 | 62.42 | +| 49 | 17.08 | 62.42 | +| 50 | 18.08 | 62.42 | +| 51 | 19.08 | 62.41 | +| 52 | 20.08 | 62.41 | +| 53 | 21.08 | 62.41 | +| 54 | 22.08 | 62.40 | +| 55 | 23.08 | 62.40 | +| 56 | 24.08 | 62.39 | +| 57 | 25.08 | 62.39 | +| 58 | 26.08 | 62.38 | +| 59 | 27.08 | 62.37 | +| 60 | 28.08 | 62.37 | +| 61 | 29.08 | 62.36 | +| 62 | 30.08 | 62.36 | +| 63 | 31.07 | 62.35 | +| 64 | 32.07 | 62.35 | +| 65 | 33.07 | 62.34 | +| 66 | 34.07 | 62.33 | +| 67 | 35.07 | 62.33 | +| 68 | 36.07 | 62.32 | +| 69 | 37.06 | 62.31 | +| 70 | 38.06 | 62.30 | +| 71 | 39.06 | 62.30 | +| 72 | 40.05 | 62.29 | +| 73 | 41.05 | 62.28 | +| 74 | 42.05 | 62.27 | +| 75 | 42.05 | 62.26 | +| 76 | 44.04 | 62.26 | +| 77 | 45.04 | 62.25 | +| 78 | 46.04 | 62.24 | +| 79 | 47.04 | 62.23 | +| 80 | 48.03 | 62.22 | +| 81 | 49.03 | 62.21 | +| 82 | 50.03 | 62.20 | +| 83 | 51.02 | 62.19 | +| 84 | 52.02 | 62.18 | +| 85 | 53.02 | 62.17 | +| 86 | 54.01 | 62.16 | +| 87 | 55.01 | 62.15 | +| 88 | 56.01 | 62.14 | +| 89 | 57.00 | 62.13 | +| 90 | 58.00 | 62.12 | +| 91 | 59.00 | 62.11 | +| 92 | 60.00 | 62.09 | +| 93 | 60.99 | 62.08 | +| 94 | 61.99 | 62.07 | +| 95 | 62.99 | 62.06 | +| 96 | 63.98 | 62.05 | +| 97 | 64.98 | 62.04 | +| 98 | 65.98 | 62.03 | +| 99 | 66.97 | 62.02 | +| 100 | 67.97 | 62.00 | +| 101 | 68.97 | 61.99 | +| 102 | 69.96 | 61.98 | +| 103 | 70.96 | 61.97 | +| 104 | 71.96 | 61.95 | +| 105 | 72.95 | 61.94 | +| 106 | 73.95 | 61.93 | +| 107 | 74.95 | 61.91 | +| 108 | 75.95 | 61.90 | +| 109 | 76.94 | 61.88 | +| 110 | 77.94 | 61.86 | +| 111 | 78.94 | 61.85 | +| 112 | 79.93 | 61.83 | +| 113 | 80.93 | 61.82 | +| 114 | 81.93 | 61.80 | +| 115 | 82.92 | 61.79 | +| 116 | 83.92 | 61.77 | +| 117 | 84.92 | 61.75 | +| 118 | 85.92 | 61.74 | +| 119 | 86.91 | 61.72 | +| 120 | 87.91 | 61.71 | +| 121 | 88.91 | 61.69 | +| 122 | 89.91 | 61.68 | +| 123 | 90.90 | 61.66 | +| 124 | 91.90 | 61.65 | +| 125 | 92.90 | 61.63 | +| 126 | 93.90 | 61.61 | +| 127 | 94.89 | 61.59 | +| 128 | 95.89 | 61.58 | +| 129 | 96.89 | 61.56 | +| 130 | 97.89 | 61.55 | +| 131 | 98.89 | 61.53 | +| 132 | 99.88 | 61.52 | +| 133 | 100.88 | 61.50 | +| 134 | 101.88 | 61.49 | +| 135 | 102.88 | 61.47 | +| 136 | 103.88 | 61.45 | +| 137 | 104.87 | 61.43 | +| 138 | 105.87 | 61.41 | +| 139 | 106.87 | 61.40 | +| 140 | 107.87 | 61.38 | +| 141 | 108.87 | 61.36 | +| 142 | 109.87 | 61.34 | +| 143 | 110.87 | 61.33 | +| 144 | 111.87 | 61.31 | +| 145 | 112.86 | 61.29 | +| 146 | 113.86 | 61.27 | +| 147 | 114.86 | 61.25 | +| 148 | 115.86 | 61.24 | +| 149 | 116.86 | 61.22 | +| 150 | 117.86 | 61.20 | +| 151 | 118.86 | 61.18 | +| 152 | 119.86 | 61.16 | +| 153 | 120.86 | 61.14 | +| 154 | 121.86 | 61.12 | +| 155 | 122.86 | 61.10 | +| 156 | 123.86 | 61.08 | +| 157 | 124.86 | 61.06 | +| 158 | 125.86 | 61.04 | +| 159 | 126.86 | 61.02 | +| 160 | 127.86 | 61.00 | +| 161 | 128.86 | 60.98 | +| 162 | 129.86 | 60.96 | +| 163 | 130.86 | 60.94 | +| 164 | 131.86 | 60.92 | +| 165 | 132.86 | 60.90 | +| 166 | 133.86 | 60.88 | +| 167 | 134.86 | 60.86 | +| 168 | 135.86 | 60.84 | +| 169 | 136.86 | 60.82 | +| 170 | 137.87 | 60.80 | +| 171 | 138.87 | 60.78 | +| 172 | 139.87 | 60.76 | +| 173 | 140.87 | 60.73 | +| 174 | 141.87 | 60.71 | +| 175 | 142.87 | 60.69 | +| 176 | 143.87 | 60.67 | +| 177 | 144.88 | 60.65 | +| 178 | 145.88 | 60.62 | +| 179 | 146.88 | 60.60 | +| 180 | 147.88 | 60.58 | +| 181 | 148.88 | 60.56 | +| 182 | 149.89 | 60.53 | +| 183 | 150.89 | 60.51 | +| 184 | 151.89 | 60.49 | +| 185 | 152.89 | 60.47 | +| 186 | 153.89 | 60.45 | +| 187 | 154.90 | 60.42 | +| 188 | 155.90 | 60.40 | +| 189 | 156.90 | 60.38 | +| 190 | 157,91 | 60.36 | +| 191 | 158.91 | 60.33 | +| 192 | 159.91 | 60.31 | +| 193 | 160.91 | 60.29 | +| 194 | 161.92 | 60.27 | +| 195 | 162.92 | 60.24 | +| 196 | 163.92 | 60.22 | +| 197 | 164.93 | 60.19 | +| 198 | 165.93 | 60.17 | +| 199 | 166.94 | 60.15 | +| 200 | 167.94 | 60.12 | +| 201 | 168.94 | 60.10 | +| 202 | 169.95 | 60.07 | +| 203 | 170.95 | 60.05 | +| 204 | 171.96 | 60.02 | +| 205 | 172.96 | 60.00 | +| 206 | 173.97 | 59.98 | +| 207 | 174.97 | 59.95 | +| 208 | 175.98 | 59.93 | +| 209 | 176.98 | 59.90 | +| 210 | 177.99 | 59.88 | +| 211 | 178.99 | 59.85 | +| 212 | 180.00 | 59.83 | +| 213 | 181.0 | 59.80 | +| 214 | 182.0 | 59.78 | +| 215 | 183.0 | 59.75 | +| 216 | 184.0 | 59.73 | +| 217 | 185.0 | 59.70 | +| 218 | 186.1 | 59.68 | +| 219 | 187.1 | 59.65 | +| 220 | 188.1 | 59.63 | +| 221 | 189.1 | 59.60 | +| 222 | 190.1 | 59.58 | +| 223 | 191.1 | 59.55 | +| 224 | 192.1 | 59.53 | +| 225 | 193.1 | 59.50 | +| 226 | 194.1 | 59.48 | +| 227 | 195.2 | 59.45 | +| 228 | 196.2 | 59.42 | +| 229 | 197.2 | 59.40 | +| 230 | 198.2 | 59.37 | +| 231 | 199.2 | 59.34 | +| 232 | 200.2 | 59.32 | +| 233 | 201.2 | 59.29 | +| 234 | 202.2 | 59.27 | +| 235 | 203.2 | 59.24 | +| 236 | 204.2 | 59.21 | +| 237 | 205.3 | 59.19 | +| 238 | 206.3 | 59.16 | +| 239 | 207.3 | 59.14 | +| 240 | 208.3 | 59.11 | +| 241 | 209.3 | 59.08 | +| 242 | 210.3 | 59.05 | +| 243 | 211.4 | 59.03 | +| 244 | 212.4 | 59.00 | +| 245 | 213.4 | 58.97 | +| 246 | 214.4 | 58.94 | +| 247 | 215.4 | 58.91 | +| 248 | 216.4 | 58.89 | +| 249 | 217.4 | 58.86 | +| 250 | 218.5 | 58.83 | +| 260 | 228.6 | 58.55 | +| 270 | 238.8 | 58.26 | +| 280 | 249.0 | 57.96 | +| 290 | 259.3 | 57.65 | +| 300 | 269.6 | 57.33 | +| 310 | 279.9 | 57.00 | +| 320 | 290.2 | 56.66 | +| 330 | 300.6 | 56.30 | +| 340 | 311.0 | 55.94 | +|___________|__________|__________| + +The gain due to superheat cannot be predicted from the formula for the +efficiency of a perfect steam engine given on page 119. This formula is +not applicable in cases where superheat is present since only a +relatively small amount of the heat in the steam is imparted at the +maximum or superheated temperature. + +The advantage of the use of high pressure steam may be also indicated by +considering the question from the aspect of volume. With an increase of +pressure comes a decrease in volume, thus one pound of saturated steam +at 100 pounds absolute pressure occupies 4.43 cubic feet, while at 200 +pounds pressure it occupies 2.29 cubic feet. If then, in separate +cylinders of the same dimensions, one pound of steam at 100 pounds +absolute pressure and one pound at 200 pounds absolute pressure enter +and are allowed to expand to the full volume of each cylinder, the +high-pressure steam, having more room and a greater range for expansion +than the low-pressure steam, will thus do more work. This increase in +the amount of work, as was the increase in temperature, is large +relative to the additional fuel required as indicated by the total heat. +In general, it may be stated that the fuel required to impart a given +amount of heat to a boiler is practically independent of the steam +pressure, since the temperature of the fire is so high as compared with +the steam temperature that a variation in the steam temperature does not +produce an appreciable effect. + +The formulae for the algebraic expression of the relation between +saturated steam pressures, temperatures and steam volumes have been up +to the present time empirical. These relations have, however, been +determined by experiment and, from the experimental data, tables have +been computed which render unnecessary the use of empirical formulae. +Such formulae may be found in any standard work of thermo-dynamics. The +following tables cover all practical cases. + +Table 22 gives the heat units contained in water above 32 degrees +Fahrenheit at different temperatures. + +Table 23 gives the properties of saturated steam for various pressures. + +Table 24 gives the properties of superheated steam at various pressures +and temperatures. + +These tables are based on those computed by Lionel S. Marks and Harvey +N. Davis, these being generally accepted as being the most correct. + + TABLE 23 + + PROPERTIES OF SATURATED STEAM + + REPRODUCED BY PERMISSION FROM + MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" + (Copyright, 1909, by Longmans, Green & Co.) + ____________________________________________________________________ +|Pressure,| Temper- |Specific Vol-|Heat of |Latent Heat|Total Heat| +| Pounds |ature De-| ume Cu. Ft. |the Liquid,| of Evap., |of Steam, | +|Absolute |grees F. | per Pound | B. t. u. | B. t. u. | B. t. u. | +|_________|_________|_____________|___________|___________|__________| +| 1 | 101.83 | 333.0 | 69.8 | 1034.6 | 1104.4 | +| 2 | 126.15 | 173.5 | 94.0 | 1021.0 | 1115.0 | +| 3 | 141.52 | 118.5 | 109.4 | 1012.3 | 1121.6 | +| 4 | 153.01 | 90.5 | 120.9 | 1005.7 | 1126.5 | +| 5 | 162.28 | 73.33 | 130.1 | 1000.3 | 1130.5 | +| 6 | 170.06 | 61.89 | 137.9 | 995.8 | 1133.7 | +| 7 | 176.85 | 53.56 | 144.7 | 991.8 | 1136.5 | +| 8 | 182.86 | 47.27 | 150.8 | 988.2 | 1139.0 | +| 9 | 188.27 | 42.36 | 156.2 | 985.0 | 1141.1 | +| 10 | 193.22 | 38.38 | 161.1 | 982.0 | 1143.1 | +| 11 | 197.75 | 35.10 | 165.7 | 979.2 | 1144.9 | +| 12 | 201.96 | 32.36 | 169.9 | 976.6 | 1146.5 | +| 13 | 205.87 | 30.03 | 173.8 | 974.2 | 1148.0 | +| 14 | 209.55 | 28.02 | 177.5 | 971.9 | 1149.4 | +| 15 | 213.0 | 26.27 | 181.0 | 969.7 | 1150.7 | +| 16 | 216.3 | 24.79 | 184.4 | 967.6 | 1152.0 | +| 17 | 219.4 | 23.38 | 187.5 | 965.6 | 1153.1 | +| 18 | 222.4 | 22.16 | 190.5 | 963.7 | 1154.2 | +| 19 | 225.2 | 21.07 | 193.4 | 961.8 | 1155.2 | +| 20 | 228.0 | 20.08 | 196.1 | 960.0 | 1156.2 | +| 22 | 233.1 | 18.37 | 201.3 | 956.7 | 1158.0 | +| 24 | 237.8 | 16.93 | 206.1 | 953.5 | 1159.6 | +| 26 | 242.2 | 15.72 | 210.6 | 950.6 | 1161.2 | +| 28 | 246.4 | 14.67 | 214.8 | 947.8 | 1162.6 | +| 30 | 250.3 | 13.74 | 218.8 | 945.1 | 1163.9 | +| 32 | 254.1 | 12.93 | 222.6 | 942.5 | 1165.1 | +| 34 | 257.6 | 12.22 | 226.2 | 940.1 | 1166.3 | +| 36 | 261.0 | 11.58 | 229.6 | 937.7 | 1167.3 | +| 38 | 264.2 | 11.01 | 232.9 | 935.5 | 1168.4 | +| 40 | 267.3 | 10.49 | 236.1 | 933.3 | 1169.4 | +| 42 | 270.2 | 10.02 | 239.1 | 931.2 | 1170.3 | +| 44 | 273.1 | 9.59 | 242.0 | 929.2 | 1171.2 | +| 46 | 275.8 | 9.20 | 244.8 | 927.2 | 1172.0 | +| 48 | 278.5 | 8.84 | 247.5 | 925.3 | 1172.8 | +| 50 | 281.0 | 8.51 | 250.1 | 923.5 | 1173.6 | +| 52 | 283.5 | 8.20 | 252.6 | 921.7 | 1174.3 | +| 54 | 285.9 | 7.91 | 255.1 | 919.9 | 1175.0 | +| 56 | 288.2 | 7.65 | 257.5 | 918.2 | 1175.7 | +| 58 | 290.5 | 7.40 | 259.8 | 916.5 | 1176.4 | +| 60 | 292.7 | 7.17 | 262.1 | 914.9 | 1177.0 | +| 62 | 294.9 | 6.95 | 264.3 | 913.3 | 1177.6 | +| 64 | 297.0 | 6.75 | 266.4 | 911.8 | 1178.2 | +| 66 | 299.0 | 6.56 | 268.5 | 910.2 | 1178.8 | +| 68 | 301.0 | 6.38 | 270.6 | 908.7 | 1179.3 | +| 70 | 302.9 | 6.20 | 272.6 | 907.2 | 1179.8 | +| 72 | 304.8 | 6.04 | 274.5 | 905.8 | 1180.4 | +| 74 | 306.7 | 5.89 | 276.5 | 904.4 | 1180.9 | +| 76 | 308.5 | 5.74 | 278.3 | 903.0 | 1181.4 | +| 78 | 310.3 | 5.60 | 280.2 | 901.7 | 1181.8 | +| 80 | 312.0 | 5.47 | 282.0 | 900.3 | 1182.3 | +| 82 | 313.8 | 5.34 | 283.8 | 899.0 | 1182.8 | +| 84 | 315.4 | 5.22 | 285.5 | 897.7 | 1183.2 | +| 86 | 317.1 | 5.10 | 287.2 | 896.4 | 1183.6 | +| 88 | 318.7 | 5.00 | 288.9 | 895.2 | 1184.0 | +| 90 | 320.3 | 4.89 | 290.5 | 893.9 | 1184.4 | +| 92 | 321.8 | 4.79 | 292.1 | 892.7 | 1184.8 | +| 94 | 323.4 | 4.69 | 293.7 | 891.5 | 1185.2 | +| 96 | 324.9 | 4.60 | 295.3 | 890.3 | 1185.6 | +| 98 | 326.4 | 4.51 | 296.8 | 889.2 | 1186.0 | +| 100 | 327.8 | 4.429 | 298.3 | 888.0 | 1186.3 | +| 105 | 331.4 | 4.230 | 302.0 | 885.2 | 1187.2 | +| 110 | 334.8 | 4.047 | 305.5 | 882.5 | 1188.0 | +| 115 | 338.1 | 3.880 | 309.0 | 879.8 | 1188.8 | +| 120 | 341.3 | 3.726 | 312.3 | 877.2 | 1189.6 | +| 125 | 344.4 | 3.583 | 315.5 | 874.7 | 1190.3 | +| 130 | 347.4 | 3.452 | 318.6 | 872.3 | 1191.0 | +| 135 | 350.3 | 3.331 | 321.7 | 869.9 | 1191.6 | +| 140 | 353.1 | 3.219 | 324.6 | 867.6 | 1192.2 | +| 145 | 355.8 | 3.112 | 327.4 | 865.4 | 1192.8 | +| 150 | 358.5 | 3.012 | 330.2 | 863.2 | 1193.4 | +| 155 | 361.0 | 2.920 | 332.9 | 861.0 | 1194.0 | +| 160 | 363.6 | 2.834 | 335.6 | 858.8 | 1194.5 | +| 165 | 366.0 | 2.753 | 338.2 | 856.8 | 1195.0 | +| 170 | 368.5 | 2.675 | 340.7 | 854.7 | 1195.4 | +| 175 | 370.8 | 2.602 | 343.2 | 852.7 | 1195.9 | +| 180 | 373.1 | 2.533 | 345.6 | 850.8 | 1196.4 | +| 185 | 375.4 | 2.468 | 348.0 | 848.8 | 1196.8 | +| 190 | 377.6 | 2.406 | 350.4 | 846.9 | 1197.3 | +| 195 | 379.8 | 2.346 | 352.7 | 845.0 | 1197.7 | +| 200 | 381.9 | 2.290 | 354.9 | 843.2 | 1198.1 | +| 205 | 384.0 | 2.237 | 357.1 | 841.4 | 1198.5 | +| 210 | 386.0 | 2.187 | 359.2 | 839.6 | 1198.8 | +| 215 | 388.0 | 2.138 | 361.4 | 837.9 | 1199.2 | +| 220 | 389.9 | 2.091 | 363.4 | 836.2 | 1199.6 | +| 225 | 391.9 | 2.046 | 365.5 | 834.4 | 1199.9 | +| 230 | 393.8 | 2.004 | 367.5 | 832.8 | 1200.2 | +| 235 | 395.6 | 1.964 | 369.4 | 831.1 | 1200.6 | +| 240 | 397.4 | 1.924 | 371.4 | 829.5 | 1200.9 | +| 245 | 399.3 | 1.887 | 373.3 | 827.9 | 1201.2 | +| 250 | 401.1 | 1.850 | 375.2 | 826.3 | 1201.5 | +|_________|_________|_____________|___________|___________|__________| + +[Illustration: Portion of 6100 Horse-power Installation of Babcock & +Wilcox Boilers Equipped with Babcock & Wilcox Chain Grate Stokers at the +Campbell Street Plant of the Louisville Railway Co., Louisville, Ky. +This Company Operates a Total of 14,000 Horse Power of Babcock & Wilcox +Boilers] + + TABLE 24 + + PROPERTIES OF SUPERHEATED STEAM + + REPRODUCED BY PERMISSION FROM + MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" + (Copyright, 1909, by Longmans, Green & Co.) + __________________________________________________________________ +| | | | +| | | Degrees of Superheat | +|Pressure| |_______________________________________________| +| Pounds |Saturated| | | | | | | +|Absolute| Steam | 50 | 100 | 150 | 200 | 250 | 300 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 162.3 | 212.3 | 262.3 | 312.3 | 362.3 | 412.3 | 462.3 | +| 5 v| 73.3 | 79.7 | 85.7 | 91.8 | 97.8 | 103.8 | 109.8 | +| h| 1130.5 |1153.5 |1176.4 |1199.5 |1222.5 |1245.6 |1268.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 193.2 | 243.2 | 293.2 | 343.2 | 393.2 | 443.2 | 493.2 | +| 10 v| 38.4 | 41.5 | 44.6 | 47.7 | 50.7 | 53.7 | 56.7 | +| h| 1143.1 |1166.3 |1189.5 |1212.7 |1236.0 |1259.3 |1282.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 213.0 | 263.0 | 313.0 | 363.0 | 413.0 | 463.0 | 513.0 | +| 15 v| 26.27 | 28.40| 30.46| 32.50| 34.53| 36.56| 38.58| +| h| 1150.7 |1174.2 |1197.6 |1221.0 |1244.4 |1267.7 |1291.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 228.0 | 278.0 | 328.0 | 378.0 | 428.0 | 478.0 | 528.0 | +| 20 v| 20.08 | 21.69| 23.25| 24.80| 26.33| 27.85| 29.37| +| h| 1156.2 |1179.9 |1203.5 |1227.1 |1250.6 |1274.1 |1297.6 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 240.1 | 290.1 | 340.1 | 390.1 | 440.1 | 490.1 | 540.1 | +| 25 v| 16.30 | 17.60| 18.86| 20.10| 21.32| 22.55| 23.77| +| h| 1160.4 |1184.4 |1208.2 |1231.9 |1255.6 |1279.2 |1302.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 250.4 | 300.4 | 350.4 | 400.4 | 450.4 | 500.4 | 550.4 | +| 30 v| 13.74 | 14.83| 15.89| 16.93| 17.97| 18.99| 20.00| +| h| 1163.9 |1188.1 |1212.1 |1236.0 |1259.7 |1283.4 |1307.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 259.3 | 309.3 | 359.3 | 409.3 | 459.3 | 509.3 | 559.3 | +| 35 v| 11.89 | 12.85| 13.75| 14.65| 15.54| 16.42| 17.30| +| h| 1166.8 |1191.3 |1215.4 |1239.4 |1263.3 |1287.1 |1310.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 267.3 | 317.3 | 367.3 | 417.3 | 467.3 | 517.3 | 567.3 | +| 40 v| 10.49 | 11.33| 12.13| 12.93| 13.70| 14.48| 15.25| +| h| 1169.4 |1194.0 |1218.4 |1242.4 |1266.4 |1290.3 |1314.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 274.5 | 324.5 | 374.5 | 424.5 | 474.5 | 524.5 | 574.5 | +| 45 v| 9.39 | 10.14| 10.86| 11.57| 12.27| 12.96| 13.65| +| h| 1171.6 |1196.6 |1221.0 |1245.2 |1269.3 |1293.2 |1317.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 281.0 | 331.0 | 381.0 | 431.0 | 481.0 | 531.0 | 581.0 | +| 50 v| 8.51 | 9.19| 9.84| 10.48| 11.11| 11.74| 12.36| +| h| 1173.6 |1198.8 |1223.4 |1247.7 |1271.8 |1295.8 |1319.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 287.1 | 337.1 | 387.1 | 437.1 | 487.1 | 537.1 | 587.1 | +| 55 v| 7.78 | 8.40| 9.00| 9.59| 10.16| 10.73| 11.30| +| h| 1175.4 |1200.8 |1225.6 |1250.0 |1274.2 |1298.1 |1322.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 292.7 | 342.7 | 392.7 | 442.7 | 492.7 | 542.7 | 592.7 | +| 60 v| 7.17 | 7.75| 8.30| 8.84| 9.36| 9.89| 10.41| +| h| 1177.0 |1202.6 |1227.6 |1252.1 |1276.4 |1300.4 |1324.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 298.0 | 348.0 | 398.0 | 448.0 | 498.0 | 548.0 | 598.0 | +| 65 v| 6.65 | 7.20| 7.70| 8.20| 8.69| 9.17| 9.65| +| h| 1178.5 |1204.4 |1229.5 |1254.0 |1278.4 |1302.4 |1326.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 302.9 | 352.9 | 402.9 | 452.9 | 502.9 | 552.9 | 602.9 | +| 70 v| 6.20 | 6.71| 7.18| 7.65| 8.11| 8.56| 9.01| +| h| 1179.8 |1205.9 |1231.2 |1255.8 |1280.2 |1304.3 |1328.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 307.6 | 357.6 | 407.6 | 457.6 | 507.6 | 557.6 | 607.6 | +| 75 v| 5.81 | 6.28| 6.73| 7.17| 7.60| 8.02| 8.44| +| h| 1181.1 |1207.5 |1232.8 |1257.5 |1282.0 |1306.1 |1330.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 312.0 | 362.0 | 412.0 | 462.0 | 512.0 | 562.0 | 612.0 | +| 80 v| 5.47 | 5.92| 6.34| 6.75| 7.17| 7.56| 7.95| +| h| 1182.3 |1208.8 |1234.3 |1259.0 |1283.6 |1307.8 |1331.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 316.3 | 366.3 | 416.3 | 466.3 | 516.3 | 566.3 | 616.3 | +| 85 v| 5.16 | 5.59| 6.99| 6.38| 6.76| 7.14| 7.51| +| h| 1183.4 |1210.2 |1235.8 |1260.6 |1285.2 |1309.4 |1333.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 320.3 | 370.3 | 420.3 | 470.3 | 520.3 | 570.3 | 620.3 | +| 90 v| 4.89 | 5.29| 5.67| 6.04| 6.40| 6.76| 7.11| +| h| 1184.4 |1211.4 |1237.2 |1262.0 |1286.6 |1310.8 |1334.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 324.1 | 374.1 | 424.1 | 474.1 | 524.1 | 574.1 | 624.1 | +| 95 v| 4.65 | 5.03| 5.39| 5.74| 6.09| 6.43| 6.76| +| h| 1185.4 |1212.6 |1238.4 |1263.4 |1288.1 |1312.3 |1336.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 327.8 | 377.8 | 427.8 | 477.8 | 527.8 | 577.8 | 627.8 | +| 100 v| 4.43 | 4.79| 5.14| 5.47| 5.80| 6.12| 6.44| +| h| 1186.3 |1213.8 |1239.7 |1264.7 |1289.4 |1313.6 |1337.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 331.4 | 381.4 | 431.4 | 481.4 | 531.4 | 581.4 | 631.4 | +| 105 v| 4.23 | 4.58| 4.91| 5.23| 5.54| 5.85| 6.15| +| h| 1187.2 |1214.9 |1240.8 |1265.9 |1290.6 |1314.9 |1339.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 334.8 | 384.8 | 434.8 | 484.8 | 534.8 | 584.8 | 634.8 | +| 110 v| 4.05 | 4.38| 4.70| 5.01| 5.31| 5.61| 5.90| +| h| 1188.0 |1215.9 |1242.0 |1267.1 |1291.9 |1316.2 |1340.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 338.1 | 388.1 | 438.1 | 488.1 | 538.1 | 588.1 | 638.1 | +| 115 v| 3.88 | 4.20| 4.51| 4.81| 5.09| 5.38| 5.66| +| h| 1188.8 |1216.9 |1243.1 |1268.2 |1293.0 |1317.3 |1341.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 341.3 | 391.3 | 441.3 | 491.3 | 541.3 | 591.3 | 641.3 | +| 120 v| 3.73 | 4.04| 4.33| 4.62| 4.89| 5.17| 5.44| +| h| 1189.6 |1217.9 |1244.1 |1269.3 |1294.1 |1318.4 |1342.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 344.4 | 394.4 | 444.4 | 494.4 | 544.4 | 594.4 | 644.4 | +| 125 v| 3.58 | 3.88| 4.17| 4.45| 4.71| 4.97| 5.23| +| h| 1190.3 |1218.8 |1245.1 |1270.4 |1295.2 |1319.5 |1343.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 347.4 | 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | +| 130 v| 3.45 | 3.74| 4.02| 4.28| 4.54| 4.80| 5.05| +| h| 1191.0 |1219.7 |1246.1 |1271.4 |1296.2 |1320.6 |1344.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 350.3 | 400.3 | 450.3 | 500.3 | 550.3 | 600.3 | 650.3 | +| 135 v| 3.33 | 3.61| 3.88| 4.14| 4.38| 4.63| 4.87| +| h| 1191.6 |1220.6 |1247.0 |1272.3 |1297.2 |1321.6 |1345.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 353.1 | 403.1 | 453.1 | 503.1 | 553.1 | 603.1 | 653.1 | +| 140 v| 3.22 | 3.49| 3.75| 4.00| 4.24| 4.48| 4.71| +| h| 1192.2 |1221.4 |1248.0 |1273.3 |1298.2 |1322.6 |1346.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 355.8 | 405.8 | 455.8 | 505.8 | 555.8 | 605.8 | 655.8 | +| 145 v| 3.12 | 3.38| 3.63| 3.87| 4.10| 4.33| 4.56| +| h| 1192.8 |1222.2 |1248.8 |1274.2 |1299.1 |1323.6 |1347.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 358.5 | 408.5 | 458.5 | 508.5 | 558.5 | 608.5 | 658.5 | +| 150 v| 3.01 | 3.27| 3.50| 3.75| 3.97| 4.19| 4.41| +| h| 1193.4 |1223.0 |1249.6 |1275.1 |1300.0 |1324.5 |1348.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 361.0 | 411.0 | 461.0 | 511.0 | 561.0 | 611.0 | 661.0 | +| 155 v| 2.92 | 3.17| 3.41| 3.63| 3.85| 4.06| 4.28| +| h| 1194.0 |1223.6 |1250.5 |1276.0 |1300.8 |1325.3 |1349.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 363.6 | 413.6 | 463.6 | 513.6 | 563.6 | 613.6 | 663.6 | +| 160 v| 2.83 | 3.07| 3.30| 3.53| 3.74| 3.95| 4.15| +| h| 1194.5 |1224.5 |1251.3 |1276.8 |1301.7 |1326.2 |1350.6 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 366.0 | 416.0 | 466.0 | 516.0 | 566.0 | 616.0 | 666.0 | +| 165 v| 2.75 | 2.99| 3.21| 3.43| 3.64| 3.84| 4.04| +| h| 1195.0 |1225.2 |1252.0 |1277.6 |1302.5 |1327.1 |1351.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 368.5 | 418.5 | 468.5 | 518.5 | 568.5 | 618.5 | 668.5 | +| 170 v| 2.68 | 2.91| 3.12| 3.34| 3.54| 3.73| 3.92| +| h| 1195.4 |1225.9 |1252.8 |1278.4 |1303.3 |1327.9 |1352.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 370.8 | 420.8 | 470.8 | 520.8 | 570.8 | 620.8 | 670.8 | +| 175 v| 2.60 | 2.83| 3.04| 3.24| 3.44| 3.63| 3.82| +| h| 1195.9 |1226.6 |1253.6 |1279.1 |1304.1 |1328.7 |1353.2 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 373.1 | 423.1 | 473.1 | 523.1 | 573.1 | 623.1 | 673.1 | +| 180 v| 2.53 | 2.75| 2.96| 3.16| 3.35| 3.54| 3.72| +| h| 1196.4 |1227.2 |1254.3 |1279.9 |1304.8 |1329.5 |1353.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 375.4 | 425.4 | 475.4 | 525.4 | 575.4 | 625.4 | 675.4 | +| 185 v| 2.47 | 2.68| 2.89| 3.08| 3.27| 3.45| 3.63| +| h| 1196.8 |1227.9 |1255.0 |1280.6 |1305.6 |1330.2 |1354.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 377.6 | 427.6 | 477.6 | 527.6 | 577.6 | 627.6 | 677.6 | +| 190 v| 2.41 | 2.62| 2.81| 3.00| 3.19| 3.37| 3.55| +| h| 1197.3 |1228.6 |1255.7 |1281.3 |1306.3 |1330.9 |1355.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 379.8 | 429.8 | 479.8 | 529.8 | 579.8 | 629.8 | 679.8 | +| 195 v| 2.35 | 2.55| 2.75| 2.93| 3.11| 3.29| 3.46| +| h| 1197.7 |1229.2 |1256.4 |1282.0 |1307.0 |1331.6 |1356.2 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 381.9 | 431.9 | 481.9 | 531.9 | 581.9 | 631.9 | 681.9 | +| 200 v| 2.29 | 2.49| 2.68| 2.86| 3.04| 3.21| 3.38| +| h| 1198.1 |1229.8 |1257.1 |1282.6 |1307.7 |1332.4 |1357.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 384.0 | 434.0 | 484.0 | 534.0 | 584.0 | 634.0 | 684.0 | +| 205 v| 2.24 | 2.44| 2.62| 2.80| 2.97| 3.14| 3.30| +| h| 1198.5 |1230.4 |1257.7 |1283.3 |1308.3 |1333.0 |1357.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 386.0 | 436.0 | 486.0 | 536.0 | 586.0 | 636.0 | 686.0 | +| 210 v| 2.19 | 2.38| 2.56| 2.74| 2.91| 3.07| 3.23| +| h| 1198.8 |1231.0 |1258.4 |1284.0 |1309.0 |1333.7 |1358.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 388.0 | 438.0 | 488.0 | 538.0 | 588.0 | 638.0 | 688.0 | +| 215 v| 2.14 | 2.33| 2.51| 2.68| 2.84| 3.00| 3.16| +| h| 1199.2 |1231.6 |1259.0 |1284.6 |1309.7 |1334.4 |1359.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 389.9 | 439.9 | 489.9 | 539.9 | 589.9 | 639.9 | 689.9 | +| 220 v| 2.09 | 2.28| 2.45| 2.62| 2.78| 2.94| 3.10| +| h| 1199.6 |1232.2 |1259.6 |1285.2 |1310.3 |1335.1 |1359.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 391.9 | 441.9 | 491.9 | 541.9 | 591.9 | 641.9 | 691.9 | +| 225 v| 2.05 | 2.23| 2.40| 2.57| 2.72| 2.88| 3.03| +| h| 1199.9 |1232.7 |1260.2 |1285.9 |1310.9 |1335.7 |1360.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 393.8 | 443.8 | 493.8 | 543.8 | 593.8 | 643.8 | 693.8 | +| 230 v| 2.00 | 2.18| 2.35| 2.51| 2.67| 2.82| 2.97| +| h| 1200.2 |1233.2 |1260.7 |1286.5 |1311.6 |1336.3 |1361.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 395.6 | 445.6 | 495.6 | 545.6 | 595.6 | 645.6 | 695.6 | +| 235 v| 1.96 | 2.14| 2.30| 2.46| 2.62| 2.77| 2.91| +| h| 1200.6 |1233.8 |1261.4 |1287.1 |1312.2 |1337.0 |1361.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | 697.4 | +| 240 v| 1.92 | 2.09| 2.26| 2.42| 2.57| 2.71| 2.85| +| h| 1200.9 |1234.3 |1261.9 |1287.6 |1312.8 |1337.6 |1362.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 399.3 | 449.3 | 499.3 | 549.3 | 599.3 | 649.3 | 699.3 | +| 245 v| 1.89 | 2.05| 2.22| 2.37| 2.52| 2.66| 2.80| +| h| 1201.2 |1234.8 |1262.5 |1288.2 |1313.3 |1338.2 |1362.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 401.0 | 451.0 | 501.0 | 551.0 | 601.0 | 651.0 | 701.0 | +| 250 v| 1.85 | 2.02| 2.17| 2.33| 2.47| 2.61| 2.75| +| h| 1201.5 |1235.4 |1263.0 |1288.8 |1313.9 |1338.8 |1363.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 402.8 | 452.8 | 502.8 | 552.8 | 602.8 | 652.8 | 702.8 | +| 255 v| 1.81 | 1.98| 2.14| 2.28| 2.43| 2.56| 2.70| +| h| 1201.8 |1235.9 |1263.6 |1289.3 |1314.5 |1339.3 |1364.1 | +|________|_________|_______|_______|_______|_______|_______|_______| + + +t = Temperature, degrees Fahrenheit. +v = Specific volume, in cubic feet, per pound. +h = Total heat from water at 32 degrees, B. t. u. + +[Graph: Temperature of Steam--Degrees Fahr. +against Temperature in Calorimeter--Degrees Fahr. + +Fig. 15. Graphic Method of Determining Moisture Contained in Steam from +Calorimeter Readings] + + + + +MOISTURE IN STEAM + + +The presence of moisture in steam causes a loss, not only in the +practical waste of the heat utilized to raise this moisture from the +temperature of the feed water to the temperature of the steam, but also +through the increased initial condensation in an engine cylinder and +through friction and other actions in a steam turbine. The presence of +such moisture also interferes with proper cylinder lubrication, causes a +knocking in the engine and a water hammer in the steam pipes. In steam +turbines it will cause erosion of the blades. + +The percentage by weight of steam in a mixture of steam and water is +called the _quality of the steam_. + +The apparatus used to determine the moisture content of steam is called +a calorimeter though since it may not measure the heat in the steam, the +name is not descriptive of the function of the apparatus. The first form +used was the "barrel calorimeter", but the liability of error was so +great that its use was abandoned. Modern calorimeters are in general of +either the throttling or separator type. + +Throttling Calorimeter--Fig. 14 shows a typical form of throttling +calorimeter. Steam is drawn from a vertical main through the sampling +nipple, passes around the first thermometer cup, then through a +one-eighth inch orifice in a disk between two flanges, and lastly around +the second thermometer cup and to the atmosphere. Thermometers are +inserted in the wells, which should be filled with mercury or heavy +cylinder oil. + +[Illustration: Fig. 14. Throttling Calorimeter and Sampling Nozzle] + +The instrument and all pipes and fittings leading to it should be +thoroughly insulated to diminish radiation losses. Care must be taken to +prevent the orifice from becoming choked with dirt and to see that no +leaks occur. The exhaust pipe should be short to prevent back pressure +below the disk. + +When steam passes through an orifice from a higher to a lower pressure, +as is the case with the throttling calorimeter, no external work has to +be done in overcoming a resistance. Hence, if there is no loss from +radiation, the quantity of heat in the steam will be exactly the same +after passing the orifice as before passing. If the higher steam +pressure is 160 pounds gauge and the lower pressure that of the +atmosphere, the total heat in a pound of dry steam at the former +pressure is 1195.9 B. t. u. and at the latter pressure 1150.4 B. t. u., +a difference of 45.4 B. t. u. As this heat will still exist in the steam +at the lower pressure, since there is no external work done, its effect +must be to superheat the steam. Assuming the specific heat of +superheated steam to be 0.47, each pound passing through will be +superheated 45.4/0.47 = 96.6 degrees. If, however, the steam had +contained one per cent of moisture, it would have contained less heat +units per pound than if it were dry. Since the latent heat of steam at +160 pounds gauge pressure is 852.8 B. t. u., it follows that the one per +cent of moisture would have required 8.5 B. t. u. to evaporate it, +leaving only 45.4 - 8.5 = 36.9 B. t. u. available for superheating; +hence, the superheat would be 36.9/0.47 = 78.5 degrees, as against 96.6 +degrees for dry steam. In a similar manner, the degree of superheat for +other percentages of moisture may be determined. The action of the +throttling calorimeter is based upon the foregoing facts, as shown +below. + +Let H = total heat of one pound of steam at boiler pressure, + L = latent heat of steam at boiler pressure, + h = total heat of steam at reduced pressure after passing + orifice, + t_{1} = temperature of saturated steam at the reduced pressure, + t_{2} = temperature of steam after expanding through the orifice + in the disc, + 0.47 = the specific heat of saturated steam at atmospheric pressure, + x = proportion by weight of moisture in steam. + +The difference in B. t. u. in a pound of steam at the boiler pressure +and after passing the orifice is the heat available for evaporating the +moisture content and superheating the steam. Therefore, + +H - h = xL + 0.47(t_{2} - t_{1}) + + H - h - 0.47(t_{2} - t_{1}) +or x = --------------------------- (4) + L + +Almost invariably the lower pressure is taken as that of the atmosphere. +Under such conditions, h = 1150.4 and t_{1} = 212 degrees. The formula +thus becomes: + + H - 1150.4 - 0.47(t_{2} - 212) +x = ------------------------------ (5) + L + +For practical work it is more convenient to dispense with the upper +thermometer in the calorimeter and to measure the pressure in the steam +main by an accurate steam pressure gauge. + +A chart may be used for determining the value of x for approximate work +without the necessity for computation. Such a chart is shown in Fig. 15 +and its use is as follows: Assume a gauge pressure of 180 pounds and a +thermometer reading of 295 degrees. The intersection of the vertical +line from the scale of temperatures as shown by the calorimeter +thermometer and the horizontal line from the scale of gauge pressures +will indicate directly the per cent of moisture in the steam as read +from the diagonal scale. In the present instance, this per cent is 1.0. + +Sources of Error in the Apparatus--A slight error may arise from the +value, 0.47, used as the specific heat of superheated steam at +atmospheric pressure. This value, however is very nearly correct and any +error resulting from its use will be negligible. + +There is ordinarily a larger source of error due to the fact that the +stem of the thermometer is not heated to its full length, to an initial +error in the thermometer and to radiation losses. + +With an ordinary thermometer immersed in the well to the 100 degrees +mark, the error when registering 300 degrees would be about 3 degrees +and the true temperature be 303 degrees.[19] + +The steam is evidently losing heat through radiation from the moment it +enters the sampling nipple. The heat available for evaporating moisture +and superheating steam after it has passed through the orifice into the +lower pressure will be diminished by just the amount lost through +radiation and the value of t_{2}, as shown by the calorimeter +thermometer, will, therefore, be lower than if there were no such loss. +The method of correcting for the thermometer and radiation error +recommended by the Power Test Committee of the American Society of +Mechanical Engineers is by referring the readings as found on the boiler +trial to a "normal" reading of the thermometer. This normal reading is +the reading of the lower calorimeter thermometer for dry saturated +steam, and should be determined by attaching the instrument to a +horizontal steam pipe in such a way that the sampling nozzle projects +upward to near the top of the pipe, there being no perforations in the +nozzle and the steam taken only through its open upper end. The test +should be made with the steam in a quiescent state and with the steam +pressure maintained as nearly as possible at the pressure observed in +the main trial, the calorimeter thermometer to be the same as was used +on the trial or one exactly similar. + +With a normal reading thus obtained for a pressure approximately the +same as existed in the trial, the true percentage of moisture in the +steam, that is, with the proper correction made for radiation, may be +calculated as follows: + +Let T denote the normal reading for the conditions existing in the +trial. The effect of radiation from the instrument as pointed out will +be to lower the temperature of the steam at the lower pressure. Let +x_{1} represent the proportion of water in the steam which will lower +its temperature an amount equal to the loss by radiation. Then, + + H - h - 0.47(T - t_{1}) +x_{1} = ----------------------- + L + +This amount of moisture, x_{1} was not in the steam originally but is +the result of condensation in the instrument through radiation. Hence, +the true amount of moisture in the steam represented by X is the +difference between the amount as determined in the trial and that +resulting from condensation, or, + +X = x - x_{1} + + H - h - 0.47(t_{2} - t_{1}) H - h - 0.47(T - t_{1}) + = --------------------------- - ----------------------- + L L + + 0.47(T - t_{2}) + = --------------- (6) + L + +As T and t_{2} are taken with the same thermometer under the same set of +conditions, any error in the reading of the thermometers will be +approximately the same for the temperatures T and t_{2} and the above +method therefore corrects for both the radiation and thermometer errors. +The theoretical readings for dry steam, where there are no losses due to +radiation, are obtainable from formula (5) by letting x = 0 and solving +for t_{2}. The difference between the theoretical reading and the normal +reading for no moisture will be the thermometer and radiation correction +to be applied in order that the correct reading of t_{2} may be +obtained. + +For any calorimeter within the range of its ordinary use, such a +thermometer and radiation correction taken from one normal reading is +approximately correct for any conditions with the same or a duplicate +thermometer. + +The percentage of moisture in the steam, corrected for thermometer error +and radiation and the correction to be applied to the particular +calorimeter used, would be determined as follows: Assume a gauge +pressure in the trial to be 180 pounds and the thermometer reading to be +295 degrees. A normal reading, taken in the manner described, gives a +value of T = 303 degrees; then, the percentage of moisture corrected for +thermometer error and radiation is, + + 0.47(303 - 295) +x = ---------------- + 845.0 + + = 0.45 per cent. + +The theoretical reading for dry steam will be, + + 1197.7 - 1150.4 - 0.47(t_{2} - 212) + 0 = ------------------------------------ + 845.0 + +t_{2} = 313 degrees. + +The thermometer and radiation correction to be applied to the instrument +used, therefore over the ordinary range of pressure is + + Correction = 313 - 303 = 10 degrees + +The chart may be used in the determination of the correct reading of +moisture percentage and the permanent radiation correction for the +instrument used without computation as follows: Assume the same trial +pressure, feed temperature and normal reading as above. If the normal +reading is found to be 303 degrees, the correction for thermometer and +radiation will be the theoretical reading for dry steam as found from +the chart, less this normal reading, or 10 degrees correction. The +correct temperature for the trial in question is, therefore, 305 +degrees. The moisture corresponding to this temperature and 180 pounds +gauge pressure will be found from the chart to be 0.45 per cent. + +[Illustration: Fig. 16. Compact Throttling Calorimeter] + +There are many forms of throttling calorimeter, all of which work upon +the same principle. The simplest one is probably that shown in Fig. 14. +An extremely convenient and compact design is shown in Fig. 16. This +calorimeter consists of two concentric metal cylinders screwed to a cap +containing a thermometer well. The steam pressure is measured by a gauge +placed in the supply pipe or other convenient location. Steam passes +through the orifice A and expands to atmospheric pressure, its +temperature at this pressure being measured by a thermometer placed in +the cup C. To prevent as far as possible radiation losses, the annular +space between the two cylinders is used as a jacket, steam being +supplied to this space through the hole B. + +The limits of moisture within which the throttling calorimeter will work +are, at sea level, from 2.88 per cent at 50 pounds gauge pressure and +7.17 per cent moisture at 250 pounds pressure. + +Separating Calorimeter--The separating calorimeter mechanically +separates the entrained water from the steam and collects it in a +reservoir, where its amount is either indicated by a gauge glass or is +drained off and weighed. Fig. 17 shows a calorimeter of this type. The +steam passes out of the calorimeter through an orifice of known size so +that its total amount can be calculated or it can be weighed. A gauge is +ordinarily provided with this type of calorimeter, which shows the +pressure in its inner chamber and the flow of steam for a given period, +this latter scale being graduated by trial. + +The instrument, like a throttling calorimeter, should be well insulated +to prevent losses from radiation. + +While theoretically the separating calorimeter is not limited in +capacity, it is well in cases where the percentage of moisture present +in the steam is known to be high, to attach a throttling calorimeter to +its exhaust. This, in effect, is the using of the separating calorimeter +as a small separator between the sampling nozzle and the throttling +instrument, and is necessary to insure the determination of the full +percentage of moisture in the steam. The sum of the percentages shown by +the two instruments is the moisture content of the steam. + +The steam passing through a separating calorimeter may be calculated by +Napier's formula, the size of the orifice being known. There are +objections to such a calculation, however, in that it is difficult to +accurately determine the areas of such small orifices. Further, small +orifices have a tendency to become partly closed by sediment that may be +carried by the steam. The more accurate method of determining the amount +of steam passing through the instrument is as follows: + +[Illustration: Fig. 17. Separating Calorimeter] + +A hose should be attached to the separator outlet leading to a vessel of +water on a platform scale graduated to 1/100 of a pound. The steam +outlet should be connected to another vessel of water resting on a +second scale. In each case, the weight of each vessel and its contents +should be noted. When ready for an observation, the instrument should be +blown out thoroughly so that there will be no water within the +separator. The separator drip should then be closed and the steam hose +inserted into the vessel of water at the same instant. When the +separator has accumulated a sufficient quantity of water, the valve of +the instrument should be closed and the hose removed from the vessel of +water. The separator should be emptied into the vessel on its scale. The +final weight of each vessel and its contents are to be noted and the +differences between the final and original weights will represent the +weight of moisture collected by the separator and the weight of steam +from which the moisture has been taken. The proportion of moisture can +then be calculated from the following formula: + + 100 w +x = ----- (7) + W - w + +Where x = per cent moisture in steam, + W = weight of steam condensed, + w = weight of moisture as taken out by the separating + calorimeter. + +Sampling Nipple--The principle source of error in steam calorimeter +determinations is the failure to obtain an average sample of the steam +delivered by the boiler and it is extremely doubtful whether such a +sample is ever obtained. The two governing features in the obtaining of +such a sample are the type of sampling nozzle used and its location. + +The American Society of Mechanical Engineers recommends a sampling +nozzle made of one-half inch iron pipe closed at the inner end and the +interior portion perforated with not less than twenty one-eighth inch +holes equally distributed from end to end and preferably drilled in +irregular or spiral rows, with the first hole not less than one-half +inch from the wall of the pipe. Many engineers object to the use of a +perforated sampling nipple because it ordinarily indicates a higher +percentage of moisture than is actually present in the steam. This is +due to the fact that if the perforations come close to the inner surface +of the pipe, the moisture, which in many instances clings to this +surface, will flow into the calorimeter and cause a large error. Where a +perforated nipple is used, in general it may be said that the +perforations should be at least one inch from the inner pipe surface. + +A sampling nipple, open at the inner end and unperforated, undoubtedly +gives as accurate a measure as can be obtained of the moisture in the +steam passing that end. It would appear that a satisfactory method of +obtaining an average sample of the steam would result from the use of an +open end unperforated nipple passing through a stuffing box which would +allow the end to be placed at any point across the diameter of the steam +pipe. + +Incidental to a test of a 15,000 K. W. steam engine turbine unit, Mr. +H. G. Stott and Mr. R. G. S. Pigott, finding no experimental data +bearing on the subject of low pressure steam quality determinations, +made a investigation of the subject and the sampling nozzle illustrated +in Fig. 18 was developed. In speaking of sampling nozzles in the +determination of the moisture content of low pressure steam, Mr. Pigott +says, "the ordinary standard perforated pipe sampler is absolutely +worthless in giving a true sample and it is vital that the sample be +abstracted from the main without changing its direction or velocity +until it is safely within the sample pipe and entirely isolated from the +rest of the steam." + +[Illustration: Fig. 18. Stott and Pigott Sampling Nozzle] + +It would appear that the nozzle illustrated is undoubtedly the best that +has been developed for use in the determination of the moisture content +of steam, not only in the case of low, but also in high pressure steam. + +Location of Sampling Nozzle--The calorimeter should be located as near +as possible to the point from which the steam is taken and the sampling +nipple should be placed in a section of the main pipe near the boiler +and where there is no chance of moisture pocketing in the pipe. The +American Society of Mechanical Engineers recommends that a sampling +nipple, of which a description has been given, should be located in a +vertical main, rising from the boiler with its closed end extending +nearly across the pipe. Where non-return valves are used, or where there +are horizontal connections leading from the boiler to a vertical outlet, +water may collect at the lower end of the uptake pipe and be blown +upward in a spray which will not be carried away by the steam owing to a +lack of velocity. A sample taken from the lower part of this pipe will +show a greater amount of moisture than a true sample. With goose-neck +connections a small amount of water may collect on the bottom of the +pipe near the upper end where the inclination is such that the tendency +to flow backward is ordinarily counterbalanced by the flow of steam +forward over its surface; but when the velocity momentarily decreases +the water flows back to the lower end of the goose-neck and increases +the moisture at that point, making it an undesirable location for +sampling. In any case, it should be borne in mind that with low +velocities the tendency is for drops of entrained water to settle to the +bottom of the pipe, and to be temporarily broken up into spray whenever +an abrupt bend or other disturbance is met. + +[Illustration: Fig. 19. Illustrating the Manner in which Erroneous +Calorimeter Readings may be Obtained due to Improper Location of Sampling +Nozzle + + Case 1--Horizontal pipe. Water flows at bottom. If perforations + in nozzle are too near bottom of pipe, water piles against + nozzle, flows into calorimeter and gives false reading. + Case 2--If nozzle located too near junction of two horizontal + runs, as at a, condensation from vertical pipe which collects at + this point will be thrown against the nozzle by the velocity of + the steam, resulting in a false reading. Nozzle should be + located far enough above junction to be removed from water kept + in motion by the steam velocity, as at b. Case 3--Condensation + in bend will be held by velocity of the steam as shown. When + velocity is diminished during firing intervals and the like + moisture flows back against nozzle, a, and false reading is + obtained. A true reading will be obtained at b provided + condensation is not blown over on nozzle. Case 4--Where + non-return valve is placed before a bend, condensation will + collect on steam line side and water will be swept by steam + velocity against nozzle and false readings result.] + +Fig. 19 indicates certain locations of sampling nozzles from which +erroneous results will be obtained, the reasons being obvious from a +study of the cuts. + +Before taking any calorimeter reading, steam should be allowed to flow +through the instrument freely until it is thoroughly heated. The method +of using a throttling calorimeter is evident from the description of the +instrument given and the principle upon which it works. + +[Illustration: Babcock & Wilcox Superheater] + + + + +SUPERHEATED STEAM + + +Superheated steam, as already stated, is steam the temperature of which +exceeds that of saturated steam at the same pressure. It is produced by +the addition of heat to saturated steam which has been removed from +contact with the water from which it was generated. The properties of +superheated steam approximate those of a perfect gas rather than of a +vapor. Saturated steam cannot be superheated when it is in contact with +water which is also heated, neither can superheated steam condense +without first being reduced to the temperature of saturated steam. Just +so long as its temperature is above that of saturated steam at a +corresponding pressure it is superheated, and before condensation can +take place that superheat must first be lost through radiation or some +other means. Table 24[20] gives such properties of superheated steam for +varying pressures as are necessary for use in ordinary engineering +practice. + +Specific Heat of Superheated Steam--The specific heat of superheated +steam at atmospheric pressure and near saturation point was determined +by Regnault, in 1862, who gives it the value of 0.48. Regnault's value +was based on four series of experiments, all at atmospheric pressure and +with about the same temperature range, the maximum of which was 231.1 +degrees centigrade. For fifty years after Regnault's determination, this +value was accepted and applied to higher pressures and temperatures as +well as to the range of his experiments. More recent investigations have +shown that the specific heat is not a constant and varies with both +pressure and the temperature. A number of experiments have been made by +various investigators and, up to the present, the most reliable appear +to be those of Knoblauch and Jacob. Messrs. Marks and Davis have used +the values as determined by Knoblauch and Jacob with slight +modifications. The first consists in a varying of the curves at low +pressures close to saturation because of thermodynamic evidence and in +view of Regnault's determination at atmospheric pressure. The second +modification is at high degrees of superheat to follow Holborn's and +Henning's curve, which is accepted as authentic. + +For the sake of convenience, the mean specific heat of superheated steam +at various pressures and temperatures is given in tabulated form in +Table 25. These values have been calculated from Marks and Davis Steam +Tables by deducting from the total heat of one pound of steam at any +pressure for any degree of superheat the total heat of one pound of +saturated steam at the same pressure and dividing the difference by the +number of degrees of superheat and, therefore, represent the average +specific heat starting from that at saturation to the value at the +particular pressure and temperature.[21] Expressed as a formula this +calculation is represented by + + H_{sup} - H_{sat} +Sp. Ht. = ----------------- (8) + S_{sup} - S_{sat} + +Where H_{sup} = total heat of one pound of superheated steam at any + pressure and temperature, + H_{sat} = total heat of one pound of saturated steam at same + pressure, + S_{sup} = temperature of superheated steam taken, + S_{sat} = temperature of saturated steam corresponding to the + pressure taken. + + TABLE 25 + + MEAN SPECIFIC HEAT OF SUPERHEATED STEAM + CALCULATED FROM MARKS AND DAVIS TABLES + _______________________________________________________________ +|Gauge | | +|Pressure | Degree of Superheat | +| |_____________________________________________________| +| | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | +|_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| +| 50 | .518| .517| .514| .513| .511| .510| .508| .507| .505| +| 60 | .528| .525| .523| .521| .519| .517| .515| .513| .512| +| 70 | .536| .534| .531| .529| .527| .524| .522| .520| .518| +| 80 | .544| .542| .539| .535| .532| .530| .528| .526| .524| +| 90 | .553| .550| .546| .543| .539| .536| .534| .532| .529| +| 100 | .562| .557| .553| .549| .544| .542| .539| .536| .533| +| 110 | .570| .565| .560| .556| .552| .548| .545| .542| .539| +| 120 | .578| .573| .567| .561| .557| .554| .550| .546| .543| +| 130 | .586| .580| .574| .569| .564| .560| .555| .552| .548| +| 140 | .594| .588| .581| .575| .570| .565| .561| .557| .553| +| 150 | .604| .595| .587| .581| .576| .570| .566| .561| .557| +| 160 | .612| .603| .596| .589| .582| .576| .571| .566| .562| +| 170 | .620| .612| .603| .595| .588| .582| .576| .571| .566| +| 180 | .628| .618| .610| .601| .593| .587| .581| .575| .570| +| 190 | .638| .627| .617| .608| .599| .592| .585| .579| .574| +| 200 | .648| .635| .624| .614| .605| .597| .590| .584| .578| +| 210 | .656| .643| .631| .620| .611| .602| .595| .588| .583| +| 220 | .664| .650| .637| .626| .616| .607| .600| .592| .586| +| 230 | .672| .658| .644| .633| .622| .613| .605| .597| .591| +| 240 | .684| .668| .653| .640| .629| .619| .610| .602| .595| +| 250 | .692| .675| .659| .645| .633| .623| .614| .606| .599| +|_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| +|Gauge | | +|Pressure | Degree of Superheat | +| |-----------------------------------------------------| +| | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 225 | 250 | +|---------+-----+-----+-----+-----+-----+-----+-----+-----+-----| +| 50 | .504| .503| .502| .501| .500| .500| .499| .497| .496| +| 60 | .511| .509| .508| .507| .506| .504| .504| .502| .500| +| 70 | .516| .515| .513| .512| .511| .510| .509| .506| .504| +| 80 | .522| .520| .518| .516| .515| .514| .513| .511| .508| +| 90 | .527| .525| .523| .521| .519| .518| .517| .514| .510| +| 100 | .531| .529| .527| .525| .523| .522| .521| .517| .513| +| 110 | .536| .534| .532| .529| .528| .526| .525| .520| .517| +| 120 | .540| .537| .535| .533| .531| .529| .528| .523| .519| +| 130 | .545| .542| .539| .537| .535| .533| .531| .527| .523| +| 140 | .550| .547| .544| .541| .539| .536| .534| .530| .526| +| 150 | .554| .550| .547| .544| .542| .539| .537| .533| .529| +| 160 | .558| .554| .551| .548| .545| .543| .541| .536| .531| +| 170 | .562| .558| .555| .552| .549| .546| .544| .538| .533| +| 180 | .566| .561| .558| .555| .552| .549| .546| .540| .536| +| 190 | .569| .565| .562| .558| .555| .552| .549| .543| .538| +| 200 | .574| .569| .566| .562| .558| .555| .552| .546| .541| +| 210 | .578| .573| .569| .565| .561| .558| .555| .549| .543| +| 220 | .581| .577| .572| .568| .564| .561| .558| .551| .545| +| 230 | .585| .580| .575| .572| .567| .564| .561| .554| .548| +| 240 | .589| .584| .579| .575| .571| .567| .564| .556| .550| +| 250 | .593| .587| .582| .577| .574| .570| .567| .559| .553| +|_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| + +Factor of Evaporation with Superheated Steam--When superheat is present +in the steam during a boiler trial, where superheated steam tables are +available, the formula for determining the factor of evaporation is that +already given, (2),[22] namely, + + H - h +Factor of evaporation = ----- + L + +Here H = total heat in one pound of superheated steam from the table, +h and L having the same values as in (2). + +Where no such tables are available but the specific heat of superheat is +known, the formula becomes: + + H - h + Sp. Ht.(T - t) +Factor of evaporation = ---------------------- + L + +Where H = total heat in one pound of saturated steam at pressure + existing in trial, + h = sensible heat above 32 degrees in one pound of water at the + temperature entering the boiler, + T = temperature of superheated steam as determined in the trial, + t = temperature of saturated steam corresponding to the boiler + pressure, +Sp. Ht. = mean specific heat of superheated steam at the pressure and + temperature as found in the trial, + L = latent heat of one pound of saturated steam at atmospheric + pressure. + +Advantages of the Use of Superheated Steam--In considering the saving +possible by the use of superheated steam, it is too often assumed that +there is only a saving in the prime movers, a saving which is at least +partially offset by an increase in the fuel consumption of the boilers +generating steam. This misconception is due to the fact that the fuel +consumption of the boiler is only considered in connection with a +definite weight of steam. It is true that where such a definite weight +is to be superheated, an added amount of fuel must be burned. With a +properly designed superheater where the combined efficiency of the +boiler and superheater will be at least as high as of a boiler alone, +the approximate increase in coal consumption for producing a given +weight of steam will be as follows: + +_Superheat_ _Added Fuel_ + _Degrees_ _Per Cent_ + 25 1.59 + 50 3.07 + 75 4.38 + 100 5.69 + 150 8.19 + 200 10.58 + +These figures represent the added fuel necessary for superheating a +definite weight of steam to the number of degrees as given. The standard +basis, however, of boiler evaporation is one of heat units and, +considered from such a standpoint, again providing the efficiency of the +boiler and superheater is as high, as of a boiler alone, there is no +additional fuel required to generate steam containing a definite number +of heat units whether such units be due to superheat or saturation. That +is, if 6 per cent more fuel is required to generate and superheat to 100 +degrees, a definite weight of steam, over what would be required to +produce the same weight of saturated steam, that steam when superheated, +will contain 6 per cent more heat units above the fuel water temperature +than if saturated. This holds true if the efficiency of the boiler and +superheater combined is the same as of the boiler alone. As a matter of +fact, the efficiency of a boiler and superheater, where the latter is +properly designed and located, will be slightly higher for the same set +of furnace conditions than would the efficiency of a boiler in which no +superheater were installed. A superheater, properly placed within the +boiler setting in such way that products of combustion for generating +saturated steam are utilized as well for superheating that steam, will +not in any way alter furnace conditions. With a given set of such +furnace conditions for a given amount of coal burned, the fact that +additional surface, whether as boiler heating or superheating surface, +is placed in such a manner that the gases must sweep over it, will tend +to lower the temperature of the exit gases. It is such a lowering of +exit gas temperatures that is the ultimate indication of added +efficiency. Though the amount of this added efficiency is difficult to +determine by test, that there is an increase is unquestionable. + +Where a properly designed superheater is installed in a boiler the +heating surface of the boiler proper, in the generation of a definite +number of heat units, is relieved of a portion of the work which would +be required were these heat units delivered in saturated steam. Such a +superheater needs practically no attention, is not subject to a large +upkeep cost or depreciation, and performs its function without in any +way interfering with the operation of the boiler. Its use, therefore +from the standpoint of the boiler room, results in a saving in wear and +tear due to the lower ratings at which the boiler may be run, or its use +will lead to the possibility of obtaining the same number of boiler +horse power from a smaller number of boilers, with the boiler heating +surface doing exactly the same amount of work as if the superheaters +were not installed. The saving due to the added boiler efficiency that +will be obtained is obvious. + +Following the course of the steam in a plant, the next advantage of the +use of superheated steam is the absence of water in the steam pipes. The +thermal conductivity of superheated steam, that is, its power to give up +its heat to surrounding bodies, is much lower than that of saturated +steam and its heat, therefore, will not be transmitted so rapidly to the +walls of the pipes as when saturated steam is flowing through the pipes. +The loss of heat radiated from a steam pipe, assuming no loss in +pressure, represents the equivalent condensation when the pipe is +carrying saturated steam. In well-covered steam mains, the heat lost by +radiation when carrying superheated steam is accompanied only by a +reduction of the superheat which, if it be sufficiently high at the +boiler, will enable a considerable amount of heat to be radiated and +still deliver dry or superheated steam to the prime movers. + +It is in the prime movers that the advantages of the use of superheated +steam are most clearly seen. + +In an engine, steam is admitted into a space that has been cooled by the +steam exhausted during the previous stroke. The heat necessary to warm +the cylinder walls from the temperature of the exhaust to that of the +entering steam can be supplied only by the entering steam. If this steam +be saturated, such an adding of heat to the walls at the expense of the +heat of the entering steam results in the condensation of a portion. +This initial condensation is seldom less than from 20 to 30 per cent of +the total weight of steam entering the cylinder. It is obvious that if +the steam entering be superheated, it must be reduced to the temperature +of saturated steam at the corresponding pressure before any condensation +can take place. If the steam be superheated sufficiently to allow a +reduction in temperature equivalent to the quantity of heat that must be +imparted to the cylinder walls and still remain superheated, it is clear +that initial condensation is avoided. For example: assume one pound of +saturated steam at 200 pounds gauge pressure to enter a cylinder which +has been cooled by the exhaust. Assume the initial condensation to be 20 +per cent. The latent heat of the steam is given up in condensation; +hence, .20 × 838 = 167.6 B. t. u. are given up by the steam. If one +pound of superheated steam enters the same cylinder, it would have to be +superheated to a point where its total heat is 1199 + 168 = 1367 +B. t. u. or, at 200 pounds gauge pressure, superheated approximately 325 +degrees if the heat given up to the cylinder walls were the same as for +the saturated steam. As superheated steam conducts heat less rapidly +than saturated steam, the amount of heat imparted will be less than for +the saturated steam and consequently the amount of superheat required to +prevent condensation will be less than the above figure. This, of +course, is the extreme case of a simple engine with the range of +temperature change a maximum. As cylinders are added, the range in each +is decreased and the condensation is proportionate. + +The true economy of the use of superheated steam is best shown in a +comparison of the "heat consumption" of an engine. This is the number of +heat units required in developing one indicated horse power and the +measure of the relative performance of two engines is based on a +comparison of their heat consumption as the measure of a boiler is based +on its evaporation from and at 212 degrees. The water consumption of an +engine in pounds per indicated horse power is in no sense a true +indication of its efficiency. The initial pressures and corresponding +temperatures may differ widely and thus make a difference in the +temperature of the exhaust and hence in the temperature of the condensed +steam returned to the boiler. For example: suppose a certain weight of +steam at 150 pounds absolute pressure and 358 degrees be expanded to +atmospheric pressure, the temperature then being 212 degrees. If the +same weight of steam be expanded from an initial pressure of 125 pounds +absolute and 344 degrees, to enable it to do the same amount of work, +that is, to give up the same amount of heat, expansion then must be +carried to a point below atmospheric pressure to, say, 13 pounds +absolute, the final temperature of the steam then being 206 degrees. In +actual practice, it has been observed that the water consumption of a +compound piston engine running on 26-inch vacuum and returning the +condensed steam at 140 degrees was approximately the same as when +running on 28-inch vacuum and returning water at 90 degrees. With an +equal water consumption for the two sets of conditions, the economy in +the former case would be greater than in the latter, since it would be +necessary to add less heat to the water returned to the boiler to raise +it to the steam temperature. + +The lower the heat consumption of an engine per indicated horse power, +the higher its economy and the less the number of heat units must be +imparted to the steam generated. This in turn leads to the lowering of +the amount of fuel that must be burned per indicated horse power. + +With the saving in fuel by the reduction of heat consumption of an +engine indicated, it remains to be shown the effect of the use of +superheated steam on such heat consumption. As already explained, the +use of superheated steam reduces condensation not only in the mains but +especially in the steam cylinder, leaving a greater quantity of steam +available to do the work. Furthermore, a portion of the saturated steam +introduced into a cylinder will condense during adiabatic expansion, +this condensation increasing as expansion progresses. Since superheated +steam cannot condense until it becomes saturated, not only is initial +condensation prevented by its use but also such condensation as would +occur during expansion. When superheated sufficiently, steam delivered +by the exhaust will still be dry. In the avoidance of such condensation, +there is a direct saving in the heat consumption of an engine, the heat +given up being utilized in the developing of power and not in changing +the condition of the working fluid. That is, while the number of heat +units lost in overcoming condensation effects would be the same in +either case, when saturated steam is condensed the water of condensation +has no power to do work while the superheated steam, even after it has +lost a like number of heat units, still has the power of expansion. The +saving through the use of superheated steam in the heat consumption of +an engine decreases demands on the boiler and hence the fuel consumption +per unit of power. + +Superheated Steam for Steam Turbines--Experience in using superheated +steam in connection with steam turbines has shown that it leads to +economy and that it undoubtedly pays to use superheated steam in place +of saturated steam. This is so well established that it is standard +practice to use superheated steam in connection with steam turbines. +Aside from the economy secured through using superheated steam, there is +an important advantage arising through the fact that it materially +reduces the erosion of the turbine blades by the action of water that +would be carried by saturated steam. In using saturated steam in a steam +turbine or piston engine, the work done on expanding the steam causes +condensation of a portion of the steam, so that even were the steam dry +on entering the turbine, it would contain water on leaving the turbine. +By superheating the steam the water that exists in the low pressure +stages of the turbine may be reduced to an amount that will not cause +trouble. + +Again, if saturated steam contains moisture, the effect of this moisture +on the economy of a steam turbine is to reduce the economy to a greater +extent than the proportion by weight of water, one per cent of water +causing approximately a falling off of 2 per cent in the economy. + +The water rate of a large economical steam turbine with superheated +steam is reduced about one per cent, for every 12 degrees of superheat +up to 200 degrees Fahrenheit of superheat. To superheat one pound of +steam 12 degrees requires about 7 B. t. u. and if 1050 B. t. u. are +required at the boiler to evaporate one pound of the saturated steam +from the temperature of the feed water, the heat required for the +superheated steam would be 1057 degrees. One per cent of saving, +therefore, in the water consumption would correspond to a net saving of +about one-third of one per cent in the coal consumption. On this basis +100 degrees of superheat with an economical steam turbine would result +in somewhat over 3 per cent of saving in the coal for equal boiler +efficiencies. As a boiler with a properly designed superheater placed +within the setting is more economical for a given capacity than a boiler +without a superheater, the minimum gain in the coal consumption would +be, say, 4 or 5 per cent as compared to a plant with the same boilers +without superheaters. + +The above estimates are on the basis of a thoroughly dry saturated steam +or steam just at the point of being superheated or containing a few +degrees of superheat. If the saturated steam is moist, the saving due to +superheat is more and ordinarily the gain in economy due to superheated +steam, for equal boiler efficiencies, as compared with commercially dry +steam is, say, 5 per cent for each 100 degrees of superheat. Aside from +this gain, as already stated, superheated steam prevents erosion of the +turbine buckets that would be caused by water in the steam, and for the +reasons enumerated it is standard practice to use superheated steam for +turbine work. The less economical the steam motor, the more the gain due +to superheated steam, and where there are a number of auxiliaries that +are run with superheated steam, the percentage of gain will be greater +than the figures given above, which are the minimum and are for the most +economical type of large steam turbines. + +An example from actual practice will perhaps best illustrate and +emphasize the foregoing facts. In October 1909, a series of comparable +tests were conducted by The Babcock & Wilcox Co. on the steam yacht +"Idalia" to determine the steam consumption both with saturated and +superheated steam of the main engine on that yacht, including as well +the feed pump, circulating pump and air pump. These tests are more +representative than are most tests of like character in that the saving +in the steam consumption of the auxiliaries, which were much more +wasteful than the main engine, formed an important factor. A résumé of +these tests was published in the Journal of the Society of Naval +Engineers, November 1909. + +The main engines of the "Idalia" are four cylinder, triple expansion, +11-1/2 × 19 inches by 22-11/16 × 18 inches stroke. Steam is supplied by +a Babcock & Wilcox marine boiler having 2500 square feet of boiler +heating surface, 340 square feet of superheating surface and 65 square +feet of grate surface. + +The auxiliaries consist of a feed pump 6 × 4 × 6 inches, an independent +air pump 6 × 12 × 8 inches, and a centrifugal pump driven by a +reciprocating engine 5-7/16 × 5 inches. Under ordinary operating +conditions the superheat existing is about 100 degrees Fahrenheit. + +Tests were made with various degrees of superheat, the amount being +varied by by-passing the gases and in the tests with the lower amounts +of superheat by passing a portion of the steam from the boiler to the +steam main without passing it through the superheater. Steam temperature +readings were taken at the engine throttle. In the tests with saturated +steam, the superheater was completely cut out of the system. Careful +calorimeter measurements were taken, showing that the saturated steam +delivered to the superheater was dry. + +The weight of steam used was determined from the weight of the condensed +steam discharge from the surface condenser, the water being pumped from +the hot well into a tank mounted on platform scales. The same +indicators, thermometers and gauges were used in all the tests, so that +the results are directly comparable. The indicators used were of the +outside spring type so that there was no effect of the temperature of +the steam. All tests were of sufficient duration to show a uniformity of +results by hours. A summary of the results secured is given in Table 26, +which shows the water rate per indicated horse power and the heat +consumption. The latter figures are computed on the basis of the heat +imparted to the steam above the actual temperature of the feed water +and, as stated, these are the results that are directly comparable. + + TABLE 26 + + RESULTS OF "IDALIA" TESTS + _______________________________________________________________________ +| | | | | | | +|Date 1909 |Oct. 11|Oct. 14|Oct. 14|Oct. 12|Oct. 13| +|_______________________________|_______|_______|_______|_______|_______| +|Degrees of superheat Fahrenheit| 0 | 57 | 88 | 96 | 105 | +|Pressures, pounds per} Throttle| 190 | 196 | 201 | 198 | 203 | +|square inch above } First | | | | | | +|Atmospheric Pressure } Receiver| 68.4 | 66.0 | 64.3 | 61.9 | 63.0 | +| } Second | | | | | | +| } Receiver| 9.7 | 9.2 | 8.7 | 7.8 | 8.4 | +|Vacuum, inches | 25.5 | 25.9 | 25.9 | 25.4 | 25.2 | +|Temperature, Degrees Fahrenheit| | | | | | +| } Feed | 201 | 206 | 205 | 202 | 200 | +| } Hot Well | 116 | 109.5 | 115 | 111.5 | 111 | +| | | | | | | +|Revolutions per minute | | | | | | +| {Air Pump | 57 | 56 | 53 | 54 | 45 | +| {Circulating Pump| 196 | 198 | 196 | 198 | 197 | +| {Main Engine | 194.3 | 191.5 | 195.1 | 191.5 | 193.1 | +|Indicated Horse Power, | | | | | | +| Main Engine | 512.3 | 495.2 | 521.1 | 498.3 | 502.2 | +|Water per hour, total pounds |9397 |8430 |8234 |7902 |7790 | +|Water per indicated | | | | | | +| Horse Power, pounds | 18.3 | 17.0 | 15.8 | 15.8 | 15.5 | +|B. t. u. per minute per | | | | | | +| indicated Horse Power | 314 | 300 | 284 | 286 | 283 | +|Per cent Saving of Steam | ... | 7.1 | 13.7 | 13.7 | 15.3 | +|Percent Saving of Fuel | | | | | | +| (computed) | ... | 4.4 | 9.5 | 8.9 | 9.9 | +|_______________________________|_______|_______|_______|_______|_______| + +The table shows that the saving in steam consumption with 105 degrees of +superheat was 15.3 per cent and in heat consumption about 10 per cent. +This may be safely stated to be a conservative representation of the +saving that may be accomplished by the use of superheated steam in a +plant as a whole, where superheated steam is furnished not only to the +main engine but also to the auxiliaries. The figures may be taken as +conservative for the reason that in addition to the saving as shown in +the table, there would be in an ordinary plant a saving much greater +than is generally realized in the drips, where the loss with saturated +steam is greatly in excess of that with superheated steam. + +The most conclusive and most practical evidence that a saving is +possible through the use of superheated steam is in the fact that in the +largest and most economical plants it is used almost without exception. +Regardless of any such evidence, however, there is a deep rooted +conviction in the minds of certain engineers that the use of superheated +steam will involve operating difficulties which, with additional first +cost, will more than offset any fuel saving. There are, of course, +conditions under which the installation of superheaters would in no way +be advisable. With a poorly designed superheater, no gain would result. +In general, it may be stated that in a new plant, properly designed, +with a boiler and superheater which will have an efficiency at least as +high as a boiler without a superheater, a gain is certain. + +Such a gain is dependent upon the class of engine and the power plant +equipment in general. In determining the advisability of making a +superheater installation, all of the factors entering into each +individual case should be considered and balanced, with a view to +determining the saving in relation to cost, maintenance, depreciation +etc. + +In highly economical plants, where the water consumption for an +indicated horse power is low, the gain will be less than would result +from the use of superheated steam in less economical plants where the +water consumption is higher. It is impossible to make an accurate +statement as to the saving possible but, broadly, it may vary from 3 to +5 per cent for 100 degrees of superheat in the large and economical +plants using turbines or steam engines, in which there is a large ratio +of expansion, to from 10 to 25 per cent for 100 degrees of superheat for +the less economical steam motors. + +Though a properly designed superheater will tend to raise rather than to +decrease the boiler efficiency, it does not follow that all superheaters +are efficient, for if the gases in passing over the superheater do not +follow the path they would ordinarily take in passing over the boiler +heating surface, a loss may result. This is noticeably true where part of +the gases are passed over the superheater and are allowed to pass over +only a part or in some cases none of the boiler heating surface. + +With moderate degrees of superheat, from 100 to 200 degrees, where the +piping is properly installed, there will be no greater operating +difficulties than with saturated steam. Engine and turbine builders +guarantee satisfactory operation with superheated steam. With high +degrees of superheat, say, over 250 degrees, apparatus of a special +nature must be used and it is questionable whether the additional care +and liability to operating difficulties will offset any fuel saving +accomplished. It is well established, however, that the operating +difficulties, with the degrees of superheat to which this article is +limited, have been entirely overcome. + +The use of cast-iron fittings with superheated steam has been widely +discussed. It is an undoubted fact that while in some instances +superheated steam has caused deterioration of such fittings, in others +cast-iron fittings have been used with 150 degrees of superheat without +the least difficulty. The quality of the cast iron used in such fittings +has doubtless a large bearing on the life of such fittings for this +service. The difficulties that have been encountered are an increase in +the size of the fittings and eventually a deterioration great enough to +lead to serious breakage, the development of cracks, and when flanges +are drawn up too tightly, the breaking of a flange from the body of the +fitting. The latter difficulty is undoubtedly due, in certain instances, +to the form of flange in which the strain of the connecting bolts tended +to distort the metal. + +The Babcock & Wilcox Co. have used steel castings in superheated steam +work over a long period and experience has shown that this metal is +suitable for the service. There seems to be a general tendency toward +the use of steel fittings. In European practice, until recently, cast +iron was used with apparently satisfactory results. The claim of +European engineers was to the effect that their cast iron was of better +quality than that found in this country and thus explained the results +secured. Recently, however, certain difficulties have been encountered +with such fittings and European engineers are leaning toward the use of +steel for this work. + +The degree of superheat produced by a superheater placed within the +boiler setting will vary according to the class of fuel used, the form +of furnace, the condition of the fire and the rate at which the boiler +is being operated. This is necessarily true of any superheater swept by +the main body of the products of combustion and is a fact that should be +appreciated by the prospective user of superheated steam. With a +properly designed superheater, however, such fluctuations would not be +excessive, provided the boilers are properly operated. As a matter of +fact the point to be guarded against in the use of superheated steam is +that a maximum should not be exceeded. While, as stated, there may be a +considerable fluctuation in the temperature of the steam as delivered +from individual superheaters, where there are a number of boilers on a +line the temperature of the combined flow of steam in the main will be +found to be practically a constant, resulting from the offsetting of +various furnace conditions of one boiler by another. + +[Illustration: 8400 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters at the Butler Street Plant of the Georgia Railway and +Power Co., Atlanta, Ga. This Company Operates a Total of 15,200 Horse +Power of Babcock & Wilcox Boilers] + + + + +PROPERTIES OF AIR + + +Pure air is a mechanical mixture of oxygen and nitrogen. While different +authorities give slightly varying values for the proportion of oxygen +and nitrogen contained, the generally accepted values are: + + By volume, oxygen 20.91 per cent, nitrogen 79.09 per cent. + By weight, oxygen 23.15 per cent, nitrogen 76.85 per cent. + +Air in nature always contains other constituents in varying amounts, +such as dust, carbon dioxide, ozone and water vapor. + +Being perfectly elastic, the density or weight per unit of volume +decreases in geometric progression with the altitude. This fact has a +direct bearing in the proportioning of furnaces, flues and stacks at +high altitudes, as will be shown later in the discussion of these +subjects. The atmospheric pressures corresponding to various altitudes +are given in Table 12. + +The weight and volume of air depend upon the pressure and the +temperature, as expressed by the formula: + +Pv = 53.33 T (9) + +Where P = the absolute pressure in pounds per square foot, + v = the volume in cubic feet of one pound of air, + T = the absolute temperature of the air in degrees Fahrenheit, + 53.33 = a constant for air derived from the ratio of pressure, volume + and temperature of a perfect gas. + +The weight of one cubic foot of air will obviously be the reciprocal of +its volume, that is, 1/v pounds. + + TABLE 27 + + VOLUME AND WEIGHT OF AIR + AT ATMOSPHERIC PRESSURE + AT VARIOUS TEMPERATURES + _______________________________________ +| | | | +| | Volume | | +| Temperature | One Pound | Weight One | +| Degrees | in | Cubic Foot | +| Fahrenheit | Cubic Feet | in Pounds | +|_____________|____________|____________| +| | | | +| 32 | 12.390 | .080710 | +| 50 | 12.843 | .077863 | +| 55 | 12.969 | .077107 | +| 60 | 13.095 | .076365 | +| 65 | 13.221 | .075637 | +| 70 | 13.347 | .074923 | +| 75 | 13.473 | .074223 | +| 80 | 13.599 | .073535 | +| 85 | 13.725 | .072860 | +| 90 | 13.851 | .072197 | +| 95 | 13.977 | .071546 | +| 100 | 14.103 | .070907 | +| 110 | 14.355 | .069662 | +| 120 | 14.607 | .068460 | +| 130 | 14.859 | .067299 | +| 140 | 15.111 | .066177 | +| 150 | 15.363 | .065092 | +| 160 | 15.615 | .064041 | +| 170 | 15.867 | .063024 | +| 180 | 16.119 | .062039 | +| 190 | 16.371 | .061084 | +| 200 | 16.623 | .060158 | +| 210 | 16.875 | .059259 | +| 212 | 16.925 | .059084 | +| 220 | 17.127 | .058388 | +| 230 | 17.379 | .057541 | +| 240 | 17.631 | .056718 | +| 250 | 17.883 | .055919 | +| 260 | 18.135 | .055142 | +| 270 | 18.387 | .054386 | +| 280 | 18.639 | .053651 | +| 290 | 18.891 | .052935 | +| 300 | 19.143 | .052238 | +| 320 | 19.647 | .050898 | +| 340 | 20.151 | .049625 | +| 360 | 20.655 | .048414 | +| 380 | 21.159 | .047261 | +| 400 | 21.663 | .046162 | +| 425 | 22.293 | .044857 | +| 450 | 22.923 | .043624 | +| 475 | 23.554 | .042456 | +| 500 | 24.184 | .041350 | +| 525 | 24.814 | .040300 | +| 550 | 25.444 | .039302 | +| 575 | 26.074 | .038352 | +| 600 | 26.704 | .037448 | +| 650 | 27.964 | .035760 | +| 700 | 29.224 | .034219 | +| 750 | 30.484 | .032804 | +| 800 | 31.744 | .031502 | +| 850 | 33.004 | .030299 | +|_____________|____________|____________| + +Example: Required the volume of air in cubic feet under 60.3 pounds +gauge pressure per square inch at 115 degrees Fahrenheit. + +P = 144 (14.7 + 60.3) = 10,800. + +T = 115 + 460 = 575 degrees. + + 53.33 × 575 +Hence v = ----------- = 2.84 cubic feet, and + 10,800 + + 1 1 +Weight per cubic foot = - = ---- = 0.352 pounds. + v 2.84 + +Table 27 gives the weights and volumes of air under atmospheric pressure +at varying temperatures. + +Formula (9) holds good for other gases with the change in the value of +the constant as follows: + +For oxygen 48.24, nitrogen 54.97, hydrogen 765.71. + +The specific heat of air at constant pressure varies with its +temperature. A number of determinations of this value have been made and +certain of those ordinarily accepted as most authentic are given in +Table 28. + + TABLE 28 + + SPECIFIC HEAT OF AIR + AT CONSTANT PRESSURE AND VARIOUS TEMPERATURES + ______________________________________________________________ +| | | | +| Temperature Range | | | +|_________________________|_______________|____________________| +| | | | | +| Degrees | Degrees | Specific Heat | Authority | +| Centigrade | Fahrenheit | | | +|____________|____________|_______________|____________________| +| | | | | +| -30- 10 | -22- 50 | 0.2377 | Regnault | +| 0-100 | 32- 212 | 0.2374 | Regnault | +| 0-200 | 32- 392 | 0.2375 | Regnault | +| 20-440 | 68- 824 | 0.2366 | Holborn and Curtis | +| 20-630 | 68-1166 | 0.2429 | Holborn and Curtis | +| 20-800 | 68-1472 | 0.2430 | Holborn and Curtis | +| 0-200 | 32- 392 | 0.2389 | Wiedemann | +|____________|____________|_______________|____________________| + +This value is of particular importance in waste heat work and it is +regrettable that there is such a variation in the different experiments. +Mallard and Le Chatelier determined values considerably higher than any +given in Table 28. All things considered in view of the discrepancy of +the values given, there appears to be as much ground for the use of a +constant value for the specific heat of air at any temperature as for a +variable value. Where this value is used throughout this book, it has +been taken as 0.24. + +Air may carry a considerable quantity of water vapor, which is +frequently 3 per cent of the total weight. This fact is of importance in +problems relating to heating drying and the compressing of air. Table 29 +gives the amount of vapor required to saturate air at different +temperatures, its weight, expansive force, etc., and contains sufficient +information for solving practically all problems of this sort that may +arise. + + TABLE 29 + + WEIGHTS OF AIR, VAPOR OF WATER, AND SATURATED MIXTURES OF AIR AND VAPOR + AT DIFFERENT TEMPERATURES, + UNDER THE ORDINARY ATMOSPHERIC PRESSURE OF 29.921 INCHES OF MERCURY + +Column Headings: + 1: Temperature Degrees Fahrenheit + 2: Volume of Dry Air at Different Temperatures, the Volume at 32 Degrees + being 1.000 + 3: Weight of Cubic Foot of Dry Air at the Different Temperatures Pounds + 4: Elastic Force of Vapor in Inches of Mercury (Regnault) + 5: Elastic Force of the Air in the Mixture of Air and Vapor in Inches of + Mercury + 6: Weight of the Air in Pounds + 7: Weight of the Vapor in Pounds + 8: Total Weight of Mixture in Pounds + 9: Weight of Vapor Mixed with One Pound of Air, in Pounds +10: Weight of Dry Air Mixed with One Pound of Vapor, in Pounds +11: Cubic Feet of Vapor from One Pound of Water at its own Pressure in + Column 4 + ____________________________________________________________________________ +| | | | | | | +| | | | | Mixtures of Air Saturated | | +| | | | | with Vapor | | +|___|_____|_____|______|______________________________________________|______| +| | | | | |Weight of Cubic Foot | | | | +| | | | | | of the Mixture of | | | | +| | | | | | Air and Vapor | | | | +| | | | | |_____________________| | | | +| | | | | | | | | | | | +| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | +|___|_____|_____|______|______|_____|_______|_______|________|________|______| +| | | | | | | | | | | | +| 0| .935|.0864| .044|29.877|.0863|.000079|.086379| .00092|1092.4 | | +| 12| .960|.0842| .074|29.849|.0840|.000130|.084130| .00155| 646.1 | | +| 22| .980|.0824| .118|29.803|.0821|.000202|.082302| .00245| 406.4 | | +| 32|1.000|.0807| .181|29.740|.0802|.000304|.080504| .00379| 263.81 |3289 | +| 42|1.020|.0791| .267|29.654|.0784|.000440|.078840| .00561| 178.18 |2252 | +| | | | | | | | | | | | +| 52|1.041|.0776| .388|29.533|.0766|.000627|.077227| .00810| 122.17 |1595 | +| 62|1.061|.0761| .556|29.365|.0747|.000881|.075581| .01179| 84.79 |1135 | +| 72|1.082|.0747| .785|29.136|.0727|.001221|.073921| .01680| 59.54 | 819 | +| 82|1.102|.0733| 1.092|28.829|.0706|.001667|.072267| .02361| 42.35 | 600 | +| 92|1.122|.0720| 1.501|28.420|.0684|.002250|.070717| .03289| 30.40 | 444 | +| | | | | | | | | | | | +|102|1.143|.0707| 2.036|27.885|.0659|.002997|.068897| .04547| 21.98 | 334 | +|112|1.163|.0694| 2.731|27.190|.0631|.003946|.067046| .06253| 15.99 | 253 | +|122|1.184|.0682| 3.621|26.300|.0599|.005142|.065042| .08584| 11.65 | 194 | +|132|1.204|.0671| 4.752|25.169|.0564|.006639|.063039| .11771| 8.49 | 151 | +|142|1.224|.0660| 6.165|23.756|.0524|.008473|.060873| .16170| 6.18 | 118 | +| | | | | | | | | | | | +|152|1.245|.0649| 7.930|21.991|.0477|.010716|.058416| .22465| 4.45 | 93.3| +|162|1.265|.0638|10.099|19.822|.0423|.013415|.055715| .31713| 3.15 | 74.5| +|172|1.285|.0628|12.758|17.163|.0360|.016682|.052682| .46338| 2.16 | 59.2| +|182|1.306|.0618|15.960|13.961|.0288|.020536|.049336| .71300| 1.402| 48.6| +|192|1.326|.0609|19.828|10.093|.0205|.025142|.045642| 1.22643| .815| 39.8| +| | | | | | | | | | | | +|202|1.347|.0600|24.450| 5.471|.0109|.030545|.041445| 2.80230| .357| 32.7| +|212|1.367|.0591|29.921| 0.000|.0000|.036820|.036820|Infinite| .000| 27.1| +|___|_____|_____|______|______|_____|_______|_______|________|________|______| + +Column 5 = barometer pressure of 29.921, minus the proportion of this +due to vapor pressure from column 4. + + + + +COMBUSTION + + +Combustion may be defined as the rapid chemical combination of oxygen +with carbon, hydrogen and sulphur, accompanied by the diffusion of heat +and light. That portion of the substance thus combined with the oxygen +is called combustible. As used in steam engineering practice, however, +the term combustible is applied to that portion of the fuel which is dry +and free from ash, thus including both oxygen and nitrogen which may be +constituents of the fuel, though not in the true sense of the term +combustible. + +Combustion is perfect when the combustible unites with the greatest +possible amount of oxygen, as when one atom of carbon unites with two +atoms of oxygen to form carbon dioxide, CO_{2}. The combustion is +imperfect when complete oxidation of the combustible does not occur, or +where the combustible does not unite with the maximum amount of oxygen, +as when one atom of carbon unites with one atom of oxygen to form carbon +monoxide, CO, which may be further burned to carbon dioxide. + +Kindling Point--Before a combustible can unite with oxygen and +combustion takes place, its temperature must first be raised to the +ignition or kindling point, and a sufficient time must be allowed for +the completion of the combustion before the temperature of the gases is +lowered below that point. Table 30, by Stromeyer, gives the approximate +kindling temperatures of different fuels. + + TABLE 30 + +KINDLING TEMPERATURE OF VARIOUS FUELS + + ____________________________________ +| | | +| | Degrees | +| | Fahrenheit | +|_________________|__________________| +| | | +| Lignite Dust | 300 | +| Dried Peat | 435 | +| Sulphur | 470 | +| Anthracite Dust | 570 | +| Coal | 600 | +| Coke | Red Heat | +| Anthracite | Red Heat, 750 | +| Carbon Monoxide | Red Heat, 1211 | +| Hydrogen | 1030 or 1290 | +|_________________|__________________| + + +Combustibles--The principal combustibles in coal and other fuels are +carbon, hydrogen and sulphur, occurring in varying proportions and +combinations. + +Carbon is by far the most abundant as is indicated in the chapters on +fuels. + +Hydrogen in a free state occurs in small quantities in some fuels, but +is usually found in combination with carbon, in the form of +hydrocarbons. The density of hydrogen is 0.0696 (Air = 1) and its weight +per cubic foot, at 32 degrees Fahrenheit and under atmospheric pressure, +is 0.005621 pounds. + +Sulphur is found in most coals and some oils. It is usually present in +combined form, either as sulphide of iron or sulphate of lime; in the +latter form it has no heat value. Its presence in fuel is objectionable +because of its tendency to aid in the formation of clinkers, and the +gases from its combustion, when in the presence of moisture, may cause +corrosion. + +Nitrogen is drawn into the furnace with the air. Its density is 0.9673 +(Air = 1); its weight, at 32 degrees Fahrenheit and under atmospheric +pressure, is 0.07829 pounds per cubic foot; each pound of air at +atmospheric pressure contains 0.7685 pounds of nitrogen, and one pound +of nitrogen is contained in 1.301 pounds of air. + +Nitrogen performs no useful office in combustion and passes through the +furnace without change. It dilutes the air, absorbs heat, reduces the +temperature of the products of combustion, and is the chief source of +heat losses in furnaces. + +Calorific Value--Each combustible element of gas will combine with +oxygen in certain definite proportions and will generate a definite +amount of heat, measured in B. t. u. This definite amount of heat per +pound liberated by perfect combustion is termed the calorific value of +that substance. Table 31, gives certain data on the reactions and +results of combustion for elementary combustibles and several compounds. + + TABLE 31 + + OXYGEN AND AIR REQUIRED FOR COMBUSTION + + AT 32 DEGREES AND 29.92 INCHES + +Column headings: + + 1: Oxidizable Substance or Combustible + 2: Chemical Symbol + 3: Atomic or Combining Weight + 4: Chemical Reaction + 5: Product of Combustion + 6: Oxygen per Pound of Column 1 Pounds + 7: Nitrogen per Pound of Column 1. 3.32[23] × O Pounds + 8: Air per Pound of Column 1. 4.32[24] × O Pounds + 9: Gaseous Product per Pound of Column 1[25] + Column 8 Pounds +10: Heat Value per Pound of Column 1 B. t. u. +11: Volumes of Column 1 Entering Combination Volume +12: Volumes of Oxygen Combining with Column 11 Volume +13: Volumes of Product Formed Volume +14: Volume per Pound of Column 1 in Gaseous Form Cubic Feet +15: Volume of Oxygen per Pound of Column 1 Cubic Feet +16: Volume of Products of Combustion per Pound of Column 1 Cubic Feet +17: Volume of Nitrogen per Pound of Column 1 3.782[26] × Column 15 Cubic + Feet +18: Volume of Gas per pound of Column 1 = Column 10 ÷ Column 17 Cubic + Feet + + BY WEIGHT + ________________________________________________________________________ +| | | | | | | +| 1 | 2 | 3 | 4 | 5 | 6 | +|________________|_______|____|________________|_________________|_______| +| | | | | | | +| Carbon | C | 12 | C+2O = CO_{2} | Carbon Dioxide | 2.667 | +| Carbon | C | 12 | C+O = CO | Carbon Monoxide | 1.333 | +| Carbon Monoxide| CO | 28 | CO+O = CO_{2} | Carbon Dioxide | .571 | +| Hydrogen | H | 1 | 2H+O = H_{2}O | Water | 8 | +| | | / CH_{4}+4O = | Carbon Dioxide \ | +| Methane | CH_{4}| 16 | | | 4 | +| | | \ CO_{2}+2H_{2}O | and Water / | +| Sulphur | S | 32 | S+2O = SO_{2} | Sulphur Dioxide | 1 | +|________________|_______|____|________________|_________________|_______| + + ________________________________________________________ +| | | | | | | +| 1 | 2 | 7 | 8 | 9 | 10 | +|________________|_______|_______|_______|_______|_______| +| | | | | | | +| Carbon | C | 8.85 | 11.52 | 12.52 | 14600 | +| Carbon | C | 4.43 | 5.76 | 6.76 | 4450 | +| Carbon Monoxide| CO | 1.90 | 2.47 | 3.47 | 10150 | +| Hydrogen | H | 26.56 | 34.56 | 35.56 | 62000 | +| | | | | | | +| Methane | CH_{4}| 13.28 | 17.28 | 18.28 | 23550 | +| | | | | | | +| Sulphur | S | 3.32 | 4.32 | 5.32 | 4050 | +|________________|_______|_______|_______|_______|_______| + + + BY VOLUME + + ________________________________________________________________ +| | | | | | | +| 1 | 2 | 11 | 12 | 13 | 14 | +|_________________|________|______|____|________________|________| +| | | | | | | +| Carbon | C | 1C | 2 | 2CO_{2} | 14.95 | +| Carbon | C | 1C | 1 | 2CO | 14.95 | +| Carbon Monoxide | CO | 2CO | 1 | 2CO_{2} | 12.80 | +| Hydrogen | H | 2H | 1 | 2H_{2}O | 179.32 | +| Methane | CH_{4} | 1C4H | 4 | 1CO_{2} 2H_{2}O| 22.41 | +| Sulphur | S | 1S | 2 | 1SO_{2} | 5.60 | +|_________________|________|______|____|________________|________| + + _____________________________________________________________ +| | | | | | | +| 1 | 2 | 15 | 16 | 17 | 18 | +|_________________|________|_______|________|________|________| +| | | | | | | +| Carbon | C | 29.89 | 29.89 | 112.98 | 142.87 | +| Carbon | C | 14.95 | 29.89 | 56.49 | 86.38 | +| Carbon Monoxide | CO | 6.40 | 12.80 | 24.20 | 37.00 | +| Hydrogen | H | 89.66 | 179.32 | 339.09 | 518.41 | +| Methane | CH_{4} | 44.83 | 67.34 | 169.55 | 236.89 | +| Sulphur | S | 11.21 | 11.21 | 42.39 | 53.60 | +|_________________|________|_______|________|________|________| + +It will be seen from this table that a pound of carbon will unite with +2-2/3 pounds of oxygen to form carbon dioxide, and will evolve 14,600 +B. t. u. As an intermediate step, a pound of carbon may unite with 1-1/3 +pounds of oxygen to form carbon monoxide and evolve 4450 B. t. u., but +in its further conversion to CO_{2} it would unite with an additional +1-1/3 times its weight of oxygen and evolve the remaining 10,150 +B. t. u. When a pound of CO burns to CO_{2}, however, only 4350 B. t. u. +are evolved since the pound of CO contains but 3/7 pound carbon. + +Air Required for Combustion--It has already been shown that each +combustible element in fuel will unite with a definite amount of oxygen. +With the ultimate analysis of the fuel known, in connection with Table +31, the theoretical amount of air required for combustion may be readily +calculated. + +Let the ultimate analysis be as follows: + + _Per Cent_ +Carbon 74.79 +Hydrogen 4.98 +Oxygen 6.42 +Nitrogen 1.20 +Sulphur 3.24 +Water 1.55 +Ash 7.82 + ------ + 100.00 + +When complete combustion takes place, as already pointed out, the carbon +in the fuel unites with a definite amount of oxygen to form CO_{2}. The +hydrogen, either in a free or combined state, will unite with oxygen to +form water vapor, H_{2}O. Not all of the hydrogen shown in a fuel +analysis, however, is available for the production of heat, as a portion +of it is already united with the oxygen shown by the analysis in the +form of water, H_{2}O. Since the atomic weights of H and O are +respectively 1 and 16, the weight of the combined hydrogen will be 1/8 +of the weight of the oxygen, and the hydrogen available for combustion +will be H - 1/8 O. In complete combustion of the sulphur, sulphur +dioxide SO_{2} is formed, which in solution in water forms sulphuric +acid. + +Expressed numerically, the theoretical amount of air for the above +analysis is as follows: + + 0.7479 C × 2-2/3 = 1.9944 O needed +( 0.0642 ) +( 0.0498 - -------) H × 8 = 0.3262 O needed +( 8 ) + 0.0324 S × 1 = 0.0324 O needed + ------ + Total 2.3530 O needed + +One pound of oxygen is contained in 4.32 pounds of air. + +The total air needed per pound of coal, therefore, will be 2.353 × 4.32 += 10.165. + +The weight of combustible per pound of fuel is .7479 + .0418[27] + .0324 ++ .012 = .83 pounds, and the air theoretically required per pound of +combustible is 10.165 ÷ .83 = 12.2 pounds. + +The above is equivalent to computing the theoretical amount of air +required per pound of fuel by the formula: + + ( O) +Weight per pound = 11.52 C + 34.56 (H - -) + 4.32 S (10) + ( 8) + +where C, H, O and S are proportional parts by weight of carbon, +hydrogen, oxygen and sulphur by ultimate analysis. + +In practice it is impossible to obtain perfect combustion with the +theoretical amount of air, and an excess may be required, amounting to +sometimes double the theoretical supply, depending upon the nature of +the fuel to be burned and the method of burning it. The reason for this +is that it is impossible to bring each particle of oxygen in the air +into intimate contact with the particles in the fuel that are to be +oxidized, due not only to the dilution of the oxygen in the air by +nitrogen, but because of such factors as the irregular thickness of the +fire, the varying resistance to the passage of the air through the fire +in separate parts on account of ash, clinker, etc. Where the +difficulties of drawing air uniformly through a fuel bed are eliminated, +as in the case of burning oil fuel or gas, the air supply may be +materially less than would be required for coal. Experiment has shown +that coal will usually require 50 per cent more than the theoretical net +calculated amount of air, or about 18 pounds per pound of fuel either +under natural or forced draft, though this amount may vary widely with +the type of furnace, the nature of the coal, and the method of firing. +If less than this amount of air is supplied, the carbon burns to +monoxide instead of dioxide and its full heat value is not developed. + +An excess of air is also a source of waste, as the products of +combustion will be diluted and carry off an excessive amount of heat in +the chimney gases, or the air will so lower the temperature of the +furnace gases as to delay the combustion to an extent that will cause +carbon monoxide to pass off unburned from the furnace. A sufficient +amount of carbon monoxide in the gases may cause the action known as +secondary combustion, by igniting or mingling with air after leaving the +furnace or in the flues or stack. Such secondary combustion which takes +place either within the setting after leaving the furnace or in the +flues or stack always leads to a loss of efficiency and, in some +instances, leads to overheating of the flues and stack. + +Table 32 gives the theoretical amount of air required for various fuels +calculated from formula (10) assuming the analyses of the fuels given in +the table. + +The process of combustion of different fuels and the effect of variation +in the air supply for their combustion is treated in detail in the +chapters dealing with the various fuels. + + TABLE 32 + + CALCULATED THEORETICAL AMOUNT OF AIR + REQUIRED PER POUND OF VARIOUS FUELS + + ____________________________________________________________ +| |Weight of Constituents in One |Air Required| +| Fuel |Pound Dry Fuel |per Pound | +| |______________________________|of Fuel | +| | Carbon | Hydrogen| Oxygen |Pounds | +| | Per Cent| Per Cent| Per Cent | | +|________________|_________|_________|__________|____________| +|Coke | 94.0 | . | . | 10.8 | +|Anthracite Coal | 91.5 | 3.5 | 2.6 | 11.7 | +|Bituminous Coal | 87.0 | 5.0 | 4.0 | 11.6 | +|Lignite | 70.0 | 5.0 | 20.0 | 8.9 | +|Wood | 50.0 | 6.0 | 43.5 | 6.0 | +|Oil | 85.0 | 13.0 | 1.0 | 14.3 | +|________________|_________|_________|__________|____________| + + + +[Illustration: 4064 HORSE-POWER Installation of Babcock & Wilcox Boilers +and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers, at +the Cosmopolitan Electric Co., Chicago, Ill.] + + + + +ANALYSIS OF FLUE GASES + + +The object of a flue gas analysis is the determination of the +completeness of the combustion of the carbon in the fuel, and the amount +and distribution of the heat losses due to incomplete combustion. The +quantities actually determined by an analysis are the relative +proportions by volume, of carbon dioxide (CO_{2}), oxygen (O), and +carbon monoxide (CO), the determinations being made in this order. + +The variations of the percentages of these gases in an analysis is best +illustrated in the consideration of the complete combustion of pure +carbon, a pound of which requires 2.67 pounds of oxygen,[28] or 32 cubic +feet at 60 degrees Fahrenheit. The gaseous product of such combustion +will occupy, when cooled, the same volume as the oxygen, namely, 32 +cubic feet. The air supplied for the combustion is made up of 20.91 per +cent oxygen and 79.09 per cent nitrogen by volume. The carbon united +with the oxygen in the form of carbon dioxide will have the same volume +as the oxygen in the air originally supplied. The volume of the nitrogen +when cooled will be the same as in the air supplied, as it undergoes no +change. Hence for complete combustion of one pound of carbon, where no +excess of air is supplied, an analysis of the products of combustion +will show the following percentages by volume: + + _Actual Volume_ + _for One Pound Carbon_ _Per Cent_ + _Cubic Feet_ _by Volume_ +Carbon Dioxide 32 = 20.91 +Oxygen 0 = 0.00 +Nitrogen 121 = 79.09 + --- ------ +Air required for one pound Carbon 153 = 100.00 + +For 50 per cent excess air the volume will be as follows: + + 153 × 1½ = 229.5 cubic feet of air per pound of carbon. + + _Actual Volume_ + _for One Pound Carbon_ _Per Cent_ + _Cubic Feet_ _by Volume_ +Carbon Dioxide 32 = 13.91 } +Oxygen 16 = 7.00 } = 20.91 per cent +Nitrogen 181.5 = 79.09 + ----- ------ + 229.5 = 100.00 + +For 100 per cent excess air the volume will be as follows: + + 153 × 2 = 306 cubic feet of air per pound of carbon. + + _Actual Volume_ + _for One Pound Carbon_ _Per Cent_ + _Cubic Feet_ _by Volume_ +Carbon Dioxide 32 = 10.45 } +Oxygen 32 = 10.45 } = 20.91 per cent +Nitrogen 242 = 79.09 + --- ------ + 306 = 100.00 + +In each case the volume of oxygen which combines with the carbon is +equal to (cubic feet of air × 20.91 per cent)--32 cubic feet. + +It will be seen that no matter what the excess of air supplied, the +actual amount of carbon dioxide per pound of carbon remains the same, +while the percentage by volume decreases as the excess of air increases. +The actual volume of oxygen and the percentage by volume increases with +the excess of air, and the percentage of oxygen is, therefore, an +indication of the amount of excess air. In each case the sum of the +percentages of CO_{2} and O is the same, 20.9. Although the volume of +nitrogen increases with the excess of air, its percentage by volume +remains the same as it undergoes no change while combustion takes place; +its percentage for any amount of air excess, therefore, will be the same +after combustion as before, if cooled to the same temperature. It must +be borne in mind that the above conditions hold only for the perfect +combustion of a pound of pure carbon. + +Carbon monoxide (CO) produced by the imperfect combustion of carbon, +will occupy twice the volume of the oxygen entering into its composition +and will increase the volume of the flue gases over that of the air +supplied for combustion in the proportion of + + 100 + ½ the per cent CO +1 to ----------------------- + 100 + +When pure carbon is the fuel, the sum of the percentages by volume of +carbon dioxide, oxygen and one-half of the carbon monoxide, must be in +the same ratio to the nitrogen in the flue gases as is the oxygen to the +nitrogen in the air supplied, that is, 20.91 to 79.09. When burning +coal, however, the percentage of nitrogen is obtained by subtracting the +sum of the percentages by volume of the other gases from 100. Thus if an +analysis shows 12.5 per cent CO_{2}, 6.5 per cent O, and 0.6 per cent +CO, the percentage of nitrogen which ordinarily is the only other +constituent of the gas which need be considered, is found as follows: + +100 - (12.5 + 6.5 + 0.6) = 80.4 per cent. + +The action of the hydrogen in the volatile constituents of the fuel is +to increase the apparent percentage of the nitrogen in the flue gases. +This is due to the fact that the water vapor formed by the combustion of +the hydrogen will condense at a temperature at which the analysis is +made, while the nitrogen which accompanied the oxygen with which the +hydrogen originally combined maintains its gaseous form and passes into +the sampling apparatus with the other gases. For this reason coals +containing high percentages of volatile matter will produce a larger +quantity of water vapor, and thus increase the apparent percentage of +nitrogen. + + +Air Required and Supplied--When the ultimate analysis of a fuel is +known, the air required for complete combustion with no excess can be +found as shown in the chapter on combustion, or from the following +approximate formula: + + Pounds of air required per pound of fuel = + + (C O S) + 34.56 (- + (H - -) + -)[29] (11) + (3 8 8) + +where C, H and O equal the percentage by weight of carbon, hydrogen and +oxygen in the fuel divided by 100. + +When the flue gas analysis is known, the total, amount of air supplied +is: + + Pounds of air supplied per pound of fuel = + + N + 3.036 (-----------) × C[30] (12) + CO_{2} + CO + +where N, CO_{2} and CO are the percentages by volume of nitrogen, carbon +dioxide and carbon monoxide in the flue gases, and C the percentage by +weight of carbon which is burned from the fuel and passes up the stack +as flue gas. This percentage of C which is burned must be distinguished +from the percentage of C as found by an ultimate analysis of the fuel. +To find the percentage of C which is burned, deduct from the total +percentage of carbon as found in the ultimate analysis, the percentage +of unconsumed carbon found in the ash. This latter quantity is the +difference between the percentage of ash found by an analysis and that +as determined by a boiler test. It is usually assumed that the entire +combustible element in the ash is carbon, which assumption is +practically correct. Thus if the ash in a boiler test were 16 per cent +and by an analysis contained 25 per cent of carbon, the percentage of +unconsumed carbon would be 16 × .25 = 4 per cent of the total coal +burned. If the coal contained by ultimate analysis 80 per cent of carbon +the percentage burned, and of which the products of combustion pass up +the chimney would be 80 - 4 = 76 per cent, which is the correct figure +to use in calculating the total amount of air supplied by formula (12). + +The weight of flue gases resulting from the combustion of a pound of dry +coal will be the sum of the weights of the air per pound of coal and the +combustible per pound of coal, the latter being equal to one minus the +percentage of ash as found in the boiler test. The weight of flue gases +per pound of dry fuel may, however, be computed directly from the +analyses, as shown later, and the direct computation is that ordinarily +used. + +The ratio of the air actually supplied per pound of fuel to that +theoretically required to burn it is: + + N +3.036(---------)×C + CO_{2}+CO +------------------ (13) + C O +34.56(- + H - -) + 3 8 + +in which the letters have the same significance as in formulae (11) and +(12). + +The ratio of the air supplied per pound of combustible to the amount +theoretically required is: + + N +------------------ (14) +N - 3.782(O - ½CO) + +which is derived as follows: + +The N in the flue gas is the content of nitrogen in the whole amount of +air supplied. The oxygen in the flue gas is that contained in the air +supplied and which was not utilized in combustion. This oxygen was +accompanied by 3.782 times its volume of nitrogen. The total amount of +excess oxygen in the flue gases is (O - ½CO); hence N - 3.782(O - ½CO) +represents the nitrogen content in the air actually required for +combustion and N ÷ (N - 3.782[O - ½CO]) is the ratio of the air supplied +to that required. This ratio minus one will be the proportion of excess +air. + +The heat lost in the flue gases is L = 0.24 W (T - t) (15) + +Where L = B. t. u. lost per pound of fuel, + W = weight of flue gases in pounds per pound of dry coal, + T = temperature of flue gases, + t = temperature of atmosphere, + 0.24 = specific heat of the flue gases. + +The weight of flue gases, W, per pound of carbon can be computed +directly from the flue gas analysis from the formula: + +11 CO_{2} + 8 O + 7 (CO + N) +---------------------------- (16) + 3 (CO_{2} + CO) + +where CO_{2}, O, CO, and N are the percentages by volume as determined +by the flue gas analysis of carbon dioxide, oxygen, carbon monoxide and +nitrogen. + +The weight of flue gas per pound of dry coal will be the weight +determined by this formula multiplied by the percentage of carbon in the +coal from an ultimate analysis. + +[Graph: Temperature of Escaping Gases--Deg. Fahr. +against Heat carried away by Chimney Gases--In B.t.u. +per pound of Carbon burned.[31] + +Fig. 20. Loss Due to Heat Carried Away by Chimney Gases for Varying +Percentages of Carbon Dioxide. Based on Boiler Room Temperature = 80 +Degrees Fahrenheit. Nitrogen in Flue Gas = 80.5 Per Cent. Carbon +Monoxide in Flue Gas = 0. Per Cent] + +Fig. 20 represents graphically the loss due to heat carried away by dry +chimney gases for varying percentages of CO_{2}, and different +temperatures of exit gases. + +The heat lost, due to the fact that the carbon in the fuel is not +completely burned and carbon monoxide is present in the flue gases, in +B. t. u. per pound of fuel burned is: + + ( CO ) +L' = 10,150 × (-----------) (17) + (CO + CO_{2}) + +where, as before, CO and CO_{2} are the percentages by volume in the +flue gases and C is the proportion by weight of carbon which is burned +and passes up the stack. + +Fig. 21 represents graphically the loss due to such carbon in the fuel +as is not completely burned but escapes up the stack in the form of +carbon monoxide. + +[Graph: Loss in B.T.U. per Pound of Carbon Burned[32] +against Per Cent CO_{2} in Flue Gas + +Fig. 21. Loss Due to Unconsumed Carbon Contained in the +CO in the Flue Gases] + +Apparatus for Flue Gas Analysis--The Orsat apparatus, illustrated in +Fig. 22, is generally used for analyzing flue gases. The burette A is +graduated in cubic centimeters up to 100, and is surrounded by a water +jacket to prevent any change in temperature from affecting the density +of the gas being analyzed. + +For accurate work it is advisable to use four pipettes, B, C, D, E, the +first containing a solution of caustic potash for the absorption of +carbon dioxide, the second an alkaline solution of pyrogallol for the +absorption of oxygen, and the remaining two an acid solution of cuprous +chloride for absorbing the carbon monoxide. Each pipette contains a +number of glass tubes, to which some of the solution clings, thus +facilitating the absorption of the gas. In the pipettes D and E, copper +wire is placed in these tubes to re-energize the solution as it becomes +weakened. The rear half of each pipette is fitted with a rubber bag, one +of which is shown at K, to protect the solution from the action of the +air. The solution in each pipette should be drawn up to the mark on the +capillary tube. + +The gas is drawn into the burette through the U-tube H, which is filled +with spun glass, or similar material, to clean the gas. To discharge any +air or gas in the apparatus, the cock G is opened to the air and the +bottle F is raised until the water in the burette reaches the 100 cubic +centimeters mark. The cock G is then turned so as to close the air +opening and allow gas to be drawn through H, the bottle F being lowered +for this purpose. The gas is drawn into the burette to a point below the +zero mark, the cock G then being opened to the air and the excess gas +expelled until the level of the water in F and in A are at the zero +mark. This operation is necessary in order to obtain the zero reading at +atmospheric pressure. + +The apparatus should be carefully tested for leakage as well as all +connections leading thereto. Simple tests can be made; for example: If +after the cock G is closed, the bottle F is placed on top of the frame +for a short time and again brought to the zero mark, the level of the +water in A is above the zero mark, a leak is indicated. + +[Illustration: Fig. 22. Orsat Apparatus] + +Before taking a final sample for analysis, the burette A should be +filled with gas and emptied once or twice, to make sure that all the +apparatus is filled with the new gas. The cock G is then closed and the +cock I in the pipette B is opened and the gas driven over into B by +raising the bottle F. The gas is drawn back into A by lowering F and +when the solution in B has reached the mark in the capillary tube, the +cock I is closed and a reading is taken on the burette, the level of the +water in the bottle F being brought to the same level as the water in A. +The operation is repeated until a constant reading is obtained, the +number of cubic centimeters being the percentage of CO_{2} in the flue +gases. + +The gas is then driven over into the pipette C and a similar operation +is carried out. The difference between the resulting reading and the +first reading gives the percentage of oxygen in the flue gases. + +The next operation is to drive the gas into the pipette D, the gas being +given a final wash in E, and then passed into the pipette C to +neutralize any hydrochloric acid fumes which may have been given off by +the cuprous chloride solution, which, especially if it be old, may give +off such fumes, thus increasing the volume of the gases and making the +reading on the burette less than the true amount. + +The process must be carried out in the order named, as the pyrogallol +solution will also absorb carbon dioxide, while the cuprous chloride +solution will also absorb oxygen. + +As the pressure of the gases in the flue is less than the atmospheric +pressure, they will not of themselves flow through the pipe connecting +the flue to the apparatus. The gas may be drawn into the pipe in the way +already described for filling the apparatus, but this is a tedious +method. For rapid work a rubber bulb aspirator connected to the air +outlet of the cock G will enable a new supply of gas to be drawn into +the pipe, the apparatus then being filled as already described. Another +form of aspirator draws the gas from the flue in a constant stream, thus +insuring a fresh supply for each sample. + +The analysis made by the Orsat apparatus is volumetric; if the analysis +by weight is required, it can be found from the volumetric analysis as +follows: + +Multiply the percentages by volume by either the densities or the +molecular weight of each gas, and divide the products by the sum of all +the products; the quotients will be the percentages by weight. For most +work sufficient accuracy is secured by using the even values of the +molecular weights. + +The even values of the molecular weights of the gases appearing in an +analysis by an Orsat are: + +Carbon Dioxide 44 +Carbon Monoxide 28 +Oxygen 32 +Nitrogen 28 + +Table 33 indicates the method of converting a volumetric flue gas +analysis into an analysis by weight. + + TABLE 33 + + CONVERSION OF A FLUE GAS ANALYSIS BY VOLUME TO ONE BY WEIGHT + +Column Headings: + +A: Analysis by Volume Per Cent +B: Molecular Weight +C: Volume times Molecular Weight +D: Analysis by Weight Per Cent + _____________________________________________________________________ +| | | | | | +| Gas | A | B | C | D | +|________________________|_______|___________|________|_______________| +| | | | | | +| | | | | | +| | | | | 536.8 | +| Carbon Dioxide CO_{2} | 12.2 | 12+(2×16) | 536.8 | ------ = 17.7 | +| | | | | 3022.8 | +| | | | | | +| | | | | 11.2 | +| Carbon Monoxide CO | .4 | 12+16 | 11.2 | ------ = .4 | +| | | | | 3022.8 | +| | | | | | +| | | | | 220.8 | +| Oxygen O | 6.9 | 2×16 | 220.8 | ------ = 7.3 | +| | | | | 3022.8 | +| | | | | | +| | | | | 2254.0 | +| Nitrogen N | 80.5 | 2×14 | 2254.0 | ------ = 74.6 | +| | | | | 3022.8 | +|________________________|_______|___________|________|_______________| +| | | | | | +| Total | 100.0 | | 3022.8 | 100.0 | +|________________________|_______|___________|________|_______________| + +Application of Formulae and Rules--Pocahontas coal is burned in the +furnace, a partial ultimate analysis being: + + _Per Cent_ +Carbon 82.1 +Hydrogen 4.25 +Oxygen 2.6 +Sulphur 1.6 +Ash 6.0 +B. t. u., per pound dry 14500 + +The flue gas analysis shows: + + _Per Cent_ + +CO_{2} 10.7 +O 9.0 +CO 0.0 +N (by difference) 80.3 + +Determine: The flue gas analysis by weight (see Table 33), the amount of +air required for perfect combustion, the actual weight of air per pound +of fuel, the weight of flue gas per pound of coal, the heat lost in the +chimney gases if the temperature of these is 500 degrees Fahrenheit, and +the ratio of the air supplied to that theoretically required. + +Solution: The theoretical weight of air required for perfect combustion, +per pound of fuel, from formula (11) will be, + + (.821 .026 .016) +W = 34.56 (---- + (.0425 - ----) + ----) = 10.88 pounds. + ( 3 8 8 ) + +If the amount of carbon which is burned and passes away as flue gas is +80 per cent, which would allow for 2.1 per cent of unburned carbon in +terms of the total weight of dry fuel burned, the weight of dry gas per +pound of carbon burned will be from formula (16): + + 11 × 10.7 + 8 × 9.0 + 7(0 + 80.3) +W = --------------------------------- = 23.42 pounds + 3(10.7 + 0) + +and the weight of flue gas per pound of coal burned will be .80 × 23.42 += 18.74 pounds. + +The heat lost in the flue gases per pound of coal burned will be from +formula (15) and the value 18.74 just determined. + +Loss = .24 × 18.74 × (500 - 60) = 1979 B. t. u. + +The percentage of heat lost in the flue gases will be 1979 ÷ 14500 = +13.6 per cent. + +The ratio of air supplied per pound of coal to that theoretically +required will be 18.74 ÷ 10.88 = 1.72 per cent. + +The ratio of air supplied per pound of combustible to that required will +be from formula (14): + + .803 +------------------------- = 1.73 +.803 - 3.782(.09 - ½ × 0) + +The ratio based on combustible will be greater than the ratio based on +fuel if there is unconsumed carbon in the ash. + + +Unreliability of CO_{2} Readings Taken Alone--It is generally assumed +that high CO_{2} readings are indicative of good combustion and hence of +high efficiency. This is true only in the sense that such high readings +do indicate the small amount of excess air that usually accompanies good +combustion, and for this reason high CO_{2} readings alone are not +considered entirely reliable. Wherever an automatic CO_{2} recorder is +used, it should be checked from time to time and the analysis carried +further with a view to ascertaining whether there is CO present. As the +percentage of CO_{2} in these gases increases, there is a tendency +toward the presence of CO, which, of course, cannot be shown by a CO_{2} +recorder, and which is often difficult to detect with an Orsat +apparatus. The greatest care should be taken in preparing the cuprous +chloride solution in making analyses and it must be known to be fresh +and capable of absorbing CO. In one instance that came to our attention, +in using an Orsat apparatus where the cuprous chloride solution was +believed to be fresh, no CO was indicated in the flue gases but on +passing the same sample into a Hempel apparatus, a considerable +percentage was found. It is not safe, therefore, to assume without +question from a high CO_{2} reading that the combustion is +correspondingly good, and the question of excess air alone should be +distinguished from that of good combustion. The effect of a small +quantity of CO, say one per cent, present in the flue gases will have a +negligible influence on the quantity of excess air, but the presence of +such an amount would mean a loss due to the incomplete combustion of the +carbon in the fuel of possibly 4.5 per cent of the total heat in the +fuel burned. When this is considered, the importance of a complete flue +gas analysis is apparent. + +Table 34 gives the densities of various gases together with other data +that will be of service in gas analysis work. + + TABLE 34 + + DENSITY OF GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE + ADAPTED FROM SMITHSONIAN TABLES + ++----------+----------+--------+---------+----------+---------------+ +| | | | | | Relative | +| | | | Weight | | Density, | +| | | | of | Volume | Hydrogen = 1 | +| | |Specific|One Cubic| of +-------+-------+ +| Gas | Chemical |Gravity | Foot |One Pound | |Approx-| +| | Symbol | Air=1 | Pounds |Cubic Feet| Exact | imate | ++----------+----------+--------+---------+----------+-------+-------+ +|Oxygen | O | 1.053 | .08922 | 11.208 | 15.87 | 16 | +|Nitrogen | N | 0.9673 | .07829 | 12.773 | 13.92 | 14 | +|Hydrogen | H | 0.0696 | .005621 | 177.90 | 1.00 | 1 | +|Carbon | | | | | | | +| Dioxide | CO_{2} | 1.5291 | .12269 | 8.151 | 21.83 | 22 | +|Carbon | | | | | | | +| Monoxide | CO | 0.9672 | .07807 | 12.809 | 13.89 | 14 | +|Methane | CH_{4} | 0.5576 | .04470 | 22.371 | 7.95 | 8 | +|Ethane |C_{2}H_{6}| 1.075 | .08379 | 11.935 | 14.91 | 15 | +|Acetylene |C_{2}H_{2}| 0.920 | .07254 | 13.785 | 12.91 | 13 | +|Sulphur | | | | | | | +| Dioxide | SO_{2} | 2.2639 | .17862 | 5.598 | 31.96 | 32 | +|Air | ... | 1.0000 | .08071 | 12.390 | ... | ... | ++----------+----------+--------+---------+----------+-------+-------+ + +[Illustration: 1942 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters in the Singer Building, New York City] + + + + +CLASSIFICATION OF FUELS + +(WITH PARTICULAR REFERENCE TO COAL) + + +Fuels for steam boilers may be classified as solid, liquid or gaseous. +Of the solid fuels, anthracite and bituminous coals are the most common, +but in this class must also be included lignite, peat, wood, bagasse and +the refuse from certain industrial processes such as sawdust, shavings, +tan bark and the like. Straw, corn and coffee husks are utilized in +isolated cases. + +The class of liquid fuels is represented chiefly by petroleum, though +coal tar and water-gas tar are used to a limited extent. + +Gaseous fuels are limited to natural gas, blast furnace gas and coke +oven gas, the first being a natural product and the two latter +by-products from industrial processes. Though waste gases from certain +processes may be considered as gaseous fuels, inasmuch as the question +of combustion does not enter, the methods of utilizing them differ from +that for combustible gaseous fuel, and the question will be dealt with +separately. + +Since coal is by far the most generally used of all fuels, this chapter +will be devoted entirely to the formation, composition and distribution +of the various grades, from anthracite to peat. The other fuels will be +discussed in succeeding chapters and their combustion dealt with in +connection with their composition. + +Formation of Coal--All coals are of vegetable origin and are the remains +of prehistoric forests. Destructive distillation due to great pressures +and temperatures, has resolved the organic matter into its invariable +ultimate constituents, carbon, hydrogen, oxygen and other substances, in +varying proportions. The factors of time, depth of beds, disturbance of +beds and the intrusion of mineral matter resulting from such +disturbances have produced the variation in the degree of evolution from +vegetable fiber to hard coal. This variation is shown chiefly in the +content of carbon, and Table 35 shows the steps of such variation. + + TABLE 35 + + APPROXIMATE CHEMICAL CHANGES FROM WOOD + FIBER TO ANTHRACITE COAL + ++----------------------+-------+--------+-------+ +|Substance |Carbon |Hydrogen|Oxygen | ++----------------------+-------+--------+-------+ +|Wood Fiber | 52.65 | 5.25 | 42.10 | +|Peat | 59.57 | 5.96 | 34.47 | +|Lignite | 66.04 | 5.27 | 28.69 | +|Earthy Brown Coal | 73.18 | 5.68 | 21.14 | +|Bituminous Coal | 75.06 | 5.84 | 19.10 | +|Semi-bituminous Coal | 89.29 | 5.05 | 5.66 | +|Anthracite Coal | 91.58 | 3.96 | 4.46 | ++----------------------+-------+--------+-------+ + +Composition of Coal--The uncombined carbon in coal is known as fixed +carbon. Some of the carbon constituent is combined with hydrogen and +this, together with other gaseous substances driven off by the +application of heat, form that portion of the coal known as volatile +matter. The fixed carbon and the volatile matter constitute the +combustible. The oxygen and nitrogen contained in the volatile matter +are not combustible, but custom has applied this term to that portion of +the coal which is dry and free from ash, thus including the oxygen and +nitrogen. + +The other important substances entering into the composition of coal are +moisture and the refractory earths which form the ash. The ash varies in +different coals from 3 to 30 per cent and the moisture from 0.75 to 45 +per cent of the total weight of the coal, depending upon the grade and +the locality in which it is mined. A large percentage of ash is +undesirable as it not only reduces the calorific value of the fuel, but +chokes up the air passages in the furnace and through the fuel bed, thus +preventing the rapid combustion necessary to high efficiency. If the +coal contains an excessive quantity of sulphur, trouble will result from +its harmful action on the metal of the boiler where moisture is present, +and because it unites with the ash to form a fusible slag or clinker +which will choke up the grate bars and form a solid mass in which large +quantities of unconsumed carbon may be imbedded. + +Moisture in coal may be more detrimental than ash in reducing the +temperature of a furnace, as it is non-combustible, absorbs heat both in +being evaporated and superheated to the temperature of the furnace +gases. In some instances, however, a certain amount of moisture in a +bituminous coal produces a mechanical action that assists in the +combustion and makes it possible to develop higher capacities than with +dry coal. + +Classification of Coal--Custom has classified coals in accordance with +the varying content of carbon and volatile matter in the combustible. +Table 36 gives the approximate percentages of these constituents for the +general classes of coals with the corresponding heat values per pound of +combustible. + + TABLE 36 + + APPROXIMATE COMPOSITION AND CALORIFIC VALUE + OF GENERAL GRADES OF COAL ON BASIS OF COMBUSTIBLE + ++-------------------+----------------------------+--------------+ +| Kind of Coal | Per Cent of Combustible | B. t. u. | +| +------------+---------------+ Per Pound of | +| |Fixed Carbon|Volatile Matter| Combustible | ++-------------------+------------+---------------+--------------+ +|Anthracite |97.0 to 92.5| 3.0 to 7.5 |14600 to 14800| +|Semi-anthracite |92.5 to 87.5| 7.5 to 12.5 |14700 to 15500| +|Semi-bituminous |87.5 to 75.0| 12.5 to 25.0 |15500 to 16000| +|Bituminous--Eastern|75.0 to 60.0| 25.0 to 40.0 |14800 to 15300| +|Bituminous--Western|65.0 to 50.0| 35.0 to 50.0 |13500 to 14800| +|Lignite | Under 50 | Over 50 |11000 to 13500| ++-------------------+------------+---------------+--------------+ + + +Anthracite--The name anthracite, or hard coal, is applied to those dry +coals containing from 3 to 7 per cent volatile matter and which do not +swell when burned. True anthracite is hard, compact, lustrous and +sometimes iridescent, and is characterized by few joints and clefts. Its +specific gravity varies from 1.4 to 1.8. In burning, it kindles slowly +and with difficulty, is hard to keep alight, and burns with a short, +almost colorless flame, without smoke. + + +Semi-anthracite coal has less density, hardness and luster than true +anthracite, and can be distinguished from it by the fact that when newly +fractured it will soot the hands. Its specific gravity is ordinarily +about 1.4. It kindles quite readily and burns more freely than the true +anthracites. + + +Semi-bituminous coal is softer than anthracite, contains more volatile +hydrocarbons, kindles more easily and burns more rapidly. It is +ordinarily free burning, has a high calorific value and is of the +highest order for steam generating purposes. + + +Bituminous coals are still softer than those described and contain still +more volatile hydrocarbons. The difference between the semi-bituminous +and the bituminous coals is an important one, economically. The former +have an average heating value per pound of combustible about 6 per cent +higher than the latter, and they burn with much less smoke in ordinary +furnaces. The distinctive characteristic of the bituminous coals is the +emission of yellow flame and smoke when burning. In color they range +from pitch black to dark brown, having a resinous luster in the most +compact specimens, and a silky luster in such specimens as show traces +of vegetable fiber. The specific gravity is ordinarily about 1.3. + +Bituminous coals are either of the caking or non-caking class. The +former, when heated, fuse and swell in size; the latter burn freely, do +not fuse, and are commonly known as free burning coals. Caking coals are +rich in volatile hydrocarbons and are valuable in gas manufacture. + +Bituminous coals absorb moisture from the atmosphere. The surface +moisture can be removed by ordinary drying, but a portion of the water +can be removed only by heating the coal to a temperature of about 250 +degrees Fahrenheit. + +Cannel coal is a variety of bituminous coal, rich in hydrogen and +hydrocarbons, and is exceedingly valuable as a gas coal. It has a dull +resinous luster and burns with a bright flame without fusing. Cannel +coal is seldom used for steam coal, though it is sometimes mixed with +semi-bituminous coal where an increased economy at high rates of +combustion is desired. The composition of cannel coal is approximately +as follows: fixed carbon, 26 to 55 per cent; volatile matter, 42 to 64 +per cent; earthy matter, 2 to 14 per cent. Its specific gravity is +approximately 1.24. + +Lignite is organic matter in the earlier stages of its conversion into +coal, and includes all varieties which are intermediate between peat and +coal of the older formation. Its specific gravity is low, being 1.2 to +1.23, and when freshly mined it may contain as high as 50 per cent of +moisture. Its appearance varies from a light brown, showing a distinctly +woody structure, in the poorer varieties, to a black, with a pitchy +luster resembling hard coal, in the best varieties. It is non-caking and +burns with a bright but slightly smoky flame with moderate heat. It is +easily broken, will not stand much handling in transportation, and if +exposed to the weather will rapidly disintegrate, which will increase +the difficulty of burning it. + +Its composition varies over wide limits. The ash may run as low as one +per cent and as high as 50 per cent. Its high content of moisture and +the large quantity of air necessary for its combustion cause large stack +losses. It is distinctly a low-grade fuel and is used almost entirely in +the districts where mined, due to its cheapness. + +Peat is organic matter in the first stages of its conversion into coal +and is found in bogs and similar places. Its moisture content when cut +is extremely high, averaging 75 or 80 per cent. It is unsuitable for +fuel until dried and even then will contain as much as 30 per cent +moisture. Its ash content when dry varies from 3 to 12 per cent. In this +country, though large deposits of peat have been found, it has not as +yet been found practicable to utilize it for steam generating purposes +in competition with coal. In some European countries, however, the peat +industry is common. + +Distribution--The anthracite coals are, with some unimportant +exceptions, confined to five small fields in Eastern Pennsylvania, as +shown in the following list. These fields are given in the order of +their hardness. + +Lehigh or Eastern Middle Field + Green Mountain District + Black Creek District + Hazelton District + Beaver Meadow District + Panther Creek District[33] + +Mahanoy or Western Field[34] + East Mahanoy District + West Mahanoy District + +Wyoming or Northern Field + Carbondale District + Scranton District + Pittston District + Wilkesbarre District + Plymouth District + +Schuylkill or Southern Field + East Schuylkill District + West Schuylkill District + Louberry District + +Lykens Valley or Southwestern Field + Lykens Valley District + Shamokin District[35] + +Anthracite is also found in Pulaski and Wythe Counties, Virginia; along +the border of Little Walker Mountain, and in Gunnison County, Colorado. +The areas in Virginia are limited, however, while in Colorado the +quality varies greatly in neighboring beds and even in the same bed. An +anthracite bed in New Mexico was described in 1870 by Dr. R. W. Raymond, +formerly United States Mining Commissioner. + +Semi-anthracite coals are found in a few small areas in the western part +of the anthracite field. The largest of these beds is the Bernice in +Sullivan County, Pennsylvania. Mr. William Kent, in his "Steam Boiler +Economy", describes this as follows: "The Bernice semi-anthracite coal +basin lies between Beech Creek on the north and Loyalsock Creek on the +south. It is six miles long, east and west, and hardly a third of a mile +across. An 8-foot vein of coal lies in a bed of 12 feet of coal and +slate. The coal of this bed is the dividing line between anthracite and +semi-anthracite, and is similar to the coal of the Lykens Valley +District. Mine analyses give a range as follows: moisture, 0.65 to 1.97; +volatile matter, 3.56 to 9.40; fixed carbon, 82.52 to 89.39; ash, 3.27 +to 9.34; sulphur, 0.24 to 1.04." + +Semi-bituminous coals are found on the eastern edge of the great +Appalachian Field. Starting with Tioga and Bradford Counties of northern +Pennsylvania, the bed runs southwest through Lycoming, Clearfield, +Centre, Huntingdon, Cambria, Somerset and Fulton Counties, Pennsylvania; +Allegheny County, Maryland; Buchannan, Dickinson, Lee, Russell, Scott, +Tazewell and Wise Counties, Virginia; Mercer, McDowell, Fayette, Raleigh +and Mineral Counties, West Virginia; and ending in northeastern +Tennessee, where a small amount of semi-bituminous is mined. + +The largest of the bituminous fields is the Appalachian. Beginning near +the northern boundary of Pennsylvania, in the western portion of the +State, it extends southwestward through West Virginia, touching Maryland +and Virginia on their western borders, passing through southeastern +Ohio, eastern Kentucky and central Tennessee, and ending in western +Alabama, 900 miles from its northern extremity. + +The next bituminous coal producing region to the west is the Northern +Field, in north central Michigan. Still further to the west, and second +in importance to the Appalachian Field, is the Eastern Interior Field. +This covers, with the exception of the upper northern portion, nearly +the entire State of Illinois, southwest Indiana and the western portion +of Kentucky. + +The Western Field extends through central and southern Iowa, western +Missouri, southwestern Kansas, eastern Oklahoma and the west central +portion of Arkansas. The Southwestern Field is confined entirely to the +north central portion of Texas, in which State there are also two small +isolated fields along the Rio Grande River. + +The remaining bituminous fields are scattered through what may be termed +the Rocky Mountain Region, extending from Montana to New Orleans. A +partial list of these fields and their location follows: + +Judith Basin Central Montana +Bull Mountain Field Central Montana +Yellowstone Region Southwestern Montana +Big Horn Basin Region Southern Montana +Big Horn Basin Region Northern Wyoming +Black Hills Region Northeastern Wyoming +Hanna Field Southern Wyoming +Green River Region Southwestern Wyoming +Yampa Field Northwestern Colorado +North Park Field Northern Colorado +Denver Region North Central Colorado +Uinta Region Western Colorado +Uinta Region Eastern Utah +Southwestern Region Southwestern Utah +Raton Mountain Region Southern Colorado +Raton Mountain Region Northern New Mexico +San Juan River Region Northwestern New Mexico +Capitan Field Southern New Mexico + +Along the Pacific Coast a few small fields are scattered in western +California, southwestern Oregon, western and northwestern Washington. + +Most of the coals in the above fields are on the border line between +bituminous and lignite. They are really a low grade of bituminous coal +and are known as sub-bituminous or black lignites. + +Lignites--These resemble the brown coals of Europe and are found in the +western states, Wyoming, New Mexico, Arizona, Utah, Montana, North +Dakota, Nevada, California, Oregon and Washington. Many of the fields +given as those containing bituminous coals in the western states also +contain true lignite. Lignite is also found in the eastern part of Texas +and in Oklahoma. + +Alaska Coals--Coal has been found in Alaska and undoubtedly is of great +value, though the extent and character of the fields have probably been +exaggerated. Great quantities of lignite are known to exist, and in +quality the coal ranges in character from lignite to anthracite. There +are at present, however, only two fields of high-grade coals known, +these being the Bering River Field, near Controllers Bay, and the +Matanuska Field, at the head of Cooks Inlet. Both of these fields are +known to contain both anthracite and high-grade bituminous coals, though +as yet they cannot be said to have been opened up. + +Weathering of Coal--The storage of coal has become within the last few +years to a certain extent a necessity due to market conditions, danger +of labor difficulties at the mines and in the railroads, and the +crowding of transportation facilities. The first cause is probably the +most important, and this is particularly true of anthracite coals where +a sliding scale of prices is used according to the season of the year. +While market conditions serve as one of the principal reasons for coal +storage, most power plants and manufacturing plants feel compelled to +protect their coal supply from the danger of strikes, car shortages and +the like, and it is customary for large power plants, railroads and coal +companies themselves, to store bituminous coal. Naval coaling stations +are also an example of what is done along these lines. + +Anthracite is the nearest approach to the ideal coal for storing. It is +not subject to spontaneous ignition, and for this reason is unlimited in +the amount that may be stored in one pile. With bituminous coals, +however, the case is different. Most bituminous coals will ignite if +placed in large enough piles and all suffer more or less from +disintegration. Coal producers only store such coals as are least liable +to ignite, and which will stand rehandling for shipment. + +The changes which take place in stored coal are of two kinds: 1st, the +oxidization of the inorganic matter such as pyrites; and 2nd, the direct +oxidization of the organic matter of the actual coal. + +The first change will result in an increased volume of the coal, and +sometimes in an increased weight, and a marked disintegration. The +changes due to direct oxidization of the coal substances usually cannot +be detected by the eye, but as they involve the oxidization of the +carbon and available hydrogen and the absorption of the oxygen by +unsaturated hydrocarbons, they are the chief cause of the weathering +losses in heat value. Numerous experiments have led to the conclusion +that this is also the cause for spontaneous combustion. + +Experiments to show loss in calorific heat values due to weathering +indicate that such loss may be as high as 10 per cent when the coal is +stored in the air, and 8.75 per cent when stored under water. It would +appear that the higher the volatile content of the coal, the greater +will be the loss in calorific value and the more subject to spontaneous +ignition. + +Some experiments made by Messrs. S. W. Parr and W. F. Wheeler, published +in 1909 by the Experiment Station of the University of Illinois, +indicate that coals of the nature found in Illinois and neighboring +states are not affected seriously during storage from the standpoint of +weight and heating value, the latter loss averaging about 3½ per cent +for the first year of storage. They found that the losses due to +disintegration and to spontaneous ignition were of greater importance. +Their conclusions agree with those deduced from the other experiments, +viz., that the storing of a larger size coal than that which is to be +used, will overcome to a certain extent the objection to disintegration, +and that the larger sizes, besides being advantageous in respect to +disintegration, are less liable to spontaneous ignition. Storage under +water will, of course, entirely prevent any fire loss and, to a great +extent, will stop disintegration and reduce the calorific losses to a +minimum. + +To minimize the danger of spontaneous ignition in storing coal, the +piles should be thoroughly ventilated. + +Pulverized Fuels--Considerable experimental work has been done with +pulverized coal, utilizing either coal dust or pulverizing such coal as +is too small to be burned in other ways. If satisfactorily fed to the +furnace, it would appear to have several advantages. The dust burned in +suspension would be more completely consumed than is the case with the +solid coals, the production of smoke would be minimized, and the process +would admit of an adjustment of the air supply to a point very close to +the amount theoretically required. This is due to the fact that in +burning there is an intimate mixture of the air and fuel. The principal +objections have been in the inability to introduce the pulverized fuel +into the furnace uniformly, the difficulty of reducing the fuel to the +same degree of fineness, liability of explosion in the furnace due to +improper mixture with the air, and the decreased capacity and efficiency +resulting from the difficulty of keeping tube surfaces clean. + +Pressed Fuels--In this class are those composed of the dust of some +suitable combustible, pressed and cemented together by a substance +possessing binding and in most cases inflammable properties. Such fuels, +known as briquettes, are extensively used in foreign countries and +consist of carbon or soft coal, too small to be burned in the ordinary +way, mixed usually with pitch or coal tar. Much experimenting has been +done in this country in briquetting fuels, the government having taken +an active interest in the question, but as yet this class of fuel has +not come into common use as the cost and difficulty of manufacture and +handling have made it impossible to place it in the market at a price to +successfully compete with coal. + +Coke is a porous product consisting almost entirely of carbon remaining +after certain manufacturing processes have distilled off the hydrocarbon +gases of the fuel used. It is produced, first, from gas coal distilled +in gas retorts; second, from gas or ordinary bituminous coals burned in +special furnaces called coke ovens; and third, from petroleum by +carrying the distillation of the residuum to a red heat. + +Coke is a smokeless fuel. It readily absorbs moisture from the +atmosphere and if not kept under cover its moisture content may be as +much as 20 per cent of its own weight. + +Gas-house coke is generally softer and more porous than oven coke, +ignites more readily, and requires less draft for its combustion. + +[Illustration: 16,000 Horse-power Installation of Babcock & Wilcox +Boilers and Superheaters at the Brunot's Island Plant of the Duquesne +Light Co., Pittsburgh, Pa.] + + + + +THE DETERMINATION OF HEATING VALUES OF FUELS + + +The heating value of a fuel may be determined either by a calculation +from a chemical analysis or by burning a sample in a calorimeter. + +In the former method the calculation should be based on an ultimate +analysis, which reduces the fuel to its elementary constituents of +carbon, hydrogen, oxygen, nitrogen, sulphur, ash and moisture, to secure +a reasonable degree of accuracy. A proximate analysis, which determines +only the percentage of moisture, fixed carbon, volatile matter and ash, +without determining the ultimate composition of the volatile matter, +cannot be used for computing the heat of combustion with the same degree +of accuracy as an ultimate analysis, but estimates may be based on the +ultimate analysis that are fairly correct. + +An ultimate analysis requires the services of a competent chemist, and +the methods to be employed in such a determination will be found in any +standard book on engineering chemistry. An ultimate analysis, while +resolving the fuel into its elementary constituents, does not reveal how +these may have been combined in the fuel. The manner of their +combination undoubtedly has a direct effect upon their calorific value, +as fuels having almost identical ultimate analyses show a difference in +heating value when tested in a calorimeter. Such a difference, however, +is slight, and very close approximations may be computed from the +ultimate analysis. + +Ultimate analyses are given on both a moist and a dry fuel basis. +Inasmuch as the latter is the basis generally accepted for the +comparison of data, it would appear that it is the best basis on which +to report such an analysis. When an analysis is given on a moist fuel +basis it may be readily converted to a dry basis by dividing the +percentages of the various constituents by one minus the percentage of +moisture, reporting the moisture content separately. + + _Moist Fuel_ _Dry Fuel_ + +C 83.95 84.45 +H 4.23 4.25 +O 3.02 3.04 +N 1.27 1.28 +S .91 .91 +Ash 6.03 6.07 + ------ + 100.00 + +Moisture .59 .59 + ------ + 100.00 + +Calculations from an Ultimate Analysis--The first formula for the +calculation of heating values from the composition of a fuel as +determined from an ultimate analysis is due to Dulong, and this formula, +slightly modified, is the most commonly used to-day. Other formulae have +been proposed, some of which are more accurate for certain specific +classes of fuel, but all have their basis in Dulong's formula, the +accepted modified form of which is: + +Heat units in B. t. u. per pound of dry fuel = + + O +14,600 C + 62,000(H - -) + 4000 S (18) + 8 + +where C, H, O and S are the proportionate parts by weight of carbon, +hydrogen, oxygen and sulphur. + +Assume a coal of the composition given. Substituting in this formula +(18), + +Heating value per pound of dry coal + + ( .0304) += 14,600 × .8445 + 62,000 (.0425 - -----) + 4000 × .0091 = 14,765 B. t. u. + ( 8 ) + +This coal, by a calorimetric test, showed 14,843 B. t. u., and from a +comparison the degree of accuracy of the formula will be noted. + +The investigation of Lord and Haas in this country, Mabler in France, +and Bunte in Germany, all show that Dulong's formula gives results +nearly identical with those obtained from calorimetric tests and may be +safely applied to all solid fuels except cannel coal, lignite, turf and +wood, provided the ultimate analysis is correct. This practically limits +its use to coal. The limiting features are the presence of hydrogen and +carbon united in the form of hydrocarbons. Such hydrocarbons are present +in coals in small quantities, but they have positive and negative heats +of combination, and in coals these appear to offset each other, +certainly sufficiently to apply the formula to such fuels. + +High and Low Heat Value of Fuels--In any fuel containing hydrogen the +calorific value as found by the calorimeter is higher than that +obtainable under most working conditions in boiler practice by an amount +equal to the latent heat of the volatilization of water. This heat would +reappear when the vapor was condensed, though in ordinary practice the +vapor passes away uncondensed. This fact gives rise to a distinction in +heat values into the so-called "higher" and "lower" calorific values. +The higher value, _i. e._, the one determined by the calorimeter, is the +only scientific unit, is the value which should be used in boiler +testing work, and is the one recommended by the American Society of +Mechanical Engineers. + +There is no absolute measure of the lower heat of combustion, and in +view of the wide difference in opinion among physicists as to the +deductions to be made from the higher or absolute unit in this +determination, the lower value must be considered an artificial unit. +The lower value entails the use of an ultimate analysis and involves +assumptions that would make the employment of such a unit impracticable +for commercial work. The use of the low value may also lead to error and +is in no way to be recommended for boiler practice. + +An example of its illogical use may be shown by the consideration of a +boiler operated in connection with a special economizer where the vapor +produced by hydrogen is partially condensed by the economizer. If the +low value were used in computing the boiler efficiency, it is obvious +that the total efficiency of the combined boiler and economizer must be +in error through crediting the combination with the heat imparted in +condensing the vapor and not charging such heat to the heat value of the +coal. + +Heating Value of Gaseous Fuels--The method of computing calorific values +from an ultimate analysis is particularly adapted to solid fuels, with +the exceptions already noted. The heating value of gaseous fuels may be +calculated by Dulong's formula provided another term is added to provide +for any carbon monoxide present. Such a method, however, involves the +separating of the constituent gases into their elementary gases, which +is oftentimes difficult and liable to simple arithmetical error. As the +combustible portion of gaseous fuels is ordinarily composed of hydrogen, +carbon monoxide and certain hydrocarbons, a determination of the +calorific value is much more readily obtained by a separation into their +constituent gases and a computation of the calorific value from a table +of such values of the constituents. Table 37 gives the calorific value +of the more common combustible gases, together with the theoretical +amount of air required for their combustion. + + TABLE 37 + + WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES + AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE + WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION + ++---------------+----------+------+-----+------+----------+-----------+ +| Gas | Symbol |Cubic |B.t.u|B.t.u.|Cubic Feet|Cubic Feet | +| | | Feet | per | per | of Air | of Air | +| | |of Gas|Pound|Cubic | Required | Required | +| | | per | | Foot |per Pound | Per Cubic | +| | |Pound | | | of Gas |Foot of Gas| ++---------------+----------+------+-----+------+----------+-----------+ +|Hydrogen | H |177.90|62000| 349 | 428.25 | 2.41 | +|Carbon Monoxide| CO | 12.81| 4450| 347 | 30.60 | 2.39 | +|Methane |CH_{4} | 22.37|23550| 1053 | 214.00 | 9.57 | +|Acetylene |C_{2}H_{2}| 13.79|21465| 1556 | 164.87 | 11.93 | +|Olefiant Gas |C_{2}H_{4}| 12.80|21440| 1675 | 183.60 | 14.33 | +|Ethane |C_{2}H_{6}| 11.94|22230| 1862 | 199.88 | 16.74 | ++---------------+----------+------+-----+------+----------+-----------+ + +In applying this table, as gas analyses may be reported either by weight +or volume, there is given in Table 33[36] a method of changing from +volumetric analysis to analysis by weight. + + +Examples: + + +1st. Assume a blast furnace gas, the analysis of which in percentages by +weight is, oxygen = 2.7, carbon monoxide = 19.5, carbon dioxide = 18.7, +nitrogen = 59.1. Here the only combustible gas is the carbon monoxide, +and the heat value will be, + +0.195 × 4450 = 867.75 B. t. u. per pound. + +The _net_ volume of air required to burn one pound of this gas will be, + +0.195 × 30.6 = 5.967 cubic feet. + + +2nd. Assume a natural gas, the analysis of which in percentages by +volume is oxygen = 0.40, carbon monoxide = 0.95, carbon dioxide = 0.34, +olefiant gas (C_{2}H_{4}) = 0.66, ethane (C_{2}H_{6}) = 3.55, marsh gas +(CH_{4}) = 72.15 and hydrogen = 21.95. All but the oxygen and the carbon +dioxide are combustibles, and the heat per cubic foot will be, + +From CO = 0.0095 × 347 = 3.30 + C_{2}H_{4} = 0.0066 × 1675 = 11.05 + C_{2}H_{6} = 0.0355 × 1862 = 66.10 + CH_{4} = 0.7215 × 1050 = 757.58 + H = 0.2195 × 349 = 76.61 + ------ + B. t. u. per cubic foot 914.64 + +The _net_ air required for combustion of one cubic foot of the gas will +be, + +CO = 0.0095 × 2.39 = 0.02 +C_{2}H_{4} = 0.0066 × 14.33 = 0.09 +C_{2}H_{6} = 0.0355 × 16.74 = 0.59 +CH_{4} = 0.7215 × 9.57 = 6.90 +H = 0.2195 × 2.41 = 0.53 + ---- + Total net air per cubic foot 8.13 + +Proximate Analysis--The proximate analysis of a fuel gives its +proportions by weight of fixed carbon, volatile combustible matter, +moisture and ash. A method of making such an analysis which has been +found to give eminently satisfactory results is described below. + +From the coal sample obtained on the boiler trial, an average sample of +approximately 40 grams is broken up and weighed. A good means of +reducing such a sample is passing it through an ordinary coffee mill. +This sample should be placed in a double-walled air bath, which should +be kept at an approximately constant temperature of 105 degrees +centigrade, the sample being weighed at intervals until a minimum is +reached. The percentage of moisture can be calculated from the loss in +such a drying. + +For the determination of the remainder of the analysis, and the heating +value of the fuel, a portion of this dried sample should be thoroughly +pulverized, and if it is to be kept, should be placed in an air-tight +receptacle. One gram of the pulverized sample should be weighed into a +porcelain crucible equipped with a well fitting lid. This crucible +should be supported on a platinum triangle and heated for seven minutes +over the full flame of a Bunsen burner. At the end of such time the +sample should be placed in a desiccator containing calcium chloride, and +when cooled should be weighed. From the loss the percentage of volatile +combustible matter may be readily calculated. + +The same sample from which the volatile matter has been driven should be +used in the determination of the percentage of ash. This percentage is +obtained by burning the fixed carbon over a Bunsen burner or in a muffle +furnace. The burning should be kept up until a constant weight is +secured, and it may be assisted by stirring with a platinum rod. The +weight of the residue determines the percentage of ash, and the +percentage of fixed carbon is easily calculated from the loss during the +determination of ash after the volatile matter has been driven off. + +Proximate analyses may be made and reported on a moist or dry basis. The +dry basis is that ordinarily accepted, and this is the basis adopted +throughout this book. The method of converting from a moist to a dry +basis is the same as described in the case of an ultimate analysis. A +proximate analysis is easily made, gives information as to the general +characteristics of a fuel and of its _relative_ heating value. + +Table 38 gives the proximate analysis and calorific value of a number of +representative coals found in the United States. + + TABLE 38 + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN COALS + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | +____|_______|________________|________________|_______________|_____________| + | | | | + | | ANTHRACITES | | +____|_______|_________________________________________________|_____________| + | | | | | | + 1 | Pa. | Carbon | Lehigh | Beaver Meadow | | + 2 | Pa. | Dauphin | Schuylkill | | Buckwheat | + 3 | Pa. | Lackawanna | Wyoming | Belleview | No. 2 Buck. | + 4 | Pa. | Lackawanna | Wyoming | Johnson | Culm. | + 5 | Pa. | Luzerne | Wyoming | Pittston | No. 2 Buck. | + 6 | Pa. | Luzerne | Wyoming | Mammoth | Large | + 7 | Pa. | Luzerne | Wyoming | Exeter | Rice | + 8 | Pa. | Northumberland | Schuylkill | Treverton | | + 9 | Pa. | Schuylkill | Schuylkill | Buck Mountain | | + 10 | Pa. | Schuylkill | | York Farm | Buckwheat | + 11 | Pa. | | | Victoria | Buckwheat | + 12 | Pa. | Carbon | Lehigh | Lehigh & | Buck. & Pea | + | | | | Wilkes C. Co. | | + 13 | Pa. | Carbon | Lehigh | | Buckwheat | + 14 | Pa. | Lackawanna | |Del. & Hud. Co.| No. 1 Buck. | +____|_______|________________|________________|_______________|_____________| + | | | | + | | SEMI-ANTHRACITES | | +____|_______|_________________________________________________|_____________| + | | | | | | + 15 | Pa. | Lycoming | Loyalsock | | | + 16 | Pa. | Sullivan | | Lopez | | + 17 | Pa. | Sullivan | Bernice | | | +____|_______|________________|________________|_______________|_____________| + | | | | + | | SEMI-BITUMINOUS | | +____|_______|_________________________________________________|_____________| + | | | | | | + 18 | Md. | Alleghany | Big Vein, | | | + | | | George's Crk. | | | + 19 | Md. | Alleghany | George's Creek | | | + 20 | Md. | Alleghany | George's Creek | | | + 21 | Md. | Alleghany | George's Creek | Ocean No. 7 | Mine run | + 22 | Md. | Alleghany | Cumberland | | | + 23 | Md. | Garrett | | Washington | Mine run | + | | | | No. 3 | | + 24 | Pa. | Bradford | | Long Valley | | + 25 | Pa. | Tioga | | Antrim | | + 26 | Pa. | Cambria | "B" or Miller | Soriman Shaft | | + | | | | C. Co. | | + 27 | Pa. | Cambria | "B" or Miller | Henrietta | | + 28 | Pa. | Cambria | "B" or Miller | Penker | | + 29 | Pa. | Cambria | "B" or Miller | Lancashire | | + 30 | Pa. | Cambria | Lower | Penn. C. & C. | Mine run | + | | | Kittanning | Co. No. 3 | | + 31 | Pa. | Cambria | Upper | Valley | Mine run | + | | | Kittanning | | | + 32 | Pa. | Clearfield | Lower | Eureka | Mine run | + | | | Kittanning | | | + 33 | Pa. | Clearfield | | Ghem | Mine run | + 34 | Pa. | Clearfield | | Osceola | | + 35 | Pa. | Clearfield | Reynoldsville | | | + 36 | Pa. | Clearfield | Atlantic- | | Mine run | + | | | Clearfield | | | + 37 | Pa. | Huntington | Barnet & Fulton| Carbon | Mine run | + 38 | Pa. | Huntington | | Rock Hill | Mine run | + 39 | Pa. | Somerset | Lower | Kimmelton | Mine run | + | | | Kittanning | | | + 40 | Pa. | Somerset | "C" Prime Vein | Jenner | Mine run | +____|_______|________________|________________|_______________|_____________| + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 1 | 1.50 | 2.41 | 90.30 | 7.29 | | Gale | + 2 | 2.15 | 12.88 | 78.23 | 8.89 | 13137 | Whitham | + 3 | 8.29 | 7.81 | 77.19 | 15.00 | 12341 | Sadtler | + 4 | 13.90 | 11.16 | 65.96 | 22.88 | 10591 | B. & W. Co. | + 5 | 3.66 | 4.40 | 78.96 | 16.64 | 12865 | B. & W. Co. | + 6 | 4.00 | 3.44 | 90.59 | 5.97 | 13720 | Carpenter | + 7 | 0.25 | 8.18 | 79.61 | 12.21 | 12400 | B. & W. Co. | + 8 | 0.84 | 6.73 | 86.39 | 6.88 | | Isherwood | + 9 | | 3.17 | 92.41 | 4.42 | 14220 | Carpenter | + 10 | 0.81 | 5.51 | 75.90 | 18.59 | 11430 | | + 11 | 4.30 | 0.55 | 86.73 | 12.72 | 12642 | B. & W. Co. | + 12 | 1.57 | 6.27 | 66.53 | 27.20 | 12848 | B. & W. Co. | + | | | | | | | + 13 | | 5.00 | 81.00 | 14.00 | 11800 | Carpenter | + 14 | 6.20 | | | 11.60 | 12100 | Denton | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 15 | 1.30 | 8.72 | 84.44 | 6.84 | | | + 16 | 5.48 | 7.53 | 81.00 | 11.47 | 13547 | B. & W. Co. | + 17 | 1.29 | 8.21 | 84.43 | 7.36 | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 18 | 3.50 | 21.33 | 72.47 | 6.20 | 14682 | B. & W. Co. | + | | | | | | | + 19 | 3.63 | 16.27 | 76.93 | 6.80 | 14695 | B. & W. Co. | + 20 | 2.28 | 19.43 | 77.44 | 6.13 | 14793 | B. & W. Co. | + 21 | 1.13 | | | | 14451 | B. & W. Co. | + 22 | 1.50 | 17.26 | 76.65 | 6.09 | 14700 | | + 23 | 2.33 | 14.38 | 74.93 | 10.49 | 14033 | U. S. Geo. S.| + | | | | | | [37] | + 24 | 1.55 | 20.33 | 68.38 | 11.29 | 12965 | | + 25 | 2.19 | 18.43 | 71.87 | 9.70 | 13500 | | + 26 | 3.40 | 20.70 | 71.84 | 7.46 | 14484 | N. Y. Ed. Co.| + | | | | | | | + 27 | 1.23 | 18.37 | 75.28 | 6.45 | 14770 | So. Eng. Co. | + 28 | 3.64 | 21.34 | 70.48 | 8.18 | 14401 | B. & W. Co. | + 29 | 4.38 | 21.20 | 70.27 | 8.53 | 14453 | B. & W. Co. | + 30 | 3.51 | 17.43 | 75.69 | 6.88 | 14279 | U. S. Geo. S.| + | | | | | | | + 31 | 3.40 | 14.89 | 75.03 | 10.08 | 14152 | B. & W. Co. | + | | | | | | | + 32 | 5.90 | 16.71 | 77.22 | 6.07 | 14843 | U. S. Geo. S.| + | | | | | | | + 33 | 3.43 | 17.53 | 69.67 | 12.80 | 13744 | B. & W. Co. | + 34 | 1.24 | 25.43 | 68.56 | 6.01 | 13589 | B. & W. Co. | + 35 | 2.91 | 21.55 | 69.03 | 9.42 | 14685 | B. & W. Co. | + 36 | 1.55 | 23.36 | 71.15 | 5.94 | 13963 | Whitham | + | | | | | | | + 37 | 4.50 | 18.34 | 73.06 | 8.60 | 13770 | B. & W. Co. | + 38 | 5.91 | 17.58 | 73.44 | 8.99 | 14105 | B. & W. Co. | + 39 | 3.09 | 17.84 | 70.47 | 11.69 | 13424 | U. S. Geo. S.| + | | | | | | | + 40 | 9.37 | 16.47 | 75.76 | 7.77 | 14507 | P. R. R. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | +____|_______|________________|________________|_______________|_____________| + | | | | | | + 41 | W. Va.| Fayette | New River | Rush Run | Mine run | + 42 | W. Va.| Fayette | New River | Loup Creek | | + 43 | W. Va.| Fayette | New River | | Slack | + 44 | W. Va.| Fayette | New River | | Mine run | + 45 | W. Va.| Fayette | New River | Rush Run | Mine run | + 46 | W. Va.| McDowell | Pocahontas | Zenith | Mine run | + | | | No. 3 | | | + 47 | W. Va.| McDowell | Tug River | Big Sandy | Mine run | + 48 | W. Va.| Mercer | Pocahontas | Mora | Lump | + 49 | W. Va.| Mineral | Elk Garden | | | + 50 | W. Va.| McDowell | Pocahontas | Flat Top | Mine run | + 51 | W. Va.| McDowell | Pocahontas | Flat Top | Slack | + 52 | W. Va.| McDowell | Pocahontas | Flat Top | Lump | +____|_______|________________|________________|_______________|_____________| + | | | | + | | BITUMINOUS | | +____|_______|_________________________________________________|_____________| + | | | | | | + 53 | Ala. | Bibb | Cahaba | Hill Creek | Mine run | + 54 | Ala. | Jefferson | Pratt | Pratt No. 13 | | + 55 | Ala. | Jefferson | Pratt | Warner | Mine run | + 56 | Ala. | Jefferson | | Coalburg | Mine run | + 57 | Ala. | Walker | Horse Creek | Ivy C. & I. | Nut | + | | | | Co. No. 8 | | + 58 | Ala. | Walker | Jagger | Galloway C. | Mine run | + | | | | Co. No. 5 | | + 59 | Ark. | Franklin | Denning | Western No. 4 | Nut | + 60 | Ark. | Sebastian | Jenny Lind | Mine No. 12 | Lump | + 61 | Ark. | Sebastian | Huntington | Cherokee | Mine run | + 62 | Col. | Boulder | South Platte | Lafayette | Mine run | + 63 | Col. | Boulder | Laramie | Simson | Mine run | + 64 | Col. | Fremont | Canon City | Chandler | Nut and | + | | | | | Slack | + 65 | Col. | Las Animas | Trinidad | Hastings | Nut | + 66 | Col. | Las Animas | Trinidad | Moreley | Slack | + 67 | Col. | Routt | Yampa | Oak Creek | | + 68 | Ill. | Christian | Pana | Penwell Col. | Lump | + 69 | Ill. | Franklin | No. 6 | Benton | Egg | + 70 | Ill. | Franklin | Big Muddy | Zeigler | ¾ inch | + 71 | Ill. | Jackson | Big Muddy | | | + 72 | Ill. | La Salle | Streator | | | + 73 | Ill. | La Salle | Streator | Marseilles | Mine run | + 74 | Ill. | Macoupin | Nilwood | Mine No. 2 | Screenings | + 75 | Ill. | Macoupin | Mt. Olive | Mine No. 2 | Mine run | + 76 | Ill. | Madison | Belleville | Donk Bros. | Lump | + 77 | Ill. | Madison | Glen Carbon | | Mine run | + 78 | Ill. | Marion | | Odin | Lump | + 79 | Ill. | Mercer | Gilchrist | | Screenings | + 80 | Ill. | Montgomery | Pana or No. 5 | Coffeen | Mine run | + 81 | Ill. | Peoria | No. 5 | Empire | | + 82 | Ill. | Perry | Du Quoin | Number 1 | Screenings | +____|_______|________________|________________|_______________|_____________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 41 | 2.14 | 22.87 | 71.56 | 5.57 | 14959 | U. S. Geo. S.| + 42 | 0.55 | 19.36 | 78.48 | 2.16 | 14975 | Hill | + 43 | 6.66 | 20.94 | 73.16 | 5.90 | 14412 | B. & W. Co. | + 44 | 2.16 | 17.82 | 75.66 | 6.52 | 14786 | B. & W. Co. | + 45 | 0.94 | 22.16 | 75.85 | 1.99 | 15007 | B. & W. Co. | + 46 | 4.85 | 17.14 | 76.54 | 6.32 | 14480 | U. S. Geo. S.| + | | | | | | | + 47 | 1.58 | 18.55 | 76.44 | 4.91 | 15170 | U. S. Geo. S.| + 48 | 1.74 | 18.55 | 75.15 | 6.30 | 15015 | U. S. Geo. S.| + 49 | 2.10 | 15.70 | 75.40 | 8.90 | 14195 | B. & W. Co. | + 50 | 0.52 | 24.02 | 74.59 | 1.39 | 14490 | B. & W. Co. | + 51 | 3.24 | 15.33 | 77.60 | 7.07 | 14653 | B. & W. Co. | + 52 | 3.63 | 16.03 | 78.04 | 5.93 | 14956 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 53 | 6.19 | 28.58 | 55.60 | 15.82 | 12576 | B. & W. Co. | + 54 | 4.29 | 25.78 | 67.68 | 6.54 | 14482 | B. & W. Co. | + 55 | 2.51 | 27.80 | 61.50 | 10.70 | 13628 | U. S. Geo. S.| + 56 | 0.94 | 31.34 | 65.65 | 3.01 | 14513 | B. & W. Co. | + 57 | 2.56 | 31.82 | 53.89 | 14.29 | 12937 | U. S. Geo. S.| + | | | | | | | + 58 | 4.83 | 34.65 | 51.12 | 14.03 | 12976 | U. S. Geo. S.| + | | | | | | | + 59 | 2.22 | 12.83 | 75.35 | 11.82 | | U. S. Geo. S.| + 60 | 1.07 | 17.04 | 74.45 | 8.51 | 14252 | U. S. Geo. S.| + 61 | 0.97 | 19.87 | 70.30 | 9.83 | 14159 | U. S. Geo. S.| + 62 | 19.48 | 38.80 | 49.00 | 12.20 | 11939 | B. & W. Co. | + 63 | 19.78 | 44.69 | 48.62 | 6.69 | 12577 | U. S. Geo. S.| + 64 | 9.37 | 38.10 | 51.75 | 10.15 | 11850 | B. & W. Co. | + | | | | | | | + 65 | 2.15 | 31.07 | 53.40 | 15.53 | 12547 | B. & W. Co. | + 66 | 1.88 | 28.47 | 55.58 | 15.95 | 12703 | B. & W. Co. | + 67 | 6.67 | 42.91 | 55.64 | 1.45 | | Hill | + 68 | 8.05 | 43.67 | 49.97 | 6.36 | 10900 | Jones | + 69 | 8.31 | 34.52 | 54.05 | 11.43 | 11727 | U. S. Geo. S.| + 70 | 13.28 | 31.97 | 57.37 | 10.66 | 12857 | U. S. Geo. S.| + 71 | 4.85 | 31.55 | 62.19 | 6.26 | 11466 | Breckenridge | + 72 | 8.40 | 41.76 | 51.42 | 6.82 | 11727 | Breckenridge | + 73 | 12.98 | 43.73 | 49.13 | 7.14 | 10899 | B. & W. Co. | + 74 | 13.34 | 34.75 | 44.55 | 20.70 | 10781 | B. & W. Co. | + 75 | 13.54 | 41.28 | 46.30 | 12.42 | 10807 | U. S. Geo. S.| + 76 | 13.47 | 38.69 | 48.07 | 13.24 | 12427 | U. S. Geo. S.| + 77 | 9.78 | 38.18 | 51.52 | 10.30 | 11672 | Bryan | + 78 | 6.20 | 42.91 | 49.06 | 8.03 | 11880 | Breckenridge | + 79 | 8.50 | 36.17 | 41.64 | 22.19 | 10497 | Breckenridge | + 80 | 11.93 | 34.05 | 49.85 | 16.10 | 10303 | U. S. Geo. S.| + 81 | 17.64 | 31.91 | 46.17 | 21.92 | 10705 | B. & W. Co. | + 82 | 9.81 | 33.67 | 48.36 | 17.97 | 11229 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | + |_______|________________|________________|_______________|_____________| + | | | | | | + 83 | Ill. | Perry | Du Quoin | Willis | Mine run | + 84 | Ill. | Sangamon | | Pawnee | Slack | + 85 | Ill. | St. Clair | Standard | Nigger Hollow | Mine run | + 86 | Ill. | St. Clair | Standard | Maryville | Mine run | + 87 | Ill. | Williamson | Big Muddy | Daws | Mine run | + 88 | Ill. | Williamson | Carterville | Carterville | | + | | | or No. 7 | | | + 89 | Ill. | Williamson | Carterville | Burr | Nut, Pea | + | | | or No. 7 | | and Slack | + 90 | Ind. | Brazil | Brazil | Gartside | Block | + 91 | Ind. | Clay | | Louise | Block | + 92 | Ind. | Green | Island City | | Mine run | + 93 | Ind. | Knox | Vein No. 5 | Tecumseh | Mine run | + 94 | Ind. | Parke | Vein No. 6 | Parke Coal Co.| Lump | + 95 | Ind. | Sullivan | Sullivan No. 6 | Mildred | Washed | + 96 | Ind. | Vigo | Number 6 | Fontanet | Mine run | + 97 | Ind. | Vigo | Number 7 | Red Bird | Mine run | + 98 | Iowa | Appanoose | Mystic | Mine No. 3 | Lump | + 99 | Iowa | Lucas | Lucas | Inland No. 1 | Mine run | +100 | Iowa | Marion | Big Vein | Liberty No. 5 | Mine run | +101 | Iowa | Polk | Third Seam | Altoona No. 4 | Lump | +102 | Iowa | Wapello | Wapello | | Lump | +103 | Kan. | Cherokee | Weir Pittsburgh| Southwestern | Lump | + | | | | Dev. Co. | | +104 | Kan. | Cherokee | Cherokee | | Screenings | +105 | Kan. | Cherokee | Cherokee | | Lump | +106 | Kan. | Linn | Boicourt | | Lump | +107 | Ky. | Bell | Straight Creek | Str. Ck. C. & | Mine run | + | | | | C. Co. | | +108 | Ky. | Hopkins | Bed No. 9 | Earlington | Lump | +109 | Ky. | Hopkins | Bed No. 9 | Barnsley | Mine run | +110 | Ky. | Hopkins | Vein No. 14 | Nebo |Pea and Slack| +111 | Ky. | Johnson | Vein No. 1 | Miller's Creek| Mine run | +112 | Ky. | Mulenburg | Bed No. 9 | Pierce |Pea and Slack| +113 | Ky. | Pulaski | | Greensburg | | +114 | Ky. | Webster | Bed No. 9 | |Pea and Slack| +115 | Ky. | Whitley | | Jellico |Nut and Slack| +116 | Mo. | Adair | | Danforth | Mine run | +117 | Mo. | Bates | Rich Hill | New Home | Mine run | +118 | Mo. | Clay | Lexington | Mo. City Coal | | + | | | | Co. | | +119 | Mo. | Lafayette | Waverly | Buckthorn | | +120 | Mo. | Lafayette | Waverly | Higbee | | +121 | Mo. | Linn | Bevier | Marceline | | +122 | Mo. | Macon | Bevier | Northwest | | + | | | | Coal Co. | | +123 | Mo. | Morgan | Morgan Co. | Morgan Co. | Mine run | + | | | | Coal Co. | | +124 | Mo. | Putnam | Mendotta | Mendotta No. 8| | +125 | N.Mex.| McKinley | Gallup | Gibson |Pea and Slack| +____|_______|________________|________________|_______________|_____________| + +______________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 83 | 7.22 | 33.06 | 53.97 | 12.97 | 11352 | U. S. Geo. S.| + 84 | 4.81 | 41.53 | 39.62 | 18.85 | 10220 | Jones | + 85 | 14.39 | 32.90 | 44.84 | 22.26 | 11059 | B. & W. Co. | + 86 | 15.71 | 38.10 | 41.10 | 20.80 | 10999 | B. & W. Co. | + 87 | 8.17 | 34.33 | 52.50 | 13.17 | 12643 | U. S. Geo. S.| + 88 | 4.66 | 35.65 | 56.86 | 7.49 | 12286 | Univ. of Ill.| + | | | | | | | + 89 | 11.91 | 33.70 | 55.90 | 10.40 | 12932 | B. & W. Co. | + | | | | | | | + 90 | 2.83 | 40.03 | 51.97 | 8.00 | 13375 | Stillman | + 91 | 0.83 | 39.70 | 52.28 | 8.02 | 13248 | Jones | + 92 | 6.17 | 35.42 | 53.55 | 11.03 | 11916 | Dearborn | + 93 | 10.73 | 35.75 | 54.46 | 9.79 | 12911 | B. & W. Co. | + 94 | 10.72 | 44.02 | 46.33 | 9.65 | 11767 | U. S. Geo. S.| + 95 | 16.59 | 42.17 | 48.44 | 9.59 | 13377 | U. S. Geo. S.| + 96 | 2.28 | 34.95 | 50.50 | 14.55 | 11920 | Dearborn | + 97 | 11.62 | 41.17 | 46.76 | 12.07 | 12740 | U. S. Geo. S.| + 98 | 13.48 | 39.40 | 43.09 | 17.51 | 11678 | U. S. Geo. S.| + 99 | 16.01 | 37.82 | 46.24 | 15.94 | 11963 | U. S. Geo. S.| +100 | 14.88 | 41.53 | 39.63 | 18.84 | 11443 | U. S. Geo. S.| +101 | 12.44 | 41.27 | 40.86 | 17.87 | 11671 | U. S. Geo. S.| +102 | 8.69 | 36.23 | 43.68 | 20.09 | 11443 | U. S. Geo. S.| +103 | 4.31 | 33.88 | 53.67 | 12.45 | 13144 | U. S. Geo. S.| + | | | | | | | +104 | 6.16 | 35.56 | 46.90 | 17.54 | 10175 | Jones | +105 | 1.81 | 34.77 | 52.77 | 12.46 | 12557 | Jones | +106 | 4.74 | 36.59 | 47.07 | 16.34 | 10392 | Jones | +107 | 2.89 | 36.67 | 57.24 | 6.09 | 14362 | U. S. Geo. S.| + | | | | | | | +108 | 6.89 | 40.30 | 55.16 | 4.54 | 13381 | St. Col. Ky. | +109 | 7.92 | 40.53 | 48.70 | 10.77 | 13036 | U. S. Geo. S.| +110 | 8.02 | 31.91 | 54.02 | 14.07 | 12448 | B. & W. Co. | +111 | 5.12 | 38.46 | 58.63 | 2.91 | 13743 | U. S. Geo. S.| +112 | 9.22 | 33.94 | 52.18 | 13.88 | 12229 | B. & W. Co. | +113 | 2.80 | 26.54 | 63.58 | 9.88 | 14095 | N. Y. Ed. Co.| +114 | 7.30 | 31.08 | 60.72 | 8.20 | 13600 | B. & W. Co. | +115 | 3.82 | 31.82 | 58.78 | 9.40 | 13175 | B. & W. Co. | +116 | 9.00 | 30.55 | 46.26 | 23.19 | 9889 | B. & W. Co. | +117 | 7.28 | 37.62 | 43.83 | 18.55 | 12109 | U. S. Geo. S.| +118 | 12.45 | 39.39 | 48.47 | 12.14 | 12875 | Univ. of Mo. | + | | | | | | | +119 | 8.58 | 41.78 | 45.99 | 12.23 | 12735 | Univ. of Mo. | +120 | 10.84 | 31.72 | 55.29 | 12.99 | 12500 | Univ. of Mo. | +121 | 9.45 | 36.72 | 52.20 | 11.08 | 13180 | Univ. of Mo. | +122 | 13.09 | 37.83 | 42.95 | 19.22 | 11500 | U. S. Geo. S.| + | | | | | | | +123 | 12.24 | 45.69 | 47.98 | 6.33 | 14197 | U. S. Geo. S.| + | | | | | | | +124 | 20.78 | 39.36 | 50.00 | 10.64 | 12602 | U. S. Geo. S.| +125 | 12.17 | 36.31 | 51.17 | 12.52 | 12126 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | + |_______|________________|________________|_______________|_____________| + | | | | | | +126 | Ohio | Athens | Hocking Valley | Sunday Creek | Slack | +127 | Ohio | Belmont | Pittsburgh | Neff Coal Co. | Mine run | + | | | No. 8 | | | +128 | Ohio | Columbiana | Middle | Palestine | | + | | | Kittanning | | | +129 | Ohio | Coshocton | Middle | Morgan Run | Mine run | + | | | Kittanning | | | +130 | Ohio | Guernsey | Vein No. 7 | Little Kate | | +131 | Ohio | Hocking | Hocking Valley | | Lump | +132 | Ohio | Hocking | Hocking Valley | | | +133 | Ohio | Jackson | Brookville | Superior | Mine run | + | | | | Coal Co. | | +134 | Ohio | Jackson | Lower | Superior | Mine run | + | | | Kittanning | Coal Co. | | +135 | Ohio | Jackson | Quakertown | Wellston | | +136 | Ohio | Jefferson | Pittsburgh | Crow Hollow | ¾ inch | + | | | or No. 8 | | | +137 | Ohio | Jefferson | Pittsburgh | Rush Run No. 1| ¾ inch | + | | | or No. 8 | | | +138 | Ohio | Perry | Hocking | Congo | | +139 | Ohio | Stark | Massillon | | Slack | +140 | Ohio | Vinton | Brookville | Clarion | Nut and | + | | | or No. 4 | | Slack | +141 | Okla. | Choctaw | McAlester | Edwards No. 1 | Mine run | +142 | Okla. | Choctaw | McAlester | Adamson | Slack | +143 | Okla. | Creek | | Henrietta | Lump and | + | | | | | Slack | +144 | Pa. | Allegheny | Pittsburgh | | Slack | + | | | 3rd Pool | | | +145 | Pa. | Allegheny | Monongahela | Turtle Creek | | +146 | Pa. | Allegheny | Pittsburgh | Bertha | ¾ inch | +147 | Pa. | Cambria | | Beach Creek | Slack | +148 | Pa. | Cambria | Miller | Lincoln | Mine run | +149 | Pa. | Clarion | Lower Freeport | | | +150 | Pa. | Fayette | Connellsville | | Slack | +151 | Pa. | Greene | Youghiogheny | | Lump | +152 | Pa. | Greene | Westmoreland | | Screenings | +153 | Pa. | Indiana | | Iselin | Mine run | +154 | Pa. | Jefferson | | Punxsutawney | Mine run | +155 | Pa. | Lawrence | Middle | | | + | | | Kittanning | | | +156 | Pa. | Mercer | Taylor | | | +157 | Pa. | Washington | Pittsburgh | Ellsworth | | +158 | Pa. | Washington | Youghiogheny | Anderson | ¾ inch | +159 | Pa. | Westmoreland | Pittsburgh | Scott Haven | Lump | +160 | Tenn. | Campbell | Jellico | | | +161 | Tenn. | Claiborne | Mingo | | | +162 | Tenn. | Marion | | Etna | | +163 | Tenn. | Morgan | Brushy Mt. | | | +164 | Tenn. | Scott | Glen Mary No. 4| Glen Mary | | +165 | Tex. | Maverick | | Eagle Pass | | +166 | Tex. | Paolo Pinto | | Thurber | Mine run | +167 | Tex. | Paolo Pinto | | Strawn | Mine run | +168 | Va. | Henrico | | Gayton | | +____|_______|________________|________________|_______________|_____________| + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | +126 | 12.16 | 34.64 | 53.10 | 12.26 | 12214 | | +127 | 5.31 | 38.78 | 52.22 | 9.00 | 12843 | U. S. Geo. S.| + | | | | | | | +128 | 2.15 | 37.57 | 51.80 | 10.63 | 13370 | Lord & Haas | + | | | | | | | +129 | | 41.76 | 45.24 | 13.00 | 13239 | B. & W. Co. | + | | | | | | | +130 | 6.19 | 33.02 | 59.96 | 7.02 | 13634 | B. & W. Co. | +131 | 6.45 | 39.12 | 50.08 | 10.80 | 12700 | Lord & Haas | +132 | 2.60 | 40.80 | 47.60 | 11.60 | 12175 | Jones | +133 | 7.59 | 38.45 | 43.99 | 17.56 | 11704 | U. S. Geo. S.| + | | | | | | | +134 | 8.99 | 41.43 | 50.06 | 8.51 | 13113 | U. S. Geo. S.| + | | | | | | | +135 | 3.38 | 35.26 | 54.18 | 7.56 | 12506 | Hill | +136 | 4.04 | 40.08 | 52.27 | 9.65 | 13374 | U. S. Geo. S.| + | | | | | | | +137 | 4.74 | 36.08 | 54.81 | 9.11 | 13532 | U. S. Geo. S.| + | | | | | | | +138 | 6 41 | 38.33 | 46.71 | 14.96 | 12284 | B. & W. Co. | +139 | 6.67 | 40.02 | 46.46 | 13.52 | 11860 | B. & W. Co. | +140 | 2.47 | 42.38 | 50.39 | 6.23 | 13421 | U. S. Geo. S.| + | | | | | | | +141 | 4.79 | 39.18 | 49.97 | 10.85 | 13005 | U. S. Geo. S.| +142 | 4.72 | 28.54 | 58.17 | 13.29 | 12105 | B. & W. Co. | +143 | 7.65 | 36.77 | 50.14 | 13.09 | 12834 | U. S. Geo. S.| + | | | | | | | +144 | 1.77 | 32.06 | 57.11 | 10.83 | 13205 | Carpenter | + | | | | | | | +145 | 1.75 | 36.85 | 53.94 | 9.21 | 13480 | Lord & Haas | +146 | 2.61 | 35.86 | 57.81 | 6.33 | 13997 | U. S. Geo. S.| +147 | 3.01 | 32.87 | 55.86 | 11.27 | 13755 | B. & W. Co. | +148 | 5.39 | 30.83 | 61.05 | 8.12 | 13600 | B. & W. Co. | +149 | 0.54 | 35.93 | 57.66 | 6.41 | 13547 | | +150 | 1.85 | 28.73 | 63.22 | 7.95 | 13775 | Whitham | +151 | 1.25 | 32.60 | 54.70 | 12.70 | 13100 | B. & W. Co. | +152 | 11.12 | 31.67 | 55.61 | 12.72 | 13100 | P. R. R. | +153 | 2.70 | 29.33 | 63.56 | 7.11 | 14220 | B. & W. Co. | +154 | 3.38 | 29.33 | 64.93 | 5.73 | 14781 | B. & W. Co. | +155 | 0.70 | 37.06 | 56.24 | 6.70 | 13840 | Lord & Haas | + | | | | | | | +156 | 4.18 | 32.19 | 55.55 | 12.26 | 12820 | B. & W. Co. | +157 | 2.46 | 35.35 | 58.46 | 6.19 | 14013 | U. S. Geo. S.| +158 | 1.00 | 39.29 | 54.80 | 5.91 | 13729 | Jones | +159 | 4.06 | 32.91 | 59.78 | 7.31 | 13934 | B. & W. Co. | +160 | 1.80 | 37.76 | 62.12 | 1.12 | 13846 | U. S. Navy | +161 | 4.40 | 34.31 | 59.22 | 6.47 | | U. S. Geo. S.| +162 | 3.16 | 32.98 | 56.59 | 10.43 | | | +163 | 1.77 | 33.46 | 54.73 | 11.87 | 13824 | B. & W. Co. | +164 | 1.53 | 40.80 | 56.78 | 2.42 | 14625 |Ky. State Col.| +165 | 5.42 | 33.73 | 44.89 | 21.38 | 10945 | B. & W. Co. | +166 | 1.90 | 36.01 | 49.09 | 14.90 | 12760 | B. & W. Co. | +167 | 4.19 | 35.40 | 52.98 | 11.62 | 13202 | B. & W. Co. | +168 | 0.82 | 17.14 | 74.92 | 7.94 | 14363 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | + |_______|________________|________________|_______________|_____________| + | | | | | | +169 | Va. | Lee | Darby | Darby | 1½ inch | +170 | Va. | Lee | McConnel | Wilson | Mine run | +171 | Va. | Wise | Upper Banner | Coburn | 3½ inch | +172 | Va. | Rockingham | | Clover Hill | | +173 | Va. | Russel | Clinchfield | | | +174 | Va. | | Monongahela | Bernmont | | +175 | W. Va.| Harrison | Pittsburgh | Ocean | Mine run | +176 | W. Va.| Harrison | | Girard | Nut, Pea | + | | | | | and Slack | +177 | W. Va.| Kanawha | Winifrede | Winifrede | | +178 | W. Va.| Kanawha | Keystone | Keystone | Mine run | +179 | W. Va.| Logan | Island Creek | |Nut and Slack| +180 | W. Va.| Marion | Fairmont | Kingmont | | +181 | W. Va.| Mingo | Thacker | Maritime | | +182 | W. Va.| Mingo | Glen Alum | Glen Alum | Mine run | +183 | W. Va.| Preston | Bakerstown | | | +184 | W. Va.| Putnam | Pittsburgh | Black Betsy | Bug dust | +185 | W. Va.| Randolph | Upper Freeport | Coalton | Lump and Nut| +____|_______|________________|________________|_______________|_____________| + | | | | + | | LIGNITES AND LIGNITIC COALS | | +____|_______|_________________________________________________|_____________| + | | | | | | +186 | Col. | Boulder | | Rex | | +187 | Col. | El Paso | | Curtis | | +188 | Col. | El Paso | | Pike View | | +189 | Col. | Gunnison | South Platte | Mt. Carbon | | +190 | Col. | Las Animas | | Acme | | +191 | Col. | | Lehigh | | | +192 |N. Dak.| McLean | | Eckland | Mine run | +193 |N. Dak.| McLean | | Wilton | Lump | +194 |N. Dak.| McLean | | Casino | | +195 |N. Dak.| Stark | Lehigh | Lehigh | Mine run | +196 |N. Dak.| William | Williston | | Mine run | +197 |N. Dak.| William | Williston | | Mine run | +198 | Tex. | Bastrop | Bastrop | Glenham | | +199 | Tex. | Houston | Crockett | | | +200 | Tex. | Houston | | Houston C. & | | + | | | | C. Co. | | +201 | Tex. | Milam | Rockdale | Worley | | +202 | Tex. | Robertson | Calvert | Coaling No. 1 | | +203 | Tex. | Wood | Hoyt | Consumer's | | + | | | | Lig. Co. | | +204 | Tex. | Wood | Hoyt | | | +205 | Wash. | King | | Black Diamond | | +206 | Wyo. | Carbon | Hanna | | Mine run | +207 | Wyo. | Crook | Black Hills | Stilwell Coal | | + | | | | Co. | | +208 | Wyo. | Sheridan | Sheridan | Monarch | | +209 | Wyo. | Sweetwater | Rock Spring | | Screenings | +210 | Wyo. | Uinta | Adaville | Lazeart | | +____|_______|________________|________________|_______________|_____________| + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | +169 | 4.35 | 38.46 | 56.91 | 4.63 | 13939 | U. S. Geo. S.| +170 | 3.35 | 36.35 | 57.88 | 5.77 | 13931 | U. S. Geo. S.| +171 | 3.05 | 32.65 | 62.73 | 4.62 | 14470 | U. S. Geo. S.| +172 | | 31.77 | 57.98 | 10.25 | 13103 | | +173 | 2.00 | 35.72 | 56.12 | 8.16 | 14200 | | +174 | | 32.00 | 59.90 | 8.10 | 13424 | Carpenter | +175 | 2.47 | 39.35 | 52.78 | 7.87 | 14202 | U. S. Geo. S.| +176 | | 36.66 | 57.49 | 5.85 | 14548 | B. & W. Co. | + | | | | | | | +177 | 1.05 | 32.74 | 64.38 | 2.88 | 14111 | Hill | +178 | 2.21 | 33.29 | 58.61 | 8.10 | 14202 | U. S. Geo. S.| +179 | 1.12 | 38.61 | 55.91 | 5.48 | 14273 | Hill | +180 | 1.90 | 35.31 | 57.34 | 7.35 | 14198 | U. S. Geo. S.| +181 | 0.68 | 31.89 | 63.48 | 4.63 | 14126 | Hill | +182 | 3.02 | 33.81 | 59.45 | 6.74 | 14414 | U. S. Geo. S.| +183 | 4.14 | 29.09 | 63.50 | 7.41 | 14546 | U. S. Geo. S.| +184 | 7.41 | 32.84 | 53.96 | 13.20 | 12568 | B. & W. Co. | +185 | 2.11 | 29.57 | 59.93 | 10.50 | 13854 | U. S. Geo. S.| +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | +186 | 16.05 | 42.12 | 47.97 | 9.91 | 10678 | B. & W. Co. | +187 | 23.25 | 42.11 | 49.38 | 8.51 | 11090 | B. & W. Co. | +188 | 23.77 | 48.70 | 41.47 | 9.83 | 10629 | B. & W. Co. | +189 | 20.38 | 46.38 | 47.50 | 6.12 | | | +190 | 16.74 | 47.90 | 44.60 | 7.50 | |Col. Sc. of M.| +191 | 18.30 | 45.29 | 44.67 | 10.04 | | | +192 | 29.65 | 45.56 | 47.05 | 7.39 | 10553 | Lord | +193 | 35.96 | 49.84 | 38.05 | 12.11 | 11036 | U. S. Geo. S.| +194 | 29.65 | 46.56 | 38.70 | 14.74 | | Lord | +195 | 35.84 | 43.84 | 39.59 | 16.57 | 10121 | U. S. Geo. S.| +196 | 41.76 | 39.37 | 48.09 | 12.54 | 10121 | B. & W. Co. | +197 | 42.74 | 40.83 | 47.79 | 11.38 | 10271 | B. & W. Co. | +198 | 32.77 | 42.76 | 36.88 | 20.36 | 8958 | B. & W. Co. | +199 | 23.27 | 40.95 | 38.37 | 20.68 | 10886 | U. S. Geo. S.| +200 | 31.48 | 46.93 | 34.40 | 18.87 | 10176 | B. & W. Co. | + | | | | | | | +201 | 32.48 | 43.04 | 41.14 | 15.82 | 10021 | B. & W. Co. | +202 | 32.01 | 43.70 | 43.08 | 13.22 | 10753 | B. & W. Co. | +203 | 33.98 | 46.97 | 41.40 | 11.63 | 10600 | U. S. Geo. S.| + | | | | | | | +204 | 30.25 | 43.27 | 41.46 | 15.27 | 10597 | | +205 | 3.71 | 48.72 | 46.56 | 4.72 | | Gale | +206 | 6.44 | 51.32 | 43.00 | 5.68 | 11607 | B. & W. Co. | +207 | 19.08 | 45.21 | 46.42 | 8.37 | 12641 | U. S. Geo. S.| + | | | | | | | +208 | 21.18 | 51.87 | 40.43 | 7.70 | 12316 | U. S. Geo. S.| +209 | 7.70 | 38.57 | 56.99 | 4.44 | 12534 | B. & W. Co. | +210 | 19.15 | 45.50 | 48.11 | 6.39 | 9868 | U. S. Geo. S.| +____|__________|__________|________|_________|________|______________| + +[Illustration: Portion of 12,080 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters at the Potomac Electric Co., Washington, +D. C.] + + TABLE 39 + + SHOWING RELATION BETWEEN PROXIMATE AND ULTIMATE ANALYSES OF COAL + +========================================================================= +| | | | Common in | +| | | |Proximate &| +| | Proximate | | Ultimate | +| | Analysis | Ultimate Analysis | Analysis | +|--------------------|-----------|--------------------------|-----------| +| | | | V | | | H | | N | | | M | +| | | | o | | | y | | i | S | | o | +| | | | l M | C | C | d | O | t | u | | i | +| S | | | a a | F a | a | r | x | r | l | | s | +| t | | | t t | i r | r | o | y | o | p | | t | +| a | Field | | i t | x b | b | g | g | g | h | A | u | +| t | or | | l e | e o | o | e | e | e | e | s | r | +| e | Bed | Mine | e r | d n | n | n | n | n | r | h | e | +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| | |Icy Coal| | | | | | | | | | +| | | & Iron | | | | | | | | | | +| | Horse | Co. | | | | | | | | | | +|Ala| Creek | No. 8 |31.81|53.90|72.02|4.78| 6.45|1.66| .80|14.29| 2.56| +|---|----------------|-----|-----|-----|----|-----|----|----|-----|-----| +| | |Central | | | | | | | | | | +| | |C. & C. | | | | | | | | | | +| | Hunt- | Co. | | | | | | | | | | +|Ark|ington | No. 3 |18.99|67.71|76.37|3.90| 3.71|1.49|1.23|13.30| 1.99| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| | Pana | Clover | | | | | | | | | | +| | or | Leaf, | | | | | | | | | | +|Ill| No. 5 | No. 1 |37.22|45.64|63.04|4.49|10.04|1.28|4.01|17.14|13.19| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |No. 5, | | | | | | | | | | | +| |Warrick| | | | | | | | | | | +|Ind| Co. |Electric|41.85|44.45|68.08|4.78| 7.56|1.35|4.53|13.70| 9.11| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |No. 11,| St. | | | | | | | | | | +| |Hopkins|Bernard,| | | | | | | | | | +|Ky | Co. | No. 11 |41.10|49.60|72.22|5.06| 8.44|1.33|3.65| 9.30| 7.76| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |"B" or | | | | | | | | | | | +| |Lower | | | | | | | | | | | +| |Kittan-| Eureka,| | | | | | | | | | +|Pa | ning | No. 31 |16.71|77.22|84.45|4.25| 3.04|1.28| .91| 6.07| .56| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |Indiana| | | | | | | | | | | +|Pa | Co. | |29.55|62.64|79.86|5.02| 4.27|1.86|1.18| 7.81| 2.90| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +|W. | Fire | Rush | | | | | | | | | | +|Va | Creek | Run |22.87|71.56|83.71|4.64| 3.67|1.70| .71| 5.57| 2.14| +========================================================================= + +Table 39 gives for comparison the ultimate and proximate analyses of +certain of the coals with which tests were made in the coal testing +plant of the United States Geological Survey at the Louisiana Purchase +Exposition at St. Louis. + +The heating value of a fuel cannot be directly computed from a proximate +analysis, due to the fact that the volatile content varies widely in +different fuels in composition and in heating value. + +Some methods have been advanced for estimating the calorific value of +coals from the proximate analysis. William Kent[38] deducted from +Mahler's tests of European coals the approximate heating value dependent +upon the content of fixed carbon in the combustible. The relation as +deduced by Kent between the heat and value per pound of combustible and +the per cent of fixed carbon referred to combustible is represented +graphically by Fig. 23. + +Goutal gives another method of determining the heat value from a +proximate analysis, in which the carbon is given a fixed value and the +heating value of the volatile matter is considered as a function of its +percentage referred to combustible. Goutal's method checks closely with +Kent's determinations. + +All the formulae, however, for computing the calorific value of coals +from a proximate analysis are ordinarily limited to certain classes of +fuels. Mr. Kent, for instance, states that his deductions are correct +within a close limit for fuels containing more than 60 per cent of fixed +carbon in the combustible, while for those containing a lower +percentage, the error may be as great as 4 per cent, either high or low. + +While the use of such computations will serve where approximate results +only are required, that they are approximate should be thoroughly +understood. + +Calorimetry--An ultimate or a proximate analysis of a fuel is useful in +determining its general characteristics, and as described on page 183, +may be used in the calculation of the approximate heating value. Where +the efficiency of a boiler is to be computed, however, this heating +value should in all instances be determined accurately by means of a +fuel calorimeter. + +[Graph: B.T.U. per Pound of Combustible +against Per Cent of Fixed Carbon in Combustible + +Fig. 23. Graphic Representation of Relation between Heat Value Per Pound +of Combustible and Fixed Carbon in Combustible as Deduced by Wm. Kent.] + +In such an apparatus the fuel is completely burned and the heat +generated by such combustion is absorbed by water, the amount of heat +being calculated from the elevation in the temperature of the water. A +calorimeter which has been accepted as the best for such work is one in +which the fuel is burned in a steel bomb filled with compressed oxygen. +The function of the oxygen, which is ordinarily under a pressure of +about 25 atmospheres, is to cause the rapid and complete combustion of +the fuel sample. The fuel is ignited by means of an electric current, +allowance being made for the heat produced by such current, and by the +burning of the fuse wire. + +A calorimeter of this type which will be found to give satisfactory +results is that of M. Pierre Mahler, illustrated in Fig. 24 and +consisting of the following parts: + +A water jacket A, which maintains constant conditions outside of the +calorimeter proper, and thus makes possible a more accurate computation +of radiation losses. + +The porcelain lined steel bomb B, in which the combustion of the fuel +takes place in compressed oxygen. + +[Illustration: Fig. 24. Mahler Bomb Calorimeter] + +The platinum pan C, for holding the fuel. + +The calorimeter proper D, surrounding the bomb and containing a definite +weighed amount of water. + +An electrode E, connecting with the fuse wire F, for igniting the fuel +placed in the pan C. + +A support G, for a water agitator. + +A thermometer I, for temperature determination of the water in the +calorimeter. The thermometer is best supported by a stand independent of +the calorimeter, so that it may not be moved by tremors in the parts of +the calorimeter, which would render the making of readings difficult. To +obtain accuracy of readings, they should be made through a telescope or +eyeglass. + +A spring and screw device for revolving the agitator. + +A lever L, by the movement of which the agitator is revolved. + +A pressure gauge M, for noting the amount of oxygen admitted to the +bomb. Between 20 and 25 atmospheres are ordinarily employed. + +An oxygen tank O. + +A battery or batteries P, the current from which heats the fuse wire +used to ignite the fuel. + +This or a similar calorimeter is used in the determination of the heat +of combustion of solid or liquid fuels. Whatever the fuel to be tested, +too much importance cannot be given to the securing of an average +sample. Where coal is to be tested, tests should be made from a portion +of the dried and pulverized laboratory sample, the methods of obtaining +which have been described. In considering the methods of calorimeter +determination, the remarks applied to coal are equally applicable to any +solid fuel, and such changes in methods as are necessary for liquid +fuels will be self-evident from the same description. + +Approximately one gram of the pulverized dried coal sample should be +placed directly in the pan of the calorimeter. There is some danger in +the using of a pulverized sample from the fact that some of it may be +blown out of the pan when oxygen is admitted. This may be at least +partially overcome by forming about two grams into a briquette by the +use of a cylinder equipped with a plunger and a screw press. Such a +briquette should be broken and approximately one gram used. If a +pulverized sample is used, care should be taken to admit oxygen slowly +to prevent blowing the coal out of the pan. The weight of the sample is +limited to approximately one gram since the calorimeter is proportioned +for the combustion of about this weight when under an oxygen pressure of +about 25 atmospheres. + +A piece of fine iron wire is connected to the lower end of the plunger +to form a fuse for igniting the sample. The weight of iron wire used is +determined, and if after combustion a portion has not been burned, the +weight of such portion is determined. In placing the sample in the pan, +and in adjusting the fuse, the top of the calorimeter is removed. It is +then replaced and carefully screwed into place on the bomb by means of a +long handled wrench furnished for the purpose. + +The bomb is then placed in the calorimeter, which has been filled with a +definite amount of water. This weight is the "water equivalent" of the +apparatus, _i. e._, the weight of water, the temperature of which would +be increased one degree for an equivalent increase in the temperature of +the combined apparatus. It may be determined by calculation from the +weights and specific heats of the various parts of the apparatus. Such a +determination is liable to error, however, as the weight of the bomb +lining can only be approximated, and a considerable portion of the +apparatus is not submerged. Another method of making such a +determination is by the adding of definite weights of warm water to +definite amounts of cooler water in the calorimeter and taking an +average of a number of experiments. The best method for the making of +such a determination is probably the burning of a definite amount of +resublimed naphthaline whose heat of combustion is known. + +The temperature of the water in the water jacket of the calorimeter +should be approximately that of the surrounding atmosphere. The +temperature of the weighed amount of water in the calorimeter is made by +some experimenters slightly greater than that of the surrounding air in +order that the initial correction for radiation will be in the same +direction as the final correction. Other experimenters start from a +temperature the same or slightly lower than the temperature of the room, +on the basis that the temperature after combustion will be slightly +higher than the room temperature and the radiation correction be either +a minimum or entirely eliminated. + +While no experiments have been made to show conclusively which of these +methods is the better, the latter is generally used. + +After the bomb has been placed in the calorimeter, it is filled with +oxygen from a tank until the pressure reaches from 20 to 25 atmospheres. +The lower pressure will be sufficient in all but exceptional cases. +Connection is then made to a current from the dry batteries in series so +arranged as to allow completion of the circuit with a switch. The +current from a lighting system should not be used for ignition, as there +is danger from sparking in burning the fuse, which may effect the +results. The apparatus is then ready for the test. + +Unquestionably the best method of taking data is by the use of +co-ordinate paper and a plotting of the data with temperatures and time +intervals as ordinates and abscissae. Such a graphic representation is +shown in Fig. 25. + +[Graph: Temperature--° C. against Time--Hours and Minutes + +Fig. 25. Graphic Method of Recording Bomb Calorimeter Results] + +After the bomb is placed in the calorimeter, and before the coal is +ignited, readings of the temperature of the water should be taken at one +minute intervals for a period long enough to insure a constant rate of +change, and in this way determine the initial radiation. The coal is +then ignited by completing the circuit, the temperature at the instant +the circuit is closed being considered the temperature at the beginning +of the combustion. After ignition the readings should be taken at +one-half minute intervals, though because of the rapidity of the +mercury's rise approximate readings only may be possible for at least a +minute after the firing, such readings, however, being sufficiently +accurate for this period. The one-half minute readings should be taken +after ignition for five minutes, and for, say, five minutes longer at +minute intervals to determine accurately the final rate of radiation. + +Fig. 25 shows the results of such readings, plotted in accordance with +the method suggested. It now remains to compute the results from this +plotted data. + +The radiation correction is first applied. Probably the most accurate +manner of making such correction is by the use of Pfaundler's method, +which is a modification of that of Regnault. This assumes that in +starting with an initial rate of radiation, as represented by the +inclination of the line AB, Fig. 25, and ending with a final radiation +represented by the inclination of the line CD, Fig. 25, that the rate of +radiation for the intermediate temperatures between the points B and C +are proportional to the initial and final rates. That is, the rate of +radiation at a point midway between B and C will be the mean between the +initial and final rates; the rate of radiation at a point three-quarters +of the distance between B and C would be the rate at B plus +three-quarters of the difference in rates at B and C, etc. This method +differs from Regnault's in that the radiation was assumed by Regnault to +be in each case proportional to the difference in temperatures between +the water of the calorimeter and the surrounding air plus a constant +found for each experiment. Pfaundler's method is more simple than that +of Regnault, and the results by the two methods are in practical +agreement. + +Expressed as a formula, Pfaundler's method is, though not in form given +by him: + + _ _ + | R' - R | +C = N|R + ------ (T" - T)| (19) + |_ T' - T _| + +Where C = correction in degree centigrade, + N = number of intervals over which correction is made, + R = initial radiation in degrees per interval, + R' = final radiation in degrees per interval, + T = average temperature for period through which initial radiation + is computed, + T" = average temperature over period of combustion[39], + T' = average temperature over period through which final radiation + is computed.[39] + +The application of this formula to Fig. 25 is as follows: + +As already stated, the temperature at the beginning of combustion is the +reading just before the current is turned on, or B in Fig. 25. The point +C or the temperature at which combustion is presumably completed, should +be taken at a point which falls well within the established final rate +of radiation, and not at the maximum temperature that the thermometer +indicates in the test, unless it lies on the straight line determining +the final radiation. This is due to the fact that in certain instances +local conditions will cause the thermometer to read higher than it +should during the time that the bomb is transmitting heat to the water +rapidly, and at other times the maximum temperature might be lower than +that which would be indicated were readings to be taken at intervals of +less than one-half minute, _i. e._, the point of maximum temperature +will fall below the line determined by the final rate of radiation. With +this understanding AB, Fig. 25, represents the time of initial +radiation, BC the time of combustion, and CD the time of final +radiation. Therefore to apply Pfaundler's correction, formula (19), to +the data as represented by Fig. 25. + +N = 6, R = 0, R' = .01, T = 20.29, T' = 22.83, + + 20.29 + 22.54 + 22.84 + 22.88 + 22.87 + 22.86 +T" = --------------------------------------------- = 22.36 + 6 + + _ _ + | .01 - 0 | +C = 6|0 + -------------(22.36 - 20.29)| + |_ 22.85 - 20.29 _| + + = 6 × .008 = .048 + +Pfaundler's formula while simple is rather long. Mr. E. H. Peabody has +devised a simpler formula with which, under proper conditions, the +variation from correction as found by Pfaundler's method is negligible. + +It was noted throughout an extended series of calorimeter tests that the +maximum temperature was reached by the thermometer slightly over one +minute after the time of firing. If this period between the time of +firing and the maximum temperature reported was exactly one minute, the +radiation through this period would equal the radiation per one-half +minute _before firing_ plus the radiation per one-half minute _after the +maximum temperature is reached_; or, the radiation through the one +minute interval would be the average of the radiation per minute before +firing and the radiation per minute after the maximum. A plotted chart +of temperatures would take the form of a curve of three straight lines +(B, C', D) in Fig. 25. Under such conditions, using the notation as in +formula (19) the correction would become, + + 2R + 2R' +C = ------- + (N - 2)R', or R + (N - 1)R' (20) + 2 + +This formula may be generalized for conditions where the maximum +temperature is reached after a period of more than one minute as +follows: + +Let M = the number of intervals between the time of firing and the +maximum temperature. Then the radiation through this period will be an +average of the radiation for M intervals before firing and for M +intervals after the maximum is recorded, or + + MR + MR' M M +C = ------- + (N - M)R' = - R + (N - -)R' (21) + 2 2 2 + +In the case of Mr. Peabody's deductions M was found to be approximately +2 and formula (21) becomes directly, C = R + (N - 1)R' or formula (20). + +The corrections to be made, as secured by the use of this formula, are +very close to those secured by Pfaundler's method, where the point of +maximum temperature is not more than five intervals later than the point +of firing. Where a longer period than this is indicated in the chart of +plotted temperatures, the approximate formula should not be used. As the +period between firing and the maximum temperature is increased, the +plotted results are further and further away from the theoretical +straight line curve. Where this period is not over five intervals, or +two and a half minutes, an approximation of the straight line curve may +be plotted by eye, and ordinarily the radiation correction to be applied +may be determined very closely from such an approximated curve. + +Peabody's approximate formula has been found from a number of tests to +give results within .003 degrees Fahrenheit for the limits within which +its application holds good as described. The value of M, which is not +necessarily a whole number, should be determined for each test, though +in all probability such a value is a constant for any individual +calorimeter which is properly operated. + +The correction for radiation as found on page 188 is in all instances to +be added to the range of temperature between the firing point and the +point chosen from which the final radiation is calculated. This +corrected range multiplied by the water equivalent of the calorimeter +gives the heat of combustion in calories of the coal burned in the +calorimeter together with that evolved by the burning of the fuse wire. +The heat evolved by the burning of the fuse wire is found from the +determination of the actual weight of wire burned and the heat of +combustion of one milligram of the wire (1.7 calories), _i. e._, +multiply the weight of wire used by 1.7, the result being in gram +calories or the heat required to raise one gram of water one degree +centigrade. + +Other small corrections to be made are those for the formation of nitric +acid and for the combustion of sulphur to sulphuric acid instead of +sulphur dioxide, due to the more complete combustion in the presence of +oxygen than would be possible in the atmosphere. + +To make these corrections the bomb of the calorimeter is carefully +washed out with water after each test and the amount of acid determined +from titrating this water with a standard solution of ammonia or of +caustic soda, all of the acid being assumed to be nitric acid. Each +cubic centimeter of the ammonia titrating solution used is equivalent to +a correction of 2.65 calories. + +As part of acidity is due to the formation of sulphuric acid, a further +correction is necessary. In burning sulphuric acid the heat evolved per +gram of sulphur is 2230 calories in excess of the heat which would be +evolved if the sulphur burned to sulphur dioxide, or 22.3 calories for +each per cent of sulphur in the coal. One cubic centimeter of the +ammonia solution is equivalent to 0.00286 grams of sulphur as sulphuric +acid, or to 0.286 × 22.3 = 6.38 calories. It is evident therefore that +after multiplying the number of cubic centimeters used in titrating by +the heat factor for nitric acid (2.65) a further correction of +6.38 - 2.65 = 3.73 is necessary for each cubic centimeter used in +titrating sulphuric instead of nitric acid. This correction will be +3.73/0.297 = 13 units for each 0.01 gram of sulphur in the coal. + +The total correction therefore for the aqueous nitric and sulphuric acid +is found by multiplying the ammonia by 2.65 and adding 13 calories for +each 0.01 gram of sulphur in the coal. This total correction is to be +deducted from the heat value as found from the corrected range and the +amount equivalent to the calorimeter. + +After each test the pan in which the coal has been burned must be +carefully examined to make sure that all of the sample has undergone +complete combustion. The presence of black specks ordinarily indicates +unburned coal, and often will be found where the coal contains bone or +slate. Where such specks are found the tests should be repeated. In +testing any fuel where it is found difficult to completely consume a +sample, a weighed amount of naphthaline may be added, the total weight +of fuel and naphthaline being approximately one gram. The naphthaline +has a known heat of combustion, samples for this purpose being +obtainable from the United States Bureau of Standards, and from the +combined heat of combustion of the fuel and naphthaline that of the +former may be readily computed. + +The heat evolved in burning of a definite weight of standard naphthaline +may also be used as a means of calibrating the calorimeter as a whole. + + + + +COMBUSTION OF COAL + + +The composition of coal varies over such a wide range, and the methods +of firing have to be altered so greatly to suit the various coals and +the innumerable types of furnaces in which they are burned, that any +instructions given for the handling of different fuels must of necessity +be of the most general character. For each kind of coal there is some +method of firing which will give the best results for each individual +set of conditions. General rules can be suggested, but the best results +can be obtained only by following such methods as experience and +practice show to be the best suited to the specific conditions. + +The question of draft is an all important factor. If this be +insufficient, proper combustion is impossible, as the suction in the +furnace will not be great enough to draw the necessary amount of air +through the fuel bed, and the gases may pass off only partially +consumed. On the other hand, an excessive draft may cause losses due to +the excess quantities of air drawn through holes in the fire. Where coal +is burned however, there are rarely complaints from excessive draft, as +this can be and should be regulated by the boiler damper to give only +the draft necessary for the particular rate of combustion desired. The +draft required for various kinds of fuel is treated in detail in the +chapter on "Chimneys and Draft". In this chapter it will be assumed that +the draft is at all times ample and that it is regulated to give the +best results for each kind of coal. + + + TABLE 40 + + ANTHRACITE COAL SIZES + + _________________________________________________________________ +| | | | +| | | Testing Segments | +| | Round Mesh | Standard Square | +| | | Mesh | +| Trade Name |__________________|__________________| +| | | | | | +| | Through | Over | Through | Over | +| | Inches | Inches | Inches | Inches | +|___________________________|_________|________|_________|________| +| | | | | | +| Broken | 4-1/2 | 3-1/4 | 4 | 2-3/4 | +| Egg | 3-1/4 | 2-3/8 | 2-3/4 | 2 | +| Stove | 2-3/8 | 1-5/8 | 2 | 1-3/8 | +| Chestnut | 1-5/8 | 7/8 | 1-3/8 | 3/4 | +| Pea | 7/8 | 5/8 | 3/4 | 1/2 | +| No. 1 Buckwheat | 5/8 | 3/8 | 1/2 | 1/4 | +| No. 2 Buckwheat or Rice | 3/8 | 3/16 | 1/4 | 1/8 | +| No. 3 Buckwheat or Barley | 3/16 | 3/32 | 1/8 | 1/16 | +|___________________________|_________|________|_________|________| + +Anthracite--Anthracite coal is ordinarily marketed under the names and +sizes given in Table 40. + +The larger sizes of anthracite are rarely used for commercial steam +generating purposes as the demand for domestic use now limits the +supply. In commercial plants the sizes generally found are Nos. 1, 2 and +3 buckwheat. In some plants where the finer sizes are used, a small +percentage of bituminous coal, say, 10 per cent, is sometimes mixed with +the anthracite and beneficial results secured both in economy and +capacity. + +Anthracite coal should be fired evenly, in small quantities and at +frequent intervals. If this method is not followed, dead spots will +appear in the fire, and if the fire gets too irregular through burning +in patches, nothing can be done to remedy it until the fire is cleaned +as a whole. After this grade of fuel has been fired it should be left +alone, and the fire tools used as little as possible. Owing to the +difficulty of igniting this fuel, care must be taken in cleaning fires. +The intervals of cleaning will, of course, depend upon the nature of the +coal and the rate of combustion. With the small sizes and moderately +high combustion rates, fires will have to be cleaned twice on each +eight-hour shift. As the fires become dirty the thickness of the fuel +bed will increase, until this depth may be 12 or 14 inches just before a +cleaning period. In cleaning, the following practice is usually +followed: The good coal on the forward half of the grate is pushed to +the rear half, and the refuse on the front portion either pulled out or +dumped. The good coal is then pulled forward onto the front part of the +grate and the refuse on the rear section dumped. The remaining good coal +is then spread evenly over the whole grate surface and the fire built up +with fresh coal. + +A ratio of grate surface to heating surface of 1 to from 35 to 40 will +under ordinary conditions develop the rated capacity of a boiler when +burning anthracite buckwheat. Where the finer sizes are used, or where +overloads are desirable, however, this ratio should preferably be 1 to +25 and a forced blast should be used. Grates 10 feet deep with a slope +of 1½ inches to the foot can be handled comfortably with this class of +fuel, and grates 12 feet deep with the same slope can be successfully +handled. Where grates over 8 feet in depth are necessary, shaking grates +or overlapping dumping grates should be used. Dumping grates may be +applied either for the whole grate surface or to the rear section. Air +openings in the grate bars should be made from 3/16 inch in width for +No. 3 buckwheat to 5/16 inch for No. 1 buckwheat. It is important that +these air openings be uniformly distributed over the whole surface to +avoid blowing holes in the fire, and it is for this reason that +overlapping grates are recommended. + +No air should be admitted over the fire. Steam is sometimes introduced +into the ashpit to soften any clinker that may form, but the quantity of +steam should be limited to that required for this purpose. The steam +that may be used in a steam jet blower for securing blast will in +certain instances assist in softening the clinker, but a much greater +quantity may be used by such an apparatus than is required for this +purpose. Combustion arches sprung above the grates have proved of +advantage in maintaining a high furnace temperature and in assisting in +the ignition of fresh coal. + +Stacks used with forced blast should be of such size as to insure a +slight suction in the furnace under any conditions of operation. A blast +up to 3 inches of water should be available for the finer sizes supplied +by engine driven fans, automatically controlled by the boiler pressure. +The blast required will increase as the depth of the fuel bed increases, +and the slight suction should be maintained in the furnace by damper +regulation. + +The use of blast with the finer sizes causes rapid fouling of the +heating surfaces of the boiler, the dust often amounting to over 10 per +cent of the total fuel fired. Economical disposal of dust and ashes is +of the utmost importance in burning fuel of this nature. Provision +should be made in the baffling of the boiler to accommodate and dispose +of this dust. Whenever conditions permit, the ashes can be economically +disposed of by flushing them out with water. + +Bituminous Coals--There is no classification of bituminous coal as to +size that holds good in all localities. The American Society of +Mechanical Engineers suggests the following grading: + + +_Eastern Bituminous Coals_-- + +(A) Run of mine coal; the unscreened coal taken from the mine. + +(B) Lump coal; that which passes over a bar-screen with openings 1¼ + inches wide. + +(C) Nut coal; that which passes through a bar-screen with 1¼-inch + openings and over one with ¾-inch openings. + +(D) Slack coal; that which passes through a bar-screen with ¾-inch + openings. + + +_Western Bituminous Coals_-- + +(E) Run of mine coal; the unscreened coal taken from the mine. + +(F) Lump coal; divided into 6-inch, 3-inch and 1¼-inch lump, according + to the diameter of the circular openings over which the respective + grades pass; also 6 × 3-inch lump and 3 × 1¼-inch lump, according as + the coal passes through a circular opening having the diameter of + the larger figure and over that of the smaller diameter. + +(G) Nut coal; divided into 3-inch steam nut, which passes through an + opening 3 inches diameter and over 1¼ inches; 1¼ inch nut, which + passes through a 1¼-inch diameter opening and over a ¾-inch + diameter opening; ¾-inch nut, which passes through a ¾-inch + diameter opening and over a 5/8-inch diameter opening. + +(H) Screenings; that which passes through a 1¼-inch diameter opening. + + +As the variation in character of bituminous coals is much greater than +in the anthracites, any rules set down for their handling must be the +more general. The difficulties in burning bituminous coals with economy +and with little or no smoke increases as the content of fixed carbon in +the coal decreases. It is their volatile content which causes the +difficulties and it is essential that the furnaces be designed to +properly handle this portion of the coal. The fixed carbon will take +care of itself, provided the volatile matter is properly burned. + +Mr. Kent, in his "Steam Boiler Economy", described the action of +bituminous coal after it is fired as follows: "The first thing that the +fine fresh coal does is to choke the air spaces existing through the bed +of coke, thus shutting off the air supply which is needed to burn the +gases produced from the fresh coal. The next thing is a very rapid +evaporation of moisture from the coal, a chilling process, which robs +the furnace of heat. Next is the formation of water-gas by the chemical +reaction, C + H_{2}O = CO + 2H, the steam being decomposed, its oxygen +burning the carbon of the coal to carbonic oxide, and the hydrogen being +liberated. This reaction takes place when steam is brought in contact +with highly heated carbon. This also is a chilling process, absorbing +heat from the furnaces. The two valuable fuel gases thus generated would +give back all the heat absorbed in their formation if they could be +burned, but there is not enough air in the furnace to burn them. +Admitting extra air through the fire door at this time will be of no +service, for the gases being comparatively cool cannot be burned unless +the air is highly heated. After all the moisture has been driven off +from the coal, the distillation of hydrocarbons begins, and a +considerable portion of them escapes unburned, owing to the deficiency +of hot air, and to their being chilled by the relatively cool heating +surfaces of the boiler. During all this time great volumes of smoke are +escaping from the chimney, together with unburned hydrogen, +hydrocarbons, and carbonic oxide, all fuel gases, while at the same time +soot is being deposited on the heating surface, diminishing its +efficiency in transmitting heat to the water." + +To burn these gases distilled from the coal, it is necessary that they +be brought into contact with air sufficiently heated to cause them to +ignite, that sufficient space be allowed for their mixture with the air, +and that sufficient time be allowed for their complete combustion before +they strike the boiler heating surfaces, since these surfaces are +comparatively cool and will lower the temperature of the gases below +their ignition point. The air drawn through the fire by the draft +suction is heated in its passage and heat is added by radiation from the +hot brick surfaces of the furnace, the air and volatile gases mixing as +this increase in temperature is taking place. Thus in most instances is +the first requirement fulfilled. The element of space for the proper +mixture of the gases with the air, and of time in which combustion is to +take place, should be taken care of by sufficiently large combustion +chambers. + +Certain bituminous coals, owing to their high volatile content, require +that the air be heated to a higher temperature than it is possible for +it to attain simply in its passage through the fire and by absorption +from the side walls of the furnace. Such coals can be burned with the +best results under fire brick arches. Such arches increase the +temperature of the furnace and in this way maintain the heat that must +be present for ignition and complete combustion of the fuels in +question. These fuels too, sometimes require additional combustion +space, and an extension furnace will give this in addition to the +required arches. + +As stated, the difficulty of burning bituminous coals successfully will +increase with the increase in volatile matter. This percentage of +volatile will affect directly the depth of coal bed to be carried and +the intervals of firing for the most satisfactory results. The variation +in the fuel over such wide ranges makes it impossible to definitely +state the thickness of fires for all classes, and experiment with the +class of fuel in use is the best method of determining how that +particular fuel should be handled. The following suggestions, which are +not to be considered in any sense hard and fast rules, may be of service +for general operating conditions for hand firing: + +Semi-bituminous coals, such as Pocahontas, New River, Clearfield, etc., +require fires from 10 to 14 inches thick; fresh coal should be fired at +intervals of 10 to 20 minutes and sufficient coal charged at each firing +to maintain a uniform thickness. Bituminous coals from Pittsburgh Region +require fires from 4 to 6 inches thick, and should be fired often in +comparatively small charges. Kentucky, Tennessee, Ohio and Illinois +coals require a thickness from 4 to 6 inches. Free burning coals from +Rock Springs, Wyoming, require from 6 to 8 inches, while the poorer +grades of Montana, Utah and Washington bituminous coals require a depth +of about 4 inches. + +In general as thin fires are found necessary, the intervals of firing +should be made more frequent and the quantity of coal fired at each +interval smaller. As thin fires become necessary due to the character of +the coal, the tendency to clinker will increase if the thickness be +increased over that found to give the best results. + +There are two general methods of hand firing: 1st, the spreading method; +and 2nd, the coking method. + +[Illustration: Babcock & Wilcox Chain Grate Stoker] + +In the spreading method but little fuel is fired at one time, and is +spread evenly over the fuel bed from front to rear. Where there is more +than one firing door the doors should be fired alternately. The +advantage of alternate firing is the whole surface of the fire is not +blanketed with green coal, and steam is generated more uniformly than if +all doors were fired at one time. Again, a better combustion results due +to the burning of more of the volatile matter directly after firing than +where all doors are fired at one time. + +In the coking method, fresh coal is fired at considerable depth at the +front of the grate and after it is partially coked it is pushed back +into the furnace. The object of such a method is the preserving of a bed +of carbon at the rear of the grate, in passing over which the volatile +gases driven off from the green coal will be burned. This method is +particularly adaptable to a grate in which the gases are made to pass +horizontally over the fire. Modern practice for hand firing leans more +and more toward the spread firing method. Again the tendency is to work +bituminous coal fires less than formerly. A certain amount of slicing +and raking may be necessary with either method of firing, but in +general, the less the fire is worked the better the results. + +Lignites--As the content of volatile matter and moisture in lignite is +higher than in bituminous coal, the difficulties encountered in burning +them are greater. A large combustion space is required and the best +results are obtained where a furnace of the reverberatory type is used, +giving the gases a long travel before meeting the tube surfaces. A fuel +bed from 4 to 6 inches in depth can be maintained, and the coal should +be fired in small quantities by the alternate method. Above certain +rates of combustion clinker forms rapidly, and a steam jet in the ashpit +for softening this clinker is often desirable. A considerable draft +should be available, but it should be carefully regulated by the boiler +damper to suit the condition of the fire. Smokelessness with hand firing +with this class of fuel is a practical impossibility. It has a strong +tendency to foul the heating surfaces rapidly and these surfaces should +be cleaned frequently. Shaking grates, intelligently handled, aid in +cleaning the fires, but their manipulation must be carefully watched to +prevent good coal being lost in the ashpit. + +Stokers--The term "automatic stoker" oftentimes conveys the erroneous +impression that such an apparatus takes care of itself, and it must be +thoroughly understood that any stoker requires expert attention to as +high if not higher degree than do hand-fired furnaces. + +Stoker-fired furnaces have many advantages over hand firing, but where a +stoker installation is contemplated there are many factors to be +considered. It is true that stokers feed coal to the fire automatically, +but if the coal has first to be fed to the stoker hopper by hand, its +automatic advantage is lost. This is as true of the removal of ash from +a stoker. In a general way, it may be stated that a stoker installation +is not advantageous except possibly for diminishing smoke, unless the +automatic feature is carried to the handling of the coal and ash, as +where coal and ash handling apparatus is not installed there is no +saving in labor. In large plants, however, stokers used in conjunction +with the modern methods of coal storage and coal and ash handling, make +possible a large labor saving. In small plants the labor saving for +stokers over hand-fired furnaces is negligible, and the expense of the +installation no less proportionately than in large plants. Stokers are, +therefore, advisable in small plants only where the saving in fuel will +be large, or where the smoke question is important. + +Interest on investment, repairs, depreciation and steam required for +blast and stoker drive must all be considered. The upkeep cost will, in +general, be higher than for hand-fired furnaces. Stokers, however, make +possible the use of cheaper fuels with as high or higher economy than is +obtainable under operating conditions in hand-fired furnaces with a +better grade of fuel. The better efficiency obtainable with a good +stoker is due to more even and continuous firing as against the +intermittent firing of hand-fired furnaces; constant air supply as +against a variation in this supply to meet varying furnace conditions in +hand-fired furnaces; and the doing away to a great extent with the +necessity of working the fires. + +Stokers under ordinary operating conditions will give more nearly +smokeless combustion than will hand-fired furnaces and for this reason +must often be installed regardless of other considerations. While a +constant air supply for a given power is theoretically secured by the +use of a stoker, and in many instances the draft is automatically +governed, the air supply should, nevertheless, be as carefully watched +and checked by flue gas analyses as in the case of hand-fired furnaces. + +There is a tendency in all stokers to cause the loss of some good fuel +or siftings in the ashpit, but suitable arrangements may be made to +reclaim this. + +In respect to efficiency of combustion, other conditions being equal, +there will be no appreciable difference with the different types of +stokers, provided that the proper type is used for the grade of fuel to +be burned and the conditions of operation to be fulfilled. No stoker +will satisfactorily handle all classes of fuel, and in making a +selection, care should be taken that the type is suited to the fuel and +the operating conditions. A cheap stoker is a poor investment. Only the +best stoker suited to the conditions which are to be met should be +adopted, for if there is to be a saving, it will more than cover the +cost of the best over the cheaper stoker. + +Mechanical Stokers are of three general types: 1st, overfeed; 2nd, +underfeed; and 3rd, traveling grate. The traveling grate stokers are +sometimes classed as overfeed but properly should be classed by +themselves as under certain conditions they are of the underfeed rather +than the overfeed type. + +Overfeed Stokers in general may be divided into two classes, the +distinction being in the direction in which the coal is fed relative to +the furnaces. In one class the coal is fed into hoppers at the front end +of the furnace onto grates with an inclination downward toward the rear +of about 45 degrees. These grates are reciprocated, being made to take +alternately level and inclined positions and this motion gradually +carries the fuel as it is burned toward the rear and bottom of the +furnace. At the bottom of the grates flat dumping sections are supplied +for completing the combustion and for cleaning. The fuel is partly +burned or coked on the upper portion of the grates, the volatile gases +driven off in this process for a perfect action being ignited and burned +in their passage over the bed of burning carbon lower on the grates, or +on becoming mixed with the hot gases in the furnace chamber. In the +second class the fuel is fed from the sides of the furnace for its full +depth from front to rear onto grates inclined toward the center of the +furnace. It is moved by rocking bars and is gradually carried to the +bottom and center of the furnace as combustion advances. Here some type +of a so-called clinker breaker removes the refuse. + +Underfeed Stokers are either horizontal or inclined. The fuel is fed +from underneath, either continuously by a screw, or intermittently by +plungers. The principle upon which these stokers base their claims for +efficiency and smokelessness is that the green fuel is fed under the +coked and burning coal, the volatile gases from this fresh fuel being +heated and ignited in their passage through the hottest portion of the +fire on the top. In the horizontal classes of underfeed stokers, the +action of a screw carries the fuel back through a retort from which it +passes upward, as the fuel above is consumed, the ash being finally +deposited on dead plates on either side of the retort, from which it can +be removed. In the inclined class, the refuse is carried downward to the +rear of the furnace where there are dumping plates, as in some of the +overfeed types. + +Underfeed stokers are ordinarily operated with a forced blast, this in +some cases being operated by the same mechanism as the stoker drive, +thus automatically meeting the requirements of various combustion rates. + +Traveling Grates are of the class best illustrated by chain grate +stokers. As implied by the name these consist of endless grates composed +of short sections of bars, passing over sprockets at the front and rear +of the furnace. Coal is fed by gravity onto the forward end of the +grates through suitable hoppers, is ignited under ignition arches and is +carried with the grate toward the rear of the furnace as its combustion +progresses. When operated properly, the combustion is completed as the +fire reaches the end of the grate and the refuse is carried over this +rear end by the grate in making the turn over the rear sprocket. In some +cases auxiliary dumping grates at the rear of the chain grates are used +with success. + +Chain grate stokers in general produce less smoke than either overfeed +or underfeed types, due to the fact that there are no cleaning periods +necessary. Such periods occur with the latter types of stokers at +intervals depending upon the character of the fuel used and the rate of +combustion. With chain grate stokers the cleaning is continuous and +automatic, and no periods occur when smoke will necessarily be produced. + +In the earlier forms, chain grates had an objectionable feature in that +the admission of large amounts of excess air at the rear of the furnace +through the grates was possible. This objection has been largely +overcome in recent models by the use of some such device as the bridge +wall water box and suitable dampers. A distinct advantage of chain +grates over other types is that they can be withdrawn from the furnace +for inspection or repairs without interfering in any way with the boiler +setting. + +This class of stoker is particularly successful in burning low grades of +coal running high in ash and volatile matter which can only be burned +with difficulty on the other types. The cost of up-keep in a chain +grate, properly constructed and operated, is low in comparison with the +same cost for other stokers. + +The Babcock & Wilcox chain grate is representative of this design of +stoker. + +Smoke--The question of smoke and smokelessness in burning fuels has +recently become a very important factor of the problem of combustion. +Cities and communities throughout the country have passed ordinances +relative to the quantities of smoke that may be emitted from a stack, +and the failure of operators to live up to the requirements of such +ordinances, resulting as it does in fines and annoyance, has brought +their attention forcibly to the matter. + +The whole question of smoke and smokelessness is to a large extent a +comparative one. There are any number of plants burning a wide variety +of fuels in ordinary hand-fired furnaces, in extension furnaces and on +automatic stokers that are operating under service conditions, +practically without smoke. It is safe to say, however, that no plant +will operate smokelessly under any and all conditions of service, nor is +there a plant in which the degree of smokelessness does not depend +largely upon the intelligence of the operating force. + +[Illustration: Fig. 26. Babcock & Wilcox Boiler and Superheater Equipped +with Babcock & Wilcox Chain Grate Stoker. This Setting has been +Particularly Successful in Minimizing Smoke] + +When a condition arises in a boiler room requiring the fires to be +brought up quickly, the operatives in handling certain types of stokers +will use their slice bars freely to break up the green portion of the +fire over the bed of partially burned coal. In fact, when a load is +suddenly thrown on a station the steam pressure can often be maintained +only in this way, and such use of the slice bar will cause smoke with +the very best type of stoker. In a certain plant using a highly volatile +coal and operating boilers equipped with ordinary hand-fired furnaces, +extension hand-fired furnaces and stokers, in which the boilers with the +different types of furnaces were on separate stacks, a difference in +smoke from the different types of furnaces was apparent at light loads, +but when a heavy load was thrown on the plant, all three stacks would +smoke to the same extent, and it was impossible to judge which type of +furnace was on one or the other of the stacks. + +In hand-fired furnaces much can be accomplished by proper firing. A +combination of the alternate and spreading methods should be used, the +coal being fired evenly, quickly, lightly and often, and the fires +worked as little as possible. Smoke can be diminished by giving the +gases a long travel under the action of heated brickwork before they +strike the boiler heating surfaces. Air introduced over the fires and +the use of heated arches, etc., for mingling the air with the gases +distilled from the coal will also diminish smoke. Extension furnaces +will undoubtedly lessen smoke where hand firing is used, due to the +increase in length of gas travel and the fact that this travel is +partially under heated brickwork. Where hand-fired grates are +immediately under the boiler tubes, and a high volatile coal is used, if +sufficient combustion space is not provided the volatile gases, +distilled as soon as the coal is thrown on the fire, strike the tube +surfaces and are cooled below the burning point before they are wholly +consumed and pass through as smoke. With an extension furnace, these +volatile gases are acted upon by the radiant heat from the extension +furnace arch and this heat, together with the added length of travel +causes their more complete combustion before striking the heating +surfaces than in the former case. + +Smoke may be diminished by employing a baffle arrangement which gives +the gases a fairly long travel under heated brickwork and by introducing +air above the fire. In many cases, however, special furnaces for smoke +reduction are installed at the expense of capacity and economy. + +From the standpoint of smokelessness, undoubtedly the best results are +obtained with a good stoker, properly operated. As stated above, the +best stoker will cause smoke under certain conditions. Intelligently +handled, however, under ordinary operating conditions, stoker-fired +furnaces are much more nearly smokeless than those which are hand fired, +and are, to all intents and purposes, smokeless. In practically all +stoker installations there enters the element of time for combustion, +the volatile gases as they are distilled being acted upon by ignition or +other arches before they strike the heating surfaces. In many instances +too, stokers are installed with an extension beyond the boiler front, +which gives an added length of travel during which, the gases are acted +upon by the radiant heat from the ignition or supplementary arches, and +here again we see the long travel giving time for the volatile gases to +be properly consumed. + +To repeat, it must be emphatically borne in mind that the question of +smokelessness is largely one of degree, and dependent to an extent much +greater than is ordinarily appreciated upon the handling of the fuel and +the furnaces by the operators, be these furnaces hand fired or +automatically fired. + +[Illustration: 3520 Horse-power Installation of Babcock & Wilcox Boilers +at the Portland Railway, Light and Power Co., Portland, Ore. These +Boilers are Equipped with Wood Refuse Extension Furnaces at the Front +and Oil Burning Furnaces at the Mud Drum End] + + + + +SOLID FUELS OTHER THAN COAL AND THEIR COMBUSTION + + +Wood--Wood is vegetable tissue which has undergone no geological change. +Usually the term is used to designate those compact substances +familiarly known as tree trunks and limbs. When newly cut, wood contains +moisture varying from 30 per cent to 50 per cent. When dried for a +period of about a year in the atmosphere, the moisture content will be +reduced to 18 or 20 per cent. + + TABLE 41 + +ULTIMATE ANALYSES AND CALORIFIC VALUES OF DRY WOOD (GOTTLIEB) + + _______________________________________________________ +| | | | | | | | +| Kind | | | | | | B. t. u.| +| of | C | H | N | O | Ash | per | +| Wood | | | | | | Pound | +|________|_______|______|______|_______|______|_________| +| | | | | | | | +| Oak | 50.16 | 6.02 | 0.09 | 43.36 | 0.37 | 8316 | +| Ash | 49.18 | 6.27 | 0.07 | 43.91 | 0.57 | 8480 | +| Elm | 48.99 | 6.20 | 0.06 | 44.25 | 0.50 | 8510 | +| Beech | 49.06 | 6.11 | 0.09 | 44.17 | 0.57 | 8391 | +| Birch | 48.88 | 6.06 | 0.10 | 44.67 | 0.29 | 8586 | +| Fir | 50.36 | 5.92 | 0.05 | 43.39 | 0.28 | 9063 | +| Pine | 50.31 | 6.20 | 0.04 | 43.08 | 0.37 | 9153 | +| Poplar | 49.37 | 6.21 | 0.96 | 41.60 | 1.86 | 7834[40]| +| Willow | 49.96 | 5.96 | 0.96 | 39.56 | 3.37 | 7926[40]| +|________|_______|______|______|_______|______|_________| + +Wood is usually classified as hard wood, including oak, maple, hickory, +birch, walnut and beech; and soft wood, including pine, fir, spruce, +elm, chestnut, poplar and willow. Contrary to general opinion, the heat +value per pound of soft wood is slightly greater than the same value per +pound of hard wood. Table 41 gives the chemical composition and the heat +values of the common woods. Ordinarily the heating value of wood is +considered equivalent to 0.4 that of bituminous coal. In considering the +calorific value of wood as given in this table, it is to be remembered +that while this value is based on air-dried wood, the moisture content +is still about 20 per cent of the whole, and the heat produced in +burning it will be diminished by this amount and by the heat required to +evaporate the moisture and superheat it to the temperature of the gases. +The heat so absorbed may be calculated by the formula giving the loss +due to moisture in the fuel, and the net calorific value determined. + +In designing furnaces for burning wood, the question resolves itself +into: 1st, the essential elements to give maximum capacity and +efficiency with this class of fuel; and 2nd, the construction which will +entail the least labor in handling and feeding the fuel and removing the +refuse after combustion. + +Wood, as used commercially for steam generating purposes, is usually a +waste product from some industrial process. At the present time refuse +from lumber and sawmills forms by far the greater part of this class of +fuel. In such refuse the moisture may run as high as 60 per cent and the +composition of the fuel may vary over wide ranges during different +portions of the mill operation. The fuel consists of sawdust, "hogged" +wood and slabs, and the percentage of each of these constituents may +vary greatly. Hogged wood is mill refuse and logs that have been passed +through a "hogging machine" or macerator. This machine, through the +action of revolving knives, cuts or shreds the wood into a state in +which it may readily be handled as fuel. + +Table 42 gives the moisture content and heat value of typical sawmill +refuse from various woods. + + TABLE 42 + + MOISTURE AND CALORIFIC VALUE OF SAWMILL REFUSE + _____________________________________________________________________ +| | | | | +| | | Per Cent | B. t. u. | +| Kind of Wood | Nature of Refuse | Moisture | per Pound | +| | | | Dry Fuel | +|_____________________|_______________________|__________|____________| +| | | | | +| Mexican White Pine | Sawdust and Hog Chips | 51.90 | 9020 | +| Yosemite Sugar Pine | Sawdust and Hog Chips | 62.85 | 9010 | +| Redwood 75%, | Sawdust, Box Mill | | | +| Douglas Fir 25% | Refuse and Hog | 42.20 | 8977[41] | +| Redwood | Sawdust and Hog Chips | 52.98 | 9040[41] | +| Redwood | Sawdust and Hog Chips | 49.11 | 9204[41] | +| Fir, Hemlock, | | | | +| Spruce and Cedar | Sawdust | 42.06 | 8949[41] | +|_____________________|_______________________|__________|____________| + +It is essential in the burning of this class of fuel that a large +combustion space be supplied, and on account of the usually high +moisture content there should be much heated brickwork to radiate heat +to the fuel bed and thus evaporate the moisture. Extension furnaces of +the proper size are usually essential for good results and when this +fuel is used alone, grates dropped to the floor line with an ashpit +below give additional volume for combustion and space for maintaining a +thick fuel bed. A thick fuel bed is necessary in order to avoid +excessive quantities of air passing through the boiler. Where the fuel +consists of hogged wood and sawdust alone, it is best to feed it +automatically into the furnace through chutes on the top of the +extension. The best results are secured when the fuel is allowed to pile +up in the furnace to a height of 3 or 4 feet in the form of a cone under +each chute. The fuel burns best when not disturbed in the furnace. Each +fuel chute, when a proper distance from the grates and with the piles +maintained at their proper height, will supply about 30 or 35 square +feet of grate surface. While large quantities of air are required for +burning this fuel, excess air is as harmful as with coal, and care must +be taken that such an excess is not admitted through fire doors or fuel +chutes. A strong natural draft usually is preferable to a blast with +this fuel. The action of blast is to make the regulation of the furnace +conditions more difficult and to blow over unconsumed fuel on the +heating surfaces and into the stack. This unconsumed fuel settling in +portions of the setting out of the direct path of the gases will have a +tendency to ignite provided any air reaches it, with results harmful to +the setting and breeching connection. This action is particularly +objectionable if these particles are carried over into the base of a +stack, where they will settle below the point at which the flue enters +and if ignited may cause the stack to become overheated and buckle. + +Whether natural draft or blast is used, much of the fuel is carried onto +the heating surfaces and these should be cleaned regularly to maintain a +good efficiency. Collecting chambers in various portions of the setting +should be provided for this unconsumed fuel, and these should be kept +clean. + +With proper draft conditions, 150 pounds of this fuel containing about +30 to 40 per cent of moisture can be burned per square foot of grate +surface per hour, and in a properly designed furnace one square foot of +grate surface can develop from 5 to 6 boiler horse power. Where the wood +contains 50 per cent of moisture or over, it is not usually safe to +figure on obtaining more than 3 to 4 horse power per square foot of +grate surface. + +Dry sawdust, chips and blocks are also used as fuel in many wood-working +industries. Here, as with the wet wood, ample combustion space should be +supplied, but as this fuel is ordinarily kiln dried, large brickwork +surfaces in the furnace are not necessary for the evaporation of +moisture in the fuel. This fuel may be burned in extension furnaces +though these are not required unless they are necessary to secure an +added furnace volume, to get in sufficient grate surface, or where such +an arrangement must be used to allow for a fuel bed of sufficient +thickness. Depth of fuel bed with the dry fuel is as important as with +the moist fuel. If extension furnaces are used with this dry wood, care +must be taken in their design that there is no excessive throttling of +the gases in the furnace, or brickwork trouble will result. In Babcock & +Wilcox boilers this fuel may be burned without extension furnaces, +provided that the boilers are set at a sufficient height to provide +ample combustion space and to allow for proper depth of fuel bed. +Sometimes this is gained by lowering the grates to the floor line and +excavating for an ashpit. Where the fuel is largely sawdust, it may be +introduced over the fire doors through inclined chutes. The old methods +of handling and collecting sawdust by means of air suction and blast +were such that the amount of air admitted through such chutes was +excessive, but with improved methods the amount of air so admitted may +be reduced to a negligible quantity. The blocks and refuse which cannot +be handled through chutes may be fired through fire doors in the front +of the boiler, which should be made sufficiently large to accommodate +the larger sizes of fuel. As with wet fuel, there will be a quantity of +unconsumed wood carried over and the heating surfaces must be kept +clean. + +In a few localities cord wood is burned. With this as with other classes +of wood fuel, a large combustion space is an essential feature. The +percentage of moisture in cord wood may make it necessary to use an +extension furnace, but ordinarily this is not required. Ample combustion +space is in most cases secured by dropping the grates to the floor line, +large double-deck fire doors being supplied at the usual fire door level +through which the wood is thrown by hand. Air is admitted under the +grates through an excavated ashpit. The side, front and rear walls of +the furnace should be corbelled out to cover about one-third of the +total grate surface. This prevents cold air from laneing up the sides of +the furnace and also reduces the grate surface. Cord wood and slabs form +an open fire through which the frictional loss of the air is much less +than in the case of sawdust or hogged material. The combustion rate with +cord wood is, therefore, higher and the grate surface may be +considerably reduced. Such wood is usually cut in lengths of 4 feet or 4 +feet 6 inches, and the depth of the grates should be kept approximately +5 feet to get the best results. + +Bagasse--Bagasse is the refuse of sugar cane from which the juice has +been extracted by pressure between the rolls of the mill. From the start +of the sugar industry bagasse has been considered the natural fuel for +sugar plantations, and in view of the importance of the industry a word +of history relative to the use of this fuel is not out of place. + +When the manufacture of sugar was in its infancy the cane was passed +through but a single mill and the defecation and concentration of the +saccharine juice took place in a series of vessels mounted one after +another over a common fire at one end and connected to a stack at the +opposite end. This primitive method was known in the English colonies as +the "Open Wall" and in the Spanish-American countries as the "Jamaica +Train". + +The evaporation and concentration of the juice in the open air and over +a direct fire required such quantities of fuel, and the bagasse, in +fact, played such an important part in the manufacture of sugar, that +oftentimes the degree of extraction, which was already low, would be +sacrificed to the necessity of obtaining a bagasse that might be readily +burned. + +The furnaces in use with these methods were as primitive as the rest of +the apparatus, and the bagasse could be burned in them only by first +drying it. This naturally required an enormous quantity of handling of +the fuel in spreading and collecting and frequently entailed a shutting +down of the mill, because a shower would spoil the supply which had been +dried. + +The difficulties arising from the necessity of drying this fuel caused a +widespread attempt on the part of inventors to the turning out of a +furnace which would successfully burn green bagasse. Some of the designs +were more or less clever, and about the year 1880 several such green +bagasse furnaces were installed. These did not come up to expectations, +however, and almost invariably they were abandoned and recourse had to +be taken to the old method of drying in the sun. + +From 1880 the new era in the sugar industry may be dated. Slavery was +almost universally abolished and it became necessary to pay for labor. +The cost of production was thus increased, while growing competition of +European beet sugar lowered the prices. The only remedy for the new +state of affairs was the cheapening of the production by the increase of +extraction and improvement in manufacture. The double mill took the +place of the single, the open wall method of extraction was replaced by +vacuum evaporative apparatus and centrifugal machines were introduced to +do the work of the great curing houses. As opposed to these +improvements, however, the steam plants remained as they started, +consisting of double flue boilers externally fired with dry bagasse. + +On several of the plantations horizontal multitubular boilers externally +fired were installed and at the time were considered the acme of +perfection. Numerous attempts were made to burn the bagasse green, among +others the step grates imported from Louisiana and known as the Leon +Marie furnaces, but satisfactory results were obtained in none of the +appliances tried. + +The Babcock & Wilcox Co. at this time turned their attention to the +problem with the results which ultimately led to its solution. Their New +Orleans representative, Mr. Frederick Cook, invented a hot forced blast +bagasse furnace and conveyed the patent rights to this company. This +furnace while not as efficient as the standard of to-day, and expensive +in its construction, did, nevertheless, burn the bagasse green and +enabled the boilers to develop their normal rated capacity. The first +furnace of this type was installed at the Southwood and Mt. Houmas +plantations and on a small plantation in Florida. About the year 1888 +two furnaces were erected in Cuba, one on the plantation Senado and the +other at the Central Hormiguero. The results obtained with these +furnaces were so remarkable in comparison with what had previously been +accomplished that the company was overwhelmed with orders. The expense +of auxiliary fuel, usually wood, which was costly and indispensable in +rainy weather, was done away with and as the mill could be operated on +bagasse alone, the steam production and the factory work could be +regulated with natural increase in daily output. + +Progress and improvement in the manufacture itself was going on at a +remarkable rate, the single grinding had been replaced by a double +grinding, this in turn by a third grinding, and finally the maceration +and dilution of the bagasse was carried to the extraction of practically +the last trace of sugar contained in it. The quantity of juice to be +treated was increased in this way 20 or 30 per cent but was accompanied +by the reduction to a minimum of the bagasse available as a fuel, and +led to demands upon the furnace beyond its capacity. + +With the improvements in the manufacture, planters had been compelled to +make enormous sacrifices to change radically their systems, and the +heavy disbursement necessary for mill apparatus left few in a financial +position to make costly installations of good furnaces. The necessity of +turning to something cheap in furnace construction but which was +nevertheless better than the early method of burning the fuel dry led to +the invention of numerous furnaces by all classes of engineers +regardless of their knowledge of the subject and based upon no +experience. None of the furnaces thus produced were in any sense +inventions but were more or less barefaced infringements of the patents +of The Babcock & Wilcox Co. As the company could not protect its rights +without hurting its clients, who in many cases against their own will +were infringing upon these patents, and as on the other hand they were +anxious to do something to meet the wants of the planters, a series of +experiments were started, at their own rather than at their customers' +expense, with a view to developing a furnace which, without being as +expensive, would still fulfill all the requirements of the manufacturer. +The result was the cold blast green bagasse furnace which is now +offered, and it has been adopted as standard for this class of work +after years of study and observation in our installations in the sugar +countries of the world. Such a furnace is described later in considering +the combustion of bagasse. + +Composition and Calorific Value of Bagasse--The proportion of fiber +contained in the cane and density of the juice are important factors in +the relation the bagasse fuel will have to the total fuel necessary to +generate the steam required in a mill's operation. A cane rich in wood +fiber produces more bagasse than a poor one and a thicker juice is +subject to a higher degree of dilution than one not so rich. + +Besides the percentage of bagasse in the cane, its physical condition +has a bearing on its calorific value. The factors here entering are the +age at which the cane must be cut, the locality in which it is grown, +etc. From the analysis of any sample of bagasse its approximate +calorific value may be calculated from the formula, + + 8550F + 7119S + 6750G - 972W +B. t. u. per pound bagasse = ---------------------------- (22) + 100 + +Where F = per cent of fiber in cane, S = per cent sucrose, G = per cent +glucose, W = per cent water. + +This formula gives the total available heat per pound of bagasse, that +is, the heat generated per pound less the heat required to evaporate its +moisture and superheat the steam thus formed to the temperature of the +stack gases. + +Three samples of bagasse in which the ash is assumed to be 3 per cent +give from the formula: + +F = 50 S and G = 4.5 W = 42.5 B. t. u. = 4183 +F = 40 S and G = 6.0 W = 51.0 B. t. u. = 3351 +F = 33.3 S and G = 7.0 W = 56.7 B. t. u. = 2797 + +A sample of Java bagasse having F = 46.5, S = 4.50, G = 0.5, W = 47.5 +gives B. t. u. 3868. + +These figures show that the dryer the bagasse is crushed, the higher the +calorific value, though this is accompanied by a decrease in sucrose. +The explanation lies in the fact that the presence of sucrose in an +analysis is accompanied by a definite amount of water, and that the +residual juice contains sufficient organic substance to evaporate the +water present when a fuel is burned in a furnace. For example, assume +the residual juice (100 per cent) to contain 12 per cent organic matter. +From the constant in formula, + +12×7119 (100-12)×972 +------- = 854.3 and ------------ = 855.4. + 100 100 + +That is, the moisture in a juice containing 12 per cent of sugar will be +evaporated by the heat developed by the combustion of the contained +sugar. It would, therefore, appear that a bagasse containing such juice +has a calorific value due only to its fiber content. This is, of course, +true only where the highest products of oxidization are formed during +the combustion of the organic matter. This is not strictly the case, +especially with a bagasse of a high moisture content which will not burn +properly but which smoulders and produces a large quantity of products +of destructive distillation, chiefly heavy hydrocarbons, which escape +unburnt. The reasoning, however, is sufficient to explain the steam +making properties of bagasse of a low sucrose content, such as are +secured in Java, as when the sucrose content is lower, the heat value is +increased by extracting more juice, and hence more sugar from it. The +sugar operations in Java exemplify this and show that with a high +dilution by maceration and heavy pressure the bagasse meets all of the +steam requirements of the mills without auxiliary fuel. + +A high percentage of silica or salts in bagasse has sometimes been +ascribed as the reason for the tendency to smoulder in certain cases of +soft fiber bagasse. This, however, is due to the large moisture content +of the sample resulting directly from the nature of the cane. Soluble +salts in the bagasse has also been given as the explanation of such +smouldering action of the fire, but here too the explanation lies solely +in the high moisture content, this resulting in the development of only +sufficient heat to evaporate the moisture. + + TABLE 43 + + ANALYSES AND CALORIFIC VALUES OF BAGASSE ++---------------------------------------------------------------------+ +|+----------+--------+-------+-------+-------+-------+-------+-------+| +|| | | | | | | |B.t.u. || +|| | | | | | | | per || +|| Source |Moisture| C | H | O | N | Ash | Pound || +|| | | | | | | | Dry || +|| | | | | | | |Bagasse|| +|+----------+--------+-------+-------+-------+-------+-------+-------+| +||Cuba | 51.50 | 43.15 | 6.00 | 47.95 | | 2.90 | 7985 || +||Cuba | 49.10 | 43.74 | 6.08 | 48.61 | | 1.57 | 8300 || +||Cuba | 42.50 | 43.61 | 6.06 | 48.45 | | 1.88 | 8240 || +||Cuba | 51.61 | 46.80 | 5.34 | 46.35 | | 1.51 | || +||Cuba | 52.80 | 46.78 | 5.74 | 45.38 | | 2.10 | || +||Porto Rico| 41.60 | 44.28 | 6.66 | 47.10 | 0.41 | 1.35 | 8359 || +||Porto Rico| 43.50 | 44.21 | 6.31 | 47.72 | 0.41 | 1.35 | 8386 || +||Porto Rico| 44.20 | 44.92 | 6.27 | 46.50 | 0.41 | 1.90 | 8380 || +||Louisiana | 52.10 | | | | | 2.27 | 8230 || +||Louisiana | 54.00 | | | | | | 8370 || +||Louisiana | 51.80 | | | | | | 8371 || +||Java | | 46.03 | 6.56 | 45.55 | 0.18 | 1.68 | 8681 || +|+----------+--------+-------+-------+-------+-------+-------+-------+| ++---------------------------------------------------------------------+ + +Table 43 gives the analyses and heat values of bagasse from various +localities. Table 44 gives the value of mill bagasse at different +extractions, which data may be of service in making approximations as to +its fuel value as compared with that of other fuels. + + TABLE 44 + + VALUE OF ONE POUND OF MILL BAGASSE AT DIFFERENT EXTRACTIONS + + 1: Per Cent Extraction of Weight of Cane + 2: Per Cent Moisture in Bagasse + 3: Per Cent in Bagasse + 4: Fuel Value, B. t. u. + 5: Per Cent in Bagasse + 6: Fuel Value, B. t. u. + 7: Per Cent in Bagasse + 8: Fuel Value, B. t. u. + 9: Total Heat Developed per Pound of Bagasse +10: Heat Required to Evaporate Moisture[42] +11: Heat Available for Steam Generation +12: Pounds of Bagasse Equivalent to one Pound of Coal of 14,000 B. t. u. + ++----------------------------------------------------------------+ +|+---+-----+----------+---------+---------+----------------+----+| +|| | | | | |B.t.u. Value per| || +|| | | Fiber | Sugar |Molasses |Pound of Bagasse| || +|| | +-----+----+----+----+----+----+-----+----+-----+ || +|| | | | | | | | | | | | || +|| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 || +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +|| BASED UPON CANE OF 12 PER CENT FIBER AND JUICE CONTAINING || +||18 PER CENT OF SOLID MATTER. REPRESENTING TROPICAL CONDITIONS || +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +||75 |42.64|48.00|3996|6.24|451 |3.12|217 |4664 |525 |4139 |3.38|| +||77 |39.22|52.17|4343|5.74|414 |2.87|200 |4958 |483 |4475 |3.13|| +||79 |35.15|57.14|4757|5.14|371 |2.57|179 |5307 |433 |4874 |2.87|| +||81 |30.21|63.16|5258|4.42|319 |2.21|154 |5731 |372 |5359 |2.61|| +||83 |24.12|70.59|5877|3.53|256 |1.76|122 |6255 |297 |5958 |2.35|| +||85 |16.20|80.00|6660|2.40|173 |1.20| 83 |6916 |200 |6716 |2.08|| +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +|| BASED UPON CANE OF 10 PER CENT FIBER AND JUICE CONTAINING || +||15 PER CENT OF SOLID MATTER. REPRESENTING LOUISIANA CONDITIONS|| +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +||75 |51.00|40.00|3330|6.00|433 |3.00|209 |3972 |678 |3294 |4.25|| +||77 |48.07|43.45|3617|5.66|409 |2.82|196 |4222 |592 |3630 |3.86|| +||79 |44.52|47.62|3964|5.24|378 |2.62|182 |4524 |548 |3976 |3.52|| +||81 |40.18|52.63|4381|4.73|342 |2.36|164 |4887 |495 |4392 |3.19|| +||83 |35.00|58.82|4897|4.12|298 |2.06|143 |5436 |431 |5005 |2.80|| +||85 |28.33|66.67|5550|3.33|241 |1.67|116 |5907 |349 |5558 |2.52|| +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| ++----------------------------------------------------------------+ + +Furnace Design and the Combustion of Bagasse--With the advance in sugar +manufacture there came, as described, a decrease in the amount of +bagasse available for fuel. As the general efficiency of a plant of this +description is measured by the amount of auxiliary fuel required per ton +of cane, the relative importance of the furnace design for the burning +of this fuel is apparent. + +In modern practice, under certain conditions of mill operation, and with +bagasse of certain physical properties, the bagasse available from the +cane ground will meet the total steam requirements of the plant as a +whole; such conditions prevail, as described, in Java. In the United +States, Cuba, Porto Rico and like countries, however, auxiliary fuel is +almost universally a necessity. The amount will vary, depending to a +great extent upon the proportion of fiber in the cane, which varies +widely with the locality and with the age at which it is cut, and to a +lesser extent upon the degree of purity of the manufactured sugar, the +use of the maceration water and the efficiency of the mill apparatus as +a whole. + +[Illustration: Fig. 27. Babcock & Wilcox Boiler Set with Green Bagasse +Furnace] + +Experience has shown that this fuel may be burned with the best results +in large quantities. A given amount of bagasse burned in one furnace +between two boilers will give better results than the same quantity +burned in a number of smaller furnaces. An objection has been raised +against such practice on the grounds that the necessity of shutting down +two boiler units when it is necessary for any reason to take off a +furnace, requires a larger combined boiler capacity to insure continuity +of service. As a matter of fact, several small furnaces will cost +considerably more than one large furnace, and the saving in original +furnace cost by such an installation, taken in conjunction with the +added efficiency of the larger furnace over the small, will probably +more than offset the cost of additional boiler units for spares. + +The essential features in furnace design for this class of fuel are +ample combustion space and a length of gas travel sufficient to enable +the gases to be completely burned before the boiler heating surfaces are +encountered. Experience has shown that better results are secured where +the fuel is burned on a hearth rather than on grates, the objection to +the latter method being that the air for combustion enters largely +around the edges, where the fuel pile is thinnest. When burned on a +hearth the air for combustion is introduced into the furnace through +several rows of tuyeres placed above and symmetrically around the +hearth. An arrangement of such tuyeres over a grate, and a proper +manipulation of the ashpit doors, will overcome largely the objection to +grates and at the same time enable other fuel to be burned in the +furnace when necessary. This arrangement of grates and tuyeres is +probably the better from a commercially efficient standpoint. Where the +air is admitted through tuyeres over the grate or hearth line, it +impinges on the fuel pile as a whole and causes a uniform combustion. +Such tuyeres connect with an annular space in which, where a blast is +used, the air pressure is controlled by a blower. + +All experience with this class of fuel indicates that the best results +are secured with high combustion rates. With a natural draft in the +furnace of, say, three-tenths inch of water, a combustion rate of from +250 to 300 pounds per square foot of grate surface per hour may be +obtained. With a blast of, say, five-tenths inch of water, this rate can +be increased to 450 pounds per square foot of grate surface per hour. +These rates apply to bagasse as fired containing approximately 50 per +cent of moisture. It would appear that the most economical results are +secured with a combustion rate of approximately 300 pounds per square +foot per hour which, as stated, may be obtained with natural draft. +Where a natural draft is available sufficient to give such a rate, it is +in general to be preferred to a blast. + +Fig. 27 shows a typical bagasse furnace with which very satisfactory +results have been obtained. The design of this furnace may be altered to +suit the boilers to which it is connected. It may be changed slightly in +its proportions and in certain instances in its position relative to the +boiler. The furnace as shown is essentially a bagasse furnace and may be +modified somewhat to accommodate auxiliary fuel. + +The fuel is ignited in a pit A on a hearth which is ordinarily +elliptical in shape. Air for combustion is admitted through the tuyeres +B connected to an annular space C through which the amount of air is +controlled. Above the pit the furnace widens out to form a combustion +space D which has a cylindrical or spherical roof with its top +ordinarily from 11 to 13 feet above the floor. The gases pass from this +space horizontally to a second combustion chamber E from which they are +led through arches F to the boiler. The arrangement of such arches is +modified to suit the boiler or boilers with which the furnace is +operated. A furnace of such design embodies the essential features of +ample combustion space and long gas travel. + +The fuel should be fed to the furnace through an opening in the roof +above the pit by some mechanical means which will insure a constant fuel +feed and at the same time prevent the inrush of cold air into the +furnace. + +This class of fuel deposits a considerable quantity of dust, which if +not removed promptly will fuse into a hard glass-like clinker. Ample +provision should be made for the removal of such dust from the furnace, +the gas ducts and the boiler setting, and these should be thoroughly +cleaned once in 24 hours. + +Table 45 gives the results of several tests on Babcock & Wilcox boilers +using fuel of this character. + + TABLE 45 + + TESTS OF BABCOCK & WILCOX BOILERS WITH GREEN BAGASSE + ____________________________________________________________________ +| Duration of Test | Hours | 12 | 10 | 10 | 10 | +| Rated Capacity of Boiler |Horse Power| 319 | 319 | 319 | 319 | +| Grate Surface |Square Feet| 33 | 33 | 16.5 | 16.5 | +| Draft in Furnace | Inches | .30 | .28 | .29 | .27 | +| Draft at Damper | Inches | .47 | .45 | .46 | .48 | +| Blast under Grates | Inches | ... | ... | ... | .34 | +| Temperature of Exit Gases | Degrees F.| 536 | 541 | 522 | 547 | +| /CO_{2} | Per Cent | 13.8 | 12.6 | 11.7 | 12.8 | +| Flue Gas Analysis { O | Per Cent | 5.9 | 7.6 | 8.2 | 6.9 | +| \CO | Per Cent | 0.0 | 0.0 | 0.0 | 0.0 | +| Bagasse per Hour as Fired | Pounds | 4980 | 4479 | 5040 | 5586 | +| Moisture in Bagasse | Per Cent |52.39 |52.93 |51.84 |51.71 | +| Dry Bagasse per Hour | Pounds | 2371 | 2108 | 2427 | 2697 | +| Dry Bagasse per Square Foot| | | | | | +| of Grate Surface per Hour| Pounds | 71.9 | 63.9 |147.1 |163.4 | +| Water per Hour from and at | | | | | | +| 212 Degrees | Pounds |10141 | 9850 |10430 |11229 | +| Per Cent of Rated Capacity | | | | | | +| Developed | Per Cent | 92.1 | 89.2 | 94.7 |102.0 | +|____________________________|___________|______|______|______|______| + +Tan Bark--Tan bark, or spent tan, is the fibrous portion of bark +remaining after use in the tanning industry. It is usually very high in +its moisture content, a number of samples giving an average of 65 per +cent or about two-thirds of the total weight of the fuel. The weight of +the spent tan is about 2.13 times as great as the weight of the bark +ground. In calorific value an average of 10 samples gives 9500 B. t. u. +per pound dry.[43] The available heat per pound as fired, owing to the +great percentage of moisture usually found, will be approximately 2700 +B. t. u. Since the weight of the spent tan as fired is 2.13 as great as +the weight of the bark as ground at the mill, one pound of ground bark +produces an available heat of approximately 5700 B. t. u. Relative to +bituminous coal, a ton of bark is equivalent to 0.4 ton of coal. An +average chemical analysis of the bark is, carbon 51.8 per cent, hydrogen +6.04, oxygen 40.74, ash 1.42. + +Tan bark is burned in isolated cases and in general the remarks on +burning wet wood fuel apply to its combustion. The essential features +are a large combustion space, large areas of heated brickwork radiating +to the fuel bed, and draft sufficient for high combustion rates. The +ratings obtainable with this class of fuel will not be as high as with +wet wood fuel, because of the heat value and the excessive moisture +content. Mr. D. M. Meyers found in a series of experiments that an +average of from 1.5 to 2.08 horse power could be developed per square +foot of grate surface with horizontal return tubular boilers. This horse +power would vary considerably with the method in which the spent tan was +fired. + +[Illustration: 686 Horse-power Babcock & Wilcox Boiler and Superheater +in Course of Erection at the Quincy, Mass., Station of the Bay State +Street Railway Co.] + + + + +LIQUID FUELS AND THEIR COMBUSTION + + +Petroleum is practically the only liquid fuel sufficiently abundant and +cheap to be used for the generation of steam. It possesses many +advantages over coal and is extensively used in many localities. + +There are three kinds of petroleum in use, namely those yielding on +distillation: 1st, paraffin; 2nd, asphalt; 3rd, olefine. To the first +group belong the oils of the Appalachian Range and the Middle West of +the United States. These are a dark brown in color with a greenish +tinge. Upon their distillation such a variety of valuable light oils are +obtained that their use as fuel is prohibitive because of price. + +To the second group belong the oils found in Texas and California. These +vary in color from a reddish brown to a jet black and are used very +largely as fuel. + +The third group comprises the oils from Russia, which, like the second, +are used largely for fuel purposes. + +The light and easily ignited constituents of petroleum, such as naphtha, +gasolene and kerosene, are oftentimes driven off by a partial +distillation, these products being of greater value for other purposes +than for use as fuel. This partial distillation does not decrease the +value of petroleum as a fuel; in fact, the residuum known in trade as +"fuel oil" has a slightly higher calorific value than petroleum and +because of its higher flash point, it may be more safely handled. +Statements made with reference to petroleum apply as well to fuel oil. + +In general crude oil consists of carbon and hydrogen, though it also +contains varying quantities of moisture, sulphur, nitrogen, arsenic, +phosphorus and silt. The moisture contained may vary from less than 1 to +over 30 per cent, depending upon the care taken to separate the water +from the oil in pumping from the well. As in any fuel, this moisture +affects the available heat of the oil, and in contracting for the +purchase of fuel of this nature it is well to limit the per cent of +moisture it may contain. A large portion of any contained moisture can +be separated by settling and for this reason sufficient storage capacity +should be supplied to provide time for such action. + +A method of obtaining approximately the percentage of moisture in crude +oil which may be used successfully, particularly with lighter oils, is +as follows. A burette graduated into 200 divisions is filled to the 100 +mark with gasolene, and the remaining 100 divisions with the oil, which +should be slightly warmed before mixing. The two are then shaken +together and any shrinkage below the 200 mark filled up with oil. The +mixture should then be allowed to stand in a warm place for 24 hours, +during which the water and silt will settle to the bottom. Their +percentage by volume can then be correctly read on the burette +divisions, and the percentage by weight calculated from the specific +gravities. This method is exceedingly approximate and where accurate +results are required it should not be used. For such work, the +distillation method should be used as follows: + +Gradually heat 100 cubic centimeters of the oil in a distillation flask +to a temperature of 150 degrees centigrade; collect the distillate in a +graduated tube and measure the resulting water. Such a method insures +complete removal of water and reduces the error arising from the slight +solubility of the water in gasolene. Two samples checked by the two +methods for the amount of moisture present gave, + + _Distillation_ _Dilution_ + _Per Cent_ _Per Cent_ + 8.71 6.25 + 8.82 6.26 + + TABLE 46 + + COMPOSITION AND CALORIFIC VALUE OF VARIOUS OILS + ++-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ +| Kind of Oil | %C | %H | %S | %O |S.G.|FP | %H2O |Btu |Authority | ++-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ +|California, Coaling | | | | |.927|134| |17117|Babcock & Wilcox Co. | +|California, Bakersfield | | | | |.975| | |17600|Wade | +|California, Bakersfield | | |1.30| |.992| | |18257|Wade | +|California, Kern River | | | | |.950|140| |18845|Babcock & Wilcox Co. | +|California, Los Angeles | | |2.56| | | | |18328|Babcock & Wilcox Co. | +|California, Los Angeles | | | | |.957|196| |18855|Babcock & Wilcox Co. | +|California, Los Angeles | | | | |.977| | .40 |18280|Babcock & Wilcox Co. | +|California, Monte Christo| | | | |.966|205| |18878|Babcock & Wilcox Co. | +|California, Whittier | | | .98| |.944| |1.06 |18507|Wade | +|California, Whittier | | | .72| |.936| |1.06 |18240|Wade | +|California |85.04|11.52|2.45| .99[44]| | |1.40 |17871|Babcock & Wilcox Co. | +|California |81.52|11.51| .55|6.92[44]| |230| |18667|U.S.N. Liquid Fuel Board| +|California | | | .87| | | | .95 |18533|Blasdale | +|California | | | | |.891|257| |18655|Babcock & Wilcox Co. | +|California | | |2.45| |.973| |1.50[45]|17976|O'Neill | +|California | | |2.46| |.975| |1.32 |18104|Shepherd | +|Texas, Beaumont |84.6 |10.9 |1.63|2.87 |.924|180| |19060|U.S.N. Liquid Fuel Board| +|Texas, Beaumont |83.3 |12.4 | .50|3.83 |.926|216| |19481|U.S.N. Liquid Fuel Board| +|Texas, Beaumont |85.0 |12.3 |1.75| .92[44]| | | |19060|Denton | +|Texas, Beaumont |86.1 |12.3 |1.60| |.942| | |20152|Sparkes | +|Texas, Beaumont | | | | |.903|222| |19349|Babcock & Wilcox Co. | +|Texas, Sabine | | | | |.937|143| |18662|Babcock & Wilcox Co. | +|Texas |87.15|12.33|0.32| |.908|370| |19338|U. S. N. | +|Texas |87.29|12.32|0.43| |.910|375| |19659|U. S. N. | +|Ohio |83.4 |14.7 |0.6 |1.3 | | | |19580| | +|Pennsylvania |84.9 |13.7 | |1.4 |.886| | |19210|Booth | +|West Virginia |84.3 |14.1 | |1.6 |.841| | |21240| | +|Mexico | | | | |.921|162| |18840|Babcock & Wilcox Co. | +|Russia, Baku |86.7 |12.9 | | |.884| | |20691|Booth | +|Russia, Novorossick |84.9 |11.6 | |3.46 | | | |19452|Booth | +|Russia, Caucasus |86.6 |12.3 | |1.10 |.938| | |20138| | +|Java |87.1 |12.0 | | .9 |.923| | |21163| | +|Austria, Galicia |82.2 |12.1 |5.7 | |.870| | |18416| | +|Italy, Parma |84.0 |13.4 |1.8 | |.786| | | | | +|Borneo |85.7 |11.0 | |3.31 | | | |19240|Orde | ++-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ + +%C = Per Cent Carbon +%H = Per Cent Hydrogen +%S = Per Cent Sulphur +%O = Per Cent Oxygen +S.G. = Specific Gravity +FP = Degrees Flash Point +%H_{2}O = Per Cent Moisture +Btu = B. t. u. Per Pound + +Calorific Value--A pound of petroleum usually has a calorific value of +from 18,000 to 22,000 B. t. u. If an ultimate analysis of an average +sample be, carbon 84 per cent, hydrogen 14 per cent, oxygen 2 per cent, +and assuming that the oxygen is combined with its equivalent of hydrogen +as water, the analysis would become, carbon 84 per cent, hydrogen 13.75 +per cent, water 2.25 per cent, and the heat value per pound including +its contained water would be, + +Carbon .8400 × 14,600 = 12,264 B. t. u. +Hydrogen .1375 × 62,100 = 8,625 B. t. u. + ------[**Should be .1375 x 62,000 = 8,525] + Total 20,889 B. t. u.[**Would be Total = 20,789] + +The nitrogen in petroleum varies from 0.008 to 1.0 per cent, while the +sulphur varies from 0.07 to 3.0 per cent. + +Table 46, compiled from various sources, gives the composition, +calorific value and other data relative to oil from different +localities. + +The flash point of crude oil is the temperature at which it gives off +inflammable gases. While information on the actual flash points of the +various oils is meager, it is, nevertheless, a question of importance in +determining their availability as fuels. In general it may be stated +that the light oils have a low, and the heavy oils a much higher flash +point. A division is sometimes made at oils having a specific gravity of +0.85, with a statement that where the specific gravity is below this +point the flash point is below 60 degrees Fahrenheit, and where it is +above, the flash point is above 60 degrees Fahrenheit. There are, +however, many exceptions to this rule. As the flash point is lower the +danger of ignition or explosion becomes greater, and the utmost care +should be taken in handling the oils with a low flash point to avoid +this danger. On the other hand, because the flash point is high is no +justification for carelessness in handling those fuels. With proper +precautions taken, in general, the use of oil as fuel is practically as +safe as the use of coal. + +Gravity of Oils--Oils are frequently classified according to their +gravity as indicated by the Beaume hydrometer scale. Such a +classification is by no means an accurate measure of their relative +calorific values. + +Petroleum as Compared with Coal--The advantages of the use of oil fuel +over coal may be summarized as follows: + +1st. The cost of handling is much lower, the oil being fed by simple +mechanical means, resulting in, + +2nd. A general labor saving throughout the plant in the elimination of +stokers, coal passers, ash handlers, etc. + +3rd. For equal heat value, oil occupies very much less space than coal. +This storage space may be at a distance from the boiler without +detriment. + +4th. Higher efficiencies and capacities are obtainable with oil than +with coal. The combustion is more perfect as the excess air is reduced +to a minimum; the furnace temperature may be kept practically constant +as the furnace doors need not be opened for cleaning or working fires; +smoke may be eliminated with the consequent increased cleanliness of the +heating surfaces. + +5th. The intensity of the fire can be almost instantaneously regulated +to meet load fluctuations. + +6th. Oil when stored does not lose in calorific value as does coal, nor +are there any difficulties arising from disintegration, such as may be +found when coal is stored. + +7th. Cleanliness and freedom from dust and ashes in the boiler room with +a consequent saving in wear and tear on machinery; little or no damage +to surrounding property due to such dust. + +The disadvantages of oil are: + +1st. The necessity that the oil have a reasonably high flash point to +minimize the danger of explosions. + +2nd. City or town ordinances may impose burdensome conditions relative +to location and isolation of storage tanks, which in the case of a plant +situated in a congested portion of the city, might make use of this fuel +prohibitive. + +3rd. Unless the boilers and furnaces are especially adapted for the use +of this fuel, the boiler upkeep cost will be higher than if coal were +used. This objection can be entirely obviated, however, if the +installation is entrusted to those who have had experience in the work, +and the operation of a properly designed plant is placed in the hands of +intelligent labor. + + TABLE 47 + + RELATIVE VALUE OF COAL AND OIL FUEL + ++------+--------+-------+-----------------------------------------------+ +|Gross | Net | Net | Water Evaporated from and at | +|Boiler| Boiler |Evap- | 212 Degrees Fahrenheit per Pound of Coal | +|Effic-|Effici- |oration+-----+-----+-----+-----+-----+-----+-----+-----+ +| iency|ency[46]| from | | | | | | | | | +| with | with |and at | | | | | | | | | +| Oil | Oil | 212 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | +| Fuel | Fuel |Degrees| | | | | | | | | +| | |Fahren-| | | | | | | | | +| | | heit +-----+-----+-----+-----+-----+-----+-----+-----+ +| | | per | | +| | | Pound | Pounds of Oil Equal to One Pound of Coal | +| | |of Oil | | ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ +| 73 | 71 | 13.54 |.3693|.4431|.5170|.5909|.6647|.7386|.8124|.8863| +| 74 | 72 | 13.73 |.3642|.4370|.5099|.5827|.6556|.7283|.8011|.8740| +| 75 | 73 | 13.92 |.3592|.4310|.5029|.5747|.6466|.7184|.7903|.8621| +| 76 | 74 | 14.11 |.3544|.4253|.4961|.5670|.6378|.7087|.7796|.8505| +| 77 | 75 | 14.30 |.3497|.4196|.4895|.5594|.6294|.6993|.7692|.8392| +| 78 | 76 | 14.49 |.3451|.4141|.4831|.5521|.6211|.6901|.7591|.8281| +| 79 | 77 | 14.68 |.3406|.4087|.4768|.5450|.6131|.6812|.7493|.8174| +| 80 | 78 | 14.87 |.3363|.4035|.4708|.5380|.6053|.6725|.7398|.8070| +| 81 | 79 | 15.06 |.3320|.3984|.4648|.5312|.5976|.6640|.7304|.7968| +| 82 | 80 | 15.25 |.3279|.3934|.4590|.5246|.5902|.6557|.7213|.7869| +| 83 | 81 | 15.44 |.3238|.3886|.4534|.5181|.5829|.6447|.7125|.7772| ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ +| | | Net | | +| | |Evap- | | +| | |oration| | +| | | from | | +| | |and at | | +| | | 212 | Barrels of Oil Equal to One Ton of Coal | +| | |Degrees| | +| | |Fahren-| | +| | | heit | | +| | | per | | +| | |Barrel | | +| | |of Oil | | ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ +| 73 | 71 | 4549 |2.198|2.638|3.077|3.516|3.955|4.395|4.835|5.275| +| 74 | 72 | 4613 |2.168|2.601|3.035|3.468|3.902|4.335|4.769|5.202| +| 75 | 73 | 4677 |2.138|2.565|2.993|3.420|3.848|4.275|4.703|5.131| +| 76 | 74 | 4741 |2.110|2.532|2.954|3.376|3.798|4.220|4.642|5.063| +| 77 | 75 | 4807 |2.082|2.498|2.914|3.330|3.746|4.162|4.578|4.994| +| 78 | 76 | 4869 |2.054|2.465|2.876|3.286|3.697|4.108|4.518|4.929| +| 79 | 77 | 4932 |2.027|2.433|2.838|3.243|3.649|4.054|4.460|4.865| +| 80 | 78 | 4996 |2.002|2.402|2.802|3.202|3.602|4.003|4.403|4.803| +| 81 | 79 | 5060 |1.976|2.371|2.767|3.162|3.557|3.952|4.348|4.743| +| 82 | 80 | 5124 |1.952|2.342|2.732|3.122|3.513|3.903|4.293|4.683| +| 83 | 81 | 5187 |1.927|2.313|2.699|3.085|3.470|3.856|4.241|4.627| ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ + +[Illustration: City of San Francisco, Cal., Fire Fighting Station. No. +1. 2800 Horse Power of Babcock & Wilcox Boilers, Equipped for Burning +Oil Fuel] + +Many tables have been published with a view to comparing the two fuels. +Such of these as are based solely on the relative calorific values of +oil and coal are of limited value, inasmuch as the efficiencies to be +obtained with oil are higher than that obtainable with coal. Table 47 +takes into consideration the variation in efficiency with the two fuels, +but is based on a constant calorific value for oil and coal. This table, +like others of a similar nature, while useful as a rough guide, cannot +be considered as an accurate basis for comparison. This is due to the +fact that there are numerous factors entering into the problem which +affect the saving possible to a much greater extent than do the relative +calorific values of two fuels. Some of the features to be considered in +arriving at the true basis for comparison are the labor saving possible, +the space available for fuel storage, the facilities for conveying the +oil by pipe lines, the hours during which a plant is in operation, the +load factor, the quantity of coal required for banking fires, etc., etc. +The only exact method of estimating the relative advantages and costs of +the two fuels is by considering the operating expenses of the plant with +each in turn, including the costs of every item entering into the +problem. + +Burning Oil Fuel--The requirements for burning petroleum are as follows: + +1st. Its atomization must be thorough. + +2nd. When atomized it must be brought into contact with the requisite +quantity of air for its combustion, and this quantity must be at the +same time a minimum to obviate loss in stack gases. + +3rd. The mixture must be burned in a furnace where a refractory material +radiates heat to assist in the combustion, and the furnace must stand up +under the high temperatures developed. + +4th. The combustion must be completed before the gases come into contact +with the heating surfaces or otherwise the flame will be extinguished, +possibly to ignite later in the flue connection or in the stack. + +5th. There must be no localization of the heat on certain portions of +the heating surfaces or trouble will result from overheating and +blistering. + +The first requirement is met by the selection of a proper burner. + +The second requirement is fulfilled by properly introducing the air into +the furnace, either through checkerwork under the burners or through +openings around them, and by controlling the quantity of air to meet +variations in furnace conditions. + +The third requirement is provided for by installing a furnace so +designed as to give a sufficient area of heated brickwork to radiate the +heat required to maintain a proper furnace temperature. + +The fourth requirement is provided for by giving ample space for the +combustion of the mixture of atomized oil and air, and a gas travel of +sufficient length to insure that this combustion be completed before the +gases strike the heating surfaces. + +The fifth requirement is fulfilled by the adoption of a suitable burner +in connection with the furnace meeting the other requirements. A burner +must be used from which the flame will not impinge directly on the +heating surface and must be located where such action cannot take place. +If suitable burners properly located are not used, not only is the heat +localized with disastrous results, but the efficiency is lowered by the +cooling of the gases before combustion is completed. + +Oil Burners--The functions of an oil burner is to atomize or vaporize +the fuel so that it may be burned like a gas. All burners may be +classified under three general types: 1st, spray burners, in which the +oil is atomized by steam or compressed air; 2nd, vapor burners, in which +the oil is converted into vapor and then passed into the furnace; 3rd, +mechanical burners, in which the oil is atomized by submitting it to a +high pressure and passing it through a small orifice. + +Vapor burners have never been in general use and will not be discussed. + +Spray burners are almost universally used for land practice and the +simplicity of the steam atomizer and the excellent economy of the better +types, together with the low oil pressure and temperature required makes +this type a favorite for stationary plants, where the loss of fresh +water is not a vital consideration. In marine work, or in any case where +it is advisable to save feed water that otherwise would have to be added +in the form of "make-up", either compressed air or mechanical means are +used for atomization. Spray burners using compressed air as the +atomizing agent are in satisfactory operation in some plants, but their +use is not general. Where there is no necessity of saving raw feed +water, the greater simplicity and economy of the steam spray atomizer is +generally the most satisfactory. The air burners require blowers, +compressors or other apparatus which occupy space that might be +otherwise utilized and require attention that is not necessary where +steam is used. + +Steam spray burners of the older types had disadvantages in that they +were so designed that there was a tendency for the nozzle to clog with +sludge or coke formed from the oil by the heat, without means of being +readily cleaned. This has been overcome in the more modern types. + +Steam spray burners, as now used, may be divided into two classes: 1st, +inside mixers; and 2nd, outside mixers. In the former the steam and oil +come into contact within the burner and the mixture is atomized in +passing through the orifice of the burner nozzle. + +[Illustration: Fig. 28. Peabody Oil Burner] + +In the outside mixing class the steam flows through a narrow slot or +horizontal row of small holes in the burner nozzle; the oil flows +through a similar slot or hole above the steam orifice, and is picked up +by the steam outside of the burner and is atomized. Fig. 28 shows a type +of the Peabody burner of this class, which has given eminent +satisfaction. The construction is evident from the cut. It will be noted +that the portions of the burner forming the orifice may be readily +replaced in case of wear, or if it is desired to alter the form of the +flame. + +Where burners of the spray type are used, heating the oil is of +advantage not only in causing it to be atomized more easily, but in +aiding economical combustion. The temperature is, of course, limited by +the flash point of the oil used, but within the limit of this +temperature there is no danger of decomposition or of carbon deposits on +the supply pipes. Such heating should be done close to the boiler to +minimize radiation loss. If the temperature is raised to a point where +an appreciable vaporization occurs, the oil will flow irregularly from +the burner and cause the flame to sputter. + +On both steam and air atomizing types, a by-pass should be installed +between the steam or air and the oil pipes to provide for the blowing +out of the oil duct. Strainers should be provided for removing sludge +from the fuel and should be so located as to allow for rapid removal, +cleaning and replacing. + +Mechanical burners have been in use for some time in European countries, +but their introduction and use has been of only recent occurrence in the +United States. Here as already stated, the means for atomization are +purely mechanical. The most successful of the mechanical atomizers up to +the present have been of the round flame type, and only these will be +considered. Experiments have been made with flat flame mechanical +burners, but their satisfactory action has been confined to instances +where it is only necessary to burn a small quantity of oil through each +individual burner. + +This system of oil burning is especially adapted for marine work as the +quantity of steam for putting pressure on the oil is small and the +condensed steam may be returned to the system. + +The only method by which successful mechanical atomization has been +accomplished is one by which the oil is given a whirling motion within +the burner tip. This is done either by forcing the oil through a passage +of helical form or by delivering it tangentially to a circular chamber +from which there is a central outlet. The oil is fed to these burners +under a pressure which varies with the make of the burner and the rates +at which individual burners are using oil. The oil particles fly off +from such a burner in straight lines in the form of a cone rather than +in the form of a spiral spray, as might be supposed. + +With burners of the mechanical atomizing design, the method of +introducing air for combustion and the velocity of this air are of the +greatest importance in securing good combustion and in the effects on +the character and shape of the flame. Such burners are located at the +front of the furnace and various methods have been tried for introducing +the air for combustion. Where, in the spray burners, air is ordinarily +admitted through a checkerwork under the burner proper, with the +mechanical burner, it is almost universally admitted around the burner. +Early experiments with these air distributors were confined largely to +single or duplicate cones used with the idea of directing the air to the +axis of the burner. A highly successful method of such air introduction, +developed by Messrs. Peabody and Irish of The Babcock & Wilcox Co., is +by means of what they term an "impeller plate". This consists of a +circular metal disk with an opening at the center for the oil burner and +with radial metal strips from the center to the periphery turned at an +angle which in the later designs may be altered to give the air supply +demanded by the rate of combustion. + +The air so admitted does not necessarily require a whirling motion, but +experiments show that where the air is brought into contact with the oil +spray with the right "twist", better combustion is secured and lower air +pressures and less refinement of adjustment of individual burners are +required. + +Mechanical burners have a distinct advantage over those in which steam +is used as the atomizing agent in that they lend themselves more readily +to adjustment under wider variations of load. For a given horse power +there will ordinarily be installed a much greater number of mechanical +than steam atomizing burners. This in itself is a means to better +regulation, for with the steam atomizing burner, if one of a number is +shut off, there is a marked decrease in efficiency. This is due to the +fact that with the air admitted under the burner, it is ordinarily +passing through the checkerwork regardless of whether it is being +utilized for combustion or not. With a mechanical burner, on the other +hand, where individual burners are shut off, air that would be admitted +for such burner, were it in operation, may also be shut off and there +will be no undue loss from excess air. + +Further adjustment to meet load conditions is possible by a change in +the oil pressure acting on all burners at once. A good burner will +atomize moderately heavy oil with an oil pressure as low as 30 pounds +per square inch and from that point up to 200 pounds or above. The +heating of the oil also has an effect on the capacity of individual +burners and in this way a third method of adjustment is given. Under +working conditions, the oil pressure remaining constant, the capacity of +each burner will decrease as the temperature of the oil is increased +though at low temperatures the reverse is the case. Some experiments +with a Texas crude oil having a flash point of 210 degrees showed that +the capacity of a mechanical atomizing burner of the Peabody type +increased from 80 degrees Fahrenheit to 110 degrees Fahrenheit, from +which point it fell off rapidly to 140 degrees and then more slowly to +the flash point. + +The above methods, together with the regulation possible through +manipulation of the boiler dampers, indicate the wide range of load +conditions that may be handled with an installation of this class of +burners. + +As has already been stated, results with mechanical atomizing burners +that may be considered very successful have been limited almost entirely +to cases where forced blast of some description has been used, the high +velocity of the air entering being of material assistance in securing +the proper mixture of air with the oil spray. Much has been done and is +being done in the way of experiment with this class of apparatus toward +developing a successful mechanical atomizing burner for use with natural +draft, and there appears to be no reason why such experiments should not +eventually produce satisfactory results. + +Steam Consumption of Burners--The Bureau of Steam Engineering, U. S. +Navy, made in 1901 an exhaustive series of tests of various oil burners +that may be considered as representing, in so far as the performance of +the burners themselves is concerned, the practice of that time. These +tests showed that a burner utilizing air as an atomizing agent, required +for compressing the air from 1.06 to 7.45 per cent of the total steam +generated, the average being 3.18 per cent. Four tests of steam +atomizing burners showed a consumption of 3.98 to 5.77 per cent of the +total steam, the average being 4.8 per cent. + +Improvement in burner design has largely reduced the steam consumption, +though to a greater degree in steam than in air atomizing burners. +Recent experiments show that a good steam atomizing burner will require +approximately 2 per cent of the total steam generated by the boiler +operated at or about its rated capacity. This figure will decrease as +the capacity is increased and is so low as to be practically negligible, +except in cases where the question of loss of feed water is all +important. There are no figures available as to the actual steam +consumption of mechanical atomizing burners but apparently this is small +if the requirement is understood to be entirely apart from the steam +consumption of the apparatus producing the forced blast. + +Capacity of Burners--A good steam atomizing burner properly located in a +well-designed oil furnace has a capacity of somewhat over 400 horse +power. This question of capacity of individual burners is largely one of +the proper relation between the number of burners used and the furnace +volume. In some recent tests with a Babcock & Wilcox boiler of 640 rated +horse power, equipped with three burners, approximately 1350 horse power +was developed with an available draft of .55 inch at the damper or 450 +horse power per burner. Four burners were also tried in the same furnace +but the total steam generated did not exceed 1350 horse power or in this +instance 338 horse power per burner. + +From the nature of mechanical atomizing burners, individual burners have +not as large a capacity as the steam atomizing class. In some tests on a +Babcock & Wilcox marine boiler, equipped with mechanical atomizing +burners, the maximum horse power developed per burner was approximately +105. Here again the burner capacity is largely one of proper relation +between furnace volume and number of burners. + +Furnace Design--Too much stress cannot be laid on the importance of +furnace design for the use of this class of fuel. Provided a good type +of burner is adopted the furnace arrangement and the method of +introducing air for combustion into the furnace are the all important +factors. No matter what the type of burner, satisfactory results cannot +be secured in a furnace not suited to the fuel. + +The Babcock & Wilcox Co. has had much experience with the burning of oil +as fuel and an extended series of experiments by Mr. E. H. Peabody led +to the development and adoption of the Peabody furnace as being most +eminently suited for this class of work. Fig. 29 shows such a furnace +applied to a Babcock & Wilcox boiler, and with slight modification it +can be as readily applied to any boiler of The Babcock & Wilcox Co. +manufacture. In the description of this furnace, its points of advantage +cover the requirements of oil-burning furnaces in general. + +The atomized oil is introduced into the furnace in the direction in +which it increases in height. This increase in furnace volume in the +direction of the flame insures free expansion and a thorough mixture of +the oil with the air, and the consequent complete combustion of the +gases before they come into contact with the tube heating surfaces. In +such a furnace flat flame burners should be used, preferably of the +Peabody type, in which the flame spreads outward toward the sides in the +form of a fan. There is no tendency of the flames to impinge directly on +the heating surfaces, and the furnace can handle any quantity of flame +without danger of tube difficulties. The burners should be so located +that the flames from individual burners do not interfere nor impinge to +any extent on the side walls of the furnace, an even distribution of +heat being secured in this manner. The burners are operated from the +boiler front and peepholes are supplied through which the operator may +watch the flame while regulating the burners. The burners can be +removed, inspected, or cleaned and replaced in a few minutes. Air is +admitted through a checkerwork of fire brick supported on the furnace +floor, the openings in the checkerwork being so arranged as to give the +best economic results in combustion. + +[Illustration: Fig. 29. Babcock & Wilcox Boiler, Equipped with a Peabody +Oil Furnace] + +With steam atomizing burners introduced through the front of the boiler +in stationary practice, it is usually in the direction in which the +furnace decreases in height and it is with such an arrangement that +difficulties through the loss of tubes may be expected. With such an +arrangement, the flame may impinge directly upon the tube surfaces and +tube troubles from this source may arise, particularly where the feed +water has a tendency toward rapid scale formation. Such difficulties may +be the result of a blowpipe action on the part of the burner, the over +heating of the tube due to oil or scale within, or the actual erosion of +the metal by particles of oil improperly atomized. Such action need not +be anticipated, provided the oil is burned with a short flame. The +flames from mechanical atomizing burners have a less velocity of +projection than those from steam atomizing burners and if introduced +into the higher end of the furnace, should not lead to tube difficulties +provided they are properly located and operated. This class of burner +also will give the most satisfactory results if introduced so that the +flames travel in the direction of increase in furnace volume. This is +perhaps best exemplified by the very good results secured with +mechanical atomizing burners and Babcock & Wilcox marine boilers in +which, due to the fact that the boilers are fired from the low end, the +flames from burners introduced through the front are in this direction. + +Operation of Burners--When burners are not in use, or when they are +being started up, care must be taken to prevent oil from flowing and +collecting on the floor of the furnace before it is ignited. In starting +a burner, the atomized fuel may be ignited by a burning wad of oil-soaked +waste held before it on an iron rod. To insure quick ignition, the steam +supply should be cut down. But little practice is required to become an +adept at lighting an oil fire. When ignition has taken place and the +furnace brought to an even heat, the steam should be cut down to the +minimum amount required for atomization. This amount can be determined +from the appearance of the flame. If sufficient steam is not supplied, +particles of burning oil will drop to the furnace floor, giving a +scintillating appearance to the flame. The steam valves should be opened +just sufficiently to overcome this scintillating action. + +Air Supply--From the nature of the fuel and the method of burning, the +quantity of air for combustion may be minimized. As with other fuels, +when the amount of air admitted is the minimum which will completely +consume the oil, the results are the best. The excess or deficiency of +air can be judged by the appearance of the stack or by observing the +gases passing through the boiler settings. A perfectly clear stack +indicates excess air, whereas smoke indicates a deficiency. With +properly designed furnaces the best results are secured by running near +the smoking point with a slight haze in the gases. A slight variation in +the air supply will affect the furnace conditions in an oil burning +boiler more than the same variation where coal is used, and for this +reason it is of the utmost importance that flue gas analysis be made +frequently on oil-burning boilers. With the air for combustion properly +regulated by adjustment of any checkerwork or any other device which may +be used, and the dampers carefully set, the flue gas analysis should +show, for good furnace conditions, a percentage of CO_{2} between 13 and +14 per cent, with either no CO or but a trace. + +In boiler plant operation it is difficult to regulate the steam supply +to the burners and the damper position to meet sudden and repeated +variations in the load. A device has been patented which automatically +regulates by means of the boiler pressure the pressure of the steam to +the burners, the oil to the burners and the position of the boiler +damper. Such a device has been shown to give good results in plant +operation where hand regulation is difficult at best, and in many +instances is unfortunately not even attempted. + +Efficiency with Oil--As pointed out in enumerating the advantages of oil +fuel over coal, higher efficiencies are obtainable with the former. With +boilers of approximately 500 horse power equipped with properly designed +furnaces and burners, an efficiency of 83 per cent is possible or making +an allowance of 2 per cent for steam used by burners, a net efficiency +of 81 per cent. The conditions under which such efficiencies are to be +secured are distinctly test conditions in which careful operation is a +prime requisite. With furnace conditions that are not conductive to the +best combustion, this figure may be decreased by from 5 to 10 per cent. +In large properly designed plants, however, the first named efficiency +may be approached for uniform running conditions, the nearness to which +it is reached depending on the intelligence of the operating crew. It +must be remembered that the use of oil fuel presents to the careless +operator possibilities for wastefulness much greater than in plants +where coal is fired, and it therefore pays to go carefully into this +feature. + +Table 48 gives some representative tests with oil fuel. + + TABLE 48 + + TESTS OF BABCOCK AND WILCOX BOILERS WITH OIL FUEL + + _______________________________________________________________________ +| | | | | +| |Pacific Light|Pacific Light|Miami Copper | +| | and Power | and Power | Company | +| Plant | Company | Company | | +| |Los Angeles, | | Miami, | +| | Cal. |Redondo, Cal.| Arizona | +|_____________________________|_____________|_____________|_____________| +| | | | | | +| Rated Capacity | Horse | | | | +| of Boiler | Power | 467 | 604 | 600 | +|__________________|__________|_____________|_____________|_____________| +| | | | | | | | | +| Duration of Test | Hours | 10 | 10 | 7 | 7 | 10 | 4 | +| | | | | | | | | +| Steam Pressure | | | | | | | | +| by Gauge | Pounds | 156.4| 156.9| 184.7| 184.9| 183.4| 189.5| +| | | | | | | | | +| Temperature of | Degrees | | | | | | | +| Feed Water | F. | 62.6| 61.1| 93.4| 101.2| 157.7| 156.6| +| | | | | | | | | +| Degrees of | Degrees | | | | | | | +| Superheat | F. | | | 83.7| 144.3| 103.4| 139.6| +| | | | | | | | | +| Factor of | | | | | | | | +| Evaporation | |1.2004|1.2020|1.2227|1.2475|1.1676|1.1886| +| | | | | | | | | +| Draft in Furnace | Inches | .02 | .05 | .014| .19 | .12 | .22 | +| | | | | | | | | +| Draft at Damper | Inches | .08 | .15 | .046| .47 | .19 | .67 | +| | | | | | | | | +| Temperature of | Degrees | | | | | | | +| Exit Gases | F. | 438 | 525 | 406 | 537 | 430 | 612 | +| _ | | | | | | | | +| Flue | CO_{2} | Per Cent | | | 14.3 | 12.1 | | | +| Gas | O | Per Cent | | | 3.8 | 6.8 | | | +| Analysis|_CO | Per Cent | | | 0.0 | 0.0 | | | +| | | | | | | | | +| Oil Burned | | | | | | | | +| per Hour | Pounds | 1147 | 1837 | 1439 | 2869 | 1404 | 3214 | +| | | | | | | | | +| Water Evaporated | | | | | | | | +| per Hour from | | | | | | | | +| from and at | Pounds | 18310| 27855| 22639| 40375| 21720| 42863| +| 212 Degrees | | | | | | | | +| | | | | | | | | +| Evaporation from | | | | | | | | +| and at 212 | | | | | | | | +| Degrees per | Pounds | 15.96| 15.16| 15.73| 14.07| 15.47| 13.34| +| Pound of Oil | | | | | | | | +| | | | | | | | | +| Per Cent of | | | | | | | | +| Rated Capacity | Pounds | 113.6| 172.9| 108.6| 193.8| 104.9| 207.1| +| Developed | | | | | | | | +| | | | | | | | | +| B. t. u. per | | | | | | | | +| Pound of Oil | B. t. u. | 18626| 18518| 18326| 18096| 18600| 18600| +| | | | | | | | | +| Efficiency | Per Cent | 83.15| 79.46| 83.29| 76.02| 80.70| 69.6 | +|__________________|__________|______|______|______|______|______|______| + +Burning Oil in Connection with Other Fuels--Considerable attention has +been recently given to the burning of oil in connection with other +fuels, and a combination of this sort may be advisable either with the +view to increasing the boiler capacity to assist over peak loads, or to +keep the boiler in operation where there is the possibility of a +temporary failure of the primary fuel. It would appear from experiments +that such a combination gives satisfactory results from the standpoint +of both capacity and efficiency, if the two fuels are burned in separate +furnaces. Satisfactory results cannot ordinarily be obtained when it is +attempted to burn oil fuel in the same furnace as the primary fuel, as +it is practically impossible to admit the proper amount of air for +combustion for each of the two fuels simultaneously. The Babcock & +Wilcox boiler lends itself readily to a double furnace arrangement and +Fig. 30 shows an installation where oil fuel is burned as an auxiliary +to wood. + +[Illustration: Fig. 30. Babcock & Wilcox Boiler Set with Combination Oil +and Wood-burning Furnace] + +Water-gas Tar--Water-gas tar, or gas-house tar, is a by-product of the +coal used in the manufacture of water gas. It is slightly heavier than +crude oil and has a comparatively low flash point. In burning, it should +be heated only to a temperature which makes it sufficiently fluid, and +any furnace suitable for crude oil is in general suitable for water-gas +tar. Care should be taken where this fuel is used to install a suitable +apparatus for straining it before it is fed to the burner. + +[Illustration: Babcock & Wilcox Boilers Fired with Blast Furnace Gas at +the Bethlehem Steel Co., Bethlehem, Pa. This Company Operates 12,900 +Horse Power of Babcock & Wilcox Boilers] + + + + +GASEOUS FUELS AND THEIR COMBUSTION + + +Of the gaseous fuels available for steam generating purposes, the most +common are blast furnace gas, natural gas and by-product coke oven gas. + +Blast furnace gas, as implied by its name, is a by-product from the +blast furnace of the iron industry. This gasification of the solid fuel +in a blast furnace results, 1st, through combustion by the oxygen of the +blast; 2nd, through contact with the incandescent ore (Fe_{2}O_{3} + C += 2 FeO + CO and FeO + C = Fe + CO); and 3rd, through the agency of +CO_{2} either formed in the process of reduction or driven from the +carbonates charged either as ore or flux. + +Approximately 90 per cent of the fuel consumed in all of the blast +furnaces of the United States is coke. The consumption of coke per ton +of iron made varies from 1600 to 3600 pounds per ton of 2240 pounds of +iron. This consumption depends upon the quality of the coal, the nature +of the ore, the quality of the pig iron produced and the equipment and +management of the plant. The average consumption, and one which is +approximately correct for ordinary conditions, is 2000 pounds of coke +per gross ton (2240 pounds) of pig iron. The gas produced in a gas +furnace per ton of pig iron is obtained from the weight of fixed carbon +gasified, the weight of the oxygen combined with the material of charge +reduced, the weight of the gaseous constituents of the flux and the +weight of air delivered by the blowing engine and the weight of volatile +combustible contained in the coke. Ordinarily, this weight of gas will +be found to be approximately five times the weight of the coke burned, +or 10,000 pounds per ton of pig iron produced. + +With the exception of the small amount of carbon in combination with +hydrogen as methane, and a very small percentage of free hydrogen, +ordinarily less than 0.1 per cent, the calorific value of blast furnace +gas is due to the CO content which when united with sufficient oxygen +when burned under a boiler, burns further to CO_{2}. The heat value of +such gas will vary in most cases from 85 to 100 B. t. u. per cubic foot +under standard conditions. In modern practice, where the blast is heated +by hot blast stoves, approximately 15 per cent of the total amount of +gas is used for this purpose, leaving 85 per cent of the total for use +under boilers or in gas engines, that is, approximately 8500 pounds of +gas per ton of pig iron produced. In a modern blast furnace plant, the +gas serves ordinarily as the only fuel required. Table 49 gives the +analyses of several samples of blast furnace gas. + + TABLE 49 + + TYPICAL ANALYSES OF BLAST FURNACE GAS + ++----------------------------------------------------------------+ +|+-----------------------+------+----+-----+----+------+--------+| +|| |CO_{2}| O | CO | H |CH_{4}| N || +|+-----------------------+------+----+-----+----+------+--------+| +||Bessemer Furnace | 9.85|0.36|32.73|3.14| .. |53.92 || +||Bessemer Furnace | 11.4 | .. |27.7 |1.9 | 0.3 |58.7 || +||Bessemer Furnace | 10.0 | .. |26.2 |3.1 | 0.2 |60.5 || +||Bessemer Furnace | 9.1 | .. |28.7 |2.7 | 0.2 |59.3 || +||Bessemer Furnace | 13.5 | .. |25.2 |1.43| .. |59.87 || +||Bessemer Furnace[47] | 10.9 | .. |27.8 |2.8 | 0.2 |58.3 || +||Ferro Manganese Furnace| 7.1 | .. |30.1 | .. | .. |62.8[48]|| +||Basic Ore Furnace | 16.0 |0.2 |23.6 | .. | .. |60.2[48]|| +|+-----------------------+------+----+-----+----+------+--------+| ++----------------------------------------------------------------+ + +Until recently, the important consideration in the burning of blast +furnace gas has been the capacity that can be developed with practically +no attention given to the aspect of efficiency. This phase of the +question is now drawing attention and furnaces especially designed for +good efficiency with this class of fuel are demanded. The essential +feature is ample combustion space, in which the combustion of gases may +be practically completed before striking the heating surfaces. The gases +have the power of burning out completely after striking the heating +surfaces, provided the initial temperature is sufficiently high, but +where the combustion is completed before such time, the results secured +are more satisfactory. A furnace volume of approximately 1 to 1.5 cubic +feet per rated boiler horse power will give a combustion space that is +ample. + +Where there is the possibility of a failure of the gas supply, or where +steam is required when the blast furnace is shut down, coal fired grates +of sufficient size to get the required capacity should be installed. +Where grates of full size are not required, ignition grates should be +installed, which need be only large enough to carry a fire for igniting +the gas or for generating a small quantity of steam when the blast +furnace is shut down. The area of such grates has no direct bearing on +the size of the boiler. The grates may be placed directly under the gas +burners in a standard position or may be placed between two bridge walls +back of the gas furnace and fired from the side of the boiler. An +advantage is claimed for the standard grate position that it minimizes +the danger of explosion on the re-ignition of gas after a temporary +stoppage of the supply and also that a considerable amount of dirt, of +which there is a good deal with this class of fuel and which is +difficult to remove, deposits on the fire and is taken out when the +fires are cleaned. In any event, regardless of the location of the +grates, ample provision should be made for removing this dust, not only +from the furnace but from the setting as a whole. + +Blast furnace gas burners are of two general types: Those in which the +air for combustion is admitted around the burner proper, and those in +which this air is admitted through the burner. Whatever the design of +burner, provision should be made for the regulation of both the air and +the gas supply independently. A gas opening of .8 square inch per rated +horse power will enable a boiler to develop its nominal rating with a +gas pressure in the main of about 2 inches. This pressure is ordinarily +from 6 to 8 inches and in this way openings of the above size will be +good for ordinary overloads. The air openings should be from .75 to .85 +square inch per rated horse power. Good results are secured by inclining +the gas burners slightly downward toward the rear of the furnace. Where +the burners are introduced over coal fired grates, they should be set +high enough to give headroom for hand firing. + +Ordinarily, individual stacks of 130 feet high with diameters as given +in Kent's table for corresponding horse power are large enough for this +class of work. Such a stack will give a draft sufficient to allow a +boiler to be operated at 175 per cent of its rated capacity, and beyond +this point the capacity will not increase proportionately with the +draft. When more than one boiler is connected with a stack, the draft +available at the damper should be equivalent to that which an individual +stack of 130 feet high would give. The draft from such a stack is +necessary to maintain a suction under all conditions throughout all +parts of the setting. If the draft is increased above that which such a +stack will give, difficulties arise from excess air for combustion with +consequent loss in efficiency. + +A poor mixing or laneing action in the furnace may result in a pulsating +effect of the gases in the setting. This action may at times be remedied +by admitting more air to the furnace. On account of the possibility of a +pulsating action of the gases under certain conditions and the puffs or +explosions, settings for this class of work should be carefully +constructed and thoroughly buckstayed and tied. + +Natural Gas--Natural gas from different localities varies considerably +in composition and heating value. In Table 50 there is given a number of +analyses and heat values for natural gas from various localities. + +This fuel is used for steam generating purposes to a considerable extent +in some localities, though such use is apparently decreasing. It is best +burned by employing a large number of small burners, each being capable +of handling 30 nominal rated horse power. The use of a large number of +burners obviates the danger of any laneing or blowpipe action, which +might be present where large burners are used. Ordinarily, such a gas, +as it enters the burners, is under a pressure of about 8 ounces. For the +purpose of comparison, all observations should be based on gas reduced +to the standard conditions of temperature and pressure, namely 32 +degrees Fahrenheit and 14.7 pounds per square inch. When the temperature +and pressure corresponding to meter readings are known, the volume of +gas under standard conditions may be obtained by multiplying the meter +readings in cubic feet by 33.54 P/T, in which P equals the absolute +pressure in pounds per square inch and T equals the absolute temperature +of the gas at the meter. In boiler testing work, the evaporation should +always be reduced to that per cubic foot of gas under standard +conditions. + + TABLE 50 + + TYPICAL ANALYSES (BY VOLUME) AND CALORIFIC VALUES OF NATURAL + GAS FROM VARIOUS LOCALITIES + ++----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ +|Locality of Well| H |CH_{4}| CO |CO_{2}| N | O | Heavy |H_{2}S|B. t. u.| +| | | | | | | |Hydro- | | per | +| | | | | | | |carbons| | Cubic | +| | | | | | | | | | Foot | +| | | | | | | | | |Calcul- | +| | | | | | | | | |ated[49]| +|----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ +|Anderson, Ind. | 1.86|93.07| 0.73| 0.26| 3.02|0.42| 0.47 | 0.15 | 1017 | +|Marion, Ind. | 1.20|93.16| 0.60| 0.30| 3.43|0.55| 0.15 | 0.20 | 1009 | +|Muncie, Ind. | 2.35|92.67| 0.45| 0.25| 3.53|0.35| 0.25 | 0.15 | 1004 | +|Olean, N. Y. | |96.50| 0.50| | |2.00| 1.00 | | 1018 | +|Findlay, O. | 1.64|93.35| 0.41| 0.25| 3.41|0.39| 0.35 | 0.20 | 1011 | +|St. Ive, Pa. | 6.10|75.54|Trace| 0.34| | | 18.12 | | 1117 | +|Cherry Tree, Pa.|22.50|60.27| | 2.28| 7.32|0.83| 6.80 | | 842 | +|Grapeville, Pa. |24.56|14.93|Trace|Trace|18.69|1.22| 40.60 | | 925 | +|Harvey Well, | | | | | | | | | | +| Butler Co., Pa.|13.50|80.00|Trace| 0.66| | | 5.72 | | 998 | +|Pittsburgh, Pa. | 9.64|57.85| 1.00| |23.41|2.10| 6.00 | | 748 | +|Pittsburgh, Pa. |20.02|72.18| 1.00| 0.80| |1.10| 4.30 | | 917 | +|Pittsburgh, Pa. |26.16|65.25| 0.80| 0.60| |0.80| 6.30 | | 899 | ++----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ + +[Illustration: 1600 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters at the Carnegie Natural Gas Co., Underwood, W. Va. +Natural Gas is the Fuel Burned under these Boilers] + +When natural gas is the only fuel, the burners should be evenly +distributed over the lower portion of the boiler front. If the fuel is +used as an auxiliary to coal, the burners may be placed through the fire +front. A large combustion space is essential and a volume of .75 cubic +feet per rated horse power will be found to give good results. The +burners should be of a design which give the gas and air a rotary motion +to insure a proper mixture. A checkerwork wall is sometimes placed in +the furnace about 3 feet from the burners to break up the flame, but +with a good design of burner this is unnecessary. Where the gas is +burned alone and no grates are furnished, good results are secured by +inclining the burner downward to the rear at a slight angle. + +By-product Coke Oven Gas--By-product coke oven gas is a product of the +destructive distillation of coal in a distilling or by-product coke +oven. In this class of apparatus the gases, instead of being burned at +the point of their origin, as in a beehive or retort coke oven, are +taken from the oven through an uptake pipe, cooled and yield as +by-products tar, ammonia, illuminating and fuel gas. A certain portion +of the gas product is burned in the ovens and the remainder used or sold +for illuminating or fuel purposes, the methods of utilizing the gas +varying with plant operation and locality. + +Table 51 gives the analyses and heat value of certain samples of +by-product coke oven gas utilized for fuel purposes. + +This gas is nearer to natural gas in its heat value than is blast +furnace gas, and in general the remarks as to the proper methods of +burning natural gas and the features to be followed in furnace design +hold as well for by-product coke oven gas. + + TABLE 51 + + TYPICAL ANALYSES OF BY-PRODUCT + COKE OVEN GAS + ++----------------------------------------------+ +|+------+-------------------------------------+| +||CO_{2}| O |CO |CH_{4}| H | N |B.t.u. per|| +|| | | | | | |Cubic Foot|| +|+------+-----+---+------+----+----+----------+| +|| 0.75 |Trace|6.0|28.15 |53.0|12.1| 505 || +|| 2.00 |Trace|3.2|18.80 |57.2|18.0| 399 || +|| 3.20 | 0.4 |6.3|29.60 |41.6|16.1| 551 || +|| 0.80 | 1.6 |4.9|28.40 |54.2|10.1| 460 || +|+------+-----+---+------+----+----+----------+| ++----------------------------------------------+ + +The essential difference in burning the two fuels is the pressure under +which it reaches the gas burner. Where this is ordinarily from 4 to 8 +ounces in the case of natural gas, it is approximately 4 inches of water +in the case of by-product coke oven gas. This necessitates the use of +larger gas openings in the burners for the latter class of fuel than for +the former. + +By-product coke oven gas comes to the burners saturated with moisture +and provision should be made for the blowing out of water of +condensation. This gas too, carries a large proportion of tar and +hydrocarbons which form a deposit in the burners and provision should be +made for cleaning this out. This is best accomplished by an attachment +which permits the blowing out of the burners by steam. + + + + +UTILIZATION OF WASTE HEAT + + +While it has been long recognized that the reclamation of heat from the +waste gases of various industrial processes would lead to a great saving +in fuel and labor, the problem has, until recently, never been given the +attention that its importance merits. It is true that installations have +been made for the utilization of such gases, but in general they have +consisted simply in the placing of a given amount of boiler heating +surface in the path of the gases and those making the installations have +been satisfied with whatever power has been generated, no attention +being given to the proportioning of either the heating surface or the +gas passages to meet the peculiar characteristics of the particular +class of waste gas available. The Babcock & Wilcox Co. has recently gone +into the question of the utilization of what has been known as waste +heat with great thoroughness, and the results secured by their +installations with practically all operations yielding such gases are +eminently successful. + + TABLE 52 + + TEMPERATURE OF WASTE GASES FROM + VARIOUS INDUSTRIAL PROCESSES + ++-----------------------------------------------------+ +|+-----------------------------------+---------------+| +||Waste Heat From |Temperature[50]|| +|| | Degrees || +|+-----------------------------------+---------------+| +||Brick Kilns | 2000-2300 || +||Zinc Furnaces | 2000-2300 || +||Copper Matte Reverberatory Furnaces| 2000-2200 || +||Beehive Coke Ovens | 1800-2000 || +||Cement Kilns | 1200-1600[51]|| +||Nickel Refining Furnaces | 1500-1750 || +||Open Hearth Steel Furnaces | 1100-1400 || +|+-----------------------------------+---------------+| ++-----------------------------------------------------+ + +The power that can be obtained from waste gases depends upon their +temperature and weight, and both of these factors vary widely in +different commercial operations. Table 52 gives a list of certain +processes yielding waste gases the heat of which is available for the +generation of steam and the approximate temperature of such gases. It +should be understood that the temperatures in the table are the average +of the range of a complete cycle of the operation and that the minimum +and maximum temperatures may vary largely from the figures given. + +The maximum available horse power that may be secured from such gases is +represented by the formula: + + W(T-t)s +H. P. = ------- (23) + 33,479 + + +Where W = the weight of gases passing per hour, + T = temperature of gases entering heating surface, + t = temperature leaving heating surface, + s = specific heat of gases. + +The initial temperature and the weight or volume of gas will depend, as +stated, upon the process involved. The exit temperature will depend, to +a certain extent, upon the temperature of the entering gases, but will +be governed mainly by the efficiency of the heating surfaces installed +for the absorption of the heat. + +Where the temperature of the gas available is high, approaching that +found in direct fired boiler practice, the problem is simple and the +question of design of boiler becomes one of adapting the proper amount +of heating surface to the volume of gas to be handled. With such +temperatures, and a volume of gas available approximately in accordance +with that found in direct fired boiler practice, a standard boiler or +one but slightly modified from the standard will serve the purpose +satisfactorily. As the temperatures become lower, however, the problem +is more difficult and the departure from standard practice more radical. +With low temperature gases, to obtain a heat transfer rate at all +comparable with that found in ordinary boiler practice, the lack of +temperature must be offset by an added velocity of the gases in their +passage over the heating surfaces. In securing the velocity necessary to +give a heat transfer rate with low temperature gases sufficient to make +the installation of waste heat boilers show a reasonable return on the +investment, the frictional resistance to the gases through the boiler +becomes greatly in excess of what would be considered good practice in +direct fired boilers. Practically all operations yielding waste gases +require that nothing be done in the way of impairing the draft at the +furnace outlet, as this might interfere with the operation of the +primary furnace. The installation of a waste heat boiler, therefore, +very frequently necessitates providing sufficient mechanical draft to +overcome the frictional resistance of the gases through the heating +surfaces and still leave ample draft available to meet the maximum +requirements of the primary furnace. + +Where the temperature and volume of the gases are in line with what are +found in ordinary direct fired practice, the area of the gas passages +may be practically standard. With the volume of gas known, the draft +loss through the heating surfaces may be obtained from experimental data +and this additional draft requirement met by the installation of a stack +sufficient to take care of this draft loss and still leave draft enough +for operating the furnace at its maximum capacity. + +Where the temperatures are low, the added frictional resistance will +ordinarily be too great to allow the draft required to be secured by +additional stack height and the installation of a fan is necessary. Such +a fan should be capable of handling the maximum volume of gas that the +furnace may produce, and of maintaining a suction equivalent to the +maximum frictional resistance of such volume through the boiler plus the +maximum draft requirement at the furnace outlet. Stacks and fans for +this class of work should be figured on the safe side. Where a fan +installation is necessary, the loss of draft in the fan connections +should be considered, and in figuring conservatively it should be +remembered that a fan of ample size may be run as economically as a +smaller fan, whereas the smaller fan, if overloaded, is operated with a +large loss in efficiency. In practically any installation where low +temperature gas requires a fan to give the proper heat transfer from the +gases, the cost of the fan and of the energy to drive it will be more +than offset by the added power from the boiler secured by its use. +Furthermore, the installation of such a fan will frequently increase the +capacity of the industrial furnace, in connection with which the waste +heat boilers are installed. + +In proportioning heating surfaces and gas passages for waste heat work +there are so many factors bearing directly on what constitutes the +proper installation that it is impossible to set any fixed rules. Each +individual installation must be considered by itself as well as the +particular characteristics of the gases available, such as their +temperature and volume, and the presence of dust or tar-like substances, +and all must be given the proper weight in the determination of the +design of the heating surfaces and gas passages for the specific set of +conditions. + +[Graph: Per Cent of Water Heating Surface passed over by Gases/Per Cent +of the Total Amount of Steam Generated in the Boiler +against Temperature in Degrees Fahrenheit of Hot Gases Sweeping Heating +Surface + +Fig. 31. Curve Showing Relation Between Gas Temperature, Heating Surface +passed over, and Amount of Steam Generated. Ten Square Feet of Heating +Surface are Assumed as Equivalent to One Boiler Horse Power] + +Fig. 31 shows the relation of gas temperatures, heating surface passed +over and work done by such surface for use in cases where the +temperatures approach those found in direct fired practice and where the +volume of gas available is approximately that with which one horse power +may be developed on 10 square feet of heating surface. The curve assumes +what may be considered standard gas passage areas, and further, that +there is no heat absorbed by direct radiation from the fire. + +Experiments have shown that this curve is very nearly correct for the +conditions assumed. Such being the case, its application in waste heat +work is clear. Decreasing or increasing the velocity of the gases over +the heating surfaces from what might be considered normal direct fired +practice, that is, decreasing or increasing the frictional loss through +the boiler will increase or decrease the amount of heating surface +necessary to develop one boiler horse power. The application of Fig. 31 +to such use may best be seen by an example: + +Assume the entering gas temperatures to be 1470 degrees and that the +gases are cooled to 570 degrees. From the curve, under what are assumed +to be standard conditions, the gases have passed over 19 per cent of +the heating surface by the time they have been cooled 1470 degrees. +When cooled to 570 degrees, 78 per cent of the heating surface has been +passed over. The work done in relation to the standard of the curve is +represented by (1470 - 570) ÷ (2500 - 500) = 45 per cent. (These +figures may also be read from the curve in terms of the per cent of the +work done by different parts of the heating surfaces.) That is, 78 per +cent - 19 per cent = 59 per cent of the standard heating surface has +done 45 per cent of the standard amount of work. 59 ÷ 45 = 1.31, which +is the ratio of surface of the assumed case to the standard case of the +curve. Expressed differently, there will be required 13.1 square feet +of heating surface in the assumed case to develop a horse power as +against 10 square feet in the standard case. + +The gases available for this class of work are almost invariably very +dirty. It is essential for the successful operation of waste-heat +boilers that ample provision be made for cleaning by the installation of +access doors through which all parts of the setting may be reached. In +many instances, such as waste-heat boilers set in connection with cement +kilns, settling chambers are provided for the dust before the gases +reach the boiler. + +By-passes for the gases should in all cases be provided to enable the +boiler to be shut down for cleaning and repairs without interfering with +the operation of the primary furnace. All connections from furnace to +boilers should be kept tight to prevent the infiltration of air, with +the consequent lowering of gas temperatures. + +Auxiliary gas or coal fired grates must be installed to insure +continuity in the operation of the boiler where the operation of the +furnace is intermittent or where it may be desired to run the boiler +with the primary furnace not in operation. Such grates are sometimes +used continuously where the gases available are not sufficient to +develop the required horse power from a given amount of heating surface. + +Fear has at times been expressed that certain waste gases, such as those +containing sulphur fumes, will have a deleterious action on the heating +surface of the boiler. This feature has been carefully watched, however, +and from plants in operation it would appear that in the absence of +water or steam leaks within the setting, there is no such harmful +action. + +[Illustration: Fig. 32. Babcock & Wilcox Boiler Arranged for Utilizing +Waste Heat from Open Hearth Furnace. This Setting may be Modified to +Take Care of Practically any Kind of Waste Gas] + + + + +CHIMNEYS AND DRAFT + + +The height and diameter of a properly designed chimney depend upon the +amount of fuel to be burned, its nature, the design of the flue, with +its arrangement relative to the boiler or boilers, and the altitude of +the plant above sea level. There are so many factors involved that as +yet there has been produced no formula which is satisfactory in taking +them all into consideration, and the methods used for determining stack +sizes are largely empirical. In this chapter a method sufficiently +comprehensive and accurate to cover all practical cases will be +developed and illustrated. + +Draft is the difference in pressure available for producing a flow of +the gases. If the gases within a stack be heated, each cubic foot will +expand, and the weight of the expanded gas per cubic foot will be less +than that of a cubic foot of the cold air outside the chimney. +Therefore, the unit pressure at the stack base due to the weight of the +column of heated gas will be less than that due to a column of cold air. +This difference in pressure, like the difference in head of water, will +cause a flow of the gases into the base of the stack. In its passage to +the stack the cold air must pass through the furnace or furnaces of the +boilers connected to it, and it in turn becomes heated. This newly +heated gas will also rise in the stack and the action will be +continuous. + +The intensity of the draft, or difference in pressure, is usually +measured in inches of water. Assuming an atmospheric temperature of 62 +degrees Fahrenheit and the temperature of the gases in the chimney as +500 degrees Fahrenheit, and, neglecting for the moment the difference in +density between the chimney gases and the air, the difference between +the weights of the external air and the internal flue gases per cubic +foot is .0347 pound, obtained as follows: + +Weight of a cubic foot of air at 62 degrees Fahrenheit = .0761 pound +Weight of a cubic foot of air at 500 degrees Fahrenheit = .0414 pound + ------------------------ + Difference = .0347 pound + +Therefore, a chimney 100 feet high, assumed for the purpose of +illustration to be suspended in the air, would have a pressure exerted +on each square foot of its cross sectional area at its base of .0347 × +100 = 3.47 pounds. As a cubic foot of water at 62 degrees Fahrenheit +weighs 62.32 pounds, an inch of water would exert a pressure of 62.32 ÷ +12 = 5.193 pounds per square foot. The 100-foot stack would, therefore, +under the above temperature conditions, show a draft of 3.47 ÷ 5.193 or +approximately 0.67 inches of water. + +The method best suited for determining the proper proportion of stacks +and flues is dependent upon the principle that if the cross sectional +area of the stack is sufficiently large for the volume of gases to be +handled, the intensity of the draft will depend directly upon the +height; therefore, the method of procedure is as follows: + + +1st. Select a stack of such height as will produce the draft required by +the particular character of the fuel and the amount to be burned per +square foot of grate surface. + + +2nd. Determine the cross sectional area necessary to handle the gases +without undue frictional losses. + + +The application of these rules follows: + +Draft Formula--The force or intensity of the draft, not allowing for the +difference in the density of the air and of the flue gases, is given by +the formula: + + / 1 1 \ +D = 0.52 H × P |--- - -----| (24) + \ T T_{1}/ + +in which + + D = draft produced, measured in inches of water, + H = height of top of stack above grate bars in feet, + P = atmospheric pressure in pounds per square inch, + T = absolute atmospheric temperature, + T_{1} = absolute temperature of stack gases. + +In this formula no account is taken of the density of the flue gases, it +being assumed that it is the same as that of air. Any error arising from +this assumption is negligible in practice as a factor of correction is +applied in using the formula to cover the difference between the +theoretical figures and those corresponding to actual operating +conditions. + +The force of draft at sea level (which corresponds to an atmospheric +pressure of 14.7 pounds per square inch) produced by a chimney 100 feet +high with the temperature of the air at 60 degrees Fahrenheit and that +of the flue gases at 500 degrees Fahrenheit is, + + / 1 1 \ +D = 0.52 × 100 × 14.7 | --- - --- | = 0.67 + \ 521 961 / + +Under the same temperature conditions this chimney at an atmospheric +pressure of 10 pounds per square inch (which corresponds to an altitude +of about 10,000 feet above sea level) would produce a draft of, + + / 1 1 \ +D = 0.52 × 100 × 10 | --- - --- | = 0.45 + \ 521 961 / + +For use in applying this formula it is convenient to tabulate values of +the product + + / 1 1 \ + 0.52 × 14.7|--- - -----| + \ T T_{1}/ + +which we will call K, for various values of T_{1}. With these values +calculated for assumed atmospheric temperature and pressure (24) becomes + + D = KH. (25) + +For average conditions the atmospheric pressure may be considered 14.7 +pounds per square inch, and the temperature 60 degrees Fahrenheit. For +these values and various stack temperatures K becomes: + +_Temperature Stack Gases_ _Constant K_ + 750 .0084 + 700 .0081 + 650 .0078 + 600 .0075 + 550 .0071 + 500 .0067 + 450 .0063 + 400 .0058 + 350 .0053 + +Draft Losses--The intensity of the draft as determined by the above +formula is theoretical and can never be observed with a draft gauge or +any recording device. However, if the ashpit doors of the boiler are +closed and there is no perceptible leakage of air through the boiler +setting or flue, the draft measured at the stack base will be +approximately the same as the theoretical draft. The difference existing +at other times represents the pressure necessary to force the gases +through the stack against their own inertia and the friction against the +sides. This difference will increase with the velocity of the gases. +With the ashpit doors closed the volume of gases passing to the stack +are a minimum and the maximum force of draft will be shown by a gauge. + +As draft measurements are taken along the path of the gases, the +readings grow less as the points at which they are taken are farther +from the stack, until in the boiler ashpit, with the ashpit doors open +for freely admitting the air, there is little or no perceptible rise in +the water of the gauge. The breeching, the boiler damper, the baffles +and the tubes, and the coal on the grates all retard the passage of the +gases, and the draft from the chimney is required to overcome the +resistance offered by the various factors. The draft at the rear of the +boiler setting where connection is made to the stack or flue may be 0.5 +inch, while in the furnace directly over the fire it may not be over, +say, 0.15 inch, the difference being the draft required to overcome the +resistance offered in forcing the gases through the tubes and around the +baffling. + +One of the most important factors to be considered in designing a stack +is the pressure required to force the air for combustion through the bed +of fuel on the grates. This pressure will vary with the nature of the +fuel used, and in many instances will be a large percentage of the total +draft. In the case of natural draft, its measure is found directly by +noting the draft in the furnace, for with properly designed ashpit doors +it is evident that the pressure under the grates will not differ +sensibly from atmospheric pressure. + +Loss in Stack--The difference between the theoretical draft as +determined by formula (24) and the amount lost by friction in the stack +proper is the available draft, or that which the draft gauge indicates +when connected to the base of the stack. The sum of the losses of draft +in the flue, boiler and furnace must be equivalent to the available +draft, and as these quantities can be determined from record of +experiments, the problem of designing a stack becomes one of +proportioning it to produce a certain available draft. + +The loss in the stack due to friction of the gases can be calculated +from the following formula: + + f W² C H +[Delta]D = -------- (26) + A³ + +in which + +[Delta]D = draft loss in inches of water, + W = weight of gas in pounds passing per second, + C = perimeter of stack in feet, + H = height of stack in feet, + f = a constant with the following values at sea level: + .0015 for steel stacks, temperature of gases 600 degrees + Fahrenheit. + .0011 for steel stacks, temperature of gases 350 degrees + Fahrenheit. + .0020 for brick or brick-lined stacks, temperature of gases + 600 degrees Fahrenheit. + .0015 for brick or brick-lined stacks, temperature of gases + 350 degrees Fahrenheit. + A = Area of stack in square feet. + +[Illustration: 24,420 Horse-power Installation of Babcock & Wilcox +Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate +Stokers in the Quarry Street Station of the Commonwealth Edison Co., +Chicago, Ill.] + +This formula can also be used for calculating the frictional losses for +flues, in which case, C = the perimeter of the flue in feet, H = the +length of the flue in feet, the other values being the same as for +stacks. + +The available draft is equal to the difference between the theoretical +draft from formula (25) and the loss from formula (26), hence: + + f W² C H +d^{1} = available draft = KH - -------- (27) + A³ + +Table 53 gives the available draft in inches that a stack 100 feet high +will produce when serving different horse powers of boilers with the +methods of calculation for other heights. + + TABLE 53 + + AVAILABLE DRAFT + + CALCULATED FOR 100-FOOT STACK OF DIFFERENT DIAMETERS ASSUMING STACK +TEMPERATURE OF 500 DEGREES FAHRENHEIT AND 100 POUNDS OF GAS PER HORSE POWER + + FOR OTHER HEIGHTS OF STACK MULTIPLY DRAFT BY HEIGHT ÷ 100 + ++-----+-------------------------------------------------------------------+ +|Horse| | +|Power| Diameter of Stack in Inches | ++-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +| |36 |42 |48 |54 |60 |66 |72 |78 |84 |90 |96 |102|108|114|120|132|144| ++-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +| 100 |.64| | | | | | | | | | | | | | | | | +| 200 |.55|.62| | | | | | | | | | | | | | | | +| 300 |.41|.55|.61| | | | | | | | | | | | | | | +| 400 |.21|.46|.56|.61| | | | | | | | | | | | | | +| 500 | |.34|.50|.57|.61| | | | | | | | | | | | | +| 600 | |.19|.42|.53|.59| | | | | | | | | | | | | +| 700 | | |.34|.48|.56|.60|.63| | | | | | | | | | | +| 800 | | |.23|.43|.52|.58|.61|.63| | | | | | | | | | +| 900 | | | |.36|.49|.56|.60|.62|.64| | | | | | | | | +|1000 | | | |.29|.45|.53|.58|.61|.63|.64| | | | | | | | +|1100 | | | | |.40|.50|.56|.60|.62|.63|.64| | | | | | | +|1200 | | | | |.35|.47|.54|.58|.61|.63|.64|.65| | | | | | +|1300 | | | | |.29|.44|.52|.57|.60|.62|.63|.64|.65| | | | | +|1400 | | | | | |.40|.49|.55|.59|.61|.63|.64|.65|.65| | | | +|1500 | | | | | |.36|.47|.53|.58|.60|.62|.63|.64|.65|.65| | | +|1600 | | | | | |.31|.43|.52|.56|.59|.62|.63|.64|.65|.65| | | +|1700 | | | | | | |.41|.50|.55|.58|.61|.62|.64|.64|.65| | | +|1800 | | | | | | |.37|.47|.54|.57|.60|.62|.63|.64|.65| | | +|1900 | | | | | | |.34|.45|.52|.56|.59|.61|.63|.64|.64| | | +|2000 | | | | | | | |.43|.50|.55|.59|.61|.62|.63|.64| | | +|2100 | | | | | | | |.40|.49|.54|.58|.60|.62|.63|.64| | | +|2200 | | | | | | | |.38|.47|.53|.57|.59|.61|.62|.64| | | +|2300 | | | | | | | |.35|.45|.52|.56|.59|.61|.62|.63| | | +|2400 | | | | | | | |.32|.43|.50|.55|.58|.60|.62|.63| | | +|2500 | | | | | | | | |.41|.49|.54|.57|.60|.61|.63| | | +|2600 | | | | | | | | | |.47|.53|.56|.59|.61|.62|.64|.65| +|2700 | | | | | | | | | |.45|.52|.55|.58|.60|.62|.64|.65| +|2800 | | | | | | | | | |.44|.59|.55|.58|.60|.61|.64|.65| +|2900 | | | | | | | | | |.42|.49|.54|.57|.59|.61|.63|.65| +|3000 | | | | | | | | | |.40|.48|.53|.56|.59|.61|.63|.64| +|3100 | | | | | | | | | |.38|.47|.52|.56|.58|.60|.63|.64| +|3200 | | | | | | | | | | |.45|.51|.55|.58|.60|.63|.64| +|3300 | | | | | | | | | | |.44|.50|.54|.57|.59|.62|.64| +|3400 | | | | | | | | | | |.42|.49|.53|.56|.59|.62|.64| +|3500 | | | | | | | | | | |.40|.48|.52|.56|.58|.62|.64| +|3600 | | | | | | | | | | | |.47|.52|.55|.58|.61|.63| +|3700 | | | | | | | | | | | |.45|.51|.55|.57|.61|.63| +|3800 | | | | | | | | | | | |.44|.50|.54|.57|.61|.63| +|3900 | | | | | | | | | | | |.43|.49|.53|.56|.60|.63| +|4000 | | | | | | | | | | | |.42|.48|.52|.56|.60|.62| +|4100 | | | | | | | | | | | |.40|.47|.52|.55|.60|.62| +|4200 | | | | | | | | | | | |.39|.46|.51|.55|.59|.62| +|4300 | | | | | | | | | | | | |.45|.50|.54|.59|.62| +|4400 | | | | | | | | | | | | |.44|.49|.53|.59|.62| +|4500 | | | | | | | | | | | | |.43|.49|.53|.58|.61| +|4600 | | | | | | | | | | | | |.42|.48|.52|.58|.61| +|4700 | | | | | | | | | | | | |.41|.47|.51|.57|.61| +|4800 | | | | | | | | | | | | |.40|.46|.51|.57|.60| +|4900 | | | | | | | | | | | | | |.45|.50|.57|.60| +|5000 | | | | | | | | | | | | | |.44|.49|.56|.60| ++-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ + +FOR OTHER STACK TEMPERATURES ADD OR DEDUCT BEFORE MULTIPLYING BY +HEIGHT ÷ 100 AS FOLLOWS[52] + +For 750 Degrees F. Add .17 inch. +For 700 Degrees F. Add .14 inch. +For 650 Degrees F. Add .11 inch. +For 600 Degrees F. Add .08 inch. +For 550 Degrees F. Add .04 inch. +For 450 Degrees F. Deduct .04 inch. +For 400 Degrees F. Deduct .09 inch. +For 350 Degrees F. Deduct .14 inch. + +[Graph: Horse Power of Boilers against Diameter of Stack in Inches + +Fig. 33. Diameter of Stacks and Horse Power they will Serve + +Computed from Formula (28). For brick or brick-lined stacks, increase +the diameter 6 per cent] + +Height and Diameter of Stacks--From this formula (27) it becomes evident +that a stack of certain diameter, if it be increased in height, will +produce the same available draft as one of larger diameter, the +additional height being required to overcome the added frictional loss. +It follows that among the various stacks that would meet the +requirements of a particular case there must be one which can be +constructed more cheaply than the others. It has been determined from +the relation of the cost of stacks to their diameters and heights, in +connection with the formula for available draft, that the minimum cost +stack has a diameter dependent solely upon the horse power of the +boilers it serves, and a height proportional to the available draft +required. + +Assuming 120 pounds of flue gas per hour for each boiler horse power, +which provides for ordinary overloads and the use of poor coal, the +method above stated gives: + +For an unlined steel stack-- + +diameter in inches = 4.68 (H. P.)^{2/5} (28) + +For a stack lined with masonry-- + +diameter in inches = 4.92 (H. P.)^{2/5} (29) + +In both of these formulae H. P. = the rated horse power of the boiler. + +From this formula the curve, Fig. 33, has been calculated and from it +the stack diameter for any boiler horse power can be selected. + +For stoker practice where a large stack serves a number of boilers, the +area is usually made about one-third more than the above rules call for, +which allows for leakage of air through the setting of any idle boilers, +irregularities in operating conditions, etc. + +Stacks with diameters determined as above will give an available draft +which bears a constant ratio of the theoretical draft, and allowing for +the cooling of the gases in their passage upward through the stack, this +ratio is 8. Using this factor in formula (25), and transposing, the +height of the chimney becomes, + + + d^{1} +H = ----- (30) + .8 K + +Where H = height of stack in feet above the level of the grates, + d^{1} = available draft required, + K = constant as in formula. + +Losses in Flues--The loss of draft in straight flues due to friction and +inertia can be calculated approximately from formula (26), which was +given for loss in stacks. It is to be borne in mind that C in this +formula is the actual perimeter of the flue and is least, relative to +the cross sectional area, when the section is a circle, is greater for a +square section, and greatest for a rectangular section. The retarding +effect of a square flue is 12 per cent greater than that of a circular +flue of the same area and that of a rectangular with sides as 1 and 1½, +15 per cent greater. The greater resistance of the more or less uneven +brick or concrete flue is provided for in the value of the constants +given for formula (26). Both steel and brick flues should be short and +should have as near a circular or square cross section as possible. +Abrupt turns are to be avoided, but as long easy sweeps require valuable +space, it is often desirable to increase the height of the stack rather +than to take up added space in the boiler room. Short right-angle turns +reduce the draft by an amount which can be roughly approximated as equal +to 0.05 inch for each turn. The turns which the gases make in leaving +the damper box of a boiler, in entering a horizontal flue and in turning +up into a stack should always be considered. The cross sectional areas +of the passages leading from the boilers to the stack should be of ample +size to provide against undue frictional loss. It is poor economy to +restrict the size of the flue and thus make additional stack height +necessary to overcome the added friction. The general practice is to +make flue areas the same or slightly larger than that of the stack; +these should be, preferably, at least 20 per cent greater, and a safe +rule to follow in figuring flue areas is to allow 35 square feet per +1000 horse power. It is unnecessary to maintain the same size of flue +the entire distance behind a row of boilers, and the areas at any point +may be made proportional to the volume of gases that will pass that +point. That is, the areas may be reduced as connections to various +boilers are passed. + +[Illustration: 6000 Horse-power Installation of Babcock & Wilcox Boilers +at the United States Navy Yard, Washington, D. C.] + +With circular steel flues of approximately the same size as the stacks, +or reduced proportionally to the volume of gases they will handle, a +convenient rule is to allow 0.1 inch draft loss per 100 feet of flue +length and 0.05 inch for each right-angle turn. These figures are also +good for square or rectangular steel flues with areas sufficiently large +to provide against excessive frictional loss. For losses in brick or +concrete flues, these figures should be doubled. + +Underground flues are less desirable than overhead or rear flues for the +reason that in most instances the gases will have to make more turns +where underground flues are used and because the cross sectional area of +such flues will oftentimes be decreased on account of an accumulation of +dirt or water which it may be impossible to remove. + +In tall buildings, such as office buildings, it is frequently necessary +in order to carry spent gases above the roofs, to install a stack the +height of which is out of all proportion to the requirements of the +boilers. In such cases it is permissible to decrease the diameter of a +stack, but care must be taken that this decrease is not sufficient to +cause a frictional loss in the stack as great as the added draft +intensity due to the increase in height, which local conditions make +necessary. + +In such cases also the fact that the stack diameter is permissibly +decreased is no reason why flue sizes connecting to the stack should be +decreased. These should still be figured in proportion to the area of +the stack that would be furnished under ordinary conditions or with an +allowance of 35 square feet per 1000 horse power, even though the cross +sectional area appears out of proportion to the stack area. + +Loss in Boiler--In calculating the available draft of a chimney 120 +pounds per hour has been used as the weight of the gases per boiler +horse power. This covers an overload of the boiler to an extent of 50 +per cent and provides for the use of poor coal. The loss in draft +through a boiler proper will depend upon its type and baffling and will +increase with the per cent of rating at which it is run. No figures can +be given which will cover all conditions, but for approximate use in +figuring the available draft necessary it may be assumed that the loss +through a boiler will be 0.25 inch where the boiler is run at rating, +0.40 inch where it is run at 150 per cent of its rated capacity, and +0.70 inch where it is run at 200 per cent of its rated capacity. + +Loss in Furnace--The draft loss in the furnace or through the fuel bed +varies between wide limits. The air necessary for combustion must pass +through the interstices of the coal on the grate. Where these are large, +as is the case with broken coal, but little pressure is required to +force the air through the bed; but if they are small, as with bituminous +slack or small sizes of anthracite, a much greater pressure is needed. +If the draft is insufficient the coal will accumulate on the grates and +a dead smoky fire will result with the accompanying poor combustion; if +the draft is too great, the coal may be rapidly consumed on certain +portions of the grate, leaving the fire thin in spots and a portion of +the grates uncovered with the resulting losses due to an excessive +amount of air. + +[Graph: Force of Draft between Furnace and Ash Pit--Inches of Water +against Pounds of Coal burned per Square Foot of Grate Surface per Hour + +Fig. 34. Draft Required at Different Combustion Rates for Various Kinds +of Coal] + +Draft Required for Different Fuels--For every kind of fuel and rate of +combustion there is a certain draft with which the best general results +are obtained. A comparatively light draft is best with the free burning +bituminous coals and the amount to use increases as the percentage of +volatile matter diminishes and the fixed carbon increases, being highest +for the small sizes of anthracites. Numerous other factors such as the +thickness of fires, the percentage of ash and the air spaces in the +grates bear directly on this question of the draft best suited to a +given combustion rate. The effect of these factors can only be found by +experiment. It is almost impossible to show by one set of curves the +furnace draft required at various rates of combustion for all of the +different conditions of fuel, etc., that may be met. The curves in Fig. +34, however, give the furnace draft necessary to burn various kinds of +coal at the combustion rates indicated by the abscissae, for a general +set of conditions. These curves have been plotted from the records of +numerous tests and allow a safe margin for economically burning coals of +the kinds noted. + +Rate of Combustion--The amount of coal which can be burned per hour per +square foot of grate surface is governed by the character of the coal +and the draft available. When the boiler and grate are properly +proportioned, the efficiency will be practically the same, within +reasonable limits, for different rates of combustion. The area of the +grate, and the ratio of this area to the boiler heating surface will +depend upon the nature of the fuel to be burned, and the stack should be +so designed as to give a draft sufficient to burn the maximum amount of +fuel per square foot of grate surface corresponding to the maximum +evaporative requirements of the boiler. + +Solution of a Problem--The stack diameter can be determined from the +curve, Fig. 33. The height can be determined by adding the draft losses +in the furnace, through the boiler and flues, and computing from formula +(30) the height necessary to give this draft. + +Example: Proportion a stack for boilers rated at 2000 horse power, +equipped with stokers, and burning bituminous coal that will evaporate 8 +pounds of water from and at 212 degrees Fahrenheit per pound of fuel; +the ratio of boiler heating surface to grate surface being 50:1; the +flues being 100 feet long and containing two right-angle turns; the +stack to be able to handle overloads of 50 per cent; and the rated horse +power of the boilers based on 10 square feet of heating surface per +horse power. + +The atmospheric temperature may be assumed as 60 degrees Fahrenheit and +the flue temperatures at the maximum overload as 550 degrees Fahrenheit. +The grate surface equals 400 square feet. + + 2000 × 34½ +The total coal burned at rating = ---------- = 8624 pounds. + 8 + +The coal per square foot of grate surface per hour at rating = + +8624 +---- = 22 pounds. + 400 + +For 50 per cent overload the combustion rate will be approximately 60 +per cent greater than this or 1.60 × 22 = 35 pounds per square foot of +grate surface per hour. The furnace draft required for the combustion +rate, from the curve, Fig. 34, is 0.6 inch. The loss in the boiler will +be 0.4 inch, in the flue 0.1 inch, and in the turns 2 × 0.05 = 0.1 inch. +The available draft required at the base of the stack is, therefore, + + _Inches_ +Boiler 0.4 +Furnace 0.6 +Flues 0.1 +Turns 0.1 + --- + Total 1.2 + +Since the available draft is 80 per cent of the theoretical draft, this +draft due to the height required is 1.2 ÷ .8 = 1.5 inch. + +The chimney constant for temperatures of 60 degrees Fahrenheit and 550 +degrees Fahrenheit is .0071 and from formula (30), + + 1.5 +H = ----- = 211 feet. + .0071 + +Its diameter from curve in Fig. 33 is 96 inches if unlined, and 102 +inches inside if lined with masonry. The cross sectional area of the +flue should be approximately 70 square feet at the point where the total +amount of gas is to be handled, tapering to the boiler farthest from the +stack to a size which will depend upon the size of the boiler units +used. + +Correction in Stack Sizes for Altitudes--It has ordinarily been assumed +that a stack height for altitude will be increased inversely as the +ratio of the barometric pressure at the altitude to that at sea level, +and that the stack diameter will increase inversely as the two-fifths +power of this ratio. Such a relation has been based on the assumption of +constant draft measured in inches of water at the base of the stack for +a given rate of operation of the boilers, regardless of altitude. + +If the assumption be made that boilers, flues and furnace remain the +same, and further that the increased velocity of a given weight of air +passing through the furnace at a higher altitude would have no effect on +the combustion, the theory has been advanced[53] that a different law +applies. + +Under the above assumptions, whenever a stack is working at its maximum +capacity at any altitude, the entire draft is utilized in overcoming the +various resistances, each of which is proportional to the square of the +velocity of the gases. Since boiler areas are fixed, all velocities may +be related to a common velocity, say, that within the stack, and all +resistances may, therefore, be expressed as proportional to the square +of the chimney velocity. The total resistance to flow, in terms of +velocity head, may be expressed in terms of weight of a column of +external air, the numerical value of such head being independent of the +barometric pressure. Likewise the draft of a stack, expressed in height +of column of external air, will be numerically independent of the +barometric pressure. It is evident, therefore, that if a given boiler +plant, with its stack operated with a fixed fuel, be transplanted from +sea level to an altitude, assuming the temperatures remain constant, the +total draft head measured in height of column of external air will be +numerically constant. The velocity of chimney gases will, therefore, +remain the same at altitude as at sea level and the weight of gases +flowing per second with a fixed velocity will be proportional to the +atmospheric density or inversely proportional to the normal barometric +pressure. + +To develop a given horse power requires a constant weight of chimney gas +and air for combustion. Hence, as the altitude is increased, the density +is decreased and, for the assumptions given above, the velocity through +the furnace, the boiler passes, breeching and flues must be +correspondingly greater at altitude than at sea level. The mean +velocity, therefore, for a given boiler horse power and constant weight +of gases will be inversely proportional to the barometric pressure and +the velocity head measured in column of external air will be inversely +proportional to the square of the barometric pressure. + +For stacks operating at altitude it is necessary not only to increase +the height but also the diameter, as there is an added resistance within +the stack due to the added friction from the additional height. This +frictional loss can be compensated by a suitable increase in the +diameter and when so compensated, it is evident that on the assumptions +as given, the chimney height would have to be increased at a ratio +inversely proportional to the square of the normal barometric pressure. + +In designing a boiler for high altitudes, as already stated, the +assumption is usually made that a given grade of fuel will require the +same draft measured in inches of water at the boiler damper as at sea +level, and this leads to making the stack height inversely as the +barometric pressures, instead of inversely as the square of the +barometric pressures. The correct height, no doubt, falls somewhere +between the two values as larger flues are usually used at the higher +altitudes, whereas to obtain the ratio of the squares, the flues must be +the same size in each case, and again the effect of an increased +velocity of a given weight of air through the fire at a high altitude, +on the combustion, must be neglected. In making capacity tests with coal +fuel, no difference has been noted in the rates of combustion for a +given draft suction measured by a water column at high and low +altitudes, and this would make it appear that the correct height to use +is more nearly that obtained by the inverse ratio of the barometric +readings than by the inverse ratio of the squares of the barometric +readings. If the assumption is made that the value falls midway between +the two formulae, the error in using a stack figured in the ordinary way +by making the height inversely proportional to the barometric readings +would differ about 10 per cent in capacity at an altitude of 10,000 +feet, which difference is well within the probable variation of the size +determined by different methods. It would, therefore, appear that ample +accuracy is obtained in all cases by simply making the height inversely +proportional to the barometric readings and increasing the diameter so +that the stacks used at high altitudes have the same frictional +resistance as those used at low altitudes, although, if desired, the +stack may be made somewhat higher at high altitudes than this rule calls +for in order to be on the safe side. + +The increase of stack diameter necessary to maintain the same friction +loss is inversely as the two-fifths power of the barometric pressure. + +Table 54 gives the ratio of barometric readings of various altitudes to +sea level, values for the square of this ratio and values of the +two-fifths power of this ratio. + + TABLE 54 + + STACK CAPACITIES, CORRECTION FACTORS FOR + ALTITUDES + + _______________________________________________________________________ +| | | | | | +| Altitude | | R | | R^{2/5} | +| Height in Feet | Normal | Ratio Barometer | | Ratio Increase | +| Above | Barometer | Reading | R² | in Stack | +| Sea Level | | Sea Level to | | Diameter | +| | | Altitude | | | +|________________|___________|_________________|_______|________________| +| | | | | | +| 0 | 30.00 | 1.000 | 1.000 | 1.000 | +| 1000 | 28.88 | 1.039 | 1.079 | 1.015 | +| 2000 | 27.80 | 1.079 | 1.064 | 1.030 | +| 3000 | 26.76 | 1.121 | 1.257 | 1.047 | +| 4000 | 25.76 | 1.165 | 1.356 | 1.063 | +| 5000 | 24.79 | 1.210 | 1.464 | 1.079 | +| 6000 | 23.87 | 1.257 | 1.580 | 1.096 | +| 7000 | 22.97 | 1.306 | 1.706 | 1.113 | +| 8000 | 22.11 | 1.357 | 1.841 | 1.130 | +| 9000 | 21.28 | 1.410 | 1.988 | 1.147 | +| 10000 | 20.49 | 1.464 | 2.144 | 1.165 | +|________________|___________|_________________|_______|________________| + +These figures show that the altitude affects the height to a much +greater extent than the diameter and that practically no increase in +diameter is necessary for altitudes up to 3000 feet. + +For high altitudes the increase in stack height necessary is, in some +cases, such as to make the proportion of height to diameter +impracticable. The method to be recommended in overcoming, at least +partially, the great increase in height necessary at high altitudes is +an increase in the grate surface of the boilers which the stack serves, +in this way reducing the combustion rate necessary to develop a given +power and hence the draft required for such combustion rate. + + TABLE 55 + + STACK SIZES BY KENT'S FORMULA + + ASSUMING 5 POUNDS OF COAL PER HORSE POWER + + + ____________________________________________________________________ +| | | | | +| | | Height of Stack in Feet |Side of| +| | |______________________________________________|Equiva-| +| Dia- | Area | | | | | | | | | | | lent | +| meter|Square| 50| 60| 70| 80 | 90 | 100| 110| 125| 150| 175|Square | +|Inches| Feet |___|___|___|____|____|____|____|____|____|____| Stack | +| | | |Inches | +| | | Commercial Horse Power | | +|______|______|______________________________________________|_______| +| | | | | | | | | | | | | | +| 33 | 5.94|106|115|125| 133| 141| 149| | | | | 30 | +| 36 | 7.07|129|141|152| 163| 173| 182| | | | | 32 | +| 39 | 8.30|155|169|183| 196| 208| 219| 229| 245| | | 35 | +| 42 | 9.62|183|200|216| 231| 245| 258| 271| 289| 316| | 38 | +| 48 | 12.57|246|269|290| 311| 330| 348| 365| 389| 426| 460| 43 | +| 54 | 15.90|318|348|376| 402| 427| 449| 472| 503| 551| 595| 48 | +| 60 | 19.64|400|437|473| 505| 536| 565| 593| 632| 692| 748| 54 | +| 66 | 23.76|490|537|580| 620| 658| 694| 728| 776| 849| 918| 59 | +| 72 | 28.27|591|646|698| 747| 792| 835| 876| 934|1023|1105| 64 | +| 78 | 33.18|700|766|828| 885| 939| 990|1038|1107|1212|1310| 70 | +| 84 | 38.48|818|896|968|1035|1098|1157|1214|1294|1418|1531| 75 | +|______|______|___|___|___|____|____|____|____|____|____|____|_______| +| | | | | +| | | Height of Stack in Feet |Side of| +| | |______________________________________________|Equiva-| +| Dia- | Area | | | | | | | | | lent | +| meter|Square| 100| 110 | 125 | 150 | 175 | 200 | 225 | 250 |Square | +|Inches| Feet |____|_____|_____|_____|_____|_____|_____|_____| Stack | +| | | |Inches | +| | | Commercial Horse Power | | +|______|______|______________________________________________|_______| +| | | | | | | | | | | | +| 90 | 44.18|1338| 1403| 1496| 1639| 1770| 1893| 2008| 2116| 80 | +| 96 | 50.27|1532| 1606| 1713| 1876| 2027| 2167| 2298| 2423| 86 | +| 102 | 56.75|1739| 1824| 1944| 2130| 2300| 2459| 2609| 2750| 91 | +| 108 | 63.62|1959| 2054| 2190| 2392| 2592| 2770| 2939| 3098| 98 | +| 114 | 70.88|2192| 2299| 2451| 2685| 2900| 3100| 3288| 3466| 101 | +| 120 | 78.54|2438| 2557| 2726| 2986| 3226| 3448| 3657| 3855| 107 | +| 126 | 86.59|2697| 2829| 3016| 3303| 3568| 3814| 4046| 4265| 112 | +| 132 | 95.03|2970| 3114| 3321| 3637| 3929| 4200| 4455| 4696| 117 | +| 144 |113.10|3554| 3726| 3973| 4352| 4701| 5026| 5331| 5618| 128 | +| 156 |132.73|4190| 4393| 4684| 5131| 5542| 5925| 6285| 6624| 138 | +| 168 |153.94|4878| 5115| 5454| 5974| 6454| 6899| 7318| 7713| 150 | +|______|______|____|_____|_____|_____|_____|_____|_____|_____|_______| + +Kent's Stack Tables--Table 55 gives, in convenient form for approximate +work, the sizes of stacks and the horse power of boilers which they will +serve. This table is a modification of Mr. William Kent's stack table +and is calculated from his formula. Provided no unusual conditions are +encountered, it is reliable for the ordinary rates of combustion with +bituminous coals. It is figured on a consumption of 5 pounds of coal +burned per hour per boiler horse power developed, this figure giving a +fairly liberal allowance for the use of poor coal and for a reasonable +overload. When the coal used is a low grade bituminous of the Middle or +Western States, it is strongly recommended that these sizes be increased +materially, such an increase being from 25 to 60 per cent, depending +upon the nature of the coal and the capacity desired. For the coal +burned per hour for any size stack given in the table, the values should +be multiplied by 5. + +A convenient rule for large stacks, 200 feet high and over, is to +provide 30 square feet of cross sectional area per 1000 rated horse +power. + +Stacks for Oil Fuel--The requirements of stacks connected to boilers +under which oil fuel is burned are entirely different from those where +coal is used. While more attention has been paid to the matter of stack +sizes for oil fuel in recent years, there has not as yet been gathered +the large amount of experimental data available for use in designing +coal stacks. + +In the case of oil-fired boilers the loss of draft through the fuel bed +is partially eliminated. While there may be practically no loss through +any checkerwork admitting air to the furnace when a boiler is new, the +areas for the air passage in this checkerwork will in a short time be +decreased, due to the silt which is present in practically all fuel oil. +The loss in draft through the boiler proper at a given rating will be +less than in the case of coal-fired boilers, this being due to a +decrease in the volume of the gases. Further, the action of the oil +burner itself is to a certain extent that of a forced draft. To offset +this decrease in draft requirement, the temperature of the gases +entering the stack will be somewhat lower where oil is used than where +coal is used, and the draft that a stack of a given height would give, +therefore, decreases. The factors as given above, affecting as they do +the intensity of the draft, affect directly the height of the stack to +be used. + +As already stated, the volume of gases from oil-fired boilers being less +than in the case of coal, makes it evident that the area of stacks for +oil fuel will be less than for coal. It is assumed that these areas will +vary directly as the volume of the gases to be handled, and this volume +for oil may be taken as approximately 60 per cent of that for coal. + +In designing stacks for oil fuel there are two features which must not +be overlooked. In coal-firing practice there is rarely danger of too +much draft. In the burning of oil, however, this may play an important +part in the reduction of plant economy, the influence of excessive draft +being more apparent where the load on the plant may be reduced at +intervals. The reason for this is that, aside from a slight decrease in +temperature at reduced loads, the tendency, due to careless firing, is +toward a constant gas flow through the boiler regardless of the rate of +operation, with the corresponding increase of excess air at light loads. +With excessive stack height, economical operation at varying loads is +almost impossible with hand control. With automatic control, however, +where stacks are necessarily high to take care of known peaks, under +lighter loads this economical operation becomes less difficult. For this +reason the question of designing a stack for a plant where the load is +known to be nearly a constant is easier than for a plant where the load +will vary over a wide range. While great care must be taken to avoid +excessive draft, still more care must be taken to assure a draft suction +within all parts of the setting under any and all conditions of +operation. It is very easily possible to more than offset the economy +gained through low draft, by the losses due to setting deterioration, +resulting from such lack of suction. Under conditions where the suction +is not sufficient to carry off the products of combustion, the action of +the heat on the setting brickwork will cause its rapid failure. + +[Illustration: 7800 Horse-power Installation of Babcock & Wilcox +Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the +Metropolitan West Side Elevated Ry. Co., Chicago, Ill.] + +It becomes evident, therefore, that the question of stack height for +oil-fired boilers is one which must be considered with the greatest of +care. The designer, on the one hand, must guard against the evils of +excessive draft with the view to plant economy, and, on the other, +against the evils of lack of draft from the viewpoint of upkeep cost. +Stacks for this work should be proportioned to give ample draft for the +maximum overload that a plant will be called upon to carry, all +conditions of overload carefully considered. At the same time, where +this maximum overload is figured liberally enough to insure a draft +suction within the setting under all conditions, care must be taken +against the installation of a stack which would give more than this +maximum draft. + + TABLE 56 + + STACK SIZES FOR OIL FUEL + + ADAPTED FROM C. R. WEYMOUTH'S TABLE (TRANS. + A. S. M. E. VOL. 34) + ++----------------------------------------------------+ +|+--------+-----------------------------------------+| +|| | Height in Feet Above Boiler Room Floor || +||Diameter+------+------+------+-----+--------------+| +|| Inches | 80 | 90 | 100 | 120 | 140 | 160 || +|+--------+------+------+------+------+------+------+| +|| 33 | 161 | 206 | 233 | 270 | 306 | 315 || +|| 36 | 208 | 253 | 295 | 331 | 363 | 387 || +|| 39 | 251 | 303 | 343 | 399 | 488 | 467 || +|| 42 | 295 | 359 | 403 | 474 | 521 | 557 || +|| 48 | 399 | 486 | 551 | 645 | 713 | 760 || +|| 54 | 519 | 634 | 720 | 847 | 933 | 1000 || +|| 60 | 657 | 800 | 913 | 1073 | 1193 | 1280 || +|| 66 | 813 | 993 | 1133 | 1333 | 1480 | 1593 || +|| 72 | 980 | 1206 | 1373 | 1620 | 1807 | 1940 || +|| 84 | 1373 | 1587 | 1933 | 2293 | 2560 | 2767 || +|| 96 | 1833 | 2260 | 2587 | 3087 | 3453 | 3740 || +|| 108 | 2367 | 2920 | 3347 | 4000 | 4483 | 4867 || +|| 120 | 3060 | 3660 | 4207 | 5040 | 5660 | 6160 || +|+--------+------+------+------+------+------+------+| ++----------------------------------------------------+ + +Figures represent nominal rated horse power. Sizes as given good for 50 +per cent overloads. + +Based on centrally located stacks, short direct flues and ordinary +operating efficiencies. + +Table 56 gives the sizes of stacks, and horse power which they will +serve for oil fuel. This table is, in modified form, one calculated by +Mr. C. R. Weymouth after an exhaustive study of data pertaining to the +subject, and will ordinarily give satisfactory results. + +Stacks for Blast Furnace Gas Work--For boilers burning blast furnace +gas, as in the case of oil-fired boilers, stack sizes as suited for coal +firing will have to be modified. The diameter of stacks for this work +should be approximately the same as for coal-fired boilers. The volume +of gases would be slightly greater than from a coal fire and would +decrease the draft with a given stack, but such a decrease due to volume +is about offset by an increase due to somewhat higher temperatures in +the case of the blast furnace gases. + +Records show that with this class of fuel 175 per cent of the rated +capacity of a boiler can be developed with a draft at the boiler damper +of from 0.75 inch to 1.0 inch, and it is well to limit the height of +stacks to one which will give this draft as a maximum. A stack of proper +diameter, 130 feet high above the ground, will produce such a draft and +this height should ordinarily not be exceeded. Until recently the +question of economy in boilers fired with blast furnace gas has not been +considered, but, aside from the economical standpoint, excessive draft +should be guarded against in order to lower the upkeep cost. + +Stacks should be made of sufficient height to produce a draft that will +develop the maximum capacity required, and this draft decreased +proportionately for loads under the maximum by damper regulation. The +amount of gas fed to a boiler for any given rating is a fixed quantity +and if a draft in excess of that required for that particular rate of +operation is supplied, economy is decreased and the wear and tear on the +setting is materially increased. Excess air which is drawn in, either +through or around the gas burners by an excessive draft, will decrease +economy, as in any other class of work. Again, as in oil-fired practice, +it is essential on the other hand that a suction be maintained within +all parts of the setting, in this case not only to provide against +setting deterioration but to protect the operators from leakage of gas +which is disagreeable and may be dangerous. Aside from the intensity of +the draft, a poor mixture of the gas and air or a "laneing" action may +lead to secondary combustion with the possibility of dangerous +explosions within the setting, may cause a pulsating action within the +setting, may increase the exit temperatures to a point where there is +danger of burning out damper boxes, and, in general, is hard on the +setting. It is highly essential, therefore, that the furnace be properly +constructed to meet the draft which will be available. + +Stacks for Wood-fired Boilers--For boilers using wood as fuel, there is +but little data upon which to base stack sizes. The loss of draft +through the bed of fuel will vary over limits even wider than in the +case of coal, for in this class of fuel the moisture may run from +practically 0.0 per cent to over 60 per cent, and the methods of +handling and firing are radically different for the different classes of +wood (see chapter on Wood-burning Furnaces). As economy is ordinarily of +little importance, high stack temperatures may be expected, and often +unavoidably large quantities of excess air are supplied due to the +method of firing. In general, it may be stated that for this class of +fuel the diameter of stacks should be at least as great as for coal-fired +boilers, while the height may be slightly decreased. It is far the best +plan in designing a stack for boilers using wood fuel to consider each +individual set of conditions that exist, rather than try to follow any +general rule. + +One factor not to be overlooked in stacks for wood burning is their +location. The fine particles of this fuel are often carried unconsumed +through the boiler, and where the stack is not on top of the boiler, +these particles may accumulate in the base of the stack below the point +at which the flue enters. Where there is any air leakage through the +base of such a stack, this fuel may become ignited and the stack burned. +Where there is a possibility of such action taking place, it is well to +line the stack with fire brick for a portion of its height. + +Draft Gauges--The ordinary form of draft gauge, Fig. 35, which consists +of a U-tube, containing water, lacks sensitiveness in measuring such +slight pressure differences as usually exist, and for that reason gauges +which multiply the draft indications are more convenient and are much +used. + +[Illustration: Fig. 35. U-tube Draft Gauge] + +[Illustration: Fig. 36. Barrus Draft Gauge] + +An instrument which has given excellent results is one introduced by Mr. +G. H. Barrus, which multiplies the ordinary indications as many times as +desired. This is illustrated in Fig. 36, and consists of a U-tube made +of one-half inch glass, surmounted by two larger tubes, or chambers, +each having a diameter of 2½ inches. Two different liquids which will +not mix, and which are of different color, are used, usually alcohol +colored red and a certain grade of lubricating oil. The movement of the +line of demarcation is proportional to the difference in the areas of +the chambers and the U-tube connecting them. The instrument is +calibrated by comparison with the ordinary U-tube gauge. + +In the Ellison form of gauge the lower portion of the ordinary U-tube +has been replaced by a tube slightly inclined to the horizontal, as +shown in Fig. 37. By this arrangement any vertical motion in the +right-hand upright tube causes a very much greater travel of the liquid +in the inclined tube, thus permitting extremely small variation in the +intensity of the draft to be read with facility. + +[Illustration: Fig. 37. Ellison Draft Gauge] + +The gauge is first leveled by means of the small level attached to it, +both legs being open to the atmosphere. The liquid is then adjusted +until its meniscus rests at the zero point on the left. The right-hand +leg is then connected to the source of draft by means of a piece of +rubber tubing. Under these circumstances, a rise of level of one inch in +the right-hand vertical tube causes the meniscus in the inclined tube to +pass from the point 0 to 1.0. The scale is divided into tenths of an +inch, and the sub-divisions are hundredths of an inch. + +The makers furnish a non-drying oil for the liquid, usually a 300 +degrees test refined petroleum. + +A very convenient form of the ordinary U-tube gauge is known as the +Peabody gauge, and it is shown in Fig. 38. This is a small modified +U-tube with a sliding scale between the two legs of the U and with +connections such that either a draft suction or a draft pressure may be +taken. The tops of the sliding pieces extending across the tubes are +placed at the bottom of the meniscus and accurate readings in hundredths +of an inch are obtained by a vernier. + +[Illustration: Fig. 38. Peabody Draft Gauge] + + + + +EFFICIENCY AND CAPACITY OF BOILERS + + +Two of the most important operating factors entering into the +consideration of what constitutes a satisfactory boiler are its +efficiency and capacity. The relation of these factors to one another +will be considered later under the selection of boilers with reference +to the work they are to accomplish. The present chapter deals with the +efficiency and capacity only with a view to making clear exactly what is +meant by these terms as applied to steam generating apparatus, together +with the methods of determining these factors by tests. + +Efficiency--The term "efficiency", specifically applied to a steam +boiler, is the ratio of heat absorbed by the boiler in the generation of +steam to the total amount of heat available in the medium utilized in +securing such generation. When this medium is a solid fuel, such as +coal, it is impossible to secure the complete combustion of the total +amount fed to the boiler. A portion is bound to drop through the grates +where it becomes mixed with the ash and, remaining unburned, produces no +heat. Obviously, it is unfair to charge the boiler with the failure to +absorb the portion of available heat in the fuel that is wasted in this +way. On the other hand, the boiler user must pay for such waste and is +justified in charging it against the combined boiler and furnace. Due to +this fact, the efficiency of a boiler, as ordinarily stated, is in +reality the combined efficiency of the boiler, furnace and grate, and + + Efficiency of boiler,} Heat absorbed per pound of fuel + furnace and grate } = ------------------------------- (31) + Heat value per pound of fuel + + +The efficiency will be the same whether based on dry fuel or on fuel as +fired, including its content of moisture. For example: If the coal +contained 3 per cent of moisture, the efficiency would be + + Heat absorbed per pound of dry coal × 0.97 + ------------------------------------------ + Heat value per pound of dry coal × 0.97 + +where 0.97 cancels and the formula becomes (31). + +The heat supplied to the boiler is due to the combustible portion of +fuel which is actually burned, irrespective of what proportion of the +total combustible fired may be.[54] This fact has led to the use of a +second efficiency basis on combustible and which is called the +efficiency of boiler and furnace[55], namely, + + Efficiency of boiler and furnace[55] + + Heat absorbed per pound of combustible[56] + = -------------------------------------- (32) + Heat value per pound of combustible + + +The efficiency so determined is used in comparing the relative +performance of boilers, irrespective of the type of grates used under +them. If the loss of fuel through the grates could be entirely overcome, +the efficiencies obtained by (31) and (32) would obviously be the same. +Hence, in the case of liquid and gaseous fuels, where there is +practically no waste, these efficiencies are almost identical. + +As a matter of fact, it is extremely difficult, if not impossible, to +determine the actual efficiency of a boiler alone, as distinguished from +the combined efficiency of boiler, grate and furnace. This is due to the +fact that the losses due to excess air cannot be correctly attributed to +either the boiler or the furnace, but only to a combination of the +complete apparatus. Attempts have been made to devise methods for +dividing the losses proportionately between the furnace and the boiler, +but such attempts are unsatisfactory and it is impossible to determine +the efficiency of a boiler apart from that of a furnace in such a way as +to make such determination of any practical value or in a way that might +not lead to endless dispute, were the question to arise in the case of a +guaranteed efficiency. From the boiler manufacturer's standpoint, the +only way of establishing an efficiency that has any value when +guarantees are to be met, is to require the grate or stoker manufacturer +to make certain guarantees as to minimum CO_{2}, maximum CO, and that +the amount of combustible in the ash and blown away with the flue gases +does not exceed a certain percentage. With such a guarantee, the +efficiency should be based on the combined furnace and boiler. + +General practice, however, has established the use of the efficiency +based upon combustible as representing the efficiency of the boiler +alone. When such an efficiency is used, its exact meaning, as pointed +out on opposite page, should be realized. + +The computation of the efficiencies described on opposite page is best +illustrated by example. + +Assume the following data to be determined from an actual boiler trial. + +Steam pressure by gauge, 200 pounds. +Feed temperature, 180 degrees. +Total weight of coal fired, 17,500 pounds. +Percentage of moisture in coal, 3 per cent. +Total ash and refuse, 2396 pounds. +Total water evaporated, 153,543 pounds. +Per cent of moisture in steam, 0.5 per cent. +Heat value per pound of dry coal, 13,516. +Heat value per pound of combustible, 15,359. + +The factor of evaporation for such a set of conditions is 1.0834. The +actual evaporation corrected for moisture in the steam is 152,775 and +the equivalent evaporation from and at 212 degrees is, therefore, +165,516 pounds. + +The total dry fuel will be 17,500 × .97 = 16,975, and the evaporation +per pound of dry fuel from and at 212 degrees will be 165,516 ÷ 16,975 = +9.75 pounds. The heat absorbed per pound of dry fuel will, therefore, be +9.75 × 970.4 = 9461 B. t. u. Hence, the efficiency by (31) will be 9461 +÷ 13,516 = 70.0 per cent. The total combustible burned will be 16,975 +- 2396 = 14,579, and the evaporation from and at 212 degrees per pound +of combustible will be 165,516 ÷ 14,579 = 11.35 pounds. Hence, the +efficiency based on combustible from (32) will be (11.35 × 97.04) ÷ +15,359 = 71.79.[**should be 71.71] + +For approximate results, a chart may be used to take the place of a +computation of efficiency. Fig. 39 shows such a chart based on the +evaporation per pound of dry fuel and the heat value per pound of dry +fuel, from which efficiencies may be read directly to within one-half of +one per cent. It is used as follows: From the intersection of the +horizontal line, representing the evaporation per pound of fuel, with +the vertical line, representing the heat value per pound, the efficiency +is read directly from the diagonal scale of efficiencies. This chart may +also be used for efficiency based upon combustible when the evaporation +from and at 212 degrees and the heat values are both given in terms of +combustible. + +[Graph: Evaporation from and at 212° per Pound of Dry Fuel +against B.T.U. per Pound of Dry Fuel + +Fig. 39. Efficiency Chart. Calculated from Marks and Davis Tables + +Diagonal Lines Represent Per Cent Efficiency] + +Boiler efficiencies will vary over a wide range, depending on a great +variety of factors and conditions. The highest efficiencies that have +been secured with coal are in the neighborhood of 82 per cent and from +that point efficiencies are found all the way down to below 50 per cent. +Table 59[57] of tests of Babcock & Wilcox boilers under varying +conditions of fuel and operation will give an idea of what may be +obtained with proper operating conditions. + +The difference between the efficiency secured in any boiler trial and +the perfect efficiency, 100 per cent, includes the losses, some of which +are unavoidable in the present state of the art, arising in the +conversion of the heat energy of the coal to the heat energy in the +steam. These losses may be classified as follows: + +1st. Loss due to fuel dropped through the grate. + +2nd. Loss due to unburned fuel which is carried by the draft, as small +particles, beyond the bridge wall into the setting or up the stack. + +3rd. Loss due to the utilization of a portion of the heat in heating the +moisture contained in the fuel from the temperature of the atmosphere to +212 degrees; to evaporate it at that temperature and to superheat the +steam thus formed to the temperature of the flue gases. This steam, of +course, is first heated to the temperature of the furnace but as it +gives up a portion of this heat in passing through the boiler, the +superheating to the temperature of the exit gases is the correct degree +to be considered. + +4th. Loss due to the water formed and by the burning of the hydrogen in +the fuel which must be evaporated and superheated as in item 3. + +5th. Loss due to the superheating of the moisture in the air supplied +from the atmospheric temperature to the temperature of the flue gases. + +6th. Loss due to the heating of the dry products of combustion to the +temperature of the flue gases. + +7th. Loss due to the incomplete combustion of the fuel when the carbon +is not completely consumed but burns to CO instead of CO_{2}. The CO +passes out of the stack unburned as a volatile gas capable of further +combustion. + +8th. Loss due to radiation of heat from the boiler and furnace settings. + +Obviously a very elaborate test would have to be made were all of the +above items to be determined accurately. In ordinary practice it has +become customary to summarize these losses as follows, the methods of +computing the losses being given in each instance by a typical example: + +(A) Loss due to the heating of moisture in the fuel from the atmospheric +temperature to 212 degrees, evaporate it at that temperature and +superheat it to the temperature of the flue gases. This in reality is +the total heat above the temperature of the air in the boiler room, in +one pound of superheated steam at atmospheric pressure at the +temperature of the flue gases, multiplied by the percentage of moisture +in the fuel. As the total heat above the temperature of the air would +have to be computed in each instance, this loss is best expressed by: + +Loss in B. t. u. per pound = W(212-t+970.4+.47(T-212)) (33) + +Where W = per cent of moisture in coal, + t = the temperature of air in the boiler room, + T = temperature of the flue gases, + .47 = the specific heat of superheated steam at the atmospheric + pressure and at the flue gas temperature, + (212-t) = B. t. u. necessary to heat one pound of water from the + temperature of the boiler room to 212 degrees, + 970.4 = B. t. u. necessary to evaporate one pound of water at 212 + degrees to steam at atmospheric pressure, +.47(T-212) = B. t. u. necessary to superheat one pound of steam at + atmospheric pressure from 212 degrees to temperature T. + +[Illustration: Portion of 15,000 Horse-power Installation of Babcock & +Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Northumberland, Pa., Plant of the Atlas Portland Cement Co. This +Company Operates a Total of 24,000 Horse Power of Babcock & Wilcox +Boilers in its Various Plants] + +(B) Loss due to heat carried away in the steam produced by the burning +of the hydrogen component of the fuel. In burning, one pound of hydrogen +unites with 8 pounds of oxygen to form 9 pounds of steam. Following the +reasoning of item (A), therefore, this loss will be: + +Loss in B. t. u. per pound = 9H((212-t)+970.4+.47(T-212)) (34) + +where H = the percentage by weight of hydrogen. + +This item is frequently considered as a part of the unaccounted for +loss, where an ultimate analysis of the fuel is not given. + +(C) Loss due to heat carried away by dry chimney gases. This is +dependent upon the weight of gas per pound of coal which may be +determined by formula (16), page 158. + +Loss in B. t. u. per pound = (T-t)×.24×W. + +Where T and t have values as in (33), + +.24 = specific heat of chimney gases, + + W = weight of dry chimney gas per pound of coal. + +(D) Loss due to incomplete combustion of the carbon content of the fuel, +that is, the burning of the carbon to CO instead of CO_{2}. + + 10,150 CO +Loss in B. t. u. per pound = C×--------- (35) + CO_{2}+CO + +C = per cent of carbon in coal by ultimate analysis, + +CO and CO_{2} = per cent of CO and CO_{2} by volume from flue gas +analysis. + +10,150 = the number of heat units generated by burning to CO_{2} one +pound of carbon contained in carbon monoxide. + +(E) Loss due to unconsumed carbon in the ash (it being usually assumed +that all the combustible in the ash is carbon). + +Loss in B. t. u. per pound = +per cent C × per cent ash × B. t. u. per pound of combustible in the ash +(usually taken as 14,600 B. t. u.) (36) + +The loss incurred in this way is, directly, the carbon in the ash in +percentage terms of the total dry coal fired, multiplied by the heat +value of carbon. + +To compute this item, which is of great importance in comparing the +relative performances of different designs of grates, an analysis of the +ash must be available. + +The other losses, namely, items 2, 5 and 8 of the first classification, +are ordinarily grouped under one item, as unaccounted for losses, and +are obviously the difference between 100 per cent and the sum of the +heat utilized and the losses accounted for as given above. Item 5, or +the loss due to the moisture in the air, may be readily computed, the +moisture being determined from wet and dry bulb thermometer readings, +but it is usually disregarded as it is relatively small, averaging, say, +one-fifth to one-half of one per cent. Lack of data may, of course, make +it necessary to include certain items of the second and ordinary +classification in this unaccounted for group. + + TABLE 57 + + DATA FROM WHICH HEAT BALANCE + (TABLE 58) IS COMPUTED + ++------------------------------------------------------+ +|+----------------------------------------------------+| +||Steam Pressure by Gauge, Pounds | 192 || +||Temperature of Feed, Degrees Fahrenheit | 180 || +||Degrees of Superheat, Degrees Fahrenheit |115.2|| +||Temperature of Boiler Room, Degrees Fahrenheit| 81 || +||Temperature of Exit Gases, Degrees Fahrenheit | 480 || +||Weight of Coal Used per Hour, Pounds | 5714|| +||Moisture, Per Cent | 1.83|| +||Dry Coal Per Hour, Pounds | 5609|| +||Ash and Refuse per Hour, Pounds | 561|| +||Ash and Refuse (of Dry Coal), Per Cent |10.00|| +||Actual Evaporation per Hour, Pounds |57036|| +|| .- C, Per Cent |78.57|| +|| | H, Per Cent | 5.60|| +||Ultimate | O, Per Cent | 7.02|| +||Analysis -+ N, Per Cent | 1.11|| +||Dry Coal | Ash, Per Cent | 6.52|| +|| '- Sulphur, Per Cent | 1.18|| +||Heat Value per Pound Dry Coal, B. t. u. |14225|| +||Heat Value per Pound Combustible, B. t. u. |15217|| +||Combustible in Ash by Analysis, Per Cent | 17.9|| +|| .- CO_{2}, Per Cent |14.33|| +||Flue Gas -+ O, Per Cent | 4.54|| +||Analysis | CO, Per Cent | 0.11|| +|| '- N, Per Cent |81.02|| +|+----------------------------------------------+-----+| ++------------------------------------------------------+ + +A schedule of the losses as outlined, requires an evaporative test of +the boiler, an analysis of the flue gases, an ultimate analysis of the +fuel, and either an ultimate or proximate analysis of the ash. As the +amount of unaccounted for losses forms a basis on which to judge the +accuracy of a test, such a schedule is called a "heat balance". + +A heat balance is best illustrated by an example: Assume the data as +given in Table 57 to be secured in an actual boiler test. + +From this data the factor of evaporation is 1.1514 and the evaporation +per hour from and at 212 degrees is 65,671 pounds. Hence the evaporation +from and at 212 degrees per pound of dry coal is 65,671÷5609 = 11.71 +pounds. The efficiency of boiler, furnace and grate is: + +(11.71×970.4)÷14,225 = 79.88 per cent. + +The heat losses are: + +(A) Loss due to moisture in coal, + += .01831 ((212-81)+970.4+.47(480-212)) += 22. B. t. u., += 0.15 per cent. + +(B) The loss due to the burning of hydrogen: + += 9×.0560((212-81)+970.4+.47(480-212)) += 618 B. t. u., += 4.34 per cent. + +(C) To compute the loss in the heat carried away by dry chimney gases +per pound of coal the weight of such gases must be first determined. +This weight per pound of coal is: + +(11CO_{2}+8O+7(CO+N)) +(-------------------)C +( 3(CO_{2}+CO) ) + +where CO_{2}, O, CO and H are the percentage by volume as determined by +the flue gas analysis and C is the percentage by weight of carbon in the +dry fuel. Hence the weight of gas per pound of coal will be, + +(11×14.33+8×4.54+7(0.11+81.02)) +(-----------------------------)×78.57 = 13.7 pounds. +( 3(14.33+0.11) ) + +Therefore the loss of heat in the dry gases carried up the chimney = + +13.7×0.24(480-81) = 1311 B. t. u., + = 9.22 per cent. + +(D) The loss due to incomplete combustion as evidenced by the presence +of CO in the flue gas analysis is: + + 0.11 +----------×.7857×10,150 = 61. B. t. u., +14.33+0.11 = .43 per cent. + +(E) The loss due to unconsumed carbon in the ash: + +The analysis of the ash showed 17.9 per cent to be combustible matter, +all of which is assumed to be carbon. The test showed 10.00 of the total +dry fuel fired to be ash. Hence 10.00×.179 = 1.79 per cent of the total +fuel represents the proportion of this total unconsumed in the ash and +the loss due to this cause is + +1.79 per cent × 14,600 = 261 B. t. u., + = 1.83 per cent. + +The heat absorbed by the boilers per pound of dry fuel is 11.71×970.4 = +11,363 B. t. u. This quantity plus losses (A), (B), (C), (D) and (E), or +11,363+22+618+1311+61+261 = 13,636 B. t. u. accounted for. The heat +value of the coal, 14,225 B. t. u., less 13,636 B. t. u., leaves 589 +B. t. u., unaccounted for losses, or 4.15 per cent. + +The heat balance should be arranged in the form indicated by Table 58. + + TABLE 58 + + HEAT BALANCE + + B. T. U. PER POUND DRY COAL 14,225 + ++----------------------------------------------------------------------+ +|+--------------------------------------------------------------------+| +|| |B. t. u.|Per Cent|| +|+--------------------------------------------------+--------+--------+| +||Heat absorbed by Boiler | 11,363 | 79.88 || +||Loss due to Evaporation of Moisture in Fuel | 22 | 0.15 || +||Loss due to Moisture formed by Burning of Hydrogen| 618 | 4.34 || +||Loss due to Heat carried away in Dry Chimney Gases| 1311 | 9.22 || +||Loss due to Incomplete Combustion of Carbon | 61 | 0.43 || +||Loss due to Unconsumed Carbon in the Ash | 261 | 1.83 || +||Loss due to Radiation and Unaccounted Losses | 589 | 4.15 || +|+--------------------------------------------------+--------+--------+| +||Total | 14,225 | 100.00 || +|+--------------------------------------------------+--------+--------+| ++----------------------------------------------------------------------+ + +Application of Heat Balance--A heat balance should be made in connection +with any boiler trial on which sufficient data for its computation has +been obtained. This is particularly true where the boiler performance +has been considered unsatisfactory. The distribution of the heat is thus +determined and any extraordinary loss may be detected. Where accurate +data for computing such a heat balance is not available, such a +calculation based on certain assumptions is sometimes sufficient to +indicate unusual losses. + +The largest loss is ordinarily due to the chimney gases, which depends +directly upon the weight of the gas and its temperature leaving the +boiler. As pointed out in the chapter on flue gas analysis, the lower +limit of the weight of gas is fixed by the minimum air supplied with +which complete combustion may be obtained. As shown, where this supply +is unduly small, the loss caused by burning the carbon to CO instead of +to CO_{2} more than offsets the gain in decreasing the weight of gas. + +The lower limit of the stack temperature, as has been shown in the +chapter on draft, is more or less fixed by the temperature necessary to +create sufficient draft suction for good combustion. With natural draft, +this lower limit is probably between 400 and 450 degrees. + +Capacity--Before the capacity of a boiler is considered, it is necessary +to define the basis to which such a term may be referred. Such a basis +is the so-called boiler horse power. + +The unit of motive power in general use among steam engineers is the +"horse power" which is equivalent to 33,000 foot pounds per minute. +Stationary boilers are at the present time rated in horse power, though +such a basis of rating may lead and has often led to a misunderstanding. +_Work_, as the term is used in mechanics, is the overcoming of +resistance through space, while _power_ is the _rate_ of work or the +amount done per unit of time. As the operation of a boiler in service +implies no motion, it can produce no power in the sense of the term as +understood in mechanics. Its operation is the generation of steam, which +acts as a medium to convey the energy of the fuel which is in the form +of heat to a prime mover in which that heat energy is converted into +energy of motion or work, and power is developed. + +If all engines developed the same amount of power from an equal amount +of heat, a boiler might be designated as one having a definite horse +power, dependent upon the amount of engine horse power its steam would +develop. Such a statement of the rating of boilers, though it would +still be inaccurate, if the term is considered in its mechanical sense, +could, through custom, be interpreted to indicate that a boiler was of +the exact capacity required to generate the steam necessary to develop a +definite amount of horse power in an engine. Such a basis of rating, +however, is obviously impossible when the fact is considered that the +amount of steam necessary to produce the same power in prime movers of +different types and sizes varies over very wide limits. + +To do away with the confusion resulting from an indefinite meaning of +the term boiler horse power, the Committee of Judges in charge of the +boiler trials at the Centennial Exposition, 1876, at Philadelphia, +ascertained that a good engine of the type prevailing at the time +required approximately 30 pounds of steam per hour per horse power +developed. In order to establish a relation between the engine power and +the size of a boiler required to develop that power, they recommended +that an evaporation of 30 pounds of water from an initial temperature of +100 degrees Fahrenheit to steam at 70 pounds gauge pressure be +considered as _one boiler horse power_. This recommendation has been +generally accepted by American engineers as a standard, and when the +term boiler horse power is used in connection with stationary +boilers[58] throughout this country,[59] without special definition, it +is understood to have this meaning. + +Inasmuch as an equivalent evaporation from and at 212 degrees Fahrenheit +is the generally accepted basis of comparison[60], it is now customary +to consider the standard boiler horse power as recommended by the +Centennial Exposition Committee, in terms of equivalent evaporation from +and at 212 degrees. This will be 30 pounds multiplied by the factor of +evaporation for 70 pounds gauge pressure and 100 degrees feed +temperature, or 1.1494. 30 × 1.1494 = 34.482, or approximately 34.5 +pounds. Hence, _one boiler horse power is equal to an evaporation of +34.5 pounds of water per hour from and at 212 degrees Fahrenheit_. The +term boiler horse power, therefore, is clearly a measure of evaporation +and not of power. + +A method of basing the horse power rating of a boiler adopted by boiler +manufacturers is that of heating surfaces. Such a method is absolutely +arbitrary and changes in no way the definition of a boiler horse power +just given. It is simply a statement by the manufacturer that his +product, under ordinary operating conditions or conditions which may be +specified, will evaporate 34.5 pounds of water from and at 212 degrees +per definite amount of heating surface provided. The amount of heating +surface that has been considered by manufacturers capable of evaporating +34.5 pounds from and at 212 degrees per hour has changed from time to +time as the art has progressed. At the present time 10 square feet of +heating surface is ordinarily considered the equivalent of one boiler +horse power among manufacturers of stationary boilers. In view of the +arbitrary nature of such rating and of the widely varying rates of +evaporation possible per square foot of heating surface with different +boilers and different operating conditions, such a basis of rating has +in reality no particular bearing on the question of horse power and +should be considered merely as a convenience. + +The whole question of a unit of boiler capacity has been widely +discussed with a view to the adoption of a standard to which there would +appear to be a more rational and definite basis. Many suggestions have +been offered as to such a basis but up to the present time there has +been none which has met with universal approval or which would appear +likely to be generally adopted. + +With the meaning of boiler horse power as given above, that is, a +measure of evaporation, it is evident that the capacity of a boiler is a +measure of the power it can develop expressed in boiler horse power. +Since it is necessary, as stated, for boiler manufacturers to adopt a +standard for reasons of convenience in selling, the horse power for +which a boiler is sold is known as its normal rated capacity. + +The efficiency of a boiler and the maximum capacity it will develop can +be determined accurately only by a boiler test. The standard methods of +conducting such tests are given on the following pages, these methods +being the recommendations of the Power Test Committee of the American +Society of Mechanical Engineers brought out in 1913.[61] Certain changes +have been made to incorporate in the boiler code such portions of the +"Instructions Regarding Tests in General" as apply to boiler testing. +Methods of calculation and such matter as are treated in other portions +of the book have been omitted from the code as noted. + +[Illustration: Portion of 2600 Horse-power Installation of Babcock & +Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Peter Schoenhofen Brewing Co., Chicago, Ill.] + + + +1. OBJECT + + +Ascertain the specific object of the test, and keep this in view not +only in the work of preparation, but also during the progress of the +test, and do not let it be obscured by devoting too close attention to +matters of minor importance. Whatever the object of the test may be, +accuracy and reliability must underlie the work from beginning to end. + +If questions of fulfillment of contract are involved, there should be a +clear understanding between all the parties, preferably in writing, as +to the operating conditions which should obtain during the trial, and as +to the methods of testing to be followed, unless these are already +expressed in the contract itself. + +Among the many objects of performance tests, the following may be noted: + + Determination of capacity and efficiency, and how these compare + with standard or guaranteed results. + + Comparison of different conditions or methods of operation. + + Determination of the cause of either inferior or superior + results. + + Comparison of different kinds of fuel. + + Determination of the effect of changes of design or proportion + upon capacity or efficiency, etc. + + + +2. PREPARATIONS + + +_(A) Dimensions:_ + +Measure the dimensions of the principal parts of the apparatus to be +tested, so far as they bear on the objects in view, or determine these +from correct working drawings. Notice the general features of the same, +both exterior and interior, and make sketches, if needed, to show +unusual points of design. + + The dimensions of the heating surfaces of boilers and + superheaters to be found are those of surfaces in contact with + the fire or hot gases. The submerged surfaces in boilers at the + mean water level should be considered as water-heating surfaces, + and other surfaces which are exposed to the gases as + superheating surfaces. + + +_(B) Examination of Plant:_ + +Make a thorough examination of the physical condition of all parts of +the plant or apparatus which concern the object in view, and record the +conditions found, together with any points in the matter of operation +which bear thereon. + + In boilers, examine for leakage of tubes and riveted or other + metal joints. Note the condition of brick furnaces, grates and + baffles. Examine brick walls and cleaning doors for air leaks, + either by shutting the damper and observing the escaping smoke + or by candle-flame test. Determine the condition of heating + surfaces with reference to exterior deposits of soot and + interior deposits of mud or scale. + + See that the steam main is so arranged that condensed and + entrained water cannot flow back into the boiler. + +If the object of the test is to determine the highest efficiency or +capacity obtainable, any physical defects, or defects of operation, +tending to make the result unfavorable should first be remedied; all +foul parts being cleaned, and the whole put in first-class condition. +If, on the other hand, the object is to ascertain the performance under +existing conditions, no such preparation is either required or desired. + + +_(C) General Precautions against Leakage:_ + +In steam tests make sure that there is no leakage through blow-offs, +drips, etc., or any steam or water connections of the plant or apparatus +undergoing test, which would in any way affect the results. All such +connections should be blanked off, or satisfactory assurance should be +obtained that there is leakage neither out nor in. This is a most +important matter, and no assurance should be considered satisfactory +unless it is susceptible of absolute demonstration. + + + +3. FUEL + + +Determine the character of fuel to be used.[62] For tests of maximum +efficiency or capacity of the boiler to compare with other boilers, the +coal should be of some kind which is commercially regarded as a standard +for the locality where the test is made. + + In the Eastern States the standards thus regarded for + semi-bituminous coals are Pocahontas (Va. and W. Va.) and New + River (W. Va.); for anthracite coals those of the No. 1 + buckwheat size, fresh-mined, containing not over 13 per cent ash + by analysis; and for bituminous coals, Youghiogheny and + Pittsburgh coals. In some sections east of the Allegheny + Mountains the semi-bituminous Clearfield (Pa.) and Cumberland + (Md.) are also considered as standards. These coals when of good + quality possess the essentials of excellence, adaptability to + various kinds of furnaces, grates, boilers, and methods of + firing required, besides being widely distributed and generally + accessible in the Eastern market. There are no special grades of + coal mined in the Western States which are widely and generally + considered as standards for testing purposes; the best coal + obtainable in any particular locality being regarded as the + standard of comparison. + +A coal selected for maximum efficiency and capacity tests, should be the +best of its class, and especially free from slagging and unusual +clinker-forming impurities. + +For guarantee and other tests with a specified coal containing not more +than a certain amount of ash and moisture, the coal selected should not +be higher in ash and in moisture than the stated amounts, because any +increase is liable to reduce the efficiency and capacity more than the +equivalent proportion of such increase. + +The size of the coal, especially where it is of the anthracite class, +should be determined by screening a suitable sample. + + + +4. APPARATUS AND INSTRUMENTS[63] + + +The apparatus and instruments required for boiler tests are: + + (A) Platform scales for weighing coal and ashes. + + (B) Graduated scales attached to the water glasses. + + (C) Tanks and platform scales for weighing water (or water + meters calibrated in place). Wherever practicable the feed water + should be weighed, especially for guarantee tests. The most + satisfactory and reliable apparatus for this purpose consists of + one or more tanks each placed on platform scales, these being + elevated a sufficient distance above the floor to empty into a + receiving tank placed below, the latter being connected to the + feed pump. Where only one weighing tank is used the receiving + tank should be of larger size than the weighing tank, to afford + sufficient reserve supply to the pump while the upper tank is + filling. If a single weighing tank is used it should preferably + be of such capacity as to require emptying not oftener than + every 5 minutes. If two or more are used the intervals between + successive emptyings should not be less than 3 minutes. + + (D) Pressure gauges, thermometers, and draft gauges. + + (E) Calorimeters for determining the calorific value of fuel and + the quality of steam. + + (F) Furnaces pyrometers. + + (G) Gas analyzing apparatus. + + + +5. OPERATING CONDITIONS + + +Determine what the operating conditions and method of firing should be +to conform to the object in view, and see that they prevail throughout +the trial, as nearly as possible. + + Where uniformity in the rate of evaporation is required, + arrangement can be usually made to dispose of the steam so that + this result can be attained. In a single boiler it may be + accomplished by discharging steam through a waste pipe and + regulating the amount by means of a valve. In a battery of + boilers, in which only one is tested, the draft may be regulated + on the remaining boilers to meet the varying demands for steam, + leaving the test boiler to work under a steady rate of + evaporation. + + + +6. DURATION + + +The duration of tests to determine the efficiency of a hand-fired +boiler, should be 10 hours of continuous running, or such time as may be +required to burn a total of 250 pounds of coal per square foot of grate. + +In the case of a boiler using a mechanical stoker, the duration, where +practicable, should be at least 24 hours. If the stoker is of a type +that permits the quantity and condition of the fuel bed at beginning and +end of the test to be accurately estimated, the duration may be reduced +to 10 hours, or such time as may be required to burn the above noted +total of 250 pounds per square foot. + + In commercial tests where the service requires continuous + operation night and day, with frequent shifts of firemen, the + duration of the test, whether the boilers are hand fired or + stoker fired, should be at least 24 hours. Likewise in + commercial tests, either of a single boiler or of a plant of + several boilers, which operate regularly a certain number of + hours and during the balance of the day the fires are banked, + the duration should not be less than 24 hours. + + The duration of tests to determine the maximum evaporative + capacity of a boiler, without determining the efficiency, should + not be less than 3 hours. + + + +7. STARTING AND STOPPING + + +The conditions regarding the temperature of the furnace and boiler, the +quantity and quality of the live coal and ash on the grates, the water +level, and the steam pressure, should be as nearly as possible the same +at the end as at the beginning of the test. + +To secure the desired equality of conditions with hand-fired boilers, +the following method should be employed: + + The furnace being well heated by a preliminary run, burn the + fire low, and thoroughly clean it, leaving enough live coal + spread evenly over the grate (say 2 to 4 inches),[64] to serve + as a foundation for the new fire. Note quickly the thickness of + the coal bed as nearly as it can be estimated or measured; also + the water level,[65] the steam pressure, and the time, and + record the latter as the starting time. Fresh coal should then + be fired from that weighed for the test, the ashpit throughly + cleaned, and the regular work of the test proceeded with. Before + the end of the test the fire should again be burned low and + cleaned in such a manner as to leave the same amount of live + coal on the grate as at the start. When this condition is + reached, observe quickly the water level,[65] the steam + pressure, and the time, and record the latter as the stopping + time. If the water level is not the same as at the beginning a + correction should be made by computation, rather than by feeding + additional water after the final readings are taken. Finally + remove the ashes and refuse from the ashpit. In a plant + containing several boilers where it is not practicable to clean + them simultaneously, the fires should be cleaned one after the + other as rapidly as may be, and each one after cleaning charged + with enough coal to maintain a thin fire in good working + condition. After the last fire is cleaned and in working + condition, burn all the fires low (say 4 to 6 inches), note + quickly the thickness of each, also the water levels, steam + pressure, and time, which last is taken as the starting time. + Likewise when the time arrives for closing the test, the fires + should be quickly cleaned one by one, and when this work is + completed they should all be burned low the same as the start, + and the various observations made as noted. In the case of a + large boiler having several furnace doors requiring the fire to + be cleaned in sections one after the other, the above directions + pertaining to starting and stopping in a plant of several + boilers may be followed. + +To obtain the desired equality of conditions of the fire when a +mechanical stoker other than a chain grate is used, the procedure should +be modified where practicable as follows: + + Regulate the coal feed so as to burn the fire to the low + condition required for cleaning. Shut off the coal-feeding + mechanism and fill the hoppers level full. Clean the ash or dump + plate, note quickly the depth and condition of the coal on the + grate, the water level,[66] the steam pressure, and the time, + and record the latter as the starting time. Then start the + coal-feeding mechanism, clean the ashpit, and proceed with the + regular work of the test. + + When the time arrives for the close of the test, shut off the + coal-feeding mechanism, fill the hoppers and burn the fire to + the same low point as at the beginning. When this condition is + reached, note the water level, the steam pressure, and the time, + and record the latter as the stopping time. Finally clean the + ashplate and haul the ashes. + + In the case of chain grate stokers, the desired operating + conditions should be maintained for half an hour before starting + a test and for a like period before its close, the height of the + throat plate and the speed of the grate being the same during + both of these periods. + + + +8. RECORDS + + +A log of the data should be entered in notebooks or on blank sheets +suitably prepared in advance. This should be done in such manner that +the test may be divided into hourly periods, or if necessary, periods of +less duration, and the leading data obtained for any one or more periods +as desired, thereby showing the degree of uniformity obtained. + +Half-hourly readings of the instruments are usually sufficient. If there +are sudden and wide fluctuations, the readings in such cases should be +taken every 15 minutes, and in some instances oftener. + + The coal should be weighed and delivered to the firemen in + portions sufficient for one hour's run, thereby ascertaining the + degree of uniformity of firing. An ample supply of coal should + be maintained at all times, but the quantity on the floor at the + end of each hour should be as small as practicable, so that the + same may be readily estimated and deducted from the total + weight. + + The records should be such as to ascertain also the consumption + of feed water each hour and thereby determine the degree of + uniformity of evaporation. + + + +9. QUALITY OF STEAM[67] + + +If the boiler does not produce superheated steam the percentage of +moisture in the steam should be determined by the use of a throttling or +separating calorimeter. If the boiler has superheating surface, the +temperature of the steam should be determined by the use of a +thermometer inserted in a thermometer well. + +For saturated steam construct a sampling pipe or nozzle made of one-half +inch iron pipe and insert it in the steam main at a point where the +entrained moisture is likely to be most thoroughly mixed. The inner end +of the pipe, which should extend nearly across to the opposite side of +the main, should be closed and interior portion perforated with not less +than twenty one-eighth inch holes equally distributed from end to end +and preferably drilled in irregular or spiral rows, with the first hole +not less than half an inch from the wall of the pipe. + + The sampling pipe should not be placed near a point where water + may pocket or where such water may effect the amount of moisture + contained in the sample. Where non-return valves are used, or + there are horizontal connections leading from the boiler to a + vertical outlet, water may collect at the lower end of the + uptake pipe and be blown upward in a spray which will not be + carried away by the steam owing to a lack of velocity. A sample + taken from the lower part of this pipe will show a greater + amount of moisture than a true sample. With goose-neck + connections a small amount of water may collect on the bottom of + the pipe near the upper end where the inclination is such that + the tendency to flow backward is ordinarily counterbalanced by + the flow of steam forward over its surface; but when the + velocity momentarily decreases the water flows back to the lower + end of the goose-neck and increases the moisture at that point, + making it an undesirable location for sampling. In any case it + must be borne in mind that with low velocities the tendency is + for drops of entrained water to settle to the bottom of the + pipe, and to be temporarily broken up into spray whenever an + abrupt bend or other disturbance is met. + +If it is necessary to attach the sampling nozzle at a point near the end +of a long horizontal run, a drip pipe should be provided a short +distance in front of the nozzle, preferably at a pocket formed by some +fitting and the water running along the bottom of the main drawn off, +weighed, and added to the moisture shown by the calorimeter; or, better, +a steam separator should be installed at the point noted. + +In testing a stationary boiler the sampling pipe should be located as +near as practicable to the boiler, and the same is true as regards the +thermometer well when the steam is superheated. In an engine or turbine +test these locations should be as near as practicable to throttle valve. +In the test of a plant where it is desired to get complete information, +especially where the steam main is unusually long, sampling nozzles or +thermometer wells should be provided at both points, so as to obtain +data at either point as may be required. + + + +10. SAMPLING AND DRYING COAL + + +During the progress of test the coal should be regularly sampled for the +purpose of analysis and determination of moisture. + +Select a representative shovelful from each barrow-load as it is drawn +from the coal pile or other source of supply, and store the samples in a +cool place in a covered metal receptacle. When all the coal has thus +been sampled, break up the lumps, thoroughly mix the whole quantity, and +finally reduce it by the process of repeated quartering and crushing to +a sample weighing about 5 pounds, the largest pieces being about the +size of a pea. From this sample two one-quart air-tight glass fruit +jars, or other air-tight vessels, are to be promptly filled and +preserved for subsequent determinations of moisture, calorific value, +and chemical composition. These operations should be conducted where the +air is cool and free from drafts. + +[Illustration: 3460 Horse-power Installation of Babcock & Wilcox Boilers +at the Chicago, Ill., Shops of the Chicago and Northwestern Ry. Co.] + +When the sample lot of coal has been reduced by quartering to, say, 100 +pounds, a portion weighing, say, 15 to 20 pounds should be withdrawn for +the purpose of immediate moisture determination. This is placed in a +shallow iron pan and dried on the hot iron boiler flue for at least 12 +hours, being weighed before and after drying on scales reading to +quarter ounces. + +The moisture thus determined is approximately reliable for anthracite +and semi-bituminous coals, but not for coals containing much inherent +moisture. For such coals, and for all absolutely reliable determinations +the method to be pursued is as follows: + + Take one of the samples contained in the glass jars, and subject + it to a thorough air drying, by spreading it in a thin layer and + exposing it for several hours to the atmosphere of a warm room, + weighing it before and after, thereby determining the quantity + of surface moisture it contains.[68] Then crush the whole of it + by running it through an ordinary coffee mill or other suitable + crusher adjusted so as to produce somewhat coarse grains (less + than 1/16 inch), thoroughly mix the crushed sample, select from + it a portion of from 10 to 50 grams,[69] weigh it in a balance + which will easily show a variation as small as 1 part in 1000, + and dry it for one hour in an air or sand bath at a temperature + between 240 and 280 degrees Fahrenheit. Weigh it and record the + loss, then heat and weigh again until the minimum weight has + been reached. The difference between the original and the + minimum weight is the moisture in the air-dried coal. The sum of + the moisture thus found and that of the surface moisture is the + total moisture. + + + +11. ASHES AND REFUSE + + +The ashes and refuse withdrawn from the furnace and ashpit during the +progress of the test and at its close should be weighed so far as +possible in a dry state. If wet the amount of moisture should be +ascertained and allowed for, a sample being taken and dried for this +purpose. This sample may serve also for analysis and the determination +of unburned carbon and fusing temperature. + +The method above described for sampling coal may also be followed for +obtaining a sample of the ashes and refuse. + + + +12. CALORIFIC TESTS AND ANALYSES OF COAL + + +The quality of the fuel should be determined by calorific tests and +analysis of the coal sample above referred to.[70] + + + +13. ANALYSES OF FLUE GASES + + +For approximate determinations of the composition of the flue gases, the +Orsat apparatus, or some modification thereof, should be employed. If +momentary samples are obtained the analyses should be made as frequently +as possible, say, every 15 to 30 minutes, depending on the skill of the +operator, noting at the time the sample is drawn the furnace and firing +conditions. If the sample drawn is a continuous one, the intervals may +be made longer. + + + +14. SMOKE OBSERVATIONS[71] + + +In tests of bituminous coals requiring a determination of the amount of +smoke produced, observations should be made regularly throughout the +trial at intervals of 5 minutes (or if necessary every minute), noting +at the same time the furnace and firing conditions. + + + +15. CALCULATION OF RESULTS + + +The methods to be followed in expressing and calculating those results +which are not self-evident are explained as follows: + + (A) _Efficiency._ The "efficiency of boiler, furnace and + grate" is the relation between the heat absorbed per pound of + coal fired, and the calorific value of one pound of coal. + + The "efficiency of boiler and furnace" is the relation between + the heat absorbed per pound of combustible burned, and the + calorific value of one pound of combustible. This expression of + efficiency furnishes a means for comparing one boiler and + furnace with another, when the losses of unburned coal due to + grates, cleanings, etc., are eliminated. + + The "combustible burned" is determined by subtracting from the + weight of coal supplied to the boiler, the moisture in the coal, + the weight of ash and unburned coal withdrawn from the furnace + and ashpit, and the weight of dust, soot, and refuse, if any, + withdrawn from the tubes, flues, and combustion chambers, + including ash carried away in the gases, if any, determined from + the analysis of coal and ash. The "combustible" used for + determining the calorific value is the weight of coal less the + moisture and ash found by analysis. + + The "heat absorbed" per pound of coal, or combustible, is + calculated by multiplying the equivalent evaporation from and at + 212 degrees per pound of coal or combustible by 970.4. + +Other items in this section which have been treated elsewhere are: + + (B) Corrections for moisture in steam. + + (C) Correction for live steam used. + + (D) Equivalent evaporation. + + (E) Heat balance. + + (F) Total heat of combustion of coal. + + (G) Air for combustion and the methods recommended for + calculating these results are in accordance with those described + in different portions of this book. + + + +16. DATA AND RESULTS + + +The data and results should be reported in accordance with either the +short form or the complete form, adding lines for data not provided for, +or omitting those not required, as may conform to the object in view. + + + +17. CHART + + +In trials having for an object the determination and exposition of the +complete boiler performance, the entire log of readings and data should +be plotted on a chart and represented graphically. + + + +18. TESTS WITH OIL AND GAS FUELS + + +Tests of boilers using oil or gas for fuel should accord with the rules +here given, excepting as they are varied to conform to the particular +characteristics of the fuel. The duration in such cases may be reduced, +and the "flying" method of starting and stopping employed. + + The table of data and results should contain items stating + character of furnace and burner, quality and composition of oil + or gas, temperature of oil, pressure of steam used for + vaporizing and quantity of steam used for both vaporizing and + for heating. + + TABLE DATA AND RESULTS OF EVAPORATIVE TEST + SHORT FORM, CODE OF 1912 + + 1 Test of.................boiler located at................................ + to determine...............conducted by.............................. + 2 Kind of furnace.......................................................... + 3 Grate surface.................................................square feet + 4 Water-heating surface.........................................square feet + 5 Superheating surface..........................................square feet + 6 Date..................................................................... + 7 Duration............................................................hours + 8 Kind and size of coal.................................................... + +AVERAGE PRESSURES, TEMPERATURES, ETC. + + 9 Steam pressure by gauge............................................pounds +10 Temperature of feed water entering boiler.........................degrees +11 Temperature of escaping gases leaving boiler......................degrees +12 Force of draft between damper and boiler...........................inches +13 Percentage of moisture in steam, + or number degrees of superheating..................per cent or degrees + +TOTAL QUANTITIES + +14 Weight of coal as fired[72]........................................pounds +15 Percentage of moisture in coal...................................per cent +16 Total weight of dry coal consumed..................................pounds +17 Total ash and refuse...............................................pounds +18 Percentage of ash and refuse in dry coal.........................per cent +19 Total weight of water fed to the boiler[73]........................pounds +20 Total water evaporated, corrected for moisture in steam............pounds +21 Total equivalent evaporation from and at 212 degrees...............pounds + +HOURLY QUANTITIES AND RATES + +22 Dry coal consumed per hour.........................................pounds +23 Dry coal per square feet of grate surface per hour.................pounds +24 Water evaporated per hour corrected for quality of steam...........pounds +25 Equivalent evaporation per hour from and at 212 degrees............pounds +26 Equivalent evaporation per hour from and at 212 degrees + per square foot of water-heating surface........................pounds + +CAPACITY + +27 Evaporation per hour from and at 212 degrees (same as Line 25).....pounds +28 Boiler horse power developed (Item 27÷34½).............boiler horse power +29 Rated capacity, in evaporation from and at 212 degrees per hour....pounds +30 Rated boiler horse power...............................boiler horse power +31 Percentage of rated capacity developed...........................per cent + +ECONOMY RESULTS + +32 Water fed per pound of coal fired (Item 19÷Item 14)................pounds +33 Water evaporated per pound of dry coal (Item 20÷Item 16)...........pounds +34 Equivalent evaporation from and at 212 degrees per pound + of dry coal (Item 21÷Item 16)...................................pounds +35 Equivalent evaporation from and at 212 degrees per pound + of combustible [Item 21÷(Item 16-Item 17)]......................pounds + +EFFICIENCY + +36 Calorific value of one pound of dry coal.........................B. t. u. +37 Calorific value of one pound of combustible......................B. t. u. + + ( Item 34×970.4) +38 Efficiency of boiler, furnace and grate (100 × -------------)....per cent + ( Item 36 ) + + ( Item 35×970.4) +39 Efficiency of boiler and furnace (100 × -------------)...........per cent + ( Item 37 ) + +COST OF EVAPORATION + +40 Cost of coal per ton of......pounds delivered in boiler room......dollars +41 Cost of coal required for evaporating 1000 pounds of water + from and at 212 degrees........................................dollars + +[Illustration: Portion of 3600 Horse-power Installation of Babcock & +Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Loomis Street Plant of the Peoples Gas Light & Coke Co., Chicago, +Ill. This Company has Installed 7780 Horse Power of Babcock & Wilcox +Boilers] + + + + +THE SELECTION OF BOILERS WITH A CONSIDERATION OF THE FACTORS DETERMINING +SUCH SELECTION + + +The selection of steam boilers is a matter to which the most careful +thought and attention may be well given. Within the last twenty years, +radical changes have taken place in the methods and appliances for the +generation and distribution of power. These changes have been made +largely in the prime movers, both as to type and size, and are best +illustrated by the changes in central station power-plant practice. It +is hardly within the scope of this work to treat of power-plant design +and the discussion will be limited to a consideration of the boiler end +of the power plant. + +As stated, the changes have been largely in prime movers, the steam +generating equipment having been considered more or less of a standard +piece of apparatus whose sole function is the transfer of the heat +liberated from the fuel by combustion to the steam stored or circulated +in such apparatus. When the fact is considered that the cost of steam +generation is roughly from 65 to 80 per cent of the total cost of power +production, it may be readily understood that the most fruitful field +for improvement exists in the boiler end of the power plant. The +efficiency of the plant as a whole will vary with the load it carries +and it is in the boiler room where such variation is largest and most +subject to control. + +The improvements to be secured in the boiler room results are not simply +a matter of dictation of operating methods. The securing of perfect +combustion, with the accompanying efficiency of heat transfer, while +comparatively simple in theory, is difficult to obtain in practical +operation. This fact is perhaps best exemplified by the difference +between test results and those obtained in daily operation even under +the most careful supervision. This difference makes it necessary to +establish a standard by which operating results may be judged, a +standard not necessarily that which might be possible under test +conditions but one which experiment shows can be secured under the very +best operating conditions. + +The study of the theory of combustion, draft, etc., as already given, +will indicate that the question of efficiency is largely a matter of +proper relation between fuel, furnace and generator. While the +possibility of a substantial saving through added efficiency cannot be +overlooked, the boiler design of the future must, even more than in the +past, be considered particularly from the aspect of reliability and +simplicity. A flexibility of operation is necessary as a guarantee of +continuity of service. + +In view of the above, before the question of the selection of boilers +can be taken up intelligently, it is necessary to consider the subjects +of boiler efficiency and boiler capacity, together with their relation +to each other. + +The criterion by which the efficiency of a boiler plant is to be judged +is the cost of the production of a definite amount of steam. Considered +in this sense, there must be included in the efficiency of a boiler +plant the simplicity of operation, flexibility and reliability of the +boiler used. The items of repair and upkeep cost are often high because +of the nature of the service. The governing factor in these items is +unquestionably the type of boiler selected. + +The features entering into the plant efficiency are so numerous that it +is impossible to make a statement as to a means of securing the highest +efficiency which will apply to all cases. Such efficiency is to be +secured by the proper relation of fuel, furnace and boiler heating +surface, actual operating conditions, which allow the approaching of the +potential efficiencies made possible by the refinement of design, and a +systematic supervision of the operation assisted by a detailed record of +performances and conditions. The question of supervision will be taken +up later in the chapter on "Operation and Care of Boilers". + +The efficiencies that may be expected from the combination of +well-designed boilers and furnaces are indicated in Table 59 in which +are given a number of tests with various fuels and under widely +different operating conditions. + +It is to be appreciated that the results obtained as given in this table +are practically all under test conditions. The nearness with which +practical operating conditions can approach these figures will depend +upon the character of the supervision of the boiler room and the +intelligence of the operating crew. The size of the plant will +ordinarily govern the expense warranted in securing the right sort of +supervision. + +The bearing that the type of boiler has on the efficiency to be expected +can only be realized from a study of the foregoing chapters. + +Capacity--Capacity, as already defined, is the ability of a definite +amount of boiler-heating surface to generate steam. Boilers are +ordinarily purchased under a manufacturer's specification, which rates a +boiler at a nominal rated horse power, usually based on 10 square feet +of heating surface per horse power. Such a builders' rating is +absolutely arbitrary and implies nothing as to the limiting amount of +water that this amount of heating surface will evaporate. It does not +imply that the evaporation of 34.5 pounds of water from and at 212 +degrees with 10 square feet of heating surface is the limit of the +capacity of the boiler. Further, from a statement that a boiler is of a +certain horse power on the manufacturer's basis, it is not to be +understood that the boiler is in any state of strain when developing +more than its rated capacity. + +Broadly stated, the evaporative capacity of a certain amount of heating +surface in a well-designed boiler, that is, the boiler horse power it is +capable of producing, is limited only by the amount of fuel that can be +burned under the boiler. While such a statement would imply that the +question of capacity to be secured was simply one of making an +arrangement by which sufficient fuel could be burned under a definite +amount of heating surface to generate the required amount of steam, +there are limiting features that must be weighed against the advantages +of high capacity developed from small heating surfaces. Briefly stated, +these factors are as follows: + +1st. Efficiency. As the capacity increases, there will in general be a +decrease in efficiency, this loss above a certain point making it +inadvisable to try to secure more than a definite horse power from a +given boiler. This loss of efficiency with increased capacity is treated +below in detail, in considering the relation of efficiency to capacity. + +2nd. Grate Ratio Possible or Practicable. All fuels have a maximum rate +of combustion, beyond which satisfactory results cannot be obtained, +regardless of draft available or which may be secured by mechanical +means. Such being the case, it is evident that with this maximum +combustion rate secured, the only method of obtaining added capacity +will be through the addition of grate surface. There is obviously a +point beyond which the grate surface for a given boiler cannot be +increased. This is due to the impracticability of handling grates above +a certain maximum size, to the enormous loss in draft pressure through a +boiler resulting from an attempt to force an abnormal quantity of gas +through the heating surface and to innumerable details of design and +maintenance that would make such an arrangement wholly unfeasible. + +3rd. Feed Water. The difficulties that may arise through the use of poor +feed water or that are liable to happen through the use of practically +any feed water have already been pointed out. This question of feed is +frequently the limiting factor in the capacity obtainable, for with an +increase in such capacity comes an added concentration of such +ingredients in the feed water as will cause priming, foaming or rapid +scale formation. Certain waters which will give no trouble that cannot +be readily overcome with the boiler run at ordinary ratings will cause +difficulties at higher ratings entirely out of proportion to any +advantage secured by an increase in the power that a definite amount of +heating surface may be made to produce. + +Where capacity in the sense of overload is desired, the type of boiler +selected will play a large part in the successful operation through such +periods. A boiler must be selected with which there is possible a +furnace arrangement that will give flexibility without undue loss in +efficiency over the range of capacity desired. The heating surface must +be so arranged that it will be possible to install in a practical +manner, sufficient grate surface at or below the maximum combustion rate +to develop the amount of power required. The design of boiler must be +such that there will be no priming or foaming at high overloads and that +any added scale formation due to such overloads may be easily removed. +Certain boilers which deliver commercially dry steam when operated at +about their normal rated capacity will prime badly when run at overloads +and this action may take place with a water that should be easily +handled by a properly designed boiler at any reasonable load. Such +action is ordinarily produced by the lack of a well defined, positive +circulation. + +Relation of Efficiency and Capacity--The statement has been made that in +general the efficiency of a boiler will decrease as the capacity is +increased. Considering the boiler alone, apart from the furnace, this +statement may be readily explained. + +Presupposing a constant furnace temperature, regardless of the capacity +at which a given boiler is run; to assure equal efficiencies at low and +high ratings, the exit temperature in the two instances would +necessarily be the same. For this temperature at the high rating, to be +identical with that at the low rating, the rate of heat transfer from +the gases to the heating surfaces would have to vary directly as the +weight or volume of such gases. Experiment has shown, however, that this +is not true but that this rate of transfer varies as some power of the +volume of gas less than one. As the heat transfer does not, therefore, +increase proportionately with the volume of gases, the exit temperature +for a given furnace temperature will be increased as the volume of gases +increases. As this is the measure of the efficiency of the heating +surface, the boiler efficiency will, therefore, decrease as the volume +of gases increases or the capacity at which the boiler is operated +increases. + +Further, a certain portion of the heat absorbed by the heating surface +is through direct radiation from the fire. Again, presupposing a +constant furnace temperature; the heat absorbed through radiation is +solely a function of the amount of surface exposed to such radiation. +Hence, for the conditions assumed, the amount of heat absorbed by +radiation at the higher ratings will be the same as at the lower ratings +but in proportion to the total absorption will be less. As the added +volume of gas does not increase the rate of heat transfer, there are +therefore two factors acting toward the decrease in the efficiency of a +boiler with an increase in the capacity. + + TABLE 59 + + TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS + + ______________________________________________________________________ +|Number| | | | Rated | +| of | Name and Location | Kind of Coal | Kind of | Horse | +| Test | of Plant | | Furnace |Power of| +| | | | | Boiler | +| | | | | | +|______|___________________________|________________|_________|________| +| |Susquehanna Coal Co., |No. 1 Anthracite|Hand | | +| 1 |Shenandoah, Pa. |Buckwheat |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Balbach Smelting & |No. 2 Buckwheat |Wilkenson| | +| 2 |Refining Co., Newark, N. J.|and Bird's-eye | Stoker | 218 | +|______|___________________________|________________|_________|________| +| |H. R. Worthington, |No. 2 Anthracite|Hand | | +| 3 |Harrison N. J. |Buckwheat |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Raymond Street Jail, |Anthracite Pea |Hand | | +| 4 |Brooklyn, N. Y. | |Fired | 155 | +|______|___________________________|________________|_________|________| +| |R. H. Macy & Co., |No. 3 Anthracite|Hand | | +| 5 |New York, N. Y. |Buckwheat |Fired | 293 | +|______|___________________________|________________|_________|________| +| |National Bureau of |Anthracite Egg |Hand | | +| 6 |Standards, Washington, D.C.| |Fired | 119 | +|______|___________________________|________________|_________|________| +| |Fred. Loeser & Co., |No. 1 Anthracite|Hand | | +| 7 |Brooklyn, N. Y. |Buckwheat |Fired | 300 | +|______|___________________________|________________|_________|________| +| |New York Edison Co., |No. 2 Anthracite|Hand | | +| 8 |New York City |Buckwheat |Fired | 374 | +|______|___________________________|________________|_________|________| +| |Sewage Pumping Station, |Hocking Valley |Hand | | +| 9 |Cleveland, O. |Lump, O. |Fired | 150 | +|______|___________________________|________________|_________|________| +| |Scioto River Pumping Sta., |Hocking Valley, |Hand | | +| 10 |Cleveland, O. |O. |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Consolidated Gas & Electric|Somerset, Pa. |Hand | | +| 11 |Co., Baltimore, Md. | |Fired | 640 | +|______|___________________________|________________|_________|________| +| |Consolidated Gas & Electric|Somerset, Pa. |Hand | | +| 12 |Co., Baltimore, Md. | |Fired | 640 | +|______|___________________________|________________|_________|________| +| |Merrimac Mfg. Co., |Georges Creek, |Hand | | +| 13 |Lowell, Mass. |Md. |Fired | 321 | +|______|___________________________|________________|_________|________| +| |Great West'n Sugar Co., |Lafayette, Col.,|HandFired| | +| 14 |Ft. Collins, Col. |Mine Run |Extension| 351 | +|______|___________________________|________________|_________|________| +| |Baltimore Sewage Pumping |New River |Hand | | +| 15 | Station | |Fired | 266 | +|______|___________________________|________________|_________|________| +| |Tennessee State Prison, |Brushy Mountain,|Hand | | +| 16 |Nashville, Tenn. |Tenn. |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Pine Bluff Corporation, |Arkansas Slack |Hand | | +| 17 |Pine Bluff, Ark. | |Fired | 298 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Valley, Pa., |Roney | | +| 18 |of N. J., Hoboken |Mine Run |Stoker | 520 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Valley, Pa., |Roney | | +| 19 |of N. J., Hoboken |Mine Run |Stoker | 520 | +|______|___________________________|________________|_________|________| +| |Frick Building, |Pittsburgh Nut |American | | +| 20 |Pittsburgh, Pa. |and Slack |Stoker | 300 | +|______|___________________________|________________|_________|________| +| |New York Edison Co., |Loyal Hanna, Pa.|Taylor | | +| 21 |New York City | |Stoker | 604 | +|______|___________________________|________________|_________|________| +| |City of Columbus, O., |Hocking Valley, |Detroit | | +| 22 |Dept. Lighting |O. |Stoker | 300 | +|______|___________________________|________________|_________|________| +| |Edison Elec. Illum. Co., |New River |Murphy | | +| 23 |Boston, Mass. | |Stoker | 508 | +|______|___________________________|________________|_________|________| +| |Colorado Springs & |Pike View, Col.,|Green Chn| | +| 24 |Interurban Ry., Col. |Mine Run |Grate | 400 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Lancashire, Pa. |B&W.Chain| | +| 25 |of N. J., Marion | |Grate | 600 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Lancashire, Pa. |B&W.Chain| | +| 26 |of N. J., Marion | |Grate | 600 | +|______|___________________________|________________|_________|________| +| |Erie County Electric Co., |Mercer County, |B&W.Chain| | +| 27 |Erie, Pa. |Pa. |Grate | 508 | +|______|___________________________|________________|_________|________| +| |Union Elec. Lt. & Pr. Co., |Mascouth, Ill. |B&W.Chain| | +| 28 |St. Louis, Mo. | |Grate | 508 | +|______|___________________________|________________|_________|________| +| |Union Elec. Lt. & Pr. Co., |St. Clair |B&W.Chain| | +| 29 |St. Louis, Mo. |County, Ill. |Grate | 508 | +|______|___________________________|________________|_________|________| +| |Commonwealth Edison Co., |Carterville, |B&W.Chain| | +| 30 |Chicago, Ill. |Ill., Screenings|Grate | 508 | +|______|___________________________|________________|_________|________| + + ________________________________________________________________ +|Number|Grate |Dura-|Steam |Temper-|Degrees|Factor| Draft | +| of |Surf. | tion|Pres. | ature | Super | of | In | At | +| Test |Square|Test | By | Water | -heat |Evapo-|Furnace|Boiler| +| | Feet |Hours|Gauge |Degrees|Degrees|ration|Inches |Damper| +| | | |Pounds| Fahr. | Fahr. | |Upr/Lwr|Inches| +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 1 | 84 | 8 | 68 | 53.9 | |1.1965| +.41 | .21 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.65 | | +| 2 | 51.6 | 7 | 136.3| 203 | 150 |1.1480| .47 | .56 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 3 | 67.6 | 8 | 139 | 139.6 | 139 |1.1984| .70 | .96 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 4 | 40 | 8 | 110.2| 137 | |1.1185| .33 | .43 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 5 | 59.5 | 10 | 133.2| 75.2 | |1.1849| .19 | .40 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 6 | 26.5 | 18 | 132.1| 70.5 | |1.1897| .33 | | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.51 | | +| 7 | 48.9 | 7 | 101. | 121.3 | |1.1333| -.20 | .30 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 8 | 59.5 | 6 | 191.8| 88.3 | |1.1771| .50 | | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 9 | 27 | 24 | 156.3| 58 | |1.2051| .10 | .24 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 10 | | 24 | 145 | 75 | |1.1866| .26 | .46 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 11 | 118 | 8 | 170 | 186.1 | 66.7 |1.1162| .34 | .42 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 12 | 118 | 7.92| 173 | 180.2 | 75.2 |1.1276| .44 | .58 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 13 | 52 | 24 | 75 | 53.3 | |1.1987| .25 | .35 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 14 | 59.5 | 8 | 105 | 35.8 | |1.2219| .17 | .38 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 15 | 59.5 | 24 | 170.1| 133 | |1.1293| .12 | .43 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 16 | 51.3 | 10 | 105 | 75.1 | |1.1814| .21 | .42 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 17 | 59.5 | 8 | 149.2| 71 | |1.1910| .35 | .59 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 18 | 103.2| 10 | 133.2| 65.3 | 65.9 |1.2346| .05 | .49 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 19 | 103.2| 9 | 139 | 64 | 80.2 |1.2358| .18 | .57 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 20 | 53 | 9 | 125 | 76.6 | |1.1826| +1.64 | .64 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 21 | 75 | 8 | 198.5| 165.1 | 104 |1.1662| +3.05 | .60 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 22 | | 9 | 140 | 67 | 180 |1.2942| .22 | .35 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 23 | 90 |16.25| 199 | 48.4 | 136.5 |1.2996| .23 | 1.27 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 24 | 103 | 8 | 129 | 56 | |1.2002| .23 | .30 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.52 | | +| 25 | 132 | 8 | 200 | 57.2 | 280.4 |1.3909| +.19 | .52 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.15 | | +| 26 | 132 | 8 | 199 | 60.7 | 171.0 |1.3191| .04 | .52 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 27 | 90 | 8 | 120 | 69.9 | |1.1888| .31 | .58 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 28 | 103.5| 8 | 180 | 46 | 113 |1.2871| .62 | 1.24 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 29 | 103.5| 8 | 183 | 53.1 | 104 |1.2725| .60 | 1.26 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 30 | 90 | 7 | 184 | 127.1 | 180 |1.2393| .68 | 1.15 | +|______|______|_____|______|_______|_______|______|_______|______| + ______________________________________________________________ +|Number|Temper-| Coal | +| of | ature | Total | Moist-| Total |Ash and| Total |DryCoal| +| Test |FlueGas|Weight:| ure | dry | Refuse|Combus-|/sq.ft.| +| |Degrees| Fired | Per | Coal | Per | tible | Grate | +| | Fahr. |Pounds | Cent | Pounds| Cent | Pounds|/Hr.Lb.| +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 1 | | 11670 | 4.45 | 11151 | 26.05 | 8248 | 16.6 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 2 | 487 | 8800 | 7.62 | 8129 | 29.82 | 5705 | 19.71 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 3 | 559 | 10799 | 6.42 | 10106 | 20.02 | 8081 | 21.77 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 4 | 427 | 5088 | 4.00 | 4884 | 19.35 | 3939 | 15.26 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 5 | 414 | 9440 | 2.14 | 9238 | 11.19 | 8204 | 15.52 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 6 | 410 | 8555 | 3.62 | 8245 | 15.73 | 6948 | 17.28 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 7 | 480 | 7130 | 7.38 | 6604 | 18.35 | 5392 | 19.29 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 8 | 449 | 7500 | 2.70 | 7298 | 27.94 | 5259 | 14.73 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 9 | 410 | 15087 | 7.50 | 13956 | 11.30 | 12379 | 21.5 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 10 | 503 | 29528 | 7.72 | 27248 | | | 24.7 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 11 | 487 | 20400 | 2.84 | 19821 | 7.83 | 18269 | 21.00 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 12 | 494 | 21332 | 2.29 | 20843 | 8.23 | 19127 | 22.31 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 13 | 516 | 24584 | 4.29 | 23529 | 7.63 | 21883 | 18.85 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 14 | 523 | 15540 | 18.64 | 12643 | | | 28.59 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 15 | 474 | 18330 | 2.03 | 17958 | 16.36 | 16096 | 12.57 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 16 | 536 | 12243 | 2.14 | 11981 | | | 23.40 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 17 | 534 | 10500 | 3.04 | 10181 | | | 21.40 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 18 | 458 | 18600 | 3.40 | 17968 | 18.38 | 14665 | 17.41 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 19 | 609 | 23400 | 2.56 | 22801 | 16.89 | 18951 | 24.55 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 20 | 518 | 10500 | 1.83 | 10308 | 12.22 | 9048 | 21.56 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 21 | 536 | 25296 | 2.20 | 24736 | | | 41.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 22 | 511 | 14263 | 8.63 | 13032 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 23 | 560 | 39670 | 4.22 | 37996 | 4.32 | 36355 | 25.98 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 24 | 538 | 23000 | 23.73 | 17542 | | | 21.36 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 25 | 590 | 32205 | 4.03 | 30907 | 15.65 | 26070 | 29.26 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 26 | 529 | 24243 | 4.09 | 23251 | 12.33 | 20385 | 22.01 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 27 | 533 | 22328 | 4.42 | 21341 | 16.88 | 17739 | 29.64 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 28 | 523 | 32163 | 13.74 | 27744 | | | 33.50 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 29 | 567 | 36150 | 14.62 | 30865 | | | 37.28 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 30 | | 30610 | 11.12 | 27206 | 14.70 | 23198 | 43.20 | +|______|_______|_______|_______|_______|_______|_______|_______| + + ______________________________________________________________ +|Number| Water | | Flue Gas Analysis | +| of |Actual | Equiv.|ditto /|% Rated|CO_{2} | O | CO | +| Test |Evapor-|Evap. @|sq.ft. |Cap'ty.| Per | Per | Per | +| | ation |>=212° |Heating|Develpd| Cent | Cent | Cent | +| |/Hr.Lb.|/Hr.Lb.|Surface|PerCent| | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 1 | 10268 | 12286 | 4.10 | 118.7 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 2 | 8246 | 9466 | 4.34 | 125.7 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 3 | 9145 | 10959 | 3.65 | 105.9 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 4 | 5006 | 5599 | 3.61 | 104.7 | 12.26 | 7.88 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 5 | 7434 | 8809 | 3.06 | 87.2 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 6 | 2903 | 3454 | 2.91 | 84.4 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 7 | 7464 | 8459 | 2.82 | 81.7 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 8 | 9164 | 10787 | 2.88 | 83.5 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 9 | 4374 | 5271 | 3.51 | 101.8 | 11.7 | 7.3 | 0.07 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 10 | 8688 | 10309 | 3.44 | 99.6 | 12.9 | 5.0 | 0.2 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 11 | 24036 | 26829 | 4.19 | 121.5 | 12.5 | 6.4 | 0.5 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 12 | 25313 | 28544 | 4.46 | 129.3 | 13.3 | 5.1 | 0.5 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 13 | 9168 | 10990 | 3.42 | 99.3 | 9.6 | 8.8 | 0.4 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 14 | 11202 | 13689 | 3.91 | 113.5 | 9.1 | 9.9 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 15 | 7565 | 8543 | 3.21 | 93.1 | 10.71 | 9.10 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 16 | 9512 | 11237 | 3.74 | 108.6 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 17 | 9257 | 11025 | 3.70 | 107.2 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 18 | 15887 | 19614 | 3.77 | 108.7 | 11.7 | 7.7 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 19 | 21320 | 26347 | 5.06 | 146.7 | 11.9 | 7.8 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 20 | 9976 | 11978 | 3.93 | 112.0 | 11.3 | 7.5 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 21 | 28451 | 33066 | 5.47 | 158.6 | 12.3 | 6.4 | 0.7 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 22 | 10467 | 13526 | 4.51 | 130.7 | 11.9 | 7.2 | 0.04 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 23 | 20700 | 26902 | 5.30 | 153.5 | 11.1 | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 24 | 14650 | 17583 | 4.40 | 127.4 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 25 | 28906 | 40205 | 6.70 | 194.2 | 10.5 | 8.3 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 26 | 23074 | 30437 | 5.07 | 147.0 | 10.1 | 9.0 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 27 | 20759 | 24678 | 4.85 | 140.8 | 10.1 | 9.1 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 28 | 21998 | 28314 | 5.67 | 161.5 | 8.7 | 10.6 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 29 | 24386 | 31031 | 6.11 | 177.1 | 8.9 | 10.7 | 0.2 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 30 | 30505 | 37805 | 7.43 | 215.7 | 10.4 | 9.4 | 0.2 | +|______|_______|_______|_______|_______|_______|_______|_______| + +_______________________________________________________ +|Number| Proximate Analysis Dry Coal | Equiv.|Combnd.| +| of |Volatl.| Fixed | Ash |B.t.u./|Evap. @|Efficy.| +| Test |Matter |Carbon | Per | Pound |>=212°/|Boiler | +| | Per | Per | Cent | Dry | Pound |& Grate| +| | Cent | Cent | | Coal |DryCoal|PerCent| +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 1 | | | 26.05 | 11913 | 8.81 | 71.8 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 2 | | | | 11104 | 8.15 | 72.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 3 | 5.55 | 80.60 | 13.87 | 12300 | 8.67 | 68.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 4 | 7.74 | 77.48 | 14.78 | 12851 | 9.17 | 69.2 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 5 | | | | 13138 | 9.53 | 69.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 6 | 6.13 | 84.86 | 9.01 | 13454 | 9.57 | 69.0 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 7 | | | | 12224 | 8.97 | 71.2 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 8 | 0.55 | 86.73 | 12.72 | 12642 | 8.87 | 68.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 9 | 39.01 | 48.08 | 12.91 | 12292 | 9.06 | 71.5 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 10 | 38.33 | 46.71 | 14.96 | 12284 | 9.08 | 71.7 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 11 | 19.86 | 73.02 | 7.12 | 14602 | 10.83 | 72.0 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 12 | 20.24 | 72.26 | 7.50 | 14381 | 10.84 | 73.2 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 13 | | | | 14955 | 11.21 | 72.7 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 14 | 39.60 | 54.46 | 5.94 | 11585 | 8.66 | 72.5 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 15 | 17.44 | 76.42 | 5.84 | 15379 | 11.42 | 72.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 16 | 33.40 | 54.73 | 11.87 | 12751 | 9.38 | 71.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 17 | 15.42 | 62.48 | 22.10 | 12060 | 8.66 | 69.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 18 | 14.99 | 75.13 | 9.88 | 14152 | 10.92 | 74.88 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 19 | 14.40 | 74.33 | 11.27 | 14022 | 10.40 | 71.97 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 20 | 32.44 | 56.71 | 10.85 | 13510 | 10.30 | 74.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 21 | 19.02 | 72.09 | 8.89 | 14105 | 10.69 | 73.5 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 22 | 32.11 | 53.93 | 13.96 | 12435 | 9.41 | 73.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 23 | 19.66 | 75.41 | 4.93 | 14910 | 11.51 | 74.9 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 24 | 43.57 | 46.22 | 10.21 | 11160 | 8.02 | 69.7 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 25 | 22.84 | 69.91 | 7.25 | 13840 | 10.41 | 72.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 26 | 32.36 | 60.67 | 6.97 | 14027 | 10.47 | 72.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 27 | 33.26 | 54.03 | 12.71 | 12742 | 9.25 | 70.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 28 | 28.96 | 46.88 | 24.16 | 10576 | 8.16 | 74.9 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 29 | 36.50 | 41.20 | 22.30 | 10849 | 8.04 | 71.9 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 30 | | | 10.24 | 13126 | 9.73 | 71.9 | +|______|_______|_______|_______|_______|_______|_______| + +[Illustration: 15400 Horse-power Installation of Babcock & Wilcox +Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate +Stokers at the Plant of the Twin City Rapid Transit Co., Minneapolis, +Minn.] + +This increase in the efficiency of the boiler alone with the decrease in +the rate at which it is operated, will hold to a point where the +radiation of heat from the boiler setting is proportionately large +enough to be a governing factor in the total amount of heat absorbed. + +The second reason given above for a decrease of boiler efficiency with +increase of capacity, viz., the effect of radiant heat, is to a greater +extent than the first reason dependent upon a constant furnace +temperature. Any increase in this temperature will affect enormously the +amount of heat absorbed by radiation, as this absorption will vary as +the fourth power of the temperature of the radiating body. In this way +it is seen that but a slight increase in furnace temperature will be +necessary to bring the proportional part, due to absorption by +radiation, of the total heat absorbed, up to its proper proportion at +the higher ratings. This factor of furnace temperature more properly +belongs to the consideration of furnace efficiency than of boiler +efficiency. There is a point, however, in any furnace above which the +combustion will be so poor as to actually reduce the furnace temperature +and, therefore, the proportion of heat absorbed through radiation by a +given amount of exposed heating surface. + +Since it is thus true that the efficiency of the boiler considered alone +will increase with a decreased capacity, it is evident that if the +furnace conditions are constant regardless of the load, that the +combined efficiency of boiler and furnace will also decrease with +increasing loads. This fact was clearly proven in the tests of the +boilers at the Detroit Edison Company.[74] The furnace arrangement of +these boilers and the great care with which the tests were run made it +possible to secure uniformly good furnace conditions irrespective of +load, and here the maximum efficiency was obtained at a point somewhat +less than the rated capacity of the boilers. + +In some cases, however, and especially in the ordinary operation of the +plant, the furnace efficiency will, up to a certain point, increase with +an increase in power. This increase in furnace efficiency is ordinarily +at a greater rate as the capacity increases than is the decrease in +boiler efficiency, with the result that the combined efficiency of +boiler and furnace will to a certain point increase with an increase in +capacity. This makes the ordinary point of maximum combined efficiency +somewhat above the rated capacity of the boiler and in many cases the +combined efficiency will be practically a constant over a considerable +range of ratings. The features limiting the establishing of the point of +maximum efficiency at a high rating are the same as those limiting the +amount of grate surface that can be installed under a boiler. The +relative efficiency of different combinations of boilers and furnaces at +different ratings depends so largely upon the furnace conditions that +what might hold for one combination would not for another. + +In view of the above, it is impossible to make a statement of the +efficiency at different capacities of a boiler and furnace which will +hold for any and all conditions. Fig. 40 shows in a general form the +relation of efficiency to capacity. This curve has been plotted from a +great number of tests, all of which were corrected to bring them to +approximately the same conditions. The curve represents test conditions. +The efficiencies represented are those which may be secured only under +such conditions. The general direction of the curve, however, will be +found to hold approximately correct for operating conditions when used +only as a guide to what may be expected. + +[Graph: Combined Efficiency of Boiler and Furnace Per Cent +against Per Cent of Boiler's Rated Capacity Developed + +Fig. 40. Approximate Variation of Efficiency with Capacity under Test +Conditions] + +Economical Loads--With the effect of capacity on economy in mind, the +question arises as to what constitutes the economical load to be +carried. In figuring on the economical load for an individual plant, the +broader economy is to be considered, that in which, against the boiler +efficiency, there is to be weighed the plant first cost, returns on such +investment, fuel cost, labor, capacity, etc., etc. This matter has been +widely discussed, but unfortunately such discussion has been largely +limited to central power station practice. The power generated in such +stations, while representing an enormous total, is by no means the +larger proportion of the total power generated throughout the country. +The factors determining the economic load for the small plant, however, +are the same as in a large, and in general the statements made relative +to the question are equally applicable. + +The economical rating at which a boiler plant should be run is dependent +solely upon the load to be carried by that individual plant and the +nature of such load. The economical load for each individual plant can +be determined only from the careful study of each individual set of +conditions or by actual trial. + +The controlling factor in the cost of the plant, regardless of the +nature of the load, is the capacity to carry the maximum peak load that +may be thrown on the plant under any conditions. + +While load conditions, do, as stated, vary in every individual plant, in +a broad sense all loads may be grouped in three classes: 1st, the +approximately constant 24-hour load; 2nd, the steady 10 or 12-hour load +usually with a noonday period of no load; 3rd, the 24-hour variable +load, found in central station practice. The economical load at which +the boiler may be run will vary with these groups: + +1st. For a constant load, 24 hours in the day, it will be found in most +cases that, when all features are considered, the most economical load +or that at which a given amount of steam can be produced the most +cheaply will be considerably over the rated horse power of the boiler. +How much above the rated capacity this most economic load will be, is +dependent largely upon the cost of coal at the plant, but under ordinary +conditions, the point of maximum economy will probably be found to be +somewhere between 25 and 50 per cent above the rated capacity of the +boilers. The capital investment must be weighed against the coal saving +through increased thermal efficiency and the labor account, which +increases with the number of units, must be given proper consideration. +When the question is considered in connection with a plant already +installed, the conditions are different from where a new plant is +contemplated. In an old plant, where there are enough boilers to operate +at low rates of capacity, the capital investment leads to a fixed +charge, and it will be found that the most economical load at which +boilers may be operated will be lower than where a new plant is under +consideration. + +2nd. For a load of 10 or 12 hours a day, either an approximately steady +load or one in which there is a peak, where the boilers have been banked +over night, the capacity at which they may be run with the best economy +will be found to be higher than for uniform 24-hour load conditions. +This is obviously due to original investment, that is, a given amount of +invested capital can be made to earn a larger return through the higher +overload, and this will hold true to a point where the added return more +than offsets the decrease in actual boiler efficiency. Here again the +determining factors of what is the economical load are the fuel and +labor cost balanced against the thermal efficiency. With a load of this +character, there is another factor which may affect the economical plant +operating load. This is from the viewpoint of spare boilers. That such +added capacity in the way of spares is necessary is unquestionable. +Since they must be installed, therefore, their presence leads to a fixed +charge and it is probable that for the plant, as a whole, the economical +load will be somewhat lower than if the boilers were considered only as +spares. That is, it may be found best to operate these spares as a part +of the regular equipment at all times except when other boilers are off +for cleaning and repairs, thus reducing the load on the individual +boilers and increasing the efficiency. Under such conditions, the added +boiler units can be considered as spares only during such time as some +of the boilers are not in operation. + +Due to the operating difficulties that may be encountered at the higher +overloads, it will ordinarily be found that the most economical ratings +at which to run boilers for such load conditions will be between 150 and +175 per cent of rating. Here again the maximum capacity at which the +boilers may be run for the best plant economy is limited by the point at +which the efficiency drops below what is warranted in view of the first +cost of the apparatus. + +3rd. The 24-hour variable load. This is a class of load carried by the +central power station, a load constant only in the sense that there are +no periods of no load and which varies widely with different portions of +the 24 hours. With such a load it is particularly difficult to make any +assertion as to the point of maximum economy that will hold for any +station, as this point is more than with any other class of load +dependent upon the factors entering into the operation of each +individual plant. + +The methods of handling a load of this description vary probably more +than with any other kind of load, dependent upon fuel, labor, type of +stoker, flexibility of combined furnace and boiler etc., etc. + +In general, under ordinary conditions such as appear in city central +power station work where the maximum peaks occur but a few times a year, +the plant should be made of such size as to enable it to carry these +peaks at the maximum possible overload on the boilers, sufficient margin +of course being allowed for insurance against interruption of service. +With the boilers operating at this maximum overload through the peaks a +large sacrifice in boiler efficiency is allowable, provided that by such +sacrifice the overload expected is secured. + +[Illustration: Portion of 4890 Horse-power Installation of Babcock & +Wilcox Boilers at the Billings Sugar Co., Billings, Mont. 694 Horse +Power of these Boilers are Equipped with Babcock and Wilcox Chain Grate +Stokers] + +Some methods of handling a load of this nature are given below: + +Certain plant operating conditions make it advisable, from the +standpoint of plant economy, to carry whatever load is on the plant at +any time on only such boilers as will furnish the power required when +operating at ratings of, say, 150 to 200 per cent. That is, all boilers +which are in service are operated at such ratings at all times, the +variation in load being taken care of by the number of boilers on the +line. Banked boilers are cut in to take care of increasing loads and +peaks and placed again on bank when the peak periods have passed. It is +probable that this method of handling central station load is to-day the +most generally used. + +Other conditions of operation make it advisable to carry the load on a +definite number of boiler units, operating these at slightly below their +rated capacity during periods of light or low loads and securing the +overload capacity during peaks by operating the same boilers at high +ratings. In this method there are no boilers kept on banked fires, the +spares being spares in every sense of the word. + +A third method of handling widely varying loads which is coming somewhat +into vogue is that of considering the plant as divided, one part to take +care of what may be considered the constant plant load, the other to +take care of the floating or variable load. With such a method that +portion of the plant carrying the steady load is so proportioned that +the boilers may be operated at the point of maximum efficiency, this +point being raised to a maximum through the use of economizers and the +general installation of any apparatus leading to such results. The +variable load will be carried on the remaining boilers of the plant +under either of the methods just given, that is, at the high ratings of +all boilers in service and banking others, or a variable capacity from +all boilers in service. + +The opportunity is again taken to indicate the very general character of +any statements made relative to the economical load for any plant and to +emphasize the fact that each individual case must be considered +independently, with the conditions of operations applicable thereto. + +With a thorough understanding of the meaning of boiler efficiency and +capacity and their relation to each other, it is possible to consider +more specifically the selection of boilers. + +The foremost consideration is, without question, the adaptability of the +design selected to the nature of the work to be done. An installation +which is only temporary in its nature would obviously not warrant the +first cost that a permanent plant would. If boilers are to carry an +intermittent and suddenly fluctuating load, such as a hoisting load or a +reversing mill load, a design would have to be selected that would not +tend to prime with the fluctuations and sudden demand for steam. A +boiler that would give the highest possible efficiency with fuel of one +description, would not of necessity give such efficiency with a +different fuel. A boiler of a certain design which might be good for +small plant practice would not, because of the limitations in +practicable size of units, be suitable for large installations. A +discussion of the relative value of designs can be carried on almost +indefinitely but enough has been said to indicate that a given design +will not serve satisfactorily under all conditions and that the +adaptability to the service required will be dependent upon the fuel +available, the class of labor procurable, the feed water that must be +used, the nature of the plant's load, the size of the plant and the +first cost warranted by the service the boiler is to fulfill. + + TABLE 60 + + ACTUAL EVAPORATION FOR DIFFERENT PRESSURES AND TEMPERATURES OF FEED + WATER CORRESPONDING TO ONE HORSE POWER (34½ POUNDS PER HOUR FROM AND AT 212 DEGREES FAHRENHEIT) + +----------------------------------------------------------------------------------------------------------------------------------------- +Temperature| | + of | Pressure by Gauge--Pounds per Square Inch | + Feed | | + Degrees | | +Fahrenheit | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 210 | 220 | 230 | 240 | 250 | +-----------+-----------------------------------------------------------------------------------------------------------------------------| + 32 |28.41|28.36|28.29|28.24|28.20|28.16|28.13|28.09|28.07|28.04|28.02|27.99|27.97|27.95|27.94|27.92|27.90|27.89|27.87|27.86|27.83| + 40 |28.61|28.54|28.49|28.44|28.40|28.35|28.32|28.29|28.26|28.23|28.21|28.18|28.16|28.14|28.12|28.11|28.09|28.07|28.06|28.05|28.03| + 50 |28.85|28.79|28.73|28.68|28.64|28.60|28.56|28.53|28.50|28.47|28.45|28.43|28.40|28.38|28.36|28.35|28.33|28.31|28.30|28.28|28.27| + 60 |29.10|29.04|28.98|28.93|28.88|28.84|28.81|28.77|28.74|28.72|28.69|28.67|28.65|28.62|28.60|28.59|28.57|28.55|28.54|28.52|28.51| + 70 |29.36|29.29|29.23|29.18|29.14|29.09|29.06|29.02|28.99|28.96|28.94|28.92|28.89|28.87|28.85|28.83|28.82|28.80|28.78|28.77|28.76| + 80 |29.62|29.55|29.49|29.44|29.39|29.35|29.31|29.27|29.24|29.22|29.19|29.17|29.14|29.12|29.10|29.08|29.07|29.05|29.03|29.02|29.00| + 90 |29.88|29.81|29.75|29.70|29.65|29.61|29.57|29.53|29.50|29.47|29.45|29.42|29.40|29.38|29.36|29.34|29.32|29.30|29.29|29.27|29.25| +100 |30.15|30.08|30.02|29.96|29.91|29.87|29.83|29.80|29.76|29.73|29.71|29.68|29.66|29.63|29.61|29.60|29.58|29.56|29.54|29.53|29.51| +110 |30.42|30.35|30.29|30.23|30.18|30.14|30.10|30.06|30.03|30.00|29.97|29.95|29.92|29.90|29.88|29.86|29.84|29.82|29.81|29.79|29.77| +120 |30.70|30.63|30.56|30.51|30.46|30.41|30.37|30.33|30.30|30.27|30.24|30.22|30.19|30.17|30.15|30.13|30.11|30.09|30.07|30.06|30.04| +130 |30.99|30.91|30.84|30.79|30.73|30.69|30.65|30.61|30.57|30.54|30.52|30.49|30.47|30.44|30.42|30.40|30.38|30.36|30.35|30.33|30.31| +140 |31.28|31.20|31.13|31.07|31.02|30.97|30.93|30.89|30.86|30.83|30.80|30.77|30.75|30.72|30.70|30.68|30.66|30.64|30.62|30.61|30.59| +150 |31.58|31.49|31.42|31.36|31.31|31.26|31.22|31.18|31.14|31.11|31.08|31.06|31.03|31.01|30.98|30.96|30.94|30.92|30.91|30.89|30.87| +160 |31.87|31.79|31.72|31.66|31.61|31.56|31.51|31.47|31.44|31.40|31.37|31.35|31.32|31.29|31.27|31.25|31.23|31.21|31.19|31.18|31.16| +170 |32.18|32.10|32.02|31.96|31.91|31.86|31.81|31.77|31.73|31.70|31.67|31.64|31.62|31.59|31.57|31.54|31.52|31.50|31.49|31.47|31.46| +180 |32.49|32.41|32.33|32.27|32.22|32.16|32.12|32.08|32.04|32.00|31.97|31.95|31.92|31.89|31.87|31.84|31.82|31.80|31.79|31.77|31.75| +190 |32.81|32.72|32.65|32.59|32.53|32.47|32.43|32.38|32.35|32.32|32.29|32.26|32.23|32.20|32.17|32.15|32.13|32.11|32.09|32.07|32.05| +200 |33.13|33.05|32.97|32.91|32.85|32.79|32.75|32.70|32.66|32.63|32.60|32.57|32.54|32.51|32.49|32.46|32.44|32.42|32.40|32.38|32.36| +210 |33.47|33.38|33.30|33.24|33.18|33.13|33.08|33.03|32.99|32.95|32.92|32.89|32.86|32.83|32.81|32.79|32.76|32.74|32.72|32.70|32.68| +----------------------------------------------------------------------------------------------------------------------------------------- + +The proper consideration can be given to the adaptability of any boiler +for the service in view only after a thorough understanding of the +requirements of a good steam boiler, with the application of what has +been said on the proper operation to the special requirements of each +case. Of almost equal importance to the factors mentioned are the +experience, the skill and responsibility of the manufacturer. + +With the design of boiler selected that is best adapted to the service +required, the next step is the determination of the boiler power +requirements. + +The amount of steam that must be generated is determined from the steam +consumption of the prime movers. It has already been indicated that such +consumption can vary over wide limits with the size and type of the +apparatus used, but fortunately all types have been so tested that +manufacturers are enabled to state within very close limits the actual +consumption under any given set of conditions. It is obvious that +conditions of operation will have a bearing on the steam consumption +that is as important as the type and size of the apparatus itself. This +being the case, any tabular information that can be given on such steam +consumption, unless it be extended to an impracticable size, is only of +use for the most approximate work and more definite figures on this +consumption should in all cases be obtained from the manufacturer of the +apparatus to be used for the conditions under which it will operate. + +To the steam consumption of the main prime movers, there is to be added +that of the auxiliaries. Again it is impossible to make a definite +statement of what this allowance should be, the figure depending wholly +upon the type and the number of such auxiliaries. For approximate work, +it is perhaps best to allow 15 or 20 per cent of the steam requirements +of the main engines, for that of auxiliaries. Whatever figure is used +should be taken high enough to be on the conservative side. + +When any such figures are based on the actual weight of steam required, +Table 60, which gives the actual evaporation for various pressures and +temperatures of feed corresponding to one boiler horse power (34.5 +pounds of water per hour from and at 212 degrees), may be of service. + +With the steam requirements known, the next step is the determination of +the number and size of boiler units to be installed. This is directly +affected by the capacity at which a consideration of the economical load +indicates is the best for the operating conditions which will exist. The +other factors entering into such determination are the size of the plant +and the character of the feed water. + +The size of the plant has its bearing on the question from the fact that +higher efficiencies are in general obtained from large units, that labor +cost decreases with the number of units, the first cost of brickwork is +lower for large than for small size units, a general decrease in the +complication of piping, etc., and in general the cost per horse power of +any design of boiler decreases with the size of units. To illustrate +this, it is only necessary to consider a plant of, say, 10,000 boiler +horse power, consisting of 40-250 horse-power units or 17-600 +horse-power units. + +The feed water available has its bearing on the subject from the other +side, for it has already been shown that very large units are not +advisable where the feed water is not of the best. + +The character of an installment is also a factor. Where, say, 1000 horse +power is installed in a plant where it is known what the ultimate +capacity is to be, the size of units should be selected with the idea of +this ultimate capacity in mind rather than the amount of the first +installation. + +Boiler service, from its nature, is severe. All boilers have to be +cleaned from time to time and certain repairs to settings, etc., are a +necessity. This makes it necessary, in determining the number of boilers +to be installed, to allow a certain number of units or spares to be +operated when any of the regular boilers must be taken off the line. +With the steam requirements determined for a plant of moderate size and +a reasonably constant load, it is highly advisable to install at least +two spare boilers where a continuity of service is essential. This +permits the taking off of one boiler for cleaning or repairs and still +allows a spare boiler in the event of some unforeseen occurrence, such +as the blowing out of a tube or the like. Investment in such spare +apparatus is nothing more nor less than insurance on the necessary +continuity of service. In small plants of, say, 500 or 600 horse power, +two spares are not usually warranted in view of the cost of such +insurance. A large plant is ordinarily laid out in a number of sections +or panels and each section should have its spare boiler or boilers even +though the sections are cross connected. In central station work, where +the peaks are carried on the boilers brought up from the bank, such +spares are, of course, in addition to these banked boilers. From the +aspect of cleaning boilers alone, the number of spare boilers is +determined by the nature of any scale that may be formed. If scale is +formed so rapidly that the boilers cannot be kept clean enough for good +operating results, by cleaning in rotation, one at a time, the number of +spares to take care of such proper cleaning will naturally increase. + +In view of the above, it is evident that only a suggestion can be made +as to the number and size of units, as no recommendation will hold for +all cases. In general, it will be found best to install units of the +largest possible size compatible with the size of the plant and +operating conditions, with the total power requirements divided among +such a number of units as will give proper flexibility of load, with +such additional units for spares as conditions of cleaning and insurance +against interruption of service warrant. + +In closing the subject of the selection of boilers, it may not be out of +place to refer to the effect of the builder's guarantee upon the +determination of design to be used. Here in one of its most important +aspects appears the responsibility of the manufacturer. Emphasis has +been laid on the difference between test results and those secured in +ordinary operating practice. That such a difference exists is well known +and it is now pretty generally realized that it is the responsible +manufacturer who, where guarantees are necessary, submits the +conservative figures, figures which may readily be exceeded under test +conditions and which may be closely approached under the ordinary plant +conditions that will be met in daily operation. + + + + +OPERATION AND CARE OF BOILERS + + +The general subject of boiler room practice may be considered from two +aspects. The first is that of the broad plant economy, with a suggestion +as to the methods to be followed in securing the best economical results +with the apparatus at hand and procurable. The second deals rather with +specific recommendations which should be followed in plant practice, +recommendations leading not only to economy but also to safety and +continuity of service. Such recommendations are dictated from an +understanding of the nature of steam generating apparatus and its +operation, as covered previously in this book. + +It has already been pointed out that the attention given in recent years +to steam generating practice has come with a realization of the wide +difference existing between the results being obtained in every-day +operation and those theoretically possible. The amount of such attention +and regulation given to the steam generating end of a power plant, +however, is comparatively small in relation to that given to the balance +of the plant, but it may be safely stated that it is here that there is +the greatest assurance of a return for the attention given. + +In the endeavor to increase boiler room efficiency, it is of the utmost +importance that a standard basis be set by which average results are to +be judged. With the theoretical efficiency obtainable varying so widely, +this standard cannot be placed at the highest efficiency that has been +obtained regardless of operating conditions. It is better set at the +best obtainable results for each individual plant under its conditions +of installation and daily operation. + +With an individual standard so set, present practice can only be +improved by a systematic effort to approach this standard. The degree +with which operating results will approximate such a standard will be +found to be directly proportional to the amount of intelligent +supervision given the operation. For such supervision to be given, it is +necessary to have not only a full realization of what the plant can do +under the best operating conditions but also a full and complete +knowledge of what it is doing under all of the different conditions that +may arise. What the plant is doing should be made a matter of continuous +record so arranged that the results may be directly compared for any +period or set of conditions, and where such results vary from the +standard set, steps must be taken immediately to remedy the causes of +such failings. Such a record is an important check in the losses in the +plant. + +As the size of the plant and the fuel consumption increase, such a check +of losses and recording of results becomes a necessity. In the larger +plants, the saving of but a fraction of one per cent in the fuel bill +represents an amount running into thousands of dollars annually, while +the expense of the proper supervision to secure such saving is small. +The methods of supervision followed in the large plants are necessarily +elaborate and complete. In the smaller plants the same methods may be +followed on a more moderate scale with a corresponding saving in fuel +and an inappreciable increase in either plant organization or expense. + +There has been within the last few years a great increase in the +practicability and reliability of the various types of apparatus by +which the records of plant operation may be secured. Much of this +apparatus is ingenious and, considering the work to be done, is +remarkably accurate. From the delicate nature of some of the apparatus, +the liability to error necessitates frequent calibration but even where +the accuracy is known to be only within limits of, say, 5 per cent +either way, the records obtained are of the greatest service in +considering relative results. Some of the records desirable and the +apparatus for securing them are given below. + +[Illustration: 2400 Horse-power Installation of Cross Drum Babcock & +Wilcox Boilers and Superheaters at the Westinghouse Electric and +Manufacturing Co., East Pittsburgh, Pa.] + +Inasmuch as the ultimate measure of the efficiency of the boiler plant +is the cost of steam generation, the important records are those of +steam generated and fuel consumed Records of temperature, analyses, +draft and the like, serve as a check on this consumption, indicating the +distribution of the losses and affording a means of remedying conditions +where improvement is possible. + +Coal Records--There are many devices on the market for conveniently +weighing the coal used. These are ordinarily accurate within close +limits, and where the size or nature of the plant warrants the +investment in such a device, its use is to be recommended. The coal +consumption should be recorded by some other method than from the +weights of coal purchased. The total weight gives no way of dividing the +consumption into periods and it will unquestionably be found to be +profitable to put into operation some scheme by which the coal is +weighed as it is used. In this way, the coal consumption, during any +specific period of the plant's operation, can be readily seen. The +simplest of such methods which may be used in small plants is the actual +weighing on scales of the fuel as it is brought into the fire room and +the recording of such weights. + +Aside from the actual weight of the fuel used, it is often advisable to +keep other coal records, coal and ash analyses and the like, for the +evaporation to be expected will be dependent upon the grade of fuel used +and its calorific value, fusibility of its ash, and like factors. + +The highest calorific value for unit cost is not necessarily the +indication of the best commercial results. The cost of fuel is governed +by this calorific value only when such value is modified by local +conditions of capacity, labor and commercial efficiency. One of the +important factors entering into fuel cost is the consideration of the +cost of ash handling and the maintenance of ash handling apparatus if +such be installed. The value of a fuel, regardless of its calorific +value, is to be based only on the results obtained in every-day plant +operation. + +Coal and ash analyses used in connection with the amount of fuel +consumed, are a direct indication of the relation between the results +being secured and the standard of results which has been set for the +plant. The methods of such analyses have already been described. The +apparatus is simple and the degree of scientific knowledge necessary is +only such as may be readily mastered by plant operatives. + +The ash content of a fuel, as indicated from a coal analysis checked +against ash weights as actually found in plant operation, acts as a +check on grate efficiency. The effect of any saving in the ashes, that +is, the permissible ash to be allowed in the fuel purchased, is +determined by the point at which the cost of handling, combined with the +falling off in the evaporation, exceeds the saving of fuel cost through +the use of poorer coal. + +Water Records--Water records with the coal consumption, form the basis +for judging the economic production of steam. The methods of securing +such records are of later introduction than for coal, but great advances +have been made in the apparatus to be used. Here possibly, to a greater +extent than in any recording device, are the records of value in +determining relative evaporation, that is, an error is rather allowable +provided such an error be reasonably constant. + +The apparatus for recording such evaporation is of two general classes: +Those measuring water before it is fed to the boiler and those measuring +the steam as it leaves. Of the first, the venturi meter is perhaps the +best known, though recently there has come into considerable vogue an +apparatus utilizing a weir notch for the measuring of such water. Both +methods are reasonably accurate and apparatus of this description has an +advantage over one measuring steam in that it may be calibrated much +more readily. Of the steam measuring devices, the one in most common use +is the steam flow meter. Provided the instruments are selected for a +proper flow, etc., they are of inestimable value in indicating the steam +consumption. Where such instruments are placed on the various engine +room lines, they will immediately indicate an excessive consumption for +any one of the units. With a steam flow meter placed on each boiler, it +is possible to fix relatively the amount produced by each boiler and, +considered in connection with some of the "check" records described +below, clearly indicate whether its portion of the total steam produced +is up to the standard set for the over-all boiler room efficiency. + +Flue Gas Analysis--The value of a flue gas analysis as a measure of +furnace efficiency has already been indicated. There are on the market a +number of instruments by which a continuous record of the carbon dioxide +in the flue gases may be secured and in general the results so recorded +are accurate. The limitations of an analysis showing only CO_{2} and the +necessity of completing such an analysis with an Orsat, or like +apparatus, and in this way checking the automatic device, have already +been pointed out, but where such records are properly checked from time +to time and are used in conjunction with a record of flue temperatures, +the losses due to excess air or incomplete combustion and the like may +be directly compared for any period. Such records act as a means for +controlling excess air and also as a check on individual firemen. + +Where the size of a plant will not warrant the purchase of an expensive +continuous CO_{2} recorder, it is advisable to make analyses of samples +for various conditions of firing and to install an apparatus whereby a +sample of flue gas covering a period of, say, eight hours, may be +obtained and such a sample afterwards analyzed. + +Temperature Records--Flue gas temperatures, feed water temperatures and +steam temperatures are all taken with recording thermometers, any number +of which will, when properly calibrated, give accurate results. + +A record of flue temperatures is serviceable in checking stack losses +and, in general, the cleanliness of the boiler. A record of steam +temperatures, where superheaters are used, will indicate excessive +fluctuations and lead to an investigation of their cause. Feed +temperatures are valuable in showing that the full benefit of the +exhaust steam is being derived. + +Draft Regulation--As the capacity of a boiler varies with the combustion +rate and this rate with the draft, an automatic apparatus satisfactorily +varying this draft with the capacity demands on the boiler will +obviously be advantageous. + +As has been pointed out, any fuel has some rate of combustion at which +the best results will be obtained. In a properly designed plant where +the load is reasonably steady, the draft necessary to secure such a rate +may be regulated automatically. + +Automatic apparatus for the regulation of draft has recently reached a +stage of perfection which in the larger plants at any rate makes its +installation advisable. The installation of a draft gauge or gauges is +strongly to be recommended and a record of such drafts should be kept as +being a check on the combustion rates. + +An important feature to be considered in the installing of all recording +apparatus is its location. Thermometers, draft gauges and flue gas +sampling pipes should be so located as to give as nearly as possible an +average of the conditions, the gases flowing freely over the ends of the +thermometers, couples and sampling pipes. With the location permanent, +there is no security that the samples may be considered an average but +in any event comparative results will be secured which will be useful in +plant operation. The best permanent location of apparatus will vary +considerably with the design of the boiler. + +It may not be out of place to refer briefly to some of the shortcomings +found in boiler room practice, with a suggestion as to a means of +overcoming them. + +1st. It is sometimes found that the operating force is not fully +acquainted with the boilers and apparatus. Probably the most general of +such shortcomings is the fixed idea in the heads of the operatives that +boilers run above their rated capacity are operating under a state of +strain and that by operating at less than their rated capacity the most +economical service is assured, whereas, by determining what a boiler +will do, it may be found that the most economical rating under the +conditions of the plant will be considerably in excess of the builder's +rating. Such ideas can be dislodged only by demonstrating to the +operatives what maximum load the boilers can carry, showing how the +economy will vary with the load and the determining of the economical +load for the individual plant in question. + +2nd. Stokers. With stoker-fired boilers, it is essential that the +operators know the limitations of their stokers as determined by their +individual installation. A thorough understanding of the requirements of +efficient handling must be insisted upon. The operatives must realize +that smokeless stacks are not necessarily the indication of good +combustion for, as has been pointed out, absolute smokelessness is +oftentimes secured at an enormous loss in efficiency through excess air. + +Another feature in stoker-fired plants is in the cleaning of fires. It +must be impressed upon the operatives that before the fires are cleaned +they should be put into condition for such cleaning. If this cleaning is +done at a definite time, regardless of whether the fires are in the best +condition for cleaning, there will be a great loss of good fuel with the +ashes. + +3rd. It is necessary that in each individual plant there be a basis on +which to judge the cleanliness of a boiler. From the operative's +standpoint, it is probably more necessary that there be a thorough +understanding of the relation between scale and tube difficulties than +between scale and efficiency. It is, of course, impossible to keep +boilers absolutely free from scale at all times, but experience in each +individual plant determines the limit to which scale can be allowed to +form before tube difficulties will begin or a perceptible falling off in +efficiency will take place. With such a limit of scale formation fixed, +the operatives should be impressed with the danger of allowing it to be +exceeded. + +4th. The operatives should be instructed as to the losses resulting from +excess air due to leaks in the setting and as to losses in efficiency +and capacity due to the by-passing of gases through the setting, that +is, not following the path of the baffles as originally installed. In +replacing tubes and in cleaning the heating surfaces, care must be taken +not to dislodge baffle brick or tile. + +[Illustration: 2000 Horse-power Installation of Babcock & Wilcox +Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the +Sunnyside Plant of the Pennsylvania Tunnel and Terminal Railroad Co., +Long Island City, N. Y.] + +5th. That an increase in the temperature of the feed reduces the amount +of work demanded from the boiler has been shown. The necessity of +keeping the feed temperature as high as the quantity of exhaust steam +will allow should be thoroughly understood. As an example of this, there +was a case brought to our attention where a large amount of exhaust +steam was wasted simply because the feed pump showed a tendency to leak +if the temperature of feed water was increased above 140 degrees. The +amount wasted was sufficient to increase the temperature to 180 degrees +but was not utilized simply because of the slight expense necessary to +overhaul the feed pump. + +The highest return will be obtained when the speed of the feed pumps is +maintained reasonably constant for should the pumps run very slowly at +times, there may be a loss of the steam from other auxiliaries by +blowing off from the heaters. + +6th. With a view to checking steam losses through the useless blowing of +safety valves, the operative should be made to realize the great amount +of steam that it is possible to get through a pipe of a given size. +Oftentimes the fireman feels a sense of security from objections to a +drop in steam simply because of the blowing of safety valves, not +considering the losses due to such a cause and makes no effort to check +this flow either by manipulation of dampers or regulation of fires. + +The few of the numerous shortcomings outlined above, which may be found +in many plants, are almost entirely due to lack of knowledge on the part +of the operating crew as to the conditions existing in their own plants +and the better performances being secured in others. Such shortcomings +can be overcome only by the education of the operatives, the showing of +the defects of present methods, and instruction in better methods. Where +such instruction is necessary, the value of records is obvious. There is +fortunately a tendency toward the employment of a better class of labor +in the boiler room, a tendency which is becoming more and more marked as +the realization of the possible saving in this end of the plant +increases. + +The second aspect of boiler room management, dealing with specific +recommendations as to the care and operation of the boilers, is dictated +largely by the nature of the apparatus. Some of the features to be +watched in considering this aspect follow. + +Before placing a new boiler in service, a careful and thorough +examination should be made of the pressure parts and the setting. The +boiler as erected should correspond in its baffle openings, where +baffles are adjustable, with the prints furnished for its erection, and +such baffles should be tight. The setting should be so constructed that +the boiler is free to expand without interfering with the brickwork. +This ability to expand applies also to blow-off and other piping. After +erection all mortar and chips of brick should be cleaned from the +pressure parts. The tie rods should be set up snug and then slacked +slightly until the setting has become thoroughly warm after the first +firing. The boiler should be examined internally before starting to +insure the absence of dirt, any foreign material such as waste, and +tools. Oil and paint are sometimes found in the interior of a new boiler +and where such is the case, a quantity of soda ash should be placed +within it, the boiler filled with water to its normal level and a slow +fire started. After twelve hours of slow simmering, the fire should be +allowed to die out, the boiler cooled slowly and then opened and washed +out thoroughly. Such a proceeding will remove all oil and grease from +the interior and prevent the possibility of foaming and tube +difficulties when the boiler is placed in service. + +The water column piping should be examined and known to be free and +clear. The water level, as indicated by the gauge glass, should be +checked by opening the gauge cocks. + +The method of drying out a brick setting before placing a boiler in +operation is described later in the discussion of boiler settings. + +A boiler should not be cut into the line with other boilers until the +pressure within it is approximately that in the steam main. The boiler +stop valve should be opened very slowly until it is fully opened. The +arrangement of piping should be such that there can be no possibility of +water collecting in a pocket between the boiler and the main, from which +it can be carried over into the steam line when a boiler is cut in. + +In regular operation the safety valve and steam gauge should be checked +daily. In small plants the steam pressure should be raised sufficiently +to cause the safety valves to blow, at which time the steam gauge should +indicate the pressure at which the valve is known to be set. If it does +not, one is in error and the gauge should be compared with one of known +accuracy and any error at once rectified. + +In large plants such a method of checking would result in losses too +great to be allowed. Here the gauges and valves are ordinarily checked +at the time a boiler is cut out, the valves being assured of not +sticking by daily instantaneous opening through manipulation by hand of +the valve lever. The daily blowing of the safety valve acts not only as +a check on the gauge but insures the valve against sticking. + +The water column should be blown down thoroughly at least once on every +shift and the height of water indicated by the glass checked by the +gauge cocks. The bottom blow-offs should be kept tight. These should be +opened at least once daily to blow from the mud drum any sediment that +may have collected and to reduce the concentration. The amount of +blowing down and the frequency is, of course, determined by the nature +of the feed water used. + +In case of low water, resulting either from carelessness or from some +unforeseen condition of operation, the essential object to be obtained +is the extinguishing of the fire in the quickest possible manner. Where +practicable, this is best accomplished by the playing of a heavy stream +of water from a hose on the fire. Another method, perhaps not so +efficient, but more generally recommended, is the covering of the fire +with wet ashes or fresh fuel. A boiler so treated should be cut out of +line after such an occurrence and a thorough inspection made to +ascertain what damage, if any, has been done before it is again placed +in service. + +The efficiency and capacity depend to an extent very much greater than +is ordinarily realized upon the cleanliness of the heating surfaces, +both externally and internally, and too much stress cannot be put upon +the necessity for systematic cleaning as a regular feature in the plant +operation. + +The outer surfaces of the tubes should be blown free from soot at +regular intervals, the frequency of such cleaning periods being +dependent upon the class of fuel used. The most efficient way of blowing +soot from the tubes is by means of a steam lance with which all parts of +the surfaces are reached and swept clean. There are numerous soot +blowing devices on the market which are designed to be permanently fixed +within the boiler setting. Where such devices are installed, there are +certain features that must be watched to avoid trouble. If there is any +leakage of water of condensation within the setting coming into contact +with the boiler tubes, it will tend toward corrosion, or if in contact +with the heated brickwork will cause rapid disintegration of the +setting. If the steam jets are so placed that they impinge directly +against the tubes, erosion may take place. Where such permanent soot +blowers are installed, too much care cannot be taken to guard against +these possibilities. + +Internally, the tubes must be kept free from scale, the ingredients of +which a study of the chapter on the impurities of water indicates are +present in varying quantities in all feed waters. Not only has the +presence of scale a direct bearing on the efficiency and capacity to be +obtained from a boiler but its absence is an assurance against the +burning out of tubes. + +In the absence of a blow-pipe action of the flames, it is impossible to +burn a metal surface where water is in intimate contact with that +surface. + +In stoker-fired plants where a blast is used, and the furnace is not +properly designed, there is a danger of a blow-pipe action if the fires +are allowed to get too thin. The rapid formation of steam at such points +of localized heat may lead to the burning of the metal of the tubes. + +Any formation of scale on the interior surface of a boiler keeps the +water from such a surface and increases its tendency to burn. Particles +of loose scale that may become detached will lodge at certain points in +the tubes and localize this tendency at such points. It is because of +the danger of detaching scale and causing loose flakes to be present +that the use of a boiler compound is not recommended for the removal of +scale that has already formed in a boiler. This question is covered in +the treatment of feed waters. If oil is allowed to enter a boiler, its +action is the same as that of scale in keeping the water away from the +metal surfaces. + +[Illustration: Fig. 41] + +It has been proven beyond a doubt that a very large percentage of tube +losses is due directly to the presence of scale which, in many +instances, has been so thin as to be considered of no moment, and the +importance of maintaining the boiler heating surfaces in a clean +condition cannot be emphasized too strongly. + +The internal cleaning can best be accomplished by means of an air or +water-driven turbine, the cutter heads of which may be changed to handle +various thicknesses of scale. Fig. 41 shows a turbine cleaner with +various cutting heads, which has been found to give satisfactory +service. + +Where a water-driven turbine is used, it should be connected to a pump +which will deliver at least 120 gallons per minute per cleaner at 150 +pounds pressure. This pressure should never be less than 90 pounds if +satisfactory results are desired. Where an air-driven turbine is used, +the pressure should be at least 100 pounds, though 150 pounds is +preferable, and sufficient water should be introduced into the tube to +keep the cutting head cool and assist in washing down the scale as it is +chipped off. + +Where scale has been allowed to accumulate to an excessive thickness, +the work of removal is difficult and tedious. Where such a heavy scale +is of sulphate formation, its removal may be assisted by filling the +boiler with water to which there has been added a quantity of soda ash, +a bucketful to each drum, starting a low fire and allowing the water to +boil for twenty-four hours with no pressure on the boiler. It should be +cooled slowly, drained, and the turbine cleaner used immediately, as the +scale will tend to harden rapidly under the action of the air. + +Where oil has been allowed to get into a boiler, it should be removed +before placing the boiler in service, as described previously where +reference is made to its removal by boiling out with soda ash. + +Where pitting or corrosion is noted, the parts affected should be +carefully cleaned and the interior of the drums should be painted with +white zinc if the boiler is to remain idle. The cause of such action +should be immediately ascertained and steps taken to apply the proper +remedy. + +When making an internal inspection of a boiler or when cleaning the +interior heating surfaces, great care must be taken to guard against the +possibility of steam entering the boiler in question from other boilers +on the same line either through the careless opening of the boiler stop +valve or some auxiliary valve or from an open blow-off. Bad accidents +through scalding have resulted from the neglect of this precaution. + +Boiler brickwork should be kept pointed up and all cracks filled. The +boiler baffles should be kept tight to prevent by-passing of any gases +through the heating surfaces. + +Boilers should be taken out of service at regular intervals for cleaning +and repairs. When this is done, the boiler should be cooled slowly, and +when possible, be allowed to stand for twenty-four hours after the fire +is drawn before opening. The cooling process should not be hurried by +allowing cold air to rush through the setting as this will invariably +cause trouble with the brickwork. When a boiler is off for cleaning, a +careful examination should be made of its condition, both external and +internal, and all leaks of steam, water and air through the setting +stopped. If water is allowed to come into contact with brickwork that is +heated, rapid disintegration will take place. If water is allowed to +come into contact with the metal of the boiler when out of service, +there is a likelihood of corrosion. + +If a boiler is to remain idle for some time, its deterioration may be +much more rapid than when in service. If the period for which it is to +be laid off is not to exceed three months, it may be filled with water +while out of service. The boiler should first be cleaned thoroughly, +internally and externally, all soot and ashes being removed from the +exterior of the pressure parts and any accumulation of scale removed +from the interior surfaces. It should then be filled with water, to +which five or six pails of soda ash have been added, a slow fire started +to drive the air from the boiler, the fire drawn and the boiler pumped +full. In this condition it may be kept for some time without bad +effects. + +If the boiler is to be out of service for more than three months, it +should be emptied, drained and thoroughly dried after being cleaned. A +tray of quick lime should be placed in each drum, the boiler closed, the +grates covered and a quantity of quick lime placed on top of the +covering. Special care should be taken to prevent air, steam or water +leaks into the boiler or onto the pressure parts to obviate danger of +corrosion. + +[Illustration: 3000 Horse-power Installation of Babcock & Wilcox Boilers +in the Main Power Plant, Chicago & Northwestern Ry. Depot, Chicago, +Ill.] + + + + +BRICKWORK BOILER SETTINGS + + +A consideration of the losses in boiler efficiency, due to the effects +of excess air, clearly indicates the necessity of maintaining the brick +setting of a boiler tight and free from air leaks. In view of the +temperatures to which certain portions of such a setting are subjected, +the material to be used in its construction must be of the best +procurable. + +Boiler settings to-day consist almost universally of brickwork--two +kinds being used, namely, red brick and fire brick. + +The red brick should only be used in such portions of the setting as are +well protected from the heat. In such location, their service is not so +severe as that of fire brick and ordinarily, if such red brick are +sound, hard, well burned and uniform, they will serve their purpose. + +The fire brick should be selected with the greatest care, as it is this +portion of the setting that has to endure the high temperatures now +developed in boiler practice. To a great extent, the life of a boiler +setting is dependent upon the quality of the fire brick used and the +care exercised in its laying. + +The best fire brick are manufactured from the fire clays of +Pennsylvania. South and west from this locality the quality of fire clay +becomes poorer as the distance increases, some of the southern fire +clays containing a considerable percentage of iron oxide. + +Until very recently, the important characteristic on which to base a +judgment of the suitability of fire brick for use in connection with +boiler settings has been considered the melting point, or the +temperature at which the brick will liquify and run. Experience has +shown, however, that this point is only important within certain limits +and that the real basis on which to judge material of this description +is, from the boiler man's standpoint, the quality of plasticity under a +given load. This tendency of a brick to become plastic occurs at a +temperature much below the melting point and to a degree that may cause +the brick to become deformed under the stress to which it is subjected. +The allowable plastic or softening temperature will naturally be +relative and dependent upon the stress to be endured. + +With the plasticity the determining factor, the perfect fire brick is +one whose critical point of plasticity lies well above the working +temperature of the fire. It is probable that there are but few brick on +the market which would not show, if tested, this critical temperature at +the stress met with in arch construction at a point less than 2400 +degrees. The fact that an arch will stand for a long period under +furnace temperatures considerably above this point is due entirely to +the fact that its temperature as a whole is far below the furnace +temperature and only about 10 per cent of its cross section nearest the +fire approaches the furnace temperature. This is borne out by the fact +that arches which are heated on both sides to the full temperature of an +ordinary furnace will first bow down in the middle and eventually fall. + +A method of testing brick for this characteristic is given in the +Technologic Paper No. 7 of the Bureau of Standards dealing with "The +testing of clay refractories with special reference to their load +carrying capacity at furnace temperatures." Referring to the test for +this specific characteristic, this publication recommends the following: +"When subjected to the load test in a manner substantially as described +in this bulletin, at 1350 degrees centigrade (2462 degrees Fahrenheit), +and under a load of 50 pounds per square inch, a standard fire brick +tested on end should show no serious deformation and should not be +compressed more than one inch, referred to the standard length of nine +inches." + +In the Bureau of Standards test for softening temperature, or critical +temperature of plasticity under the specified load, the brick are tested +on end. In testing fire brick for boiler purposes such a method might be +criticised, because such a test is a compression test and subject to +errors from unequal bearing surfaces causing shear. Furthermore, a +series of samples, presumably duplicates, will not fail in the same way, +due to the mechanical variation in the manufacture of the brick. Arches +that fail through plasticity show that the tensile strength of the brick +is important, this being evidenced by the fact that the bottom of a +wedge brick in an arch that has failed is usually found to be wider than +the top and the adjacent bricks are firmly cemented together. + +A better method of testing is that of testing the brick as a beam +subjected to its own weight and not on end. This method has been used +for years in Germany and is recommended by the highest authorities in +ceramics. It takes into account the failure by tension in the brick as +well as by compression and thus covers the tension element which is +important in arch construction. + +The plastic point under a unit stress of 100 pounds per square inch, +which may be taken as the average maximum arch stress, should be above +2800 degrees to give perfect results and should be above 2400 degrees to +enable the brick to be used with any degree of satisfaction. + +The other characteristics by which the quality of a fire brick is to be +judged are: + +Fusion point. In view of the fact that the critical temperature of +plasticity is below the fusion point, this is only important as an +indication from high fusion point of a high temperature of plasticity. + +Hardness. This is a relative quality based on an arbitrary scale of 10 +and is an indication of probable cracking and spalling. + +Expansion. The lineal expansion per brick in inches. This characteristic +in conjunction with hardness is a measure of the physical movement of +the brick as affecting a mass of brickwork, such movement resulting in +cracked walls, etc. The expansion will vary between wide limits in +different brick and provided such expansion is not in excess of, say, +.05 inch in a 9-inch brick, when measured at 2600 degrees, it is not +particularly important in a properly designed furnace, though in general +the smaller the expansion the better. + +Compression. The strength necessary to cause crushing of the brick at +the center of the 4½ inch face by a steel block one inch square. The +compression should ordinarily be low, a suggested standard being that a +brick show signs of crushing at 7500 pounds. + +Size of Nodules. The average size of flint grains when the brick is +carefully crushed. The scale of these sizes may be considered: Small, +size of anthracite rice; large, size of anthracite pea. + +Ratio of Nodules. The percentage of a given volume occupied by the flint +grains. This scale may be considered: High, 90 to 100 per cent; medium, +50 to 90 per cent; low, 10 to 50 per cent. + +The statement of characteristics suggested as desirable, are for arch +purposes where the hardest service is met. For side wall purposes the +compression and hardness limit may be raised considerably and the +plastic point lowered. + +Aside from the physical properties by which a fire brick is judged, it +is sometimes customary to require a chemical analysis of the brick. Such +an analysis is only necessary as determining the amount of total basic +fluxes (K_{2}O, Na_{2}O, CaO, MgO and FeO). These fluxes are ordinarily +combined into one expression, indicated by the symbol RO. This total +becomes important only above 0.2 molecular equivalent as expressed in +ceramic empirical formulae, and this limit should not be exceeded.[75] + +From the nature of fire brick, their value can only be considered from a +relative standpoint. Generally speaking, what are known as first-grade +fire brick may be divided into three classes, suitable for various +conditions of operation, as follows: + +Class A. For stoker-fired furnaces where high overloads are to be +expected or where other extreme conditions of service are apt to occur. + +Class B. For ordinary stoker settings where there will be no excessive +overloads required from the boiler or any hand-fired furnaces where the +rates of driving will be high for such practice. + +Class C. For ordinary hand-fired settings where the presumption is that +the boilers will not be overloaded except at rare intervals and for +short periods only. + +Table 61 gives the characteristics of these three classes according to +the features determining the quality. This table indicates that the +hardness of the brick in general increases with the poorer qualities. +Provided the hardness is sufficient to enable the brick to withstand its +load, additional hardness is a detriment rather than an advantage. + + TABLE 61 + + APPROXIMATE CLASSIFICATION OF FIRE BRICK + + ________________________________________________________________________ +| | | | | +| Characteristics | Class A | Class B | Class C | +|_____________________|________________|________________|________________| +| | | | | +| Fuse Point, Degrees | Safe at Degrees| Safe at Degrees| Safe at Degrees| +| Fahrenheit | 3200-3300 | 2900-3200 | 2900-3000 | +| | | | | +| Compression Pounds | 6500-7500 | 7500-11,000 | 8500-15,000 | +| | | | | +| Hardness Relative | 1-2 | 2-4 | 4-6 | +| | | | | +| Size of Nodules | Medium | Medium to |Medium to Large | +| | | Medium Large | | +| | | | | +| Ratio of Nodules | High | Medium to High | Medium Low | +| | | | to Medium | +|_____________________|________________|________________|________________| + +An approximate determination of the quality of a fire brick may be made +from the appearance of a fracture. Where such a fracture is open, clean, +white and flinty, the brick in all probability is of a good quality. If +this fracture has the fine uniform texture of bread, the brick is +probably poor. + +In considering the heavy duty of brick in boiler furnaces, experience +shows that arches are the only part that ordinarily give trouble. These +fail from the following causes: + +Bad workmanship in laying up of brick. This feature is treated below. + +The tendency of a brick to become plastic at a temperature below the +fusing point. The limits of allowable plastic temperature have already +been pointed out. + +Spalling. This action occurs on the inner ends of combustion arches +where they are swept by gases at a high velocity at the full furnace +temperature. The most troublesome spalling arises through cold air +striking the heated brickwork. Failure from this cause is becoming rare, +due to the large increase in number of stoker installations in which +rapid temperature changes are to a great degree eliminated. Furthermore, +there are a number of brick on the market practically free from such +defects and where a new brick is considered, it can be tried out and if +the defect exists, can be readily detected and the brick discarded. + +Failures of arches from the expansive power of brick are also rare, due +to the fact that there are a number of brick in which the expansion is +well within the allowable limits and the ease with which such defects +may be determined before a brick is used. + +Failures through chemical disintegration. Failure through this cause is +found only occasionally in brick containing a high percentage of iron +oxide. + +With the grade of brick selected best suited to the service of the +boiler to be set, the other factor affecting the life of the setting is +the laying. It is probable that more setting difficulties arise from the +improper workmanship in the laying up of brick than from poor material, +and to insure a setting which will remain tight it is necessary that the +masonry work be done most carefully. This is particularly true where the +boiler is of such a type as to require combustion arches in the furnace. + +Red brick should be laid in a thoroughly mixed mortar composed of one +volume of Portland cement, 3 volumes of unslacked lime and 16 volumes of +clear sharp sand. Not less than 2½ bushels of lime should be used in the +laying up of 1000 brick. Each brick should be thoroughly embedded and +all joints filled. Where red brick and fire brick are both used in the +same wall, they should be carried up at the same time and thoroughly +bonded to each other. + +All fire brick should be dry when used and protected from moisture until +used. Each brick should be dipped in a thin fire clay wash, "rubbed and +shoved" into place, and tapped with a wooden mallet until it touches the +brick next below it. It must be recognized that fire clay is not a +cement and that it has little or no holding power. Its action is that of +a filler rather than a binder and no fire-clay wash should be used which +has a consistency sufficient to permit the use of a trowel. + +All fire-brick linings should be laid up four courses of headers and one +stretcher. Furnace center walls should be entirely of fire brick. If the +center of such walls are built of red brick, they will melt down and +cause the failure of the wall as a whole. + +Fire-brick arches should be constructed of selected brick which are +smooth, straight and uniform. The frames on which such arches are built, +called arch centers, should be constructed of batten strips not over 2 +inches wide. The brick should be laid on these centers in courses, not +in rings, each joint being broken with a bond equal to the length of +half a brick. Each course should be first tried in place dry, and +checked with a straight edge to insure a uniform thickness of joint +between courses. Each brick should be dipped on one side and two edges +only and tapped into place with a mallet. Wedge brick courses should be +used only where necessary to keep the bottom faces of the straight brick +course in even contact with the centers. When such contact cannot be +exactly secured by the use of wedge brick, the straight brick should +lean away from the center of the arch rather than toward it. When the +arch is approximately two-thirds completed, a trial ring should be laid +to determine whether the key course will fit. When some cutting is +necessary to secure such a fit, it should be done on the two adjacent +courses on the side of the brick away from the key. It is necessary that +the keying course be a true fit from top to bottom, and after it has +been dipped and driven it should not extend below the surface of the +arch, but preferably should have its lower ledge one-quarter inch above +this surface. After fitting, the keys should be dipped, replaced +loosely, and the whole course driven uniformly into place by means of a +heavy hammer and a piece of wood extending the full length of the keying +course. Such a driving in of this course should raise the arch as a +whole from the center. The center should be so constructed that it may +be dropped free of the arch when the key course is in place and removed +from the furnace without being burned out. + +[Illustration: A Typical Steel Casing for a Babcock & Wilcox Boiler +Built by The Babcock & Wilcox Co.] + +Care of Brickwork--Before a boiler is placed in service, it is essential +that the brickwork setting be thoroughly and properly dried, or +otherwise the setting will invariably crack. The best method of starting +such a process is to block open the boiler damper and the ashpit doors +as soon as the brickwork is completed and in this way maintain a free +circulation of air through the setting. If possible, such preliminary +drying should be continued for several days before any fire is placed in +the furnace. When ready for the drying out fire, wood should be used at +the start in a light fire which may be gradually built up as the walls +become warm. After the walls have become thoroughly heated, coal may be +fired and the boiler placed in service. + +As already stated, the life of a boiler setting is dependent to a large +extent upon the material entering into its construction and the care +with which such material is laid. A third and equally important factor +in the determining of such life is the care given to the maintaining of +the setting in good condition after the boiler is placed in operation. +This feature is discussed more fully in the chapter dealing with general +boiler room management. + +Steel Casings--In the chapter dealing with the losses operating against +high efficiencies as indicated by the heat balance, it has been shown +that a considerable portion of such losses is due to radiation and to +air infiltration into the boiler setting. These losses have been +variously estimated from 2 to 10 per cent, depending upon the condition +of the setting and the amount of radiation surface, the latter in turn +being dependent upon the size of the boiler used. In the modern efforts +after the highest obtainable plant efficiencies much has been done to +reduce such losses by the use of an insulated steel casing covering the +brickwork. In an average size boiler unit the use of such casing, when +properly installed, will reduce radiation losses from one to two per +cent., over what can be accomplished with the best brick setting without +such casing and, in addition, prevent the loss due to the infiltration +of air, which may amount to an additional five per cent., as compared +with brick settings that are not maintained in good order. Steel plate, +or steel plate backed by asbestos mill-board, while acting as a +preventative against the infiltration of air through the boiler setting, +is not as effective from the standpoint of decreasing radiation losses +as a casing properly insulated from the brick portion of the setting by +magnesia block and asbestos mill-board. A casing which has been found to +give excellent results in eliminating air leakage and in the reduction +of radiation losses is clearly illustrated on page 306. + +Many attempts have been made to use some material other than brick for +boiler settings but up to the present nothing has been found that may be +considered successful or which will give as satisfactory service under +severe conditions as properly laid brickwork. + + + + +BOILER ROOM PIPING + + +In the design of a steam plant, the piping system should receive the +most careful consideration. Aside from the constructive details, good +practice in which is fairly well established, the important factors are +the size of the piping to be employed and the methods utilized in +avoiding difficulties from the presence in the system of water of +condensation and the means employed toward reducing radiation losses. + +Engineering opinion varies considerably on the question of material of +pipes and fittings for different classes of work, and the following is +offered simply as a suggestion of what constitutes good representative +practice. + +All pipe should be of wrought iron or soft steel. Pipe at present is +made in "standard", "extra strong"[76] and "double extra strong" +weights. Until recently, a fourth weight approximately 10 per cent +lighter than standard and known as "Merchants" was built but the use of +this pipe has largely gone out of practice. Pipe sizes, unless otherwise +stated, are given in terms of nominal internal diameter. Table 62 gives +the dimensions and some general data on standard and extra strong +wrought-iron pipe. + + TABLE 62 + + DIMENSIONS OF STANDARD AND EXTRA STRONG[76] + WROUGHT-IRON AND STEEL PIPE + + _______________________________________________________________ +| | | | +| | Diameter | Circumference | +| |__________________________|__________________________| +| | | | | | +| |External| Internal |External| Internal | +| |Standard|_________________|Standard|_________________| +| | and | | | and | | | +| Nominal | Extra |Standard| Extra | Extra |Standard| Extra | +| Size | Strong | | Strong | Strong | | Strong | +|_________|________|________|________|________|________|________| +| | | | | | | | +| 1/8 | .405 | .269 | .215 | 1.272 | .848 | .675 | +| 1/4 | .540 | .364 | .302 | 1.696 | 1.144 | .949 | +| 3/8 | .675 | .493 | .423 | 2.121 | 1.552 | 1.329 | +| 1/2 | .840 | .622 | .546 | 2.639 | 1.957 | 1.715 | +| 3/4 | 1.050 | .824 | .742 | 3.299 | 2.589 | 2.331 | +| 1 | 1.315 | 1.049 | .957 | 4.131 | 3.292 | 3.007 | +| 1-1/4 | 1.660 | 1.380 | 1.278 | 5.215 | 4.335 | 4.015 | +| 1-1/2 | 1.900 | 1.610 | 1.500 | 5.969 | 5.061 | 4.712 | +| 2 | 2.375 | 2.067 | 1.939 | 7.461 | 6.494 | 6.092 | +| 2-1/2 | 2.875 | 2.469 | 2.323 | 9.032 | 7.753 | 7.298 | +| 3 | 3.500 | 3.068 | 2.900 | 10.996 | 9.636 | 9.111 | +| 3-1/2 | 4.000 | 3.548 | 3.364 | 12.566 | 11.146 | 10.568 | +| 4 | 4.500 | 4.026 | 3.826 | 14.137 | 12.648 | 12.020 | +| 4-1/2 | 5.000 | 4.506 | 4.290 | 15.708 | 14.162 | 13.477 | +| 5 | 5.563 | 5.047 | 4.813 | 17.477 | 15.849 | 15.121 | +| 6 | 6.625 | 6.065 | 5.761 | 20.813 | 19.054 | 18.099 | +| 7 | 7.625 | 7.023 | 6.625 | 23.955 | 22.063 | 20.813 | +| 8 | 8.625 | 7.981 | 7.625 | 27.096 | 25.076 | 23.955 | +| 9 | 9.625 | 8.941 | 8.625 | 30.238 | 28.089 | 27.096 | +| 10 | 10.750 | 10.020 | 9.750 | 33.772 | 31.477 | 30.631 | +| 11 | 11.750 | 11.000 | 10.750 | 36.914 | 34.558 | 33.772 | +| 12 | 12.750 | 12.000 | 11.750 | 40.055 | 37.700 | 36.914 | +|_________|________|________|________|________|________|________| + + + __________________________________________________________ +| | | | | +| | | Length | | +| | Internal | of | Nominal Weight | +| | Transverse |Pipe in | Pounds per | +| | Area |Feet per| Foot | +| |_____________________| Square |_________________| +| | | |Foot of | | | +| Nominal | Standard | Extra |External|Standard| Extra | +| Size | | Strong |Surface | | Strong | +|_________|__________|__________|________|________|________| +| | | | | | | +| 1/8 | .0573 | .0363 | 9.440 | .244 | .314 | +| 1/4 | .1041 | .0716 | 7.075 | .424 | .535 | +| 3/8 | .1917 | .1405 | 5.657 | .567 | .738 | +| 1/2 | .3048 | .2341 | 4.547 | .850 | 1.087 | +| 3/4 | .5333 | .4324 | 3.637 | 1.130 | 1.473 | +| 1 | .8626 | .7193 | 2.904 | 1.678 | 2.171 | +| 1-1/4 | 1.496 | 1.287 | 2.301 | 2.272 | 2.996 | +| 1-1/2 | 2.038 | 1.767 | 2.010 | 2.717 | 3.631 | +| 2 | 3.356 | 2.953 | 1.608 | 3.652 | 5.022 | +| 2-1/2 | 4.784 | 4.238 | 1.328 | 5.793 | 7.661 | +| 3 | 7.388 | 6.605 | 1.091 | 7.575 | 10.252 | +| 3-1/2 | 9.887 | 8.888 | .955 | 9.109 | 12.505 | +| 4 | 12.730 | 11.497 | .849 | 10.790 | 14.983 | +| 4-1/2 | 15.961 | 14.454 | .764 | 12.538 | 17.611 | +| 5 | 19.990 | 18.194 | .687 | 14.617 | 20.778 | +| 6 | 28.888 | 26.067 | .577 | 18.974 | 28.573 | +| 7 | 38.738 | 34.472 | .501 | 23.544 | 38.048 | +| 8 | 50.040 | 45.664 | .443 | 28.544 | 43.388 | +| 9 | 62.776 | 58.426 | .397 | 33.907 | 48.728 | +| 10 | 78.839 | 74.662 | .355 | 40.483 | 54.735 | +| 11 | 95.033 | 90.763 | .325 | 45.557 | 60.075 | +| 12 | 113.098 | 108.43 | .299 | 49.562 | 65.415 | +|_________|__________|__________|________|________|________| + +Dimensions are nominal and except where noted are in inches. + +In connection with pipe sizes, Table 63, giving certain tube data may be +found to be of service. + + TABLE 63 + + TUBE DATA, STANDARD OPEN HEARTH OR LAP WELDED STEEL TUBES + ++-----+--+----+-----+------+------+------+------+-------+-------+-------+ +|S E D|B | T | I D |Circumference| Transverse |Square |Length |Nominal| +|i x i|. | h | n i | | Area | Feet |in Feet|Weight | +|z t a|W | i | t a | |Square Inches| of | per |Pounds | +|e e m|. | c | e m +------+------+------+------+ Exter |Square | per | +| r e| | k | r e |Exter-|Inter-|Exter-|Inter-| -nal |Foot of| Foot | +| n t|G | n | n t | nal | nal | nal | nal |Surface| Exter | | +| a e|a | e | a e | | | | | per | -nal | | +| l r|u | s | l r | | | | |Foot of|Surface| | +| |g | s | | | | | |Length | | | +| |e | | | | | | | | | | ++-----+--+----+-----+------+------+------+------+-------+-------+-------+ +|1-1/2|10|.134|1.232| 4.712| 3.870|1.7671|1.1921| .392 | 2.546 | 1.955 | +|1-1/2| 9|.148|1.204| 4.712| 3.782|1.7671|1.1385| .392 | 2.546 | 2.137 | +|1-1/2| 8|.165|1.170| 4.712| 3.676|1.7671|1.0751| .392 | 2.546 | 2.353 | +| 2 |10|.134|1.732| 6.283| 5.441|3.1416|2.3560| .523 | 1.909 | 2.670 | +| 2 | 9|.148|1.704| 6.283| 5.353|3.1416|2.2778| .523 | 1.909 | 2.927 | +| 2 | 8|.165|1.670| 6.283| 5.246|3.1416|2.1904| .523 | 1.909 | 3.234 | +|3-1/4|11|.120|3.010|10.210| 9.456|8.2958|7.1157| .850 | 1.175 | 4.011 | +|3-1/4|10|.134|2.982|10.210| 9.368|8.2958|6.9840| .850 | 1.175 | 4.459 | +|3-1/4| 9|.148|2.954|10.210| 9.280|8.2958|6.8535| .850 | 1.175 | 4.903 | +| 4 |10|.134|3.732|12.566|11.724|12.566|10.939| 1.047 | .954 | 5.532 | +| 4 | 9|.148|3.704|12.566|11.636|12.566|10.775| 1.047 | .954 | 6.000 | +| 4 | 8|.165|3.670|12.566|11.530|12.566|10.578| 1.047 | .954 | 6.758 | ++-----+--+----+-----+------+------+------+------+-------+-------+-------+ + +Dimensions are nominal and except where noted are in inches. + +Pipe Material and Thickness--For saturated steam pressures not exceeding +160 pounds, all pipe over 14 inches should be 3/8 inch thick O. D. pipe. +All other pipe should be standard full weight, except high pressure +feed[77] and blow-off lines, which should be extra strong. + +For pressures above 150 pounds up to 200 pounds with superheated steam, +all high pressure feed and blow-off lines, high pressure steam lines +having threaded flanges, and straight runs and bends of high pressure +steam lines 6 inches and under having Van Stone joints should be extra +strong. All piping 7 inches and over having Van Stone joints should be +full weight soft flanging pipe of special quality. Pipe 14 inches and +over should be 3/8 inch thick O. D. pipe. All pipes for these pressures +not specified above should be full weight pipe. + +Flanges--For saturated steam, 160 pounds working pressure, all flanges +for wrought-iron pipe should be cast-iron threaded. All high pressure +threaded flanges should have the diameter thickness and drilling in +accordance with the "manufacturer's standard" for "extra heavy" flanges. +All low pressure flanges should have diameter, thickness and drilling in +accordance with "manufacturer's standard" for "standard flanges." + +The flanges on high pressure lines should be counterbored to receive +pipe and prevent the threads from shouldering. The pipe should be +screwed through the flange at least 1/16 inch, placed in machine and +after facing off the end one smooth cut should be taken over the face of +the flange to make it square with the axis of the pipe. + +[Illustration: 2000 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Kentucky Electric Co., Louisville, Ky.] + +For pressures above 160 pounds, where superheated steam is used, all +high pressure steam lines 4 inches and over should have solid rolled +steel flanges and special upset lapped joints. In the manufacture of +such joints, the ends of the pipe are heated and upset against the face +of a holding mandrel conforming to the shape of the flange, the lapped +portion of the pipe being flattened out against the face of the mandrel, +the upsetting action maintaining the desired thickness of the lap. When +cool, both sides of the lap are faced to form a uniform thickness and an +even bearing against flange and gasket. The joint, therefore, is a +strictly metal to metal joint, the flanges merely holding the lapped +ends of the pipe against the gasket. + +A special grade of soft flanging pipe is selected to prevent breaking. +The bending action is a severe test of the pipe and if it withstands the +bending process and the pressure tests, the reliability of the joint is +assured. Such a joint is called a Van Stone joint, though many +modifications and improvements have been made since the joint was +originally introduced. + +The diameter and thickness of such flanges should be special extra +heavy. Such flanges should be turned to diameter, their fronts faced and +the backs machined in lieu of spot facing. + +In lines other than given for pressures over 150 pounds, all flanges for +wrought-iron pipe should be threaded. All threaded flanges for high +pressure superheated lines 3½ inches and under should be "semi-steel" +extra heavy. Flanges for other than steam lines should be manufacturer's +standard extra heavy. + +Welded flanges are frequently used in place of those described with +satisfactory results. + +Fittings--For saturated steam under pressures up to 160 pounds, all +fittings 3½ inches and under should be screwed. Fittings 4 inches and +over should have flanged ends. Fittings for this pressure should be of +cast iron and should have heavy leads and full taper threads. Flanged +fittings in high pressure lines should be extra heavy, and in low +pressure lines standard weight. Where possible in high pressure flanges +and fittings, bolt surfaces should be spot faced to provide suitable +bearing for bolt heads and nuts. + +Fittings for superheated steam up to 70 degrees at pressures above 160 +pounds are sometimes of cast iron.[78] For superheat above 70 degrees +such fittings should be "steel castings" and in general these fittings +are recommended for any degree of superheat. Fittings for other than +high pressure work may be of cast iron, except where superheated steam +is carried, where they should be of "wrought steel" or "hard metal". +Fittings 3½ inches and under should be screwed, 4 inches and over +flanged. + +Flanges for pressures up to 160 pounds in pipes and fittings for low +pressure lines, and any fittings for high pressure lines should have +plain faces, smooth tool finish, scored with V-shaped grooves for rubber +gaskets. High pressure line flanges should have raised faces, projecting +the full available diameter inside the bolt holes. These faces should be +similarly scored. + +All pipe ½ inch and under should have ground joint unions suitable for +the pressure required. Pipe ¾ inch and over should have cast-iron +flanged unions. Unions are to be preferred to wrought-iron couplings +wherever possible to facilitate dismantling. + +Valves--For 150 pounds working pressure, saturated steam, all valves 2 +inches and under may have screwed ends; 2½ inches and over should be +flanged. All high pressure steam valves 6 inches and over should have +suitable by-passes. All valves for use with superheated steam should be +of special construction. For pressures above 160 pounds, where the +superheat does not exceed 70 degrees, valve bodies, caps and yokes are +sometimes made of cast iron, though ordinarily semi-steel will give +better satisfaction. The spindles of such valves should be of bronze and +there should be special necks with condensing chambers to prevent the +superheated steam from blowing through the packing. For pressures over +160 pounds and degrees of superheat above 70, all valves 3 inches and +over should have valve bodies, caps and yokes of steel castings. +Spindles should be of some non-corrosive metal, such as "monel metal". +Seat rings should be removable of the same non-corrosive metal as should +the spindle seats and plug faces. + +All salt water valves should have bronze spindles, sleeves and packing +seats. + +The suggestions as to flanges for different classes of service made on +page 311 hold as well for valve flanges, except that such flanges are +not scored. + +Automatic stop and check valves are coming into general use with boilers +and such use is compulsory under the boiler regulations of certain +communities. Where used, they should be preferably placed directly on +the boiler nozzle. Where two or more boilers are on one line, in +addition to the valve at the boiler, whether this be an automatic valve +or a gate valve, there should be an additional gate valve on each boiler +branch at the main steam header. + +Relief valves should be furnished at the discharge side of each feed +pump and on the discharge side of each feed heater of the closed type. + +Feed Lines--Feed lines should in all instances be made of extra strong +pipe due to the corrosive action of hot feed water. While it has been +suggested above that cast-iron threaded flanges should be used in such +lines, due to the sudden expansion of such pipe in certain instances +cast-iron threaded flanges crack before they become thoroughly heated +and expand, and for this reason cast-steel threaded flanges will give +more satisfactory results. In some instances, wrought-steel and Van +Stone joints have been used in feed lines and this undoubtedly is better +practice than the use of cast-steel threaded work, though the additional +cost is not warranted in all stations. + +Feed valves should always be of the globe pattern. A gate valve cannot +be closely regulated and often clatters owing to the pulsations of the +feed pump. + +Gaskets--For steam and water lines where the pressure does not exceed +160 pounds, wire insertion rubber gaskets 1/16 inch thick will be found +to give good service. For low pressure lines, canvas insertion black +rubber gaskets are ordinarily used. For oil lines special gaskets are +necessary. + +For pressure above 160 pounds carrying superheated steam, corrugated +steel gaskets extending the full available diameter inside of the bolt +holes give good satisfaction. For high pressure water lines wire +inserted rubber gaskets are used, and for low pressure flanged joints +canvas inserted rubber gaskets. + +Size of Steam Lines--The factors affecting the proper size of steam +lines are the radiation from such lines and the velocity of steam within +them. As the size of the steam line increases, there will be an increase +in the radiation.[79] As the size decreases, the steam velocity and the +pressure drop for a given quantity of steam naturally increases. + +There is a marked tendency in modern practice toward higher steam +velocities, particularly in the case of superheated steam. It was +formerly considered good practice to limit this velocity to 6000 feet +per minute but this figure is to-day considered low. + +In practice the limiting factor in the velocity advisable is the +allowable pressure drop. In the description of the action of the +throttling calorimeter, it has been demonstrated that there is no loss +accompanying a drop in pressure, the difference in energy between the +higher and lower pressures appearing as heat, which, in the case of +steam flowing through a pipe, may evaporate any condensation present or +may be radiated from the pipe. A decrease in pipe area decreases the +radiating surface of the pipe and thus the possible condensation. As the +heat liberated by the pressure drop is utilized in overcoming or +diminishing the tendency toward condensation and the heat loss through +radiation, the steam as it enters the prime mover will be drier or more +highly superheated where high steam velocities are used than where they +are lower, and if enough excess pressure is carried at the boilers to +maintain the desired pressure at the prime mover, the pressure drop +results in an actual saving rather than a loss. The whole is analogous +to standard practice in electrical distributing systems where generator +voltage is adjusted to suit the loss in the feeder lines. + +In modern practice, with superheated steam, velocities of 15,000 feet +per minute are not unusual and this figure is very frequently exceeded. + +Piping System Design--With the proper size of pipe to be used +determined, the most important factor is the provision for the removal +of water of condensation that will occur in any system. Such +condensation cannot be wholly overcome and if the water of condensation +is carried to the prime mover, difficulties will invariably result. +Water is practically incompressible and its effect when traveling at +high velocities differs little from that of a solid body of equal +weight, hence impact against elbows, valves or other obstructions, is +the equivalent of a heavy hammer blow that may result in the fracture of +the pipe. If there is not sufficient water in the system to produce this +result, it will certainly cause knocking and vibration in the pipe, +resulting eventually in leaky joints. Where the water reaches the prime +mover, its effect will vary from disagreeable knocking to disruption. +Too frequently when there are disastrous results from such a cause the +boilers are blamed for delivering wet steam when, as a matter of fact, +the evil is purely a result of poor piping design, the most common cause +of such an action being the pocketing of the water in certain parts of +the piping from whence it is carried along in slugs by the steam. The +action is particularly severe if steam is admitted to a cold pipe +containing water, as the water may then form a partial vacuum by +condensing the steam and be projected at a very high velocity through +the pipes producing a characteristic sharp metallic knock which often +causes bursting of the pipe or fittings. The amount of water present +through condensation may be appreciated when it is considered that +uncovered 6-inch pipe 150 feet long carrying 3600 pounds of high +pressure steam per hour will condense approximately 6 per cent of the +total steam carried through radiation. It follows that efficient means +of removing condensation water are absolutely imperative and the +following suggestions as to such means may be of service: + +The pitch of all pipe should be in the direction of the flow of steam. +Wherever a rise is necessary, a drain should be installed. All main +headers and important branches should end in a drop leg and each such +drop leg and any low points in the system should be connected to the +drainage pump. A similar connection should be made to every fitting +where there is danger of a water pocket. + +Branch lines should never be taken from the bottom of a main header but +where possible should be taken from the top. Each engine supply pipe +should have its own separator placed as near the throttle as possible. +Such separators should be drained to the drainage system. + +Check valves are frequently placed in drain pipes to prevent steam from +entering any portion of the system that may be shut off. + +Valves should be so located that they cannot form water pockets when +either open or closed. Globe valves will form a water pocket in the +piping to which they are connected unless set with the stem horizontal, +while gate valves may be set with the spindle vertical or at an angle. +Where valves are placed directly on the boiler nozzle, a drain should be +provided above them. + +High pressure drains should be trapped to both feed heaters and waste +headers. Traps and meters should be provided with by-passes. Cylinder +drains, heater blow-offs and drains, boiler blow-offs and similar lines +should be led to waste. The ends of cylinder drains should not extend +below the surface of water, for on starting up or on closing the +throttle valve with the drains open, water may be drawn back into the +cylinders. + + TABLE 64 + + RADIATION FROM COVERED AND UNCOVERED STEAM PIPES + + CALCULATED FOR 160 POUNDS PRESSURE AND 60 DEGREES TEMPERATURE + ++---------------------------------------------------------------------+ +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| | | | | | | | || +|| Pipe | |1/2 |3/4 | 1 |1-1/4|1-1/2| || +||Inches| Thickness of Covering |inch|inch|inch|inch |inch |Bare || +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |149 |118 | 99 | 86 | 79 | 597 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |240 |190 |161 | 138 | 127 | 959 || +|| 2 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.770|.613|.519|.445 |.410 |3.198|| +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |247 |193 |160 | 139 | 123 |1085 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |210 |164 |136 | 118 | 104 | 921 || +|| 4 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.677|.592|.439|.381 |.335 |2.970|| +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |352 |269 |221 | 190 | 167 |1555 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |203 |155 |127 | 110 | 96 | 897 || +|| 6 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.655|.500|.410|.355 |.310 |2.89 || +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |443 |337 |276 | 235 | 207 |1994 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |196 |149 |122 | 104 | 92 | 883 || +|| 8 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.632|.481|.394|.335 |.297 |2.85 || +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |549 |416 |337 | 287 | 250 |2468 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |195 |148 |120 | 102 | 89 | 877 || +|| 10 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.629|.477|.387|.329 |.287 |2.83 || +|+------+---------------------------+----+----+----+-----+-----+-----+| ++---------------------------------------------------------------------+ + +Covering--Magnesia, canvas covered. + +For calculating radiation for pressure and temperature other than 160 +pounds, and 60 degrees, use B. t. u. figures for one degree difference. + +Radiation from Pipes--The evils of the presence of condensed steam in +piping systems have been thoroughly discussed above and in some of the +previous articles. Condensation resulting from radiation, while it +cannot be wholly obviated, can, by proper installation, be greatly +reduced. + +Bare pipe will radiate approximately 3 B. t. u. per hour per square foot +of exposed surface per one degree of difference in temperature between +the steam contained and the external air. This figure may be reduced to +from 0.3 to 0.4 B. t. u. for the same conditions by a 1½ inch insulating +covering. Table 64 gives the radiation losses for bare and covered pipes +with different thicknesses of magnesia covering. + +Many experiments have been made as to the relative efficiencies of +different kinds of covering. Table 65 gives some approximately relative +figures based on one inch covering from experiments by Paulding, +Jacobus, Brill and others. + + TABLE 65 + + APPROXIMATE + EFFICIENCIES OF VARIOUS + COVERINGS REFERRED TO + BARE PIPES ++--------------------------------+ +|+-------------------+----------+| +|| Covering |Efficiency|| +|+-------------------+----------+| +||Asbestocel | 76.8 || +||Gast's Air Cell | 74.4 || +||Asbesto Sponge Felt| 85.0 || +||Magnesia | 83.5 || +||Asbestos Navy Brand| 82.0 || +||Asbesto Sponge Hair| 86.0 || +||Asbestos Fire Felt | 73.5 || +|+-------------------+----------+| ++--------------------------------+ + +Based on one-inch covering. + +The following suggestions may be of service: + +Exposed radiating surfaces of all pipes, all high pressure steam +flanges, valve bodies and fittings, heaters and separators, should be +covered with non-conducting material wherever such covering will improve +plant economy. All main steam lines, engine and boiler branches, should +be covered with 2 inches of 85 per cent carbonate of magnesia or the +equivalent. Other lines may be covered with one inch of the same +material. All covering should be sectional in form and large surfaces +should be covered with blocks, except where such material would be +difficult to install, in which case plastic material should be used. In +the case of flanges the covering should be tapered back from the flange +in order that the bolts may be removed. + +All surfaces should be painted before the covering is applied. Canvas is +ordinarily placed over the covering, held in place by wrought-iron or +brass bands. + +Expansion and Support of Pipe--It is highly important that the piping be +so run that there will be no undue strains through the action of +expansion. Certain points are usually securely anchored and the +expansion of the piping at other points taken care of by providing +supports along which the piping will slide or by means of flexible +hangers. Where pipe is supported or anchored, it should be from the +building structure and not from boilers or prime movers. Where supports +are furnished, they should in general be of any of the numerous sliding +supports that are available. Expansion is taken care of by such a method +of support and by the providing of large radius bends where necessary. + +It was formerly believed that piping would actually expand under steam +temperatures about one-half the theoretical amount due to the fact that +the exterior of the pipe would not reach the full temperature of the +steam contained. It would appear, however from recent experiments that +such actual expansion will in the case of well-covered pipe be very +nearly the theoretical amount. In one case noted, a steam header 293 +feet long when heated under a working pressure of 190 pounds, the steam +superheated approximately 125 degrees, expanded 8¾ inches; the +theoretical amount of expansion under the conditions would be +approximately 9-35/64 inches. + +[Illustration: Bankers Trust Building, New York City, Operation 900 +Horse Power of Babcock & Wilcox Boilers] + + + + +FLOW OF STEAM THROUGH PIPES AND ORIFICES + + +Various formulae for the flow of steam through pipes have been advanced, +all having their basis upon Bernoulli's theorem of the flow of water +through circular pipes with the proper modifications made for the +variation in constants between steam and water. The loss of energy due +to friction in a pipe is given by Unwin (based upon Weisbach) as + + f 2 v² W L + E_{f} = ---------- (37) + gd + +where E is the energy loss in foot pounds due to the friction of W units +of weight of steam passing with a velocity of v feet per second through +a pipe d feet in diameter and L feet long; g represents the acceleration +due to gravity (32.2) and f the coefficient of friction. + +Numerous values have been given for this coefficient of friction, f, +which, from experiment, apparently varies with both the diameter of pipe +and the velocity of the passing steam. There is no authentic data on the +rate of this variation with velocity and, as in all experiments, the +effect of change of velocity has seemed less than the unavoidable errors +of observation, the coefficient is assumed to vary only with the size of +the pipe. + +Unwin established a relation for this coefficient for steam at a +velocity of 100 feet per second, + + / 3 \ + f = K| 1 + --- | (38) + \ 10d / + +where K is a constant experimentally determined, and d the internal +diameter of the pipe in feet. + +If h represents the loss of head in feet, then + + + f 2 v² W L + E_{f} = Wh = ---------- (39) + gd + + f 2 v² L + and h = -------- (40) + gd + +If D represents the density of the steam or weight per cubic foot, and p +the loss of pressure due to friction in pounds per square inch, then + + hD + p = --- (41) + 144 + +and from equations (38), (40) and (41), + + D v² L / 3 \ + p = -------- × K | 1 + --- | (42) + 72 g d \ 10d / + +To convert the velocity term and to reduce to units ordinarily used, let +d_{1} the diameter of pipe in inches = 12d, and w = the flow in pounds +per minute; then + + [pi] / d_{1}\ + w = 60v × --- | ---- |^{2} D + 4 \ 12 / + + 9.6 w + and v = -------------- + [pi] d_{1}^2 D + + +Substituting this value and that of d in formula (42) + + / 3.6 \ w^{2} L + p = 0.04839 K | 1 + ----- | ----------- (43) + \ d_{1} / D d_{1}^{5} + + Some of the experimental determinations for the value of K are: + K = .005 for water (Unwin). + K = .005 for air (Arson). + K = .0028 for air (St. Gothard tunnel experiments). + K = .0026 for steam (Carpenter at Oriskany). + K = .0027 for steam (G. H. Babcock). + +The value .0027 is apparently the most nearly correct, and substituting +in formula (43) gives, + + / 3.6 \ w^{2} L + p = 0.000131 | 1 + ---- | ----------- (44) + \ d_{1}/ D d_{1}^{5} + + + / pDd_{1}^{5} \ + w = 87 | -------------- |^{½} (45) + | / 3.6 \ | + | | 1 + ---- | L | + \ \ d_{1}/ / + +Where w = the weight of steam passing in pounds per minute, + p = the difference in pressure between the two ends of the pipe in + pounds per square inch, + D = density of steam or weight per cubic foot,[80] + d_{1} = internal diameter of pipe in inches, + L = length of pipe in feet. + + TABLE 66 + + FLOW OF STEAM THROUGH PIPES ++---------------------------------------------------------------------------------------+ +|Initl|Diameter[81] of Pipe in Inches, Length of Pipe = 240 Diameters | +|Gauge|---------------------------------------------------------------------------------+ +|Press| ¾ | 1 | 1½ | 2 | 2½ | 3 | 4 | 5 | 6 | 8 | 10 | 12 | 15 | 18 | +|Pound|---------------------------------------------------------------------------------+ +|/SqIn| Weight of Steam per Minute, in Pounds, With One Pound Loss of Pressure | ++-----+---------------------------------------------------------------------------------+ +| 1 |1.16|2.07| 5.7|10.27|15.45|25.38| 46.85| 77.3|115.9|211.4| 341.1| 502.4| 804|1177| +| 10 |1.44|2.57| 7.1|12.72|19.15|31.45| 58.05| 95.8|143.6|262.0| 422.7| 622.5| 996|1458| +| 20 |1.70|3.02| 8.3|14.94|22.49|36.94| 68.20|112.6|168.7|307.8| 496.5| 731.3|1170|1713| +| 30 |1.91|3.40| 9.4|16.84|25.35|41.63| 76.84|126.9|190.1|346.8| 559.5| 824.1|1318|1930| +| 40 |2.10|3.74|10.3|18.51|27.87|45.77| 84.49|139.5|209.0|381.3| 615.3| 906.0|1450|2122| +| 50 |2.27|4.04|11.2|20.01|30.13|49.48| 91.34|150.8|226.0|412.2| 665.0| 979.5|1567|2294| +| 60 |2.43|4.32|11.9|21.38|32.19|52.87| 97.60|161.1|241.5|440.5| 710.6|1046.7|1675|2451| +| 70 |2.57|4.58|12.6|22.65|34.10|56.00|103.37|170.7|255.8|466.5| 752.7|1108.5|1774|2596| +| 80 |2.71|4.82|13.3|23.82|35.87|58.91|108.74|179.5|269.0|490.7| 791.7|1166.1|1866|2731| +| 90 |2.83|5.04|13.9|24.92|37.52|61.62|113.74|187.8|281.4|513.3| 828.1|1219.8|1951|2856| +| 100 |2.95|5.25|14.5|25.96|39.07|64.18|118.47|195.6|293.1|534.6| 862.6|1270.1|2032|2975| +| 120 |3.16|5.63|15.5|27.85|41.93|68.87|127.12|209.9|314.5|573.7| 925.6|1363.3|2181|3193| +| 150 |3.45|6.14|17.0|30.37|45.72|75.09|138.61|228.8|343.0|625.5|1009.2|1486.5|2378|3481| ++---------------------------------------------------------------------------------------+ + +This formula is the most generally accepted for the flow of steam in +pipes. Table 66 is calculated from this formula and gives the amount of +steam passing per minute that will flow through straight smooth pipes +having a length of 240 diameters from various initial pressures with one +pound difference between the initial and final pressures. + +To apply this table for other lengths of pipe and pressure losses other +than those assumed, let L = the length and d the diameter of the pipe, +both in inches; l, the loss in pounds; Q, the weight under the +conditions assumed in the table, and Q_{1}, the weight for the changed +conditions. + +For any length of pipe, if the weight of steam passing is the same as +given in the table, the loss will be, + + L + l = ---- (46) + 240d + +If the pipe length is the same as assumed in the table but the loss is +different, the quantity of steam passing per minute will be, + + Q_{1} = Ql^{½} (47) + +For any assumed pipe length and loss of pressure, the weight will be, + + /240dl\ + Q_{1} = Q|-----|^{½} (48) + \ L / + + TABLE 67 + + FLOW OF STEAM THROUGH PIPES + LENGTH OF PIPE 1000 FEET + ++--------------------------------------------------++----------------------------------------+ +| Discharge in Pounds per Minute corresponding to || Drop in Pressure in | +| Drop in Pressure on Right for Pipe Diameters || Pounds per Square Inch corresponding | +| in Inches in Top Line || to Discharge on Left: Densities | +| || and corresponding Absolute Pressures | +| || per Square Inch in First Two Lines | ++--------------------------------------------------++----------------------------------------+ +| Diameter[82]--Discharge || Density--Pressure--Drop | ++--------------------------------------------------++----------------------------------------+ +| 12 | 10 | 8 | 6 | 4 | 3 | 2½| 2 | 1½| 1 ||.208 |.230|.284|.328|.401|.443|.506|.548| +| In | In | In | In | In | In | In | In | In | In || 90 | 100| 125| 150| 180| 200| 230| 250| ++--------------------------------------------------++-------+--------------------------------+ +|2328|1443| 799| 371|123. |55.9|28.8|18.1|6.81|2.52||18.10|16.4|13.3|11.1|9.39|8.50|7.44|6.87| +|2165|1341| 742| 344|114.6|51.9|27.6|16.8|6.52|2.34||15.60|14.1|11.4|9.60|8.09|7.33|6.41|5.92| +|1996|1237| 685| 318|106.0|47.9|26.4|15.5|6.24|2.16||13.3 |12.0|9.74|8.18|6.90|6.24|5.47|5.05| +|1830|1134| 628| 292| 97.0|43.9|25.2|14.2|5.95|1.98||11.1 |10.0|8.13|6.83|5.76|5.21|4.56|4.21| +|1663|1031| 571| 265| 88.2|39.9|24.0|12.9|5.67|1.80|| 9.25|8.36|6.78|5.69|4.80|4.34|3.80|3.51| +|1580| 979| 542| 252| 83.8|37.9|22.8|12.3|5.29|1.71|| 8.33|7.53|6.10|5.13|4.32|3.91|3.42|3.16| +|1497| 928| 514| 239| 79.4|35.9|21.6|11.6|5.00|1.62|| 7.48|6.76|5.48|4.60|3.88|3.51|3.07|2.84| +|1414| 876| 485| 226| 75.0|33.9|20.4|10.9|4.72|1.53|| 6.67|6.03|4.88|4.10|3.46|3.13|2.74|2.53| +|1331| 825| 457| 212| 70.6|31.9|19.2|10.3|4.43|1.44|| 5.91|5.35|4.33|3.64|3.07|2.78|2.43|2.24| +|1248| 873| 428| 199| 66.2|23.9|18.0|9.68|4.15|1.35|| 5.19|4.69|3.80|3.19|2.69|2.44|2.13|1.97| +|1164| 722| 400| 186| 61.7|27.9|16.8|9.03|3.86|1.26|| 4.52|4.09|3.31|2.78|2.34|2.12|1.86|1.72| +|1081| 670| 371| 172| 57.3|25.9|15.6|8.38|3.68|1.17|| 3.90|3.53|2.86|2.40|2.02|1.83|1.60|1.48| +| 998| 619| 343| 159| 52.9|23.9|14.4|7.74|3.40|1.08|| 3.32|3.00|2.43|2.04|1.72|1.56|1.36|1.26| +| 915| 567| 314| 146| 48.5|21.9|13.2|7.10|3.11|0.99|| 2.79|2.52|2.04|1.72|1.45|1.31|1.15|1.06| +| 832| 516| 286| 132| 44.1|20.0|12.0|6.45|2.83|0.90|| 2.31|2.09|1.69|1.42|1.20|1.08|.949|.877| +| 748| 464| 257| 119| 39.7|18.0|10.8|5.81|2.55|0.81|| 1.87|1.69|1.37|1.15| .97|.878|.769|.710| +| 665| 412| 228| 106| 35.3|16.0| 9.6|5.16|2.26|0.72|| 1.47|1.33|1.08|.905|.762|.690|.604|.558| +| 582| 361| 200|92.8| 30.9|14.0| 8.4|4.52|1.98|0.63|| 1.13|1.02|.828|.695|.586|.531|.456|.429| ++--------------------------------------------------++----------------------------------------+ + +To get the pressure drop for lengths other than 1000 feet, multiply by +lengths in feet ÷ 1000. + +Example: Find the weight of steam at 100 pounds initial gauge pressure, +which will pass through a 6-inch pipe 720 feet long with a pressure drop +of 4 pounds. Under the conditions assumed in the table, 293.1 pounds +would flow per minute; hence, Q = 293.1, and + + _ _ + | 240×6×4 | +Q_{1} = 293.1 | ------- |^{½} = 239.9 pounds + |_ 720×12_| + +Table 67 may be frequently found to be of service in problems involving +the flow of steam. This table was calculated by Mr. E. C. Sickles for a +pipe 1000 feet long from formula (45), except that from the use of a +value of the constant K = .0026 instead of .0027, the constant in the +formula becomes 87.45 instead of 87. + +In using this table, the pressures and densities to be considered, as +given at the top of the right-hand portion, are the mean of the initial +and final pressures and densities. Its use is as follows: Assume an +allowable drop of pressure through a given length of pipe. From the +value as found in the right-hand column under the column of mean +pressure, as determined by the initial and final pressures, pass to the +left-hand portion of the table along the same line until the quantity is +found corresponding to the flow required. The size of the pipe at the +head of this column is that which will carry the required amount of +steam with the assumed pressure drop. + +The table may be used conversely to determine the pressure drop through +a pipe of a given diameter delivering a specified amount of steam by +passing from the known figure in the left to the column on the right +headed by the pressure which is the mean of the initial and final +pressures corresponding to the drop found and the actual initial +pressure present. + +For a given flow of steam and diameter of pipe, the drop in pressure is +proportional to the length and if discharge quantities for other lengths +of pipe than 1000 feet are required, they may be found by proportion. + + TABLE 68 + + FLOW OF STEAM INTO THE ATMOSPHERE + __________________________________________________________________ +| | | | | | +| Absolute | Velocity | Actual | Discharge | Horse Power | +| Initial | of Outflow | Velocity | per Square | per Square | +| Pressure | at Constant | of Outflow | Inch of | Inch of | +| per Square | Density | Expanded | Orifice | Orifice if | +| Inch | Feet per | Feet per | per Minute | Horse Power | +| Pounds | Second | Second | Pounds | = 30 Pounds | +| | | | | per Hour | +|____________|_____________|____________|____________|_____________| +| | | | | | +| 25.37 | 863 | 1401 | 22.81 | 45.6 | +| 30. | 867 | 1408 | 26.84 | 53.7 | +| 40. | 874 | 1419 | 35.18 | 70.4 | +| 50. | 880 | 1429 | 44.06 | 88.1 | +| 60. | 885 | 1437 | 52.59 | 105.2 | +| 70. | 889 | 1444 | 61.07 | 122.1 | +| 75. | 891 | 1447 | 65.30 | 130.6 | +| 90. | 895 | 1454 | 77.94 | 155.9 | +| 100. | 898 | 1459 | 86.34 | 172.7 | +| 115. | 902 | 1466 | 98.76 | 197.5 | +| 135. | 906 | 1472 | 115.61 | 231.2 | +| 155. | 910 | 1478 | 132.21 | 264.4 | +| 165. | 912 | 1481 | 140.46 | 280.9 | +| 215. | 919 | 1493 | 181.58 | 363.2 | +|____________|_____________|____________|____________|_____________| + + +Elbows, globe valves and a square-ended entrance to pipes all offer +resistance to the passage of steam. It is customary to measure the +resistance offered by such construction in terms of the diameter of the +pipe. Many formulae have been advanced for computing the length of pipe +in diameters equivalent to such fittings or valves which offer +resistance. These formulae, however vary widely and for ordinary +purposes it will be sufficiently accurate to allow for resistance at the +entrance of a pipe a length equal to 60 times the diameter; for a right +angle elbow, a length equal to 40 diameters, and for a globe valve a +length equal to 60 diameters. + +The flow of steam of a higher toward a lower pressure increases as the +difference in pressure increases to a point where the external pressure +becomes 58 per cent of the absolute initial pressure. Below this point +the flow is neither increased nor decreased by a reduction of the +external pressure, even to the extent of a perfect vacuum. The lowest +pressure for which this statement holds when steam is discharged into +the atmosphere is 25.37 pounds. For any pressure below this figure, the +atmospheric pressure, 14.7 pounds, is greater than 58 per cent of the +initial pressure. Table 68, by D. K. Clark, gives the velocity of +outflow at constant density, the actual velocity of outflow expanded +(the atmospheric pressure being taken as 14.7 pounds absolute, and the +ratio of expansion in the nozzle being 1.624), and the corresponding +discharge per square inch of orifice per minute. + +Napier deduced an approximate formula for the outflow of steam into the +atmosphere which checks closely with the figures just given. This +formula is: + + pa +W = ---- (49) + 70 + +Where W = the pounds of steam flowing per second, + p = the absolute pressure in pounds per square inch, + and a = the area of the orifice in square inches. + +In some experiments made by Professor C. H. Peabody, in the flow of +steam through pipes from ¼ inch to 1½ inches long and ¼ inch in +diameter, with rounded entrances, the greatest difference from Napier's +formula was 3.2 per cent excess of the experimental over the calculated +results. + +For steam flowing through an orifice from a higher to a lower pressure +where the lower pressure is greater than 58 per cent of the higher, the +flow per minute may be calculated from the formula: + +W = 1.9AK ((P - d)d)^{½} (50) + +Where W = the weight of steam discharged in pounds per minute, + A = area of orifice in square inches, + P = the absolute initial pressure in pounds per square inch, + d = the difference in pressure between the two sides in pounds + per square inch, + K = a constant = .93 for a short pipe, and .63 for a hole in a + thin plate or a safety valve. + +[Illustration: Vesta Coal Co., California, Pa., Operating at this Plant +3160 Horse Power of Babcock & Wilcox Boilers] + + + + +HEAT TRANSFER + + +The rate at which heat is transmitted from a hot gas to a cooler metal +surface over which the gas is flowing has been the subject of a great +deal of investigation both from the experimental and theoretical side. A +more or less complete explanation of this process is necessary for a +detailed analysis of the performance of steam boilers. Such information +at the present is almost entirely lacking and for this reason a boiler, +as a physical piece of apparatus, is not as well understood as it might +be. This, however, has had little effect in its practical development +and it is hardly possible that a more complete understanding of the +phenomena discussed will have any radical effect on the present design. + +The amount of heat that is transferred across any surface is usually +expressed as a product, of which one factor is the slope or linear rate +of change in temperature and the other is the amount of heat transferred +per unit's difference in temperature in unit's length. In Fourier's +analytical theory of the conduction of heat, this second factor is taken +as a constant and is called the "conductivity" of the substance. +Following this practice, the amount of heat absorbed by any surface from +a hot gas is usually expressed as a product of the difference in +temperature between the gas and the absorbing surface into a factor +which is commonly designated the "transfer rate". There has been +considerable looseness in the writings of even the best authors as to +the way in which the gas temperature difference is to be measured. If +the gas varies in temperature across the section of the channel through +which it is assumed to flow, and most of them seem to consider that this +would be the case, there are two mean gas temperatures, one the mean of +the actual temperatures at any time across the section, and the other +the mean temperature of the entire volume of the gas passing such a +section in any given time. Since the velocity of flow will of a +certainty vary across the section, this second mean temperature, which +is one tacitly assumed in most instances, may vary materially from the +first. The two mean temperatures are only approximately equal when the +actual temperature measured across the section is very nearly a +constant. In what follows it will be assumed that the mean temperature +measured in the second way is referred to. In English units the +temperature difference is expressed in Fahrenheit degrees and the +transfer rate in B. t. u.'s per hour per square foot of surface. Pecla, +who seems to have been one of the first to consider this subject +analytically, assumed that the transfer rate was constant and +independent both of the temperature differences and the velocity of the +gas over the surface. Rankine, on the other hand, assumed that the +transfer rate, while independent of the velocity of the gas, was +proportional to the temperature difference, and expressed the total +amount of heat absorbed as proportional to the square of the difference +in temperature. Neither of these assumptions has any warrant in either +theory or experiment and they are only valuable in so far as their use +determine formulae that fit experimental results. Of the two, Rankine's +assumption seems to lead to formulae that more nearly represent actual +conditions. It has been quite fully developed by William Kent in his +"Steam Boiler Economy". Professor Osborne Reynolds, in a short paper +reprinted in Volume I of his "Scientific Papers", suggests that the +transfer rate is proportional to the product of the density and velocity +of the gas and it is to be assumed that he had in mind the mean +velocity, density and temperature over the section of the channel +through which the gas was assumed to flow. Contrary to prevalent +opinion, Professor Reynolds gave neither a valid experimental nor a +theoretical explanation of his formula and the attempts that have been +made since its first publication to establish it on any theoretical +basis can hardly be considered of scientific value. Nevertheless, +Reynolds' suggestion was really the starting point of the scientific +investigation of this subject and while his formula cannot in any sense +be held as completely expressing the facts, it is undoubtedly correct to +a first approximation for small temperature differences if the additive +constant, which in his paper he assumed as negligible, is given a +value.[83] + +Experimental determinations have been made during the last few years of +the heat transfer rate in cylindrical tubes at comparatively low +temperatures and small temperature differences. The results at different +velocities have been plotted and an empirical formula determined +expressing the transfer rate with the velocity as a factor. The exponent +of the power of the velocity appearing in the formula, according to +Reynolds, would be unity. The most probable value, however, deduced from +most of the experiments makes it less than unity. After considering +experiments of his own, as well as experiments of others, Dr. Wilhelm +Nusselt[84] concludes that the evidence supports the following formulae: + + _ _ + [lambda]_{w} | w c_{p} [delta] | +a = b ------------ | --------------- |^{u} + d^{1-u} |_ [lambda] _| + + Where a is the transfer rate in calories per hour per square meter + of surface per degree centigrade difference in temperature, + u is a physical constant equal to .786 from Dr. Nusselt's + experiments, + b is a constant which, for the units given below, is 15.90, + w is the mean velocity of the gas in meters per second, + c_{p} is the specific heat of the gas at its mean temperature + and pressure in calories per kilogram, + [delta] is the density in kilograms per cubic meter, + [lambda] is the conductivity at the mean temperature and pressure in + calories per hour per square meter per degree centigrade + temperature drop per meter, +[lambda]_{w} is the conductivity of the steam at the temperature of the + tube wall, + d is the diameter of the tube in meters. + +If the unit of time for the velocity is made the hour, and in the place +of the product of the velocity and density is written its equivalent, +the weight of gas flowing per hour divided by the area of the tube, this +equation becomes: + + _ _ + [lambda]_{w} | Wc_{p} | +a = .0255 ------------ | --------- |^{.786} + d^{.214} |_ A[lambda] _| + +where the quantities are in the units mentioned, or, since the constants +are absolute constants, in English units, + + a is the transfer rate in B. t. u. per hour per square foot + of surface per degree difference in temperature, + W is the weight in pounds of the gas flowing through the tube + per hour, + A is the area of the tube in square feet, + d is the diameter of the tube in feet, + c_{p} is the specific heat of the gas at constant pressure, + [lambda] is the conductivity of the gas at the mean temperature and + pressure in B. t. u. per hour per square foot of surface + per degree Fahrenheit drop in temperature per foot, +[lambda]_{w} is the conductivity of the steam at the temperature of the + wall of the tube. + +The conductivities of air, carbonic acid gas and superheated steam, as +affected by the temperature, in English units, are: + +Conductivity of air .0122 (1 + .00132 T) +Conductivity of carbonic acid gas .0076 (1 + .00229 T) +Conductivity of superheated steam .0119 (1 + .00261 T) + +where T is the temperature in degrees Fahrenheit. + +Nusselt's formulae can be taken as typical of the number of other +formulae proposed by German, French and English writers.[85] Physical +properties, in addition to the density, are introduced in the form of +coefficients from a consideration of the physical dimensions of the +various units and of the theoretical formulae that are supposed to +govern the flow of the gas and the transfer of heat. All assume that the +correct method of representing the heat transfer rate is by the use of +one term, which seems to be unwarranted and probably has been adopted on +account of the convenience in working up the results by plotting them +logarithmically. This was the method Professor Reynolds used in +determining his equation for the loss in head in fluids flowing through +cylindrical pipes and it is now known that the derived equation cannot +be considered as anything more than an empirical formula. It, therefore, +is well for anyone considering this subject to understand at the outset +that the formulae discussed are only of an empirical nature and +applicable to limited ranges of temperature under the conditions +approximately the same as those surrounding the experiments from which +the constants of the formula were determined. + +It is not probable that the subject of heat transfer in boilers will +ever be on any other than an experimental basis until the mathematical +expression connecting the quantity of fluid which will flow through a +channel of any section under a given head has been found and some +explanation of its derivation obtained. Taking the simplest possible +section, namely, a circle, it is found that at low velocities the loss +of head is directly proportional to the velocity and the fluid flows in +straight stream lines or the motion is direct. This motion is in exact +accordance with the theoretical equations of the motion of a viscous +fluid and constitutes almost a direct proof that the fundamental +assumptions on which these equations are based are correct. When, +however, the velocity exceeds a value which is determinable for any size +of tube, the direct or stream line motion breaks down and is replaced by +an eddy or mixing flow. In this flow the head loss by friction is +approximately, although not exactly, proportional to the square of the +velocity. No explanation of this has ever been found in spite of the +fact that the subject has been treated by the best mathematicians and +physicists for years back. It is to be assumed that the heat transferred +during the mixing flow would be at a much higher rate than with the +direct or stream line flow, and Professors Croker and Clement[86] have +demonstrated that this is true, the increase in the transfer being so +marked as to enable them to determine the point of critical velocity +from observing the rise in temperature of water flowing through a tube +surrounded by a steam jacket. + +The formulae given apply only to a mixing flow and inasmuch as, from +what has just been stated, this form of motion does not exist from zero +velocity upward, it follows that any expression for the heat transfer +rate that would make its value zero when the velocity is zero, can +hardly be correct. Below the critical velocity, the transfer rate seems +to be little affected by change in velocity and Nusselt,[87] in another +paper which mathematically treats the direct or stream line flow, +concludes that, while it is approximately constant as far as the +velocity is concerned in a straight cylindrical tube, it would vary from +point to point of the tube, growing less as the surface passed over +increased. + +It should further be noted that no account in any of this experimental +work has been taken of radiation of heat from the gas. Since the common +gases absorb very little radiant heat at ordinary temperatures, it has +been assumed that they radiate very little at any temperature. This may +or may not be true, but certainly a visible flame must radiate as well +as absorb heat. However this radiation may occur, since it would be a +volume phenomenon rather than a surface phenomenon it would be +considered somewhat differently from ordinary radiation. It might apply +as increasing the conductivity of the gas which, however independent of +radiation, is known to increase with the temperature. It is, therefore, +to be expected that at high temperatures the rate of transfer will be +greater than at low temperatures. The experimental determinations of +transfer rates at high temperatures are lacking. + +Although comparatively nothing is known concerning the heat radiation +from gases at high temperatures, there is no question but what a large +proportion of the heat absorbed by a boiler is received direct as +radiation from the furnace. Experiments show that the lower row of tubes +of a Babcock & Wilcox boiler absorb heat at an average rate per square +foot of surface between the first baffle and the front headers +equivalent to the evaporation of from 50 to 75 pounds of water from and +at 212 degrees Fahrenheit per hour. Inasmuch as in these experiments no +separation could be made between the heat absorbed by the bottom of the +tube and that absorbed by the top, the average includes both maximum and +minimum rates for those particular tubes and it is fair to assume that +the portion of the tubes actually exposed to the furnace radiations +absorb heat at a higher rate. Part of this heat was, of course absorbed +by actual contact between the hot gases and the boiler heating surface. +A large portion of it, however, must have been due to radiation. Whether +this radiant heat came from the fire surface and the brickwork and +passed through the gases in the furnace with little or no absorption, or +whether, on the other hand, the radiation were absorbed by the furnace +gases and the heat received by the boiler was a secondary radiation from +the gases themselves and at a rate corresponding to the actual gas +temperature, is a question. If the radiations are direct, then the term +"furnace temperature", as usually used has no scientific meaning, for +obviously the temperature of the gas in the furnace would be entirely +different from the radiation temperature, even were it possible to +attach any significance to the term "radiation temperature", and it is +not possible to do this unless the radiations are what are known as +"full radiations" from a so-called "black body". If furnace radiation +takes place in this manner, the indications of a pyrometer placed in a +furnace are hard to interpret and such temperature measurements can be +of little value. If the furnace gases absorb the radiations from the +fire and from the brickwork of the side walls and in their turn radiate +heat to the boiler surface, it is scientifically correct to assume that +the actual or sensible temperature of the gas would be measured by a +pyrometer and the amount of radiation could be calculated from this +temperature by Stefan's law, which is to the effect that the rate of +radiation is proportional to the fourth power of the absolute +temperature, using the constant with the resulting formula that has been +determined from direct experiment and other phenomena. With this +understanding of the matter, the radiations absorbed by a boiler can be +taken as equal to that absorbed by a flat surface, covering the portion +of the boiler tubes exposed to the furnace and at the temperature of the +tube surface, when completely exposed on one side to the radiations from +an atmosphere at the temperature in the furnace. With this assumption, +if S^{1} is the area of the surface, T the absolute temperature of the +furnace gases, t the absolute temperature of the tube surface of the +boiler, the heat absorbed per hour measured in B. t. u.'s is equal to + + _ _ + | / T \ / t \ | +1600 | |----|^{4} - |----|^{4}| S^{1} + |_\1000/ \1000/ _| + +In using this formula, or in any work connected with heat transfer, the +external temperature of the boiler heating surface can be taken as that +of saturated steam at the pressure under which the boiler is working, +with an almost negligible error, since experiments have shown that with +a surface clean internally, the external surface is only a few degrees +hotter than the water in contact with the inner surface, even at the +highest rates of evaporation. Further than this, it is not conceivable +that in a modern boiler there can be much difference in the temperature +of the boiler in the different parts, or much difference between the +temperature of the water and the temperature of the steam in the drums +which is in contact with it. + +If the total evaporation of a boiler measured in B. t. u.'s per hour is +represented by E, the furnace temperature by T_{1}, the temperature of +the gas leaving the boiler by T_{2}, the weight of gas leaving the +furnace and passing through the setting per hour by W, the specific heat +of the gas by C, it follows from the fact that the total amount of heat +absorbed is equal to the heat received from radiation plus the heat +removed from the gases by cooling from the temperature T_{1} to the +temperature T_{2}, that + + _ _ + | / T \ / t \ | +E = 1600 | |----|^{4} - |----|^{4}| S^{1} + WC(T_{1} - T_{2}) + |_\1000/ \1000/ _| + +This formula can be used for calculating the furnace temperature when E, +t and T_{2} are known but it must be remembered that an assumption +which is probably, in part at least, incorrect is implied in using it or +in using any similar formula. Expressed in this way, however, it seems +more rational than the one proposed a few years ago by Dr. Nicholson[88] +where, in place of the surface exposed to radiation, he uses the grate +surface and assumes the furnace gas temperature as equal to the fire +temperature. + +If the heat transfer rate is taken as independent of the gas temperature +and the heat absorbed by an element of the surface in a given time is +equated to the heat given out from the gas passing over this surface in +the same time, a single integration gives + + Rs +(T - t) = (T_{1} - t) e^{- --} + WC + +where s is the area of surface passed over by the gases from the furnace +to any point where the gas temperature T is measured, and the rate of +heat transfer is R. As written, this formula could be used for +calculating the temperature of the gas at any point in the boiler +setting. Gas temperatures, however, calculated in this way are not to be +depended upon as it is known that the transfer rate is not independent +of the temperature. Again, if the transfer rate is assumed as varying +directly with the weight of the gases passing, which is Reynolds' +suggestion, it is seen that the weight of the gases entirely disappears +from the formula and as a consequence if the formula was correct, as +long as the temperature of the gas entering the surface from the furnace +was the same, the temperatures throughout the setting would be the same. +This is known also to be incorrect. If, however, in place of T is +written T_{2} and in place of s is written S, the entire surface of the +boiler, and the formula is re-arranged, it becomes: + + _ _ + WC | T_{1} - t | +R = --- Log[89]| --------- | + S |_ T_{2} - t _| + +This formula can be considered as giving a way of calculating an average +transfer rate. It has been used in this way for calculating the average +transfer rate from boiler tests in which the capacity has varied from an +evaporation of a little over 3 pounds per square foot of surface up to +15 pounds. When plotted against the gas weights, it was found that the +points were almost exactly on a line. This line, however, did not pass +through the zero point but started at a point corresponding to +approximately a transfer rate of 2. Checked out against many other +tests, the straight line law seems to hold generally and this is true +even though material changes are made in the method of calculating the +furnace temperature. The inclination of the line, however, varied +inversely as the average area for the passage of the gas through the +boiler. If A is the average area between all the passes of the boiler, +the heat transfer rate in Babcock & Wilcox type boilers with ordinary +clean surfaces can be determined to a rather close approximation from +the formula: + + W +R = 2.00 + .0014 - + A + +The manner in which A appears in this formula is the same as it would +appear in any formula in which the heat transfer rate was taken as +depending upon the product of the velocity and the density of the gas +jointly, since this product, as pointed out above, is equivalent to W/A. +Nusselt's experiments, as well as those of others, indicate that the +ratio appears in the proper way. + +While the underlying principles from which the formula for this average +transfer rate was determined are questionable and at best only +approximately correct, it nevertheless follows that assuming the +transfer rate as determined experimentally, the formula can be used in +an inverse way for calculating the amount of surface required in a +boiler for cooling the gases through a range of temperature covered by +the experiments and it has been found that the results bear out this +assumption. The practical application of the theory of heat transfer, as +developed at present, seems consequently to rest on these last two +formulae, which from their nature are more or less empirical. + +Through the range in the production of steam met with in boilers now in +service which in the marine type extends to the average evaporation of +12 to 15 pounds of water from and at 212 degrees Fahrenheit per square +foot of surface, the constant 2 in the approximate formula for the +average heat transfer rate constitutes quite a large proportion of the +total. The comparative increase in the transfer rate due to a change in +weight of the gases is not as great consequently as it would be if this +constant were zero. For this reason, with the same temperature of the +gases entering the boiler surface, there will be a gradual increase in +the temperature of the gases leaving the surface as the velocity or +weight of flow increases and the proportion of the heat contained in the +gases entering the boiler which is absorbed by it is gradually reduced. +It is, of course, possible that the weight of the gases could be +increased to such an amount or the area for their passage through the +boiler reduced by additional baffles until the constant term in the heat +transfer formula would be relatively unimportant. Under such conditions, +as pointed out previously, the final gas temperature would be unaffected +by a further increase in the velocity of the flow and the fraction of +the heat carried by the gases removed by the boiler would be constant. +Actual tests of waste heat boilers in which the weight of gas per square +foot of sectional area for its passage is many times more than in +ordinary installations show, however, that this condition has not been +attained and it will probably never be attained in any practical +installation. It is for this reason that the conclusions of Dr. +Nicholson in the paper referred to and of Messrs. Kreisinger and Ray in +the pamphlet "The Transmission of Heat into Steam Boilers", published by +the Department of the Interior in 1912, are not applicable without +modification to boiler design. + +In superheaters the heat transfer is effected in two different stages; +the first transfer is from the hot gas to the metal of the superheater +tube and the second transfer is from the metal of the tube to the steam +on the inside. There is, theoretically, an intermediate stage in the +transfer of the heat from the outside to the inside surface of the tube. +The conductivity of steel is sufficient, however, to keep the +temperatures of the two sides of the tube very nearly equal to each +other so that the effect of the transfer in the tube itself can be +neglected. The transfer from the hot gas to the metal of the tube takes +place in the same way as with the boiler tubes proper, regard being paid +to the temperature of the tube which increases as the steam is heated. +The transfer from the inside surface of the tube to the steam is the +inverse of the process of the transfer of the heat on the outside and +seems to follow the same laws. The transfer rate, therefore, will +increase with the velocity of the steam through the tube. For this +reason, internal cores are quite often used in superheaters and actually +result in an increase in the amount of superheat obtained from a given +surface. The average transfer rate in superheaters based on a difference +in mean temperature between the gas on the outside of the tubes and the +steam on the inside of the tubes is if R is the transfer rate from the +gas to the tube and r the rate from the tube to the steam: + + Rr + ----- + R + r + +and is always less than either R or r. This rate is usually greater than +the average transfer rate for the boiler as computed in the way outlined +in the preceding paragraphs. Since, however, steam cannot, under any +imagined set of conditions, take up more heat from a tube than would +water at the same average temperature, this fact supports the contention +made that the actual transfer rate in a boiler must increase quite +rapidly with the temperatures. The actual transfer rates in superheaters +are affected by so many conditions that it has not so far been possible +to evolve any formula of practical value. + +[Illustration: Iron City Brewery of the Pittsburgh Brewing Co., +Pittsburgh, Pa, Operating in this Plant 2000 Horse Power of Babcock & +Wilcox Boilers] + + + + +INDEX + + PAGE + +Absolute pressure 117 +Absolute zero 80 +Accessibility of Babcock & Wilcox boiler 59 +Acidity in boiler feed water 106 +Actual evap. corresponding to boiler horse power 288 +Advantages of Babcock & Wilcox boilers 61 + Stoker firing 195 + Water tube over fire tube boilers 61 +Air, composition of 147 + In boiler feed water 106 + Properties of 147 + Required for combustion 152, 156 + Specific heat of 148 + Supplied for combustion 157 + Vapor in 149 + Volume of 147 + Weight of 147 +Alkalinity in boiler feed water 103 + Testing feed for 103 +Altitude, boiling point of water at 97 + Chimney sizes corrected for 248 +Alum in feed water treatment 106 +A. S. M. E. code for boiler testing 267 +Analyses, comparison of proximate and ultimate 183 + Proximate coal, and heating values 177 +Analysis, coal, proximate, methods of 176 + Coal, ultimate 173 + Determination of heating value from 173 +Analysis, Flue gas 155 + Flue gas, methods of 160 + Flue gas, object of 155 +Anthracite coal 166 + Combustion rates with 246 + Distribution of 167 + Draft required for 246 + Firing 190 + Grate ratio for 191 + Semi 166 + Sizes of 190 + Steam as aid to burning 191 + Thickness of fires with 191 +Arches, fire brick, as aid to combustion 190 + Fire brick, for 304 + Fire brick, laying 305 +Automatic stokers, advantages of 195 + Overfeed 196 + Traveling grate 197 + Traveling grate, Babcock & Wilcox 194 + Underfeed 196 +Auxiliaries, exhaust from, in heating feed water 113 + Superheated steam with 142 +Auxiliary grates, with blast furnace gas 228 + With oil fuel 225 + With waste heat 235 +Babcock, G. H., lecture on circulation of water in Boilers 28 + Lecture on theory of steam making 92 +Babcock & Wilcox Co., Works at Barberton, Ohio 7 + Works at Bayonne, N. J. 6 +Babcock & Wilcox boiler, accessibility of 59 + Advantages of 61 + Circulation of water in 57, 66 + Construction of 49 + Cross boxes 50 + Cross drum 53 + Cross drum, dry steam with 71 + Drumheads 49 + Drums 49 + Durability 75 + Evolution of 39 + Fittings 55 + Fixtures 55 + Fronts 53 + Handhole fittings 50, 51 + Headers 50, 51 + Inclined header, wrought steel 54 + Inspection 75 + Life of 76 + Materials entering into the construction of 59 + Mud drums 51 + Path of gases in 57 + Path of water in 57 + Rear tube doors of 53, 74 + Repairs 75 + Safety of 66 + Sections 50 + Set for utilizing waste heat 236 + Set with Babcock & Wilcox chain grate stoker 12 + Set with bagasse furnace 208 + Set with Peabody oil furnace 222 + Supports, cross drum 53 + Supports, longitudinal drum 52 + Tube doors 53 + Vertical header, cast iron 58 + Vertical header, wrought steel 48 +Babcock & Wilcox chain grate stoker 194 +Babcock & Wilcox superheater 136 +Bagasse, composition of 206 + Furnace 209 + Heat, value of 206 + Tests of Babcock & Wilcox boilers with 210 + Value of diffusion 207 +Barium carbonate in feed water treatment 106 +Barium hydrate in feed water treatment 106 +Barrus draft gauge 254 +Bituminous coal, classification of 167 + Combustion rates with 246 + Composition of 177 + Distribution of 168 + Firing methods 193 + Semi 166 + Sizes of 191 + Thickness of fire with 193 +Blast furnace gas, burners for 228 + Combustion of 228 + Composition of 227 + Stacks for 228 +Boiler, Blakey's 23 + Brickwork, care of 307 + Circulation of water in steam 28 + Compounds 109 + Development of water tube 23 + Eve's 24 + Evolution of Babcock & Wilcox 39 + Fire tube, compared with water tube 61 + Guerney's 24 + Horse power 263 + Loads, economical 283 + Perkins' 24 + Room piping 108 + Room practice 297 + Rumsey's 23 + Stevens', John 23 + Stevens', John Cox 23 + Units, number of 289 + Units, size of 289 + Wilcox's 25 + Woolf's 23 +Boilers, capacity of 278 + Care of 291 + Efficiency of 256 + Horse power of 265 + Operation of 291 + Requirements of steam 27 + Testing 267 +Boiling point 86 + Of various substances 86 + Of water as affected by altitude 97 +Brick, fire 304 + Arches 305 + Classification of 304 + Compression of 303 + Expansion of 303 + Hardness of 303 + Laying up 305 + Nodules, ratio of 303 + Nodules, size of 303 + Plasticity of 302 +Brick, red 302 +Brickwork, care of 307 +British thermal unit 83 +Burners, blast furnace gas 228 + By-product coke oven gas 231 + Natural gas 231 + Oil 217 + Oil, capacity of 221 + Oil, mechanical atomizing 219 + Oil, operation of 223 + Oil, steam atomizing 218 + Oil, steam consumption of 220 +Burning hydrogen, loss due to moisture formed in 261 +By-product coke oven gas burners 231 +By-product coke oven gas, combustion of 231 +By-product coke oven gas, composition and heat value of 231 +Calorie 83 +Calorific value (see Heat value). +Calorimeter, coal, Mahler bomb 184 + Mahler bomb, method of correction 187 + Mahler bomb, method of operation of 185 +Calorimeter, steam, compact type of throttling 132 + Correction for 131 + Location of nozzles for 134 + Normal reading 131 + Nozzles 134 + Separating 133 + Throttling 129 +Capacity of boilers 264, 278 + As affecting economy 276 + Economical loads 283 + With bagasse 210 + With blast furnace gas 228 + With coal 280 + With oil fuel 224 +Capacity of natural gas burners 229 +Capacity of oil burners 221 +Carbon dioxide in flue gases 154 + Unreliability of readings taken alone 162 +Carbon, fixed 165 + Incomplete combustion of, loss due to 158 + Monoxide, heat value of 151 + Monoxide, in flue gases 155 + Unconsumed in ash, loss due to 261 +Care of boilers when out of service 300 +Casings, boilers 307 +Causticity of feed water 103 + Testing for 105 +Celsius thermometer scale 79 +Centigrade thermometer scale 79 +Chain grate stoker, Babcock & Wilcox 194 +Chemicals required in feed water treatment 105 +Chimney gases, losses in 158, 159 +Chimneys (see Draft). + Correction in dimensions for altitude 248 + Diameter of 243 + Draft available from 241 + Draft loss in 239 + For blast furnace gas 253 + For oil fuel 251 + For wood fuel 254 + Height of 243 + Horse power they will serve 250 +Circulation of water in Babcock & Wilcox boilers 57, 66 + Of water in steam boilers 28 + Results of defective 62, 66, 67 +Classification of coals 166 + Fire brick 304 + Feed water difficulties 100 + Fuels 165 +Cleaners, turbine tube 299 +Cleaning, ease of, Babcock & Wilcox boilers 73 +Closed feed water heaters 111 +Coal, Alaska 169 + Analyses and heat value 177 + Analysis, proximate 176 + Analysis, ultimate 173 + Anthracite 166 + Bituminous 167 + Cannel 167 + Classification of 165, 166 + Combustion of 190 + Comparison with oil 214 + Consumption, increase due to superheat 139 + Distribution of 167 + Formation of 165 + Lignite 167 + Records 293 + Semi-anthracite 166 + Semi-bituminous 166 + Sizes of anthracite 190 + Sizes of bituminous 191 +Code of A. S. M. E. for boiler testing 267 +Coefficient of expansion of various substances 87 +Coke 171 + Oven gas, by-product, burners 231 + Oven gas, by-product, combustion of 231 + Oven gas, by-product, composition and heat value of 231 +Coking method of firing 195 +Color as indication of temperature 91 +Combination furnaces 224 +Combustible in fuels 150 +Combustion 150 + Air required for 152, 156 + Air supplied for 157 +Combustion of coal 190 + Of gaseous fuels 227 + Of liquid fuels 212 + Of solid fuels other than coal 201 +Composition of bagasse 205 + Blast furnace gas 227 + By-product coke oven gas 231 + Coals 177 + Natural gas 229 + Oil 213 + Wood 201 +Compounds, boiler 109 +Compressibility of water 97 +Compression of fire brick 303 +Condensation, effect of superheated steam on 140 + In steam pipes 313 +Consumption, heat, of engines 141 +Correction, stem, for thermometers 80 + For normal reading in steam calorimeter 131 + For radiation, bomb calorimeter 187 +Corrosion 101, 106 +Coverings, pipe 315 +Cross drum, Babcock & Wilcox boiler 52, 53, 60 + Dry steam with 71 +Draft area as affecting economy in Babcock & Wilcox boilers 70 + Available from chimneys 241 +Draft loss in chimneys 239 + Loss in boilers 245 + Loss in flues 243 + Loss in furnaces 245 +Draft required for anthracite 246 + Required for various fuels 246 +Drums, Babcock & Wilcox, cross 53 + Cross, boxes 50 + Heads 49 + Longitudinal 49 + Manholes 49 + Nozzles on 50 +Dry steam in Babcock & Wilcox boilers 71 +Density of gases 147 + Steam 115 +Dulong's formula for heating value 173 +Ebullition, point of 86 +Economizers 111 +Efficiency of boilers, chart of 258 + Combustible basis 256 + Dry coal basis 256 + Increase in, due to superheaters 139 + Losses in (see Heat balance) 259 + Testing 267 + Test _vs._ operating 278 + Variation in, with capacity 284 + With coal 288 + With oil 224 +Ellison draft gauge 254 +Engine, Hero's 13 +Engines, superheated steam with 141 +Equivalent evaporation from and at 212 degrees 116 +Eve's boiler 24 +Evolution of Babcock & Wilcox boiler 39 +Exhaust steam from auxiliaries 113 +Expansion, coefficient of 87 + Of fire brick 303 + Of pipe 315 + Pyrometer 89 +Factor of evaporation 117 +Fahrenheit thermometer scale 79 +Fans, use of, in waste heat work 233 +Feed water, air in 106 + As affecting capacity 279 + Boiler 100 +Feed water heaters, closed 111 + Economizers 111 + Open 111 +Feed water heating, methods of 111 + Saving by 110 +Feed water, impurities in 100 + Lines 312 + Method of feeding 110 +Feed water treatment 102 + Chemical 102 + Chemical, lime and soda process 102 + Chemical, lime process 102 + Chemical, soda process 102 + Chemicals used in lime and soda process 105 + Combined heat and chemical 105 + Heat 102 + Less usual reagents 106 +Firing, advantages of stoker 195 + Methods for anthracite 190 + Bituminous 193 + Lignite 195 +Fittings, handhole in Babcock & Wilcox boilers 50, 51 + Pipe 311 + Superheated steam 145 + With Babcock & Wilcox boilers 55 +Fixtures with Babcock & Wilcox boilers 55 +Flanges, pipe 309 +Flow of steam into pressure above atmosphere 317 + Into the atmosphere 328 + Through orifices 317 + Through pipes 317 +Flue gas analysis 155 + Conversion of volumetric to weight 161 + Methods of making 160 + Object of 155 + Orsat apparatus 159 +Flue gas, composition of 155 + Losses in 158, 159 + Weight per pound of carbon in fuel 158 + Weight per pound of fuel 158 + Weight resulting from combustion 157 +Foaming 102, 107 +Fuel analysis, proximate 176 + Ultimate 173 +Fuel calorimeter, Mabler bomb 184 +Tests, method of making 186 +Fuels, classification of 165 + Gaseous, and their combustion 227 +Fuels, liquid, and their combustion 212 + Solid, coal 190 + Solid, other than coal 201 +Furnace, bagasse 209 + Blast furnace gas 228 + By-product coke oven gas 231 + Combination wood and oil 225 + Efficiency of 283 + Natural gas 229 + Peabody oil 222 + Webster 55 + Wood burning 201, 202 +Galvanic action 107 +Gas, blast furnace, burners 228 + Combustion of 228 + Composition of 227 +Gas, by-product coke oven, burners 231 + Combustion of 231 + Composition of and heat value 231 +Gas, natural, burners 229 + Combustion of 229 + Composition and heat value of 229 +Gases, chimney, losses in 158, 159 + Density of 163 + Flue (see Flue gases). + Path of in Babcock & Wilcox boilers 57 + Waste (see Waste heat) 232 +Gaskets 312 +Gauges, draft, Barrus 254 + Ellison 255 + Peabody 255 + U-tube 254 +Gauges, vacuum 117 +Grate ratio for anthracite 191 +Gravity of oils 214 +Grooving 102 +Guerney's boiler 24 +Handhole fittings for Babcock & Wilcox boilers 50, 51 +Handholes in Babcock & Wilcox boilers 50, 51 +Hardness of boiler feed water 102 + Permanent 102 + Temporary 102 + Testing for 105 +Hardness of fire brick 303 +Heat and chemical methods of treating feed water 105 + And its measurement 79 + Balance 262 + Consumption of engines 141 + Latent 84 + Of liquid 120 + Sensible 84 + Specific (see Specific heat) 83 + Total 86 + Transfer 323 +Heat value of bagasse 205 + By-product coke oven gas 231 + Coal 177 +Heat value of fuels, determination of 173 + Determination of Kent's approximate method 183 + High and low 174 +Heat value of natural gas 229 + Oil 215 + Wood 201 +Heat waste (see Waste heat) 232 +Heaters, feed water, closed 111 + Economizers 111 + Open 111 +Heating feed water, saving by 110 +Hero's engine 13 +High and low heat value of fuels 174 +High pressure steam, advantages of use of 119 +High temperature measurements, accuracy of 89 +Horse power, boiler 265 + Evaporation (actual) corresponding to 288 + Rated boiler 265 + Stacks for various, of boilers 250 +Hydrogen in flue gases 156 +Ice, specific heat of 99 +"Idalia", tests with superheated steam on yacht 143 +Impurities in boiler feed water 100 +Incomplete combustion of carbon, loss due to 158 +Injectors, efficiency of 112 + Relative efficiency of, and pumps 112 +Iron alum in feed water treatment 106 +Kent, Wm., determination of heat value from analysis 183 + Stack table 250 +Kindling point 150 +Latent heat 84, 115 +Laying of fire brick 305 + Red brick 305 +Lignite, analyses of 181 + Combustion of 195 +Lime and soda treatment of boiler feed 102 + Used in chemical treatment of feed 105 +Lime treatment of boiler feed water 102 +Liquid fuels and their combustion 212 +Loads, economical boiler 283 +Losses due to excess air 158 + Due to unburned carbon 158 + Due to unconsumed carbon in the ash 261 +Losses in efficiency (see Heat balance). + In flue gases 158, 159 +Low water in boilers 298 +Melting points of metals 91 +Mercurial pyrometers 89 +Moisture in coal, determination of 176 + In fuels, losses due to 259 + In steam, determination of 129 +Mud drum of Babcock & Wilcox boiler 51 +Napier's formula for flow of steam 321 +Natural gas, burners for 229 + Combustion of 229 + Composition and heat value of 229 +Nitrate of silver in testing feed water 105 +Nitrogen, as indication of excess air 157 + In air 147 + In flue gases 157 +Nodules, fire brick, ratio of 303 + Size of 303 +Normal reading, throttling calorimeter 131 +Nozzles, steam sampling for calorimeter 134 + Location of 134 +Oil fuel, burners (see Burners). + Capacity with 224 + Combustion of 217 + Comparison with coal 214 + Composition and heat value of 213 + Efficiency with 224 + Furnaces for 221 + Gravity of 214 + In combination with other fuels 224 + Stacks for 251 + Tests with 224 +Open hearth furnace, Babcock & Wilcox boiler set + for utilizing waste heat from 236 +Open heaters, feed water 111 +Operation of boilers 291 +Optical pyrometers 91 +Orsat apparatus 160 +Oxalate of soda in feed water treatment 106 +Oxygen in air 147 + Flue gases 155 +Peabody draft gauge 255 + Formulae for coal calorimeter correction 188 + Furnace for oil fuel 221, 222 + Oil burner 218 +Peat 167 +Perkins' boiler 24 +Pfaundler's method of coal calorimeter radiation correction 187 +Pipe coverings 315 + Data 308 + Expansion of 315 +Pipe fittings 311 + Flanges 309 + Flow of steam through 317 + Radiation from bare and covered 314 + Sizes 312 + Supports for 315 +Piping, boiler room 308 +Pitting 102 +Plant records, coal 293 + Draft 294 + Temperature 294 + Water 293 +Plasticity of fire brick 302 +Pressed fuels 171 +Priming in boilers 102 + Methods of treating for 107 +Properties of water 96 +Proximate analyses of coal 177 +Proximate analysis 173 + Method of making 176 +Pulverized fuels 170 +Pump, efficiency of feed 112 +Pyrometers, expansion 89 + Mercurial 89 + Optical 91 + Radiation 90 + Thermo-electric 90 +Quality of steam 129 +Radiation correction for coal calorimeter 187, 188 + Correction for steam calorimeter 131 + Effect of superheated steam on 140 + From pipes 314 + Losses in efficiency due to 307 + Pyrometers 90 +Ratio of air supplied to that required for combustion 157 +Reagents, less usual in feed treatment 106 +Records, plant, coal 293 + Draft 294 + Temperature 294 + Water 293 +Requirements of steam boilers 27 + As indicated by evolution of Babcock & Wilcox 45 +Rumsey's boiler 23 +Safety of Babcock & Wilcox boilers 66 +Salts responsible for scale 101 + Solubility of 101 +Sampling coal 271 + Nozzles for steam 134 + Nozzles for steam, location of 134 + Steam 134 + Steam, errors in 135 +Saturated air 149 +Saving by heating feed 110 + With superheat in "Idalia" tests 143 + With superheat in prime movers 140, 142 +Scale (see Thermometers) 101 +Sea water, composition of 97 +Sections, Babcock & Wilcox boiler 50 +Selection of boilers 277 +Sensible heat 84 +Separating steam calorimeter 132 +Sizes of anthracite coal 190 + Bituminous coal 191 +Smoke, methods of eliminating 197 +Smokelessness, relative nature of 197 + With hand-fired furnaces 199 + With stoker-fired furnaces 199 +Soda, lime and, treatment of feed 103 + Oxalate of, in treatment of feed 106 + Removal of scale aided by 300 + Silicate of, in treatment of feed 106 + Treatment of boiler feed 103 +Space occupied by Babcock & Wilcox boilers 66 +Specific heat 83 +Specific heat of air 148 + Ice 99 + Saturated steam 99 +Specific heat of superheated steam 137 + Various solids, liquids and gases 85 + Water 99 +Spreading method of firing 193 +Stacks and draft (see Chimneys) 237 +Stacks for blast furnace gas 228 + Oil fuel 251 + Wood 202, 254 +Stayed surfaces, absence of, in Babcock & Wilcox boilers 69 + Difficulties arising from use of 67 +Steam 115 + As aid to combustion of anthracite 191 + As aid to combustion of lignite 195 + Consumption of prime movers 289 + Density of 115 + Flow of, into atmosphere 320 + Flow of, into pressure above atmosphere 318 + Flow of, through pipes 317 + High pressure, advantage of 119 + History of generation and use of 13 + Making, theory of 92 + Moisture in 129 + Properties of, for vacuum 119 + Properties of saturated 122 + Properties of superheated 125 + Quality of 129 + Saturated 115 + Specific heat of saturated 99 + Specific heat of superheated 137 + Specific volume of 115 + Superheated 137 + Superheaters (see Superheated steam). +Steaming, quick, with Babcock & Wilcox boilers 73 +Stem Correction, thermometer 80 +Stevens, John, boiler 23 +Stevens, John Cox, boiler 23 +Stokers, automatic, advantages of 195 + Babcock & Wilcox chain grate 194 + Overfeed 196 + Smokelessness with 199 + Traveling grate 197 + Underfeed 196 +Superheated steam 137 + Additional fuel for 139 + Effect on condensation 140 + Effect on radiation 140 + Fittings for use with 145 + "Idalia" tests with 143 + Specific heat of 137 + Variation in temperature of 145 + With turbines 142 +Superheater, Babcock & Wilcox 136 + Effect of on boiler efficiency 139 +Supports, Babcock & Wilcox boiler 52, 53 +Tan bark 210 +Tar, water gas 225 +Temperature, accuracy of high, measurements 89 + As indicated by color 91 + Of waste gases 232 + Records 294 +Test conditions _vs._ operating conditions 278 +Testing, boiler, A. S. M. E. code for 267 +Tests of Babcock & Wilcox boilers with bagasse 210 + Coal 280 + Oil 224 +Theory of steam making 92 +Thermo-electric pyrometers 90 +Thermometer scale, celsius 79 +Thermometer scale, centigrade 76 + Fahrenheit 79 + Réaumur 79 +Thermometer scales, comparison of 80 + Conversion of 80 +Thermometer stem correction for 80 +Thermometers, glass for 79 +Throttling calorimeter 129 +Total heat 86, 115 +Treatment of boiler feed water (see Feed water) 102 + Chemicals used in 105 + Less usual reagents in 106 +Tube data 309 + Doors in Babcock & Wilcox boilers 53 + Tubes in Babcock & Wilcox boilers 50 +Ultimate analyses of coal 183 + Analysis of fuels 173 +Unaccounted losses in efficiency 261 +Unconsumed carbon in ash 261 +Units, boiler, number of 289 + Size of 289 +Units, British thermal 83 +Unreliability of CO_{2} readings alone 162 +Vacuum gauges 117 + Properties of steam for 119 +Valves used with superheated steam 312 +Variation in properties of saturated steam 119 + Superheat from boilers 145 +Volume of air 147 + Water 96 +Volume, specific, of steam 115 +Waste heat, auxiliary grates with boilers for 235 + Babcock & Wilcox boilers set for use with 236 + Boiler design for 233 + Curve of temperature, heat absorption, and heating surface 235 + Draft for 233 + Fans for use with 233 + Power obtainable from 232 + Temperature of, from various processes 232 + Utilization of 232 +Water, air in boiler feed 106 + Boiling points of 97 + Compressibility of 97 +Water feed, impurities in 100 + Methods of feeding to boiler 132 + Saving by heating 110 + Treatment (see Feed water). +Water-gas tar 225 + Heat of the liquid 120 + Path of, in Babcock & Wilcox boilers 57 + Properties of 96 + Records 293 + Specific heat of 99 + Volume of 96 + Weight of 96, 120 +Watt, James 17 +Weathering of coal 169 +Webster furnace 55 +Weight of air 147 +Wilcox boiler 25 +Wood, combustion of dry 202 + Wet 203 + Composition and heat value of 201 + Furnace design for 201 + Moisture in 201 + Sawmill refuse 202 +Woolf s boiler 24 +Zero, absolute 81 + + + + +FOOTNOTES + + +[Footnote 1: See discussion by George H. Babcock, of Stirling's paper on +"Water-tube and Shell Boilers", in Transactions, American Society of +Mechanical Engineers, Volume VI., Page 601.] + +[Footnote 2: When one temperature alone is given the "true" specific +heat is given; otherwise the value is the "mean" specific heat for the +range of temperature given.] + +[Footnote 3: For variation, see Table 13.] + +[Footnote 4: Where range of temperature is given, coefficient is mean +over range.] + +[Footnote 5: Coefficient of cubical expansion.] + +[Footnote 6: Le Chatelier's Investigations.] + +[Footnote 7: Burgess-Le Chatelier.] + +[Footnote 8: For accuracy of high temperature measurements, see Table +7.] + +[Footnote 9: Messrs. White & Taylor Trans. A. S. M. E., Vol. XXI, 1900.] + +[Footnote 10: See Scientific American Supplement, 624, 625, December, +1887.] + +[Footnote 11: 460 degrees below the zero of Fahrenheit. This is the +nearest approximation in whole degrees to the latest determinations of +the absolute zero of temperature] + +[Footnote 12: Marks and Davis] + +[Footnote 13: See page 120.] + +[Footnote 14: See Trans., A. S. M. E., Vol. XIV., Page 79.] + +[Footnote 15: Some waters, not naturally acid, become so at high +temperatures, as when chloride of magnesia decomposes with the formation +of free hydrochloride acid; such phenomena become more serious with an +increase in pressure and temperature.] + +[Footnote 16: L. M. Booth Company.] + +[Footnote 17: Based on lime containing 90 per cent calcium oxide.] + +[Footnote 18: Based on soda containing 58 per cent sodium oxide.] + +[Footnote 19: See Stem Correction, page 80.] + +[Footnote 20: See pages 125 to 127.] + +[Footnote 21: The actual specific heat at a particular temperature and +pressure is that corresponding to a change of one degree one way or the +other and differs considerably from the average value for the particular +temperature and pressure given in the table. The mean values given in +the table give correct results when employed to determine the factor of +evaporation whereas the actual values at the particular temperatures and +pressures would not.] + +[Footnote 22: See page 117.] + +[Footnote 23: Ratio by weight of O to N in air.] + +[Footnote 24: 4.32 pounds of air contains one pound of O.] + +[Footnote 25: Per pound of C in the CO.] + +[Footnote 26: Ratio by volume of O to N in air.] + +[Footnote 27: Available hydrogen.] + +[Footnote 28: See Table 31, page 151.] + +[Footnote 29: This formula is equivalent to (10) given in chapter on +combustion. 34.56 = theoretical air required for combustion of one pound +of H (see Table 31).] + +[Footnote 30: For degree of accuracy of this formula, see Transactions, +A. S. M. E., Volume XXI, 1900, page 94.] + +[Footnote 31: For loss per pound of coal multiply by per cent of carbon +in coal by ultimate analysis.] + +[Footnote 32: For loss per pound of coal multiply by per cent of carbon +in coal by ultimate analysis.] + +[Footnote 33: The Panther Creek District forms a part of what is known +as the Southern Field; in the matter of hardness, however, these coals +are more nearly akin to Lehigh coals.] + +[Footnote 34: Sometimes called Western Middle or Northern Schuylkill +Field.] + +[Footnote 35: Geographically, the Shamokin District is part of the +Western Middle Mahanoy Field, but the coals found in this section +resemble more closely those of the Wyoming Field.] + +[Footnote 36: See page 161.] + +[Footnote 37: U. S. Geological Survey.] + +[Footnote 38: See "Steam Boiler Economy", page 47, First Edition.] + +[Footnote 39: To agree with Pfaundler's formula the end ordinates should +be given half values in determining T", _i. e._, T" = ((Temp. at B + +Temp. at C) ÷ 2 + Temp. all other ordinates) ÷ N] + +[Footnote 40: B. t. u. calculated.] + +[Footnote 41: Average of two samples.] + +[Footnote 42: Assuming bagasse temperature = 80 degrees Fahrenheit and +exit gas temperature = 500 degrees Fahrenheit.] + +[Footnote 43: Dr. Henry C. Sherman. Columbia University.] + +[Footnote 44: Includes N.] + +[Footnote 45: Includes silt.] + +[Footnote 46: Net efficiency = gross efficiency less 2 per cent for +steam used in atomizing oil. + +Heat value of oil = 18500 B. t. u. + +One ton of coal weighs 2000 pounds. One barrel of oil weighs 336 pounds. +One gallon of oil weighs 8 pounds.] + +[Footnote 47: Average of 20 samples.] + +[Footnote 48: Includes H and CH_{4}.] + +[Footnote 49: B. t. u. approximate. For method of calculation, see page +175.] + +[Footnote 50: Temperatures are average over one cycle of operation and +may vary widely as to maximum and minimum.] + +[Footnote 51: Dependant upon length of kiln.] + +[Footnote 52: Results secured by this method will be approximately +correct.] + +[Footnote 53: See "Chimneys for Crude Oil", C. R. Weymouth, Trans. +A. S. M. E., Dec. 1912.] + +[Footnote 54: To determine the portion of the fuel which is actually +burned, the weight of ashes should be computed from the total weight of +coal burned and the coal and ash analyses in order to allow for any ash +that may be blown away with the flue gases. In many cases the ash so +computed is considerably higher than that found in the test.] + +[Footnote 55: As distinguished from the efficiency of boiler, furnace +and grate.] + +[Footnote 56: To obtain the efficiency of the boiler as an absorber of +the heat contained in the hot gases, this should be the heat generated +per pound of combustible corrected so that any heat lost through +incomplete combustion will not be charged to the boiler. This, however, +does not eliminate the furnace as the presence of excess air in the +gases lowers the efficiency and the ability to run without excess air +depends on the design and operation of the furnace. The efficiency based +on the total heat value per pound of combustible is, however, ordinarily +taken as the efficiency of the boiler notwithstanding the fact that it +necessarily involves the furnace.] + +[Footnote 57: See pages 280 and 281.] + +[Footnote 58: Where the horse power of marine boilers is stated, it +generally refers to and is synonymous with the horse power developed by +the engines which they serve.] + +[Footnote 59: In other countries, boilers are ordinarily rated not in +horse power but by specifying the quantity of water they are capable of +evaporating from and at 212 degrees or under other conditions.] + +[Footnote 60: See equivalent evaporation from and at 212 degrees, page +116.] + +[Footnote 61: The recommendations are those made in the preliminary +report of the Committee on Power Tests and at the time of going to press +have not been finally accepted by the Society as a whole.] + +[Footnote 62: This code relates primarily to tests made with coal.] + +[Footnote 63: The necessary apparatus and instruments are described +elsewhere. No definite rules can be given for location of instruments. +For suggestions on location, see A. S. M. E. Code of 1912, Appendix 24. +For calibration of instruments, see Code, Vol. XXXIV, Trans., +A. S. M. E., pages 1691-1702 and 1713-14.] + +[Footnote 64: One to two inches for small anthracite coals.] + +[Footnote 65: Do not blow down the water-glass column for at least one +hour before these readings are taken. An erroneous indication may +otherwise be caused by a change of temperature and density of the water +within the column and connecting pipe.] + +[Footnote 66: Do not blow down the water-glass column for at least one +hour before these readings are taken. An erroneous indication may +otherwise be caused by a change of temperature and density of the water +within the column and connecting pipe.] + +[Footnote 67: For calculations relating to quality of steam, see page +129.] + +[Footnote 68: Where the coal is very moist, a portion of the moisture +will cling to the walls of the jar, and in such case the jar and fuel +together should be dried out in determining the total moisture.] + +[Footnote 69: Say ½ ounce to 2 ounces.] + +[Footnote 70: For methods of analysis, see page 176.] + +[Footnote 71: For suggestions relative to Smoke Observations, see +A. S. M. E. Code of 1912, Appendix 16 and 17.] + +[Footnote 72: The term "as fired" means actual condition including +moisture, corrected for estimated difference in weight of coal on the +grate at beginning and end.] + +[Footnote 73: Corrected for inequality of water level and steam pressure +at beginning and end.] + +[Footnote 74: See Transactions, A. S. M. E., Volume XXXIII, 1912.] + +[Footnote 75: For methods of determining, see Technologic Paper No. 7, +Bureau of Standards, page 44.] + +[Footnote 76: Often called extra heavy pipe.] + +[Footnote 77: See Feed Piping, page 312.] + +[Footnote 78: See Superheat Chapter, page 145.] + +[Footnote 79: See Radiation from Steam Lines, page 314.] + +[Footnote 80: D, the density, is taken as the mean of the density at the +initial and final pressures.] + +[Footnote 81: Diameters up to 5 inches, inclusive, are _actual_ +diameters of standard pipe, see Table 62, page 308.] + +[Footnote 82: Diameters up to 4 inches, inclusive, are _actual_ internal +diameters, see Table 62, page 308.] + +[Footnote 83: H. P. Jordan, "Proceedings of the Institute of Mechanical +Engineers", 1909.] + +[Footnote 84: "Zeitschrift des Vereines Deutscher Ingenieur", 1909, page +1750.] + +[Footnote 85: Heinrich Gröber--Zeit. d. Ver. Ing., March 1912, December +1912. Leprince-Ringuet--Revue de Mecanique. July 1911. John Perry--"The +Steam Engine". T. E. Stanton--Philosophical Transactions, 1897. Dr. +J. T. Nicholson--Proceedings Institute of Engineers & Shipbuilders in +Scotland, 1910. W. E. Dally--Proceedings Institute of Mechanical +Engineers, 1909.] + +[Footnote 86: Proceedings Royal Society, Vol. LXXI.] + +[Footnote 87: Zeitschrift des Vereines Deutscher Ingenieur, 1910, page +1154.] + +[Footnote 88: Proceedings Institute of Engineers and Shipbuilders, +1910.] + +[Footnote 89: Natural or Hyperbolic Logarithm.] + + + + + + +End of the Project Gutenberg EBook of Steam, Its Generation and Use, by +Babcock & Wilcox Co. + +*** END OF THIS PROJECT GUTENBERG EBOOK STEAM, ITS GENERATION AND USE *** + +***** This file should be named 22657-8.txt or 22657-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/2/6/5/22657/ + +Produced by Juliet Sutherland, Tony Browne, and the Online +Distributed Proofreading Team at http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Steam, Its Generation and Use + +Author: Babcock & Wilcox Co. + +Release Date: September 18, 2007 [EBook #22657] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK STEAM, ITS GENERATION AND USE *** + + + + +Produced by Juliet Sutherland, Tony Browne, and the Online +Distributed Proofreading Team at http://www.pgdp.net + + + + + + + + + +STEAM + +ITS GENERATION AND USE + +[Illustration] + +THE BABCOCK & WILCOX CO. +NEW YORK + + + + +Thirty-fifth Edition + +4th Issue + +Copyright, 1919, by The Babcock & Wilcox Co. + + * * * * * + +Bartlett Orr Press + +New York + + + + +THE BABCOCK & WILCOX CO. + +85 LIBERTY STREET, NEW YORK, U. S. A. + +_Works_ + +BAYONNE NEW JERSEY +BARBERTON OHIO + +_Officers_ + +W. D. HOXIE, _President_ +E. H. WELLS, _Chairman of the Board_ +A. G. PRATT, _Vice-President_ + +_Branch Offices_ + +ATLANTA Candler Building +BOSTON 35 Federal Street +CHICAGO Marquette Building +CINCINNATI Traction Building +CLEVELAND New Guardian Building +DENVER 435 Seventeenth Street +HAVANA, CUBA 104 Calle de Aguiar +HOUSTON Southern Pacific Building +LOS ANGELES I. N. Van Nuy's Building +NEW ORLEANS Shubert Arcade +PHILADELPHIA North American Building +PITTSBURGH Farmers' Deposit Bank Building +SALT LAKE CITY Kearns Building +SAN FRANCISCO Sheldon Building +SEATTLE L. C. Smith Building +TUCSON, ARIZ. Santa Rita Hotel Building +SAN JUAN, PORTO RICO Royal Bank Building + +_Export Department, New York: Alberto de Verastegni, Director_ + +TELEGRAPHIC ADDRESS: FOR NEW YORK, "GLOVEBOXES" +FOR HAVANA, "BABCOCK" + +[Illustration: Works of The Babcock & Wilcox Co., at Bayonne, New Jersey] + +[Illustration: Works of The Babcock & Wilcox Co., at Barberton, Ohio] + +[Illustration: Works of Babcock & Wilcox, Limited, Renfrew, SCOTLAND] + + + + +BABCOCK & WILCOX Limited + +ORIEL HOUSE, FARRINGDON STREET, LONDON, E. C. +WORKS: RENFREW, SCOTLAND + +_Directors_ + +JOHN DEWRANCE, _Chairman_ CHARLES A. KNIGHT +ARTHUR T. SIMPSON J. H. R. KEMNAL +WILLIAM D. HOXIE _Managing Director_ +E. H. WELLS WALTER COLLS, _Secretary_ + +_Branch Offices in Great Britain_ + +GLASGOW: 29 St. Vincent Place +BIRMINGHAM: Winchester House +CARDIFF: 129 Bute Street +BELFAST: Ocean Buildings, Donegal Square, E. +MANCHESTER: 30 Cross Street +MIDDLESBROUGH: The Exchange +NEWCASTLE: 42 Westgate Road +SHEFFIELD: 14 Bank Chambers, Fargate + +_Offices Abroad_ + +BOMBAY: Wheeler's Building, Hornby Road, Fort +BRUSSELS: 187 Rue Royal +BILBAO: 1 Plaza de Albia +CALCUTTA: Clive Building +JOHANNESBURG: Consolidated Buildings +LIMA: Peru +LISBON: 84-86 Rua do Commercio +MADRID: Ventura de la Vega +MELBOURNE: 9 William Street +MEXICO: 22-23 Tiburcio +MILAN: 22 Via Principe Umberto +MONTREAL: College Street, St. Henry +NAPLES: 107 Via Santa Lucia +SHANGHAI: 1a Jinkee Road +SYDNEY: 427-429 Sussex Street +TOKYO: Japan +TORONTO: Traders' Bank Building + +_Representatives and Licensees in_ + +ADELAIDE, South Australia +ATHENS, Greece +AUCKLAND, New Zealand +BAHIA, Brazil +BANGKOK, Siam +BARCELONA, Spain +BRUNN, Austria +BUCHAREST, Roumania +BUDAPEST, Hungary +BUENOS AYRES, Argentine Rep. +CAIRO, Egypt +CHILE, Valparaiso, So. America +CHRISTIANIA, Norway +COLOMBO, Ceylon +COPENHAGEN, Denmark +ESKILSTUNA, Sweden +GIJON, Spain +HELSINGFORS, Finland +HENGELO, Holland +KIMBERLEY, South Africa +MOSCOW, Russia +PERTH, Western Australia +POLAND, Berlin +RANGOON, Burma +RIO DE JANEIRO, Brazil +SMYRNA, Asia Minor +SOURABAYA, Java +ST. PETERSBURG, Russia +TAMMERFORS, Finland +THE HAGUE, Holland + +TELEGRAPHIC ADDRESS FOR ALL OFFICES EXCEPT BOMBAY AND CALCUTTA: "BABCOCK" +FOR BOMBAY AND CALCUTTA: "BOILER" + +[Illustration: Fonderies et Ateliers de la Courneuve, Chaudieres Babcock +& Wilcox, Paris, France] + + + + +FONDERIES ET ATELIERS DE LA COURNEUVE +CHAUDIERES + +BABCOCK & WILCOX + +6 RUE LAFERRIERE, PARIS + +WORKS: SEINE--LA COURNEUVE + +_Directors_ + +EDMOND DUPUIS J. H. R. KEMNAL +ETIENNE BESSON IRENEE CHAVANNE +CHARLES A. KNIGHT JULES LEMAIRE + +_Branch Offices_ + +BORDEAUX: 30 Boulevard Antoine Gautier +LILLE: 23 Rue Faidherbe +LYON: 28 Quai de la Guillotier +MARSEILLE: 21 Cours Devilliers +MONTPELLIER: 1 Rue Boussairolles +NANCY: 2 Rue de Lorraine +ST. ETIENNE: 13 Rue de la Bourse + +REPRESENTATIVE FOR SWITZERLAND: SPOERRI & CIE, ZURICH + +TELEGRAPHIC ADDRESS: "BABCOCK-PARIS" + +[Illustration: Wrought-steel Vertical Header Longitudinal Drum +Babcock & Wilcox Boiler, Equipped with Babcock & Wilcox Superheater and +Babcock & Wilcox Chain Grate Stoker] + + + + +THE EARLY HISTORY OF THE GENERATION AND USE OF STEAM + + +While the time of man's first knowledge and use of the expansive force +of the vapor of water is unknown, records show that such knowledge +existed earlier than 150 B. C. In a treatise of about that time entitled +"Pneumatica", Hero, of Alexander, described not only existing devices of +his predecessors and contemporaries but also an invention of his own +which utilized the expansive force of steam for raising water above its +natural level. He clearly describes three methods in which steam might +be used directly as a motive of power; raising water by its elasticity, +elevating a weight by its expansive power and producing a rotary motion +by its reaction on the atmosphere. The third method, which is known as +"Hero's engine", is described as a hollow sphere supported over a +caldron or boiler by two trunnions, one of which was hollow, and +connected the interior of the sphere with the steam space of the +caldron. Two pipes, open at the ends and bent at right angles, were +inserted at opposite poles of the sphere, forming a connection between +the caldron and the atmosphere. Heat being applied to the caldron, the +steam generated passed through the hollow trunnion to the sphere and +thence into the atmosphere through the two pipes. By the reaction +incidental to its escape through these pipes, the sphere was caused to +rotate and here is the primitive steam reaction turbine. + +Hero makes no suggestions as to application of any of the devices he +describes to a useful purpose. From the time of Hero until the late +sixteenth and early seventeenth centuries, there is no record of +progress, though evidence is found that such devices as were described +by Hero were sometimes used for trivial purposes, the blowing of an +organ or the turning of a skillet. + +Mathesius, the German author, in 1571; Besson, a philosopher and +mathematician at Orleans; Ramelli, in 1588; Battista Delia Porta, a +Neapolitan mathematician and philosopher, in 1601; Decause, the French +engineer and architect, in 1615; and Branca, an Italian architect, in +1629, all published treatises bearing on the subject of the generation +of steam. + +To the next contributor, Edward Somerset, second Marquis of Worcester, +is apparently due the credit of proposing, if not of making, the first +useful steam engine. In the "Century of Scantlings and Inventions", +published in London in 1663, he describes devices showing that he had in +mind the raising of water not only by forcing it from two receivers by +direct steam pressure but also for some sort of reciprocating piston +actuating one end of a lever, the other operating a pump. His +descriptions are rather obscure and no drawings are extant so that it is +difficult to say whether there were any distinctly novel features to his +devices aside from the double action. While there is no direct authentic +record that any of the devices he described were actually constructed, +it is claimed by many that he really built and operated a steam engine +containing pistons. + +In 1675, Sir Samuel Moreland was decorated by King Charles II, for a +demonstration of "a certain powerful machine to raise water." Though +there appears to be no record of the design of this machine, the +mathematical dictionary, published in 1822, credits Moreland with the +first account of a steam engine, on which subject he wrote a treatise +that is still preserved in the British Museum. + +[Illustration: 397 Horse-power Babcock & Wilcox Boiler in Course of +Erection at the Plant of the Crocker Wheeler Co., Ampere, N. J.] + +Dr. Denys Papin, an ingenious Frenchman, invented in 1680 "a steam +digester for extracting marrowy, nourishing juices from bones by +enclosing them in a boiler under heavy pressure," and finding danger +from explosion, added a contrivance which is the first safety valve on +record. + +The steam engine first became commercially successful with Thomas +Savery. In 1699, Savery exhibited before the Royal Society of England +(Sir Isaac Newton was President at the time), a model engine which +consisted of two copper receivers alternately connected by a three-way +hand-operated valve, with a boiler and a source of water supply. When +the water in one receiver had been driven out by the steam, cold water +was poured over its outside surface, creating a vacuum through +condensation and causing it to fill again while the water in the other +reservoir was being forced out. A number of machines were built on this +principle and placed in actual use as mine pumps. + +The serious difficulty encountered in the use of Savery's engine was the +fact that the height to which it could lift water was limited by the +pressure the boiler and vessels could bear. Before Savery's engine was +entirely displaced by its successor, Newcomen's, it was considerably +improved by Desaguliers, who applied the Papin safety valve to the +boiler and substituted condensation by a jet within the vessel for +Savery's surface condensation. + +In 1690, Papin suggested that the condensation of steam should be +employed to make a vacuum beneath a cylinder which had previously been +raised by the expansion of steam. This was the earliest cylinder and +piston steam engine and his plan took practical shape in Newcomen's +atmospheric engine. Papin's first engine was unworkable owing to the +fact that he used the same vessel for both boiler and cylinder. A small +quantity of water was placed in the bottom of the vessel and heat was +applied. When steam formed and raised the piston, the heat was withdrawn +and the piston did work on its down stroke under pressure of the +atmosphere. After hearing of Savery's engine, Papin developed an +improved form. Papin's engine of 1705 consisted of a displacement +chamber in which a floating diaphragm or piston on top of the water kept +the steam and water from direct contact. The water delivered by the +downward movement of the piston under pressure, to a closed tank, flowed +in a continuous stream against the vanes of a water wheel. When the +steam in the displacement chamber had expanded, it was exhausted to the +atmosphere through a valve instead of being condensed. The engine was, +in fact, a non-condensing, single action steam pump with the steam and +pump cylinders in one. A curious feature of this engine was a heater +placed in the diaphragm. This was a mass of heated metal for the purpose +of keeping the steam dry or preventing condensation during expansion. +This device might be called the first superheater. + +Among the various inventions attributed to Papin was a boiler with an +internal fire box, the earliest record of such construction. + +While Papin had neglected his earlier suggestion of a steam and piston +engine to work on Savery's ideas, Thomas Newcomen, with his assistant, +John Cawley, put into practical form Papin's suggestion of 1690. Steam +admitted from the boiler to a cylinder raised a piston by its expansion, +assisted by a counter-weight on the other end of a beam actuated by the +piston. The steam valve was then shut and the steam condensed by a jet +of cold water. The piston was then forced downward by atmospheric +pressure and did work on the pump. The condensed water in the cylinder +was expelled through an escapement valve by the next entry of steam. +This engine used steam having pressure but little, if any, above that of +the atmosphere. + +[Illustration: Two Units of 8128 Horse Power of Babcock & Wilcox Boilers +and Superheaters at the Fisk Street Station of the Commonwealth Edison +Co., Chicago, Ill., 50,400 Horse Power being Installed in this Station. +The Commonwealth Edison Co. Operates in its Various Stations a Total of +86,000 Horse Power of Babcock & Wilcox Boilers, all Fitted with Babcock +& Wilcox Superheaters and Equipped with Babcock & Wilcox Chain Grate +Stokers] + +In 1711, this engine was introduced into mines for pumping purposes. +Whether its action was originally automatic or whether dependent upon +the hand operation of the valves is a question of doubt. The story +commonly believed is that a boy, Humphrey Potter, in 1713, whose duty it +was to open and shut such valves of an engine he attended, by suitable +cords and catches attached to the beam, caused the engine to +automatically manipulate these valves. This device was simplified in +1718 by Henry Beighton, who suspended from the bottom, a rod called the +plug-tree, which actuated the valve by tappets. By 1725, this engine was +in common use in the collieries and was changed but little for a matter +of sixty or seventy years. Compared with Savery's engine, from the +aspect of a pumping engine, Newcomen's was a distinct advance, in that +the pressure in the pumps was in no manner dependent upon the steam +pressure. In common with Savery's engine, the losses from the alternate +heating and cooling of the steam cylinder were enormous. Though +obviously this engine might have been modified to serve many purposes, +its use seems to have been limited almost entirely to the pumping of +water. + +The rivalry between Savery and Papin appears to have stimulated +attention to the question of fuel saving. Dr. John Allen, in 1730, +called attention to the fact that owing to the short length of time of +the contact between the gases and the heating surfaces of the boiler, +nearly half of the heat of the fire was lost. With a view to overcoming +this loss at least partially, he used an internal furnace with a smoke +flue winding through the water in the form of a worm in a still. In +order that the length of passage of the gases might not act as a damper +on the fire, Dr. Allen recommended the use of a pair of bellows for +forcing the sluggish vapor through the flue. This is probably the first +suggested use of forced draft. In forming an estimate of the quantity of +fuel lost up the stack, Dr. Allen probably made the first boiler test. + +Toward the end of the period of use of Newcomen's atmospheric engine, +John Smeaton, who, about 1770, built and installed a number of large +engines of this type, greatly improved the design in its mechanical +details. + +[Illustration: Erie County Electric Co., Erie, Pa., Operating 3082 Horse +Power of Babcock & Wilcox Boilers and Superheaters, Equipped with +Babcock & Wilcox Chain Grate Stokers] + +The improvement in boiler and engine design of Smeaton, Newcomen and +their contemporaries, were followed by those of the great engineer, +James Watt, an instrument maker of Glasgow. In 1763, while repairing a +model of Newcomen's engine, he was impressed by the great waste of steam +to which the alternating cooling and heating of the engine gave rise. +His remedy was the maintaining of the cylinder as hot as the entering +steam and with this in view he added a vessel separate from the +cylinder, into which the steam should pass from the cylinder and be +there condensed either by the application of cold water outside or by a +jet from within. To preserve a vacuum in his condenser, he added an air +pump which should serve to remove the water of condensation and air +brought in with the injection water or due to leakage. As the cylinder +no longer acted as a condenser, he could maintain it at a high +temperature by covering it with non-conducting material and, in +particular, by the use of a steam jacket. Further and with the same +object in view, he covered the top of the cylinder and introduced steam +above the piston to do the work previously accomplished by atmospheric +pressure. After several trials with an experimental apparatus based on +these ideas, Watt patented his improvements in 1769. Aside from their +historical importance, Watt's improvements, as described in his +specification, are to this day a statement of the principles which guide +the scientific development of the steam engine. His words are: + + "My method of lessening the consumption of steam, and + consequently fuel, in fire engines, consists of the following + principles: + + "First, That vessel in which the powers of steam are to be + employed to work the engine, which is called the cylinder in + common fire engines, and which I call the steam vessel, must, + during the whole time the engine is at work, be kept as hot as + the steam that enters it; first, by enclosing it in a case of + wood, or any other materials that transmit heat slowly; + secondly, by surrounding it with steam or other heated bodies; + and, thirdly, by suffering neither water nor any other substance + colder than the steam to enter or touch it during that time. + + "Secondly, In engines that are to be worked wholly or partially + by condensation of steam, the steam is to be condensed in + vessels distinct from the steam vessels or cylinders, although + occasionally communicating with them; these vessels I call + condensers; and, whilst the engines are working, these + condensers ought at least to be kept as cold as the air in the + neighborhood of the engines, by application of water or other + cold bodies. + + "Thirdly, Whatever air or other elastic vapor is not condensed + by the cold of the condenser, and may impede the working of the + engine, is to be drawn out of the steam vessels or condensers by + means of pumps, wrought by the engines themselves, or otherwise. + + "Fourthly, I intend in many cases to employ the expansive force + of steam to press on the pistons, or whatever may be used + instead of them, in the same manner in which the pressure of the + atmosphere is now employed in common fire engines. In cases + where cold water cannot be had in plenty, the engines may be + wrought by this force of steam only, by discharging the steam + into the air after it has done its office.... + + "Sixthly, I intend in some cases to apply a degree of cold not + capable of reducing the steam to water, but of contracting it + considerably, so that the engines shall be worked by the + alternate expansion and contraction of the steam. + + "Lastly, Instead of using water to render the pistons and other + parts of the engine air and steam tight, I employ oils, wax, + resinous bodies, fat of animals, quick-silver and other metals + in their fluid state." + +The fifth claim was for a rotary engine, and need not be quoted here. + +The early efforts of Watt are typical of those of the poor inventor +struggling with insufficient resources to gain recognition and it was +not until he became associated with the wealthy manufacturer, Mattheu +Boulton of Birmingham, that he met with the success upon which his +present fame is based. In partnership with Boulton, the business of the +manufacture and the sale of his engines were highly successful in spite +of vigorous attacks on the validity of his patents. + +Though the fourth claim of Watt's patent describes a non-condensing +engine which would require high pressures, his aversion to such practice +was strong. Notwithstanding his entire knowledge of the advantages +through added expansion under high pressure, he continued to use +pressures not above 7 pounds per square inch above the atmosphere. To +overcome such pressures, his boilers were fed through a stand-pipe of +sufficient height to have the column of water offset the pressure within +the boiler. Watt's attitude toward high pressure made his influence felt +long after his patents had expired. + +[Illustration: Portion of 9600 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain +Grate Stokers at the Blue Island, Ill., Plant of the Public Service Co. +of Northern Illinois. This Company Operates 14,580 Horse Power of +Babcock & Wilcox Boilers and Superheaters in its Various Stations] + +In 1782, Watt patented two other features which he had invented as early +as 1769. These were the double acting engine, that is, the use of steam +on both sides of the piston and the use of steam expansively, that is, +the shutting off of steam from the cylinder when the piston had made but +a portion of its stroke, the power for the completion of the stroke +being supplied by the expansive force of the steam already admitted. + +He further added a throttle valve for the regulation of steam admission, +invented the automatic governor and the steam indicator, a mercury steam +gauge and a glass water column. + +It has been the object of this brief history of the early developments +in the use of steam to cover such developments only through the time of +James Watt. The progress of the steam engine from this time through the +stages of higher pressures, combining of cylinders, the application of +steam vehicles and steamboats, the adding of third and fourth cylinders, +to the invention of the turbine with its development and the +accompanying development of the reciprocating engine to hold its place, +is one long attribute to the inventive genius of man. + +While little is said in the biographies of Watt as to the improvement of +steam boilers, all the evidence indicates that Boulton and Watt +introduced the first "wagon boiler", so called because of its shape. In +1785, Watt took out a number of patents for variations in furnace +construction, many of which contain the basic principles of some of the +modern smoke preventing furnaces. Until the early part of the nineteenth +century, the low steam pressures used caused but little attention to be +given to the form of the boiler operated in connection with the engines +above described. About 1800, Richard Trevithick, in England, and Oliver +Evans, in America, introduced non-condensing, and for that time, high +pressure steam engines. To the initiative of Evans may be attributed the +general use of high pressure steam in the United States, a feature which +for many years distinguished American from European practice. The demand +for light weight and economy of space following the beginning of steam +navigation and the invention of the locomotive required boilers designed +and constructed to withstand heavier pressures and forced the adoption +of the cylindrical form of boiler. There are in use to-day many examples +of every step in the development of steam boilers from the first plain +cylindrical boiler to the most modern type of multi-tubular locomotive +boiler, which stands as the highest type of fire-tube boiler +construction. + +The early attempts to utilize water-tube boilers were few. A brief +history of the development of the boilers, in which this principle was +employed, is given in the following chapter. From this history it will +be clearly indicated that the first commercially successful utilization +of water tubes in a steam generator is properly attributed to George H. +Babcock and Stephen Wilcox. + +[Illustration: Copyright by Underwood & Underwood + +Woolworth Building, New York City, Operating 2454 Horse Power of +Babcock & Wilcox Boilers] + + + + +BRIEF HISTORY OF WATER-TUBE BOILERS[1] + + +As stated in the previous chapter, the first water-tube boiler was built +by John Blakey and was patented by him in 1766. Several tubes +alternately inclined at opposite angles were arranged in the furnaces, +the adjacent tube ends being connected by small pipes. The first +successful user of water-tube boilers, however, was James Rumsey, an +American inventor, celebrated for his early experiments in steam +navigation, and it is he who may be truly classed as the originator of +the water-tube boiler. In 1788 he patented, in England, several forms of +boilers, some of which were of the water-tube type. One had a fire box +with flat top and sides, with horizontal tubes across the fire box +connecting the water spaces. Another had a cylindrical fire box +surrounded by an annular water space and a coiled tube was placed within +the box connecting at its two ends with the water space. This was the +first of the "coil boilers". Another form in the same patent was the +vertical tubular boiler, practically as made at the present time. + +[Illustration: Blakey, 1766] + +The first boiler made of a combination of small tubes, connected at one +end to a reservoir, was the invention of another American, John Stevens, +in 1804. This boiler was actually employed to generate steam for running +a steamboat on the Hudson River, but like all the "porcupine" boilers, +of which type it was the first, it did not have the elements of a +continued success. + +[Illustration: John Stevens, 1804] + +Another form of water tube was patented in 1805 by John Cox Stevens, a +son of John Stevens. This boiler consisted of twenty vertical tubes, 1-1/4 +inches internal diameter and 40-1/2 inches long, arranged in a circle, the +outside diameter of which was approximately 12 inches, connecting a +water chamber at the bottom with a steam chamber at the top. The steam +and water chambers were annular spaces of small cross section and +contained approximately 33 cubic inches. The illustration shows the cap +of the steam chamber secured by bolts. The steam outlet pipe "A" is a +pipe of one inch diameter, the water entering through a similar aperture +at the bottom. One of these boilers was for a long time at the Stevens +Institute of Technology at Hoboken, and is now in the Smithsonian +Institute at Washington. + +[Illustration: John Cox Stevens, 1805] + +About the same time, Jacob Woolf built a boiler of large horizontal +tubes, extending across the furnace and connected at the ends to a +longitudinal drum above. The first purely sectional water-tube boiler +was built by Julius Griffith, in 1821. In this boiler, a number of +horizontal water tubes were connected to vertical side pipes, the side +pipes were connected to horizontal gathering pipes, and these latter in +turn to a steam drum. + +In 1822, Jacob Perkins constructed a flash boiler for carrying what was +then considered a high pressure. A number of cast-iron bars having 1-1/2 +inches annular holes through them and connected at their outer ends by a +series of bent pipes, outside of the furnace walls, were arranged in +three tiers over the fire. The water was fed slowly to the upper tier by +a force pump and steam in the superheated state was discharged to the +lower tiers into a chamber from which it was taken to the engine. + +[Illustration: Joseph Eve, 1825] + +The first sectional water-tube boiler, with a well-defined circulation, +was built by Joseph Eve, in 1825. The sections were composed of small +tubes with a slight double curve, but being practically vertical, fixed +in horizontal headers, which headers were in turn connected to a steam +space above and a water space below formed of larger pipes. The steam +and water spaces were connected by outside pipes to secure a circulation +of the water up through the sections and down through the external +pipes. In the same year, John M'Curdy of New York, built a "Duplex Steam +Generator" of "tubes of wrought or cast iron or other material" arranged +in several horizontal rows, connected together alternately at the front +and rear by return bends. In the tubes below the water line were placed +interior circular vessels closed at the ends in order to expose a thin +sheet of water to the action of the fire. + +[Illustration: Gurney, 1826] + +In 1826, Goldsworthy Gurney built a number of boilers, which he used on +his steam carriages. A number of small tubes were bent into the shape of +a "U" laid sidewise and the ends were connected with larger horizontal +pipes. These were connected by vertical pipes to permit of circulation +and also to a vertical cylinder which served as a steam and water +reservoir. In 1828, Paul Steenstrup made the first shell boiler with +vertical water tubes in the large flues, similar to the boiler known as +the "Martin" and suggesting the "Galloway". + +The first water-tube boiler having fire tubes within water tubes was +built in 1830, by Summers & Ogle. Horizontal connections at the top and +bottom were connected by a series of vertical water tubes, through which +were fire tubes extending through the horizontal connections, the fire +tubes being held in place by nuts, which also served to make the joint. + +[Illustration: Stephen Wilcox, 1856] + +Stephen Wilcox, in 1856, was the first to use inclined water tubes +connecting water spaces at the front and rear with a steam space above. +The first to make such inclined tubes into a sectional form was Twibill, +in 1865. He used wrought-iron tubes connected at the front and rear with +standpipes through intermediate connections. These standpipes carried +the system to a horizontal cross drum at the top, the entrained water +being carried to the rear. + +Clarke, Moore, McDowell, Alban and others worked on the problem of +constructing water-tube boilers, but because of difficulties of +construction involved, met with no practical success. + +[Illustration: Twibill, 1865] + +It may be asked why water-tube boilers did not come into more general +use at an early date, that is, why the number of water-tube boilers +built was so small in comparison to the number of shell boilers. The +reason for this is found in the difficulties involved in the design and +construction of water-tube boilers, which design and construction +required a high class of engineering and workmanship, while the plain +cylindrical boiler is comparatively easy to build. The greater skill +required to make a water-tube boiler successful is readily shown in the +great number of failures in the attempts to make them. + +[Illustration: Partial View of 7000 Horse-power Installation of Babcock +& Wilcox Boilers at the Philadelphia, Pa., Plant of the Baldwin +Locomotive Works. This Company Operates in its Various Plants a Total of +9280 Horse Power of Babcock & Wilcox Boilers] + + + + +REQUIREMENTS OF STEAM BOILERS + + +Since the first appearance in "Steam" of the following "Requirements of +a Perfect Steam Boiler", the list has been copied many times either word +for word or clothed in different language and applied to some specific +type of boiler design or construction. In most cases, although full +compliance with one or more of the requirements was structurally +impossible, the reader was left to infer that the boiler under +consideration possessed all the desirable features. It is noteworthy +that this list of requirements, as prepared by George H. Babcock and +Stephen Wilcox, in 1875, represents the best practice of to-day. +Moreover, coupled with the boiler itself, which is used in the largest +and most important steam generating plants throughout the world, the +list forms a fitting monument to the foresight and genius of the +inventors. + + + +REQUIREMENTS OF A PERFECT STEAM BOILER + + +1st. Proper workmanship and simple construction, using materials which +experience has shown to be the best, thus avoiding the necessity of +early repairs. + + +2nd. A mud drum to receive all impurities deposited from the water, and +so placed as to be removed from the action of the fire. + + +3rd. A steam and water capacity sufficient to prevent any fluctuation in +steam pressure or water level. + + +4th. A water surface for the disengagement of the steam from the water, +of sufficient extent to prevent foaming. + + +5th. A constant and thorough circulation of water throughout the boiler, +so as to maintain all parts at the same temperature. + + +6th. The water space divided into sections so arranged that, should any +section fail, no general explosion can occur and the destructive effects +will be confined to the escape of the contents. Large and free passages +between the different sections to equalize the water line and pressure +in all. + + +7th. A great excess of strength over any legitimate strain, the boiler +being so constructed as to be free from strains due to unequal +expansion, and, if possible, to avoid joints exposed to the direct +action of the fire. + + +8th. A combustion chamber so arranged that the combustion of the gases +started in the furnace may be completed before the gases escape to the +chimney. + + +9th. The heating surface as nearly as possible at right angles to the +currents of heated gases, so as to break up the currents and extract the +entire available heat from the gases. + + +10th. All parts readily accessible for cleaning and repairs. This is a +point of the greatest importance as regards safety and economy. + + +11th. Proportioned for the work to be done, and capable of working to +its full rated capacity with the highest economy. + + +12th. Equipped with the very best gauges, safety valves and other +fixtures. + + +The exhaustive study made of each one of these requirements is shown by +the following extract from a lecture delivered by Mr. Geo. H. Babcock at +Cornell University in 1890 upon the subject: + + + +THE CIRCULATION OF WATER IN STEAM BOILERS + + +You have all noticed a kettle of water boiling over the fire, the fluid +rising somewhat tumultuously around the edges of the vessel, and +tumbling toward the center, where it descends. Similar currents are in +action while the water is simply being heated, but they are not +perceptible unless there are floating particles in the liquid. These +currents are caused by the joint action of the added temperature and two +or more qualities which the water possesses. + +1st. Water, in common with most other substances, expands when heated; a +statement, however, strictly true only when referred to a temperature +above 39 degrees F. or 4 degrees C., but as in the making of steam we +rarely have to do with temperatures so low as that, we may, for our +present purposes, ignore that exception. + +2nd. Water is practically a non-conductor of heat, though not entirely +so. If ice-cold water was kept boiling at the surface the heat would not +penetrate sufficiently to begin melting ice at a depth of 3 inches in +less than about two hours. As, therefore, the heated water cannot impart +its heat to its neighboring particles, it remains expanded and rises by +its levity, while colder portions come to be heated in turn, thus +setting up currents in the fluid. + +Now, when all the water has been heated to the boiling point +corresponding to the pressure to which it is subjected, each added unit +of heat converts a portion, about 7 grains in weight, into vapor, +greatly increasing its volume; and the mingled steam and water rises +more rapidly still, producing ebullition such as we have noticed in the +kettle. So long as the quantity of heat added to the contents of the +kettle continues practically constant, the conditions remain similar to +those we noticed at first, a tumultuous lifting of the water around the +edges, flowing toward the center and thence downward; if, however, the +fire be quickened, the upward currents interfere with the downward and +the kettle boils over (Fig. 1). + +[Illustration: Fig. 1] + +If now we put in the kettle a vessel somewhat smaller (Fig. 2) with a +hole in the bottom and supported at a proper distance from the side so +as to separate the upward from the downward currents, we can force the +fires to a very much greater extent without causing the kettle to boil +over, and when we place a deflecting plate so as to guide the rising +column toward the center it will be almost impossible to produce that +effect. This is the invention of Perkins in 1831 and forms the basis of +very many of the arrangements for producing free circulation of the +water in boilers which have been made since that time. It consists in +dividing the currents so that they will not interfere each with the +other. + +[Illustration: Fig. 2] + +But what is the object of facilitating the circulation of water in +boilers? Why may we not safely leave this to the unassisted action of +nature as we do in culinary operations? We may, if we do not care for +the three most important aims in steam-boiler construction, namely, +efficiency, durability, and safety, each of which is more or less +dependent upon a proper circulation of the water. As for efficiency, we +have seen one proof in our kettle. When we provided means to preserve +the circulation, we found that we could carry a hotter fire and boil +away the water much more rapidly than before. It is the same in a steam +boiler. And we also noticed that when there was nothing but the +unassisted circulation, the rising steam carried away so much water in +the form of foam that the kettle boiled over, but when the currents were +separated and an unimpeded circuit was established, this ceased, and a +much larger supply of steam was delivered in a comparatively dry state. +Thus, circulation increases the efficiency in two ways: it adds to the +ability to take up the heat, and decreases the liability to waste that +heat by what is technically known as priming. There is yet another way +in which, incidentally, circulation increases efficiency of surface, and +that is by preventing in a greater or less degree the formation of +deposits thereon. Most waters contain some impurity which, when the +water is evaporated, remains to incrust the surface of the vessel. This +incrustation becomes very serious sometimes, so much so as to almost +entirely prevent the transmission of heat from the metal to the water. +It is said that an incrustation of only one-eighth inch will cause a +loss of 25 per cent in efficiency, and this is probably within the truth +in many cases. Circulation of water will not prevent incrustation +altogether, but it lessens the amount in all waters, and almost entirely +so in some, thus adding greatly to the efficiency of the surface. + +[Illustration: Fig. 3] + +A second advantage to be obtained through circulation is durability of +the boiler. This it secures mainly by keeping all parts at a nearly +uniform temperature. The way to secure the greatest freedom from unequal +strains in a boiler is to provide for such a circulation of the water as +will insure the same temperature in all parts. + +3rd. Safety follows in the wake of durability, because a boiler which is +not subject to unequal strains of expansion and contraction is not only +less liable to ordinary repairs, but also to rupture and disastrous +explosion. By far the most prolific cause of explosions is this same +strain from unequal expansions. + +[Illustration: Fig. 4] + +[Illustration: 386 Horse-power Installation of Babcock & Wilcox Boilers +at B. F. Keith's Theatre, Boston, Mass.] + +Having thus briefly looked at the advantages of circulation of water in +steam boilers, let us see what are the best means of securing it under +the most efficient conditions We have seen in our kettle that one +essential point was that the currents should be kept from interfering +with each other. If we could look into an ordinary return tubular boiler +when steaming, we should see a curious commotion of currents rushing +hither and thither, and shifting continually as one or the other +contending force gained a momentary mastery. The principal upward +currents would be found at the two ends, one over the fire and the other +over the first foot or so of the tubes. Between these, the downward +currents struggle against the rising currents of steam and water. At a +sudden demand for steam, or on the lifting of the safety valve, the +pressure being slightly reduced, the water jumps up in jets at every +portion of the surface, being lifted by the sudden generation of steam +throughout the body of water. You have seen the effect of this sudden +generation of steam in the well-known experiment with a Florence flask, +to which a cold application is made while boiling water under pressure +is within. You have also witnessed the geyser-like action when water is +boiled in a test tube held vertically over a lamp (Fig. 3). + +[Illustration: Fig. 5] + +If now we take a U-tube depending from a vessel of water (Fig. 4) and +apply the lamp to one leg a circulation is at once set up within it, and +no such spasmodic action can be produced. Thus U-tube is the +representative of the true method of circulation within a water-tube +boiler properly constructed. We can, for the purpose of securing more +heating surface, extend the heated leg into a long incline (Fig. 5), +when we have the well-known inclined-tube generator. Now, by adding +other tubes, we may further increase the heating surface (Fig. 6), while +it will still be the U-tube in effect and action. In such a construction +the circulation is a function of the difference in density of the two +columns. Its velocity is measured by the well-known Torricellian +formula, V = (2gh)^{.5}, or, approximately V = 8(h)^{.5}, h being measured +in terms of the lighter fluid. This velocity will increase until the +rising column becomes all steam, but the quantity or weight circulated +will attain a maximum when the density of the mingled steam and water in +the rising column becomes one-half that of the solid water in the +descending column which is nearly coincident with the condition of half +steam and half water, the weight of the steam being very slight compared +to that of the water. + +[Illustration: Fig. 6] + +It becomes easy by this rule to determine the circulation in any given +boiler built on this principle, provided the construction is such as to +permit a free flow of the water. Of course, every bend detracts a little +and something is lost in getting up the velocity, but when the boiler is +well arranged and proportioned these retardations are slight. + +Let us take for example one of the 240 horse-power Babcock & Wilcox +boilers here in the University. The height of the columns may be taken +as 4-1/2 feet, measuring from the surface of the water to about the center +of the bundle of tubes over the fire, and the head would be equal to +this height at the maximum of circulation. We should, therefore, have a +velocity of 8(4-1/2)^{.5} = 16.97, say 17 feet per second. There are in +this boiler fourteen sections, each having a 4-inch tube opening into the +drum, the area of which (inside) is 11 square inches, the fourteen +aggregating 154 square inches, or 1.07 square feet. This multiplied by +the velocity, 16.97 feet, gives 18.16 cubic feet mingled steam and water +discharged per second, one-half of which, or 9.08 cubic feet, is steam. +Assuming this steam to be at 100 pounds gauge pressure, it will weigh +0.258 pound per cubic foot. Hence, 2.34 pounds of steam will be +discharged per second, and 8,433 pounds per hour. Dividing this by 30, +the number of pounds representing a boiler horse power, we get 281.1 +horse power, about 17 per cent, in excess of the rated power of the +boiler. The water at the temperature of steam at 100 pounds pressure +weighs 56 pounds per cubic foot, and the steam 0.258 pound, so that the +steam forms but 1/218 part of the mixture by weight, and consequently +each particle of water will make 218 circuits before being evaporated +when working at this capacity, and circulating the maximum weight of +water through the tubes. + +[Illustration: A Portion of 9600 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters Being Erected at the South Boston, +Mass., Station of the Boston Elevated Railway Co. This Company Operates +in its Various Stations a Total of 46,400 Horse Power of Babcock & +Wilcox Boilers] + +[Illustration: Fig. 7] + +It is evident that at the highest possible velocity of exit from the +generating tubes, nothing but steam will be delivered and there will be +no circulation of water except to supply the place of that evaporated. +Let us see at what rate of steaming this would occur with the boiler +under consideration. We shall have a column of steam, say 4 feet high on +one side and an equal column of water on the other. Assuming, as before, +the steam at 100 pounds and the water at same temperature, we will have +a head of 866 feet of steam and an issuing velocity of 235.5 feet per +second. This multiplied by 1.07 square feet of opening by 3,600 seconds +in an hour, and by 0.258 gives 234,043 pounds of steam, which, though +only one-eighth the weight of mingled steam and water delivered at the +maximum, gives us 7,801 horse power, or 32 times the rated power of the +boiler. Of course, this is far beyond any possibility of attainment, so +that it may be set down as certain that this boiler cannot be forced to +a point where there will not be an efficient circulation of the water. +By the same method of calculation it may be shown that when forced to +double its rated power, a point rarely expected to be reached in +practice, about two-thirds the volume of mixture of steam and water +delivered into the drum will be steam, and that the water will make 110 +circuits while being evaporated. Also that when worked at only about +one-quarter its rated capacity, one-fifth of the volume will be steam +and the water will make the rounds 870 times before it becomes steam. +You will thus see that in the proportions adopted in this boiler there +is provision for perfect circulation under all the possible conditions +of practice. + +[Illustration: Fig. 8 [Developed to show Circulation]] + +In designing boilers of this style it is necessary to guard against +having the uptake at the upper end of the tubes too large, for if +sufficiently large to allow downward currents therein, the whole effect +of the rising column in increasing the circulation in the tubes is +nullified (Fig. 7). This will readily be seen if we consider the uptake +very large when the only head producing circulation in the tubes will be +that due to the inclination of each tube taken by itself. This objection +is only overcome when the uptake is so small as to be entirely filled +with the ascending current of mingled steam and water. It is also +necessary that this uptake should be practically direct, and it should +not be composed of frequent enlargements and contractions. Take, for +instance, a boiler well known in Europe, copied and sold here under +another name. It is made up of inclined tubes secured by pairs into +boxes at the ends, which boxes are made to communicate with each other +by return bends opposite the ends of the tubes. These boxes and return +bends form an irregular uptake, whereby the steam is expected to rise to +a reservoir above. You will notice (Fig. 8) that the upward current of +steam and water in the return bend meets and directly antagonizes the +upward current in the adjoining tube. Only one result can follow. If +their velocities are equal, the momentum of both will be neutralized and +all circulation stopped, or, if one be stronger, it will cause a back +flow in the other by the amount of difference in force, with practically +the same result. + +[Illustration: 4880 Horse-power Installation of Babcock & Wilcox Boilers +at the Open Hearth Plant of the Cambria Steel Co., Johnstown, Pa. This +Company Operates a Total of 52,000 Horse Power of Babcock & Wilcox +Boilers] + +[Illustration: Fig. 9] + +In a well-known boiler, many of which were sold, but of which none are +now made and a very few are still in use, the inventor claimed that the +return bends and small openings against the tubes were for the purpose +of "restricting the circulation" and no doubt they performed well that +office; but excepting for the smallness of the openings they were not as +efficient for that purpose as the arrangement shown in Fig. 8. + +[Illustration: Fig. 10] + +Another form of boiler, first invented by Clarke or Crawford, and lately +revived, has the uptake made of boxes into which a number, generally +from two to four tubes, are expanded, the boxes being connected together +by nipples (Fig. 9). It is a well-known fact that where a fluid flows +through a conduit which enlarges and then contracts, the velocity is +lost to a greater or less extent at the enlargements, and has to be +gotten up again at the contractions each time, with a corresponding loss +of head. The same thing occurs in the construction shown in Fig. 9. The +enlargements and contractions quite destroy the head and practically +overcome the tendency of the water to circulate. + +A horizontal tube stopped at one end, as shown in Fig. 10, can have no +proper circulation within it. If moderately driven, the water may +struggle in against the issuing steam sufficiently to keep the surface +covered, but a slight degree of forcing will cause it to act like the +test tube in Fig. 3, and the more there are of them in a given boiler +the more spasmodic will be its working. + +The experiment with our kettle (Fig. 2) gives the clue to the best means +of promoting circulation in ordinary shell boilers. Steenstrup or +"Martin" and "Galloway" water tubes placed in such boilers also assist +in directing the circulation therein, but it is almost impossible to +produce in shell boilers, by any means the circulation of all the water +in one continuous round, such as marks the well-constructed water-tube +boiler. + +As I have before remarked, provision for a proper circulation of water +has been almost universally ignored in designing steam boilers, +sometimes to the great damage of the owner, but oftener to the jeopardy +of the lives of those who are employed to run them. The noted case of +the Montana and her sister ship, where some $300,000 was thrown away in +trying an experiment which a proper consideration of this subject would +have avoided, is a case in point; but who shall count the cost of life +and treasure not, perhaps, directly traceable to, but, nevertheless, due +entirely to such neglect in design and construction of the thousands of +boilers in which this necessary element has been ignored? + + +In the light of the performance of the exacting conditions of present +day power-plant practice, a review of this lecture and of the foregoing +list of requirements reveals the insight of the inventors of the Babcock +& Wilcox boiler into the fundamental principles of steam generator +design and construction. + +Since the Babcock & Wilcox boiler became thoroughly established as a +durable and efficient steam generator, many types of water-tube boilers +have appeared on the market. Most of them, failing to meet enough of the +requirements of a perfect boiler, have fallen by the wayside, while a +few failing to meet all of the requirements, have only a limited field +of usefulness. None have been superior, and in the most cases the most +ardent admirers of other boilers have been satisfied in looking up to +the Babcock & Wilcox boiler as a standard and in claiming that the newer +boilers were "just as good." + +Records of recent performances under the most severe conditions of +services on land and sea, show that the Babcock & Wilcox boiler can be +run continually and regularly at higher overloads, with higher +efficiency, and lower upkeep cost than any other boiler on the market. +It is especially adapted for power-plant work where it is necessary to +use a boiler in which steam can be raised quickly and the boiler placed +on the line either from a cold state or from a banked fire in the +shortest possible time, and with which the capacity, with clean feed +water, will be largely limited by the amount of coal that can be burned +in the furnace. + +The distribution of the circulation through the separate headers and +sections and the action of the headers in forcing a maximum and +continuous circulation in the lower tubes, permit the operation of the +Babcock & Wilcox boiler without objectionable priming, with a higher +degree of concentration of salts in the water than is possible in any +other type of boiler. + +Repeated daily performances at overloads have demonstrated beyond a +doubt the correctness of Mr. Babcock's computation regarding the +circulating tube and header area required for most efficient +circulation. They also have proved that enlargement of the area of +headers and circulating tubes beyond a certain point diminishes the head +available for causing circulation and consequently limits the ability of +the boiler to respond to demands for overloads. + +In this lecture Mr. Babcock made the prediction that with the +circulating tube area proportioned in accordance with the principles +laid down, the Babcock & Wilcox boiler could be continuously run at +double its nominal rating, which at that time was based on 12 square +feet of heating surface per horse power. This prediction is being +fulfilled daily in all the large and prominent power plants in this +country and abroad, and it has been repeatedly demonstrated that with +clean water and clean tube surfaces it is possible to safely operate at +over 300 per cent of the nominal rating. + +In the development of electrical power stations it becomes more and more +apparent that it is economical to run a boiler at high ratings during +the times of peak loads, as by so doing the lay-over losses are +diminished and the economy of the plant as a whole is increased. + +The number and importance of the large electric lighting and power +stations constructed during the last ten years that are equipped with +Babcock & Wilcox boilers, is a most gratifying demonstration of the +merit of the apparatus, especially in view of their satisfactory +operation under conditions which are perhaps more exacting than those of +any other service. + +Time, the test of all, results with boilers as with other things, in the +survival of the fittest. When judged on this basis the Babcock & Wilcox +boiler stands pre-eminent in its ability to cover the whole field of +steam generation with the highest commercial efficiency obtainable. Year +after year the Babcock & Wilcox boiler has become more firmly +established as the standard of excellence in the boiler making art. + +[Illustration: South Boston Station of the Boston Elevated Ry. Co., +Boston, Mass. 9600 Horse Power of Babcock & Wilcox Boilers and +Superheaters Installed in this Station] + +[Illustration: 3600 Horse-power Installation of Babcock & Wilcox Boilers +at the Phipps Power House of the Duquesne Light Company, Pittsburgh, +Pa.] + + + + +EVOLUTION OF THE BABCOCK & WILCOX WATER-TUBE BOILER + + +Quite as much may be learned from the records of failures as from those +of success. Where a device has been once fairly tried and found to be +imperfect or impracticable, the knowledge of that trial is of advantage +in further investigation. Regardless of the lesson taught by failure, +however, it is an almost every-day occurrence that some device or +construction which has been tried and found wanting, if not worthless, +is again introduced as a great improvement upon a device which has shown +by its survival to be the fittest. + +The success of the Babcock & Wilcox boiler is due to many years of +constant adherence to one line of research, in which an endeavor has +been made to introduce improvements with the view to producing a boiler +which would most effectively meet the demands of the times. During the +periods that this boiler has been built, other companies have placed on +the market more than thirty water-tube or sectional water-tube boilers, +most of which, though they may have attained some distinction and sale, +have now entirely disappeared. The following incomplete list will serve +to recall the names of some of the boilers that have had a vogue at +various times, but which are now practically unknown: Dimpfel, Howard, +Griffith & Wundrum, Dinsmore, Miller "Fire Box", Miller "American", +Miller "Internal Tube", Miller "Inclined Tube", Phleger, Weigant, the +Lady Verner, the Allen, the Kelly, the Anderson, the Rogers & Black, the +Eclipse or Kilgore, the Moore, the Baker & Smith, the Renshaw, the +Shackleton, the "Duplex", the Pond & Bradford, the Whittingham, the +Bee, the Hazleton or "Common Sense", the Reynolds, the Suplee or Luder, +the Babbit, the Reed, the Smith, the Standard, etc., etc. + +It is with the object of protecting our customers and friends from loss +through purchasing discarded ideas that there is given on the following +pages a brief history of the development of the Babcock & Wilcox boiler +as it is built to-day. The illustrations and brief descriptions indicate +clearly the various designs and constructions that have been used and +that have been replaced, as experience has shown in what way improvement +might be made. They serve as a history of the experimental steps in the +development of the present Babcock & Wilcox boiler, the value and +success of which, as a steam generator, is evidenced by the fact that +the largest and most discriminating users continue to purchase them +after years of experience in their operation. + +[Illustration: No. 1] + +No. 1. The original Babcock & Wilcox boiler was patented in 1867. The +main idea in its design was safety, to which all other features were +sacrificed wherever they conflicted. The boiler consisted of a nest of +horizontal tubes, serving as a steam and water reservoir, placed above +and connected at each end by bolted joints to a second nest of inclined +heating tubes filled with water. The tubes were placed one above the +other in vertical rows, each row and its connecting end forming a single +casting. Hand-holes were placed at each end for cleaning. Internal tubes +were placed within the inclined tubes with a view to aiding circulation. + +No. 2. This boiler was the same as No. 1, except that the internal +circulating tubes were omitted as they were found to hinder rather than +help the circulation. + +Nos. 1 and 2 were found to be faulty in both material and design, cast +metal proving unfit for heating surfaces placed directly over the fire, +as it cracked as soon as any scale formed. + +No. 3. Wrought-iron tubes were substituted for the cast-iron heating +tubes, the ends being brightened, laid in moulds, and the headers cast +on. + +The steam and water capacity in this design were insufficient to secure +regularity of action, there being no reserve upon which to draw during +firing or when the water was fed intermittently. The attempt to dry the +steam by superheating it in the nest of tubes forming the steam space +was found to be impracticable. The steam delivered was either wet, dry +or superheated, according to the rate at which it was being drawn from +the boiler. Sediment was found to lodge in the lowermost point of the +boiler at the rear end and the exposed portions cracked off at this +point when subjected to the furnace heat. + +[Illustration: No. 4] + +No. 4. A plain cylinder, carrying the water line at its center and +leaving the upper half for steam space, was substituted for the nest of +tubes forming the steam and water space in Nos. 1, 2 and 3. The sections +were made as in No. 3 and a mud drum added to the rear end of the +sections at the point that was lowest and farthest removed from the +fire. The gases were made to pass off at one side and did not come into +contact with the mud drum. Dry steam was obtained through the increase +of separating surface and steam space and the added water capacity +furnished a storage for heat to tide over irregularities of firing and +feeding. By the addition of the drum, the boiler became a serviceable +and practical design, retaining all of the features of safety. As the +drum was removed from the direct action of the fire, it was not +subjected to excessive strain due to unequal expansion, and its +diameter, if large in comparison with that of the tubes formerly used, +was small when compared with that of cylindrical boilers. Difficulties +were encountered in this boiler in securing reliable joints between the +wrought-iron tubes and the cast-iron headers. + +[Illustration: No. 5] + +No. 5. In this design, wrought-iron water legs were substituted for the +cast-iron headers, the tubes being expanded into the inside sheets and a +large cover placed opposite the front end of the tubes for cleaning. The +tubes were staggered one above the other, an arrangement found to be +more efficient in the absorption of heat than where they were placed in +vertical rows. In other respects, the boiler was similar to No. 4, +except that it had lost the important element of safety through the +introduction of the very objectionable feature of flat stayed surfaces. +The large doors for access to the tubes were also a cause of weakness. + +An installation of these boilers was made at the plant of the Calvert +Sugar Refinery in Baltimore, and while they were satisfactory in their +operation, were never duplicated. + +[Illustration: No. 6] + +No. 6. This was a modification of No. 5 in which longer tubes were used +and over which the gases were caused to make three passes with a view of +better economy. In addition, some of the stayed surfaces were omitted +and handholes substituted for the large access doors. A number of +boilers of this design were built but their excessive first cost, the +lack of adjustability of the structure under varying temperatures, and +the inconvenience of transportation, led to No. 7. + +[Illustration: No. 7] + +No. 7. In this boiler, the headers and water legs were replaced by +T-heads screwed to the ends of the inclined tubes. The faces of these Ts +were milled and the tubes placed one above the other with the milled +faces metal to metal. Long bolts passed through each vertical section of +the T-heads and through connecting boxes on the heads of the drums +holding the whole together. A large number of boilers of this design +were built and many were in successful operation for over twenty years. +In most instances, however, they were altered to later types. + +[Illustration: No. 8] + +[Illustration: No. 9] + +Nos. 8 and 9. These boilers were known as the Griffith & Wundrum type, +the concern which built them being later merged in The Babcock & Wilcox +Co. Experiments were made with this design with four passages of the +gases across the tubes and the downward circulation of the water at the +rear of the boiler was carried to the bottom row of tubes. In No. 9 an +attempt was made to increase the safety and reduce the cost by reducing +the amount of steam and water capacity. A drum at right angles to the +line of tubes was used but as there was no provision made to secure dry +steam, the results were not satisfactory. The next move in the direction +of safety was the employment of several drums of small diameter instead +of a single drum. + +[Illustration: No. 10] + +This is shown in No. 10. A nest of small horizontal drums, 15 inches in +diameter, was used in place of the single drum of larger diameter. A set +of circulation tubes was placed at an intermediate angle between the +main bank of heating tubes and the horizontal drums forming the steam +reservoir. These circulators were to return to the rear end of the +circulating tubes the water carried up by the circulation, and in this +way were to allow only steam to be delivered to the small drums above. +There was no improvement in the action of this boiler over that of No. +9. + +The four passages of the gas over the tubes tried in Nos. 8, 9 and 10 +were not found to add to the economy of the boiler. + +[Illustration: No. 11] + +No. 11. A trial was next made of a box coil system, in which the water +was made to transverse the furnace several times before being delivered +to the drum above. The tendency here, as in all similar boilers, was to +form steam in the middle of the coil and blow the water from each end, +leaving the tubes practically dry until the steam found an outlet and +the water returned. This boiler had, in addition to a defective +circulation, a decidedly geyser-like action and produced wet steam. + +[Illustration: No. 12] + +All of the types mentioned, with the exception of Nos. 5 and 6, had +between their several parts a large number of bolted joints which were +subjected to the action of the fire. When these boilers were placed in +operation it was demonstrated that as soon as any scale formed on the +heating surfaces, leaks were caused due to unequal expansion. + +No. 12. With this boiler, an attempt was made to remove the joints from +the fire and to increase the heating surface in a given space. Water +tubes were expanded into both sides of wrought-iron boxes, openings +being made for the admission of water and the exit of steam. Fire tubes +were placed inside the water tubes to increase the heating surface. This +design was abandoned because of the rapid stopping up of the tubes by +scale and the impossibility of cleaning them. + +[Illustration: No. 13] + +No. 13. Vertical straight line headers of cast iron, each containing two +rows of tubes, were bolted to a connection leading to the steam and +water drum above. + +[Illustration: No. 14] + +No. 14. A wrought-iron box was substituted for the double cast-iron +headers. In this design, stays were necessary and were found, as always, +to be an element to be avoided wherever possible. The boiler was an +improvement on No. 6, however. A slanting bridge wall was introduced +underneath the drum to throw a larger portion of its heating surface +into the combustion chamber under the bank of tubes. + +This bridge wall was found to be difficult to keep in repair and was of +no particular benefit. + +[Illustration: No. 15] + +No. 15. Each row of tubes was expanded at each end into a continuous +header, cast of car wheel metal. The headers had a sinuous form so that +they would lie close together and admit of a staggered position of the +tubes when assembled. While other designs of header form were tried +later, experience with Nos. 14 and 15 showed that the style here adopted +was the best for all purposes and it has not been changed materially +since. The drum in this design was supported by girders resting on the +brickwork. Bolted joints were discarded, with the exception of those +connecting the headers to the front and rear ends of the drums and the +bottom of the rear headers to the mud drum. Even such joints, however, +were found objectionable and were superseded in subsequent construction +by short lengths of tubes expanded into bored holes. + +[Illustration: No. 16] + +No. 16. In this design, headers were tried which were made in the form +of triangular boxes, in each of which there were three tubes expanded. +These boxes were alternately reversed and connected by short lengths of +expanded tubes, being connected to the drum by tubes bent in a manner to +allow them to enter the shell normally. The joints between headers +introduced an element of weakness and the connections to the drum were +insufficient to give adequate circulation. + +[Illustration: No. 17] + +No. 17. Straight horizontal headers were next tried, alternately shifted +right and left to allow a staggering of tubes. These headers were +connected to each other and to the drums by expanded nipples. The +objections to this boiler were almost the same as those to No. 16. + +[Illustration: No. 18] + +[Illustration: No. 19] + +Nos. 18 and 19. These boilers were designed primarily for fire +protection purposes, the requirements demanding a small, compact boiler +with ability to raise steam quickly. These both served the purpose +admirably but, as in No. 9, the only provision made for the securing of +dry steam was the use of the steam dome, shown in the illustration. This +dome was found inadequate and has since been abandoned in nearly all +forms of boiler construction. No other remedy being suggested at the +time, these boilers were not considered as desirable for general use as +Nos. 21 and 22. In Europe, however, where small size units were more in +demand, No. 18 was modified somewhat and used largely with excellent +results. These experiments, as they may now be called, although many +boilers of some of the designs were built, clearly demonstrated that the +best construction and efficiency required adherence to the following +elements of design: + + +1st. Sinuous headers for each vertical row of tubes. + + +2nd. A separate and independent connection with the drum, both front and +rear, for each vertical row of tubes. + +[Illustration: No. 20A] + +[Illustration: No. 20B] + + +3rd. All joints between parts of the boiler proper to be made without +bolts or screw plates. + + +4th. No surfaces to be used which necessitate the use of stays. + + +5th. The boiler supported independently of the brickwork so as to allow +freedom for expansion and contraction as it is heated or cooled. + + +6th. Ample diameter of steam and water drums, these not to be less than +30 inches except for small size units. + + +7th. Every part accessible for cleaning and repairs. + + +With these points having been determined, No. 20 was designed. This +boiler had all the desirable features just enumerated, together with a +number of improvements as to detail of construction. The general form of +No. 15 was adhered to but the bolted connections between sections and +drum and sections and mud drum were discarded in favor of connections +made by short lengths of boiler tubes expanded into the adjacent parts. +This boiler was suspended from girders, like No. 15, but these in turn +were carried on vertical supports, leaving the pressure parts entirely +free from the brickwork, the mutually deteriorating strains present +where one was supported by the other being in this way overcome. +Hundreds of thousands of horse power of this design were built, giving +great satisfaction. The boiler was known as the "C. I. F." (cast-iron +front) style, an ornamental cast-iron front having been usually +furnished. + +[Illustration: No. 21] + +The next step, and the one which connects the boilers as described above +to the boiler as it is built to-day, was the design illustrated in No. +21. These boilers were known as the "W. I. F." style, the fronts +furnished as part of the equipment being constructed largely of wrought +iron. The cast-iron drumheads used in No. 20 were replaced by +wrought-steel flanged and "bumped" heads. The drums were made longer and +the sections connected to wrought-steel cross boxes riveted to the +bottom of the drums. The boilers were supported by girders and columns +as in No. 20. + +[Illustration: No. 22] + +No. 22. This boiler, which is designated as the "Vertical Header" type, +has the same general features of construction as No. 21, except that the +tube sheet side of the headers is "stepped" to allow the headers to be +placed vertically and at right angles to the drum and still maintain the +tubes at the angle used in Nos. 20 and 21. + +[Illustration: No. 23] + +No. 23, or the cross drum design of boiler, is a development of the +Babcock & Wilcox marine boiler, in which the cross drum is used +exclusively. The experience of the Glasgow Works of The Babcock & +Wilcox, Ltd., with No. 18 proved that proper attention to details of +construction would make it a most desirable form of boiler where +headroom was limited. A large number of this design have been +successfully installed and are giving satisfactory results under widely +varying conditions. The cross drum boiler is also built in a vertical +header design. + +Boilers Nos. 21, 22 and 23, with a few modifications, are now the +standard forms. These designs are illustrated, as they are constructed +to-day, on pages 48, 52, 54, 58 and 60. + +The last step in the development of the water-tube boiler, beyond which +it seems almost impossible for science and skill to advance, consists in +the making of all pressure parts of the boiler of wrought steel, +including sinuous headers, cross boxes, nozzles, and the like. This +construction was the result of the demands of certain Continental laws +that are coming into general vogue in this country. The Babcock & Wilcox +Co. have at the present time a plant producing steel forgings that have +been pronounced by the _London Engineer_ to be "a perfect triumph +of the forgers' art". + +The various designs of this all wrought-steel boiler are fully +illustrated in the following pages. + +[Illustration: Wrought-steel Vertical Header Longitudinal Drum Babcock & +Wilcox Boiler, Equipped with Babcock & Wilcox Superheater and Babcock & +Wilcox Chain Grate Stoker] + + + + +THE BABCOCK & WILCOX BOILER + + +The following brief description of the Babcock & Wilcox boiler will +clearly indicate the manner in which it fulfills the requirements of the +perfect steam boiler already enumerated. + +The Babcock & Wilcox boiler is built in two general classes, the +longitudinal drum type and the cross drum type. Either of these designs +may be constructed with vertical or inclined headers, and the headers in +turn may be of wrought steel or cast iron dependent upon the working +pressure for which the boiler is constructed. The headers may be of +different lengths, that is, may connect different numbers of tubes, and +it is by a change in the number of tubes in height per section and the +number of sections in width that the size of the boiler is varied. + +The longitudinal drum boiler is the generally accepted standard of +Babcock & Wilcox construction. The cross drum boiler, though originally +designed to meet certain conditions of headroom, has become popular for +numerous classes of work where low headroom is not a requirement which +must be met. + +LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type of +boiler is made up of a drum or drums, depending upon the width of the +boiler extending longitudinally over the other pressure parts. To the +drum or drums there are connected through cross boxes at either end the +sections, which are made up of headers and tubes. At the lower end of +the sections there is a mud drum extending entirely across the setting +and connected to all sections. The connections between all parts are by +short lengths of tubes expanded into bored seats. + +[Illustration: Forged-steel Drumhead with Manhole Plate in Position] + +The drums are of three sheets, of such thickness as to give the required +factor of safety under the maximum pressure for which the boiler is +constructed. The circular seams are ordinarily single lap riveted though +these may be double lap riveted to meet certain requirements of pressure +or of specifications. The longitudinal seams are properly proportioned +butt and strap or lap riveted joints dependent upon the pressure for +which the boilers are built. Where butt strap joints are used the straps +are bent to the proper radius in an hydraulic press. The courses are +built independently to template and are assembled by an hydraulic +forcing press. All riveted holes are punched one-quarter inch smaller +than the size of rivets as driven and are reamed to full size after the +plates are assembled. All rivets are driven by hydraulic pressure and +held until black. + +[Illustration: Forged-steel Drumhead Interior] + +The drumheads are hydraulic forged at a single heat, the manhole opening +and stiffening ring being forged in position. Flat raised seats for +water column and feed connections are formed in the forging. + +All heads are provided with manholes, the edges of which are turned +true. The manhole plates are of forged steel and turned to fit manhole +opening. These plates are held in position by forged-steel guards and +bolts. + +The drum nozzles are of forged steel, faced, and fitted with taper +thread stud bolts. + +[Illustration: Forged-steel Drum Nozzle] + +Cross boxes by means of which the sections are attached to the drums, +are of forged steel, made from a single sheet. + +Where two or more drums are used in one boiler they are connected by a +cross pipe having a flanged outlet for the steam connection. + +[Illustration: Forged-steel Cross Box] + +The sections are built of 4-inch hot finished seamless open-hearth steel +tubes of No. 10 B. W. G. where the boilers are built for working +pressures up to 210 pounds. Where the working pressure is to be above +this and below 260 pounds, No. 9 B. W. G. tubes are supplied. + +[Illustration: Inside Handhole Fittings Wrought-steel Vertical Header] + +The tubes are expanded into headers of serpentine or sinuous form, which +dispose the tubes in a staggered position when assembled as a complete +boiler. These headers are of wrought steel or of cast iron, the latter +being ordinarily supplied where the working pressure is not to exceed +160 pounds. The headers may be either vertical or inclined as shown in +the various illustrations of assembled boilers. + +[Illustration: Wrought-steel Vertical Header] + +Opposite each tube end in the headers there is placed a handhole of +sufficient size to permit the cleaning, removal or renewal of a tube. +These openings in the wrought steel vertical headers are elliptical in +shape, machine faced, and milled to a true plane back from the edge a +sufficient distance to make a seat. The openings are closed by inside +fitting forged plates, shouldered to center in the opening, their +flanged seats milled to a true plane. These plates are held in position +by studs and forged-steel binders and nuts. The joints between plates +and headers are made with a thin gasket. + +[Illustration: Inside Handhole Fitting Wrought-steel Inclined Header] + +In the wrought-steel inclined headers the handhole openings are either +circular or elliptical, the former being ordinarily supplied. The +circular openings have a raised seat milled to a true plane. The +openings are closed on the outside by forged-steel caps, milled and +ground true, held in position by forged-steel safety clamps and secured +by ball-headed bolts to assure correct alignment. With this style of +fitting, joints are made tight, metal to metal, without packing of any +kind. + +[Illustration: Wrought-steel Inclined Header] + +Where elliptical handholes are furnished they are faced inside, closed +by inside fitting forged-steel plates, held to their seats by studs and +secured by forged-steel binders and nuts. + +The joints between plates and header are made with a thin gasket. + +[Illustration: Cast-iron Vertical Header] + +The vertical cast-iron headers have elliptical handholes with raised +seats milled to a true plane. These are closed on the outside by +cast-iron caps milled true, held in position by forged-steel safety +clamps, which close the openings from the inside and which are secured +by ball-headed bolts to assure proper alignment. All joints are made +tight, metal to metal, without packing of any kind. + +The mud drum to which the sections are attached at the lower end of the +rear headers, is a forged-steel box 7-1/4 inches square, and of such +length as to be connected to all headers by means of wrought nipples +expanded into counterbored seats. The mud drum is furnished with handholes +for cleaning, these being closed from the inside by forged-steel plates +with studs, and secured on a faced seat in the mud drum by forged-steel +binders and nuts. The joints between the plates and the drum are made +with thin gaskets. The mud drum is tapped for blow-off connection. + +All connections between drums and sections and between sections and mud +drum are of hot finished seamless open-hearth steel tubes of No. 9 +B. W. G. + +Boilers of the longitudinal drum type are suspended front and rear from +wrought-steel supporting frames entirely independent of the brickwork. +This allows for expansion and contraction of the pressure parts without +straining either the boiler or the brickwork, and also allows of +brickwork repair or renewal without in any way disturbing the boiler or +its connections. + +[Illustration: Babcock & Wilcox Wrought-steel Vertical Header Cross Drum +Boiler] + +CROSS DRUM CONSTRUCTION--The cross drum type of boilers differs from the +longitudinal only in drum construction and method of support. The drum +in this type is placed transversely across the rear of the boiler and is +connected to the sections by means of circulating tubes expanded into +bored seats. + +The drums for all pressures are of two sheets of sufficient thickness to +give the required factor of safety. The longitudinal seams are double +riveted butt strapped, the straps being bent to the proper radius in an +hydraulic press. The circulating tubes are expanded into the drums at +the seams, the butt straps serving as tube seats. + +The drumheads, drum fittings and features of riveting are the same in +the cross drum as in the longitudinal types. The sections and mud drum +are also the same for the two types. + +Cross drum boilers are supported at the rear on the mud drum which rests +on cast-iron foundation plates. They are suspended at the front from a +wrought-iron supporting frame, each section being suspended +independently from the cross members by hook suspension bolts. This +method of support is such as to allow for expansion and contraction +without straining either the boiler or the brickwork and permits of +repair or renewal of the latter without in any way disturbing the boiler +or its connections. + +The following features of design and of attachments supplied are the +same for all types. + +FRONTS--Ornamental fronts are fitted to the front supporting frame. +These have large doors for access to the front headers and panels above +the fire fronts. The fire fronts where furnished have independent frames +for fire doors which are bolted on, and ashpit doors fitted with blast +catches. The lugs on door frames and on doors are cast solid. The faces +of doors and of frames are planed and the lugs milled. The doors and +frames are placed in their final relative position, clamped, and the +holes for hinge pins drilled while thus held. A perfect alignment of +door and frame is thus assured and the method is representative of the +care taken in small details of manufacture. + +The front as a whole is so arranged that any stoker may be applied with +but slight modification wherever boilers are set with sufficient furnace +height. + +[Illustration: Cross Drum Boiler Front] + +In the vertical header boilers large wrought-iron doors, which give +access to the rear headers, are attached to the rear supporting frame. + +[Illustration: Wrought-steel Inclined Header Longitudinal Drum Babcock & +Wilcox Boiler, Equipped with Babcock & Wilcox Superheater] + +[Illustration: Automatic Drumhead Stop and Check Valve] + +FITTINGS--Each boiler is provided with the following fittings as part of +the standard equipment: + +Blow-off connections and valves attached to the mud drum. + +Safety valves placed on nozzles on the steam drums. + +A water column connected to the front of the drum. + +A steam gauge attached to the boiler front. + +Feed water connection and valves. A flanged stop and check valve of +heavy pattern is attached directly to each drumhead, closing +automatically in case of a rupture in the feed line. + +All valves and fittings are substantially built and are of designs which +by their successful service for many years have become standard with The +Babcock & Wilcox Co. + +The fixtures that are supplied with the boilers consist of: + +Dead plates and supports, the plates arranged for a fire brick lining. + +A full set of grate bars and bearers, the latter fitted with expansion +sockets for side walls. + +Flame bridge plates with necessary fastenings, and special fire brick +for lining same. + +Bridge wall girder for hanging bridge wall with expansion sockets for +side walls. + +A full set of access and cleaning doors through which all portions of +the pressure parts may be reached. + +A swing damper and frame with damper operating rig. + +There are also supplied with each boiler a wrench for handhole nuts, a +water-driven turbine tube cleaner, a set of fire tools and a metal steam +hose and cleaning pipe equipped with a special nozzle for blowing dust +and soot from the tubes. + +Aside from the details of design and construction as covered in the +foregoing description, a study of the illustrations will make clear the +features of the boiler as a whole which have led to its success. + +The method of supporting the boiler has been described. This allows it +to be hung at any height that may be necessary to properly handle the +fuel to be burned or to accommodate the stoker to be installed. The +height of the nest of tubes which forms the roof of the furnace is thus +the controlling feature in determining the furnace height, or the +distance from the front headers to the floor line. The sides and front +of the furnace are formed by the side and front boiler walls. The rear +wall of the furnace consists of a bridge wall built from the bottom of +the ashpit to the lower row of tubes. The location of this wall may be +adjusted within limits to give the depth of furnace demanded by the fuel +used. Ordinarily the bridge wall is the determining feature in the +locating of the front baffle. Where a great depth of furnace is +necessary, in which case, if the front baffle were placed at the bridge +wall the front pass of the boiler would be relatively too long, a +patented construction is used which maintains the baffle in what may be +considered its normal position, and a connection made between the baffle +and the bridge wall by means of a tile roof. Such furnace construction +is known as a "Webster" furnace. + +[Illustration: Longitudinal Drum Boiler--Front View] + +A consideration of this furnace will clearly indicate its adaptability, +by reason of its flexibility, for any fuel and any design of stoker. The +boiler lends itself readily to installation with an extension or Dutch +oven furnace if this be demanded by the fuel to be used, and in general +it may be stated that a satisfactory furnace arrangement may be made in +connection with a Babcock & Wilcox boiler for burning any fuel, solid, +liquid or gaseous. + +The gases of combustion evolved in the furnace above described are led +over the heating surfaces by two baffles. These are formed of cast-iron +baffle plates lined with special fire brick and held in position by tube +clamps. The front baffle leads the gases through the forward portion of +the tubes to a chamber beneath the drum or drums. It is in this chamber +that a superheater is installed where such an apparatus is desired. The +gases make a turn over the front baffle, are led downward through the +central portion of the tubes, called the second pass, by means of a +hanging bridge wall of brick and the second baffle, around which they +make a second turn upward, pass through the rear portion of the tubes +and are led to the stack or flue through a damper box in the rear wall, +or around the drums to a damper box placed overhead. + +The space beneath the tubes between the bridge wall and the rear boiler +wall forms a pocket into which much of the soot from the gases in their +downward passage through the second pass will be deposited and from +which it may be readily cleaned through doors furnished for the purpose. + +The gas passages are ample and are so proportioned that the resistance +offered to the gases is only such as will assure the proper abstraction +of heat from the gases without causing undue friction, requiring +excessive draft. + +[Illustration: Partial Vertical Section Showing Method of Introducing +Feed Water] + +The method in which the feed water is introduced through the front +drumhead of the boiler is clearly seen by reference to the illustration. +From this point of introduction the water passes to the rear of the +drum, downward through the rear circulating tubes to the sections, +upward through the tubes of the sections to the front headers and +through these headers and front circulating tubes again to the drum +where such water as has not been formed into steam retraces its course. +The steam formed in the passage through the tubes is liberated as the +water reaches the front of the drum. The steam so formed is stored in +the steam space above the water line, from which it is drawn through a +so-called "dry pipe." The dry pipe in the Babcock & Wilcox boiler is +misnamed, as in reality it fulfills none of the functions ordinarily +attributed to such a device. This function is usually to restrict the +flow of steam from a boiler with a view to avoid priming. In the Babcock +& Wilcox boiler its function is simply that of a collecting pipe, and as +the aggregate area of the holes in it is greatly in excess of the area +of the steam outlet from the drum, it is plain that there can be no +restriction through this collecting pipe. It extends nearly the length +of the drum, and draws steam evenly from the whole length of the steam +space. + +[Illustration: Cast-iron Vertical Header Longitudinal Drum Babcock & +Wilcox Boiler] + +[Illustration: + Closed Open + +Patented Side Dusting Doors] + +The large tube doors through which access is had to the front headers +and the doors giving such access to the rear headers in boilers of the +vertical header type have already been described and are shown clearly +by the illustrations on pages 56 and 74. In boilers of the inclined +header type, access to the rear headers is secured through the chamber +formed by the headers and the rear boiler wall. Large doors in the sides +of the setting give full access to all parts for inspection and for +removal of accumulations of soot. Small dusting doors are supplied for +the side walls through which all of the heating surfaces may be cleaned +by means of a steam dusting lance. These side dusting doors are a +patented feature and the shutters are self closing. In wide boilers +additional cleaning doors are supplied at the top of the setting to +insure ease in reaching all portions of the heating surface. + +The drums are accessible for inspection through the manhole openings. +The removal of the handhole plates makes possible the inspection of each +tube for its full length and gives the assurance that no defect can +exist that cannot be actually seen. This is particularly advantageous +when inspecting for the presence of scale. + +The materials entering into the construction of the Babcock & Wilcox +boiler are the best obtainable for the special purpose for which they +are used and are subjected to rigid inspection and tests. + +The boilers are manufactured by means of the most modern shop equipment +and appliances in the hands of an old and well-tried organization of +skilled mechanics under the supervision of experienced engineers. + +[Illustration: Cast-iron Vertical Header Cross Drum Babcock & Wilcox +Boiler] + + + + +ADVANTAGES OF THE BABCOCK & WILCOX BOILER + + +The advantages of the Babcock & Wilcox boiler may perhaps be most +clearly set forth by a consideration, 1st, of water-tube boilers as a +class as compared with shell and fire-tube boilers; and 2nd, of the +Babcock & Wilcox boiler specifically as compared with other designs of +water-tube boilers. + + + +WATER-TUBE _VERSUS_ FIRE-TUBE BOILERS + + +Safety--The most important requirement of a steam boiler is that it +shall be safe in so far as danger from explosion is concerned. If the +energy in a large shell boiler under pressure is considered, the thought +of the destruction possible in the case of an explosion is appalling. +The late Dr. Robert H. Thurston, Dean of Sibley College, Cornell +University, and past president of the American Society of Mechanical +Engineers, estimated that there is sufficient energy stored in a plain +cylinder boiler under 100 pounds steam pressure to project it in case of +an explosion to a height of over 3-1/2 miles; a locomotive boiler at 125 +pounds pressure from one-half to one-third of a mile; and a 60 +horse-power return tubular boiler under 75 pounds pressure somewhat over +a mile. To quote: "A cubic foot of heated water under a pressure of from +60 to 70 pounds per square inch has about the same energy as one pound +of gunpowder." From such a consideration, it may be readily appreciated +how the advent of high pressure steam was one of the strongest factors +in forcing the adoption of water-tube boilers. A consideration of the +thickness of material necessary for cylinders of various diameters under +a steam pressure of 200 pounds and assuming an allowable stress of +12,000 pounds per square inch, will perhaps best illustrate this point. +Table 1 gives such thicknesses for various diameters of cylinders not +taking into consideration the weakening effect of any joints which may +be necessary. The rapidity with which the plate thickness increases with +the diameter is apparent and in practice, due to the fact that riveted +joints must be used, the thicknesses as given in the table, with the +exception of the first, must be increased from 30 to 40 per cent. + +In a water-tube boiler the drums seldom exceed 48 inches in diameter and +the thickness of plate required, therefore, is never excessive. The +thinner metal can be rolled to a more uniform quality, the seams admit +of better proportioning, and the joints can be more easily and perfectly +fitted than is the case where thicker plates are necessary. All of these +points contribute toward making the drums of water-tube boilers better +able to withstand the stress which they will be called upon to endure. + +The essential constructive difference between water-tube and fire-tube +boilers lies in the fact that the former is composed of parts of +relatively small diameter as against the large diameters necessary in +the latter. + +The factor of safety of the boiler parts which come in contact with the +most intense heat in water-tube boilers can be made much higher than +would be practicable in a shell boiler. Under the assumptions considered +above in connection with the thickness of plates required, a number 10 +gauge tube (0.134 inch), which is standard in Babcock & Wilcox boilers +for pressures up to 210 pounds under the same allowable stress as was +used in computing Table 1, the safe working pressure for the tubes is +870 pounds per square inch, indicating the very large margin of safety +of such tubes as compared with that possible with the shell of a boiler. + + TABLE 1 + +PLATE THICKNESS REQUIRED + FOR VARIOUS CYLINDER + DIAMETERS + + ALLOWABLE STRESS, + 12000 POUNDS PER + SQUARE INCH, + 200 POUNDS GAUGE + PRESSURE, NO JOINTS + ++---------+-----------+ +|Diameter | Thickness | +|Inches | Inches | ++---------+-----------+ +| 4 | 0.033 | +| 36 | 0.300 | +| 48 | 0.400 | +| 60 | 0.500 | +| 72 | 0.600 | +| 108 | 0.900 | +| 120 | 1.000 | +| 144 | 1.200 | ++---------+-----------+ + +A further advantage in the water-tube boiler as a class is the +elimination of all compressive stresses. Cylinders subjected to external +pressures, such as fire tubes or the internally fired furnaces of +certain types of boilers, will collapse under a pressure much lower than +that which they could withstand if it were applied internally. This is +due to the fact that if there exists any initial distortion from its +true shape, the external pressure will tend to increase such distortion +and collapse the cylinder, while an internal pressure tends to restore +the cylinder to its original shape. + +Stresses due to unequal expansion have been a fruitful source of trouble +in fire-tube boilers. + +In boilers of the shell type, the riveted joints of the shell, with +their consequent double thickness of metal exposed to the fire, gives +rise to serious difficulties. Upon these points are concentrated all +strains of unequal expansion, giving rise to frequent leaks and +oftentimes to actual ruptures. Moreover, in the case of such rupture, +the whole body of contained water is liberated instantaneously and a +disastrous and usually fatal explosion results. + +Further, unequal strains result in shell or fire-tube boilers due to the +difference in temperature of the various parts. This difference in +temperature results from the lack of positive well defined circulation. +While such a circulation does not necessarily accompany all water-tube +designs, in general, the circulation in water-tube boilers is much more +defined than in fire-tube or shell boilers. + +A positive and efficient circulation assures that all portions of the +pressure parts will be at approximately the same temperature and in this +way strains resulting from unequal temperatures are obviated. + +If a shell or fire-tubular boiler explodes, the apparatus as a whole is +destroyed. In the case of water-tube boilers, the drums are ordinarily +so located that they are protected from intense heat and any rupture is +usually in the case of a tube. Tube failures, resulting from blisters or +burning, are not serious in their nature. Where a tube ruptures because +of a flaw in the metal, the result may be more severe, but there cannot +be the disastrous explosion such as would occur in the case of the +explosion of a shell boiler. + +To quote Dr. Thurston, relative to the greater safety of the water-tube +boiler: "The stored available energy is usually less than that of any of +the other stationary boilers and not very far from the amount stored, +pound for pound, in the plain tubular boiler. It is evident that their +admitted safety from destructive explosion does not come from this +relation, however, but from the division of the contents into small +portions and especially from those details of construction which make it +tolerably certain that any rupture shall be local. A violent explosion +can only come from the general disruption of a boiler and the liberation +at once of large masses of steam and water." + +Economy--The requirement probably next in importance to safety in a +steam boiler is economy in the use of fuel. To fulfill such a +requirement, the three items, of proper grate for the class of fuel to +be burned, a combustion chamber permitting complete combustion of gases +before their escape to the stack, and the heating surface of such a +character and arrangement that the maximum amount of available heat may +be extracted, must be co-ordinated. + +Fire-tube boilers from the nature of their design do not permit the +variety of combinations of grate surface, heating surface, and +combustion space possible in practically any water-tube boiler. + +In securing the best results in fuel economy, the draft area in a boiler +is an important consideration. In fire-tube boilers this area is limited +to the cross sectional area of the fire tubes, a condition further +aggravated in a horizontal boiler by the tendency of the hot gases to +pass through the upper rows of tubes instead of through all of the tubes +alike. In water-tube boilers the draft area is that of the space outside +of the tubes and is hence much greater than the cross sectional area of +the tubes. + +Capacity--Due to the generally more efficient circulation found in +water-tube than in fire-tube boilers, rates of evaporation are possible +with water-tube boilers that cannot be approached where fire-tube +boilers are employed. + +Quick Steaming--Another important result of the better circulation +ordinarily found in water-tube boilers is in their ability to raise +steam rapidly in starting and to meet the sudden demands that may be +thrown on them. + +In a properly designed water-tube boiler steam may be raised from a cold +boiler to 200 pounds pressure in less than one-half hour. + +For the sake of comparison with the figure above, it may be stated that +in the U. S. Government Service the shortest time allowed for getting up +steam in Scotch marine boilers is 6 hours and the time ordinarily +allowed is 12 hours. In large double-ended Scotch boilers, such as are +generally used in Trans-Atlantic service, the fires are usually started +24 hours before the time set for getting under way. This length of time +is necessary for such boilers in order to eliminate as far as possible +excessive strains resulting from the sudden application of heat to the +surfaces. + +Accessibility--In the "Requirements of a Perfect Steam Boiler", as +stated by Mr. Babcock, he demonstrates the necessity for complete +accessibility to all portions of the boiler for cleaning, inspection and +repair. + +Cleaning--When the great difference is realized in performance, both as +to economy and capacity of a clean boiler and one in which the heating +surfaces have been allowed to become fouled, it may be appreciated that +the ability to keep heating surfaces clean internally and externally is +a factor of the highest importance. + +Such results can be accomplished only by the use of a design in boiler +construction which gives complete accessibility to all portions. In +fire-tube boilers the tubes are frequently nested together with a space +between them often less than 1-1/4 inches and, as a consequence, nearly the +entire tube surface is inaccessible. When scale forms upon such tubes it +is impossible to remove it completely from the inside of the boiler and +if it is removed by a turbine hammer, there is no way of knowing how +thorough a job has been done. With the formation of such scale there is +danger through overheating and frequent tube renewals are necessary. + +[Illustration: Portion of 29,000 Horse-power Installation of Babcock & +Wilcox Boilers in the L Street Station of the Edison Electric +Illuminating Co. of Boston, Mass. This Company Operates in its Various +Stations a Total of 39,000 Horse Power of Babcock & Wilcox Boilers] + +In Scotch marine boilers, even with the engines operating condensing, +complete tube renewals at intervals of six or seven years are required, +while large replacements are often necessary in less than one year. In +return tubular boilers operated with bad feed water, complete tube +renewals annually are not uncommon. In this type of boiler much sediment +falls on the bottom sheets where the intense heat to which they are +subjected bakes it to such an excessive hardness that the only method of +removing it is to chisel it out. This can be done only by omitting tubes +enough to leave a space into which a man can crawl and the discomforts +under which he must work are apparent. Unless such a deposit is removed, +a burned and buckled plate will invariably result, and if neglected too +long an explosion will follow. + +In vertical fire-tube boilers using a water leg construction, a deposit +of mud in such legs is an active agent in causing corrosion and the +difficulty of removing such deposit through handholes is well known. A +complete removal is practically impossible and as a last resort to +obviate corrosion in certain designs, the bottom of the water legs in +some cases have been made of copper. A thick layer of mud and scale is +also liable to accumulate on the crown sheet of such boilers and may +cause the sheet to crack and lead to an explosion. + +The soot and fine coal swept along with the gases by the draft will +settle in fire tubes and unless removed promptly, must be cut out with a +special form of scraper. It is not unusual where soft coal is used to +find tubes half filled with soot, which renders useless a large portion +of the heating surface and so restricts the draft as to make it +difficult to burn sufficient coal to develop the required power from +such heating surface as is not covered by soot. + +Water-tube boilers in general are from the nature of their design more +readily accessible for cleaning than are fire-tube boilers. + +Inspection--The objections given above in the consideration of the +inability to properly clean fire-tube boilers hold as well for the +inspection of such boilers. + +Repairs--The lack of accessibility in fire-tube boilers further leads to +difficulties where repairs are required. + +In fire-tube boilers tube renewals are a serious undertaking. The +accumulation of hard deposit on the exterior of the surfaces so enlarges +the tubes that it is oftentimes difficult, if not impossible, to draw +them through the tube sheets and it is usually necessary to cut out such +tubes as will allow access to the one which has failed and remove them +through the manhole. + +When a tube sheet blisters, the defective part must be cut out by +hand-tapped holes drilled by ratchets and as it is frequently impossible +to get space in which to drive rivets, a "soft patch" is necessary. This +is but a makeshift at best and usually results in either a reduction of +the safe working pressure or in the necessity for a new plate. If the +latter course is followed, the old plate must be cut out, a new one +scribed to place to locate rivet holes and in order to obtain room for +driving rivets, the boiler will have to be re-tubed. + +The setting must, of course, be at least partially torn out and +replaced. + +In case of repairs, of such nature in fire-tube boilers, the working +pressure of such repaired boilers will frequently be lowered by the +insurance companies when the boiler is again placed in service. + +In the case of a rupture in a water-tube boiler, the loss will +ordinarily be limited to one or two tubes which can be readily replaced. +The fire-tube boiler will be so completely demolished that the question +of repairs will be shifted from the boiler to the surrounding property, +the damage to which will usually exceed many times the cost of a boiler +of a type which would have eliminated the possibility of a disastrous +explosion. In considering the proper repair cost of the two types of +boilers, the fact should not be overlooked that it is poor economy to +invest large sums in equipment that, through a possible accident to the +boiler may be wholly destroyed or so damaged that the cost of repairs, +together with the loss of time while such repairs are being made, would +purchase boilers of absolute safety and leave a large margin beside. The +possibility of loss of human life should also be considered, though this +may seem a far cry from the question of repair costs. + +Space Occupied--The space required for the boilers in a plant often +exceeds the requirements for the remainder of the plant equipment. Any +saving of space in a boiler room will be a large factor in reducing the +cost of real estate and of the building. Even when the boiler plant is +comparatively small, the saving in space frequently will amount to a +considerable percentage of the cost of the boilers. Table 2 shows the +difference in floor space occupied by fire-tube boilers and Babcock & +Wilcox boilers of the same capacity, the latter being taken as +representing the water-tube class. This saving in space will increase +with the size of the plant for the reason that large size boiler units +while common in water-tube practice are impracticable in fire-tube +practice. + + TABLE 2 + + COMPARATIVE APPROXIMATE FLOOR + SPACE OCCUPIED BY BABCOCK & WILCOX + AND H. R. T. BOILERS + ++------------+----------------+---------------+ +|Size of unit|Babcock & Wilcox| H. R. T. | +|Horse Power |Feet and Inches |Feet and Inches| ++------------+----------------+---------------+ +| 100 | 7 3 x 19 9 | 10 0 x 20 0 | +| 150 | 7 10 x 19 9 | 10 0 x 22 6 | +| 200 | 9 0 x 19 9 | 11 6 x 23 10 | +| 250 | 9 0 x 19 9 | 11 6 x 23 10 | +| 300 | 10 2 x 19 9 | 12 0 x 25 0 | ++------------+----------------+---------------+ + + + +BABCOCK & WILCOX BOILERS AS COMPARED WITH OTHER WATER-TUBE DESIGNS + + +It must be borne in mind that the simple fact that a boiler is of the +water-tube design does not as a necessity indicate that it is a good or +safe boiler. + +Safety--Many of the water-tube boilers on the +market are as lacking as are fire-tube boilers in the positive +circulation which, as has been demonstrated by Mr. Babcock's lecture, is +so necessary in the requirements of the perfect steam boiler. In boilers +using water-leg construction, there is danger of defective circulation, +leaks are common, and unsuspected corrosion may be going on in portions +of the boiler that cannot be inspected. Stresses due to unequal +expansion of the metal cannot be well avoided but they may be minimized +by maintaining at the same temperature all pressure parts of the boiler. +The result is to be secured only by means of a well defined circulation. + +The main feature to which the Babcock & Wilcox boiler owes its safety is +the construction made possible by the use of headers, by which the water +in each vertical row of tubes is separated from that in the adjacent +rows. This construction results in the very efficient circulation +produced through the breaking up of the steam and water in the front +headers, the effect of these headers in producing such a positive +circulation having been clearly demonstrated in Mr. Babcock's lecture. +The use of a number of sections, thus composed of headers and tubes, has +a distinct advantage over the use of a common chamber at the outlet ends +of the tubes. In the former case the circulation of water in one +vertical row of tubes cannot interfere with that in the other rows, +while in the latter construction there will be downward as well as +upward currents and such downward currents tend to neutralize any good +effect there might be through the diminution of the density of the water +column by the steam. + +Further, the circulation results directly from the design of the boiler +and requires no assistance from "retarders", check valves and the like, +within the boiler. All such mechanical devices in the interior of a +boiler serve only to complicate the design and should not be used. + +This positive and efficient circulation assures that all portions of the +pressure parts of the Babcock & Wilcox boiler will be at approximately +the same temperature and in this way strains resulting from unequal +temperatures are obviated. + +Where the water throughout the boiler is at the temperature of the steam +contained, a condition to be secured only by proper circulation, danger +from internal pitting is minimized, or at least limited only to effects +of the water fed the boiler. Where the water in any portion of the +boiler is lower than the temperature of the steam corresponding to the +pressure carried, whether the fact that such lower temperatures exist as +a result of lack of circulation, or because of intentional design, +internal pitting or corrosion will almost invariably result. + +Dr. Thurston has already been quoted to the effect that the admitted +safety of a water-tube boiler is the result of the division of its +contents into small portions. In boilers using a water-leg construction, +while the danger from explosion will be largely limited to the tubes, +there is the danger, however, that such legs may explode due to the +deterioration of their stays, and such an explosion might be almost as +disastrous as that of a shell boiler. The headers in a Babcock & Wilcox +boiler are practically free from any danger of explosion. Were such an +explosion to occur, it would still be localized to a much larger extent +than in the case of a water-leg boiler and the header construction thus +almost absolutely localizes any danger from such a cause. + +Staybolts are admittedly an undesirable element of construction in any +boiler. They are wholly objectionable and the only reason for the +presence of staybolts in a boiler is to enable a cheaper form of +construction to be used than if they were eliminated. + +In boilers utilizing in their design flat-stayed surfaces, or staybolt +construction under pressure, corrosion and wear and tear in service +tends to weaken some single part subject to continual strain, the result +being an increased strain on other parts greatly in excess of that for +which an allowance can be made by any reasonable factor of safety. Where +the construction is such that the weakening of a single part will +produce a marked decrease in the safety and reliability of the whole, it +follows of necessity, that there will be a corresponding decrease in the +working pressure which may be safely carried. + +In water-leg boilers, the use of such flat-stayed surfaces under +pressure presents difficulties that are practically unsurmountable. Such +surfaces exposed to the heat of the fire are subject to unequal +expansion, distortion, leakage and corrosion, or in general, to many of +the objections that have already been advanced against the fire-tube +boilers in the consideration of water-tube boilers as a class in +comparison with fire-tube boilers. + +[Illustration: McAlpin Hotel, New York City, Operating 2360 Horse Power +of Babcock & Wilcox Boilers] + +Aside from the difficulties that may arise in actual service due to the +failure of staybolts, or in general, due to the use of flat-stayed +surfaces, constructional features are encountered in the actual +manufacture of such boilers that make it difficult if not impossible to +produce a first-class mechanical job. It is practically impossible in +the building of such a boiler to so design and place the staybolts that +all will be under equal strain. Such unequal strains, resulting from +constructional difficulties, will be greatly multiplied when such a +boiler is placed in service. Much of the riveting in boilers of this +design must of necessity be hand work, which is never the equal of +machine riveting. The use of water-leg construction ordinarily requires +the flanging of large plates, which is difficult, and because of the +number of heats necessary and the continual working of the material, may +lead to the weakening of such plates. + +In vertical or semi-vertical water-tube boilers utilizing flat-stayed +surfaces under pressure, these surfaces are ordinarily so located as to +offer a convenient lodging place for flue dust, which fuses into a hard +mass, is difficult of removal and under which corrosion may be going on +with no possibility of detection. + +Where stayed surfaces or water legs are features in the design of a +water-tube boiler, the factor of safety of such parts must be most +carefully considered. In such parts too, is the determination of the +factor most difficult, and because of the "rule-of-thumb" determination +frequently necessary, the factor of safety becomes in reality a factor +of ignorance. As opposed to such indeterminate factors of safety, in the +Babcock & Wilcox boiler, when the factor of safety for the drum or drums +has been determined, and such a factor may be determined accurately, the +factors for all other portions of the pressure parts are greatly in +excess of that of the drum. All Babcock & Wilcox boilers are built with +a factor of safety of at least five, and inasmuch as the factor of the +safety of the tubes and headers is greatly in excess of this figure, it +applies specifically to the drum or drums. This factor represents a +greater degree of safety than a considerably higher factor applied to a +boiler in which the shell or any riveted portion is acted upon directly +by the fire, or the same factor applied to a boiler utilizing +flat-stayed surface construction, where the accurate determination of +the limiting factor of safety is difficult, if not impossible. + +That the factor of safety of stayed surfaces is questionable may perhaps +be best realized from a consideration of the severe requirements as to +such factor called for by the rules and regulations of the Board of +Supervising Inspectors, U. S. Government. + +In view of the above, the absence of any stayed surfaces in the Babcock +& Wilcox boiler is obviously a distinguishing advantage where safety is +a factor. It is of interest to note, in the article on the evolution of +the Babcock & Wilcox boiler, that staybolt construction was used in +several designs, found unsatisfactory and unsafe, and discarded. + +Another feature in the design of the Babcock & Wilcox boiler tending +toward added safety is its manner of suspension. This has been indicated +in the previous chapter and is of such nature that all of the pressure +parts are free to expand or contract under variations of temperature +without in any way interfering with any part of the boiler setting. The +sectional nature of the boiler allows a flexibility under varying +temperature changes that practically obviates internal strain. + +In boilers utilizing water-leg construction, on the other hand, the +construction is rigid, giving rise to serious internal strains and the +method of support ordinarily made necessary by the boiler design is not +only unmechanical but frequently dangerous, due to the fact that proper +provision is not made for expansion and contraction under temperature +variations. + +Boilers utilizing water-leg construction are not ordinarily provided +with mud drums. This is a serious defect in that it allows impurities +and sediment to collect in a portion of the boiler not easily inspected, +and corrosion may result. + +Economy--That the water-tube boiler as a class lends itself more readily +than does the fire-tube boiler to a variation in the relation of grate +surface, heating surface and combustion space has been already pointed +out. In economy again, the construction made possible by the use of +headers in Babcock & Wilcox boilers appears as a distinct advantage. +Because of this construction, there is a flexibility possible, in an +unlimited variety of heights and widths that will satisfactorily meet +the special requirements of the fuel to be burned in individual cases. + +An extended experience in the design of furnaces best suited for a wide +variety of fuels has made The Babcock & Wilcox Co. leaders in the field +of economy. Furnaces have been built and are in successful operation for +burning anthracite and bituminous coals, lignite, crude oil, gas-house +tar, wood, sawdust and shavings, bagasse, tan bark, natural gas, blast +furnace gas, by-product coke oven gas and for the utilization of waste +heat from commercial processes. The great number of Babcock & Wilcox +boilers now in satisfactory operation under such a wide range of fuel +conditions constitutes an unimpeachable testimonial to the ability to +meet all of the many conditions of service. + +The limitations in the draft area of fire-tube boilers as affecting +economy have been pointed out. That a greater draft area is possible in +water-tube boilers does not of necessity indicate that proper advantage +of this fact is taken in all boilers of the water-tube class. In the +Babcock & Wilcox boiler, the large draft area taken in connection with +the effective baffling allows the gases to be brought into intimate +contact with all portions of the heating surfaces and renders such +surfaces highly efficient. + +In certain designs of water-tube boilers the baffling is such as to +render ineffective certain portions of the heating surface, due to the +tendency of soot and dirt to collect on or behind baffles, in this way +causing the interposition of a layer of non-conducting material between +the hot gases and the heating surfaces. + +In Babcock & Wilcox boilers the standard baffle arrangement is such as +to allow the installation of a superheater without in any way altering +the path of the gases from furnace to stack, or requiring a change in +the boiler design. In certain water-tube boilers the baffle arrangement +is such that if a superheater is to be installed a complete change in +the ordinary baffle design is necessary. Frequently to insure +sufficiently hot gas striking the heating surfaces, a portion is +by-passed directly from the furnace to the superheater chamber without +passing over any of the boiler heating surfaces. Any such arrangement +will lead to a decrease in economy and the use of boilers requiring it +should be avoided. + +Capacity--Babcock & Wilcox boilers are run successfully in every-day +practice at higher ratings than any other boilers in practical service. +The capacities thus obtainable are due directly to the efficient +circulation already pointed out. Inasmuch as the construction utilizing +headers has a direct bearing in producing such circulation, it is also +connected with the high capacities obtainable with this apparatus. + +Where intelligently handled and kept properly cleaned, Babcock & Wilcox +boilers are operated in many plants at from 200 to 225 per cent of their +rated evaporative capacity and it is not unusual for them to be operated +at 300 per cent of such rated capacity during periods of peak load. + +Dry Steam--In the list of the requirements of the perfect steam boiler, +the necessity that dry steam be generated has been pointed out. The +Babcock & Wilcox boiler will deliver dry steam under higher capacities +and poorer conditions of feed water than any other boiler now +manufactured. Certain boilers will, when operated at ordinary ratings, +handle poor feed water and deliver steam in which the moisture content +is not objectionable. When these same boilers are driven at high +overloads, there will be a direct tendency to prime and the percentage +of moisture in the steam delivered will be high. This tendency is the +result of the lack of proper circulation and once more there is seen the +advantage of the headers of the Babcock & Wilcox boiler, resulting as it +does in the securing of a positive circulation. + +In the design of the Babcock & Wilcox boiler sufficient space is +provided between the steam outlet and the disengaging point to insure +the steam passing from the boiler in a dry state without entraining or +again picking up any particles of water in its passage even at high +rates of evaporation. Ample time is given for a complete separation of +steam from the water at the disengaging surface before the steam is +carried from the boiler. These two features, which are additional causes +for the ability of the Babcock & Wilcox boiler to deliver dry steam, +result from the proper proportioning of the steam and water space of the +boiler. From the history of the development of the boiler, it is evident +that the cubical capacity per horse power of the steam and water space +has been adopted after numerous experiments. + +That the "dry pipe" serves in no way the generally understood function +of such device has been pointed out. As stated, the function of the "dry +pipe" in a Babcock & Wilcox boiler is simply that of a collecting pipe +and this statement holds true regardless of the rate of operation of the +boiler. + +In certain boilers, "superheating surface" is provided to "dry the +steam," or to remove the moisture due to priming or foaming. Such +surface is invariably a source of trouble unless the steam is initially +dry and a boiler which will deliver dry steam is obviously to be +preferred to one in which surface must be supplied especially for such +purpose. Where superheaters are installed with Babcock & Wilcox boilers, +they are in every sense of the word superheaters and not driers, the +steam being delivered to them in a dry state. + +The question has been raised in connection with the cross drum design of +the Babcock & Wilcox boiler as to its ability to deliver dry steam. +Experience has shown the absolute lack of basis for any such objection. +The Babcock & Wilcox Company at its Bayonne Works some time ago made a +series of experiments to see in what manner the steam generated was +separated from the water either in the drum or in its passage to the +drum. Glass peepholes were installed in each end of a drum in a boiler +of the marine design, at the point midway between that at which the +horizontal circulating tubes entered the drum and the drum baffle plate. +By holding a light at one of these peepholes the action in the drum was +clearly seen through the other. It was found that with the boiler +operated under three-quarter inch ashpit pressure, which, with the fuel +used would be equivalent to approximately 185 per cent of rating for +stationary boiler practice, that each tube was delivering with great +velocity a stream of solid water, which filled the tube for half its +cross sectional area. There was no spray or mist accompanying such +delivery, clearly indicating that the steam had entirely separated from +the water in its passage through the horizontal circulating tubes, which +in the boiler in question were but 50 inches long. + +[Illustration: Northwest Station of the Commonwealth Edison Co., +Chicago, Ill. This Installation Consists of 11,360 Horse Power of +Babcock & Wilcox Boilers and Superheaters, Equipped with Babcock & +Wilcox Chain Grate Stokers] + +These experiments proved conclusively that the size of the steam drums +in the cross drum design has no appreciable effect in determining the +amount of liberating surface, and that sufficient liberating surface is +provided in the circulating tubes alone. If further proof of the ability +of this design of boiler to deliver dry steam is required, such proof is +perhaps best seen in the continued use of the Babcock & Wilcox marine +boiler, in which the cross drum is used exclusively, and with which +rates of evaporation are obtained far in excess of those secured in +ordinary practice. + +Quick Steaming--The advantages of water-tube boilers as a class over +fire-tube boilers in ability to raise steam quickly have been indicated. + +Due to the constant and thorough circulation resulting from the +sectional nature of the Babcock & Wilcox boiler, steam may be raised +more rapidly than in practically any other water-tube design. + +In starting up a cold Babcock & Wilcox boiler with either coal or oil +fuel, where a proper furnace arrangement is supplied, steam may be +raised to a pressure of 200 pounds in less than half an hour. With a +Babcock & Wilcox boiler in a test where forced draft was available, +steam was raised from an initial temperature of the boiler and its +contained water of 72 degrees to a pressure of 200 pounds, in 12-1/2 +minutes after lighting the fire. The boiler also responds quickly in +starting from banked fires, especially where forced draft is available. + +In Babcock & Wilcox boilers the water is divided into many small streams +which circulate without undue frictional resistance in thin envelopes +passing through the hottest part of the furnace, the steam being carried +rapidly to the disengaging surface. There is no part of the boiler +exposed to the heat of the fire that is not in contact with water +internally, and as a result there is no danger of overheating on +starting up quickly nor can leaks occur from unequal expansion such as +might be the case where an attempt is made to raise steam rapidly in +boilers using water leg construction. + +Storage Capacity for Steam and Water--Where sufficient steam and water +capacity are not provided in a boiler, its action will be irregular, the +steam pressure varying over wide limits and the water level being +subject to frequent and rapid fluctuation. + +Owing to the small relative weight of steam, water capacity is of +greater importance in this respect than steam space. With a gauge +pressure of 180 pounds per square inch, 8 cubic feet of steam, which is +equivalent to one-half cubic foot of water space, are required to supply +one boiler horse power for one minute and if no heat be supplied to the +boiler during such an interval, the pressure will drop to 150 pounds per +square inch. The volume of steam space, therefore, may be over rated, +but if this be too small, the steam passing off will carry water with it +in the form of spray. Too great a water space results in slow steaming +and waste of fuel in starting up; while too much steam space adds to the +radiating surface and increases the losses from that cause. + +That the steam and water space of the Babcock & Wilcox boiler are the +result of numerous experiments has previously been pointed out. + +Accessibility--Cleaning. That water-tube boilers are more accessible as +a class than are fire-tube boilers has been indicated. All water-tube +boilers, however, are not equally accessible. In certain designs, due to +the arrangement of baffling used it is practically impossible to remove +all deposits of soot and dirt. Frequently, in order to cheapen the +product, sufficient cleaning and access doors are not supplied as part +of the boiler equipment. The tendency of soot to collect on the crown +sheets of certain vertical water-tube boilers has been noted. Such +deposits are difficult to remove and if corrosion goes on beneath such a +covering the sheet may crack and an explosion result. + +[Illustration: Rear View--Longitudinal Drum Vertical Header Boiler, +Showing Access Doors to Rear Headers] + +It is almost impossible to thoroughly clean water legs internally, and +in such places also is there a tendency to unsuspected corrosion under +deposits that cannot be removed. + +In Babcock & Wilcox boilers every portion of the interior of the heating +surfaces can be reached and kept clean, while any soot deposited on the +exterior surfaces can be blown off while the boiler is under pressure. + +Inspection--The accessibility which makes possible the thorough cleaning +of all portions of the Babcock & Wilcox boiler also provides a means for +a thorough inspection. + +Drums are accessible for internal inspection by the removal of the +manhole plates. Front headers may be inspected through large doors +furnished for the purpose. Rear headers in the inclined header designs +may be inspected from the chamber formed by such headers and the rear +wall of the boiler. In the vertical header designs rear tube doors are +furnished, as has been stated. In certain designs of water-tube boilers +in order to assure accessibility for inspection of the rear ends of the +tubes, the rear portion of the boiler is exposed to the atmosphere with +resulting excessive radiation losses. In other designs the means of +access to the rear ends of the tubes are of a makeshift and +unworkmanlike character. + +By the removal of handhole plates, all tubes in a Babcock & Wilcox +boiler may be inspected for their full length either for the presence of +scale or for suspected corrosion. + +Repairs--In Babcock & Wilcox boilers the possession of great strength, +the elimination of stresses due to uneven temperatures and of the +resulting danger of leaks and corrosion, the protection of the drums +from the intense heat of the fire, and the decreased liability of the +scale forming matter to lodge on the hottest tube surfaces, all tend to +minimize the necessity for repairs. The tubes of the Babcock & Wilcox +boiler are practically the only part which may need renewal and these +only at infrequent intervals When necessary, such renewals may be made +cheaply and quickly. A small stock of tubes, 4 inches in diameter, of +sufficient length for the boiler used, is all that need be carried to +make renewals. + +Repairs in water-leg boilers are difficult at best and frequently +unsatisfactory when completed. When staybolt replacements are necessary, +in order to get at the inner sheet of the water leg, several tubes must +in some cases be cut out. Not infrequently a replacement of an entire +water leg is necessary and this is difficult and requires a lengthy +shutdown. With the Babcock & Wilcox boiler, on the other hand, even if +it is necessary to replace a section, this may be done in a few hours +after the boiler is cool. + +In the case of certain staybolt failures the working pressure of a +repaired boiler utilizing such construction will frequently be lowered +by the insurance companies when the boiler is again placed in service. +The sectional nature of the Babcock & Wilcox boiler enables it to +maintain its original working pressure over long periods of time, almost +regardless of the nature of any repair that may be required. + +[Illustration: 1456 Horse-power Installation of Babcock & Wilcox Boilers +at the Raritan Woolen Mills, Raritan, N. J. The First of These Boilers +were Installed in 1878 and 1881 and are still Operated at 80 Pounds +Pressure] + +Durability--Babcock & Wilcox boilers are being operated in every-day +service with entirely satisfactory results and under the same steam +pressure as that for which they were originally sold that have been +operated from thirty to thirty-five years. It is interesting to note in +considering the life of a boiler that the length of life of a Babcock & +Wilcox boiler must be taken as the criterion of what length of life is +possible. This is due to the fact that there are Babcock & Wilcox +boilers in operation to-day that have been in service from a time that +antedates by a considerable margin that at which the manufacturer of any +other water-tube boiler now on the market was started. + +Probably the very best evidence of the value of the Babcock & Wilcox +boiler as a steam generator and of the reliability of the apparatus, is +seen in the sales of the company. Since the company was formed, there +have been sold throughout the world over 9,900,000 horse power. + +A feature that cannot be overlooked in the consideration of the +advantages of the Babcock & Wilcox boiler is the fact that as a part of +the organization back of the boiler, there is a body of engineers of +recognized ability, ready at all times to assist its customers in every +possible way. + +[Illustration: 2400 Horse-power Installation of Babcock & Wilcox Boilers +in the Union Station Power House of the Pennsylvania Railroad Co., +Pittsburgh, Pa. This Company has a Total of 28,500 Horse Power of +Babcock & Wilcox Boilers Installed] + + + + +HEAT AND ITS MEASUREMENT + + +The usual conception of heat is that it is a form of energy produced by +the vibratory motion of the minute particles or molecules of a body. All +bodies are assumed to be composed of these molecules, which are held +together by mutual cohesion and yet are in a state of continual +vibration. The hotter a body or the more heat added to it, the more +vigorous will be the vibrations of the molecules. + +As is well known, the effect of heat on a body may be to change its +temperature, its volume, or its state, that is, from solid to liquid or +from liquid to gaseous. Where water is melted from ice and evaporated +into steam, the various changes are admirably described in the lecture +by Mr. Babcock on "The Theory of Steam Making", given in the next +chapter. + +The change in temperature of a body is ordinarily measured by +thermometers, though for very high temperatures so-called pyrometers are +used. The latter are dealt with under the heading "High Temperature +Measurements" at the end of this chapter. + +[Illustration: Fig. 11] + +By reason of the uniform expansion of mercury and its great +sensitiveness to heat, it is the fluid most commonly used in the +construction of thermometers. In all thermometers the freezing point and +the boiling point of water, under mean or average atmospheric pressure +at sea level, are assumed as two fixed points, but the division of the +scale between these two points varies in different countries. The +freezing point is determined by the use of melting ice and for this +reason is often called the melting point. There are in use three +thermometer scales known as the Fahrenheit, the Centigrade or Celsius, +and the Reaumur. As shown in Fig. 11, in the Fahrenheit scale, the space +between the two fixed points is divided into 180 parts; the boiling +point is marked 212, and the freezing point is marked 32, and zero is a +temperature which, at the time this thermometer was invented, was +incorrectly imagined to be the lowest temperature attainable. In the +centigrade and the Reaumur scales, the distance between the two fixed +points is divided into 100 and 80 parts, respectively. In each of these +two scales the freezing point is marked zero, and the boiling point is +marked 100 in the centigrade and 80 in the Reaumur. Each of the 180, 100 +or 80 divisions in the respective thermometers is called a degree. + +Table 3 and appended formulae are useful for converting from one scale +to another. + +In the United States the bulbs of high-grade thermometers are usually +made of either Jena 58^{III} borosilicate thermometer glass or Jena +16^{III} glass, the stems being made of ordinary glass. The Jena +16^{III} glass is not suitable for use at temperatures much above 850 +degrees Fahrenheit and the harder Jena 59^{III} should be used in +thermometers for temperatures higher than this. + +Below the boiling point, the hydrogen-gas thermometer is the almost +universal standard with which mercurial thermometers may be compared, +while above this point the nitrogen-gas thermometer is used. In both of +these standards the change in temperature is measured by the change in +pressure of a constant volume of the gas. + +In graduating a mercurial thermometer for the Fahrenheit scale, +ordinarily a degree is represented as 1/180 part of the volume of the +stem between the readings at the melting point of ice and the boiling +point of water. For temperatures above the latter, the scale is extended +in degrees of the same volume. For very accurate work, however, the +thermometer may be graduated to read true-gas-scale temperatures by +comparing it with the gas thermometer and marking the temperatures at 25 +or 50 degree intervals. Each degree is then 1/25 or 1/50 of the volume +of the stem in each interval. + +Every thermometer, especially if intended for use above the boiling +point, should be suitably annealed before it is used. If this is not +done, the true melting point and also the "fundamental interval", that +is, the interval between the melting and the boiling points, may change +considerably. After continued use at the higher temperatures also, the +melting point will change, so that the thermometer must be calibrated +occasionally to insure accurate readings. + + TABLE 3 + + COMPARISON OF THERMOMETER SCALES + ++---------------+----------+----------+----------+ +| |Fahrenheit|Centigrade| Reaumur | ++---------------+----------+----------+----------+ +|Absolute Zero | -459.64 | -273.13 | -218.50 | +| | 0 | -17.78 | -14.22 | +| | 10 | -12.22 | -9.78 | +| | 20 | -6.67 | -5.33 | +| | 30 | -1.11 | -0.89 | +|Freezing Point | 32 | 0 | 0 | +|Maximum Density| | | | +| of Water | 39.1 | 3.94 | 3.15 | +| | 50 | 10 | 8 | +| | 75 | 23.89 | 19.11 | +| | 100 | 37.78 | 30.22 | +| | 200 | 93.33 | 74.67 | +|Boiling Point | 212 | 100 | 80 | +| | 250 | 121.11 | 96.89 | +| | 300 | 148.89 | 119.11 | +| | 350 | 176.67 | 141.33 | ++---------------+----------+----------+----------+ + +F = 9/5C+32deg. = 9/4R+32deg. + +C = 5/9(F-32deg.) = 5/4R + +R = 4/9(F-32deg.) = 4/5C + +As a general rule thermometers are graduated to read correctly for total +immersion, that is, with bulb and stem of the thermometer at the same +temperature, and they should be used in this way when compared with a +standard thermometer. If the stem emerges into space either hotter or +colder than that in which the bulb is placed, a "stem correction" must +be applied to the observed temperature in addition to any correction +that may be found in the comparison with the standard. For instance, for +a particular thermometer, comparison with the standard with both fully +immersed made necessary the following corrections: + +_Temperature_ _Correction_ + 40deg.F 0.0 + 100 0.0 + 200 0.0 + 300 +2.5 + 400 -0.5 + 500 -2.5 + +When the sign of the correction is positive (+) it must be added to the +observed reading, and when the sign is a negative (-) the correction +must be subtracted. The formula for the stem correction is as follows: + +Stem correction = 0.000085 x n (T-t) + +in which T is the observed temperature, t is the mean temperature of the +emergent column, n is the number of degrees of mercury column emergent, +and 0.000085 is the difference between the coefficient of expansion of +the mercury and that in the glass in the stem. + +Suppose the observed temperature is 400 degrees and the thermometer is +immersed to the 200 degrees mark, so that 200 degrees of the mercury +column project into the air. The mean temperature of the emergent column +may be found by tying another thermometer on the stem with the bulb at +the middle of the emergent mercury column as in Fig. 12. Suppose this +mean temperature is 85 degrees, then + +Stem correction = 0.000085 x 200 x (400 - 85) = 5.3 degrees. + +As the stem is at a lower temperature than the bulb, the thermometer +will evidently read too low, so that this correction must be added to +the observed reading to find the reading corresponding to total +immersion. The corrected reading will therefore be 405.3 degrees. If +this thermometer is to be corrected in accordance with the calibrated +corrections given above, we note that a further correction of 0.5 must +be applied to the observed reading at this temperature, so that the +correct temperature is 405.3 - 0.5 = 404.8 degrees or 405 degrees. + +[Illustration: Fig. 12] + +[Illustration: Fig. 13] + +Fig. 12 shows how a stem correction can be obtained for the case just +described. + +Fig. 13 affords an opportunity for comparing the scale of a thermometer +correct for total immersion with one which will read correctly when +submerged to the 300 degrees mark, the stem being exposed at a mean +temperature of 110 degrees Fahrenheit, a temperature often prevailing +when thermometers are used for measuring temperatures in steam mains. + +Absolute Zero--Experiments show that at 32 degrees Fahrenheit a perfect +gas expands 1/491.64 part of its volume if its pressure remains constant +and its temperature is increased one degree. Thus if gas at 32 degrees +Fahrenheit occupies 100 cubic feet and its temperature is increased one +degree, its volume will be increased to 100 + 100/491.64 = 100.203 cubic +feet. For a rise of two degrees the volume would be 100 + (100 x 2) / +491.64 = 100.406 cubic feet. If this rate of expansion per one degree +held good at all temperatures, and experiment shows that it does above +the freezing point, the gas, if its pressure remained the same, would +double its volume, if raised to a temperature of 32 + 491.64 = 523.64 +degrees Fahrenheit, while under a diminution of temperature it would +shrink and finally disappear at a temperature of 491.64 - 32 = 459.64 +degrees below zero Fahrenheit. While undoubtedly some change in the law +would take place before the lower temperature could be reached, there is +no reason why the law may not be used within the range of temperature +where it is known to hold good. From this explanation it is evident that +under a constant pressure the volume of a gas will vary as the number of +degrees between its temperature and the temperature of -459.64 degrees +Fahrenheit. To simplify the application of the law, a new thermometric +scale is constructed as follows: the point corresponding to -460 degrees +Fahrenheit, is taken as the zero point on the new scale, and the degrees +are identical in magnitude with those on the Fahrenheit scale. +Temperatures referred to this new scale are called absolute temperatures +and the point -460 degrees Fahrenheit (= -273 degrees centigrade) is +called the absolute zero. To convert any temperature Fahrenheit to +absolute temperature, add 460 degrees to the temperature on the +Fahrenheit scale: thus 54 degrees Fahrenheit will be 54 + 460 = 514 +degrees absolute temperature; 113 degrees Fahrenheit will likewise be +equal to 113 + 460 = 573 degrees absolute temperature. If one pound of +gas is at a temperature of 54 degrees Fahrenheit and another pound is at +a temperature of 114 degrees Fahrenheit the respective volumes at a +given pressure would be in the ratio of 514 to 573. + +[Illustration: Ninety-sixth Street Station of the New York Railways Co., +New York City, Operating 20,000 Horse Power of Babcock & Wilcox Boilers. +This Company and its Allied Companies Operate a Total of 100,000 Horse +Power of Babcock & Wilcox Boilers] + +British Thermal Unit--The quantitative measure of heat is the British +thermal unit, ordinarily written B. t. u. This is the quantity of heat +required to raise the temperature of one pound of pure water one degree +at 62 degrees Fahrenheit; that is, from 62 degrees to 63 degrees. In the +metric system this unit is the _calorie_ and is the heat necessary +to raise the temperature of one kilogram of pure water from 15 degrees +to 16 degrees centigrade. These two definitions lead to a discrepancy of +0.03 of 1 per cent, which is insignificant for engineering purposes, and +in the following the B. t. u. is taken with this discrepancy ignored. +The discrepancy is due to the fact that there is a slight difference in +the specific heat of water at 15 degrees centigrade and 62 degrees +Fahrenheit. The two units may be compared thus: + +1 Calorie = 3.968 B. t. u. 1 B. t. u. = 0.252 Calories. + +_Unit_ _Water_ _Temperature Rise_ +1 B. t. u. 1 Pound 1 Degree Fahrenheit +1 Calorie 1 Kilogram 1 Degree centigrade + +But 1 kilogram = 2.2046 pounds and 1 degree centigrade = 9/5 degree +Fahrenheit. + +Hence 1 calorie = (2.2046 x 9/5) = 3.968 B. t. u. + + +The heat values in B. t. u. are ordinarily given per pound, and the heat +values in calories per kilogram, in which case the B. t. u. per pound +are approximately equivalent to 9/5 the calories per kilogram. + +As determined by Joule, heat energy has a certain definite relation to +work, one British thermal unit being equivalent from his determinations +to 772 foot pounds. Rowland, a later investigator, found that 778 foot +pounds were a more exact equivalent. Still later investigations indicate +that the correct value for a B. t. u. is 777.52 foot pounds or +approximately 778. The relation of heat energy to work as determined is +a demonstration of the first law of thermo-dynamics, namely, that heat +and mechanical energy are mutually convertible in the ratio of 778 foot +pounds for one British thermal unit. This law, algebraically expressed, +is W = JH; W being the work done in foot pounds, H being the heat in +B. t. u., and J being Joules equivalent. Thus 1000 B. t. u.'s would be +capable of doing 1000 x 778 = 778000 foot pounds of work. + +Specific Heat--The specific heat of a substance is the quantity of heat +expressed in thermal units required to raise or lower the temperature of +a unit weight of any substance at a given temperature one degree. This +quantity will vary for different substances For example, it requires +about 16 B. t. u. to raise the temperature of one pound of ice 32 +degrees or 0.5 B. t. u. to raise it one degree, while it requires +approximately 180 B. t. u. to raise the temperature of one pound of +water 180 degrees or one B. t. u. for one degree. + +If then, a pound of water be considered as a standard, the ratio of the +amount of heat required to raise a similar unit of any other substance +one degree, to the amount required to raise a pound of water one degree +is known as the specific heat of that substance. Thus since one pound of +water required one B. t. u. to raise its temperature one degree, and one +pound of ice requires about 0.5 degrees to raise its temperature one +degree, the ratio is 0.5 which is the specific heat of ice. To be exact, +the specific heat of ice is 0.504, hence 32 degrees x 0.504 = 16.128 +B. t. u. would be required to raise the temperature of one pound of ice +from 0 to 32 degrees. For solids, at ordinary temperatures, the specific +heat may be considered a constant for each individual substance, +although it is variable for high temperatures. In the case of gases a +distinction must be made between specific heat at constant volume, and +at constant pressure. + +Where specific heat is stated alone, specific heat at ordinary +temperature is implied, and _mean_ specific heat refers to the average +value of this quantity between the temperatures named. + +The specific heat of a mixture of gases is obtained by multiplying the +specific heat of each constituent gas by the percentage by weight of +that gas in the mixture, and dividing the sum of the products by 100. +The specific heat of a gas whose composition by weight is CO_{2}, 13 per +cent; CO, 0.4 per cent; O, 8 per cent; N, 78.6 per cent, is found as +follows: + +CO_{2} : 13 x 0.217 = 2.821 +CO : 0.4 x 0.2479 = 0.09916 +O : 8 x 0.2175 = 1.74000 +N : 78.6 x 0.2438 = 19.16268 + -------- + 100.0 23.82284 + +and 23.8228 / 100 = 0.238 = specific heat of the gas. + + +The specific heats of various solids, liquids and gases are given in +Table 4. + +Sensible Heat--The heat utilized in raising the temperature of a body, +as that in raising the temperature of water from 32 degrees up to the +boiling point, is termed sensible heat. In the case of water, the +sensible heat required to raise its temperature from the freezing point +to the boiling point corresponding to the pressure under which +ebullition occurs, is termed the heat of the liquid. + +Latent Heat--Latent heat is the heat which apparently disappears in +producing some change in the condition of a body without increasing its +temperature If heat be added to ice at freezing temperature, the ice +will melt but its temperature will not be raised. The heat so utilized +in changing the condition of the ice is the latent heat and in this +particular case is known as the latent heat of fusion. If heat be added +to water at 212 degrees under atmospheric pressure, the water will not +become hotter but will be evaporated into steam, the temperature of +which will also be 212 degrees. The heat so utilized is called the +latent heat of evaporation and is the heat which apparently disappears +in causing the substance to pass from a liquid to a gaseous state. + + TABLE 4 + + SPECIFIC HEATS OF VARIOUS SUBSTANCES ++--------------------------------------------------------------------+ +| SOLIDS | ++-------------------------------+----------------+-------------------+ +| | Temperature[2]| | +| | Degrees | Specific | +| | Fahrenheit | Heat | ++-------------------------------+----------------+-------------------+ +| Copper | 59-460 | .0951 | +| Gold | 32-212 | .0316 | +| Wrought Iron | 59-212 | .1152 | +| Cast Iron | 68-212 | .1189 | +| Steel (soft) | 68-208 | .1175 | +| Steel (hard) | 68-208 | .1165 | +| Zinc | 32-212 | .0935 | +| Brass (yellow) | 32 | .0883 | +| Glass (normal ther. 16^{III}) | 66-212 | .1988 | +| Lead | 59 | .0299 | +| Platinum | 32-212 | .0323 | +| Silver | 32-212 | .0559 | +| Tin | -105-64 | .0518 | +| Ice | | .5040 | +| Sulphur (newly fused) | | .2025 | ++-------------------------------+----------------+-------------------+ +| LIQUIDS | ++-------------------------------+----------------+-------------------+ +| | Temperature[2]| | +| | Degrees | Specific | +| | Fahrenheit | Heat | ++-------------------------------+----------------+-------------------+ +| Water[3] | 59 | 1.0000 | +| Alcohol | 32 | .5475 | +| | 176 | .7694 | +| Mercury | 32 | .03346 | +| Benzol | 50 | .4066 | +| | 122 | .4502 | +| Glycerine | 59-102 | .576 | +| Lead (Melted) | to 360 | .0410 | +| Sulphur (melted) | 246-297 | .2350 | +| Tin (melted) | | .0637 | +| Sea Water (sp. gr. 1.0043) | 64 | .980 | +| Sea Water (sp. gr. 1.0463) | 64 | .903 | +| Oil of Turpentine | 32 | .411 | +| Petroleum | 64-210 | .498 | +| Sulphuric Acid | 68-133 | .3363 | ++-------------------------------+----------------+-------------------+ +| GASES | ++--------------------------+---------------+--------------+----------+ +| | | Specific | Specific | +| | Temperature[2]| Heat at | Heat at | +| | Degrees | Constant | Constant | +| | Fahrenheit | Pressure | Volume | ++--------------------------+---------------+--------------+----------+ +| Air | 32-392 | .2375 | .1693 | +| Oxygen | 44-405 | .2175 | .1553 | +| Nitrogen | 32-392 | .2438 | .1729 | +| Hydrogen | 54-388 | 3.4090 | 2.4141 | +| Superheated Steam | | See table 25 | | +| Carbon Monoxide | 41-208 | .2425 | .1728 | +| Carbon Dioxide | 52-417 | .2169 | .1535 | +| Methane | 64-406 | .5929 | .4505 | +| Blast Fur. Gas (approx.) | ... | .2277 | ... | +| Flue gas (approx.) | ... | .2400 | ... | ++--------------------------+---------------+--------------+----------+ + +Latent heat is not lost, but reappears whenever the substances pass +through a reverse cycle, from a gaseous to a liquid, or from a liquid to +a solid state. It may, therefore, be defined as stated, as the heat +which apparently disappears, or is lost to thermometric measurement, +when the molecular constitution of a body is being changed. Latent heat +is expended in performing the work of overcoming the molecular cohesion +of the particles of the substance and in overcoming the resistance of +external pressure to change of volume of the heated body. Latent heat of +evaporation, therefore, may be said to consist of internal and external +heat, the former being utilized in overcoming the molecular resistance +of the water in changing to steam, while the latter is expended in +overcoming any resistance to the increase of its volume during +formation. In evaporating a pound of water at 212 degrees to steam at +212 degrees, 897.6 B. t. u. are expended as internal latent heat and +72.8 B. t. u. as external latent heat. For a more detailed description +of the changes brought about in water by sensible and latent heat, the +reader is again referred to the chapter on "The Theory of Steam Making". + +Ebullition--The temperature of ebullition of any liquid, or its boiling +point, may be defined as the temperature which exists where the addition +of heat to the liquid no longer increases its temperature, the heat +added being absorbed or utilized in converting the liquid into vapor. +This temperature is dependent upon the pressure under which the liquid +is evaporated, being higher as the pressure is greater. + + TABLE 5 + +BOILING POINTS AT ATMOSPHERIC PRESSURE + ++---------------------+--------------+ +| | Degrees | +| | Fahrenheit | ++---------------------+--------------+ +| Ammonia | 140 | +| Bromine | 145 | +| Alcohol | 173 | +| Benzine | 212 | +| Water | 212 | +| Average Sea Water | 213.2 | +| Saturated Brine | 226 | +| Mercury | 680 | ++---------------------+--------------+ + +Total Heat of Evaporation--The quantity of heat required to raise a unit +of any liquid from the freezing point to any given temperature, and to +entirely evaporate it at that temperature, is the total heat of +evaporation of the liquid for that temperature. It is the sum of the +heat of the liquid and the latent heat of evaporation. + +To recapitulate, the heat added to a body is divided as follows: + +Total heat = Heat to change the temperature + heat to overcome the + molecular cohesion + heat to overcome the external pressure + resisting an increase of volume of the body. + +Where water is converted into steam, this total heat is divided as +follows: + +Total heat = Heat to change the temperature of the water + heat to + separate the molecules of the water + heat to overcome + resistance to increase in volume of the steam, + = Heat of the liquid + internal latent heat + external + latent heat, + = Heat of the liquid + total latent heat of steam, + = Total heat of evaporation. + +The steam tables given on pages 122 to 127 give the heat of the liquid +and the total latent heat through a wide range of temperatures. + +Gases--When heat is added to gases there is no internal work done; hence +the total heat is that required to change the temperature plus that +required to do the external work. If the gas is not allowed to expand +but is preserved at constant volume, the entire heat added is that +required to change the temperature only. + +Linear Expansion of Substances by Heat--To find the increase in the +length of a bar of any material due to an increase of temperature, +multiply the number of degrees of increase in temperature by the +coefficient of expansion for one degree and by the length of the bar. +Where the coefficient of expansion is given for 100 degrees, as in Table +6, the result should be divided by 100. The expansion of metals per one +degree rise of temperature increases slightly as high temperatures are +reached, but for all practical purposes it may be assumed to be constant +for a given metal. + + TABLE 6 + + LINEAL EXPANSION OF SOLIDS AT ORDINARY TEMPERATURES + + (Tabular values represent increase per foot per 100 degrees increase + in temperature, Fahrenheit or centigrade) + ++-------------------+--------------+----------------+----------------+ +| | Temperature | | | +| | Conditions[4]|Coefficient per |Coefficient per | +| Substance | Degrees | 100 Degrees | 100 Degrees | +| | Fahrenheit | Fahrenheit | Centigrade | ++-------------------+--------------+----------------+----------------+ +|Brass (cast) | 32 to 212 | .001042 | .001875 | +|Brass (wire) | 32 to 212 | .001072 | .001930 | +|Copper | 32 to 212 | .000926 | .001666 | +|Glass (English | | | | +|flint) | 32 to 212 | .000451 | .000812 | +|Glass (French | | | | +|flint) | 32 to 212 | .000484 | .000872 | +|Gold | 32 to 212 | .000816 | .001470 | +|Granite (average) | 32 to 212 | .000482 | .000868 | +|Iron (cast) | 104 | .000589 | .001061 | +|Iron (soft forged) | 0 to 212 | .000634 | .001141 | +|Iron (wire) | 32 to 212 | .000800 | .001440 | +|Lead | 32 to 212 | .001505 | .002709 | +|Mercury | 32 to 212 | .009984[5] | .017971 | +|Platinum | 104 | .000499 | .000899 | +|Limestone | 32 to 212 | .000139 | .000251 | +|Silver | 104 | .001067 | .001921 | +|Steel (Bessemer | | | | +|rolled, hard) | 0 to 212 | .00056 | .00101 | +|Steel (Bessemer | | | | +|rolled, soft) | 0 to 212 | .00063 | .00117 | +|Steel (cast, | | | | +|French) | 104 | .000734 | .001322 | +|Steel (cast | | | | +|annealed, English) | 104 | .000608 | .001095 | ++-------------------+--------------+----------------+----------------+ + +High Temperature Measurements--The temperatures to be dealt with in +steam-boiler practice range from those of ordinary air and steam to the +temperatures of burning fuel. The gases of combustion, originally at the +temperature of the furnace, cool as they pass through each successive +bank of tubes in the boiler, to nearly the temperature of the steam, +resulting in a wide range of temperatures through which definite +measurements are sometimes required. + +Of the different methods devised for ascertaining these temperatures, +some of the most important are as follows: + + 1st. Mercurial pyrometers for temperatures up to 1000 degrees + Fahrenheit. + + 2nd. Expansion pyrometers for temperatures up to 1500 degrees + Fahrenheit. + + 3rd. Calorimetry for temperatures up to 2000 degrees Fahrenheit. + + 4th. Thermo-electric pyrometers for temperatures up to 2900 + degrees Fahrenheit. + + 5th. Melting points of metal which flow at various temperatures + up to the melting point of platinum 3227 degrees Fahrenheit. + + 6th. Radiation pyrometers for temperatures up to 3600 degrees + Fahrenheit. + + 7th. Optical pyrometers capable of measuring temperatures up to + 12,600 degrees Fahrenheit.[6] For ordinary boiler practice + however, their range is 1600 to 3600 degrees Fahrenheit. + +[Illustration: 228 Horse-power Babcock & Wilcox Boiler, Installed at the +Wentworth Institute, Boston, Mass.] + +Table 7 gives the degree of accuracy of high temperature measurements. + + TABLE 7 + + ACCURACY OF HIGH TEMPERATURE MEASUREMENTS[7] + ++------------------------+------------------------+ +| Centigrade | Fahrenheit | ++-------------+----------+-------------+----------+ +| | Accuracy | | Accuracy | +| Temperature | Plus or | Temperature | Plus or | +| Range | Minus | Range | Minus | +| | Degrees | | Degrees | ++-------------+----------+-------------+----------+ +| 200- 500 | 0.5 | 392- 932 | 0.9 | +| 500- 800 | 2 | 932-1472 | 3.6 | +| 800-1100 | 3 | 1472-2012 | 5.4 | +| 1100-1600 | 15 | 2012-2912 | 27 | +| 1600-2000 | 25 | 2912-3632 | 45 | ++-------------+----------+-------------+----------+ + + +Mercurial Pyrometers--At atmospheric pressure mercury boils at 676 +degrees Fahrenheit and even at lower temperatures the mercury in +thermometers will be distilled and will collect in the upper part of the +stem. Therefore, for temperatures much above 400 degrees Fahrenheit, +some inert gas, such as nitrogen or carbon dioxide, must be forced under +pressure into the upper part of the thermometer stem. The pressure at +600 degrees Fahrenheit is about 15 pounds, or slightly above that of the +atmosphere, at 850 degrees about 70 pounds, and at 1000 degrees about +300 pounds. + +Flue-gas temperatures are nearly always taken with mercurial +thermometers as they are the most accurate and are easy to read and +manipulate. Care must be taken that the bulb of the instrument projects +into the path of the moving gases in order that the temperature may +truly represent the flue gas temperature. No readings should be +considered until the thermometer has been in place long enough to heat +it up to the full temperature of the gases. + + +Expansion Pyrometers--Brass expands about 50 per cent more than iron and +in both brass and iron the expansion is nearly proportional to the +increase in temperature. This phenomenon is utilized in expansion +pyrometers by enclosing a brass rod in an iron pipe, one end of the rod +being rigidly attached to a cap at the end of the pipe, while the other +is connected by a multiplying gear to a pointer moving around a +graduated dial. The whole length of the expansion piece must be at a +uniform temperature before a correct reading can be obtained. This fact, +together with the lost motion which is likely to exist in the mechanism +connected to the pointer, makes the expansion pyrometer unreliable; it +should be used only when its limitations are thoroughly understood and +it should be carefully calibrated. Unless the brass and iron are known +to be of the same temperature, its action will be anomalous: for +instance, if it be allowed to cool after being exposed to a high +temperature, the needle will rise before it begins to fall. Similarly, a +rise in temperature is first shown by the instrument as a fall. The +explanation is that the iron, being on the outside, heats or cools more +quickly than the brass. + + +Calorimetry--This method derives its name from the fact that the process +is the same as the determination of the specific heat of a substance by +the water calorimeter, except that in one case the temperature is known +and the specific heat is required, while in the other the specific heat +is known and the temperature is required. The temperature is found as +follows: + +A given weight of some substance such as iron, nickel or fire brick, is +heated to the unknown temperature and then plunged into water and the +rise in temperature noted. + +If X = temperature to be measured, w = weight of heated body in pounds, +W = weight of water in pounds, T = final temperature of water, t = +difference between initial and final temperatures of water, s = known +specific heat of body. Then X = T + Wt / ws + +Any temperatures secured by this method are affected by so many sources +of error that the results are very approximate. + +Thermo-electric Pyrometers--When wires of two different metals are +joined at one end and heated, an electromotive force will be set up +between the free ends of the wires. Its amount will depend upon the +composition of the wires and the difference in temperature between the +two. If a delicate galvanometer of high resistance be connected to the +"thermal couple", as it is called, the deflection of the needle, after a +careful calibration, will indicate the temperature very accurately. + +In the thermo-electric pyrometer of Le Chatelier, the wires used are +platinum and a 10 per cent alloy of platinum and rhodium, enclosed in +porcelain tubes to protect them from the oxidizing influence of the +furnace gases. The couple with its protecting tubes is called an +"element". The elements are made in different lengths to suit +conditions. + +It is not necessary for accuracy to expose the whole length of the +element to the temperature to be measured, as the electromotive force +depends only upon the temperature of the juncture at the closed end of +the protecting tube and that of the cold end of the element. The +galvanometer can be located at any convenient point, since the length of +the wires leading to it simply alter the resistance of the circuit, for +which allowance may be made. + +The advantages of the thermo-electric pyrometer are accuracy over a wide +range of temperatures, continuity of readings, and the ease with which +observations can be taken. Its disadvantages are high first cost and, in +some cases, extreme delicacy. + +Melting Points of Metals--The approximate temperature of a furnace or +flue may be determined, if so desired, by introducing certain metals of +which the melting points are known. The more common metals form a series +in which the respective melting points differ by 100 to 200 degrees +Fahrenheit, and by using these in order, the temperature can be fixed +between the melting points of some two of them. This method lacks +accuracy, but it suffices for determinations where approximate readings +are satisfactory. + +The approximate melting points of certain metals that may be used for +determinations of this nature are given in Table 8. + +Radiation Pyrometers--These are similar to thermo-electric pyrometers in +that a thermo-couple is employed. The heat rays given out by the hot +body fall on a concave mirror and are brought to a focus at a point at +which is placed the junction of a thermo-couple. The temperature +readings are obtained from an indicator similar to that used with +thermo-electric pyrometers. + +Optical Pyrometers--Of the optical pyrometers the Wanner is perhaps the +most reliable. The principle on which this instrument is constructed is +that of comparing the quantity of light emanating from the heated body +with a constant source of light, in this case a two-volt osmium lamp. +The lamp is placed at one end of an optical tube, while at the other an +eyepiece is provided and a scale. A battery of cells furnishes the +current for the lamp. On looking through the pyrometer, a circle of red +light appears, divided into distinct halves of different intensities. +Adjustment may be made so that the two halves appear alike and a reading +is then taken from the scale. The temperatures are obtained from a table +of temperatures corresponding to scale readings. For standardizing the +osmium lamp, an amylacetate lamp, is provided with a stand for holding +the optical tube. + + TABLE 8 + +APPROXIMATE MELTING POINTS OF METALS[8] + ++-----------------+------------------+ +| Metal | Temperature | +| |Degrees Fahrenheit| ++-----------------+------------------+ +|Wrought Iron | 2737 | +|Pig Iron (gray) | 2190-2327 | +|Cast Iron (white)| 2075 | +|Steel | 2460-2550 | +|Steel (cast) | 2500 | +|Copper | 1981 | +|Zinc | 786 | +|Antimony | 1166 | +|Lead | 621 | +|Bismuth | 498 | +|Tin | 449 | +|Platinum | 3191 | +|Gold | 1946 | +|Silver | 1762 | +|Aluminum | 1216 | ++-----------------+------------------+ + + +Determination of Temperature from Character of Emitted Light--As a +further means of determining approximately the temperature of a furnace, +Table 9, compiled by Messrs. White & Taylor, may be of service. The +color at a given temperature is approximately the same for all kinds of +combustibles under similar conditions. + + TABLE 9 + + CHARACTER OF EMITTED LIGHT AND CORRESPONDING + APPROXIMATE TEMPERATURE[9] + ++--------------------------------------+-----------+ +| Character of Emitted Light |Temperature| +| | Degrees | +| | Fahrenheit| ++--------------------------------------+-----------+ +|Dark red, blood red, low red | 1050 | +|Dark cherry red | 1175 | +|Cherry, full red | 1375 | +|Light cherry, bright cherry, light red| 1550 | +|Orange | 1650 | +|Light orange | 1725 | +|Yellow | 1825 | +|Light yellow | 1975 | +|White | 2200 | ++--------------------------------------+-----------+ + + + + +THE THEORY OF STEAM MAKING + +[Extracts from a Lecture delivered by George H. Babcock, at Cornell +University, 1887[10]] + + +The chemical compound known as H_{2}O exists in three states or +conditions--ice, water and steam; the only difference between these +states or conditions is in the presence or absence of a quantity of +energy exhibited partly in the form of heat and partly in molecular +activity, which, for want of a better name, we are accustomed to call +"latent heat"; and to transform it from one state to another we have +only to supply or extract heat. For instance, if we take a quantity of +ice, say one pound, at absolute zero[11] and supply heat, the first +effect is to raise its temperature until it arrives at a point 492 +Fahrenheit degrees above the starting point. Here it stops growing +warmer, though we keep on adding heat. It, however, changes from ice to +water, and when we have added sufficient heat to have made it, had it +remained ice, 283 degrees hotter or a temperature of 315 degrees +Fahrenheit's thermometer, it has all become water, at the same +temperature at which it commenced to change, namely, 492 degrees above +absolute zero, or 32 degrees by Fahrenheit's scale. Let us still +continue to add heat, and it will now grow warmer again, though at a +slower rate--that is, it now takes about double the quantity of heat to +raise the pound one degree that it did before--until it reaches a +temperature of 212 degrees Fahrenheit, or 672 degrees absolute (assuming +that we are at the level of the sea). Here we find another critical +point. However much more heat we may apply, the water, as water, at that +pressure, cannot be heated any hotter, but changes on the addition of +heat to steam; and it is not until we have added heat enough to have +raised the temperature of the water 966 degrees, or to 1,178 degrees by +Fahrenheit's thermometer (presuming for the moment that its specific +heat has not changed since it became water), that it has all become +steam, which steam, nevertheless, is at the temperature of 212 degrees, +at which the water began to change. Thus over four-fifths of the heat +which has been added to the water has disappeared, or become insensible +in the steam to any of our instruments. + +It follows that if we could reduce steam at atmospheric pressure to +water, without loss of heat, the heat stored within it would cause the +water to be red hot; and if we could further change it to a solid, like +ice, without loss of heat, the solid would be white hot, or hotter than +melted steel--it being assumed, of course, that the specific heat of the +water and ice remain normal, or the same as they respectively are at the +freezing point. + +After steam has been formed, a further addition of heat increases the +temperature again at a much faster ratio to the quantity of heat added, +which ratio also varies according as we maintain a constant pressure or +a constant volume; and I am not aware that any other critical point +exists where this will cease to be the fact until we arrive at that very +high temperature, known as the point of dissociation, at which it +becomes resolved into its original gases. + +The heat which has been absorbed by one pound of water to convert it +into a pound of steam at atmospheric pressure is sufficient to have +melted 3 pounds of steel or 13 pounds of gold. This has been transformed +into something besides heat; stored up to reappear as heat when the +process is reversed. That condition is what we are pleased to call +latent heat, and in it resides mainly the ability of the steam to do +work. + +[Graph: Temperature in Fahrenheit Degrees (from Absolute Zero) +against Quantity of Heat in British Thermal Units] + +The diagram shows graphically the relation of heat to temperature, the +horizontal scale being quantity of heat in British thermal units, and +the vertical temperature in Fahrenheit degrees, both reckoned from +absolute zero and by the usual scale. The dotted lines for ice and water +show the temperature which would have been obtained if the conditions +had not changed. The lines marked "gold" and "steel" show the relation +to heat and temperature and the melting points of these metals. All the +inclined lines would be slightly curved if attention had been paid to +the changing specific heat, but the curvature would be small. It is +worth noting that, with one or two exceptions, the curves of all +substances lie between the vertical and that for water. That is to say, +that water has a greater capacity for heat than all other substances +except two, hydrogen and bromine. + +In order to generate steam, then, only two steps are required: 1st, +procure the heat, and 2nd, transfer it to the water. Now, you have it +laid down as an axiom that when a body has been transferred or +transformed from one place or state into another, the same work has been +done and the same energy expended, whatever may have been the +intermediate steps or conditions, or whatever the apparatus. Therefore, +when a given quantity of water at a given temperature has been made into +steam at a given temperature, a certain definite work has been done, and +a certain amount of energy expended, from whatever the heat may have +been obtained, or whatever boiler may have been employed for the +purpose. + +A pound of coal or any other fuel has a definite heat producing +capacity, and is capable of evaporating a definite quantity of water +under given conditions. That is the limit beyond which even perfection +cannot go, and yet I have known, and doubtless you have heard of, cases +where inventors have claimed, and so-called engineers have certified to, +much higher results. + +The first step in generating steam is in burning the fuel to the best +advantage. A pound of carbon will generate 14,500 British thermal units, +during combustion into carbonic dioxide, and this will be the same, +whatever the temperature or the rapidity at which the combustion may +take place. If possible, we might oxidize it at as slow a rate as that +with which iron rusts or wood rots in the open air, or we might burn it +with the rapidity of gunpowder, a ton in a second, yet the total heat +generated would be precisely the same. Again, we may keep the +temperature down to the lowest point at which combustion can take place, +by bringing large bodies of air in contact with it, or otherwise, or we +may supply it with just the right quantity of pure oxygen, and burn it +at a temperature approaching that of dissociation, and still the heat +units given off will be neither more nor less. It follows, therefore, +that great latitude in the manner or rapidity of combustion may be taken +without affecting the quantity of heat generated. + +But in practice it is found that other considerations limit this +latitude, and that there are certain conditions necessary in order to +get the most available heat from a pound of coal. There are three ways, +and only three, in which the heat developed by the combustion of coal in +a steam boiler furnace may be expended. + +1st, and principally. It should be conveyed to the water in the boiler, +and be utilized in the production of steam. To be perfect, a boiler +should so utilize all the heat of combustion, but there are no perfect +boilers. + +2nd. A portion of the heat of combustion is conveyed up the chimney in +the waste gases. This is in proportion to the weight of the gases, and +the difference between their temperature and that of the air and coal +before they entered the fire. + +3rd. Another portion is dissipated by radiation from the sides of the +furnace. In a stove the heat is all used in these latter two ways, +either it goes off through the chimney or is radiated into the +surrounding space. It is one of the principal problems of boiler +engineering to render the amount of heat thus lost as small as possible. + +The loss from radiation is in proportion to the amount of surface, its +nature, its temperature, and the time it is exposed. This loss can be +almost entirely eliminated by thick walls and a smooth white or polished +surface, but its amount is ordinarily so small that these extraordinary +precautions do not pay in practice. + +It is evident that the temperature of the escaping gases cannot be +brought below that of the absorbing surfaces, while it may be much +greater even to that of the fire. This is supposing that all of the +escaping gases have passed through the fire. In case air is allowed to +leak into the flues, and mingle with the gases after they have left the +heating surfaces, the temperature may be brought down to almost any +point above that of the atmosphere, but without any reduction in the +amount of heat wasted. It is in this way that those low chimney +temperatures are sometimes attained which pass for proof of economy with +the unobserving. All surplus air admitted to the fire, or to the gases +before they leave the heating surfaces, increases the losses. + +We are now prepared to see why and how the temperature and the rapidity +of combustion in the boiler furnace affect the economy, and that though +the amount of heat developed may be the same, the heat available for the +generation of steam may be much less with one rate or temperature of +combustion than another. + +Assuming that there is no air passing up the chimney other than that +which has passed through the fire, the higher the temperature of the +fire and the lower that of the escaping gases the better the economy, +for the losses by the chimney gases will bear the same proportion to the +heat generated by the combustion as the temperature of those gases bears +to the temperature of the fire. That is to say, if the temperature of +the fire is 2500 degrees and that of the chimney gases 500 degrees above +that of the atmosphere, the loss by the chimney will be 500/2500 = 20 +per cent. Therefore, as the escaping gases cannot be brought below the +temperature of the absorbing surface, which is practically a fixed +quantity, the temperature of the fire must be high in order to secure +good economy. + +The losses by radiation being practically proportioned to the time +occupied, the more coal burned in a given furnace in a given time, the +less will be the proportionate loss from that cause. + +It therefore follows that we should burn our coal rapidly and at a high +temperature to secure the best available economy. + +[Illustration: Portion of 9880 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain +Grate Stokers at the South Side Elevated Ry. Co., Chicago, Ill.] + + + + +PROPERTIES OF WATER + + +Pure water is a chemical compound of one volume of oxygen and two +volumes of hydrogen, its chemical symbol being H_{2}O. + +The weight of water depends upon its temperature. Its weight at four +temperatures, much used in physical calculations, is given in Table 10. + + TABLE 10 + + WEIGHT OF WATER AT TEMPERATURES + USED IN PHYSICAL CALCULATIONS + ++---------------------------+----------+----------+ +| Temperature Degrees |Weight per|Weight per| +| Fahrenheit |Cubic Foot|Cubic Inch| +| | Pounds | Pounds | ++---------------------------+----------+----------+ +|At 32 degrees or freezing | | | +| point at sea level | 62.418 | 0.03612 | +|At 39.2 degrees or point of| | | +| maximum density | 62.427 | 0.03613 | +|At 62 degrees or standard | | | +| temperature | 62.355 | 0.03608 | +|At 212 degrees or boiling | | | +| point at sea level | 59.846 | 0.03469 | ++---------------------------+----------+----------+ + +While authorities differ as to the weight of water, the range of values +given for 62 degrees Fahrenheit (the standard temperature ordinarily +taken) being from 62.291 pounds to 62.360 pounds per cubic foot, the +value 62.355 is generally accepted as the most accurate. + +A United States standard gallon holds 231 cubic inches and weighs, at 62 +degrees Fahrenheit, approximately 8-1/3 pounds. + +A British Imperial gallon holds 277.42 cubic inches and weighs, at 62 +degrees Fahrenheit, 10 pounds. + +The above are the true weights corrected for the effect of the buoyancy +of the air, or the weight in vacuo. If water is weighed in air in the +ordinary way, there is a correction of about one-eighth of one per cent +which is usually negligible. + + TABLE 11 + +VOLUME AND WEIGHT OF DISTILLED WATER AT + VARIOUS TEMPERATURES[12] + ++-----------+---------------+----------+ +|Temperature|Relative Volume|Weight per| +| Degrees | Water at 39.2 |Cubic Foot| +| Fahrenheit| Degrees = 1 | Pounds | ++-----------+---------------+----------+ +| 32 | 1.000176 | 62.42 | +| 39.2 | 1.000000 | 62.43 | +| 40 | 1.000004 | 62.43 | +| 50 | 1.00027 | 62.42 | +| 60 | 1.00096 | 62.37 | +| 70 | 1.00201 | 62.30 | +| 80 | 1.00338 | 62.22 | +| 90 | 1.00504 | 62.11 | +| 100 | 1.00698 | 62.00 | +| 110 | 1.00915 | 61.86 | +| 120 | 1.01157 | 61.71 | +| 130 | 1.01420 | 61.55 | +| 140 | 1.01705 | 61.38 | +| 150 | 1.02011 | 61.20 | +| 160 | 1.02337 | 61.00 | +| 170 | 1.02682 | 60.80 | +| 180 | 1.03047 | 60.58 | +| 190 | 1.03431 | 60.36 | +| 200 | 1.03835 | 60.12 | +| 210 | 1.04256 | 59.88 | +| 212 | 1.04343 | 59.83 | +| 220 | 1.0469 | 59.63 | +| 230 | 1.0515 | 59.37 | +| 240 | 1.0562 | 59.11 | +| 250 | 1.0611 | 58.83 | +| 260 | 1.0662 | 58.55 | +| 270 | 1.0715 | 58.26 | +| 280 | 1.0771 | 57.96 | +| 290 | 1.0830 | 57.65 | +| 300 | 1.0890 | 57.33 | +| 310 | 1.0953 | 57.00 | +| 320 | 1.1019 | 56.66 | +| 330 | 1.1088 | 56.30 | +| 340 | 1.1160 | 55.94 | +| 350 | 1.1235 | 55.57 | +| 360 | 1.1313 | 55.18 | +| 370 | 1.1396 | 54.78 | +| 380 | 1.1483 | 54.36 | +| 390 | 1.1573 | 53.94 | +| 400 | 1.167 | 53.5 | +| 410 | 1.177 | 53.0 | +| 420 | 1.187 | 52.6 | +| 430 | 1.197 | 52.2 | +| 440 | 1.208 | 51.7 | +| 450 | 1.220 | 51.2 | +| 460 | 1.232 | 50.7 | +| 470 | 1.244 | 50.2 | +| 480 | 1.256 | 49.7 | +| 490 | 1.269 | 49.2 | +| 500 | 1.283 | 48.7 | +| 510 | 1.297 | 48.1 | +| 520 | 1.312 | 47.6 | +| 530 | 1.329 | 47.0 | +| 540 | 1.35 | 46.3 | +| 550 | 1.37 | 45.6 | +| 560 | 1.39 | 44.9 | ++-----------+---------------+----------+ + +Water is but slightly compressible and for all practical purposes may be +considered non-compressible. The coefficient of compressibility ranges +from 0.000040 to 0.000051 per atmosphere at ordinary temperatures, this +coefficient decreasing as the temperature increases. + +Table 11 gives the weight in vacuo and the relative volume of a cubic +foot of distilled water at various temperatures. + +The weight of water at the standard temperature being taken as 62.355 +pounds per cubic foot, the pressure exerted by the column of water of +any stated height, and conversely the height of any column required to +produce a stated pressure, may be computed as follows: + +The pressure in pounds per square foot = 62.355 x height of column in +feet. + +The pressure in pounds per square inch = 0.433 x height of column in +feet. + +Height of column in feet = pressure in pounds per square foot / 62.355. + +Height of column in feet = pressure in pounds per square inch / 0.433. + +Height of column in inches = pressure in pounds per square inch x 27.71. + +Height of column in inches = pressure in ounces per square inch x 1.73. + +By a change in the weights given above, the pressure exerted and height +of column may be computed for temperatures other than 62 degrees. + +A pressure of one pound per square inch is exerted by a column of water +2.3093 feet or 27.71 inches high at 62 degrees Fahrenheit. + +Water in its natural state is never found absolutely pure. In solvent +power water has a greater range than any other liquid. For common salt, +this is approximately a constant at all temperatures, while with such +impurities as magnesium and sodium sulphates, this solvent power +increases with an increase in temperature. + + TABLE 12 + + BOILING POINT OF WATER AT VARIOUS ALTITUDES + ++--------------+----------------+-------------+---------------+ +|Boiling Point | Altitude Above | Atmospheric | Barometer | +| Degrees | Sea Level | Pressure | Reduced | +| Fahrenheit | Feet | Pounds per | to 32 Degrees | +| | | Square Inch | Inches | ++--------------+----------------+-------------+---------------+ +| 184 | 15221 | 8.20 | 16.70 | +| 185 | 14649 | 8.38 | 17.06 | +| 186 | 14075 | 8.57 | 17.45 | +| 187 | 13498 | 8.76 | 17.83 | +| 188 | 12934 | 8.95 | 18.22 | +| 189 | 12367 | 9.14 | 18.61 | +| 190 | 11799 | 9.34 | 19.02 | +| 191 | 11243 | 9.54 | 19.43 | +| 192 | 10685 | 9.74 | 19.85 | +| 193 | 10127 | 9.95 | 20.27 | +| 194 | 9579 | 10.17 | 20.71 | +| 195 | 9031 | 10.39 | 21.15 | +| 196 | 8481 | 10.61 | 21.60 | +| 197 | 7932 | 10.83 | 22.05 | +| 198 | 7381 | 11.06 | 22.52 | +| 199 | 6843 | 11.29 | 22.99 | +| 200 | 6304 | 11.52 | 23.47 | +| 201 | 5764 | 11.76 | 23.95 | +| 202 | 5225 | 12.01 | 24.45 | +| 203 | 4697 | 12.26 | 24.96 | +| 204 | 4169 | 12.51 | 25.48 | +| 205 | 3642 | 12.77 | 26.00 | +| 206 | 3115 | 13.03 | 26.53 | +| 207 | 2589 | 13.30 | 27.08 | +| 208 | 2063 | 13.57 | 27.63 | +| 209 | 1539 | 13.85 | 28.19 | +| 210 | 1025 | 14.13 | 28.76 | +| 211 | 512 | 14.41 | 29.33 | +| 212 | Sea Level | 14.70 | 29.92 | ++--------------+----------------+-------------+---------------+ + +Sea water contains on an average approximately 3.125 per cent of its +weight of solid matter or a thirty-second part of the weight of the +water and salt held in solution. The approximate composition of this +solid matter will be: sodium chloride 76 per cent, magnesium chloride 10 +per cent, magnesium sulphate 6 per cent, calcium sulphate 5 per cent, +calcium carbonate 0.5 per cent, other substances 2.5 per cent. + +[Illustration: 7200 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters at the Capital Traction Co., Washington, D. C.] + +The boiling point of water decreases as the altitude above sea level +increases. Table 12 gives the variation in the boiling point with the +altitude. + +Water has a greater specific heat or heat-absorbing capacity than any +other known substance (bromine and hydrogen excepted) and its specific +heat is the basis for measurement of the capacity of heat absorption of +all other substances. From the definition, the specific heat of water is +the number of British thermal units required to raise one pound of water +one degree. This specific heat varies with the temperature of the water. +The generally accepted values are given in Table 13, which indicates the +values as determined by Messrs. Marks and Davis and Mr. Peabody. + + TABLE 13 + + SPECIFIC HEAT OF WATER AT VARIOUS TEMPERATURES + ++----------------------+--------------------------------+ +| MARKS AND DAVIS | PEABODY | +| From Values of | From Values of | +| Barnes and Dieterici | Barnes and Regnault | ++-----------+----------+---------------------+----------+ +|Temperature| Specific | Temperature | Specific | ++-----------+ Heat +----------+----------+ Heat | +| Degrees | | Degrees | Degrees | | +|Fahrenheit | |Centigrade|Fahrenheit| | ++-----------+----------+----------+----------+----------+ +| 30 | 1.0098 | 0 | 32 | 1.0094 | +| 40 | 1.0045 | 5 | 41 | 1.0053 | +| 50 | 1.0012 | 10 | 50 | 1.0023 | +| 55 | 1.0000 | 15 | 59 | 1.0003 | +| 60 | 0.9990 | 16.11 | 61 | 1.0000 | +| 70 | 0.9977 | 20 | 68 | 0.9990 | +| 80 | 0.9970 | 25 | 77 | 0.9981 | +| 90 | 0.9967 | 30 | 86 | 0.9976 | +| 100 | 0.9967 | 35 | 95 | 0.9974 | +| 110 | 0.9970 | 40 | 104 | 0.9974 | +| 120 | 0.9974 | 45 | 113 | 0.9976 | +| 130 | 0.9979 | 50 | 122 | 0.9980 | +| 140 | 0.9986 | 55 | 131 | 0.9985 | +| 150 | 0.9994 | 60 | 140 | 0.9994 | +| 160 | 1.0002 | 65 | 149 | 1.0004 | +| 170 | 1.0010 | 70 | 158 | 1.0015 | +| 180 | 1.0019 | 75 | 167 | 1.0028 | +| 190 | 1.0029 | 80 | 176 | 1.0042 | +| 200 | 1.0039 | 85 | 185 | 1.0056 | +| 210 | 1.0052 | 90 | 194 | 1.0071 | +| 220 | 1.007 | 95 | 203 | 1.0086 | +| 230 | 1.009 | 100 | 212 | 1.0101 | ++-----------+----------+----------+----------+----------+ + +In consequence of this variation in specific heat, the variation in the +heat of the liquid of the water at different temperatures is not a +constant. Table 22[13] gives the heat of the liquid in a pound of water +at temperatures ranging from 32 to 340 degrees Fahrenheit. + +The specific heat of ice at 32 degrees is 0.463. The specific heat of +saturated steam (ice and saturated steam representing the other forms in +which water may exist), is something that is difficult to define in any +way which will not be misleading. When no liquid is present the specific +heat of saturated steam is negative.[14] The use of the value of the +specific heat of steam is practically limited to instances where +superheat is present, and the specific heat of superheated steam is +covered later in the book. + + + + +BOILER FEED WATER + + +All natural waters contain some impurities which, when introduced into a +boiler, may appear as solids. In view of the apparent present-day +tendency toward large size boiler units and high overloads, the +importance of the use of pure water for boiler feed purposes cannot be +over-estimated. + +Ordinarily, when water of sufficient purity for such use is not at hand, +the supply available may be rendered suitable by some process of +treatment. Against the cost of such treatment, there are many factors to +be considered. With water in which there is a marked tendency toward +scale formation, the interest and depreciation on the added boiler units +necessary to allow for the systematic cleaning of certain units must be +taken into consideration. Again there is a considerable loss in taking +boilers off for cleaning and replacing them on the line. On the other +hand, the decrease in capacity and efficiency accompanying an increased +incrustation of boilers in use has been too generally discussed to need +repetition here. Many experiments have been made and actual figures +reported as to this decrease, but in general, such figures apply only to +the particular set of conditions found in the plant where the boiler in +question was tested. So many factors enter into the effect of scale on +capacity and economy that it is impossible to give any accurate figures +on such decrease that will serve all cases, but that it is large has +been thoroughly proven. + +While it is almost invariably true that practically any cost of +treatment will pay a return on the investment of the apparatus, the fact +must not be overlooked that there are certain waters which should never +be used for boiler feed purposes and which no treatment can render +suitable for such purpose. In such cases, the only remedy is the +securing of other feed supply or the employment of evaporators for +distilling the feed water as in marine service. + + TABLE 14 + + APPROXIMATE CLASSIFICATION OF IMPURITIES FOUND IN FEED WATERS + THEIR EFFECT AND ORDINARY METHODS OF RELIEF + ++-----------------------+--------------+-----------------------------+ +| Difficulty Resulting | Nature of | Ordinary Method of | +| from Presence of | Difficulty | Overcoming or Relieving | ++-----------------------+--------------+-----------------------------+ +| Sediment, Mud, etc. | Incrustation | Settling tanks, filtration, | +| | | blowing down. | +| | | | +| Readily Soluble Salts | Incrustation | Blowing down. | +| | | | +| Bicarbonates of Lime, | Incrustation | Heating feed. Treatment by | +| Magnesia, etc. | | addition of lime or of lime | +| | | and soda. Barium carbonate. | +| | | | +| Sulphate of Lime | Incrustation | Treatment by addition of | +| | | soda. Barium carbonate. | +| | | | +| Chloride and Sulphate | Corrosion | Treatment by addition of | +| of Magnesium | | carbonate of soda. | +| | | | +| Acid | Corrosion | Alkali. | +| | | | +| Dissolved Carbonic | Corrosion | Heating feed. Keeping air | +| Acid and Oxygen | | from feed. Addition of | +| | | caustic soda or slacked | +| | | lime. | +| | | | +| Grease | Corrosion | Filter. Iron alum as | +| | | coagulent. Neutralization | +| | | by carbonate of soda. Use | +| | | of best hydrocarbon oils. | +| | | | +| Organic Matter | Corrosion | Filter. Use of coagulent. | +| | | | +| Organic Matter | Priming | Settling tanks. Filter in | +| (Sewage) | | connection with coagulent. | +| | | | +| Carbonate of Soda in | Priming | Barium carbonate. New feed | +| large quantities | | supply. If from treatment, | +| | | change. | ++-----------------------+--------------+-----------------------------+ + +It is evident that the whole subject of boiler feed waters and their +treatment is one for the chemist rather than for the engineer. A brief +outline of the difficulties that may be experienced from the use of poor +feed water and a suggestion as to a method of overcoming certain of +these difficulties is all that will be attempted here. Such a brief +outline of the subject, however, will indicate the necessity for a +chemical analysis of any water before a treatment is tried and the +necessity of adapting the treatment in each case to the nature of the +difficulties that may be experienced. + +Table 14 gives a list of impurities which may be found in boiler feed +water, grouped according to their effect on boiler operation and giving +the customary method used for overcoming difficulty to which they lead. + + +Scale--Scale is formed on boiler heating surfaces by the depositing of +impurities in the feed water in the form of a more or less hard adherent +crust. Such deposits are due to the fact that water loses its soluble +power at high temperatures or because the concentration becomes so high, +due to evaporation, that the impurities crystallize and adhere to the +boiler surfaces. The opportunity for formation of scale in a boiler will +be apparent when it is realized that during a month's operation of a 100 +horse-power boiler, 300 pounds of solid matter may be deposited from +water containing only 7 grains per gallon, while some spring and well +waters contain sufficient to cause a deposit of as high as 2000 pounds. + +The salts usually responsible for such incrustation are the carbonates +and sulphates of lime and magnesia, and boiler feed treatment in general +deals with the getting rid of these salts more or less completely. + + TABLE 15 + + SOLUBILITY OF MINERAL SALTS IN WATER (SPARKS) +IN GRAINS PER U. S. GALLON (58,381 GRAINS), EXCEPT AS NOTED + ++------------------------------+------------+-------------+ +|Temperature Degrees Fahrenheit| 60 Degrees | 212 Degrees | ++------------------------------+------------+-------------+ +|Calcium Carbonate | 2.5 | 1.5 | +|Calcium Sulphate | 140.0 | 125.0 | +|Magnesium Carbonate | 1.0 | 1.8 | +|Magnesium Sulphate | 3.0 pounds | 12.0 pounds | +|Sodium Chloride | 3.5 pounds | 4.0 pounds | +|Sodium Sulphate | 1.1 pounds | 5.0 pounds | ++------------------------------+------------+-------------+ + + CALCIUM SULPHATE AT TEMPERATURE ABOVE + 212 DEGREES (CHRISTIE) + ++------------------------------+----+----+-------+----+---+ +|Temperature degrees Fahrenheit|284 |329 |347-365| 464|482| +|Corresponding gauge pressure | 38 | 87 |115-149| 469|561| +|Grains per gallon |45.5|32.7| 15.7 |10.5|9.3| ++------------------------------+----+----+-------+----+---+ + +Table 15 gives the solubility of these mineral salts in water at various +temperatures in grains per U. S. gallon (58,381 grains). It will be seen +from this table that the carbonates of lime and magnesium are not +soluble above 212 degrees, and calcium sulphate while somewhat insoluble +above 212 degrees becomes more greatly so as the temperature increases. + +Scale is also formed by the settling of mud and sediment carried in +suspension in water. This may bake or be cemented to a hard scale when +mixed with other scale-forming ingredients. + + +Corrosion--Corrosion, or a chemical action leading to the actual +destruction of the boiler metal, is due to the solvent or oxidizing +properties of the feed water. It results from the presence of acid, +either free or developed[15] in the feed, the admixture of air with the +feed water, or as a result of a galvanic action. In boilers it takes +several forms: + +1st. Pitting, which consists of isolated spots of active corrosion which +does not attack the boiler as a whole. + +2nd. General corrosion, produced by naturally acid waters and where the +amount is so even and continuous that no accurate estimate of the metal +eaten away may be made. + +3rd. Grooving, which, while largely a mechanical action which may occur +in neutral waters, is intensified by acidity. + +Foaming--This phenomenon, which ordinarily occurs with waters +contaminated with sewage or organic growths, is due to the fact that the +suspended particles collect on the surface of the water in the boiler +and render difficult the liberation of steam bubbles arising to that +surface. It sometimes occurs with water containing carbonates in +solution in which a light flocculent precipitate will be formed on the +surface of the water. Again, it is the result of an excess of sodium +carbonate used in treatment for some other difficulty where animal or +vegetable oil finds its way into the boiler. + +Priming--Priming, or the passing off of steam from a boiler in belches, +is caused by the concentration of sodium carbonate, sodium sulphate or +sodium chloride in solution. Sodium sulphate is found in many southern +waters and also where calcium or magnesium sulphate is precipitated with +soda ash. + +Treatment of Feed Water--For scale formation. The treatment of feed +water, carrying scale-forming ingredients, is along two main lines: 1st, +by chemical means by which such impurities as are carried by the water +are caused to precipitate; and 2nd, by the means of heat, which results +in the reduction of the power of water to hold certain salts in +solution. The latter method alone is sufficient in the case of certain +temporarily hard waters, but the heat treatment, in general, is used in +connection with a chemical treatment to assist the latter. + +Before going further into detail as to the treatment of water, it may be +well to define certain terms used. + +_Hardness_, which is the most widely known evidence of the presence in +water of scale-forming matter, is that quality, the variation of which +makes it more difficult to obtain a lather or suds from soap in one +water than in another. This action is made use of in the soap test for +hardness described later. Hardness is ordinarily classed as either +temporary or permanent. Temporarily hard waters are those containing +carbonates of lime and magnesium, which may be precipitated by boiling +at 212 degrees and which, if they contain no other scale-forming +ingredients, become "soft" under such treatment. Permanently hard waters +are those containing mainly calcium sulphate, which is only precipitated +at the high temperatures found in the boiler itself, 300 degrees +Fahrenheit or more. The scale of hardness is an arbitrary one, based on +the number of grains of solids per gallon and waters may be classed on +such a basis as follows: 1-10 grain per gallon, soft water; 10-20 grain +per gallon, moderately hard water; above 25 grains per gallon, very hard +water. + +_Alkalinity_ is a general term used for waters containing compounds with +the power of neutralizing acids. + +_Causticity_, as used in water treatment, is a term coined by A. McGill, +indicating the presence of an excess of lime added during treatment. +Though such presence would also indicate alkalinity, the term is +arbitrarily used to apply to those hydrates whose presence is indicated +by phenolphthalein. + +Of the chemical methods of water treatment, there are three general +processes: + +1st. Lime Process. The lime process is used for waters containing +bicarbonates of lime and magnesia. Slacked lime in solution, as lime +water, is the reagent used. This combines with the carbonic acid which +is present, either free or as carbonates, to form an insoluble +monocarbonate of lime. The soluble bicarbonates of lime and magnesia, +losing their carbonic acid, thereby become insoluble and precipitate. + +2nd. Soda Process. The soda process is used for waters containing +sulphates of lime and magnesia. Carbonate of soda and hydrate of soda +(caustic soda) are used either alone or together as the reagents. +Carbonate of soda, added to water containing little or no carbonic acid +or bicarbonates, decomposes the sulphates to form insoluble carbonate of +lime or magnesia which precipitate, the neutral soda remaining in +solution. If free carbonic acid or bicarbonates are present, bicarbonate +of lime is formed and remains in solution, though under the action of +heat, the carbon dioxide will be driven off and insoluble monocarbonates +will be formed. Caustic soda used in this process causes a more +energetic action, it being presumed that the caustic soda absorbs the +carbonic acid, becomes carbonate of soda and acts as above. + +3rd. Lime and Soda Process. This process, which is the combination of +the first two, is by far the most generally used in water purification. +Such a method is used where sulphates of lime and magnesia are contained +in the water, together with such quantity of carbonic acid or +bicarbonates as to impair the action of the soda. Sufficient soda is +used to break down the sulphates of lime and magnesia and as much lime +added as is required to absorb the carbonic acid not taken up in the +soda reaction. + +All of the apparatus for effecting such treatment of feed waters is +approximately the same in its chemical action, the numerous systems +differing in the methods of introduction and handling of the reagents. + +The methods of testing water treated by an apparatus of this description +follow. + +When properly treated, alkalinity, hardness and causticity should be in +the approximate relation of 6, 5 and 4. When too much lime is used in +the treatment, the causticity in the purified water, as indicated by the +acid test, will be nearly equal to the alkalinity. If too little lime is +used, the causticity will fall to approximately half the alkalinity. The +hardness should not be in excess of two points less than the alkalinity. +Where too great a quantity of soda is used, the hardness is lowered and +the alkalinity raised. If too little soda, the hardness is raised and +the alkalinity lowered. + +Alkalinity and causticity are tested with a standard solution of +sulphuric acid. A standard soap solution is used for testing for +hardness and a silver nitrate solution may also be used for determining +whether an excess of lime has been used in the treatment. + +Alkalinity: To 50 cubic centimeters of treated water, to which there has +been added sufficient methylorange to color it, add the acid solution, +drop by drop, until the mixture is on the point of turning red. As the +acid solution is first added, the red color, which shows quickly, +disappears on shaking the mixture, and this color disappears more slowly +as the critical point is approached. One-tenth cubic centimeter of the +standard acid solution corresponds to one degree of alkalinity. + +[Illustration: 2640 Horse-power Installation of Babcock & Wilcox Boilers +at the Botany Worsted Mills, Passaic, N. J.] + +Causticity: To 50 cubic centimeters of treated water, to which there has +been added one drop of phenolphthalein dissolved in alcohol to give the +water a pinkish color, add the acid solution, drop by drop, shaking +after each addition, until the color entirely disappears. One-tenth +cubic centimeter of acid solution corresponds to one degree of +causticity. + +The alkalinity may be determined from the same sample tested for +causticity by the coloring with methylorange and adding the acid until +the sample is on the point of turning red. The total acid added in +determining both causticity and alkalinity in this case is the measure +of the alkalinity. + +Hardness: 100 cubic centimeters of the treated water is used for this +test, one cubic centimeter of the soap solution corresponding to one +degree of hardness. The soap solution is added a very little at a time +and the whole violently shaken. Enough of the solution must be added to +make a permanent lather or foam, that is, the soap bubbles must not +disappear after the shaking is stopped. + +Excess of lime as determined by nitrate of silver: If there is an excess +of lime used in the treatment, a sample will become a dark brown by the +addition of a small quantity of silver nitrate, otherwise a milky white +solution will be formed. + +Combined Heat and Chemical Treatment: Heat is used in many systems of +feed treatment apparatus as an adjunct to the chemical process. Heat +alone will remove temporary hardness by the precipitation of carbonates +of lime and magnesia and, when used in connection with the chemical +process, leaves only the permanent hardness or the sulphates of lime to +be taken care of by chemical treatment. + + TABLE 16 + + REAGENTS REQUIRED IN LIME AND SODA PROCESS + FOR TREATING 1000 U. S. GALLONS OF WATER + PER GRAIN PER GALLON OF CONTAINED IMPURITIES[16] + ++-----------------------+-----------+-----------+ +| | Lime[17] | Soda[18] | +| | Pounds | Pounds | ++-----------------------+-----------+-----------+ +| Calcium Carbonate | 0.098 | ... | +| Calcium Sulphate | ... | 0.124 | +| Calcium Chloride | ... | 0.151 | +| Calcium Nitrate | ... | 0.104 | +| Magnesium Carbonate | 0.234 | ... | +| Magnesium Sulphate | 0.079 | 0.141 | +| Magnesium Chloride | 0.103 | 0.177 | +| Magnesium Nitrate | 0.067 | 0.115 | +| Ferrous Carbonate | 0.169 | ... | +| Ferrous Sulphate | 0.070 | 0.110 | +| Ferric Sulphate | 0.074 | 0.126 | +| Aluminum Sulphate | 0.087 | 0.147 | +| Free Sulphuric Acid | 0.100 | 0.171 | +| Sodium Carbonate | 0.093 | ... | +| Free Carbon Dioxide | 0.223 | ... | +| Hydrogen Sulphite | 0.288 | ... | ++-----------------------+-----------+-----------+ + +The chemicals used in the ordinary lime and soda process of feed water +treatment are common lime and soda. The efficiency of such apparatus +will depend wholly upon the amount and character of the impurities in +the water to be treated. Table 16 gives the amount of lime and soda +required per 1000 gallons for each grain per gallon of the various +impurities found in the water. This table is based on lime containing 90 +per cent calcium oxide and soda containing 58 per cent sodium oxide, +which correspond to the commercial quality ordinarily purchasable. From +this table and the cost of the lime and soda, the cost of treating any +water per 1000 gallons may be readily computed. + +Less Usual Reagents--Barium hydrate is sometimes used to reduce +permanent hardness or the calcium sulphate component. Until recently, +the high cost of barium hydrate has rendered its use prohibitive but at +the present it is obtained as a by-product in cement manufacture and it +may be purchased at a more reasonable figure than heretofore. It acts +directly on the soluble sulphates to form barium sulphate which is +insoluble and may be precipitated. Where this reagent is used, it is +desirable that the reaction be allowed to take place outside of the +boiler, though there are certain cases where its internal use is +permissible. + +Barium carbonate is sometimes used in removing calcium sulphate, the +products of the reaction being barium sulphate and calcium carbonate, +both of which are insoluble and may be precipitated. As barium carbonate +in itself is insoluble, it cannot be added to water as a solution and +its use should, therefore, be confined to treatment outside of the +boiler. + +Silicate of soda will precipitate calcium carbonate with the formation +of a gelatinous silicate of lime and carbonate of soda. If calcium +sulphate is also present, carbonate of soda is formed in the above +reaction, which in turn will break down the sulphate. + +Oxalate of soda is an expensive but efficient reagent which forms a +precipitate of calcium oxalate of a particularly insoluble nature. + +Alum and iron alum will act as efficient coagulents where organic matter +is present in the water. Iron alum has not only this property but also +that of reducing oil discharged from surface condensers to a condition +in which it may be readily removed by filtration. + +Corrosion--Where there is a corrosive action because of the presence of +acid in the water or of oil containing fatty acids which will decompose +and cause pitting wherever the sludge can find a resting place, it may +be overcome by the neutralization of the water by carbonate of soda. +Such neutralization should be carried to the point where the water will +just turn red litmus paper blue. As a preventative of such action +arising from the presence of the oil, only the highest grades of +hydrocarbon oils should be used. + +Acidity will occur where sea water is present in a boiler. There is the +possibility of such an occurrence in marine practice and in stationary +plants using sea water for condensing, due to leaky condenser tubes, +priming in the evaporators, etc. Such acidity is caused through the +dissociation of magnesium chloride into hydrochloride acid and magnesia +under high temperatures. The acid in contact with the metal forms an +iron salt which immediately upon its formation is neutralized by the +free magnesia in the water, thereby precipitating iron oxide and +reforming magnesium chloride. The preventive for corrosion arising from +such acidity is the keeping tight of the condenser. Where it is +unavoidable that some sea water should find its way into a boiler, the +acidity resulting should be neutralized by soda ash. This will convert +the magnesium chloride into magnesium carbonate and sodium chloride, +neither of which is corrosive but both of which are scale-forming. + +The presence of air in the feed water which is sucked in by the feed +pump is a well recognized cause of corrosion. Air bubbles form below the +water line and attack the metal of the boiler, the oxygen of the air +causing oxidization of the boiler metal and the formation of rust. The +particle of rust thus formed is swept away by the circulation or is +dislodged by expansion and the minute pit thus left forms an ideal +resting place for other air bubbles and the continuation of the +oxidization process. The prevention is, of course, the removing of the +air from the feed water. In marine practice, where there has been +experienced the most difficulty from this source, it has been found to +be advantageous to pump the water from the hot well to a filter tank +placed above the feed pump suction valves. In this way the air is +liberated from the surface of the tank and a head is assured for the +suction end of the pump. In this same class of work, the corrosive +action of air is reduced by introducing the feed through a spray nozzle +into the steam space above the water line. + +Galvanic action, resulting in the eating away of the boiler metal +through electrolysis was formerly considered practically the sole cause +of corrosion. But little is known of such action aside from the fact +that it does take place in certain instances. The means adopted as a +remedy is usually the installation of zinc plates within the boiler, +which must have positive metallic contact with the boiler metal. In this +way, local electrolytic effects are overcome by a still greater +electrolytic action at the expense of the more positive zinc. The +positive contact necessary is difficult to maintain and it is +questionable just what efficacy such plates have except for a short +period after their installation when the contact is known to be +positive. Aside from protection from such electrolytic action, however, +the zinc plates have a distinct use where there is the liability of air +in the feed, as they offer a substance much more readily oxidized by +such air than the metal of the boiler. + +Foaming--Where foaming is caused by organic matter in suspension, it may +be largely overcome by filtration or by the use of a coagulent in +connection with filtration, the latter combination having come recently +into considerable favor. Alum, or potash alum, and iron alum, which in +reality contains no alumina and should rather be called potassia-ferric, +are the coagulents generally used in connection with filtration. Such +matter as is not removed by filtration may, under certain conditions, be +handled by surface blowing. In some instances, settling tanks are used +for the removal of matter in suspension, but where large quantities of +water are required, filtration is ordinarily substituted on account of +the time element and the large area necessary in settling tanks. + +Where foaming occurs as the result of overtreatment of the feed water, +the obvious remedy is a change in such treatment. + +Priming--Where priming is caused by excessive concentration of salts +within a boiler, it may be overcome largely by frequent blowing down. +The degree of concentration allowable before priming will take place +varies widely with conditions of operation and may be definitely +determined only by experience with each individual set of conditions. It +is the presence of the salts that cause priming that may result in the +absolute unfitness of water for boiler feed purposes. Where these salts +exist in such quantities that the amount of blowing down necessary to +keep the degree of concentration below the priming point results in +excessive losses, the only remedy is the securing of another supply of +feed, and the results will warrant the change almost regardless of the +expense. In some few instances, the impurities may be taken care of by +some method of water treatment but such water should be submitted to an +authority on the subject before any treatment apparatus is installed. + +[Illustration: 3000 Horse-power Installation of Cross Drum Babcock & +Wilcox Boilers and Superheaters Equipped with Babcock & Wilcox Chain +Grate Stokers at the Washington Terminal Co., Washington, D. C.] + +Boiler Compounds--The method of treatment of feed water by far the most +generally used is by the use of some of the so-called boiler compounds. +There are many reliable concerns handling such compounds who +unquestionably secure the promised results, but there is a great +tendency toward looking on the compound as a "cure all" for any water +difficulties and care should be taken to deal only with reputable +concerns. + +The composition of these compounds is almost invariably based on soda +with certain tannic substances and in some instances a gelatinous +substance which is presumed to encircle scale particles and prevent +their adhering to the boiler surfaces. The action of these compounds is +ordinarily to reduce the calcium sulphate in the water by means of +carbonate of soda and to precipitate it as a muddy form of calcium +carbonate which may be blown off. The tannic compounds are used in +connection with the soda with the idea of introducing organic matter +into any scale already formed. When it has penetrated to the boiler +metal, decomposition of the scale sets in, causing a disruptive effect +which breaks the scale from the metal sometimes in large slabs. It is +this effect of boiler compounds that is to be most carefully guarded +against or inevitable trouble will result from the presence of loose +scale with the consequent danger of tube losses through burning. + +When proper care is taken to suit the compound to the water in use, the +results secured are fairly effective. In general, however, the use of +compounds may only be recommended for the prevention of scale rather +than with the view to removing scale which has already formed, that is, +the compounds should be introduced with the feed water only when the +boiler has been thoroughly cleaned. + + + + +FEED WATER HEATING AND METHODS OF FEEDING + + +Before water fed into a boiler can be converted into steam, it must be +first heated to a temperature corresponding to the pressure within the +boiler. Steam at 160 pounds gauge pressure has a temperature of +approximately 371 degrees Fahrenheit. If water is fed to the boiler at +60 degrees Fahrenheit, each pound must have 311 B. t. u. added to it to +increase its temperature 371 degrees, which increase must take place +before the water can be converted into steam. As it requires 1167.8 +B. t. u. to raise one pound of water from 60 to 371 degrees and to +convert it into steam at 160 pounds gauge pressure, the 311 degrees +required simply to raise the temperature of the water from 60 to 371 +degrees will be approximately 27 per cent of the total. If, therefore, +the temperature of the water can be increased from 60 to 371 degrees +before it is introduced into a boiler by the utilization of heat from +some source that would otherwise be wasted, there will be a saving in +the fuel required of 311 / 1167.8 = 27 per cent, and there will be a net +saving, provided the cost of maintaining and operating the apparatus for +securing this saving is less than the value of the heat thus saved. + +The saving in the fuel due to the heating of feed water by means of heat +that would otherwise be wasted may be computed from the formula: + + 100 (t - t_{i}) +Fuel saving per cent = --------------- (1) + H + 32 - t_{i} + +where, t = temperature of feed water after heating, t_{i} = temperature +of feed water before heating, and H = total heat above 32 degrees per +pound of steam at the boiler pressure. Values of H may be found in Table +23. Table 17 has been computed from this formula to show the fuel saving +under the conditions assumed with the boiler operating at 180 pounds +gauge pressure. + + TABLE 17 + + SAVING IN FUEL, IN PER CENT, BY HEATING FEED WATER + GAUGE PRESSURE 180 POUNDS + ++-----------+-----------------------------------------+ +| Initial | Final Temperature--Degrees Fahrenheit | +|Temperature|-----+-----+-----+-----+-----+-----+-----| +| Fahrenheit| 120 | 140 | 160 | 180 | 200 | 250 | 300 | ++-----------+-----+-----+-----+-----+-----+-----+-----+ +| 32 | 7.35| 9.02|10.69|12.36|14.04|18.20|22.38| +| 35 | 7.12| 8.79|10.46|12.14|13.82|18.00|22.18| +| 40 | 6.72| 8.41|10.09|11.77|13.45|17.65|21.86| +| 45 | 6.33| 8.02| 9.71|11.40|13.08|17.30|21.52| +| 50 | 5.93| 7.63| 9.32|11.02|12.72|16.95|21.19| +| 55 | 5.53| 7.24| 8.94|10.64|12.34|16.60|20.86| +| 60 | 5.13| 6.84| 8.55|10.27|11.97|16.24|20.52| +| 65 | 4.72| 6.44| 8.16| 9.87|11.59|15.88|20.18| +| 70 | 4.31| 6.04| 7.77| 9.48|11.21|15.52|19.83| +| 75 | 3.90| 5.64| 7.36| 9.09|10.82|15.16|19.48| +| 80 | 3.48| 5.22| 6.96| 8.70|10.44|14.79|19.13| +| 85 | 3.06| 4.80| 6.55| 8.30|10.05|14.41|18.78| +| 90 | 2.63| 4.39| 6.14| 7.89| 9.65|14.04|18.43| +| 95 | 2.20| 3.97| 5.73| 7.49| 9.25|13.66|18.07| +| 100 | 1.77| 3.54| 5.31| 7.08| 8.85|13.28|17.70| +| 110 | .89| 2.68| 4.47| 6.25| 8.04|12.50|16.97| +| 120 | .00| 1.80| 3.61| 5.41| 7.21|11.71|16.22| +| 130 | | .91| 2.73| 4.55| 6.37|10.91|15.46| +| 140 | | .00| 1.84| 3.67| 5.51|10.09|14.68| +| 150 | | | .93| 2.78| 4.63| 9.26|13.89| +| 160 | | | .00| 1.87| 3.74| 8.41|13.09| +| 170 | | | | .94| 2.83| 7.55|12.27| +| 180 | | | | .00| 1.91| 6.67|11.43| +| 190 | | | | | .96| 5.77|10.58| +| 200 | | | | | .00| 4.86| 9.71| +| 210 | | | | | | 3.92| 8.82| ++-----------+-----+-----+-----+-----+-----+-----+-----+ + +Besides the saving in fuel effected by the use of feed water heaters, +other advantages are secured. The time required for the conversion of +water into steam is diminished and the steam capacity of the boiler +thereby increased. Further, the feeding of cold water into a boiler has +a tendency toward the setting up of temperature strains, which are +diminished in proportion as the temperature of the feed approaches that +of the steam. An important additional advantage of heating feed water is +that in certain types of heaters a large portion of the scale forming +ingredients are precipitated before entering the boiler, with a +consequent saving in cleaning and losses through decreased efficiency +and capacity. + +In general, feed water heaters may be divided into closed heaters, open +heaters and economizers; the first two depend for their heat upon +exhaust, or in some cases live steam, while the last class utilizes the +heat of the waste flue gases to secure the same result. The question of +the type of apparatus to be installed is dependent upon the conditions +attached to each individual case. + +In closed heaters the feed water and the exhaust steam do not come into +actual contact with each other. Either the steam or the water passes +through tubes surrounded by the other medium, as the heater is of the +steam-tube or water-tube type. A closed heater is best suited for water +free from scale-forming matter, as such matter soon clogs the passages. +Cleaning such heaters is costly and the efficiency drops off rapidly as +scale forms. A closed heater is not advisable where the engines work +intermittently, as is the case with mine hoisting engines. In this class +of work the frequent coolings between operating periods and the sudden +heatings when operation commences will tend to loosen the tubes or even +pull them apart. For this reason, an open heater, or economizer, will +give more satisfactory service with intermittently operating apparatus. + +Open heaters are best suited for waters containing scale-forming matter. +Much of the temporary hardness may be precipitated in the heater and the +sediment easily removed. Such heaters are frequently used with a reagent +for precipitating permanent hardness in the combined heat and chemical +treatment of feed water. The so-called live steam purifiers are open +heaters, the water being raised to the boiling temperature and the +carbonates and a portion of the sulphates being precipitated. The +disadvantage of this class of apparatus is that some of the sulphates +remain in solution to be precipitated as scale when concentrated in the +boiler. Sufficient concentration to have such an effect, however, may +often be prevented by frequent blowing down. + +Economizers find their largest field where the design of the boiler is +such that the maximum possible amount of heat is not extracted from the +gases of combustion. The more wasteful the boiler, the greater the +saving effected by the use of the economizer, and it is sometimes +possible to raise the temperature of the feed water to that of high +pressure steam by the installation of such an apparatus, the saving +amounting in some cases to as much as 20 per cent. The fuel used bears +directly on the question of the advisability of an economizer +installation, for when oil is the fuel a boiler efficiency of 80 per +cent or over is frequently realized, an efficiency which would leave a +small opportunity for a commercial gain through the addition of an +economizer. + +From the standpoint of space requirements, economizers are at a +disadvantage in that they are bulky and require a considerable increase +over space occupied by a heater of the exhaust type. They also require +additional brickwork or a metal casing, which increases the cost. +Sometimes, too, the frictional resistance of the gases through an +economizer make its adaptability questionable because of the draft +conditions. When figuring the net return on economizer investment, all +of these factors must be considered. + +When the feed water is such that scale will quickly encrust the +economizer and throw it out of service for cleaning during an excessive +portion of the time, it will be necessary to purify water before +introducing it into an economizer to make it earn a profit on the +investment. + +From the foregoing, it is clearly indicated that it is impossible to +make a definite statement as to the relative saving by heating feed +water in any of the three types. Each case must be worked out +independently and a decision can be reached only after an exhaustive +study of all the conditions affecting the case, including the time the +plant will be in service and probable growth of the plant. When, as a +result of such study, the possible methods for handling the problem have +been determined, the solution of the best apparatus can be made easily +by the balancing of the saving possible by each method against its first +cost, depreciation, maintenance and cost of operation. + +Feeding of Water--The choice of methods to be used in introducing feed +water into a boiler lies between an injector and a pump. In most plants, +an injector would not be economical, as the water fed by such means must +be cold, a fact which makes impossible the use of a heater before the +water enters the injector. Such a heater might be installed between the +injector and the boiler but as heat is added to the water in the +injector, the heater could not properly fulfill its function. + + TABLE 18 + + COMPARISON OF PUMPS AND INJECTORS + _________________________________________________________________________ +| | | | +| Method of Supplying | | | +| Feed-water to Boiler | Relative amount of | Saving of fuel over| +| Temperature of feed-water as | coal required per | the amount required| +| delivered to the pump or to | unit of time, the | when the boiler is | +| injector, 60 degrees Fahren- | amount for a direct-| fed by a direct- | +| heit. Rate of evaporation of | acting pump, feeding| acting pump without| +| boiler, to pounds of water | water at 60 degrees | heater | +| per pound of coal from and | without a heater, | Per Cent | +| at 212 degrees Fahrenheit | being taken as unity| | +|______________________________|_____________________|____________________| +| | | | +| Direct-acting Pump feeding | | | +| water at 60 degrees without | | | +| a heater | 1.000 | .0 | +| | | | +| Injector feeding water at | | | +| 150 degrees without a heater | .985 | 1.5 | +| Injector feeding through a | | | +| heater in which the water is | | | +| heated from 150 to 200 | | | +| degrees | .938 | 6.2 | +| | | | +| Direct-acting Pump feeding | | | +| water through a heater in | | | +| which it is heated from 60 | | | +| to 200 degrees | .879 | 12.1 | +| | | | +| Geared Pump run from the | | | +| engine, feeding water | | | +| through a heater in which it | | | +| is heated from 60 to 200 | | | +| degrees | .868 | 13.2 | +|______________________________|_____________________|____________________| + +The injector, considered only in the light of a combined heater and +pump, is claimed to have a thermal efficiency of 100 per cent, since all +of the heat in the steam used is returned to the boiler with the water. +This claim leads to an erroneous idea. If a pump is used in feeding the +water to a boiler and the heat in the exhaust from the pump is imparted +to the feed water, the pump has as high a thermal efficiency as the +injector. The pump has the further advantage that it uses so much less +steam for the forcing of a given quantity of water into the boiler that +it makes possible a greater saving through the use of the exhaust from +other auxiliaries for heating the feed, which exhaust, if an injector +were used, would be wasted, as has been pointed out. + +In locomotive practice, injectors are used because there is no exhaust +steam available for heating the feed, this being utilized in producing a +forced draft, and because of space requirements. In power plant work, +however, pumps are universally used for regular operation, though +injectors are sometimes installed as an auxiliary method of feeding. + +Table 18 shows the relative value of injectors, direct-acting steam +pumps and pumps driven from the engine, the data having been obtained +from actual experiment. It will be noted that when feeding cold water +direct to the boilers, the injector has a slightly greater economy but +when feeding through a heater, the pump is by far the more economical. + +Auxiliaries--It is the general impression that auxiliaries will take +less steam if the exhaust is turned into the condensers, in this way +reducing the back pressure. As a matter of fact, vacuum is rarely +registered on an indicator card taken from the cylinders of certain +types of auxiliaries unless the exhaust connection is short and without +bends, as long pipes and many angles offset the effect of the condenser. +On the other hand, if the exhaust steam from the auxiliaries can be used +for heating the feed water, all of the latent heat less only the loss +due to radiation is returned to the boiler and is saved instead of being +lost in the condensing water or wasted with the free exhaust. Taking +into consideration the plant as a whole, it would appear that the +auxiliary machinery, under such conditions, is more efficient than the +main engines. + +[Illustration: Portion of 4160 Horse-power Installation of Babcock & +Wilcox Boilers at the Prudential Life Insurance Co. Building, Newark, +N. J.] + + + + +STEAM + + +When a given weight of a perfect gas is compressed or expanded at a +constant temperature, the product of the pressure and volume is a +constant. Vapors, which are liquids in aeriform condition, on the other +hand, can exist only at a definite pressure corresponding to each +temperature if in the saturated state, that is, the pressure is a +function of the temperature only. Steam is water vapor, and at a +pressure of, say, 150 pounds absolute per square inch saturated steam +can exist only at a temperature 358 degrees Fahrenheit. Hence if the +pressure of saturated steam be fixed, its temperature is also fixed, and +_vice versa_. + +Saturated steam is water vapor in the condition in which it is generated +from water with which it is in contact. Or it is steam which is at the +maximum pressure and density possible at its temperature. If any change +be made in the temperature or pressure of steam, there will be a +corresponding change in its condition. If the pressure be increased or +the temperature decreased, a portion of the steam will be condensed. If +the temperature be increased or the pressure decreased, a portion of the +water with which the steam is in contact will be evaporated into steam. +Steam will remain saturated just so long as it is of the same pressure +and temperature as the water with which it can remain in contact without +a gain or loss of heat. Moreover, saturated steam cannot have its +temperature lowered without a lowering of its pressure, any loss of heat +being made up by the latent heat of such portion as will be condensed. +Nor can the temperature of saturated steam be increased except when +accompanied by a corresponding increase in pressure, any added heat +being expended in the evaporation into steam of a portion of the water +with which it is in contact. + +Dry saturated steam contains no water. In some cases, saturated steam is +accompanied by water which is carried along with it, either in the form +of a spray or is blown along the surface of the piping, and the steam is +then said to be wet. The percentage weight of the steam in a mixture of +steam and water is called the quality of the steam. Thus, if in a +mixture of 100 pounds of steam and water there is three-quarters of a +pound of water, the quality of the steam will be 99.25. + +Heat may be added to steam not in contact with water, such an addition +of heat resulting in an increase of temperature and pressure if the +volume be kept constant, or an increase in temperature and volume if the +pressure remain constant. Steam whose temperature thus exceeds that of +saturated steam at a corresponding pressure is said to be superheated +and its properties approximate those of a perfect gas. + +As pointed out in the chapter on heat, the heat necessary to raise one +pound of water from 32 degrees Fahrenheit to the point of ebullition is +called the _heat of the liquid_. The heat absorbed during ebullition +consists of that necessary to dissociate the molecules, or the _inner +latent heat_, and that necessary to overcome the resistance to the +increase in volume, or the _outer latent heat_. These two make up the +_latent heat of evaporation_ and the sum of this latent heat of +evaporation and the heat of the liquid make the _total heat_ of the +steam. These values for various pressures are given in the steam tables, +pages 122 to 127. + +The specific volume of saturated steam at any pressure is the volume in +cubic feet of one pound of steam at that pressure. + +The density of saturated steam, that is, its weight per cubic foot, is +obviously the reciprocal of the specific volume. This density varies as +the 16/17 power over the ordinary range of pressures used in steam +boiler work and may be found by the formula, D = .003027p^{.941}, which +is correct within 0.15 per cent up to 250 pounds pressure. + +The relative volume of steam is the ratio of the volume of a given +weight to the volume of the same weight of water at 39.2 degrees +Fahrenheit and is equal to the specific volume times 62.427. + +As vapors are liquids in their gaseous form and the boiling point is the +point of change in this condition, it is clear that this point is +dependent upon the pressure under which the liquid exists. This fact is +of great practical importance in steam condenser work and in many +operations involving boiling in an open vessel, since in the latter case +its altitude will have considerable influence. The relation between +altitude and boiling point of water is shown in Table 12. + +The conditions of feed temperature and steam pressure in boiler tests, +fuel performances and the like, will be found to vary widely in +different trials. In order to secure a means for comparison of different +trials, it is necessary to reduce all results to some common basis. The +method which has been adopted for the reduction to a comparable basis is +to transform the evaporation under actual conditions of steam pressure +and feed temperature which exist in the trial to an equivalent +evaporation under a set of standard conditions. These standard +conditions presuppose a feed water temperature of 212 degrees Fahrenheit +and a steam pressure equal to the normal atmospheric pressure at sea +level, 14.7 pounds absolute. Under such conditions steam would be +generated _at_ a temperature of 212 degrees, the temperature +corresponding to atmospheric pressure at sea level, _from_ water at 212 +degrees. The weight of water which _would_ be evaporated under the +assumed standard conditions by exactly the amount of heat absorbed by +the boiler under actual conditions existing in the trial, is, therefore, +called the equivalent evaporation "from and at 212 degrees." + +The factor for reducing the weight of water actually converted into +steam from the temperature of the feed, at the steam pressure existing +in the trial, to the equivalent evaporation under standard conditions is +called the _factor of evaporation._ This factor is the ratio of the +total heat added to one pound of steam under the standard conditions to +the heat added to each pound of steam in heating the water from the +temperature of the feed in the trial to the temperature corresponding to +the pressure existing in the trial. This heat added is obviously the +difference between the total heat of evaporation of the steam at the +pressure existing in the trial and the heat of the liquid in the water +at the temperature at which it was fed in the trial. To illustrate by an +example: + +In a boiler trial the temperature of the feed water is 60 degrees +Fahrenheit and the pressure under which steam is delivered is 160.3 +pounds gauge pressure or 175 pounds absolute pressure. The total heat of +one pound of steam at 175 pounds pressure is 1195.9 B. t. u. measured +above the standard temperature of 32 degrees Fahrenheit. But the water +fed to the boiler contained 28.08 B. t. u. as the heat of the liquid +measured above 32 degrees Fahrenheit. Therefore, to each pound of steam +there has been added 1167.82 B. t. u. To evaporate one pound of water +under standard conditions would, on the other hand, have required but +970.4 B. t. u., which, as described, is the latent heat of evaporation +at 212 degrees Fahrenheit. Expressed differently, the total heat of one +pound of steam at the pressure corresponding to a temperature of 212 +degrees is 1150.4 B. t. u. One pound of water at 212 degrees contains +180 B. t. u. of sensible heat above 32 degrees Fahrenheit. Hence, under +standard conditions, 1150.4 - 180 = 970.4 B. t. u. is added in the +changing of one pound of water into steam at atmospheric pressure and a +temperature of 212 degrees. This is in effect the definition of the +latent heat of evaporation. + +Hence, if conditions of the trial had been standard, only 970.4 B. t. u. +would be required and the ratio of 1167.82 to 970.4 B. t. u. is the +ratio determining the factor of evaporation. The factor in the assumed +case is 1167.82 / 970.4 = 1.2034 and if the same amount of heat had been +absorbed under standard conditions as was absorbed in the trial +condition, 1.2034 times the amount of steam would have been generated. +Expressed as a formula for use with any set of conditions, the factor +is, + + H - h +F = ----- (2) + 970.4 + +Where H = the total heat of steam above 32 degrees Fahrenheit from steam + tables, + h = sensible heat of feed water above 32 degrees Fahrenheit from + Table 22. + +In the form above, the factor may be determined with either saturated or +superheated steam, provided that in the latter case values of H are +available for varying degrees of superheat and pressures. + +Where such values are not available, the form becomes, + + H - h + s(t_{sup} - t_{sat}) +F = ---------------------------- (3) + 970.4 + +Where s = mean specific heat of superheated steam at the + pressure existing in the trial from saturated + steam to the temperature existing in the trial, + t_{sup} = final temperature of steam, + t_{sat} = temperature of saturated steam, corresponding to + pressure existing, +(t_{sup} - t_{sat}) = degrees of superheat. + +The specific heat of superheated steam will be taken up later. + +Table 19 gives factors of evaporation for saturated steam boiler trials +to cover a large range of conditions. Except for the most refined work, +intermediate values may be determined by interpolation. + +Steam gauges indicate the pressure above the atmosphere. As has been +pointed out, the atmospheric pressure changes according to the altitude +and the variation in the barometer. Hence, calculations involving the +properties of steam are based on _absolute_ pressures, which are equal +to the gauge pressure plus the atmospheric pressure in pounds to the +square inch. This latter is generally assumed to be 14.7 pounds per +square inch at sea level, but for other levels it must be determined +from the barometric reading at that place. + +Vacuum gauges indicate the difference, expressed in inches of mercury, +between atmospheric pressure and the pressure within the vessel to which +the gauge is attached. For approximate purposes, 2.04 inches height of +mercury may be considered equal to a pressure of one pound per square +inch at the ordinary temperatures at which mercury gauges are used. +Hence for any reading of the vacuum gauge in inches, G, the absolute +pressure for any barometer reading in inches, B, will be (B - G) / 2.04. +If the barometer is 30 inches measured at ordinary temperatures and not +corrected to 32 degrees Fahrenheit and the vacuum gauge 24 inches, the +absolute pressure will be (30 - 24) / 2.04 = 2.9 pounds per square inch. + + TABLE 19 + + FACTORS OF EVAPORATION + CALCULATED FROM MARKS AND DAVIS TABLES + + ______________________________________________________________________ +| | | +|Feed | | +|Temp- | | +|erature| | +|Degrees| Steam Pressure by Gauge | +|Fahren-| | +|heit | | +|_______|______________________________________________________________| +| | | | | | | | | +| | 50 | 60 | 70 | 80 | 90 | 100 | 110 | +|_______|________|________|________|________|________|________|________| +| | | | | | | | | +| 32 | 1.2143 | 1.2170 | 1.2194 | 1.2215 | 1.2233 | 1.2233 | 1.2265 | +| 40 | 1.2060 | 1.2087 | 1.2111 | 1.2131 | 1.2150 | 1.2168 | 1.2181 | +| 50 | 1.1957 | 1.1984 | 1.2008 | 1.2028 | 1.2047 | 1.2065 | 1.2079 | +| 60 | 1.1854 | 1.1881 | 1.1905 | 1.1925 | 1.1944 | 1.1961 | 1.1976 | +| 70 | 1.1750 | 1.1778 | 1.1802 | 1.1822 | 1.1841 | 1.1859 | 1.1873 | +| 80 | 1.1649 | 1.1675 | 1.1699 | 1.1720 | 1.1738 | 1.1756 | 1.1770 | +| 90 | 1.1545 | 1.1572 | 1.1596 | 1.1617 | 1.1636 | 1.1653 | 1.1668 | +| 100 | 1.1443 | 1.1470 | 1.1493 | 1.1514 | 1.1533 | 1.1550 | 1.1565 | +| 110 | 1.1340 | 1.1367 | 1.1391 | 1.1411 | 1.1430 | 1.1448 | 1.1462 | +| 120 | 1.1237 | 1.1264 | 1.1288 | 1.1309 | 1.1327 | 1.1345 | 1.1359 | +| 130 | 1.1134 | 1.1161 | 1.1185 | 1.1206 | 1.1225 | 1.1242 | 1.1257 | +| 140 | 1.1031 | 1.1058 | 1.1082 | 1.1103 | 1.1122 | 1.1139 | 1.1154 | +| 150 | 1.0928 | 1.0955 | 1.0979 | 1.1000 | 1.1019 | 1.1036 | 1.1051 | +| 160 | 1.0825 | 1.0852 | 1.0876 | 1.0897 | 1.0916 | 1.0933 | 1.0948 | +| 170 | 1.0722 | 1.0749 | 1.0773 | 1.0794 | 1.0813 | 1.0830 | 1.0845 | +| 180 | 1.0619 | 1.0646 | 1.0670 | 1.0691 | 1.0709 | 1.0727 | 1.0741 | +| 190 | 1.0516 | 1.0543 | 1.0567 | 1.0587 | 1.0606 | 1.0624 | 1.0638 | +| 200 | 1.0412 | 1.0439 | 1.0463 | 1.0484 | 1.0503 | 1.0520 | 1.0535 | +| 210 | 1.0309 | 1.0336 | 1.0360 | 1.0380 | 1.0399 | 1.0417 | 1.0432 | +|_______|________|________|________|________|________|________|________| + ______________________________________________________________________ +| | | +|Feed | | +|Temp- | | +|erature| | +|Degrees| Steam Pressure by Gauge | +|Fahren-| | +|heit | | +|_______|______________________________________________________________| +| | | | | | | | | +| | 120 | 130 | 140 | 150 | 160 | 170 | 180 | +|_______|________|________|________|________|________|________|________| +| | | | | | | | | +| 32 | 1.2280 | 1.2292 | 1.2304 | 1.2314 | 1.2323 | 1.2333 | 1.2342 | +| 40 | 1.2196 | 1.2209 | 1.2221 | 1.2231 | 1.2241 | 1.2250 | 1.2259 | +| 50 | 1.2093 | 1.2106 | 1.2117 | 1.2128 | 1.2137 | 1.2147 | 1.2156 | +| 60 | 1.1990 | 1.2003 | 1.2014 | 1.2025 | 1.2034 | 1.2044 | 1.2053 | +| 70 | 1.1887 | 1.1900 | 1.1911 | 1.1922 | 1.1931 | 1.1941 | 1.1950 | +| 80 | 1.1785 | 1.1797 | 1.1809 | 1.1819 | 1.1828 | 1.1838 | 1.1847 | +| 90 | 1.1682 | 1.1695 | 1.1706 | 1.1717 | 1.1725 | 1.1735 | 1.1744 | +| 100 | 1.1579 | 1.1592 | 1.1603 | 1.1614 | 1.1623 | 1.1633 | 1.1642 | +| 110 | 1.1477 | 1.1489 | 1.1500 | 1.1511 | 1.1520 | 1.1530 | 1.1539 | +| 120 | 1.1374 | 1.1386 | 1.1398 | 1.1408 | 1.1418 | 1.1427 | 1.1436 | +| 130 | 1.1271 | 1.1284 | 1.1295 | 1.1305 | 1.1315 | 1.1324 | 1.1333 | +| 140 | 1.1168 | 1.1181 | 1.1192 | 1.1203 | 1.1212 | 1.1221 | 1.1230 | +| 150 | 1.1065 | 1.1078 | 1.1089 | 1.1099 | 1.1109 | 1.1118 | 1.1127 | +| 160 | 1.0962 | 1.0975 | 1.0986 | 1.0997 | 1.1006 | 1.1015 | 1.1024 | +| 170 | 1.0859 | 1.0872 | 1.0883 | 1.0893 | 1.0903 | 1.0912 | 1.0921 | +| 180 | 1.0756 | 1.0768 | 1.0780 | 1.0790 | 1.0800 | 1.0809 | 1.0818 | +| 190 | 1.0653 | 1.0665 | 1.0676 | 1.0687 | 1.0696 | 1.0706 | 1.0715 | +| 200 | 1.0549 | 1.0562 | 1.0573 | 1.0584 | 1.0593 | 1.0602 | 1.0611 | +| 210 | 1.0446 | 1.0458 | 1.0469 | 1.0480 | 1.0489 | 1.0499 | 1.0508 | +|_______|________|________|________|________|________|________|________| + ______________________________________________________________________ +| | | +|Feed | | +|Temp- | | +|erature| | +|Degrees| Steam Pressure by Gauge | +|Fahren-| | +|heit | | +|_______|______________________________________________________________| +| | | | | | | | | +| | 190 | 200 | 210 | 220 | 230 | 240 | 250 | +|_______|________|________|________|________|________|________|________| +| | | | | | | | | +| 32 | 1.2350 | 1.2357 | 1.2364 | 1.2372 | 1.2378 | 1.2384 | 1.2390 | +| 40 | 1.2267 | 1.2274 | 1.2282 | 1.2289 | 1.2295 | 1.2301 | 1.2307 | +| 50 | 1.2164 | 1.2171 | 1.2178 | 1.2186 | 1.2192 | 1.2198 | 1.2204 | +| 60 | 1.2061 | 1.2068 | 1.2075 | 1.2083 | 1.2089 | 1.2095 | 1.2101 | +| 70 | 1.1958 | 1.1965 | 1.1972 | 1.1980 | 1.1986 | 1.1992 | 1.1998 | +| 80 | 1.1855 | 1.1863 | 1.1869 | 1.1877 | 1.1883 | 1.1889 | 1.1895 | +| 90 | 1.1750 | 1.1760 | 1.1766 | 1.1774 | 1.1780 | 1.1786 | 1.1792 | +| 100 | 1.1650 | 1.1657 | 1.1664 | 1.1671 | 1.1678 | 1.1684 | 1.1690 | +| 110 | 1.1547 | 1.1554 | 1.1562 | 1.1569 | 1.1575 | 1.1581 | 1.1587 | +| 120 | 1.1444 | 1.1452 | 1.1459 | 1.1466 | 1.1472 | 1.1478 | 1.1484 | +| 130 | 1.1341 | 1.1349 | 1.1356 | 1.1363 | 1.1369 | 1.1375 | 1.1381 | +| 140 | 1.1239 | 1.1246 | 1.1253 | 1.1260 | 1.1266 | 1.1272 | 1.1278 | +| 150 | 1.1136 | 1.1143 | 1.1150 | 1.1157 | 1.1163 | 1.1169 | 1.1176 | +| 160 | 1.1033 | 1.1040 | 1.1047 | 1.1054 | 1.1060 | 1.1066 | 1.1073 | +| 170 | 1.0930 | 1.0937 | 1.0944 | 1.0951 | 1.0957 | 1.0963 | 1.0969 | +| 180 | 1.0826 | 1.0834 | 1.0841 | 1.0848 | 1.0854 | 1.0860 | 1.0866 | +| 190 | 1.0723 | 1.0730 | 1.0737 | 1.0745 | 1.0751 | 1.0757 | 1.0763 | +| 200 | 1.0620 | 1.0627 | 1.0634 | 1.0641 | 1.0647 | 1.0653 | 1.0660 | +| 210 | 1.0516 | 1.0523 | 1.0530 | 1.0538 | 1.0544 | 1.0550 | 1.0556 | +|_______|________|________|________|________|________|________|________| + +The temperature, pressure and other properties of steam for varying +amounts of vacuum and the pressure above vacuum corresponding to each +inch of reading of the vacuum gauge are given in Table 20. + + TABLE 20 + + PROPERTIES OF SATURATED STEAM FOR VARYING AMOUNTS OF VACUUM + CALCULATED FROM MARKS AND DAVIS TABLES + ______________________________________________________________________ +| | | | | | | | +| | | | Heat of | Latent | Total | | +| | | Temp- | the Liquid| Heat | Heat | | +| | | erature | Above | Above | Above |Density or| +| | Absolute | Degrees | 32 De- | 32 De- | 32 De- |Weight per| +| Vacuum | Pressure | Fahren- | grees | grees | grees |Cubic Foot| +|Ins. Hg.| Pounds | heit | B. t. u. |B. t. u.|B. t. u.| Pounds | +|________|__________|_________|___________|________|________|__________| +| | | | | | | | +| 29.5 | .207 | 54.1 | 22.18 | 1061.0 | 1083.2 | 0.000678 | +| 29 | .452 | 76.6 | 44.64 | 1048.7 | 1093.3 | 0.001415 | +| 28.5 | .698 | 90.1 | 58.09 | 1041.1 | 1099.2 | 0.002137 | +| 28 | .944 | 99.9 | 67.87 | 1035.6 | 1103.5 | 0.002843 | +| 27 | 1.44 | 112.5 | 80.4 | 1028.6 | 1109.0 | 0.00421 | +| 26 | 1.93 | 124.5 | 92.3 | 1022.0 | 1114.3 | 0.00577 | +| 25 | 2.42 | 132.6 | 100.5 | 1017.3 | 1117.8 | 0.00689 | +| 24 | 2.91 | 140.1 | 108.0 | 1013.1 | 1121.1 | 0.00821 | +| 22 | 3.89 | 151.7 | 119.6 | 1006.4 | 1126.0 | 0.01078 | +| 20 | 4.87 | 161.1 | 128.9 | 1001.0 | 1129.9 | 0.01331 | +| 18 | 5.86 | 168.9 | 136.8 | 996.4 | 1133.2 | 0.01581 | +| 16 | 6.84 | 175.8 | 143.6 | 992.4 | 1136.0 | 0.01827 | +| 14 | 7.82 | 181.8 | 149.7 | 988.8 | 1138.5 | 0.02070 | +| 12 | 8.80 | 187.2 | 155.1 | 985.6 | 1140.7 | 0.02312 | +| 10 | 9.79 | 192.2 | 160.1 | 982.6 | 1142.7 | 0.02554 | +| 5 | 12.24 | 202.9 | 170.8 | 976.0 | 1146.8 | 0.03148 | +|________|__________|_________|___________|________|________|__________| + +From the steam tables, the condensed Table 21 of the properties of steam +at different pressures may be constructed. From such a table there may +be drawn the following conclusions. + + TABLE 21 + + VARIATION IN PROPERTIES OF + SATURATED STEAM WITH PRESSURE + ___________________________________________________ +| | | | | | +| Pressure |Temperature | Heat of | Latent | Total | +| Pounds | Degrees | Liquid | Heat | Heat | +| Absolute | Fahrenheit |B. t. u. |B. t. u.|B. t. u.| +|__________|____________|_________|________|________| +| | | | | | +| 14.7 | 212.0 | 180.0 | 970.4 | 1150.4 | +| 20.0 | 228.0 | 196.1 | 960.0 | 1156.2 | +| 100.0 | 327.8 | 298.3 | 888.0 | 1186.3 | +| 300.0 | 417.5 | 392.7 | 811.3 | 1204.1 | +|__________|____________|_________|________|________| + +As the pressure and temperature increase, the latent heat decreases. +This decrease, however, is less rapid than the corresponding increase in +the heat of the liquid and hence the total heat increases with an +increase in the pressure and temperature. The percentage increase in the +total heat is small, being 0.5, 3.1, and 4.7 per cent for 20, 100, and +300 pounds absolute pressure respectively above the total heat in one +pound of steam at 14.7 pounds absolute. The temperatures, on the other +hand, increase at the rates of 7.5, 54.6, and 96.9 per cent. The +efficiency of a perfect steam engine is proportional to the expression +(t - t_{1})/t in which t and t_{1} are the absolute temperatures of the +saturated steam at admission and exhaust respectively. While actual +engines only approximate the ideal engine in efficiency, yet they follow +the same general law. Since the exhaust temperature cannot be lowered +beyond present practice, it follows that the only available method of +increasing the efficiency is by an increase in the temperature of the +steam at admission. How this may be accomplished by an increase of +pressure is clearly shown, for the increase of fuel necessary to +increase the pressure is negligible, as shown by the total heat, while +the increase in economy, due to the higher pressure, will result +directly from the rapid increase of the corresponding temperature. + + TABLE 22 + + HEAT UNITS PER POUND AND + WEIGHT PER CUBIC FOOT OF WATER + BETWEEN 32 DEGREES FAHRENHEIT AND + 340 DEGREES FAHRENHEIT + _________________________________ +| | | | +|Temperature|Heat Units| Weight | +| Degrees | per | per | +| Fahrenheit| Pound |Cubic Foot| +|___________|__________|__________| +| | | | +| 32 | 0.00 | 62.42 | +| 33 | 1.01 | 62.42 | +| 34 | 2.01 | 62.42 | +| 35 | 3.02 | 62.43 | +| 36 | 4.03 | 62.43 | +| 37 | 5.04 | 62.43 | +| 38 | 6.04 | 62.43 | +| 39 | 7.05 | 62.43 | +| 40 | 8.05 | 62.43 | +| 41 | 9.05 | 62.43 | +| 42 | 10.06 | 62.43 | +| 43 | 11.06 | 62.43 | +| 44 | 12.06 | 62.43 | +| 45 | 13.07 | 62.42 | +| 46 | 14.07 | 62.42 | +| 47 | 15.07 | 62.42 | +| 48 | 16.07 | 62.42 | +| 49 | 17.08 | 62.42 | +| 50 | 18.08 | 62.42 | +| 51 | 19.08 | 62.41 | +| 52 | 20.08 | 62.41 | +| 53 | 21.08 | 62.41 | +| 54 | 22.08 | 62.40 | +| 55 | 23.08 | 62.40 | +| 56 | 24.08 | 62.39 | +| 57 | 25.08 | 62.39 | +| 58 | 26.08 | 62.38 | +| 59 | 27.08 | 62.37 | +| 60 | 28.08 | 62.37 | +| 61 | 29.08 | 62.36 | +| 62 | 30.08 | 62.36 | +| 63 | 31.07 | 62.35 | +| 64 | 32.07 | 62.35 | +| 65 | 33.07 | 62.34 | +| 66 | 34.07 | 62.33 | +| 67 | 35.07 | 62.33 | +| 68 | 36.07 | 62.32 | +| 69 | 37.06 | 62.31 | +| 70 | 38.06 | 62.30 | +| 71 | 39.06 | 62.30 | +| 72 | 40.05 | 62.29 | +| 73 | 41.05 | 62.28 | +| 74 | 42.05 | 62.27 | +| 75 | 42.05 | 62.26 | +| 76 | 44.04 | 62.26 | +| 77 | 45.04 | 62.25 | +| 78 | 46.04 | 62.24 | +| 79 | 47.04 | 62.23 | +| 80 | 48.03 | 62.22 | +| 81 | 49.03 | 62.21 | +| 82 | 50.03 | 62.20 | +| 83 | 51.02 | 62.19 | +| 84 | 52.02 | 62.18 | +| 85 | 53.02 | 62.17 | +| 86 | 54.01 | 62.16 | +| 87 | 55.01 | 62.15 | +| 88 | 56.01 | 62.14 | +| 89 | 57.00 | 62.13 | +| 90 | 58.00 | 62.12 | +| 91 | 59.00 | 62.11 | +| 92 | 60.00 | 62.09 | +| 93 | 60.99 | 62.08 | +| 94 | 61.99 | 62.07 | +| 95 | 62.99 | 62.06 | +| 96 | 63.98 | 62.05 | +| 97 | 64.98 | 62.04 | +| 98 | 65.98 | 62.03 | +| 99 | 66.97 | 62.02 | +| 100 | 67.97 | 62.00 | +| 101 | 68.97 | 61.99 | +| 102 | 69.96 | 61.98 | +| 103 | 70.96 | 61.97 | +| 104 | 71.96 | 61.95 | +| 105 | 72.95 | 61.94 | +| 106 | 73.95 | 61.93 | +| 107 | 74.95 | 61.91 | +| 108 | 75.95 | 61.90 | +| 109 | 76.94 | 61.88 | +| 110 | 77.94 | 61.86 | +| 111 | 78.94 | 61.85 | +| 112 | 79.93 | 61.83 | +| 113 | 80.93 | 61.82 | +| 114 | 81.93 | 61.80 | +| 115 | 82.92 | 61.79 | +| 116 | 83.92 | 61.77 | +| 117 | 84.92 | 61.75 | +| 118 | 85.92 | 61.74 | +| 119 | 86.91 | 61.72 | +| 120 | 87.91 | 61.71 | +| 121 | 88.91 | 61.69 | +| 122 | 89.91 | 61.68 | +| 123 | 90.90 | 61.66 | +| 124 | 91.90 | 61.65 | +| 125 | 92.90 | 61.63 | +| 126 | 93.90 | 61.61 | +| 127 | 94.89 | 61.59 | +| 128 | 95.89 | 61.58 | +| 129 | 96.89 | 61.56 | +| 130 | 97.89 | 61.55 | +| 131 | 98.89 | 61.53 | +| 132 | 99.88 | 61.52 | +| 133 | 100.88 | 61.50 | +| 134 | 101.88 | 61.49 | +| 135 | 102.88 | 61.47 | +| 136 | 103.88 | 61.45 | +| 137 | 104.87 | 61.43 | +| 138 | 105.87 | 61.41 | +| 139 | 106.87 | 61.40 | +| 140 | 107.87 | 61.38 | +| 141 | 108.87 | 61.36 | +| 142 | 109.87 | 61.34 | +| 143 | 110.87 | 61.33 | +| 144 | 111.87 | 61.31 | +| 145 | 112.86 | 61.29 | +| 146 | 113.86 | 61.27 | +| 147 | 114.86 | 61.25 | +| 148 | 115.86 | 61.24 | +| 149 | 116.86 | 61.22 | +| 150 | 117.86 | 61.20 | +| 151 | 118.86 | 61.18 | +| 152 | 119.86 | 61.16 | +| 153 | 120.86 | 61.14 | +| 154 | 121.86 | 61.12 | +| 155 | 122.86 | 61.10 | +| 156 | 123.86 | 61.08 | +| 157 | 124.86 | 61.06 | +| 158 | 125.86 | 61.04 | +| 159 | 126.86 | 61.02 | +| 160 | 127.86 | 61.00 | +| 161 | 128.86 | 60.98 | +| 162 | 129.86 | 60.96 | +| 163 | 130.86 | 60.94 | +| 164 | 131.86 | 60.92 | +| 165 | 132.86 | 60.90 | +| 166 | 133.86 | 60.88 | +| 167 | 134.86 | 60.86 | +| 168 | 135.86 | 60.84 | +| 169 | 136.86 | 60.82 | +| 170 | 137.87 | 60.80 | +| 171 | 138.87 | 60.78 | +| 172 | 139.87 | 60.76 | +| 173 | 140.87 | 60.73 | +| 174 | 141.87 | 60.71 | +| 175 | 142.87 | 60.69 | +| 176 | 143.87 | 60.67 | +| 177 | 144.88 | 60.65 | +| 178 | 145.88 | 60.62 | +| 179 | 146.88 | 60.60 | +| 180 | 147.88 | 60.58 | +| 181 | 148.88 | 60.56 | +| 182 | 149.89 | 60.53 | +| 183 | 150.89 | 60.51 | +| 184 | 151.89 | 60.49 | +| 185 | 152.89 | 60.47 | +| 186 | 153.89 | 60.45 | +| 187 | 154.90 | 60.42 | +| 188 | 155.90 | 60.40 | +| 189 | 156.90 | 60.38 | +| 190 | 157,91 | 60.36 | +| 191 | 158.91 | 60.33 | +| 192 | 159.91 | 60.31 | +| 193 | 160.91 | 60.29 | +| 194 | 161.92 | 60.27 | +| 195 | 162.92 | 60.24 | +| 196 | 163.92 | 60.22 | +| 197 | 164.93 | 60.19 | +| 198 | 165.93 | 60.17 | +| 199 | 166.94 | 60.15 | +| 200 | 167.94 | 60.12 | +| 201 | 168.94 | 60.10 | +| 202 | 169.95 | 60.07 | +| 203 | 170.95 | 60.05 | +| 204 | 171.96 | 60.02 | +| 205 | 172.96 | 60.00 | +| 206 | 173.97 | 59.98 | +| 207 | 174.97 | 59.95 | +| 208 | 175.98 | 59.93 | +| 209 | 176.98 | 59.90 | +| 210 | 177.99 | 59.88 | +| 211 | 178.99 | 59.85 | +| 212 | 180.00 | 59.83 | +| 213 | 181.0 | 59.80 | +| 214 | 182.0 | 59.78 | +| 215 | 183.0 | 59.75 | +| 216 | 184.0 | 59.73 | +| 217 | 185.0 | 59.70 | +| 218 | 186.1 | 59.68 | +| 219 | 187.1 | 59.65 | +| 220 | 188.1 | 59.63 | +| 221 | 189.1 | 59.60 | +| 222 | 190.1 | 59.58 | +| 223 | 191.1 | 59.55 | +| 224 | 192.1 | 59.53 | +| 225 | 193.1 | 59.50 | +| 226 | 194.1 | 59.48 | +| 227 | 195.2 | 59.45 | +| 228 | 196.2 | 59.42 | +| 229 | 197.2 | 59.40 | +| 230 | 198.2 | 59.37 | +| 231 | 199.2 | 59.34 | +| 232 | 200.2 | 59.32 | +| 233 | 201.2 | 59.29 | +| 234 | 202.2 | 59.27 | +| 235 | 203.2 | 59.24 | +| 236 | 204.2 | 59.21 | +| 237 | 205.3 | 59.19 | +| 238 | 206.3 | 59.16 | +| 239 | 207.3 | 59.14 | +| 240 | 208.3 | 59.11 | +| 241 | 209.3 | 59.08 | +| 242 | 210.3 | 59.05 | +| 243 | 211.4 | 59.03 | +| 244 | 212.4 | 59.00 | +| 245 | 213.4 | 58.97 | +| 246 | 214.4 | 58.94 | +| 247 | 215.4 | 58.91 | +| 248 | 216.4 | 58.89 | +| 249 | 217.4 | 58.86 | +| 250 | 218.5 | 58.83 | +| 260 | 228.6 | 58.55 | +| 270 | 238.8 | 58.26 | +| 280 | 249.0 | 57.96 | +| 290 | 259.3 | 57.65 | +| 300 | 269.6 | 57.33 | +| 310 | 279.9 | 57.00 | +| 320 | 290.2 | 56.66 | +| 330 | 300.6 | 56.30 | +| 340 | 311.0 | 55.94 | +|___________|__________|__________| + +The gain due to superheat cannot be predicted from the formula for the +efficiency of a perfect steam engine given on page 119. This formula is +not applicable in cases where superheat is present since only a +relatively small amount of the heat in the steam is imparted at the +maximum or superheated temperature. + +The advantage of the use of high pressure steam may be also indicated by +considering the question from the aspect of volume. With an increase of +pressure comes a decrease in volume, thus one pound of saturated steam +at 100 pounds absolute pressure occupies 4.43 cubic feet, while at 200 +pounds pressure it occupies 2.29 cubic feet. If then, in separate +cylinders of the same dimensions, one pound of steam at 100 pounds +absolute pressure and one pound at 200 pounds absolute pressure enter +and are allowed to expand to the full volume of each cylinder, the +high-pressure steam, having more room and a greater range for expansion +than the low-pressure steam, will thus do more work. This increase in +the amount of work, as was the increase in temperature, is large +relative to the additional fuel required as indicated by the total heat. +In general, it may be stated that the fuel required to impart a given +amount of heat to a boiler is practically independent of the steam +pressure, since the temperature of the fire is so high as compared with +the steam temperature that a variation in the steam temperature does not +produce an appreciable effect. + +The formulae for the algebraic expression of the relation between +saturated steam pressures, temperatures and steam volumes have been up +to the present time empirical. These relations have, however, been +determined by experiment and, from the experimental data, tables have +been computed which render unnecessary the use of empirical formulae. +Such formulae may be found in any standard work of thermo-dynamics. The +following tables cover all practical cases. + +Table 22 gives the heat units contained in water above 32 degrees +Fahrenheit at different temperatures. + +Table 23 gives the properties of saturated steam for various pressures. + +Table 24 gives the properties of superheated steam at various pressures +and temperatures. + +These tables are based on those computed by Lionel S. Marks and Harvey +N. Davis, these being generally accepted as being the most correct. + + TABLE 23 + + PROPERTIES OF SATURATED STEAM + + REPRODUCED BY PERMISSION FROM + MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" + (Copyright, 1909, by Longmans, Green & Co.) + ____________________________________________________________________ +|Pressure,| Temper- |Specific Vol-|Heat of |Latent Heat|Total Heat| +| Pounds |ature De-| ume Cu. Ft. |the Liquid,| of Evap., |of Steam, | +|Absolute |grees F. | per Pound | B. t. u. | B. t. u. | B. t. u. | +|_________|_________|_____________|___________|___________|__________| +| 1 | 101.83 | 333.0 | 69.8 | 1034.6 | 1104.4 | +| 2 | 126.15 | 173.5 | 94.0 | 1021.0 | 1115.0 | +| 3 | 141.52 | 118.5 | 109.4 | 1012.3 | 1121.6 | +| 4 | 153.01 | 90.5 | 120.9 | 1005.7 | 1126.5 | +| 5 | 162.28 | 73.33 | 130.1 | 1000.3 | 1130.5 | +| 6 | 170.06 | 61.89 | 137.9 | 995.8 | 1133.7 | +| 7 | 176.85 | 53.56 | 144.7 | 991.8 | 1136.5 | +| 8 | 182.86 | 47.27 | 150.8 | 988.2 | 1139.0 | +| 9 | 188.27 | 42.36 | 156.2 | 985.0 | 1141.1 | +| 10 | 193.22 | 38.38 | 161.1 | 982.0 | 1143.1 | +| 11 | 197.75 | 35.10 | 165.7 | 979.2 | 1144.9 | +| 12 | 201.96 | 32.36 | 169.9 | 976.6 | 1146.5 | +| 13 | 205.87 | 30.03 | 173.8 | 974.2 | 1148.0 | +| 14 | 209.55 | 28.02 | 177.5 | 971.9 | 1149.4 | +| 15 | 213.0 | 26.27 | 181.0 | 969.7 | 1150.7 | +| 16 | 216.3 | 24.79 | 184.4 | 967.6 | 1152.0 | +| 17 | 219.4 | 23.38 | 187.5 | 965.6 | 1153.1 | +| 18 | 222.4 | 22.16 | 190.5 | 963.7 | 1154.2 | +| 19 | 225.2 | 21.07 | 193.4 | 961.8 | 1155.2 | +| 20 | 228.0 | 20.08 | 196.1 | 960.0 | 1156.2 | +| 22 | 233.1 | 18.37 | 201.3 | 956.7 | 1158.0 | +| 24 | 237.8 | 16.93 | 206.1 | 953.5 | 1159.6 | +| 26 | 242.2 | 15.72 | 210.6 | 950.6 | 1161.2 | +| 28 | 246.4 | 14.67 | 214.8 | 947.8 | 1162.6 | +| 30 | 250.3 | 13.74 | 218.8 | 945.1 | 1163.9 | +| 32 | 254.1 | 12.93 | 222.6 | 942.5 | 1165.1 | +| 34 | 257.6 | 12.22 | 226.2 | 940.1 | 1166.3 | +| 36 | 261.0 | 11.58 | 229.6 | 937.7 | 1167.3 | +| 38 | 264.2 | 11.01 | 232.9 | 935.5 | 1168.4 | +| 40 | 267.3 | 10.49 | 236.1 | 933.3 | 1169.4 | +| 42 | 270.2 | 10.02 | 239.1 | 931.2 | 1170.3 | +| 44 | 273.1 | 9.59 | 242.0 | 929.2 | 1171.2 | +| 46 | 275.8 | 9.20 | 244.8 | 927.2 | 1172.0 | +| 48 | 278.5 | 8.84 | 247.5 | 925.3 | 1172.8 | +| 50 | 281.0 | 8.51 | 250.1 | 923.5 | 1173.6 | +| 52 | 283.5 | 8.20 | 252.6 | 921.7 | 1174.3 | +| 54 | 285.9 | 7.91 | 255.1 | 919.9 | 1175.0 | +| 56 | 288.2 | 7.65 | 257.5 | 918.2 | 1175.7 | +| 58 | 290.5 | 7.40 | 259.8 | 916.5 | 1176.4 | +| 60 | 292.7 | 7.17 | 262.1 | 914.9 | 1177.0 | +| 62 | 294.9 | 6.95 | 264.3 | 913.3 | 1177.6 | +| 64 | 297.0 | 6.75 | 266.4 | 911.8 | 1178.2 | +| 66 | 299.0 | 6.56 | 268.5 | 910.2 | 1178.8 | +| 68 | 301.0 | 6.38 | 270.6 | 908.7 | 1179.3 | +| 70 | 302.9 | 6.20 | 272.6 | 907.2 | 1179.8 | +| 72 | 304.8 | 6.04 | 274.5 | 905.8 | 1180.4 | +| 74 | 306.7 | 5.89 | 276.5 | 904.4 | 1180.9 | +| 76 | 308.5 | 5.74 | 278.3 | 903.0 | 1181.4 | +| 78 | 310.3 | 5.60 | 280.2 | 901.7 | 1181.8 | +| 80 | 312.0 | 5.47 | 282.0 | 900.3 | 1182.3 | +| 82 | 313.8 | 5.34 | 283.8 | 899.0 | 1182.8 | +| 84 | 315.4 | 5.22 | 285.5 | 897.7 | 1183.2 | +| 86 | 317.1 | 5.10 | 287.2 | 896.4 | 1183.6 | +| 88 | 318.7 | 5.00 | 288.9 | 895.2 | 1184.0 | +| 90 | 320.3 | 4.89 | 290.5 | 893.9 | 1184.4 | +| 92 | 321.8 | 4.79 | 292.1 | 892.7 | 1184.8 | +| 94 | 323.4 | 4.69 | 293.7 | 891.5 | 1185.2 | +| 96 | 324.9 | 4.60 | 295.3 | 890.3 | 1185.6 | +| 98 | 326.4 | 4.51 | 296.8 | 889.2 | 1186.0 | +| 100 | 327.8 | 4.429 | 298.3 | 888.0 | 1186.3 | +| 105 | 331.4 | 4.230 | 302.0 | 885.2 | 1187.2 | +| 110 | 334.8 | 4.047 | 305.5 | 882.5 | 1188.0 | +| 115 | 338.1 | 3.880 | 309.0 | 879.8 | 1188.8 | +| 120 | 341.3 | 3.726 | 312.3 | 877.2 | 1189.6 | +| 125 | 344.4 | 3.583 | 315.5 | 874.7 | 1190.3 | +| 130 | 347.4 | 3.452 | 318.6 | 872.3 | 1191.0 | +| 135 | 350.3 | 3.331 | 321.7 | 869.9 | 1191.6 | +| 140 | 353.1 | 3.219 | 324.6 | 867.6 | 1192.2 | +| 145 | 355.8 | 3.112 | 327.4 | 865.4 | 1192.8 | +| 150 | 358.5 | 3.012 | 330.2 | 863.2 | 1193.4 | +| 155 | 361.0 | 2.920 | 332.9 | 861.0 | 1194.0 | +| 160 | 363.6 | 2.834 | 335.6 | 858.8 | 1194.5 | +| 165 | 366.0 | 2.753 | 338.2 | 856.8 | 1195.0 | +| 170 | 368.5 | 2.675 | 340.7 | 854.7 | 1195.4 | +| 175 | 370.8 | 2.602 | 343.2 | 852.7 | 1195.9 | +| 180 | 373.1 | 2.533 | 345.6 | 850.8 | 1196.4 | +| 185 | 375.4 | 2.468 | 348.0 | 848.8 | 1196.8 | +| 190 | 377.6 | 2.406 | 350.4 | 846.9 | 1197.3 | +| 195 | 379.8 | 2.346 | 352.7 | 845.0 | 1197.7 | +| 200 | 381.9 | 2.290 | 354.9 | 843.2 | 1198.1 | +| 205 | 384.0 | 2.237 | 357.1 | 841.4 | 1198.5 | +| 210 | 386.0 | 2.187 | 359.2 | 839.6 | 1198.8 | +| 215 | 388.0 | 2.138 | 361.4 | 837.9 | 1199.2 | +| 220 | 389.9 | 2.091 | 363.4 | 836.2 | 1199.6 | +| 225 | 391.9 | 2.046 | 365.5 | 834.4 | 1199.9 | +| 230 | 393.8 | 2.004 | 367.5 | 832.8 | 1200.2 | +| 235 | 395.6 | 1.964 | 369.4 | 831.1 | 1200.6 | +| 240 | 397.4 | 1.924 | 371.4 | 829.5 | 1200.9 | +| 245 | 399.3 | 1.887 | 373.3 | 827.9 | 1201.2 | +| 250 | 401.1 | 1.850 | 375.2 | 826.3 | 1201.5 | +|_________|_________|_____________|___________|___________|__________| + +[Illustration: Portion of 6100 Horse-power Installation of Babcock & +Wilcox Boilers Equipped with Babcock & Wilcox Chain Grate Stokers at the +Campbell Street Plant of the Louisville Railway Co., Louisville, Ky. +This Company Operates a Total of 14,000 Horse Power of Babcock & Wilcox +Boilers] + + TABLE 24 + + PROPERTIES OF SUPERHEATED STEAM + + REPRODUCED BY PERMISSION FROM + MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS" + (Copyright, 1909, by Longmans, Green & Co.) + __________________________________________________________________ +| | | | +| | | Degrees of Superheat | +|Pressure| |_______________________________________________| +| Pounds |Saturated| | | | | | | +|Absolute| Steam | 50 | 100 | 150 | 200 | 250 | 300 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 162.3 | 212.3 | 262.3 | 312.3 | 362.3 | 412.3 | 462.3 | +| 5 v| 73.3 | 79.7 | 85.7 | 91.8 | 97.8 | 103.8 | 109.8 | +| h| 1130.5 |1153.5 |1176.4 |1199.5 |1222.5 |1245.6 |1268.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 193.2 | 243.2 | 293.2 | 343.2 | 393.2 | 443.2 | 493.2 | +| 10 v| 38.4 | 41.5 | 44.6 | 47.7 | 50.7 | 53.7 | 56.7 | +| h| 1143.1 |1166.3 |1189.5 |1212.7 |1236.0 |1259.3 |1282.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 213.0 | 263.0 | 313.0 | 363.0 | 413.0 | 463.0 | 513.0 | +| 15 v| 26.27 | 28.40| 30.46| 32.50| 34.53| 36.56| 38.58| +| h| 1150.7 |1174.2 |1197.6 |1221.0 |1244.4 |1267.7 |1291.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 228.0 | 278.0 | 328.0 | 378.0 | 428.0 | 478.0 | 528.0 | +| 20 v| 20.08 | 21.69| 23.25| 24.80| 26.33| 27.85| 29.37| +| h| 1156.2 |1179.9 |1203.5 |1227.1 |1250.6 |1274.1 |1297.6 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 240.1 | 290.1 | 340.1 | 390.1 | 440.1 | 490.1 | 540.1 | +| 25 v| 16.30 | 17.60| 18.86| 20.10| 21.32| 22.55| 23.77| +| h| 1160.4 |1184.4 |1208.2 |1231.9 |1255.6 |1279.2 |1302.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 250.4 | 300.4 | 350.4 | 400.4 | 450.4 | 500.4 | 550.4 | +| 30 v| 13.74 | 14.83| 15.89| 16.93| 17.97| 18.99| 20.00| +| h| 1163.9 |1188.1 |1212.1 |1236.0 |1259.7 |1283.4 |1307.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 259.3 | 309.3 | 359.3 | 409.3 | 459.3 | 509.3 | 559.3 | +| 35 v| 11.89 | 12.85| 13.75| 14.65| 15.54| 16.42| 17.30| +| h| 1166.8 |1191.3 |1215.4 |1239.4 |1263.3 |1287.1 |1310.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 267.3 | 317.3 | 367.3 | 417.3 | 467.3 | 517.3 | 567.3 | +| 40 v| 10.49 | 11.33| 12.13| 12.93| 13.70| 14.48| 15.25| +| h| 1169.4 |1194.0 |1218.4 |1242.4 |1266.4 |1290.3 |1314.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 274.5 | 324.5 | 374.5 | 424.5 | 474.5 | 524.5 | 574.5 | +| 45 v| 9.39 | 10.14| 10.86| 11.57| 12.27| 12.96| 13.65| +| h| 1171.6 |1196.6 |1221.0 |1245.2 |1269.3 |1293.2 |1317.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 281.0 | 331.0 | 381.0 | 431.0 | 481.0 | 531.0 | 581.0 | +| 50 v| 8.51 | 9.19| 9.84| 10.48| 11.11| 11.74| 12.36| +| h| 1173.6 |1198.8 |1223.4 |1247.7 |1271.8 |1295.8 |1319.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 287.1 | 337.1 | 387.1 | 437.1 | 487.1 | 537.1 | 587.1 | +| 55 v| 7.78 | 8.40| 9.00| 9.59| 10.16| 10.73| 11.30| +| h| 1175.4 |1200.8 |1225.6 |1250.0 |1274.2 |1298.1 |1322.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 292.7 | 342.7 | 392.7 | 442.7 | 492.7 | 542.7 | 592.7 | +| 60 v| 7.17 | 7.75| 8.30| 8.84| 9.36| 9.89| 10.41| +| h| 1177.0 |1202.6 |1227.6 |1252.1 |1276.4 |1300.4 |1324.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 298.0 | 348.0 | 398.0 | 448.0 | 498.0 | 548.0 | 598.0 | +| 65 v| 6.65 | 7.20| 7.70| 8.20| 8.69| 9.17| 9.65| +| h| 1178.5 |1204.4 |1229.5 |1254.0 |1278.4 |1302.4 |1326.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 302.9 | 352.9 | 402.9 | 452.9 | 502.9 | 552.9 | 602.9 | +| 70 v| 6.20 | 6.71| 7.18| 7.65| 8.11| 8.56| 9.01| +| h| 1179.8 |1205.9 |1231.2 |1255.8 |1280.2 |1304.3 |1328.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 307.6 | 357.6 | 407.6 | 457.6 | 507.6 | 557.6 | 607.6 | +| 75 v| 5.81 | 6.28| 6.73| 7.17| 7.60| 8.02| 8.44| +| h| 1181.1 |1207.5 |1232.8 |1257.5 |1282.0 |1306.1 |1330.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 312.0 | 362.0 | 412.0 | 462.0 | 512.0 | 562.0 | 612.0 | +| 80 v| 5.47 | 5.92| 6.34| 6.75| 7.17| 7.56| 7.95| +| h| 1182.3 |1208.8 |1234.3 |1259.0 |1283.6 |1307.8 |1331.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 316.3 | 366.3 | 416.3 | 466.3 | 516.3 | 566.3 | 616.3 | +| 85 v| 5.16 | 5.59| 6.99| 6.38| 6.76| 7.14| 7.51| +| h| 1183.4 |1210.2 |1235.8 |1260.6 |1285.2 |1309.4 |1333.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 320.3 | 370.3 | 420.3 | 470.3 | 520.3 | 570.3 | 620.3 | +| 90 v| 4.89 | 5.29| 5.67| 6.04| 6.40| 6.76| 7.11| +| h| 1184.4 |1211.4 |1237.2 |1262.0 |1286.6 |1310.8 |1334.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 324.1 | 374.1 | 424.1 | 474.1 | 524.1 | 574.1 | 624.1 | +| 95 v| 4.65 | 5.03| 5.39| 5.74| 6.09| 6.43| 6.76| +| h| 1185.4 |1212.6 |1238.4 |1263.4 |1288.1 |1312.3 |1336.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 327.8 | 377.8 | 427.8 | 477.8 | 527.8 | 577.8 | 627.8 | +| 100 v| 4.43 | 4.79| 5.14| 5.47| 5.80| 6.12| 6.44| +| h| 1186.3 |1213.8 |1239.7 |1264.7 |1289.4 |1313.6 |1337.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 331.4 | 381.4 | 431.4 | 481.4 | 531.4 | 581.4 | 631.4 | +| 105 v| 4.23 | 4.58| 4.91| 5.23| 5.54| 5.85| 6.15| +| h| 1187.2 |1214.9 |1240.8 |1265.9 |1290.6 |1314.9 |1339.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 334.8 | 384.8 | 434.8 | 484.8 | 534.8 | 584.8 | 634.8 | +| 110 v| 4.05 | 4.38| 4.70| 5.01| 5.31| 5.61| 5.90| +| h| 1188.0 |1215.9 |1242.0 |1267.1 |1291.9 |1316.2 |1340.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 338.1 | 388.1 | 438.1 | 488.1 | 538.1 | 588.1 | 638.1 | +| 115 v| 3.88 | 4.20| 4.51| 4.81| 5.09| 5.38| 5.66| +| h| 1188.8 |1216.9 |1243.1 |1268.2 |1293.0 |1317.3 |1341.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 341.3 | 391.3 | 441.3 | 491.3 | 541.3 | 591.3 | 641.3 | +| 120 v| 3.73 | 4.04| 4.33| 4.62| 4.89| 5.17| 5.44| +| h| 1189.6 |1217.9 |1244.1 |1269.3 |1294.1 |1318.4 |1342.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 344.4 | 394.4 | 444.4 | 494.4 | 544.4 | 594.4 | 644.4 | +| 125 v| 3.58 | 3.88| 4.17| 4.45| 4.71| 4.97| 5.23| +| h| 1190.3 |1218.8 |1245.1 |1270.4 |1295.2 |1319.5 |1343.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 347.4 | 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | +| 130 v| 3.45 | 3.74| 4.02| 4.28| 4.54| 4.80| 5.05| +| h| 1191.0 |1219.7 |1246.1 |1271.4 |1296.2 |1320.6 |1344.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 350.3 | 400.3 | 450.3 | 500.3 | 550.3 | 600.3 | 650.3 | +| 135 v| 3.33 | 3.61| 3.88| 4.14| 4.38| 4.63| 4.87| +| h| 1191.6 |1220.6 |1247.0 |1272.3 |1297.2 |1321.6 |1345.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 353.1 | 403.1 | 453.1 | 503.1 | 553.1 | 603.1 | 653.1 | +| 140 v| 3.22 | 3.49| 3.75| 4.00| 4.24| 4.48| 4.71| +| h| 1192.2 |1221.4 |1248.0 |1273.3 |1298.2 |1322.6 |1346.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 355.8 | 405.8 | 455.8 | 505.8 | 555.8 | 605.8 | 655.8 | +| 145 v| 3.12 | 3.38| 3.63| 3.87| 4.10| 4.33| 4.56| +| h| 1192.8 |1222.2 |1248.8 |1274.2 |1299.1 |1323.6 |1347.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 358.5 | 408.5 | 458.5 | 508.5 | 558.5 | 608.5 | 658.5 | +| 150 v| 3.01 | 3.27| 3.50| 3.75| 3.97| 4.19| 4.41| +| h| 1193.4 |1223.0 |1249.6 |1275.1 |1300.0 |1324.5 |1348.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 361.0 | 411.0 | 461.0 | 511.0 | 561.0 | 611.0 | 661.0 | +| 155 v| 2.92 | 3.17| 3.41| 3.63| 3.85| 4.06| 4.28| +| h| 1194.0 |1223.6 |1250.5 |1276.0 |1300.8 |1325.3 |1349.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 363.6 | 413.6 | 463.6 | 513.6 | 563.6 | 613.6 | 663.6 | +| 160 v| 2.83 | 3.07| 3.30| 3.53| 3.74| 3.95| 4.15| +| h| 1194.5 |1224.5 |1251.3 |1276.8 |1301.7 |1326.2 |1350.6 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 366.0 | 416.0 | 466.0 | 516.0 | 566.0 | 616.0 | 666.0 | +| 165 v| 2.75 | 2.99| 3.21| 3.43| 3.64| 3.84| 4.04| +| h| 1195.0 |1225.2 |1252.0 |1277.6 |1302.5 |1327.1 |1351.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 368.5 | 418.5 | 468.5 | 518.5 | 568.5 | 618.5 | 668.5 | +| 170 v| 2.68 | 2.91| 3.12| 3.34| 3.54| 3.73| 3.92| +| h| 1195.4 |1225.9 |1252.8 |1278.4 |1303.3 |1327.9 |1352.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 370.8 | 420.8 | 470.8 | 520.8 | 570.8 | 620.8 | 670.8 | +| 175 v| 2.60 | 2.83| 3.04| 3.24| 3.44| 3.63| 3.82| +| h| 1195.9 |1226.6 |1253.6 |1279.1 |1304.1 |1328.7 |1353.2 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 373.1 | 423.1 | 473.1 | 523.1 | 573.1 | 623.1 | 673.1 | +| 180 v| 2.53 | 2.75| 2.96| 3.16| 3.35| 3.54| 3.72| +| h| 1196.4 |1227.2 |1254.3 |1279.9 |1304.8 |1329.5 |1353.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 375.4 | 425.4 | 475.4 | 525.4 | 575.4 | 625.4 | 675.4 | +| 185 v| 2.47 | 2.68| 2.89| 3.08| 3.27| 3.45| 3.63| +| h| 1196.8 |1227.9 |1255.0 |1280.6 |1305.6 |1330.2 |1354.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 377.6 | 427.6 | 477.6 | 527.6 | 577.6 | 627.6 | 677.6 | +| 190 v| 2.41 | 2.62| 2.81| 3.00| 3.19| 3.37| 3.55| +| h| 1197.3 |1228.6 |1255.7 |1281.3 |1306.3 |1330.9 |1355.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 379.8 | 429.8 | 479.8 | 529.8 | 579.8 | 629.8 | 679.8 | +| 195 v| 2.35 | 2.55| 2.75| 2.93| 3.11| 3.29| 3.46| +| h| 1197.7 |1229.2 |1256.4 |1282.0 |1307.0 |1331.6 |1356.2 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 381.9 | 431.9 | 481.9 | 531.9 | 581.9 | 631.9 | 681.9 | +| 200 v| 2.29 | 2.49| 2.68| 2.86| 3.04| 3.21| 3.38| +| h| 1198.1 |1229.8 |1257.1 |1282.6 |1307.7 |1332.4 |1357.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 384.0 | 434.0 | 484.0 | 534.0 | 584.0 | 634.0 | 684.0 | +| 205 v| 2.24 | 2.44| 2.62| 2.80| 2.97| 3.14| 3.30| +| h| 1198.5 |1230.4 |1257.7 |1283.3 |1308.3 |1333.0 |1357.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 386.0 | 436.0 | 486.0 | 536.0 | 586.0 | 636.0 | 686.0 | +| 210 v| 2.19 | 2.38| 2.56| 2.74| 2.91| 3.07| 3.23| +| h| 1198.8 |1231.0 |1258.4 |1284.0 |1309.0 |1333.7 |1358.4 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 388.0 | 438.0 | 488.0 | 538.0 | 588.0 | 638.0 | 688.0 | +| 215 v| 2.14 | 2.33| 2.51| 2.68| 2.84| 3.00| 3.16| +| h| 1199.2 |1231.6 |1259.0 |1284.6 |1309.7 |1334.4 |1359.1 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 389.9 | 439.9 | 489.9 | 539.9 | 589.9 | 639.9 | 689.9 | +| 220 v| 2.09 | 2.28| 2.45| 2.62| 2.78| 2.94| 3.10| +| h| 1199.6 |1232.2 |1259.6 |1285.2 |1310.3 |1335.1 |1359.8 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 391.9 | 441.9 | 491.9 | 541.9 | 591.9 | 641.9 | 691.9 | +| 225 v| 2.05 | 2.23| 2.40| 2.57| 2.72| 2.88| 3.03| +| h| 1199.9 |1232.7 |1260.2 |1285.9 |1310.9 |1335.7 |1360.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 393.8 | 443.8 | 493.8 | 543.8 | 593.8 | 643.8 | 693.8 | +| 230 v| 2.00 | 2.18| 2.35| 2.51| 2.67| 2.82| 2.97| +| h| 1200.2 |1233.2 |1260.7 |1286.5 |1311.6 |1336.3 |1361.0 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 395.6 | 445.6 | 495.6 | 545.6 | 595.6 | 645.6 | 695.6 | +| 235 v| 1.96 | 2.14| 2.30| 2.46| 2.62| 2.77| 2.91| +| h| 1200.6 |1233.8 |1261.4 |1287.1 |1312.2 |1337.0 |1361.7 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | 697.4 | +| 240 v| 1.92 | 2.09| 2.26| 2.42| 2.57| 2.71| 2.85| +| h| 1200.9 |1234.3 |1261.9 |1287.6 |1312.8 |1337.6 |1362.3 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 399.3 | 449.3 | 499.3 | 549.3 | 599.3 | 649.3 | 699.3 | +| 245 v| 1.89 | 2.05| 2.22| 2.37| 2.52| 2.66| 2.80| +| h| 1201.2 |1234.8 |1262.5 |1288.2 |1313.3 |1338.2 |1362.9 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 401.0 | 451.0 | 501.0 | 551.0 | 601.0 | 651.0 | 701.0 | +| 250 v| 1.85 | 2.02| 2.17| 2.33| 2.47| 2.61| 2.75| +| h| 1201.5 |1235.4 |1263.0 |1288.8 |1313.9 |1338.8 |1363.5 | +|________|_________|_______|_______|_______|_______|_______|_______| +| t| 402.8 | 452.8 | 502.8 | 552.8 | 602.8 | 652.8 | 702.8 | +| 255 v| 1.81 | 1.98| 2.14| 2.28| 2.43| 2.56| 2.70| +| h| 1201.8 |1235.9 |1263.6 |1289.3 |1314.5 |1339.3 |1364.1 | +|________|_________|_______|_______|_______|_______|_______|_______| + + +t = Temperature, degrees Fahrenheit. +v = Specific volume, in cubic feet, per pound. +h = Total heat from water at 32 degrees, B. t. u. + +[Graph: Temperature of Steam--Degrees Fahr. +against Temperature in Calorimeter--Degrees Fahr. + +Fig. 15. Graphic Method of Determining Moisture Contained in Steam from +Calorimeter Readings] + + + + +MOISTURE IN STEAM + + +The presence of moisture in steam causes a loss, not only in the +practical waste of the heat utilized to raise this moisture from the +temperature of the feed water to the temperature of the steam, but also +through the increased initial condensation in an engine cylinder and +through friction and other actions in a steam turbine. The presence of +such moisture also interferes with proper cylinder lubrication, causes a +knocking in the engine and a water hammer in the steam pipes. In steam +turbines it will cause erosion of the blades. + +The percentage by weight of steam in a mixture of steam and water is +called the _quality of the steam_. + +The apparatus used to determine the moisture content of steam is called +a calorimeter though since it may not measure the heat in the steam, the +name is not descriptive of the function of the apparatus. The first form +used was the "barrel calorimeter", but the liability of error was so +great that its use was abandoned. Modern calorimeters are in general of +either the throttling or separator type. + +Throttling Calorimeter--Fig. 14 shows a typical form of throttling +calorimeter. Steam is drawn from a vertical main through the sampling +nipple, passes around the first thermometer cup, then through a +one-eighth inch orifice in a disk between two flanges, and lastly around +the second thermometer cup and to the atmosphere. Thermometers are +inserted in the wells, which should be filled with mercury or heavy +cylinder oil. + +[Illustration: Fig. 14. Throttling Calorimeter and Sampling Nozzle] + +The instrument and all pipes and fittings leading to it should be +thoroughly insulated to diminish radiation losses. Care must be taken to +prevent the orifice from becoming choked with dirt and to see that no +leaks occur. The exhaust pipe should be short to prevent back pressure +below the disk. + +When steam passes through an orifice from a higher to a lower pressure, +as is the case with the throttling calorimeter, no external work has to +be done in overcoming a resistance. Hence, if there is no loss from +radiation, the quantity of heat in the steam will be exactly the same +after passing the orifice as before passing. If the higher steam +pressure is 160 pounds gauge and the lower pressure that of the +atmosphere, the total heat in a pound of dry steam at the former +pressure is 1195.9 B. t. u. and at the latter pressure 1150.4 B. t. u., +a difference of 45.4 B. t. u. As this heat will still exist in the steam +at the lower pressure, since there is no external work done, its effect +must be to superheat the steam. Assuming the specific heat of +superheated steam to be 0.47, each pound passing through will be +superheated 45.4/0.47 = 96.6 degrees. If, however, the steam had +contained one per cent of moisture, it would have contained less heat +units per pound than if it were dry. Since the latent heat of steam at +160 pounds gauge pressure is 852.8 B. t. u., it follows that the one per +cent of moisture would have required 8.5 B. t. u. to evaporate it, +leaving only 45.4 - 8.5 = 36.9 B. t. u. available for superheating; +hence, the superheat would be 36.9/0.47 = 78.5 degrees, as against 96.6 +degrees for dry steam. In a similar manner, the degree of superheat for +other percentages of moisture may be determined. The action of the +throttling calorimeter is based upon the foregoing facts, as shown +below. + +Let H = total heat of one pound of steam at boiler pressure, + L = latent heat of steam at boiler pressure, + h = total heat of steam at reduced pressure after passing + orifice, + t_{1} = temperature of saturated steam at the reduced pressure, + t_{2} = temperature of steam after expanding through the orifice + in the disc, + 0.47 = the specific heat of saturated steam at atmospheric pressure, + x = proportion by weight of moisture in steam. + +The difference in B. t. u. in a pound of steam at the boiler pressure +and after passing the orifice is the heat available for evaporating the +moisture content and superheating the steam. Therefore, + +H - h = xL + 0.47(t_{2} - t_{1}) + + H - h - 0.47(t_{2} - t_{1}) +or x = --------------------------- (4) + L + +Almost invariably the lower pressure is taken as that of the atmosphere. +Under such conditions, h = 1150.4 and t_{1} = 212 degrees. The formula +thus becomes: + + H - 1150.4 - 0.47(t_{2} - 212) +x = ------------------------------ (5) + L + +For practical work it is more convenient to dispense with the upper +thermometer in the calorimeter and to measure the pressure in the steam +main by an accurate steam pressure gauge. + +A chart may be used for determining the value of x for approximate work +without the necessity for computation. Such a chart is shown in Fig. 15 +and its use is as follows: Assume a gauge pressure of 180 pounds and a +thermometer reading of 295 degrees. The intersection of the vertical +line from the scale of temperatures as shown by the calorimeter +thermometer and the horizontal line from the scale of gauge pressures +will indicate directly the per cent of moisture in the steam as read +from the diagonal scale. In the present instance, this per cent is 1.0. + +Sources of Error in the Apparatus--A slight error may arise from the +value, 0.47, used as the specific heat of superheated steam at +atmospheric pressure. This value, however is very nearly correct and any +error resulting from its use will be negligible. + +There is ordinarily a larger source of error due to the fact that the +stem of the thermometer is not heated to its full length, to an initial +error in the thermometer and to radiation losses. + +With an ordinary thermometer immersed in the well to the 100 degrees +mark, the error when registering 300 degrees would be about 3 degrees +and the true temperature be 303 degrees.[19] + +The steam is evidently losing heat through radiation from the moment it +enters the sampling nipple. The heat available for evaporating moisture +and superheating steam after it has passed through the orifice into the +lower pressure will be diminished by just the amount lost through +radiation and the value of t_{2}, as shown by the calorimeter +thermometer, will, therefore, be lower than if there were no such loss. +The method of correcting for the thermometer and radiation error +recommended by the Power Test Committee of the American Society of +Mechanical Engineers is by referring the readings as found on the boiler +trial to a "normal" reading of the thermometer. This normal reading is +the reading of the lower calorimeter thermometer for dry saturated +steam, and should be determined by attaching the instrument to a +horizontal steam pipe in such a way that the sampling nozzle projects +upward to near the top of the pipe, there being no perforations in the +nozzle and the steam taken only through its open upper end. The test +should be made with the steam in a quiescent state and with the steam +pressure maintained as nearly as possible at the pressure observed in +the main trial, the calorimeter thermometer to be the same as was used +on the trial or one exactly similar. + +With a normal reading thus obtained for a pressure approximately the +same as existed in the trial, the true percentage of moisture in the +steam, that is, with the proper correction made for radiation, may be +calculated as follows: + +Let T denote the normal reading for the conditions existing in the +trial. The effect of radiation from the instrument as pointed out will +be to lower the temperature of the steam at the lower pressure. Let +x_{1} represent the proportion of water in the steam which will lower +its temperature an amount equal to the loss by radiation. Then, + + H - h - 0.47(T - t_{1}) +x_{1} = ----------------------- + L + +This amount of moisture, x_{1} was not in the steam originally but is +the result of condensation in the instrument through radiation. Hence, +the true amount of moisture in the steam represented by X is the +difference between the amount as determined in the trial and that +resulting from condensation, or, + +X = x - x_{1} + + H - h - 0.47(t_{2} - t_{1}) H - h - 0.47(T - t_{1}) + = --------------------------- - ----------------------- + L L + + 0.47(T - t_{2}) + = --------------- (6) + L + +As T and t_{2} are taken with the same thermometer under the same set of +conditions, any error in the reading of the thermometers will be +approximately the same for the temperatures T and t_{2} and the above +method therefore corrects for both the radiation and thermometer errors. +The theoretical readings for dry steam, where there are no losses due to +radiation, are obtainable from formula (5) by letting x = 0 and solving +for t_{2}. The difference between the theoretical reading and the normal +reading for no moisture will be the thermometer and radiation correction +to be applied in order that the correct reading of t_{2} may be +obtained. + +For any calorimeter within the range of its ordinary use, such a +thermometer and radiation correction taken from one normal reading is +approximately correct for any conditions with the same or a duplicate +thermometer. + +The percentage of moisture in the steam, corrected for thermometer error +and radiation and the correction to be applied to the particular +calorimeter used, would be determined as follows: Assume a gauge +pressure in the trial to be 180 pounds and the thermometer reading to be +295 degrees. A normal reading, taken in the manner described, gives a +value of T = 303 degrees; then, the percentage of moisture corrected for +thermometer error and radiation is, + + 0.47(303 - 295) +x = ---------------- + 845.0 + + = 0.45 per cent. + +The theoretical reading for dry steam will be, + + 1197.7 - 1150.4 - 0.47(t_{2} - 212) + 0 = ------------------------------------ + 845.0 + +t_{2} = 313 degrees. + +The thermometer and radiation correction to be applied to the instrument +used, therefore over the ordinary range of pressure is + + Correction = 313 - 303 = 10 degrees + +The chart may be used in the determination of the correct reading of +moisture percentage and the permanent radiation correction for the +instrument used without computation as follows: Assume the same trial +pressure, feed temperature and normal reading as above. If the normal +reading is found to be 303 degrees, the correction for thermometer and +radiation will be the theoretical reading for dry steam as found from +the chart, less this normal reading, or 10 degrees correction. The +correct temperature for the trial in question is, therefore, 305 +degrees. The moisture corresponding to this temperature and 180 pounds +gauge pressure will be found from the chart to be 0.45 per cent. + +[Illustration: Fig. 16. Compact Throttling Calorimeter] + +There are many forms of throttling calorimeter, all of which work upon +the same principle. The simplest one is probably that shown in Fig. 14. +An extremely convenient and compact design is shown in Fig. 16. This +calorimeter consists of two concentric metal cylinders screwed to a cap +containing a thermometer well. The steam pressure is measured by a gauge +placed in the supply pipe or other convenient location. Steam passes +through the orifice A and expands to atmospheric pressure, its +temperature at this pressure being measured by a thermometer placed in +the cup C. To prevent as far as possible radiation losses, the annular +space between the two cylinders is used as a jacket, steam being +supplied to this space through the hole B. + +The limits of moisture within which the throttling calorimeter will work +are, at sea level, from 2.88 per cent at 50 pounds gauge pressure and +7.17 per cent moisture at 250 pounds pressure. + +Separating Calorimeter--The separating calorimeter mechanically +separates the entrained water from the steam and collects it in a +reservoir, where its amount is either indicated by a gauge glass or is +drained off and weighed. Fig. 17 shows a calorimeter of this type. The +steam passes out of the calorimeter through an orifice of known size so +that its total amount can be calculated or it can be weighed. A gauge is +ordinarily provided with this type of calorimeter, which shows the +pressure in its inner chamber and the flow of steam for a given period, +this latter scale being graduated by trial. + +The instrument, like a throttling calorimeter, should be well insulated +to prevent losses from radiation. + +While theoretically the separating calorimeter is not limited in +capacity, it is well in cases where the percentage of moisture present +in the steam is known to be high, to attach a throttling calorimeter to +its exhaust. This, in effect, is the using of the separating calorimeter +as a small separator between the sampling nozzle and the throttling +instrument, and is necessary to insure the determination of the full +percentage of moisture in the steam. The sum of the percentages shown by +the two instruments is the moisture content of the steam. + +The steam passing through a separating calorimeter may be calculated by +Napier's formula, the size of the orifice being known. There are +objections to such a calculation, however, in that it is difficult to +accurately determine the areas of such small orifices. Further, small +orifices have a tendency to become partly closed by sediment that may be +carried by the steam. The more accurate method of determining the amount +of steam passing through the instrument is as follows: + +[Illustration: Fig. 17. Separating Calorimeter] + +A hose should be attached to the separator outlet leading to a vessel of +water on a platform scale graduated to 1/100 of a pound. The steam +outlet should be connected to another vessel of water resting on a +second scale. In each case, the weight of each vessel and its contents +should be noted. When ready for an observation, the instrument should be +blown out thoroughly so that there will be no water within the +separator. The separator drip should then be closed and the steam hose +inserted into the vessel of water at the same instant. When the +separator has accumulated a sufficient quantity of water, the valve of +the instrument should be closed and the hose removed from the vessel of +water. The separator should be emptied into the vessel on its scale. The +final weight of each vessel and its contents are to be noted and the +differences between the final and original weights will represent the +weight of moisture collected by the separator and the weight of steam +from which the moisture has been taken. The proportion of moisture can +then be calculated from the following formula: + + 100 w +x = ----- (7) + W - w + +Where x = per cent moisture in steam, + W = weight of steam condensed, + w = weight of moisture as taken out by the separating + calorimeter. + +Sampling Nipple--The principle source of error in steam calorimeter +determinations is the failure to obtain an average sample of the steam +delivered by the boiler and it is extremely doubtful whether such a +sample is ever obtained. The two governing features in the obtaining of +such a sample are the type of sampling nozzle used and its location. + +The American Society of Mechanical Engineers recommends a sampling +nozzle made of one-half inch iron pipe closed at the inner end and the +interior portion perforated with not less than twenty one-eighth inch +holes equally distributed from end to end and preferably drilled in +irregular or spiral rows, with the first hole not less than one-half +inch from the wall of the pipe. Many engineers object to the use of a +perforated sampling nipple because it ordinarily indicates a higher +percentage of moisture than is actually present in the steam. This is +due to the fact that if the perforations come close to the inner surface +of the pipe, the moisture, which in many instances clings to this +surface, will flow into the calorimeter and cause a large error. Where a +perforated nipple is used, in general it may be said that the +perforations should be at least one inch from the inner pipe surface. + +A sampling nipple, open at the inner end and unperforated, undoubtedly +gives as accurate a measure as can be obtained of the moisture in the +steam passing that end. It would appear that a satisfactory method of +obtaining an average sample of the steam would result from the use of an +open end unperforated nipple passing through a stuffing box which would +allow the end to be placed at any point across the diameter of the steam +pipe. + +Incidental to a test of a 15,000 K. W. steam engine turbine unit, Mr. +H. G. Stott and Mr. R. G. S. Pigott, finding no experimental data +bearing on the subject of low pressure steam quality determinations, +made a investigation of the subject and the sampling nozzle illustrated +in Fig. 18 was developed. In speaking of sampling nozzles in the +determination of the moisture content of low pressure steam, Mr. Pigott +says, "the ordinary standard perforated pipe sampler is absolutely +worthless in giving a true sample and it is vital that the sample be +abstracted from the main without changing its direction or velocity +until it is safely within the sample pipe and entirely isolated from the +rest of the steam." + +[Illustration: Fig. 18. Stott and Pigott Sampling Nozzle] + +It would appear that the nozzle illustrated is undoubtedly the best that +has been developed for use in the determination of the moisture content +of steam, not only in the case of low, but also in high pressure steam. + +Location of Sampling Nozzle--The calorimeter should be located as near +as possible to the point from which the steam is taken and the sampling +nipple should be placed in a section of the main pipe near the boiler +and where there is no chance of moisture pocketing in the pipe. The +American Society of Mechanical Engineers recommends that a sampling +nipple, of which a description has been given, should be located in a +vertical main, rising from the boiler with its closed end extending +nearly across the pipe. Where non-return valves are used, or where there +are horizontal connections leading from the boiler to a vertical outlet, +water may collect at the lower end of the uptake pipe and be blown +upward in a spray which will not be carried away by the steam owing to a +lack of velocity. A sample taken from the lower part of this pipe will +show a greater amount of moisture than a true sample. With goose-neck +connections a small amount of water may collect on the bottom of the +pipe near the upper end where the inclination is such that the tendency +to flow backward is ordinarily counterbalanced by the flow of steam +forward over its surface; but when the velocity momentarily decreases +the water flows back to the lower end of the goose-neck and increases +the moisture at that point, making it an undesirable location for +sampling. In any case, it should be borne in mind that with low +velocities the tendency is for drops of entrained water to settle to the +bottom of the pipe, and to be temporarily broken up into spray whenever +an abrupt bend or other disturbance is met. + +[Illustration: Fig. 19. Illustrating the Manner in which Erroneous +Calorimeter Readings may be Obtained due to Improper Location of Sampling +Nozzle + + Case 1--Horizontal pipe. Water flows at bottom. If perforations + in nozzle are too near bottom of pipe, water piles against + nozzle, flows into calorimeter and gives false reading. + Case 2--If nozzle located too near junction of two horizontal + runs, as at a, condensation from vertical pipe which collects at + this point will be thrown against the nozzle by the velocity of + the steam, resulting in a false reading. Nozzle should be + located far enough above junction to be removed from water kept + in motion by the steam velocity, as at b. Case 3--Condensation + in bend will be held by velocity of the steam as shown. When + velocity is diminished during firing intervals and the like + moisture flows back against nozzle, a, and false reading is + obtained. A true reading will be obtained at b provided + condensation is not blown over on nozzle. Case 4--Where + non-return valve is placed before a bend, condensation will + collect on steam line side and water will be swept by steam + velocity against nozzle and false readings result.] + +Fig. 19 indicates certain locations of sampling nozzles from which +erroneous results will be obtained, the reasons being obvious from a +study of the cuts. + +Before taking any calorimeter reading, steam should be allowed to flow +through the instrument freely until it is thoroughly heated. The method +of using a throttling calorimeter is evident from the description of the +instrument given and the principle upon which it works. + +[Illustration: Babcock & Wilcox Superheater] + + + + +SUPERHEATED STEAM + + +Superheated steam, as already stated, is steam the temperature of which +exceeds that of saturated steam at the same pressure. It is produced by +the addition of heat to saturated steam which has been removed from +contact with the water from which it was generated. The properties of +superheated steam approximate those of a perfect gas rather than of a +vapor. Saturated steam cannot be superheated when it is in contact with +water which is also heated, neither can superheated steam condense +without first being reduced to the temperature of saturated steam. Just +so long as its temperature is above that of saturated steam at a +corresponding pressure it is superheated, and before condensation can +take place that superheat must first be lost through radiation or some +other means. Table 24[20] gives such properties of superheated steam for +varying pressures as are necessary for use in ordinary engineering +practice. + +Specific Heat of Superheated Steam--The specific heat of superheated +steam at atmospheric pressure and near saturation point was determined +by Regnault, in 1862, who gives it the value of 0.48. Regnault's value +was based on four series of experiments, all at atmospheric pressure and +with about the same temperature range, the maximum of which was 231.1 +degrees centigrade. For fifty years after Regnault's determination, this +value was accepted and applied to higher pressures and temperatures as +well as to the range of his experiments. More recent investigations have +shown that the specific heat is not a constant and varies with both +pressure and the temperature. A number of experiments have been made by +various investigators and, up to the present, the most reliable appear +to be those of Knoblauch and Jacob. Messrs. Marks and Davis have used +the values as determined by Knoblauch and Jacob with slight +modifications. The first consists in a varying of the curves at low +pressures close to saturation because of thermodynamic evidence and in +view of Regnault's determination at atmospheric pressure. The second +modification is at high degrees of superheat to follow Holborn's and +Henning's curve, which is accepted as authentic. + +For the sake of convenience, the mean specific heat of superheated steam +at various pressures and temperatures is given in tabulated form in +Table 25. These values have been calculated from Marks and Davis Steam +Tables by deducting from the total heat of one pound of steam at any +pressure for any degree of superheat the total heat of one pound of +saturated steam at the same pressure and dividing the difference by the +number of degrees of superheat and, therefore, represent the average +specific heat starting from that at saturation to the value at the +particular pressure and temperature.[21] Expressed as a formula this +calculation is represented by + + H_{sup} - H_{sat} +Sp. Ht. = ----------------- (8) + S_{sup} - S_{sat} + +Where H_{sup} = total heat of one pound of superheated steam at any + pressure and temperature, + H_{sat} = total heat of one pound of saturated steam at same + pressure, + S_{sup} = temperature of superheated steam taken, + S_{sat} = temperature of saturated steam corresponding to the + pressure taken. + + TABLE 25 + + MEAN SPECIFIC HEAT OF SUPERHEATED STEAM + CALCULATED FROM MARKS AND DAVIS TABLES + _______________________________________________________________ +|Gauge | | +|Pressure | Degree of Superheat | +| |_____________________________________________________| +| | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | +|_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| +| 50 | .518| .517| .514| .513| .511| .510| .508| .507| .505| +| 60 | .528| .525| .523| .521| .519| .517| .515| .513| .512| +| 70 | .536| .534| .531| .529| .527| .524| .522| .520| .518| +| 80 | .544| .542| .539| .535| .532| .530| .528| .526| .524| +| 90 | .553| .550| .546| .543| .539| .536| .534| .532| .529| +| 100 | .562| .557| .553| .549| .544| .542| .539| .536| .533| +| 110 | .570| .565| .560| .556| .552| .548| .545| .542| .539| +| 120 | .578| .573| .567| .561| .557| .554| .550| .546| .543| +| 130 | .586| .580| .574| .569| .564| .560| .555| .552| .548| +| 140 | .594| .588| .581| .575| .570| .565| .561| .557| .553| +| 150 | .604| .595| .587| .581| .576| .570| .566| .561| .557| +| 160 | .612| .603| .596| .589| .582| .576| .571| .566| .562| +| 170 | .620| .612| .603| .595| .588| .582| .576| .571| .566| +| 180 | .628| .618| .610| .601| .593| .587| .581| .575| .570| +| 190 | .638| .627| .617| .608| .599| .592| .585| .579| .574| +| 200 | .648| .635| .624| .614| .605| .597| .590| .584| .578| +| 210 | .656| .643| .631| .620| .611| .602| .595| .588| .583| +| 220 | .664| .650| .637| .626| .616| .607| .600| .592| .586| +| 230 | .672| .658| .644| .633| .622| .613| .605| .597| .591| +| 240 | .684| .668| .653| .640| .629| .619| .610| .602| .595| +| 250 | .692| .675| .659| .645| .633| .623| .614| .606| .599| +|_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| +|Gauge | | +|Pressure | Degree of Superheat | +| |-----------------------------------------------------| +| | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 225 | 250 | +|---------+-----+-----+-----+-----+-----+-----+-----+-----+-----| +| 50 | .504| .503| .502| .501| .500| .500| .499| .497| .496| +| 60 | .511| .509| .508| .507| .506| .504| .504| .502| .500| +| 70 | .516| .515| .513| .512| .511| .510| .509| .506| .504| +| 80 | .522| .520| .518| .516| .515| .514| .513| .511| .508| +| 90 | .527| .525| .523| .521| .519| .518| .517| .514| .510| +| 100 | .531| .529| .527| .525| .523| .522| .521| .517| .513| +| 110 | .536| .534| .532| .529| .528| .526| .525| .520| .517| +| 120 | .540| .537| .535| .533| .531| .529| .528| .523| .519| +| 130 | .545| .542| .539| .537| .535| .533| .531| .527| .523| +| 140 | .550| .547| .544| .541| .539| .536| .534| .530| .526| +| 150 | .554| .550| .547| .544| .542| .539| .537| .533| .529| +| 160 | .558| .554| .551| .548| .545| .543| .541| .536| .531| +| 170 | .562| .558| .555| .552| .549| .546| .544| .538| .533| +| 180 | .566| .561| .558| .555| .552| .549| .546| .540| .536| +| 190 | .569| .565| .562| .558| .555| .552| .549| .543| .538| +| 200 | .574| .569| .566| .562| .558| .555| .552| .546| .541| +| 210 | .578| .573| .569| .565| .561| .558| .555| .549| .543| +| 220 | .581| .577| .572| .568| .564| .561| .558| .551| .545| +| 230 | .585| .580| .575| .572| .567| .564| .561| .554| .548| +| 240 | .589| .584| .579| .575| .571| .567| .564| .556| .550| +| 250 | .593| .587| .582| .577| .574| .570| .567| .559| .553| +|_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| + +Factor of Evaporation with Superheated Steam--When superheat is present +in the steam during a boiler trial, where superheated steam tables are +available, the formula for determining the factor of evaporation is that +already given, (2),[22] namely, + + H - h +Factor of evaporation = ----- + L + +Here H = total heat in one pound of superheated steam from the table, +h and L having the same values as in (2). + +Where no such tables are available but the specific heat of superheat is +known, the formula becomes: + + H - h + Sp. Ht.(T - t) +Factor of evaporation = ---------------------- + L + +Where H = total heat in one pound of saturated steam at pressure + existing in trial, + h = sensible heat above 32 degrees in one pound of water at the + temperature entering the boiler, + T = temperature of superheated steam as determined in the trial, + t = temperature of saturated steam corresponding to the boiler + pressure, +Sp. Ht. = mean specific heat of superheated steam at the pressure and + temperature as found in the trial, + L = latent heat of one pound of saturated steam at atmospheric + pressure. + +Advantages of the Use of Superheated Steam--In considering the saving +possible by the use of superheated steam, it is too often assumed that +there is only a saving in the prime movers, a saving which is at least +partially offset by an increase in the fuel consumption of the boilers +generating steam. This misconception is due to the fact that the fuel +consumption of the boiler is only considered in connection with a +definite weight of steam. It is true that where such a definite weight +is to be superheated, an added amount of fuel must be burned. With a +properly designed superheater where the combined efficiency of the +boiler and superheater will be at least as high as of a boiler alone, +the approximate increase in coal consumption for producing a given +weight of steam will be as follows: + +_Superheat_ _Added Fuel_ + _Degrees_ _Per Cent_ + 25 1.59 + 50 3.07 + 75 4.38 + 100 5.69 + 150 8.19 + 200 10.58 + +These figures represent the added fuel necessary for superheating a +definite weight of steam to the number of degrees as given. The standard +basis, however, of boiler evaporation is one of heat units and, +considered from such a standpoint, again providing the efficiency of the +boiler and superheater is as high, as of a boiler alone, there is no +additional fuel required to generate steam containing a definite number +of heat units whether such units be due to superheat or saturation. That +is, if 6 per cent more fuel is required to generate and superheat to 100 +degrees, a definite weight of steam, over what would be required to +produce the same weight of saturated steam, that steam when superheated, +will contain 6 per cent more heat units above the fuel water temperature +than if saturated. This holds true if the efficiency of the boiler and +superheater combined is the same as of the boiler alone. As a matter of +fact, the efficiency of a boiler and superheater, where the latter is +properly designed and located, will be slightly higher for the same set +of furnace conditions than would the efficiency of a boiler in which no +superheater were installed. A superheater, properly placed within the +boiler setting in such way that products of combustion for generating +saturated steam are utilized as well for superheating that steam, will +not in any way alter furnace conditions. With a given set of such +furnace conditions for a given amount of coal burned, the fact that +additional surface, whether as boiler heating or superheating surface, +is placed in such a manner that the gases must sweep over it, will tend +to lower the temperature of the exit gases. It is such a lowering of +exit gas temperatures that is the ultimate indication of added +efficiency. Though the amount of this added efficiency is difficult to +determine by test, that there is an increase is unquestionable. + +Where a properly designed superheater is installed in a boiler the +heating surface of the boiler proper, in the generation of a definite +number of heat units, is relieved of a portion of the work which would +be required were these heat units delivered in saturated steam. Such a +superheater needs practically no attention, is not subject to a large +upkeep cost or depreciation, and performs its function without in any +way interfering with the operation of the boiler. Its use, therefore +from the standpoint of the boiler room, results in a saving in wear and +tear due to the lower ratings at which the boiler may be run, or its use +will lead to the possibility of obtaining the same number of boiler +horse power from a smaller number of boilers, with the boiler heating +surface doing exactly the same amount of work as if the superheaters +were not installed. The saving due to the added boiler efficiency that +will be obtained is obvious. + +Following the course of the steam in a plant, the next advantage of the +use of superheated steam is the absence of water in the steam pipes. The +thermal conductivity of superheated steam, that is, its power to give up +its heat to surrounding bodies, is much lower than that of saturated +steam and its heat, therefore, will not be transmitted so rapidly to the +walls of the pipes as when saturated steam is flowing through the pipes. +The loss of heat radiated from a steam pipe, assuming no loss in +pressure, represents the equivalent condensation when the pipe is +carrying saturated steam. In well-covered steam mains, the heat lost by +radiation when carrying superheated steam is accompanied only by a +reduction of the superheat which, if it be sufficiently high at the +boiler, will enable a considerable amount of heat to be radiated and +still deliver dry or superheated steam to the prime movers. + +It is in the prime movers that the advantages of the use of superheated +steam are most clearly seen. + +In an engine, steam is admitted into a space that has been cooled by the +steam exhausted during the previous stroke. The heat necessary to warm +the cylinder walls from the temperature of the exhaust to that of the +entering steam can be supplied only by the entering steam. If this steam +be saturated, such an adding of heat to the walls at the expense of the +heat of the entering steam results in the condensation of a portion. +This initial condensation is seldom less than from 20 to 30 per cent of +the total weight of steam entering the cylinder. It is obvious that if +the steam entering be superheated, it must be reduced to the temperature +of saturated steam at the corresponding pressure before any condensation +can take place. If the steam be superheated sufficiently to allow a +reduction in temperature equivalent to the quantity of heat that must be +imparted to the cylinder walls and still remain superheated, it is clear +that initial condensation is avoided. For example: assume one pound of +saturated steam at 200 pounds gauge pressure to enter a cylinder which +has been cooled by the exhaust. Assume the initial condensation to be 20 +per cent. The latent heat of the steam is given up in condensation; +hence, .20 x 838 = 167.6 B. t. u. are given up by the steam. If one +pound of superheated steam enters the same cylinder, it would have to be +superheated to a point where its total heat is 1199 + 168 = 1367 +B. t. u. or, at 200 pounds gauge pressure, superheated approximately 325 +degrees if the heat given up to the cylinder walls were the same as for +the saturated steam. As superheated steam conducts heat less rapidly +than saturated steam, the amount of heat imparted will be less than for +the saturated steam and consequently the amount of superheat required to +prevent condensation will be less than the above figure. This, of +course, is the extreme case of a simple engine with the range of +temperature change a maximum. As cylinders are added, the range in each +is decreased and the condensation is proportionate. + +The true economy of the use of superheated steam is best shown in a +comparison of the "heat consumption" of an engine. This is the number of +heat units required in developing one indicated horse power and the +measure of the relative performance of two engines is based on a +comparison of their heat consumption as the measure of a boiler is based +on its evaporation from and at 212 degrees. The water consumption of an +engine in pounds per indicated horse power is in no sense a true +indication of its efficiency. The initial pressures and corresponding +temperatures may differ widely and thus make a difference in the +temperature of the exhaust and hence in the temperature of the condensed +steam returned to the boiler. For example: suppose a certain weight of +steam at 150 pounds absolute pressure and 358 degrees be expanded to +atmospheric pressure, the temperature then being 212 degrees. If the +same weight of steam be expanded from an initial pressure of 125 pounds +absolute and 344 degrees, to enable it to do the same amount of work, +that is, to give up the same amount of heat, expansion then must be +carried to a point below atmospheric pressure to, say, 13 pounds +absolute, the final temperature of the steam then being 206 degrees. In +actual practice, it has been observed that the water consumption of a +compound piston engine running on 26-inch vacuum and returning the +condensed steam at 140 degrees was approximately the same as when +running on 28-inch vacuum and returning water at 90 degrees. With an +equal water consumption for the two sets of conditions, the economy in +the former case would be greater than in the latter, since it would be +necessary to add less heat to the water returned to the boiler to raise +it to the steam temperature. + +The lower the heat consumption of an engine per indicated horse power, +the higher its economy and the less the number of heat units must be +imparted to the steam generated. This in turn leads to the lowering of +the amount of fuel that must be burned per indicated horse power. + +With the saving in fuel by the reduction of heat consumption of an +engine indicated, it remains to be shown the effect of the use of +superheated steam on such heat consumption. As already explained, the +use of superheated steam reduces condensation not only in the mains but +especially in the steam cylinder, leaving a greater quantity of steam +available to do the work. Furthermore, a portion of the saturated steam +introduced into a cylinder will condense during adiabatic expansion, +this condensation increasing as expansion progresses. Since superheated +steam cannot condense until it becomes saturated, not only is initial +condensation prevented by its use but also such condensation as would +occur during expansion. When superheated sufficiently, steam delivered +by the exhaust will still be dry. In the avoidance of such condensation, +there is a direct saving in the heat consumption of an engine, the heat +given up being utilized in the developing of power and not in changing +the condition of the working fluid. That is, while the number of heat +units lost in overcoming condensation effects would be the same in +either case, when saturated steam is condensed the water of condensation +has no power to do work while the superheated steam, even after it has +lost a like number of heat units, still has the power of expansion. The +saving through the use of superheated steam in the heat consumption of +an engine decreases demands on the boiler and hence the fuel consumption +per unit of power. + +Superheated Steam for Steam Turbines--Experience in using superheated +steam in connection with steam turbines has shown that it leads to +economy and that it undoubtedly pays to use superheated steam in place +of saturated steam. This is so well established that it is standard +practice to use superheated steam in connection with steam turbines. +Aside from the economy secured through using superheated steam, there is +an important advantage arising through the fact that it materially +reduces the erosion of the turbine blades by the action of water that +would be carried by saturated steam. In using saturated steam in a steam +turbine or piston engine, the work done on expanding the steam causes +condensation of a portion of the steam, so that even were the steam dry +on entering the turbine, it would contain water on leaving the turbine. +By superheating the steam the water that exists in the low pressure +stages of the turbine may be reduced to an amount that will not cause +trouble. + +Again, if saturated steam contains moisture, the effect of this moisture +on the economy of a steam turbine is to reduce the economy to a greater +extent than the proportion by weight of water, one per cent of water +causing approximately a falling off of 2 per cent in the economy. + +The water rate of a large economical steam turbine with superheated +steam is reduced about one per cent, for every 12 degrees of superheat +up to 200 degrees Fahrenheit of superheat. To superheat one pound of +steam 12 degrees requires about 7 B. t. u. and if 1050 B. t. u. are +required at the boiler to evaporate one pound of the saturated steam +from the temperature of the feed water, the heat required for the +superheated steam would be 1057 degrees. One per cent of saving, +therefore, in the water consumption would correspond to a net saving of +about one-third of one per cent in the coal consumption. On this basis +100 degrees of superheat with an economical steam turbine would result +in somewhat over 3 per cent of saving in the coal for equal boiler +efficiencies. As a boiler with a properly designed superheater placed +within the setting is more economical for a given capacity than a boiler +without a superheater, the minimum gain in the coal consumption would +be, say, 4 or 5 per cent as compared to a plant with the same boilers +without superheaters. + +The above estimates are on the basis of a thoroughly dry saturated steam +or steam just at the point of being superheated or containing a few +degrees of superheat. If the saturated steam is moist, the saving due to +superheat is more and ordinarily the gain in economy due to superheated +steam, for equal boiler efficiencies, as compared with commercially dry +steam is, say, 5 per cent for each 100 degrees of superheat. Aside from +this gain, as already stated, superheated steam prevents erosion of the +turbine buckets that would be caused by water in the steam, and for the +reasons enumerated it is standard practice to use superheated steam for +turbine work. The less economical the steam motor, the more the gain due +to superheated steam, and where there are a number of auxiliaries that +are run with superheated steam, the percentage of gain will be greater +than the figures given above, which are the minimum and are for the most +economical type of large steam turbines. + +An example from actual practice will perhaps best illustrate and +emphasize the foregoing facts. In October 1909, a series of comparable +tests were conducted by The Babcock & Wilcox Co. on the steam yacht +"Idalia" to determine the steam consumption both with saturated and +superheated steam of the main engine on that yacht, including as well +the feed pump, circulating pump and air pump. These tests are more +representative than are most tests of like character in that the saving +in the steam consumption of the auxiliaries, which were much more +wasteful than the main engine, formed an important factor. A resume of +these tests was published in the Journal of the Society of Naval +Engineers, November 1909. + +The main engines of the "Idalia" are four cylinder, triple expansion, +11-1/2 x 19 inches by 22-11/16 x 18 inches stroke. Steam is supplied by +a Babcock & Wilcox marine boiler having 2500 square feet of boiler +heating surface, 340 square feet of superheating surface and 65 square +feet of grate surface. + +The auxiliaries consist of a feed pump 6 x 4 x 6 inches, an independent +air pump 6 x 12 x 8 inches, and a centrifugal pump driven by a +reciprocating engine 5-7/16 x 5 inches. Under ordinary operating +conditions the superheat existing is about 100 degrees Fahrenheit. + +Tests were made with various degrees of superheat, the amount being +varied by by-passing the gases and in the tests with the lower amounts +of superheat by passing a portion of the steam from the boiler to the +steam main without passing it through the superheater. Steam temperature +readings were taken at the engine throttle. In the tests with saturated +steam, the superheater was completely cut out of the system. Careful +calorimeter measurements were taken, showing that the saturated steam +delivered to the superheater was dry. + +The weight of steam used was determined from the weight of the condensed +steam discharge from the surface condenser, the water being pumped from +the hot well into a tank mounted on platform scales. The same +indicators, thermometers and gauges were used in all the tests, so that +the results are directly comparable. The indicators used were of the +outside spring type so that there was no effect of the temperature of +the steam. All tests were of sufficient duration to show a uniformity of +results by hours. A summary of the results secured is given in Table 26, +which shows the water rate per indicated horse power and the heat +consumption. The latter figures are computed on the basis of the heat +imparted to the steam above the actual temperature of the feed water +and, as stated, these are the results that are directly comparable. + + TABLE 26 + + RESULTS OF "IDALIA" TESTS + _______________________________________________________________________ +| | | | | | | +|Date 1909 |Oct. 11|Oct. 14|Oct. 14|Oct. 12|Oct. 13| +|_______________________________|_______|_______|_______|_______|_______| +|Degrees of superheat Fahrenheit| 0 | 57 | 88 | 96 | 105 | +|Pressures, pounds per} Throttle| 190 | 196 | 201 | 198 | 203 | +|square inch above } First | | | | | | +|Atmospheric Pressure } Receiver| 68.4 | 66.0 | 64.3 | 61.9 | 63.0 | +| } Second | | | | | | +| } Receiver| 9.7 | 9.2 | 8.7 | 7.8 | 8.4 | +|Vacuum, inches | 25.5 | 25.9 | 25.9 | 25.4 | 25.2 | +|Temperature, Degrees Fahrenheit| | | | | | +| } Feed | 201 | 206 | 205 | 202 | 200 | +| } Hot Well | 116 | 109.5 | 115 | 111.5 | 111 | +| | | | | | | +|Revolutions per minute | | | | | | +| {Air Pump | 57 | 56 | 53 | 54 | 45 | +| {Circulating Pump| 196 | 198 | 196 | 198 | 197 | +| {Main Engine | 194.3 | 191.5 | 195.1 | 191.5 | 193.1 | +|Indicated Horse Power, | | | | | | +| Main Engine | 512.3 | 495.2 | 521.1 | 498.3 | 502.2 | +|Water per hour, total pounds |9397 |8430 |8234 |7902 |7790 | +|Water per indicated | | | | | | +| Horse Power, pounds | 18.3 | 17.0 | 15.8 | 15.8 | 15.5 | +|B. t. u. per minute per | | | | | | +| indicated Horse Power | 314 | 300 | 284 | 286 | 283 | +|Per cent Saving of Steam | ... | 7.1 | 13.7 | 13.7 | 15.3 | +|Percent Saving of Fuel | | | | | | +| (computed) | ... | 4.4 | 9.5 | 8.9 | 9.9 | +|_______________________________|_______|_______|_______|_______|_______| + +The table shows that the saving in steam consumption with 105 degrees of +superheat was 15.3 per cent and in heat consumption about 10 per cent. +This may be safely stated to be a conservative representation of the +saving that may be accomplished by the use of superheated steam in a +plant as a whole, where superheated steam is furnished not only to the +main engine but also to the auxiliaries. The figures may be taken as +conservative for the reason that in addition to the saving as shown in +the table, there would be in an ordinary plant a saving much greater +than is generally realized in the drips, where the loss with saturated +steam is greatly in excess of that with superheated steam. + +The most conclusive and most practical evidence that a saving is +possible through the use of superheated steam is in the fact that in the +largest and most economical plants it is used almost without exception. +Regardless of any such evidence, however, there is a deep rooted +conviction in the minds of certain engineers that the use of superheated +steam will involve operating difficulties which, with additional first +cost, will more than offset any fuel saving. There are, of course, +conditions under which the installation of superheaters would in no way +be advisable. With a poorly designed superheater, no gain would result. +In general, it may be stated that in a new plant, properly designed, +with a boiler and superheater which will have an efficiency at least as +high as a boiler without a superheater, a gain is certain. + +Such a gain is dependent upon the class of engine and the power plant +equipment in general. In determining the advisability of making a +superheater installation, all of the factors entering into each +individual case should be considered and balanced, with a view to +determining the saving in relation to cost, maintenance, depreciation +etc. + +In highly economical plants, where the water consumption for an +indicated horse power is low, the gain will be less than would result +from the use of superheated steam in less economical plants where the +water consumption is higher. It is impossible to make an accurate +statement as to the saving possible but, broadly, it may vary from 3 to +5 per cent for 100 degrees of superheat in the large and economical +plants using turbines or steam engines, in which there is a large ratio +of expansion, to from 10 to 25 per cent for 100 degrees of superheat for +the less economical steam motors. + +Though a properly designed superheater will tend to raise rather than to +decrease the boiler efficiency, it does not follow that all superheaters +are efficient, for if the gases in passing over the superheater do not +follow the path they would ordinarily take in passing over the boiler +heating surface, a loss may result. This is noticeably true where part of +the gases are passed over the superheater and are allowed to pass over +only a part or in some cases none of the boiler heating surface. + +With moderate degrees of superheat, from 100 to 200 degrees, where the +piping is properly installed, there will be no greater operating +difficulties than with saturated steam. Engine and turbine builders +guarantee satisfactory operation with superheated steam. With high +degrees of superheat, say, over 250 degrees, apparatus of a special +nature must be used and it is questionable whether the additional care +and liability to operating difficulties will offset any fuel saving +accomplished. It is well established, however, that the operating +difficulties, with the degrees of superheat to which this article is +limited, have been entirely overcome. + +The use of cast-iron fittings with superheated steam has been widely +discussed. It is an undoubted fact that while in some instances +superheated steam has caused deterioration of such fittings, in others +cast-iron fittings have been used with 150 degrees of superheat without +the least difficulty. The quality of the cast iron used in such fittings +has doubtless a large bearing on the life of such fittings for this +service. The difficulties that have been encountered are an increase in +the size of the fittings and eventually a deterioration great enough to +lead to serious breakage, the development of cracks, and when flanges +are drawn up too tightly, the breaking of a flange from the body of the +fitting. The latter difficulty is undoubtedly due, in certain instances, +to the form of flange in which the strain of the connecting bolts tended +to distort the metal. + +The Babcock & Wilcox Co. have used steel castings in superheated steam +work over a long period and experience has shown that this metal is +suitable for the service. There seems to be a general tendency toward +the use of steel fittings. In European practice, until recently, cast +iron was used with apparently satisfactory results. The claim of +European engineers was to the effect that their cast iron was of better +quality than that found in this country and thus explained the results +secured. Recently, however, certain difficulties have been encountered +with such fittings and European engineers are leaning toward the use of +steel for this work. + +The degree of superheat produced by a superheater placed within the +boiler setting will vary according to the class of fuel used, the form +of furnace, the condition of the fire and the rate at which the boiler +is being operated. This is necessarily true of any superheater swept by +the main body of the products of combustion and is a fact that should be +appreciated by the prospective user of superheated steam. With a +properly designed superheater, however, such fluctuations would not be +excessive, provided the boilers are properly operated. As a matter of +fact the point to be guarded against in the use of superheated steam is +that a maximum should not be exceeded. While, as stated, there may be a +considerable fluctuation in the temperature of the steam as delivered +from individual superheaters, where there are a number of boilers on a +line the temperature of the combined flow of steam in the main will be +found to be practically a constant, resulting from the offsetting of +various furnace conditions of one boiler by another. + +[Illustration: 8400 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters at the Butler Street Plant of the Georgia Railway and +Power Co., Atlanta, Ga. This Company Operates a Total of 15,200 Horse +Power of Babcock & Wilcox Boilers] + + + + +PROPERTIES OF AIR + + +Pure air is a mechanical mixture of oxygen and nitrogen. While different +authorities give slightly varying values for the proportion of oxygen +and nitrogen contained, the generally accepted values are: + + By volume, oxygen 20.91 per cent, nitrogen 79.09 per cent. + By weight, oxygen 23.15 per cent, nitrogen 76.85 per cent. + +Air in nature always contains other constituents in varying amounts, +such as dust, carbon dioxide, ozone and water vapor. + +Being perfectly elastic, the density or weight per unit of volume +decreases in geometric progression with the altitude. This fact has a +direct bearing in the proportioning of furnaces, flues and stacks at +high altitudes, as will be shown later in the discussion of these +subjects. The atmospheric pressures corresponding to various altitudes +are given in Table 12. + +The weight and volume of air depend upon the pressure and the +temperature, as expressed by the formula: + +Pv = 53.33 T (9) + +Where P = the absolute pressure in pounds per square foot, + v = the volume in cubic feet of one pound of air, + T = the absolute temperature of the air in degrees Fahrenheit, + 53.33 = a constant for air derived from the ratio of pressure, volume + and temperature of a perfect gas. + +The weight of one cubic foot of air will obviously be the reciprocal of +its volume, that is, 1/v pounds. + + TABLE 27 + + VOLUME AND WEIGHT OF AIR + AT ATMOSPHERIC PRESSURE + AT VARIOUS TEMPERATURES + _______________________________________ +| | | | +| | Volume | | +| Temperature | One Pound | Weight One | +| Degrees | in | Cubic Foot | +| Fahrenheit | Cubic Feet | in Pounds | +|_____________|____________|____________| +| | | | +| 32 | 12.390 | .080710 | +| 50 | 12.843 | .077863 | +| 55 | 12.969 | .077107 | +| 60 | 13.095 | .076365 | +| 65 | 13.221 | .075637 | +| 70 | 13.347 | .074923 | +| 75 | 13.473 | .074223 | +| 80 | 13.599 | .073535 | +| 85 | 13.725 | .072860 | +| 90 | 13.851 | .072197 | +| 95 | 13.977 | .071546 | +| 100 | 14.103 | .070907 | +| 110 | 14.355 | .069662 | +| 120 | 14.607 | .068460 | +| 130 | 14.859 | .067299 | +| 140 | 15.111 | .066177 | +| 150 | 15.363 | .065092 | +| 160 | 15.615 | .064041 | +| 170 | 15.867 | .063024 | +| 180 | 16.119 | .062039 | +| 190 | 16.371 | .061084 | +| 200 | 16.623 | .060158 | +| 210 | 16.875 | .059259 | +| 212 | 16.925 | .059084 | +| 220 | 17.127 | .058388 | +| 230 | 17.379 | .057541 | +| 240 | 17.631 | .056718 | +| 250 | 17.883 | .055919 | +| 260 | 18.135 | .055142 | +| 270 | 18.387 | .054386 | +| 280 | 18.639 | .053651 | +| 290 | 18.891 | .052935 | +| 300 | 19.143 | .052238 | +| 320 | 19.647 | .050898 | +| 340 | 20.151 | .049625 | +| 360 | 20.655 | .048414 | +| 380 | 21.159 | .047261 | +| 400 | 21.663 | .046162 | +| 425 | 22.293 | .044857 | +| 450 | 22.923 | .043624 | +| 475 | 23.554 | .042456 | +| 500 | 24.184 | .041350 | +| 525 | 24.814 | .040300 | +| 550 | 25.444 | .039302 | +| 575 | 26.074 | .038352 | +| 600 | 26.704 | .037448 | +| 650 | 27.964 | .035760 | +| 700 | 29.224 | .034219 | +| 750 | 30.484 | .032804 | +| 800 | 31.744 | .031502 | +| 850 | 33.004 | .030299 | +|_____________|____________|____________| + +Example: Required the volume of air in cubic feet under 60.3 pounds +gauge pressure per square inch at 115 degrees Fahrenheit. + +P = 144 (14.7 + 60.3) = 10,800. + +T = 115 + 460 = 575 degrees. + + 53.33 x 575 +Hence v = ----------- = 2.84 cubic feet, and + 10,800 + + 1 1 +Weight per cubic foot = - = ---- = 0.352 pounds. + v 2.84 + +Table 27 gives the weights and volumes of air under atmospheric pressure +at varying temperatures. + +Formula (9) holds good for other gases with the change in the value of +the constant as follows: + +For oxygen 48.24, nitrogen 54.97, hydrogen 765.71. + +The specific heat of air at constant pressure varies with its +temperature. A number of determinations of this value have been made and +certain of those ordinarily accepted as most authentic are given in +Table 28. + + TABLE 28 + + SPECIFIC HEAT OF AIR + AT CONSTANT PRESSURE AND VARIOUS TEMPERATURES + ______________________________________________________________ +| | | | +| Temperature Range | | | +|_________________________|_______________|____________________| +| | | | | +| Degrees | Degrees | Specific Heat | Authority | +| Centigrade | Fahrenheit | | | +|____________|____________|_______________|____________________| +| | | | | +| -30- 10 | -22- 50 | 0.2377 | Regnault | +| 0-100 | 32- 212 | 0.2374 | Regnault | +| 0-200 | 32- 392 | 0.2375 | Regnault | +| 20-440 | 68- 824 | 0.2366 | Holborn and Curtis | +| 20-630 | 68-1166 | 0.2429 | Holborn and Curtis | +| 20-800 | 68-1472 | 0.2430 | Holborn and Curtis | +| 0-200 | 32- 392 | 0.2389 | Wiedemann | +|____________|____________|_______________|____________________| + +This value is of particular importance in waste heat work and it is +regrettable that there is such a variation in the different experiments. +Mallard and Le Chatelier determined values considerably higher than any +given in Table 28. All things considered in view of the discrepancy of +the values given, there appears to be as much ground for the use of a +constant value for the specific heat of air at any temperature as for a +variable value. Where this value is used throughout this book, it has +been taken as 0.24. + +Air may carry a considerable quantity of water vapor, which is +frequently 3 per cent of the total weight. This fact is of importance in +problems relating to heating drying and the compressing of air. Table 29 +gives the amount of vapor required to saturate air at different +temperatures, its weight, expansive force, etc., and contains sufficient +information for solving practically all problems of this sort that may +arise. + + TABLE 29 + + WEIGHTS OF AIR, VAPOR OF WATER, AND SATURATED MIXTURES OF AIR AND VAPOR + AT DIFFERENT TEMPERATURES, + UNDER THE ORDINARY ATMOSPHERIC PRESSURE OF 29.921 INCHES OF MERCURY + +Column Headings: + 1: Temperature Degrees Fahrenheit + 2: Volume of Dry Air at Different Temperatures, the Volume at 32 Degrees + being 1.000 + 3: Weight of Cubic Foot of Dry Air at the Different Temperatures Pounds + 4: Elastic Force of Vapor in Inches of Mercury (Regnault) + 5: Elastic Force of the Air in the Mixture of Air and Vapor in Inches of + Mercury + 6: Weight of the Air in Pounds + 7: Weight of the Vapor in Pounds + 8: Total Weight of Mixture in Pounds + 9: Weight of Vapor Mixed with One Pound of Air, in Pounds +10: Weight of Dry Air Mixed with One Pound of Vapor, in Pounds +11: Cubic Feet of Vapor from One Pound of Water at its own Pressure in + Column 4 + ____________________________________________________________________________ +| | | | | | | +| | | | | Mixtures of Air Saturated | | +| | | | | with Vapor | | +|___|_____|_____|______|______________________________________________|______| +| | | | | |Weight of Cubic Foot | | | | +| | | | | | of the Mixture of | | | | +| | | | | | Air and Vapor | | | | +| | | | | |_____________________| | | | +| | | | | | | | | | | | +| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | +|___|_____|_____|______|______|_____|_______|_______|________|________|______| +| | | | | | | | | | | | +| 0| .935|.0864| .044|29.877|.0863|.000079|.086379| .00092|1092.4 | | +| 12| .960|.0842| .074|29.849|.0840|.000130|.084130| .00155| 646.1 | | +| 22| .980|.0824| .118|29.803|.0821|.000202|.082302| .00245| 406.4 | | +| 32|1.000|.0807| .181|29.740|.0802|.000304|.080504| .00379| 263.81 |3289 | +| 42|1.020|.0791| .267|29.654|.0784|.000440|.078840| .00561| 178.18 |2252 | +| | | | | | | | | | | | +| 52|1.041|.0776| .388|29.533|.0766|.000627|.077227| .00810| 122.17 |1595 | +| 62|1.061|.0761| .556|29.365|.0747|.000881|.075581| .01179| 84.79 |1135 | +| 72|1.082|.0747| .785|29.136|.0727|.001221|.073921| .01680| 59.54 | 819 | +| 82|1.102|.0733| 1.092|28.829|.0706|.001667|.072267| .02361| 42.35 | 600 | +| 92|1.122|.0720| 1.501|28.420|.0684|.002250|.070717| .03289| 30.40 | 444 | +| | | | | | | | | | | | +|102|1.143|.0707| 2.036|27.885|.0659|.002997|.068897| .04547| 21.98 | 334 | +|112|1.163|.0694| 2.731|27.190|.0631|.003946|.067046| .06253| 15.99 | 253 | +|122|1.184|.0682| 3.621|26.300|.0599|.005142|.065042| .08584| 11.65 | 194 | +|132|1.204|.0671| 4.752|25.169|.0564|.006639|.063039| .11771| 8.49 | 151 | +|142|1.224|.0660| 6.165|23.756|.0524|.008473|.060873| .16170| 6.18 | 118 | +| | | | | | | | | | | | +|152|1.245|.0649| 7.930|21.991|.0477|.010716|.058416| .22465| 4.45 | 93.3| +|162|1.265|.0638|10.099|19.822|.0423|.013415|.055715| .31713| 3.15 | 74.5| +|172|1.285|.0628|12.758|17.163|.0360|.016682|.052682| .46338| 2.16 | 59.2| +|182|1.306|.0618|15.960|13.961|.0288|.020536|.049336| .71300| 1.402| 48.6| +|192|1.326|.0609|19.828|10.093|.0205|.025142|.045642| 1.22643| .815| 39.8| +| | | | | | | | | | | | +|202|1.347|.0600|24.450| 5.471|.0109|.030545|.041445| 2.80230| .357| 32.7| +|212|1.367|.0591|29.921| 0.000|.0000|.036820|.036820|Infinite| .000| 27.1| +|___|_____|_____|______|______|_____|_______|_______|________|________|______| + +Column 5 = barometer pressure of 29.921, minus the proportion of this +due to vapor pressure from column 4. + + + + +COMBUSTION + + +Combustion may be defined as the rapid chemical combination of oxygen +with carbon, hydrogen and sulphur, accompanied by the diffusion of heat +and light. That portion of the substance thus combined with the oxygen +is called combustible. As used in steam engineering practice, however, +the term combustible is applied to that portion of the fuel which is dry +and free from ash, thus including both oxygen and nitrogen which may be +constituents of the fuel, though not in the true sense of the term +combustible. + +Combustion is perfect when the combustible unites with the greatest +possible amount of oxygen, as when one atom of carbon unites with two +atoms of oxygen to form carbon dioxide, CO_{2}. The combustion is +imperfect when complete oxidation of the combustible does not occur, or +where the combustible does not unite with the maximum amount of oxygen, +as when one atom of carbon unites with one atom of oxygen to form carbon +monoxide, CO, which may be further burned to carbon dioxide. + +Kindling Point--Before a combustible can unite with oxygen and +combustion takes place, its temperature must first be raised to the +ignition or kindling point, and a sufficient time must be allowed for +the completion of the combustion before the temperature of the gases is +lowered below that point. Table 30, by Stromeyer, gives the approximate +kindling temperatures of different fuels. + + TABLE 30 + +KINDLING TEMPERATURE OF VARIOUS FUELS + + ____________________________________ +| | | +| | Degrees | +| | Fahrenheit | +|_________________|__________________| +| | | +| Lignite Dust | 300 | +| Dried Peat | 435 | +| Sulphur | 470 | +| Anthracite Dust | 570 | +| Coal | 600 | +| Coke | Red Heat | +| Anthracite | Red Heat, 750 | +| Carbon Monoxide | Red Heat, 1211 | +| Hydrogen | 1030 or 1290 | +|_________________|__________________| + + +Combustibles--The principal combustibles in coal and other fuels are +carbon, hydrogen and sulphur, occurring in varying proportions and +combinations. + +Carbon is by far the most abundant as is indicated in the chapters on +fuels. + +Hydrogen in a free state occurs in small quantities in some fuels, but +is usually found in combination with carbon, in the form of +hydrocarbons. The density of hydrogen is 0.0696 (Air = 1) and its weight +per cubic foot, at 32 degrees Fahrenheit and under atmospheric pressure, +is 0.005621 pounds. + +Sulphur is found in most coals and some oils. It is usually present in +combined form, either as sulphide of iron or sulphate of lime; in the +latter form it has no heat value. Its presence in fuel is objectionable +because of its tendency to aid in the formation of clinkers, and the +gases from its combustion, when in the presence of moisture, may cause +corrosion. + +Nitrogen is drawn into the furnace with the air. Its density is 0.9673 +(Air = 1); its weight, at 32 degrees Fahrenheit and under atmospheric +pressure, is 0.07829 pounds per cubic foot; each pound of air at +atmospheric pressure contains 0.7685 pounds of nitrogen, and one pound +of nitrogen is contained in 1.301 pounds of air. + +Nitrogen performs no useful office in combustion and passes through the +furnace without change. It dilutes the air, absorbs heat, reduces the +temperature of the products of combustion, and is the chief source of +heat losses in furnaces. + +Calorific Value--Each combustible element of gas will combine with +oxygen in certain definite proportions and will generate a definite +amount of heat, measured in B. t. u. This definite amount of heat per +pound liberated by perfect combustion is termed the calorific value of +that substance. Table 31, gives certain data on the reactions and +results of combustion for elementary combustibles and several compounds. + + TABLE 31 + + OXYGEN AND AIR REQUIRED FOR COMBUSTION + + AT 32 DEGREES AND 29.92 INCHES + +Column headings: + + 1: Oxidizable Substance or Combustible + 2: Chemical Symbol + 3: Atomic or Combining Weight + 4: Chemical Reaction + 5: Product of Combustion + 6: Oxygen per Pound of Column 1 Pounds + 7: Nitrogen per Pound of Column 1. 3.32[23] x O Pounds + 8: Air per Pound of Column 1. 4.32[24] x O Pounds + 9: Gaseous Product per Pound of Column 1[25] + Column 8 Pounds +10: Heat Value per Pound of Column 1 B. t. u. +11: Volumes of Column 1 Entering Combination Volume +12: Volumes of Oxygen Combining with Column 11 Volume +13: Volumes of Product Formed Volume +14: Volume per Pound of Column 1 in Gaseous Form Cubic Feet +15: Volume of Oxygen per Pound of Column 1 Cubic Feet +16: Volume of Products of Combustion per Pound of Column 1 Cubic Feet +17: Volume of Nitrogen per Pound of Column 1 3.782[26] x Column 15 Cubic + Feet +18: Volume of Gas per pound of Column 1 = Column 10 / Column 17 Cubic + Feet + + BY WEIGHT + ________________________________________________________________________ +| | | | | | | +| 1 | 2 | 3 | 4 | 5 | 6 | +|________________|_______|____|________________|_________________|_______| +| | | | | | | +| Carbon | C | 12 | C+2O = CO_{2} | Carbon Dioxide | 2.667 | +| Carbon | C | 12 | C+O = CO | Carbon Monoxide | 1.333 | +| Carbon Monoxide| CO | 28 | CO+O = CO_{2} | Carbon Dioxide | .571 | +| Hydrogen | H | 1 | 2H+O = H_{2}O | Water | 8 | +| | | / CH_{4}+4O = | Carbon Dioxide \ | +| Methane | CH_{4}| 16 | | | 4 | +| | | \ CO_{2}+2H_{2}O | and Water / | +| Sulphur | S | 32 | S+2O = SO_{2} | Sulphur Dioxide | 1 | +|________________|_______|____|________________|_________________|_______| + + ________________________________________________________ +| | | | | | | +| 1 | 2 | 7 | 8 | 9 | 10 | +|________________|_______|_______|_______|_______|_______| +| | | | | | | +| Carbon | C | 8.85 | 11.52 | 12.52 | 14600 | +| Carbon | C | 4.43 | 5.76 | 6.76 | 4450 | +| Carbon Monoxide| CO | 1.90 | 2.47 | 3.47 | 10150 | +| Hydrogen | H | 26.56 | 34.56 | 35.56 | 62000 | +| | | | | | | +| Methane | CH_{4}| 13.28 | 17.28 | 18.28 | 23550 | +| | | | | | | +| Sulphur | S | 3.32 | 4.32 | 5.32 | 4050 | +|________________|_______|_______|_______|_______|_______| + + + BY VOLUME + + ________________________________________________________________ +| | | | | | | +| 1 | 2 | 11 | 12 | 13 | 14 | +|_________________|________|______|____|________________|________| +| | | | | | | +| Carbon | C | 1C | 2 | 2CO_{2} | 14.95 | +| Carbon | C | 1C | 1 | 2CO | 14.95 | +| Carbon Monoxide | CO | 2CO | 1 | 2CO_{2} | 12.80 | +| Hydrogen | H | 2H | 1 | 2H_{2}O | 179.32 | +| Methane | CH_{4} | 1C4H | 4 | 1CO_{2} 2H_{2}O| 22.41 | +| Sulphur | S | 1S | 2 | 1SO_{2} | 5.60 | +|_________________|________|______|____|________________|________| + + _____________________________________________________________ +| | | | | | | +| 1 | 2 | 15 | 16 | 17 | 18 | +|_________________|________|_______|________|________|________| +| | | | | | | +| Carbon | C | 29.89 | 29.89 | 112.98 | 142.87 | +| Carbon | C | 14.95 | 29.89 | 56.49 | 86.38 | +| Carbon Monoxide | CO | 6.40 | 12.80 | 24.20 | 37.00 | +| Hydrogen | H | 89.66 | 179.32 | 339.09 | 518.41 | +| Methane | CH_{4} | 44.83 | 67.34 | 169.55 | 236.89 | +| Sulphur | S | 11.21 | 11.21 | 42.39 | 53.60 | +|_________________|________|_______|________|________|________| + +It will be seen from this table that a pound of carbon will unite with +2-2/3 pounds of oxygen to form carbon dioxide, and will evolve 14,600 +B. t. u. As an intermediate step, a pound of carbon may unite with 1-1/3 +pounds of oxygen to form carbon monoxide and evolve 4450 B. t. u., but +in its further conversion to CO_{2} it would unite with an additional +1-1/3 times its weight of oxygen and evolve the remaining 10,150 +B. t. u. When a pound of CO burns to CO_{2}, however, only 4350 B. t. u. +are evolved since the pound of CO contains but 3/7 pound carbon. + +Air Required for Combustion--It has already been shown that each +combustible element in fuel will unite with a definite amount of oxygen. +With the ultimate analysis of the fuel known, in connection with Table +31, the theoretical amount of air required for combustion may be readily +calculated. + +Let the ultimate analysis be as follows: + + _Per Cent_ +Carbon 74.79 +Hydrogen 4.98 +Oxygen 6.42 +Nitrogen 1.20 +Sulphur 3.24 +Water 1.55 +Ash 7.82 + ------ + 100.00 + +When complete combustion takes place, as already pointed out, the carbon +in the fuel unites with a definite amount of oxygen to form CO_{2}. The +hydrogen, either in a free or combined state, will unite with oxygen to +form water vapor, H_{2}O. Not all of the hydrogen shown in a fuel +analysis, however, is available for the production of heat, as a portion +of it is already united with the oxygen shown by the analysis in the +form of water, H_{2}O. Since the atomic weights of H and O are +respectively 1 and 16, the weight of the combined hydrogen will be 1/8 +of the weight of the oxygen, and the hydrogen available for combustion +will be H - 1/8 O. In complete combustion of the sulphur, sulphur +dioxide SO_{2} is formed, which in solution in water forms sulphuric +acid. + +Expressed numerically, the theoretical amount of air for the above +analysis is as follows: + + 0.7479 C x 2-2/3 = 1.9944 O needed +( 0.0642 ) +( 0.0498 - -------) H x 8 = 0.3262 O needed +( 8 ) + 0.0324 S x 1 = 0.0324 O needed + ------ + Total 2.3530 O needed + +One pound of oxygen is contained in 4.32 pounds of air. + +The total air needed per pound of coal, therefore, will be 2.353 x 4.32 += 10.165. + +The weight of combustible per pound of fuel is .7479 + .0418[27] + .0324 ++ .012 = .83 pounds, and the air theoretically required per pound of +combustible is 10.165 / .83 = 12.2 pounds. + +The above is equivalent to computing the theoretical amount of air +required per pound of fuel by the formula: + + ( O) +Weight per pound = 11.52 C + 34.56 (H - -) + 4.32 S (10) + ( 8) + +where C, H, O and S are proportional parts by weight of carbon, +hydrogen, oxygen and sulphur by ultimate analysis. + +In practice it is impossible to obtain perfect combustion with the +theoretical amount of air, and an excess may be required, amounting to +sometimes double the theoretical supply, depending upon the nature of +the fuel to be burned and the method of burning it. The reason for this +is that it is impossible to bring each particle of oxygen in the air +into intimate contact with the particles in the fuel that are to be +oxidized, due not only to the dilution of the oxygen in the air by +nitrogen, but because of such factors as the irregular thickness of the +fire, the varying resistance to the passage of the air through the fire +in separate parts on account of ash, clinker, etc. Where the +difficulties of drawing air uniformly through a fuel bed are eliminated, +as in the case of burning oil fuel or gas, the air supply may be +materially less than would be required for coal. Experiment has shown +that coal will usually require 50 per cent more than the theoretical net +calculated amount of air, or about 18 pounds per pound of fuel either +under natural or forced draft, though this amount may vary widely with +the type of furnace, the nature of the coal, and the method of firing. +If less than this amount of air is supplied, the carbon burns to +monoxide instead of dioxide and its full heat value is not developed. + +An excess of air is also a source of waste, as the products of +combustion will be diluted and carry off an excessive amount of heat in +the chimney gases, or the air will so lower the temperature of the +furnace gases as to delay the combustion to an extent that will cause +carbon monoxide to pass off unburned from the furnace. A sufficient +amount of carbon monoxide in the gases may cause the action known as +secondary combustion, by igniting or mingling with air after leaving the +furnace or in the flues or stack. Such secondary combustion which takes +place either within the setting after leaving the furnace or in the +flues or stack always leads to a loss of efficiency and, in some +instances, leads to overheating of the flues and stack. + +Table 32 gives the theoretical amount of air required for various fuels +calculated from formula (10) assuming the analyses of the fuels given in +the table. + +The process of combustion of different fuels and the effect of variation +in the air supply for their combustion is treated in detail in the +chapters dealing with the various fuels. + + TABLE 32 + + CALCULATED THEORETICAL AMOUNT OF AIR + REQUIRED PER POUND OF VARIOUS FUELS + + ____________________________________________________________ +| |Weight of Constituents in One |Air Required| +| Fuel |Pound Dry Fuel |per Pound | +| |______________________________|of Fuel | +| | Carbon | Hydrogen| Oxygen |Pounds | +| | Per Cent| Per Cent| Per Cent | | +|________________|_________|_________|__________|____________| +|Coke | 94.0 | . | . | 10.8 | +|Anthracite Coal | 91.5 | 3.5 | 2.6 | 11.7 | +|Bituminous Coal | 87.0 | 5.0 | 4.0 | 11.6 | +|Lignite | 70.0 | 5.0 | 20.0 | 8.9 | +|Wood | 50.0 | 6.0 | 43.5 | 6.0 | +|Oil | 85.0 | 13.0 | 1.0 | 14.3 | +|________________|_________|_________|__________|____________| + + + +[Illustration: 4064 HORSE-POWER Installation of Babcock & Wilcox Boilers +and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers, at +the Cosmopolitan Electric Co., Chicago, Ill.] + + + + +ANALYSIS OF FLUE GASES + + +The object of a flue gas analysis is the determination of the +completeness of the combustion of the carbon in the fuel, and the amount +and distribution of the heat losses due to incomplete combustion. The +quantities actually determined by an analysis are the relative +proportions by volume, of carbon dioxide (CO_{2}), oxygen (O), and +carbon monoxide (CO), the determinations being made in this order. + +The variations of the percentages of these gases in an analysis is best +illustrated in the consideration of the complete combustion of pure +carbon, a pound of which requires 2.67 pounds of oxygen,[28] or 32 cubic +feet at 60 degrees Fahrenheit. The gaseous product of such combustion +will occupy, when cooled, the same volume as the oxygen, namely, 32 +cubic feet. The air supplied for the combustion is made up of 20.91 per +cent oxygen and 79.09 per cent nitrogen by volume. The carbon united +with the oxygen in the form of carbon dioxide will have the same volume +as the oxygen in the air originally supplied. The volume of the nitrogen +when cooled will be the same as in the air supplied, as it undergoes no +change. Hence for complete combustion of one pound of carbon, where no +excess of air is supplied, an analysis of the products of combustion +will show the following percentages by volume: + + _Actual Volume_ + _for One Pound Carbon_ _Per Cent_ + _Cubic Feet_ _by Volume_ +Carbon Dioxide 32 = 20.91 +Oxygen 0 = 0.00 +Nitrogen 121 = 79.09 + --- ------ +Air required for one pound Carbon 153 = 100.00 + +For 50 per cent excess air the volume will be as follows: + + 153 x 1-1/2 = 229.5 cubic feet of air per pound of carbon. + + _Actual Volume_ + _for One Pound Carbon_ _Per Cent_ + _Cubic Feet_ _by Volume_ +Carbon Dioxide 32 = 13.91 } +Oxygen 16 = 7.00 } = 20.91 per cent +Nitrogen 181.5 = 79.09 + ----- ------ + 229.5 = 100.00 + +For 100 per cent excess air the volume will be as follows: + + 153 x 2 = 306 cubic feet of air per pound of carbon. + + _Actual Volume_ + _for One Pound Carbon_ _Per Cent_ + _Cubic Feet_ _by Volume_ +Carbon Dioxide 32 = 10.45 } +Oxygen 32 = 10.45 } = 20.91 per cent +Nitrogen 242 = 79.09 + --- ------ + 306 = 100.00 + +In each case the volume of oxygen which combines with the carbon is +equal to (cubic feet of air x 20.91 per cent)--32 cubic feet. + +It will be seen that no matter what the excess of air supplied, the +actual amount of carbon dioxide per pound of carbon remains the same, +while the percentage by volume decreases as the excess of air increases. +The actual volume of oxygen and the percentage by volume increases with +the excess of air, and the percentage of oxygen is, therefore, an +indication of the amount of excess air. In each case the sum of the +percentages of CO_{2} and O is the same, 20.9. Although the volume of +nitrogen increases with the excess of air, its percentage by volume +remains the same as it undergoes no change while combustion takes place; +its percentage for any amount of air excess, therefore, will be the same +after combustion as before, if cooled to the same temperature. It must +be borne in mind that the above conditions hold only for the perfect +combustion of a pound of pure carbon. + +Carbon monoxide (CO) produced by the imperfect combustion of carbon, +will occupy twice the volume of the oxygen entering into its composition +and will increase the volume of the flue gases over that of the air +supplied for combustion in the proportion of + + 100 + the per cent CO / 2 +1 to ------------------------- + 100 + +When pure carbon is the fuel, the sum of the percentages by volume of +carbon dioxide, oxygen and one-half of the carbon monoxide, must be in +the same ratio to the nitrogen in the flue gases as is the oxygen to the +nitrogen in the air supplied, that is, 20.91 to 79.09. When burning +coal, however, the percentage of nitrogen is obtained by subtracting the +sum of the percentages by volume of the other gases from 100. Thus if an +analysis shows 12.5 per cent CO_{2}, 6.5 per cent O, and 0.6 per cent +CO, the percentage of nitrogen which ordinarily is the only other +constituent of the gas which need be considered, is found as follows: + +100 - (12.5 + 6.5 + 0.6) = 80.4 per cent. + +The action of the hydrogen in the volatile constituents of the fuel is +to increase the apparent percentage of the nitrogen in the flue gases. +This is due to the fact that the water vapor formed by the combustion of +the hydrogen will condense at a temperature at which the analysis is +made, while the nitrogen which accompanied the oxygen with which the +hydrogen originally combined maintains its gaseous form and passes into +the sampling apparatus with the other gases. For this reason coals +containing high percentages of volatile matter will produce a larger +quantity of water vapor, and thus increase the apparent percentage of +nitrogen. + + +Air Required and Supplied--When the ultimate analysis of a fuel is +known, the air required for complete combustion with no excess can be +found as shown in the chapter on combustion, or from the following +approximate formula: + + Pounds of air required per pound of fuel = + + (C O S) + 34.56 (- + (H - -) + -)[29] (11) + (3 8 8) + +where C, H and O equal the percentage by weight of carbon, hydrogen and +oxygen in the fuel divided by 100. + +When the flue gas analysis is known, the total, amount of air supplied +is: + + Pounds of air supplied per pound of fuel = + + N + 3.036 (-----------) x C[30] (12) + CO_{2} + CO + +where N, CO_{2} and CO are the percentages by volume of nitrogen, carbon +dioxide and carbon monoxide in the flue gases, and C the percentage by +weight of carbon which is burned from the fuel and passes up the stack +as flue gas. This percentage of C which is burned must be distinguished +from the percentage of C as found by an ultimate analysis of the fuel. +To find the percentage of C which is burned, deduct from the total +percentage of carbon as found in the ultimate analysis, the percentage +of unconsumed carbon found in the ash. This latter quantity is the +difference between the percentage of ash found by an analysis and that +as determined by a boiler test. It is usually assumed that the entire +combustible element in the ash is carbon, which assumption is +practically correct. Thus if the ash in a boiler test were 16 per cent +and by an analysis contained 25 per cent of carbon, the percentage of +unconsumed carbon would be 16 x .25 = 4 per cent of the total coal +burned. If the coal contained by ultimate analysis 80 per cent of carbon +the percentage burned, and of which the products of combustion pass up +the chimney would be 80 - 4 = 76 per cent, which is the correct figure +to use in calculating the total amount of air supplied by formula (12). + +The weight of flue gases resulting from the combustion of a pound of dry +coal will be the sum of the weights of the air per pound of coal and the +combustible per pound of coal, the latter being equal to one minus the +percentage of ash as found in the boiler test. The weight of flue gases +per pound of dry fuel may, however, be computed directly from the +analyses, as shown later, and the direct computation is that ordinarily +used. + +The ratio of the air actually supplied per pound of fuel to that +theoretically required to burn it is: + + N +3.036(---------)xC + CO_{2}+CO +------------------ (13) + C O +34.56(- + H - -) + 3 8 + +in which the letters have the same significance as in formulae (11) and +(12). + +The ratio of the air supplied per pound of combustible to the amount +theoretically required is: + + N +------------------- (14) +N - 3.782(O - CO/2) + +which is derived as follows: + +The N in the flue gas is the content of nitrogen in the whole amount of +air supplied. The oxygen in the flue gas is that contained in the air +supplied and which was not utilized in combustion. This oxygen was +accompanied by 3.782 times its volume of nitrogen. The total amount of +excess oxygen in the flue gases is (O - CO/2); hence N - 3.782(O - CO/2) +represents the nitrogen content in the air actually required for +combustion and N / (N - 3.782[O - CO/2]) is the ratio of the air supplied +to that required. This ratio minus one will be the proportion of excess +air. + +The heat lost in the flue gases is L = 0.24 W (T - t) (15) + +Where L = B. t. u. lost per pound of fuel, + W = weight of flue gases in pounds per pound of dry coal, + T = temperature of flue gases, + t = temperature of atmosphere, + 0.24 = specific heat of the flue gases. + +The weight of flue gases, W, per pound of carbon can be computed +directly from the flue gas analysis from the formula: + +11 CO_{2} + 8 O + 7 (CO + N) +---------------------------- (16) + 3 (CO_{2} + CO) + +where CO_{2}, O, CO, and N are the percentages by volume as determined +by the flue gas analysis of carbon dioxide, oxygen, carbon monoxide and +nitrogen. + +The weight of flue gas per pound of dry coal will be the weight +determined by this formula multiplied by the percentage of carbon in the +coal from an ultimate analysis. + +[Graph: Temperature of Escaping Gases--Deg. Fahr. +against Heat carried away by Chimney Gases--In B.t.u. +per pound of Carbon burned.[31] + +Fig. 20. Loss Due to Heat Carried Away by Chimney Gases for Varying +Percentages of Carbon Dioxide. Based on Boiler Room Temperature = 80 +Degrees Fahrenheit. Nitrogen in Flue Gas = 80.5 Per Cent. Carbon +Monoxide in Flue Gas = 0. Per Cent] + +Fig. 20 represents graphically the loss due to heat carried away by dry +chimney gases for varying percentages of CO_{2}, and different +temperatures of exit gases. + +The heat lost, due to the fact that the carbon in the fuel is not +completely burned and carbon monoxide is present in the flue gases, in +B. t. u. per pound of fuel burned is: + + ( CO ) +L' = 10,150 x (-----------) (17) + (CO + CO_{2}) + +where, as before, CO and CO_{2} are the percentages by volume in the +flue gases and C is the proportion by weight of carbon which is burned +and passes up the stack. + +Fig. 21 represents graphically the loss due to such carbon in the fuel +as is not completely burned but escapes up the stack in the form of +carbon monoxide. + +[Graph: Loss in B.T.U. per Pound of Carbon Burned[32] +against Per Cent CO_{2} in Flue Gas + +Fig. 21. Loss Due to Unconsumed Carbon Contained in the +CO in the Flue Gases] + +Apparatus for Flue Gas Analysis--The Orsat apparatus, illustrated in +Fig. 22, is generally used for analyzing flue gases. The burette A is +graduated in cubic centimeters up to 100, and is surrounded by a water +jacket to prevent any change in temperature from affecting the density +of the gas being analyzed. + +For accurate work it is advisable to use four pipettes, B, C, D, E, the +first containing a solution of caustic potash for the absorption of +carbon dioxide, the second an alkaline solution of pyrogallol for the +absorption of oxygen, and the remaining two an acid solution of cuprous +chloride for absorbing the carbon monoxide. Each pipette contains a +number of glass tubes, to which some of the solution clings, thus +facilitating the absorption of the gas. In the pipettes D and E, copper +wire is placed in these tubes to re-energize the solution as it becomes +weakened. The rear half of each pipette is fitted with a rubber bag, one +of which is shown at K, to protect the solution from the action of the +air. The solution in each pipette should be drawn up to the mark on the +capillary tube. + +The gas is drawn into the burette through the U-tube H, which is filled +with spun glass, or similar material, to clean the gas. To discharge any +air or gas in the apparatus, the cock G is opened to the air and the +bottle F is raised until the water in the burette reaches the 100 cubic +centimeters mark. The cock G is then turned so as to close the air +opening and allow gas to be drawn through H, the bottle F being lowered +for this purpose. The gas is drawn into the burette to a point below the +zero mark, the cock G then being opened to the air and the excess gas +expelled until the level of the water in F and in A are at the zero +mark. This operation is necessary in order to obtain the zero reading at +atmospheric pressure. + +The apparatus should be carefully tested for leakage as well as all +connections leading thereto. Simple tests can be made; for example: If +after the cock G is closed, the bottle F is placed on top of the frame +for a short time and again brought to the zero mark, the level of the +water in A is above the zero mark, a leak is indicated. + +[Illustration: Fig. 22. Orsat Apparatus] + +Before taking a final sample for analysis, the burette A should be +filled with gas and emptied once or twice, to make sure that all the +apparatus is filled with the new gas. The cock G is then closed and the +cock I in the pipette B is opened and the gas driven over into B by +raising the bottle F. The gas is drawn back into A by lowering F and +when the solution in B has reached the mark in the capillary tube, the +cock I is closed and a reading is taken on the burette, the level of the +water in the bottle F being brought to the same level as the water in A. +The operation is repeated until a constant reading is obtained, the +number of cubic centimeters being the percentage of CO_{2} in the flue +gases. + +The gas is then driven over into the pipette C and a similar operation +is carried out. The difference between the resulting reading and the +first reading gives the percentage of oxygen in the flue gases. + +The next operation is to drive the gas into the pipette D, the gas being +given a final wash in E, and then passed into the pipette C to +neutralize any hydrochloric acid fumes which may have been given off by +the cuprous chloride solution, which, especially if it be old, may give +off such fumes, thus increasing the volume of the gases and making the +reading on the burette less than the true amount. + +The process must be carried out in the order named, as the pyrogallol +solution will also absorb carbon dioxide, while the cuprous chloride +solution will also absorb oxygen. + +As the pressure of the gases in the flue is less than the atmospheric +pressure, they will not of themselves flow through the pipe connecting +the flue to the apparatus. The gas may be drawn into the pipe in the way +already described for filling the apparatus, but this is a tedious +method. For rapid work a rubber bulb aspirator connected to the air +outlet of the cock G will enable a new supply of gas to be drawn into +the pipe, the apparatus then being filled as already described. Another +form of aspirator draws the gas from the flue in a constant stream, thus +insuring a fresh supply for each sample. + +The analysis made by the Orsat apparatus is volumetric; if the analysis +by weight is required, it can be found from the volumetric analysis as +follows: + +Multiply the percentages by volume by either the densities or the +molecular weight of each gas, and divide the products by the sum of all +the products; the quotients will be the percentages by weight. For most +work sufficient accuracy is secured by using the even values of the +molecular weights. + +The even values of the molecular weights of the gases appearing in an +analysis by an Orsat are: + +Carbon Dioxide 44 +Carbon Monoxide 28 +Oxygen 32 +Nitrogen 28 + +Table 33 indicates the method of converting a volumetric flue gas +analysis into an analysis by weight. + + TABLE 33 + + CONVERSION OF A FLUE GAS ANALYSIS BY VOLUME TO ONE BY WEIGHT + +Column Headings: + +A: Analysis by Volume Per Cent +B: Molecular Weight +C: Volume times Molecular Weight +D: Analysis by Weight Per Cent + _____________________________________________________________________ +| | | | | | +| Gas | A | B | C | D | +|________________________|_______|___________|________|_______________| +| | | | | | +| | | | | | +| | | | | 536.8 | +| Carbon Dioxide CO_{2} | 12.2 | 12+(2x16) | 536.8 | ------ = 17.7 | +| | | | | 3022.8 | +| | | | | | +| | | | | 11.2 | +| Carbon Monoxide CO | .4 | 12+16 | 11.2 | ------ = .4 | +| | | | | 3022.8 | +| | | | | | +| | | | | 220.8 | +| Oxygen O | 6.9 | 2x16 | 220.8 | ------ = 7.3 | +| | | | | 3022.8 | +| | | | | | +| | | | | 2254.0 | +| Nitrogen N | 80.5 | 2x14 | 2254.0 | ------ = 74.6 | +| | | | | 3022.8 | +|________________________|_______|___________|________|_______________| +| | | | | | +| Total | 100.0 | | 3022.8 | 100.0 | +|________________________|_______|___________|________|_______________| + +Application of Formulae and Rules--Pocahontas coal is burned in the +furnace, a partial ultimate analysis being: + + _Per Cent_ +Carbon 82.1 +Hydrogen 4.25 +Oxygen 2.6 +Sulphur 1.6 +Ash 6.0 +B. t. u., per pound dry 14500 + +The flue gas analysis shows: + + _Per Cent_ + +CO_{2} 10.7 +O 9.0 +CO 0.0 +N (by difference) 80.3 + +Determine: The flue gas analysis by weight (see Table 33), the amount of +air required for perfect combustion, the actual weight of air per pound +of fuel, the weight of flue gas per pound of coal, the heat lost in the +chimney gases if the temperature of these is 500 degrees Fahrenheit, and +the ratio of the air supplied to that theoretically required. + +Solution: The theoretical weight of air required for perfect combustion, +per pound of fuel, from formula (11) will be, + + (.821 .026 .016) +W = 34.56 (---- + (.0425 - ----) + ----) = 10.88 pounds. + ( 3 8 8 ) + +If the amount of carbon which is burned and passes away as flue gas is +80 per cent, which would allow for 2.1 per cent of unburned carbon in +terms of the total weight of dry fuel burned, the weight of dry gas per +pound of carbon burned will be from formula (16): + + 11 x 10.7 + 8 x 9.0 + 7(0 + 80.3) +W = --------------------------------- = 23.42 pounds + 3(10.7 + 0) + +and the weight of flue gas per pound of coal burned will be .80 x 23.42 += 18.74 pounds. + +The heat lost in the flue gases per pound of coal burned will be from +formula (15) and the value 18.74 just determined. + +Loss = .24 x 18.74 x (500 - 60) = 1979 B. t. u. + +The percentage of heat lost in the flue gases will be 1979 / 14500 = +13.6 per cent. + +The ratio of air supplied per pound of coal to that theoretically +required will be 18.74 / 10.88 = 1.72 per cent. + +The ratio of air supplied per pound of combustible to that required will +be from formula (14): + + .803 +------------------------- = 1.73 +.803 - 3.782(.09 - 0 / 2) + +The ratio based on combustible will be greater than the ratio based on +fuel if there is unconsumed carbon in the ash. + + +Unreliability of CO_{2} Readings Taken Alone--It is generally assumed +that high CO_{2} readings are indicative of good combustion and hence of +high efficiency. This is true only in the sense that such high readings +do indicate the small amount of excess air that usually accompanies good +combustion, and for this reason high CO_{2} readings alone are not +considered entirely reliable. Wherever an automatic CO_{2} recorder is +used, it should be checked from time to time and the analysis carried +further with a view to ascertaining whether there is CO present. As the +percentage of CO_{2} in these gases increases, there is a tendency +toward the presence of CO, which, of course, cannot be shown by a CO_{2} +recorder, and which is often difficult to detect with an Orsat +apparatus. The greatest care should be taken in preparing the cuprous +chloride solution in making analyses and it must be known to be fresh +and capable of absorbing CO. In one instance that came to our attention, +in using an Orsat apparatus where the cuprous chloride solution was +believed to be fresh, no CO was indicated in the flue gases but on +passing the same sample into a Hempel apparatus, a considerable +percentage was found. It is not safe, therefore, to assume without +question from a high CO_{2} reading that the combustion is +correspondingly good, and the question of excess air alone should be +distinguished from that of good combustion. The effect of a small +quantity of CO, say one per cent, present in the flue gases will have a +negligible influence on the quantity of excess air, but the presence of +such an amount would mean a loss due to the incomplete combustion of the +carbon in the fuel of possibly 4.5 per cent of the total heat in the +fuel burned. When this is considered, the importance of a complete flue +gas analysis is apparent. + +Table 34 gives the densities of various gases together with other data +that will be of service in gas analysis work. + + TABLE 34 + + DENSITY OF GASES AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE + ADAPTED FROM SMITHSONIAN TABLES + ++----------+----------+--------+---------+----------+---------------+ +| | | | | | Relative | +| | | | Weight | | Density, | +| | | | of | Volume | Hydrogen = 1 | +| | |Specific|One Cubic| of +-------+-------+ +| Gas | Chemical |Gravity | Foot |One Pound | |Approx-| +| | Symbol | Air=1 | Pounds |Cubic Feet| Exact | imate | ++----------+----------+--------+---------+----------+-------+-------+ +|Oxygen | O | 1.053 | .08922 | 11.208 | 15.87 | 16 | +|Nitrogen | N | 0.9673 | .07829 | 12.773 | 13.92 | 14 | +|Hydrogen | H | 0.0696 | .005621 | 177.90 | 1.00 | 1 | +|Carbon | | | | | | | +| Dioxide | CO_{2} | 1.5291 | .12269 | 8.151 | 21.83 | 22 | +|Carbon | | | | | | | +| Monoxide | CO | 0.9672 | .07807 | 12.809 | 13.89 | 14 | +|Methane | CH_{4} | 0.5576 | .04470 | 22.371 | 7.95 | 8 | +|Ethane |C_{2}H_{6}| 1.075 | .08379 | 11.935 | 14.91 | 15 | +|Acetylene |C_{2}H_{2}| 0.920 | .07254 | 13.785 | 12.91 | 13 | +|Sulphur | | | | | | | +| Dioxide | SO_{2} | 2.2639 | .17862 | 5.598 | 31.96 | 32 | +|Air | ... | 1.0000 | .08071 | 12.390 | ... | ... | ++----------+----------+--------+---------+----------+-------+-------+ + +[Illustration: 1942 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters in the Singer Building, New York City] + + + + +CLASSIFICATION OF FUELS + +(WITH PARTICULAR REFERENCE TO COAL) + + +Fuels for steam boilers may be classified as solid, liquid or gaseous. +Of the solid fuels, anthracite and bituminous coals are the most common, +but in this class must also be included lignite, peat, wood, bagasse and +the refuse from certain industrial processes such as sawdust, shavings, +tan bark and the like. Straw, corn and coffee husks are utilized in +isolated cases. + +The class of liquid fuels is represented chiefly by petroleum, though +coal tar and water-gas tar are used to a limited extent. + +Gaseous fuels are limited to natural gas, blast furnace gas and coke +oven gas, the first being a natural product and the two latter +by-products from industrial processes. Though waste gases from certain +processes may be considered as gaseous fuels, inasmuch as the question +of combustion does not enter, the methods of utilizing them differ from +that for combustible gaseous fuel, and the question will be dealt with +separately. + +Since coal is by far the most generally used of all fuels, this chapter +will be devoted entirely to the formation, composition and distribution +of the various grades, from anthracite to peat. The other fuels will be +discussed in succeeding chapters and their combustion dealt with in +connection with their composition. + +Formation of Coal--All coals are of vegetable origin and are the remains +of prehistoric forests. Destructive distillation due to great pressures +and temperatures, has resolved the organic matter into its invariable +ultimate constituents, carbon, hydrogen, oxygen and other substances, in +varying proportions. The factors of time, depth of beds, disturbance of +beds and the intrusion of mineral matter resulting from such +disturbances have produced the variation in the degree of evolution from +vegetable fiber to hard coal. This variation is shown chiefly in the +content of carbon, and Table 35 shows the steps of such variation. + + TABLE 35 + + APPROXIMATE CHEMICAL CHANGES FROM WOOD + FIBER TO ANTHRACITE COAL + ++----------------------+-------+--------+-------+ +|Substance |Carbon |Hydrogen|Oxygen | ++----------------------+-------+--------+-------+ +|Wood Fiber | 52.65 | 5.25 | 42.10 | +|Peat | 59.57 | 5.96 | 34.47 | +|Lignite | 66.04 | 5.27 | 28.69 | +|Earthy Brown Coal | 73.18 | 5.68 | 21.14 | +|Bituminous Coal | 75.06 | 5.84 | 19.10 | +|Semi-bituminous Coal | 89.29 | 5.05 | 5.66 | +|Anthracite Coal | 91.58 | 3.96 | 4.46 | ++----------------------+-------+--------+-------+ + +Composition of Coal--The uncombined carbon in coal is known as fixed +carbon. Some of the carbon constituent is combined with hydrogen and +this, together with other gaseous substances driven off by the +application of heat, form that portion of the coal known as volatile +matter. The fixed carbon and the volatile matter constitute the +combustible. The oxygen and nitrogen contained in the volatile matter +are not combustible, but custom has applied this term to that portion of +the coal which is dry and free from ash, thus including the oxygen and +nitrogen. + +The other important substances entering into the composition of coal are +moisture and the refractory earths which form the ash. The ash varies in +different coals from 3 to 30 per cent and the moisture from 0.75 to 45 +per cent of the total weight of the coal, depending upon the grade and +the locality in which it is mined. A large percentage of ash is +undesirable as it not only reduces the calorific value of the fuel, but +chokes up the air passages in the furnace and through the fuel bed, thus +preventing the rapid combustion necessary to high efficiency. If the +coal contains an excessive quantity of sulphur, trouble will result from +its harmful action on the metal of the boiler where moisture is present, +and because it unites with the ash to form a fusible slag or clinker +which will choke up the grate bars and form a solid mass in which large +quantities of unconsumed carbon may be imbedded. + +Moisture in coal may be more detrimental than ash in reducing the +temperature of a furnace, as it is non-combustible, absorbs heat both in +being evaporated and superheated to the temperature of the furnace +gases. In some instances, however, a certain amount of moisture in a +bituminous coal produces a mechanical action that assists in the +combustion and makes it possible to develop higher capacities than with +dry coal. + +Classification of Coal--Custom has classified coals in accordance with +the varying content of carbon and volatile matter in the combustible. +Table 36 gives the approximate percentages of these constituents for the +general classes of coals with the corresponding heat values per pound of +combustible. + + TABLE 36 + + APPROXIMATE COMPOSITION AND CALORIFIC VALUE + OF GENERAL GRADES OF COAL ON BASIS OF COMBUSTIBLE + ++-------------------+----------------------------+--------------+ +| Kind of Coal | Per Cent of Combustible | B. t. u. | +| +------------+---------------+ Per Pound of | +| |Fixed Carbon|Volatile Matter| Combustible | ++-------------------+------------+---------------+--------------+ +|Anthracite |97.0 to 92.5| 3.0 to 7.5 |14600 to 14800| +|Semi-anthracite |92.5 to 87.5| 7.5 to 12.5 |14700 to 15500| +|Semi-bituminous |87.5 to 75.0| 12.5 to 25.0 |15500 to 16000| +|Bituminous--Eastern|75.0 to 60.0| 25.0 to 40.0 |14800 to 15300| +|Bituminous--Western|65.0 to 50.0| 35.0 to 50.0 |13500 to 14800| +|Lignite | Under 50 | Over 50 |11000 to 13500| ++-------------------+------------+---------------+--------------+ + + +Anthracite--The name anthracite, or hard coal, is applied to those dry +coals containing from 3 to 7 per cent volatile matter and which do not +swell when burned. True anthracite is hard, compact, lustrous and +sometimes iridescent, and is characterized by few joints and clefts. Its +specific gravity varies from 1.4 to 1.8. In burning, it kindles slowly +and with difficulty, is hard to keep alight, and burns with a short, +almost colorless flame, without smoke. + + +Semi-anthracite coal has less density, hardness and luster than true +anthracite, and can be distinguished from it by the fact that when newly +fractured it will soot the hands. Its specific gravity is ordinarily +about 1.4. It kindles quite readily and burns more freely than the true +anthracites. + + +Semi-bituminous coal is softer than anthracite, contains more volatile +hydrocarbons, kindles more easily and burns more rapidly. It is +ordinarily free burning, has a high calorific value and is of the +highest order for steam generating purposes. + + +Bituminous coals are still softer than those described and contain still +more volatile hydrocarbons. The difference between the semi-bituminous +and the bituminous coals is an important one, economically. The former +have an average heating value per pound of combustible about 6 per cent +higher than the latter, and they burn with much less smoke in ordinary +furnaces. The distinctive characteristic of the bituminous coals is the +emission of yellow flame and smoke when burning. In color they range +from pitch black to dark brown, having a resinous luster in the most +compact specimens, and a silky luster in such specimens as show traces +of vegetable fiber. The specific gravity is ordinarily about 1.3. + +Bituminous coals are either of the caking or non-caking class. The +former, when heated, fuse and swell in size; the latter burn freely, do +not fuse, and are commonly known as free burning coals. Caking coals are +rich in volatile hydrocarbons and are valuable in gas manufacture. + +Bituminous coals absorb moisture from the atmosphere. The surface +moisture can be removed by ordinary drying, but a portion of the water +can be removed only by heating the coal to a temperature of about 250 +degrees Fahrenheit. + +Cannel coal is a variety of bituminous coal, rich in hydrogen and +hydrocarbons, and is exceedingly valuable as a gas coal. It has a dull +resinous luster and burns with a bright flame without fusing. Cannel +coal is seldom used for steam coal, though it is sometimes mixed with +semi-bituminous coal where an increased economy at high rates of +combustion is desired. The composition of cannel coal is approximately +as follows: fixed carbon, 26 to 55 per cent; volatile matter, 42 to 64 +per cent; earthy matter, 2 to 14 per cent. Its specific gravity is +approximately 1.24. + +Lignite is organic matter in the earlier stages of its conversion into +coal, and includes all varieties which are intermediate between peat and +coal of the older formation. Its specific gravity is low, being 1.2 to +1.23, and when freshly mined it may contain as high as 50 per cent of +moisture. Its appearance varies from a light brown, showing a distinctly +woody structure, in the poorer varieties, to a black, with a pitchy +luster resembling hard coal, in the best varieties. It is non-caking and +burns with a bright but slightly smoky flame with moderate heat. It is +easily broken, will not stand much handling in transportation, and if +exposed to the weather will rapidly disintegrate, which will increase +the difficulty of burning it. + +Its composition varies over wide limits. The ash may run as low as one +per cent and as high as 50 per cent. Its high content of moisture and +the large quantity of air necessary for its combustion cause large stack +losses. It is distinctly a low-grade fuel and is used almost entirely in +the districts where mined, due to its cheapness. + +Peat is organic matter in the first stages of its conversion into coal +and is found in bogs and similar places. Its moisture content when cut +is extremely high, averaging 75 or 80 per cent. It is unsuitable for +fuel until dried and even then will contain as much as 30 per cent +moisture. Its ash content when dry varies from 3 to 12 per cent. In this +country, though large deposits of peat have been found, it has not as +yet been found practicable to utilize it for steam generating purposes +in competition with coal. In some European countries, however, the peat +industry is common. + +Distribution--The anthracite coals are, with some unimportant +exceptions, confined to five small fields in Eastern Pennsylvania, as +shown in the following list. These fields are given in the order of +their hardness. + +Lehigh or Eastern Middle Field + Green Mountain District + Black Creek District + Hazelton District + Beaver Meadow District + Panther Creek District[33] + +Mahanoy or Western Field[34] + East Mahanoy District + West Mahanoy District + +Wyoming or Northern Field + Carbondale District + Scranton District + Pittston District + Wilkesbarre District + Plymouth District + +Schuylkill or Southern Field + East Schuylkill District + West Schuylkill District + Louberry District + +Lykens Valley or Southwestern Field + Lykens Valley District + Shamokin District[35] + +Anthracite is also found in Pulaski and Wythe Counties, Virginia; along +the border of Little Walker Mountain, and in Gunnison County, Colorado. +The areas in Virginia are limited, however, while in Colorado the +quality varies greatly in neighboring beds and even in the same bed. An +anthracite bed in New Mexico was described in 1870 by Dr. R. W. Raymond, +formerly United States Mining Commissioner. + +Semi-anthracite coals are found in a few small areas in the western part +of the anthracite field. The largest of these beds is the Bernice in +Sullivan County, Pennsylvania. Mr. William Kent, in his "Steam Boiler +Economy", describes this as follows: "The Bernice semi-anthracite coal +basin lies between Beech Creek on the north and Loyalsock Creek on the +south. It is six miles long, east and west, and hardly a third of a mile +across. An 8-foot vein of coal lies in a bed of 12 feet of coal and +slate. The coal of this bed is the dividing line between anthracite and +semi-anthracite, and is similar to the coal of the Lykens Valley +District. Mine analyses give a range as follows: moisture, 0.65 to 1.97; +volatile matter, 3.56 to 9.40; fixed carbon, 82.52 to 89.39; ash, 3.27 +to 9.34; sulphur, 0.24 to 1.04." + +Semi-bituminous coals are found on the eastern edge of the great +Appalachian Field. Starting with Tioga and Bradford Counties of northern +Pennsylvania, the bed runs southwest through Lycoming, Clearfield, +Centre, Huntingdon, Cambria, Somerset and Fulton Counties, Pennsylvania; +Allegheny County, Maryland; Buchannan, Dickinson, Lee, Russell, Scott, +Tazewell and Wise Counties, Virginia; Mercer, McDowell, Fayette, Raleigh +and Mineral Counties, West Virginia; and ending in northeastern +Tennessee, where a small amount of semi-bituminous is mined. + +The largest of the bituminous fields is the Appalachian. Beginning near +the northern boundary of Pennsylvania, in the western portion of the +State, it extends southwestward through West Virginia, touching Maryland +and Virginia on their western borders, passing through southeastern +Ohio, eastern Kentucky and central Tennessee, and ending in western +Alabama, 900 miles from its northern extremity. + +The next bituminous coal producing region to the west is the Northern +Field, in north central Michigan. Still further to the west, and second +in importance to the Appalachian Field, is the Eastern Interior Field. +This covers, with the exception of the upper northern portion, nearly +the entire State of Illinois, southwest Indiana and the western portion +of Kentucky. + +The Western Field extends through central and southern Iowa, western +Missouri, southwestern Kansas, eastern Oklahoma and the west central +portion of Arkansas. The Southwestern Field is confined entirely to the +north central portion of Texas, in which State there are also two small +isolated fields along the Rio Grande River. + +The remaining bituminous fields are scattered through what may be termed +the Rocky Mountain Region, extending from Montana to New Orleans. A +partial list of these fields and their location follows: + +Judith Basin Central Montana +Bull Mountain Field Central Montana +Yellowstone Region Southwestern Montana +Big Horn Basin Region Southern Montana +Big Horn Basin Region Northern Wyoming +Black Hills Region Northeastern Wyoming +Hanna Field Southern Wyoming +Green River Region Southwestern Wyoming +Yampa Field Northwestern Colorado +North Park Field Northern Colorado +Denver Region North Central Colorado +Uinta Region Western Colorado +Uinta Region Eastern Utah +Southwestern Region Southwestern Utah +Raton Mountain Region Southern Colorado +Raton Mountain Region Northern New Mexico +San Juan River Region Northwestern New Mexico +Capitan Field Southern New Mexico + +Along the Pacific Coast a few small fields are scattered in western +California, southwestern Oregon, western and northwestern Washington. + +Most of the coals in the above fields are on the border line between +bituminous and lignite. They are really a low grade of bituminous coal +and are known as sub-bituminous or black lignites. + +Lignites--These resemble the brown coals of Europe and are found in the +western states, Wyoming, New Mexico, Arizona, Utah, Montana, North +Dakota, Nevada, California, Oregon and Washington. Many of the fields +given as those containing bituminous coals in the western states also +contain true lignite. Lignite is also found in the eastern part of Texas +and in Oklahoma. + +Alaska Coals--Coal has been found in Alaska and undoubtedly is of great +value, though the extent and character of the fields have probably been +exaggerated. Great quantities of lignite are known to exist, and in +quality the coal ranges in character from lignite to anthracite. There +are at present, however, only two fields of high-grade coals known, +these being the Bering River Field, near Controllers Bay, and the +Matanuska Field, at the head of Cooks Inlet. Both of these fields are +known to contain both anthracite and high-grade bituminous coals, though +as yet they cannot be said to have been opened up. + +Weathering of Coal--The storage of coal has become within the last few +years to a certain extent a necessity due to market conditions, danger +of labor difficulties at the mines and in the railroads, and the +crowding of transportation facilities. The first cause is probably the +most important, and this is particularly true of anthracite coals where +a sliding scale of prices is used according to the season of the year. +While market conditions serve as one of the principal reasons for coal +storage, most power plants and manufacturing plants feel compelled to +protect their coal supply from the danger of strikes, car shortages and +the like, and it is customary for large power plants, railroads and coal +companies themselves, to store bituminous coal. Naval coaling stations +are also an example of what is done along these lines. + +Anthracite is the nearest approach to the ideal coal for storing. It is +not subject to spontaneous ignition, and for this reason is unlimited in +the amount that may be stored in one pile. With bituminous coals, +however, the case is different. Most bituminous coals will ignite if +placed in large enough piles and all suffer more or less from +disintegration. Coal producers only store such coals as are least liable +to ignite, and which will stand rehandling for shipment. + +The changes which take place in stored coal are of two kinds: 1st, the +oxidization of the inorganic matter such as pyrites; and 2nd, the direct +oxidization of the organic matter of the actual coal. + +The first change will result in an increased volume of the coal, and +sometimes in an increased weight, and a marked disintegration. The +changes due to direct oxidization of the coal substances usually cannot +be detected by the eye, but as they involve the oxidization of the +carbon and available hydrogen and the absorption of the oxygen by +unsaturated hydrocarbons, they are the chief cause of the weathering +losses in heat value. Numerous experiments have led to the conclusion +that this is also the cause for spontaneous combustion. + +Experiments to show loss in calorific heat values due to weathering +indicate that such loss may be as high as 10 per cent when the coal is +stored in the air, and 8.75 per cent when stored under water. It would +appear that the higher the volatile content of the coal, the greater +will be the loss in calorific value and the more subject to spontaneous +ignition. + +Some experiments made by Messrs. S. W. Parr and W. F. Wheeler, published +in 1909 by the Experiment Station of the University of Illinois, +indicate that coals of the nature found in Illinois and neighboring +states are not affected seriously during storage from the standpoint of +weight and heating value, the latter loss averaging about 3-1/2 per cent +for the first year of storage. They found that the losses due to +disintegration and to spontaneous ignition were of greater importance. +Their conclusions agree with those deduced from the other experiments, +viz., that the storing of a larger size coal than that which is to be +used, will overcome to a certain extent the objection to disintegration, +and that the larger sizes, besides being advantageous in respect to +disintegration, are less liable to spontaneous ignition. Storage under +water will, of course, entirely prevent any fire loss and, to a great +extent, will stop disintegration and reduce the calorific losses to a +minimum. + +To minimize the danger of spontaneous ignition in storing coal, the +piles should be thoroughly ventilated. + +Pulverized Fuels--Considerable experimental work has been done with +pulverized coal, utilizing either coal dust or pulverizing such coal as +is too small to be burned in other ways. If satisfactorily fed to the +furnace, it would appear to have several advantages. The dust burned in +suspension would be more completely consumed than is the case with the +solid coals, the production of smoke would be minimized, and the process +would admit of an adjustment of the air supply to a point very close to +the amount theoretically required. This is due to the fact that in +burning there is an intimate mixture of the air and fuel. The principal +objections have been in the inability to introduce the pulverized fuel +into the furnace uniformly, the difficulty of reducing the fuel to the +same degree of fineness, liability of explosion in the furnace due to +improper mixture with the air, and the decreased capacity and efficiency +resulting from the difficulty of keeping tube surfaces clean. + +Pressed Fuels--In this class are those composed of the dust of some +suitable combustible, pressed and cemented together by a substance +possessing binding and in most cases inflammable properties. Such fuels, +known as briquettes, are extensively used in foreign countries and +consist of carbon or soft coal, too small to be burned in the ordinary +way, mixed usually with pitch or coal tar. Much experimenting has been +done in this country in briquetting fuels, the government having taken +an active interest in the question, but as yet this class of fuel has +not come into common use as the cost and difficulty of manufacture and +handling have made it impossible to place it in the market at a price to +successfully compete with coal. + +Coke is a porous product consisting almost entirely of carbon remaining +after certain manufacturing processes have distilled off the hydrocarbon +gases of the fuel used. It is produced, first, from gas coal distilled +in gas retorts; second, from gas or ordinary bituminous coals burned in +special furnaces called coke ovens; and third, from petroleum by +carrying the distillation of the residuum to a red heat. + +Coke is a smokeless fuel. It readily absorbs moisture from the +atmosphere and if not kept under cover its moisture content may be as +much as 20 per cent of its own weight. + +Gas-house coke is generally softer and more porous than oven coke, +ignites more readily, and requires less draft for its combustion. + +[Illustration: 16,000 Horse-power Installation of Babcock & Wilcox +Boilers and Superheaters at the Brunot's Island Plant of the Duquesne +Light Co., Pittsburgh, Pa.] + + + + +THE DETERMINATION OF HEATING VALUES OF FUELS + + +The heating value of a fuel may be determined either by a calculation +from a chemical analysis or by burning a sample in a calorimeter. + +In the former method the calculation should be based on an ultimate +analysis, which reduces the fuel to its elementary constituents of +carbon, hydrogen, oxygen, nitrogen, sulphur, ash and moisture, to secure +a reasonable degree of accuracy. A proximate analysis, which determines +only the percentage of moisture, fixed carbon, volatile matter and ash, +without determining the ultimate composition of the volatile matter, +cannot be used for computing the heat of combustion with the same degree +of accuracy as an ultimate analysis, but estimates may be based on the +ultimate analysis that are fairly correct. + +An ultimate analysis requires the services of a competent chemist, and +the methods to be employed in such a determination will be found in any +standard book on engineering chemistry. An ultimate analysis, while +resolving the fuel into its elementary constituents, does not reveal how +these may have been combined in the fuel. The manner of their +combination undoubtedly has a direct effect upon their calorific value, +as fuels having almost identical ultimate analyses show a difference in +heating value when tested in a calorimeter. Such a difference, however, +is slight, and very close approximations may be computed from the +ultimate analysis. + +Ultimate analyses are given on both a moist and a dry fuel basis. +Inasmuch as the latter is the basis generally accepted for the +comparison of data, it would appear that it is the best basis on which +to report such an analysis. When an analysis is given on a moist fuel +basis it may be readily converted to a dry basis by dividing the +percentages of the various constituents by one minus the percentage of +moisture, reporting the moisture content separately. + + _Moist Fuel_ _Dry Fuel_ + +C 83.95 84.45 +H 4.23 4.25 +O 3.02 3.04 +N 1.27 1.28 +S .91 .91 +Ash 6.03 6.07 + ------ + 100.00 + +Moisture .59 .59 + ------ + 100.00 + +Calculations from an Ultimate Analysis--The first formula for the +calculation of heating values from the composition of a fuel as +determined from an ultimate analysis is due to Dulong, and this formula, +slightly modified, is the most commonly used to-day. Other formulae have +been proposed, some of which are more accurate for certain specific +classes of fuel, but all have their basis in Dulong's formula, the +accepted modified form of which is: + +Heat units in B. t. u. per pound of dry fuel = + + O +14,600 C + 62,000(H - -) + 4000 S (18) + 8 + +where C, H, O and S are the proportionate parts by weight of carbon, +hydrogen, oxygen and sulphur. + +Assume a coal of the composition given. Substituting in this formula +(18), + +Heating value per pound of dry coal + + ( .0304) += 14,600 x .8445 + 62,000 (.0425 - -----) + 4000 x .0091 = 14,765 B. t. u. + ( 8 ) + +This coal, by a calorimetric test, showed 14,843 B. t. u., and from a +comparison the degree of accuracy of the formula will be noted. + +The investigation of Lord and Haas in this country, Mabler in France, +and Bunte in Germany, all show that Dulong's formula gives results +nearly identical with those obtained from calorimetric tests and may be +safely applied to all solid fuels except cannel coal, lignite, turf and +wood, provided the ultimate analysis is correct. This practically limits +its use to coal. The limiting features are the presence of hydrogen and +carbon united in the form of hydrocarbons. Such hydrocarbons are present +in coals in small quantities, but they have positive and negative heats +of combination, and in coals these appear to offset each other, +certainly sufficiently to apply the formula to such fuels. + +High and Low Heat Value of Fuels--In any fuel containing hydrogen the +calorific value as found by the calorimeter is higher than that +obtainable under most working conditions in boiler practice by an amount +equal to the latent heat of the volatilization of water. This heat would +reappear when the vapor was condensed, though in ordinary practice the +vapor passes away uncondensed. This fact gives rise to a distinction in +heat values into the so-called "higher" and "lower" calorific values. +The higher value, _i. e._, the one determined by the calorimeter, is the +only scientific unit, is the value which should be used in boiler +testing work, and is the one recommended by the American Society of +Mechanical Engineers. + +There is no absolute measure of the lower heat of combustion, and in +view of the wide difference in opinion among physicists as to the +deductions to be made from the higher or absolute unit in this +determination, the lower value must be considered an artificial unit. +The lower value entails the use of an ultimate analysis and involves +assumptions that would make the employment of such a unit impracticable +for commercial work. The use of the low value may also lead to error and +is in no way to be recommended for boiler practice. + +An example of its illogical use may be shown by the consideration of a +boiler operated in connection with a special economizer where the vapor +produced by hydrogen is partially condensed by the economizer. If the +low value were used in computing the boiler efficiency, it is obvious +that the total efficiency of the combined boiler and economizer must be +in error through crediting the combination with the heat imparted in +condensing the vapor and not charging such heat to the heat value of the +coal. + +Heating Value of Gaseous Fuels--The method of computing calorific values +from an ultimate analysis is particularly adapted to solid fuels, with +the exceptions already noted. The heating value of gaseous fuels may be +calculated by Dulong's formula provided another term is added to provide +for any carbon monoxide present. Such a method, however, involves the +separating of the constituent gases into their elementary gases, which +is oftentimes difficult and liable to simple arithmetical error. As the +combustible portion of gaseous fuels is ordinarily composed of hydrogen, +carbon monoxide and certain hydrocarbons, a determination of the +calorific value is much more readily obtained by a separation into their +constituent gases and a computation of the calorific value from a table +of such values of the constituents. Table 37 gives the calorific value +of the more common combustible gases, together with the theoretical +amount of air required for their combustion. + + TABLE 37 + + WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES + AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE + WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION + ++---------------+----------+------+-----+------+----------+-----------+ +| Gas | Symbol |Cubic |B.t.u|B.t.u.|Cubic Feet|Cubic Feet | +| | | Feet | per | per | of Air | of Air | +| | |of Gas|Pound|Cubic | Required | Required | +| | | per | | Foot |per Pound | Per Cubic | +| | |Pound | | | of Gas |Foot of Gas| ++---------------+----------+------+-----+------+----------+-----------+ +|Hydrogen | H |177.90|62000| 349 | 428.25 | 2.41 | +|Carbon Monoxide| CO | 12.81| 4450| 347 | 30.60 | 2.39 | +|Methane |CH_{4} | 22.37|23550| 1053 | 214.00 | 9.57 | +|Acetylene |C_{2}H_{2}| 13.79|21465| 1556 | 164.87 | 11.93 | +|Olefiant Gas |C_{2}H_{4}| 12.80|21440| 1675 | 183.60 | 14.33 | +|Ethane |C_{2}H_{6}| 11.94|22230| 1862 | 199.88 | 16.74 | ++---------------+----------+------+-----+------+----------+-----------+ + +In applying this table, as gas analyses may be reported either by weight +or volume, there is given in Table 33[36] a method of changing from +volumetric analysis to analysis by weight. + + +Examples: + + +1st. Assume a blast furnace gas, the analysis of which in percentages by +weight is, oxygen = 2.7, carbon monoxide = 19.5, carbon dioxide = 18.7, +nitrogen = 59.1. Here the only combustible gas is the carbon monoxide, +and the heat value will be, + +0.195 x 4450 = 867.75 B. t. u. per pound. + +The _net_ volume of air required to burn one pound of this gas will be, + +0.195 x 30.6 = 5.967 cubic feet. + + +2nd. Assume a natural gas, the analysis of which in percentages by +volume is oxygen = 0.40, carbon monoxide = 0.95, carbon dioxide = 0.34, +olefiant gas (C_{2}H_{4}) = 0.66, ethane (C_{2}H_{6}) = 3.55, marsh gas +(CH_{4}) = 72.15 and hydrogen = 21.95. All but the oxygen and the carbon +dioxide are combustibles, and the heat per cubic foot will be, + +From CO = 0.0095 x 347 = 3.30 + C_{2}H_{4} = 0.0066 x 1675 = 11.05 + C_{2}H_{6} = 0.0355 x 1862 = 66.10 + CH_{4} = 0.7215 x 1050 = 757.58 + H = 0.2195 x 349 = 76.61 + ------ + B. t. u. per cubic foot 914.64 + +The _net_ air required for combustion of one cubic foot of the gas will +be, + +CO = 0.0095 x 2.39 = 0.02 +C_{2}H_{4} = 0.0066 x 14.33 = 0.09 +C_{2}H_{6} = 0.0355 x 16.74 = 0.59 +CH_{4} = 0.7215 x 9.57 = 6.90 +H = 0.2195 x 2.41 = 0.53 + ---- + Total net air per cubic foot 8.13 + +Proximate Analysis--The proximate analysis of a fuel gives its +proportions by weight of fixed carbon, volatile combustible matter, +moisture and ash. A method of making such an analysis which has been +found to give eminently satisfactory results is described below. + +From the coal sample obtained on the boiler trial, an average sample of +approximately 40 grams is broken up and weighed. A good means of +reducing such a sample is passing it through an ordinary coffee mill. +This sample should be placed in a double-walled air bath, which should +be kept at an approximately constant temperature of 105 degrees +centigrade, the sample being weighed at intervals until a minimum is +reached. The percentage of moisture can be calculated from the loss in +such a drying. + +For the determination of the remainder of the analysis, and the heating +value of the fuel, a portion of this dried sample should be thoroughly +pulverized, and if it is to be kept, should be placed in an air-tight +receptacle. One gram of the pulverized sample should be weighed into a +porcelain crucible equipped with a well fitting lid. This crucible +should be supported on a platinum triangle and heated for seven minutes +over the full flame of a Bunsen burner. At the end of such time the +sample should be placed in a desiccator containing calcium chloride, and +when cooled should be weighed. From the loss the percentage of volatile +combustible matter may be readily calculated. + +The same sample from which the volatile matter has been driven should be +used in the determination of the percentage of ash. This percentage is +obtained by burning the fixed carbon over a Bunsen burner or in a muffle +furnace. The burning should be kept up until a constant weight is +secured, and it may be assisted by stirring with a platinum rod. The +weight of the residue determines the percentage of ash, and the +percentage of fixed carbon is easily calculated from the loss during the +determination of ash after the volatile matter has been driven off. + +Proximate analyses may be made and reported on a moist or dry basis. The +dry basis is that ordinarily accepted, and this is the basis adopted +throughout this book. The method of converting from a moist to a dry +basis is the same as described in the case of an ultimate analysis. A +proximate analysis is easily made, gives information as to the general +characteristics of a fuel and of its _relative_ heating value. + +Table 38 gives the proximate analysis and calorific value of a number of +representative coals found in the United States. + + TABLE 38 + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN COALS + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | +____|_______|________________|________________|_______________|_____________| + | | | | + | | ANTHRACITES | | +____|_______|_________________________________________________|_____________| + | | | | | | + 1 | Pa. | Carbon | Lehigh | Beaver Meadow | | + 2 | Pa. | Dauphin | Schuylkill | | Buckwheat | + 3 | Pa. | Lackawanna | Wyoming | Belleview | No. 2 Buck. | + 4 | Pa. | Lackawanna | Wyoming | Johnson | Culm. | + 5 | Pa. | Luzerne | Wyoming | Pittston | No. 2 Buck. | + 6 | Pa. | Luzerne | Wyoming | Mammoth | Large | + 7 | Pa. | Luzerne | Wyoming | Exeter | Rice | + 8 | Pa. | Northumberland | Schuylkill | Treverton | | + 9 | Pa. | Schuylkill | Schuylkill | Buck Mountain | | + 10 | Pa. | Schuylkill | | York Farm | Buckwheat | + 11 | Pa. | | | Victoria | Buckwheat | + 12 | Pa. | Carbon | Lehigh | Lehigh & | Buck. & Pea | + | | | | Wilkes C. Co. | | + 13 | Pa. | Carbon | Lehigh | | Buckwheat | + 14 | Pa. | Lackawanna | |Del. & Hud. Co.| No. 1 Buck. | +____|_______|________________|________________|_______________|_____________| + | | | | + | | SEMI-ANTHRACITES | | +____|_______|_________________________________________________|_____________| + | | | | | | + 15 | Pa. | Lycoming | Loyalsock | | | + 16 | Pa. | Sullivan | | Lopez | | + 17 | Pa. | Sullivan | Bernice | | | +____|_______|________________|________________|_______________|_____________| + | | | | + | | SEMI-BITUMINOUS | | +____|_______|_________________________________________________|_____________| + | | | | | | + 18 | Md. | Alleghany | Big Vein, | | | + | | | George's Crk. | | | + 19 | Md. | Alleghany | George's Creek | | | + 20 | Md. | Alleghany | George's Creek | | | + 21 | Md. | Alleghany | George's Creek | Ocean No. 7 | Mine run | + 22 | Md. | Alleghany | Cumberland | | | + 23 | Md. | Garrett | | Washington | Mine run | + | | | | No. 3 | | + 24 | Pa. | Bradford | | Long Valley | | + 25 | Pa. | Tioga | | Antrim | | + 26 | Pa. | Cambria | "B" or Miller | Soriman Shaft | | + | | | | C. Co. | | + 27 | Pa. | Cambria | "B" or Miller | Henrietta | | + 28 | Pa. | Cambria | "B" or Miller | Penker | | + 29 | Pa. | Cambria | "B" or Miller | Lancashire | | + 30 | Pa. | Cambria | Lower | Penn. C. & C. | Mine run | + | | | Kittanning | Co. No. 3 | | + 31 | Pa. | Cambria | Upper | Valley | Mine run | + | | | Kittanning | | | + 32 | Pa. | Clearfield | Lower | Eureka | Mine run | + | | | Kittanning | | | + 33 | Pa. | Clearfield | | Ghem | Mine run | + 34 | Pa. | Clearfield | | Osceola | | + 35 | Pa. | Clearfield | Reynoldsville | | | + 36 | Pa. | Clearfield | Atlantic- | | Mine run | + | | | Clearfield | | | + 37 | Pa. | Huntington | Barnet & Fulton| Carbon | Mine run | + 38 | Pa. | Huntington | | Rock Hill | Mine run | + 39 | Pa. | Somerset | Lower | Kimmelton | Mine run | + | | | Kittanning | | | + 40 | Pa. | Somerset | "C" Prime Vein | Jenner | Mine run | +____|_______|________________|________________|_______________|_____________| + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 1 | 1.50 | 2.41 | 90.30 | 7.29 | | Gale | + 2 | 2.15 | 12.88 | 78.23 | 8.89 | 13137 | Whitham | + 3 | 8.29 | 7.81 | 77.19 | 15.00 | 12341 | Sadtler | + 4 | 13.90 | 11.16 | 65.96 | 22.88 | 10591 | B. & W. Co. | + 5 | 3.66 | 4.40 | 78.96 | 16.64 | 12865 | B. & W. Co. | + 6 | 4.00 | 3.44 | 90.59 | 5.97 | 13720 | Carpenter | + 7 | 0.25 | 8.18 | 79.61 | 12.21 | 12400 | B. & W. Co. | + 8 | 0.84 | 6.73 | 86.39 | 6.88 | | Isherwood | + 9 | | 3.17 | 92.41 | 4.42 | 14220 | Carpenter | + 10 | 0.81 | 5.51 | 75.90 | 18.59 | 11430 | | + 11 | 4.30 | 0.55 | 86.73 | 12.72 | 12642 | B. & W. Co. | + 12 | 1.57 | 6.27 | 66.53 | 27.20 | 12848 | B. & W. Co. | + | | | | | | | + 13 | | 5.00 | 81.00 | 14.00 | 11800 | Carpenter | + 14 | 6.20 | | | 11.60 | 12100 | Denton | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 15 | 1.30 | 8.72 | 84.44 | 6.84 | | | + 16 | 5.48 | 7.53 | 81.00 | 11.47 | 13547 | B. & W. Co. | + 17 | 1.29 | 8.21 | 84.43 | 7.36 | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 18 | 3.50 | 21.33 | 72.47 | 6.20 | 14682 | B. & W. Co. | + | | | | | | | + 19 | 3.63 | 16.27 | 76.93 | 6.80 | 14695 | B. & W. Co. | + 20 | 2.28 | 19.43 | 77.44 | 6.13 | 14793 | B. & W. Co. | + 21 | 1.13 | | | | 14451 | B. & W. Co. | + 22 | 1.50 | 17.26 | 76.65 | 6.09 | 14700 | | + 23 | 2.33 | 14.38 | 74.93 | 10.49 | 14033 | U. S. Geo. S.| + | | | | | | [37] | + 24 | 1.55 | 20.33 | 68.38 | 11.29 | 12965 | | + 25 | 2.19 | 18.43 | 71.87 | 9.70 | 13500 | | + 26 | 3.40 | 20.70 | 71.84 | 7.46 | 14484 | N. Y. Ed. Co.| + | | | | | | | + 27 | 1.23 | 18.37 | 75.28 | 6.45 | 14770 | So. Eng. Co. | + 28 | 3.64 | 21.34 | 70.48 | 8.18 | 14401 | B. & W. Co. | + 29 | 4.38 | 21.20 | 70.27 | 8.53 | 14453 | B. & W. Co. | + 30 | 3.51 | 17.43 | 75.69 | 6.88 | 14279 | U. S. Geo. S.| + | | | | | | | + 31 | 3.40 | 14.89 | 75.03 | 10.08 | 14152 | B. & W. Co. | + | | | | | | | + 32 | 5.90 | 16.71 | 77.22 | 6.07 | 14843 | U. S. Geo. S.| + | | | | | | | + 33 | 3.43 | 17.53 | 69.67 | 12.80 | 13744 | B. & W. Co. | + 34 | 1.24 | 25.43 | 68.56 | 6.01 | 13589 | B. & W. Co. | + 35 | 2.91 | 21.55 | 69.03 | 9.42 | 14685 | B. & W. Co. | + 36 | 1.55 | 23.36 | 71.15 | 5.94 | 13963 | Whitham | + | | | | | | | + 37 | 4.50 | 18.34 | 73.06 | 8.60 | 13770 | B. & W. Co. | + 38 | 5.91 | 17.58 | 73.44 | 8.99 | 14105 | B. & W. Co. | + 39 | 3.09 | 17.84 | 70.47 | 11.69 | 13424 | U. S. Geo. S.| + | | | | | | | + 40 | 9.37 | 16.47 | 75.76 | 7.77 | 14507 | P. R. R. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | +____|_______|________________|________________|_______________|_____________| + | | | | | | + 41 | W. Va.| Fayette | New River | Rush Run | Mine run | + 42 | W. Va.| Fayette | New River | Loup Creek | | + 43 | W. Va.| Fayette | New River | | Slack | + 44 | W. Va.| Fayette | New River | | Mine run | + 45 | W. Va.| Fayette | New River | Rush Run | Mine run | + 46 | W. Va.| McDowell | Pocahontas | Zenith | Mine run | + | | | No. 3 | | | + 47 | W. Va.| McDowell | Tug River | Big Sandy | Mine run | + 48 | W. Va.| Mercer | Pocahontas | Mora | Lump | + 49 | W. Va.| Mineral | Elk Garden | | | + 50 | W. Va.| McDowell | Pocahontas | Flat Top | Mine run | + 51 | W. Va.| McDowell | Pocahontas | Flat Top | Slack | + 52 | W. Va.| McDowell | Pocahontas | Flat Top | Lump | +____|_______|________________|________________|_______________|_____________| + | | | | + | | BITUMINOUS | | +____|_______|_________________________________________________|_____________| + | | | | | | + 53 | Ala. | Bibb | Cahaba | Hill Creek | Mine run | + 54 | Ala. | Jefferson | Pratt | Pratt No. 13 | | + 55 | Ala. | Jefferson | Pratt | Warner | Mine run | + 56 | Ala. | Jefferson | | Coalburg | Mine run | + 57 | Ala. | Walker | Horse Creek | Ivy C. & I. | Nut | + | | | | Co. No. 8 | | + 58 | Ala. | Walker | Jagger | Galloway C. | Mine run | + | | | | Co. No. 5 | | + 59 | Ark. | Franklin | Denning | Western No. 4 | Nut | + 60 | Ark. | Sebastian | Jenny Lind | Mine No. 12 | Lump | + 61 | Ark. | Sebastian | Huntington | Cherokee | Mine run | + 62 | Col. | Boulder | South Platte | Lafayette | Mine run | + 63 | Col. | Boulder | Laramie | Simson | Mine run | + 64 | Col. | Fremont | Canon City | Chandler | Nut and | + | | | | | Slack | + 65 | Col. | Las Animas | Trinidad | Hastings | Nut | + 66 | Col. | Las Animas | Trinidad | Moreley | Slack | + 67 | Col. | Routt | Yampa | Oak Creek | | + 68 | Ill. | Christian | Pana | Penwell Col. | Lump | + 69 | Ill. | Franklin | No. 6 | Benton | Egg | + 70 | Ill. | Franklin | Big Muddy | Zeigler | 3/4 inch | + 71 | Ill. | Jackson | Big Muddy | | | + 72 | Ill. | La Salle | Streator | | | + 73 | Ill. | La Salle | Streator | Marseilles | Mine run | + 74 | Ill. | Macoupin | Nilwood | Mine No. 2 | Screenings | + 75 | Ill. | Macoupin | Mt. Olive | Mine No. 2 | Mine run | + 76 | Ill. | Madison | Belleville | Donk Bros. | Lump | + 77 | Ill. | Madison | Glen Carbon | | Mine run | + 78 | Ill. | Marion | | Odin | Lump | + 79 | Ill. | Mercer | Gilchrist | | Screenings | + 80 | Ill. | Montgomery | Pana or No. 5 | Coffeen | Mine run | + 81 | Ill. | Peoria | No. 5 | Empire | | + 82 | Ill. | Perry | Du Quoin | Number 1 | Screenings | +____|_______|________________|________________|_______________|_____________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 41 | 2.14 | 22.87 | 71.56 | 5.57 | 14959 | U. S. Geo. S.| + 42 | 0.55 | 19.36 | 78.48 | 2.16 | 14975 | Hill | + 43 | 6.66 | 20.94 | 73.16 | 5.90 | 14412 | B. & W. Co. | + 44 | 2.16 | 17.82 | 75.66 | 6.52 | 14786 | B. & W. Co. | + 45 | 0.94 | 22.16 | 75.85 | 1.99 | 15007 | B. & W. Co. | + 46 | 4.85 | 17.14 | 76.54 | 6.32 | 14480 | U. S. Geo. S.| + | | | | | | | + 47 | 1.58 | 18.55 | 76.44 | 4.91 | 15170 | U. S. Geo. S.| + 48 | 1.74 | 18.55 | 75.15 | 6.30 | 15015 | U. S. Geo. S.| + 49 | 2.10 | 15.70 | 75.40 | 8.90 | 14195 | B. & W. Co. | + 50 | 0.52 | 24.02 | 74.59 | 1.39 | 14490 | B. & W. Co. | + 51 | 3.24 | 15.33 | 77.60 | 7.07 | 14653 | B. & W. Co. | + 52 | 3.63 | 16.03 | 78.04 | 5.93 | 14956 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 53 | 6.19 | 28.58 | 55.60 | 15.82 | 12576 | B. & W. Co. | + 54 | 4.29 | 25.78 | 67.68 | 6.54 | 14482 | B. & W. Co. | + 55 | 2.51 | 27.80 | 61.50 | 10.70 | 13628 | U. S. Geo. S.| + 56 | 0.94 | 31.34 | 65.65 | 3.01 | 14513 | B. & W. Co. | + 57 | 2.56 | 31.82 | 53.89 | 14.29 | 12937 | U. S. Geo. S.| + | | | | | | | + 58 | 4.83 | 34.65 | 51.12 | 14.03 | 12976 | U. S. Geo. S.| + | | | | | | | + 59 | 2.22 | 12.83 | 75.35 | 11.82 | | U. S. Geo. S.| + 60 | 1.07 | 17.04 | 74.45 | 8.51 | 14252 | U. S. Geo. S.| + 61 | 0.97 | 19.87 | 70.30 | 9.83 | 14159 | U. S. Geo. S.| + 62 | 19.48 | 38.80 | 49.00 | 12.20 | 11939 | B. & W. Co. | + 63 | 19.78 | 44.69 | 48.62 | 6.69 | 12577 | U. S. Geo. S.| + 64 | 9.37 | 38.10 | 51.75 | 10.15 | 11850 | B. & W. Co. | + | | | | | | | + 65 | 2.15 | 31.07 | 53.40 | 15.53 | 12547 | B. & W. Co. | + 66 | 1.88 | 28.47 | 55.58 | 15.95 | 12703 | B. & W. Co. | + 67 | 6.67 | 42.91 | 55.64 | 1.45 | | Hill | + 68 | 8.05 | 43.67 | 49.97 | 6.36 | 10900 | Jones | + 69 | 8.31 | 34.52 | 54.05 | 11.43 | 11727 | U. S. Geo. S.| + 70 | 13.28 | 31.97 | 57.37 | 10.66 | 12857 | U. S. Geo. S.| + 71 | 4.85 | 31.55 | 62.19 | 6.26 | 11466 | Breckenridge | + 72 | 8.40 | 41.76 | 51.42 | 6.82 | 11727 | Breckenridge | + 73 | 12.98 | 43.73 | 49.13 | 7.14 | 10899 | B. & W. Co. | + 74 | 13.34 | 34.75 | 44.55 | 20.70 | 10781 | B. & W. Co. | + 75 | 13.54 | 41.28 | 46.30 | 12.42 | 10807 | U. S. Geo. S.| + 76 | 13.47 | 38.69 | 48.07 | 13.24 | 12427 | U. S. Geo. S.| + 77 | 9.78 | 38.18 | 51.52 | 10.30 | 11672 | Bryan | + 78 | 6.20 | 42.91 | 49.06 | 8.03 | 11880 | Breckenridge | + 79 | 8.50 | 36.17 | 41.64 | 22.19 | 10497 | Breckenridge | + 80 | 11.93 | 34.05 | 49.85 | 16.10 | 10303 | U. S. Geo. S.| + 81 | 17.64 | 31.91 | 46.17 | 21.92 | 10705 | B. & W. Co. | + 82 | 9.81 | 33.67 | 48.36 | 17.97 | 11229 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | + |_______|________________|________________|_______________|_____________| + | | | | | | + 83 | Ill. | Perry | Du Quoin | Willis | Mine run | + 84 | Ill. | Sangamon | | Pawnee | Slack | + 85 | Ill. | St. Clair | Standard | Nigger Hollow | Mine run | + 86 | Ill. | St. Clair | Standard | Maryville | Mine run | + 87 | Ill. | Williamson | Big Muddy | Daws | Mine run | + 88 | Ill. | Williamson | Carterville | Carterville | | + | | | or No. 7 | | | + 89 | Ill. | Williamson | Carterville | Burr | Nut, Pea | + | | | or No. 7 | | and Slack | + 90 | Ind. | Brazil | Brazil | Gartside | Block | + 91 | Ind. | Clay | | Louise | Block | + 92 | Ind. | Green | Island City | | Mine run | + 93 | Ind. | Knox | Vein No. 5 | Tecumseh | Mine run | + 94 | Ind. | Parke | Vein No. 6 | Parke Coal Co.| Lump | + 95 | Ind. | Sullivan | Sullivan No. 6 | Mildred | Washed | + 96 | Ind. | Vigo | Number 6 | Fontanet | Mine run | + 97 | Ind. | Vigo | Number 7 | Red Bird | Mine run | + 98 | Iowa | Appanoose | Mystic | Mine No. 3 | Lump | + 99 | Iowa | Lucas | Lucas | Inland No. 1 | Mine run | +100 | Iowa | Marion | Big Vein | Liberty No. 5 | Mine run | +101 | Iowa | Polk | Third Seam | Altoona No. 4 | Lump | +102 | Iowa | Wapello | Wapello | | Lump | +103 | Kan. | Cherokee | Weir Pittsburgh| Southwestern | Lump | + | | | | Dev. Co. | | +104 | Kan. | Cherokee | Cherokee | | Screenings | +105 | Kan. | Cherokee | Cherokee | | Lump | +106 | Kan. | Linn | Boicourt | | Lump | +107 | Ky. | Bell | Straight Creek | Str. Ck. C. & | Mine run | + | | | | C. Co. | | +108 | Ky. | Hopkins | Bed No. 9 | Earlington | Lump | +109 | Ky. | Hopkins | Bed No. 9 | Barnsley | Mine run | +110 | Ky. | Hopkins | Vein No. 14 | Nebo |Pea and Slack| +111 | Ky. | Johnson | Vein No. 1 | Miller's Creek| Mine run | +112 | Ky. | Mulenburg | Bed No. 9 | Pierce |Pea and Slack| +113 | Ky. | Pulaski | | Greensburg | | +114 | Ky. | Webster | Bed No. 9 | |Pea and Slack| +115 | Ky. | Whitley | | Jellico |Nut and Slack| +116 | Mo. | Adair | | Danforth | Mine run | +117 | Mo. | Bates | Rich Hill | New Home | Mine run | +118 | Mo. | Clay | Lexington | Mo. City Coal | | + | | | | Co. | | +119 | Mo. | Lafayette | Waverly | Buckthorn | | +120 | Mo. | Lafayette | Waverly | Higbee | | +121 | Mo. | Linn | Bevier | Marceline | | +122 | Mo. | Macon | Bevier | Northwest | | + | | | | Coal Co. | | +123 | Mo. | Morgan | Morgan Co. | Morgan Co. | Mine run | + | | | | Coal Co. | | +124 | Mo. | Putnam | Mendotta | Mendotta No. 8| | +125 | N.Mex.| McKinley | Gallup | Gibson |Pea and Slack| +____|_______|________________|________________|_______________|_____________| + +______________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | + 83 | 7.22 | 33.06 | 53.97 | 12.97 | 11352 | U. S. Geo. S.| + 84 | 4.81 | 41.53 | 39.62 | 18.85 | 10220 | Jones | + 85 | 14.39 | 32.90 | 44.84 | 22.26 | 11059 | B. & W. Co. | + 86 | 15.71 | 38.10 | 41.10 | 20.80 | 10999 | B. & W. Co. | + 87 | 8.17 | 34.33 | 52.50 | 13.17 | 12643 | U. S. Geo. S.| + 88 | 4.66 | 35.65 | 56.86 | 7.49 | 12286 | Univ. of Ill.| + | | | | | | | + 89 | 11.91 | 33.70 | 55.90 | 10.40 | 12932 | B. & W. Co. | + | | | | | | | + 90 | 2.83 | 40.03 | 51.97 | 8.00 | 13375 | Stillman | + 91 | 0.83 | 39.70 | 52.28 | 8.02 | 13248 | Jones | + 92 | 6.17 | 35.42 | 53.55 | 11.03 | 11916 | Dearborn | + 93 | 10.73 | 35.75 | 54.46 | 9.79 | 12911 | B. & W. Co. | + 94 | 10.72 | 44.02 | 46.33 | 9.65 | 11767 | U. S. Geo. S.| + 95 | 16.59 | 42.17 | 48.44 | 9.59 | 13377 | U. S. Geo. S.| + 96 | 2.28 | 34.95 | 50.50 | 14.55 | 11920 | Dearborn | + 97 | 11.62 | 41.17 | 46.76 | 12.07 | 12740 | U. S. Geo. S.| + 98 | 13.48 | 39.40 | 43.09 | 17.51 | 11678 | U. S. Geo. S.| + 99 | 16.01 | 37.82 | 46.24 | 15.94 | 11963 | U. S. Geo. S.| +100 | 14.88 | 41.53 | 39.63 | 18.84 | 11443 | U. S. Geo. S.| +101 | 12.44 | 41.27 | 40.86 | 17.87 | 11671 | U. S. Geo. S.| +102 | 8.69 | 36.23 | 43.68 | 20.09 | 11443 | U. S. Geo. S.| +103 | 4.31 | 33.88 | 53.67 | 12.45 | 13144 | U. S. Geo. S.| + | | | | | | | +104 | 6.16 | 35.56 | 46.90 | 17.54 | 10175 | Jones | +105 | 1.81 | 34.77 | 52.77 | 12.46 | 12557 | Jones | +106 | 4.74 | 36.59 | 47.07 | 16.34 | 10392 | Jones | +107 | 2.89 | 36.67 | 57.24 | 6.09 | 14362 | U. S. Geo. S.| + | | | | | | | +108 | 6.89 | 40.30 | 55.16 | 4.54 | 13381 | St. Col. Ky. | +109 | 7.92 | 40.53 | 48.70 | 10.77 | 13036 | U. S. Geo. S.| +110 | 8.02 | 31.91 | 54.02 | 14.07 | 12448 | B. & W. Co. | +111 | 5.12 | 38.46 | 58.63 | 2.91 | 13743 | U. S. Geo. S.| +112 | 9.22 | 33.94 | 52.18 | 13.88 | 12229 | B. & W. Co. | +113 | 2.80 | 26.54 | 63.58 | 9.88 | 14095 | N. Y. Ed. Co.| +114 | 7.30 | 31.08 | 60.72 | 8.20 | 13600 | B. & W. Co. | +115 | 3.82 | 31.82 | 58.78 | 9.40 | 13175 | B. & W. Co. | +116 | 9.00 | 30.55 | 46.26 | 23.19 | 9889 | B. & W. Co. | +117 | 7.28 | 37.62 | 43.83 | 18.55 | 12109 | U. S. Geo. S.| +118 | 12.45 | 39.39 | 48.47 | 12.14 | 12875 | Univ. of Mo. | + | | | | | | | +119 | 8.58 | 41.78 | 45.99 | 12.23 | 12735 | Univ. of Mo. | +120 | 10.84 | 31.72 | 55.29 | 12.99 | 12500 | Univ. of Mo. | +121 | 9.45 | 36.72 | 52.20 | 11.08 | 13180 | Univ. of Mo. | +122 | 13.09 | 37.83 | 42.95 | 19.22 | 11500 | U. S. Geo. S.| + | | | | | | | +123 | 12.24 | 45.69 | 47.98 | 6.33 | 14197 | U. S. Geo. S.| + | | | | | | | +124 | 20.78 | 39.36 | 50.00 | 10.64 | 12602 | U. S. Geo. S.| +125 | 12.17 | 36.31 | 51.17 | 12.52 | 12126 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | + |_______|________________|________________|_______________|_____________| + | | | | | | +126 | Ohio | Athens | Hocking Valley | Sunday Creek | Slack | +127 | Ohio | Belmont | Pittsburgh | Neff Coal Co. | Mine run | + | | | No. 8 | | | +128 | Ohio | Columbiana | Middle | Palestine | | + | | | Kittanning | | | +129 | Ohio | Coshocton | Middle | Morgan Run | Mine run | + | | | Kittanning | | | +130 | Ohio | Guernsey | Vein No. 7 | Little Kate | | +131 | Ohio | Hocking | Hocking Valley | | Lump | +132 | Ohio | Hocking | Hocking Valley | | | +133 | Ohio | Jackson | Brookville | Superior | Mine run | + | | | | Coal Co. | | +134 | Ohio | Jackson | Lower | Superior | Mine run | + | | | Kittanning | Coal Co. | | +135 | Ohio | Jackson | Quakertown | Wellston | | +136 | Ohio | Jefferson | Pittsburgh | Crow Hollow | 3/4 inch | + | | | or No. 8 | | | +137 | Ohio | Jefferson | Pittsburgh | Rush Run No. 1| 3/4 inch | + | | | or No. 8 | | | +138 | Ohio | Perry | Hocking | Congo | | +139 | Ohio | Stark | Massillon | | Slack | +140 | Ohio | Vinton | Brookville | Clarion | Nut and | + | | | or No. 4 | | Slack | +141 | Okla. | Choctaw | McAlester | Edwards No. 1 | Mine run | +142 | Okla. | Choctaw | McAlester | Adamson | Slack | +143 | Okla. | Creek | | Henrietta | Lump and | + | | | | | Slack | +144 | Pa. | Allegheny | Pittsburgh | | Slack | + | | | 3rd Pool | | | +145 | Pa. | Allegheny | Monongahela | Turtle Creek | | +146 | Pa. | Allegheny | Pittsburgh | Bertha | 3/4 inch | +147 | Pa. | Cambria | | Beach Creek | Slack | +148 | Pa. | Cambria | Miller | Lincoln | Mine run | +149 | Pa. | Clarion | Lower Freeport | | | +150 | Pa. | Fayette | Connellsville | | Slack | +151 | Pa. | Greene | Youghiogheny | | Lump | +152 | Pa. | Greene | Westmoreland | | Screenings | +153 | Pa. | Indiana | | Iselin | Mine run | +154 | Pa. | Jefferson | | Punxsutawney | Mine run | +155 | Pa. | Lawrence | Middle | | | + | | | Kittanning | | | +156 | Pa. | Mercer | Taylor | | | +157 | Pa. | Washington | Pittsburgh | Ellsworth | | +158 | Pa. | Washington | Youghiogheny | Anderson | 3/4 inch | +159 | Pa. | Westmoreland | Pittsburgh | Scott Haven | Lump | +160 | Tenn. | Campbell | Jellico | | | +161 | Tenn. | Claiborne | Mingo | | | +162 | Tenn. | Marion | | Etna | | +163 | Tenn. | Morgan | Brushy Mt. | | | +164 | Tenn. | Scott | Glen Mary No. 4| Glen Mary | | +165 | Tex. | Maverick | | Eagle Pass | | +166 | Tex. | Paolo Pinto | | Thurber | Mine run | +167 | Tex. | Paolo Pinto | | Strawn | Mine run | +168 | Va. | Henrico | | Gayton | | +____|_______|________________|________________|_______________|_____________| + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | +126 | 12.16 | 34.64 | 53.10 | 12.26 | 12214 | | +127 | 5.31 | 38.78 | 52.22 | 9.00 | 12843 | U. S. Geo. S.| + | | | | | | | +128 | 2.15 | 37.57 | 51.80 | 10.63 | 13370 | Lord & Haas | + | | | | | | | +129 | | 41.76 | 45.24 | 13.00 | 13239 | B. & W. Co. | + | | | | | | | +130 | 6.19 | 33.02 | 59.96 | 7.02 | 13634 | B. & W. Co. | +131 | 6.45 | 39.12 | 50.08 | 10.80 | 12700 | Lord & Haas | +132 | 2.60 | 40.80 | 47.60 | 11.60 | 12175 | Jones | +133 | 7.59 | 38.45 | 43.99 | 17.56 | 11704 | U. S. Geo. S.| + | | | | | | | +134 | 8.99 | 41.43 | 50.06 | 8.51 | 13113 | U. S. Geo. S.| + | | | | | | | +135 | 3.38 | 35.26 | 54.18 | 7.56 | 12506 | Hill | +136 | 4.04 | 40.08 | 52.27 | 9.65 | 13374 | U. S. Geo. S.| + | | | | | | | +137 | 4.74 | 36.08 | 54.81 | 9.11 | 13532 | U. S. Geo. S.| + | | | | | | | +138 | 6 41 | 38.33 | 46.71 | 14.96 | 12284 | B. & W. Co. | +139 | 6.67 | 40.02 | 46.46 | 13.52 | 11860 | B. & W. Co. | +140 | 2.47 | 42.38 | 50.39 | 6.23 | 13421 | U. S. Geo. S.| + | | | | | | | +141 | 4.79 | 39.18 | 49.97 | 10.85 | 13005 | U. S. Geo. S.| +142 | 4.72 | 28.54 | 58.17 | 13.29 | 12105 | B. & W. Co. | +143 | 7.65 | 36.77 | 50.14 | 13.09 | 12834 | U. S. Geo. S.| + | | | | | | | +144 | 1.77 | 32.06 | 57.11 | 10.83 | 13205 | Carpenter | + | | | | | | | +145 | 1.75 | 36.85 | 53.94 | 9.21 | 13480 | Lord & Haas | +146 | 2.61 | 35.86 | 57.81 | 6.33 | 13997 | U. S. Geo. S.| +147 | 3.01 | 32.87 | 55.86 | 11.27 | 13755 | B. & W. Co. | +148 | 5.39 | 30.83 | 61.05 | 8.12 | 13600 | B. & W. Co. | +149 | 0.54 | 35.93 | 57.66 | 6.41 | 13547 | | +150 | 1.85 | 28.73 | 63.22 | 7.95 | 13775 | Whitham | +151 | 1.25 | 32.60 | 54.70 | 12.70 | 13100 | B. & W. Co. | +152 | 11.12 | 31.67 | 55.61 | 12.72 | 13100 | P. R. R. | +153 | 2.70 | 29.33 | 63.56 | 7.11 | 14220 | B. & W. Co. | +154 | 3.38 | 29.33 | 64.93 | 5.73 | 14781 | B. & W. Co. | +155 | 0.70 | 37.06 | 56.24 | 6.70 | 13840 | Lord & Haas | + | | | | | | | +156 | 4.18 | 32.19 | 55.55 | 12.26 | 12820 | B. & W. Co. | +157 | 2.46 | 35.35 | 58.46 | 6.19 | 14013 | U. S. Geo. S.| +158 | 1.00 | 39.29 | 54.80 | 5.91 | 13729 | Jones | +159 | 4.06 | 32.91 | 59.78 | 7.31 | 13934 | B. & W. Co. | +160 | 1.80 | 37.76 | 62.12 | 1.12 | 13846 | U. S. Navy | +161 | 4.40 | 34.31 | 59.22 | 6.47 | | U. S. Geo. S.| +162 | 3.16 | 32.98 | 56.59 | 10.43 | | | +163 | 1.77 | 33.46 | 54.73 | 11.87 | 13824 | B. & W. Co. | +164 | 1.53 | 40.80 | 56.78 | 2.42 | 14625 |Ky. State Col.| +165 | 5.42 | 33.73 | 44.89 | 21.38 | 10945 | B. & W. Co. | +166 | 1.90 | 36.01 | 49.09 | 14.90 | 12760 | B. & W. Co. | +167 | 4.19 | 35.40 | 52.98 | 11.62 | 13202 | B. & W. Co. | +168 | 0.82 | 17.14 | 74.92 | 7.94 | 14363 | B. & W. Co. | +____|__________|__________|________|_________|________|______________| + +APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF CERTAIN TYPICAL AMERICAN +COALS--Continued + +____________________________________________________________________________ + | | | | | | + | | | | | | +No. | State | County | Field, Bed | Mine | Size | + | | | or Vein | | | + | | | | | | + | | | | | | + |_______|________________|________________|_______________|_____________| + | | | | | | +169 | Va. | Lee | Darby | Darby | 1-1/2 inch | +170 | Va. | Lee | McConnel | Wilson | Mine run | +171 | Va. | Wise | Upper Banner | Coburn | 3-1/2 inch | +172 | Va. | Rockingham | | Clover Hill | | +173 | Va. | Russel | Clinchfield | | | +174 | Va. | | Monongahela | Bernmont | | +175 | W. Va.| Harrison | Pittsburgh | Ocean | Mine run | +176 | W. Va.| Harrison | | Girard | Nut, Pea | + | | | | | and Slack | +177 | W. Va.| Kanawha | Winifrede | Winifrede | | +178 | W. Va.| Kanawha | Keystone | Keystone | Mine run | +179 | W. Va.| Logan | Island Creek | |Nut and Slack| +180 | W. Va.| Marion | Fairmont | Kingmont | | +181 | W. Va.| Mingo | Thacker | Maritime | | +182 | W. Va.| Mingo | Glen Alum | Glen Alum | Mine run | +183 | W. Va.| Preston | Bakerstown | | | +184 | W. Va.| Putnam | Pittsburgh | Black Betsy | Bug dust | +185 | W. Va.| Randolph | Upper Freeport | Coalton | Lump and Nut| +____|_______|________________|________________|_______________|_____________| + | | | | + | | LIGNITES AND LIGNITIC COALS | | +____|_______|_________________________________________________|_____________| + | | | | | | +186 | Col. | Boulder | | Rex | | +187 | Col. | El Paso | | Curtis | | +188 | Col. | El Paso | | Pike View | | +189 | Col. | Gunnison | South Platte | Mt. Carbon | | +190 | Col. | Las Animas | | Acme | | +191 | Col. | | Lehigh | | | +192 |N. Dak.| McLean | | Eckland | Mine run | +193 |N. Dak.| McLean | | Wilton | Lump | +194 |N. Dak.| McLean | | Casino | | +195 |N. Dak.| Stark | Lehigh | Lehigh | Mine run | +196 |N. Dak.| William | Williston | | Mine run | +197 |N. Dak.| William | Williston | | Mine run | +198 | Tex. | Bastrop | Bastrop | Glenham | | +199 | Tex. | Houston | Crockett | | | +200 | Tex. | Houston | | Houston C. & | | + | | | | C. Co. | | +201 | Tex. | Milam | Rockdale | Worley | | +202 | Tex. | Robertson | Calvert | Coaling No. 1 | | +203 | Tex. | Wood | Hoyt | Consumer's | | + | | | | Lig. Co. | | +204 | Tex. | Wood | Hoyt | | | +205 | Wash. | King | | Black Diamond | | +206 | Wyo. | Carbon | Hanna | | Mine run | +207 | Wyo. | Crook | Black Hills | Stilwell Coal | | + | | | | Co. | | +208 | Wyo. | Sheridan | Sheridan | Monarch | | +209 | Wyo. | Sweetwater | Rock Spring | | Screenings | +210 | Wyo. | Uinta | Adaville | Lazeart | | +____|_______|________________|________________|_______________|_____________| + +_____________________________________________________________________ + | | | | + | Proximate Analysis (Dry Coal) |B. t. u.| | +No. |________________________________________| Per | | + | | | | | Pound | Authority | + | Moisture | Volatile | Fixed | Ash | Dry | | + | | Matter | Carbon | | Coal | | +____|__________|__________|________|_________|________|______________| + | | | | | | | +169 | 4.35 | 38.46 | 56.91 | 4.63 | 13939 | U. S. Geo. S.| +170 | 3.35 | 36.35 | 57.88 | 5.77 | 13931 | U. S. Geo. S.| +171 | 3.05 | 32.65 | 62.73 | 4.62 | 14470 | U. S. Geo. S.| +172 | | 31.77 | 57.98 | 10.25 | 13103 | | +173 | 2.00 | 35.72 | 56.12 | 8.16 | 14200 | | +174 | | 32.00 | 59.90 | 8.10 | 13424 | Carpenter | +175 | 2.47 | 39.35 | 52.78 | 7.87 | 14202 | U. S. Geo. S.| +176 | | 36.66 | 57.49 | 5.85 | 14548 | B. & W. Co. | + | | | | | | | +177 | 1.05 | 32.74 | 64.38 | 2.88 | 14111 | Hill | +178 | 2.21 | 33.29 | 58.61 | 8.10 | 14202 | U. S. Geo. S.| +179 | 1.12 | 38.61 | 55.91 | 5.48 | 14273 | Hill | +180 | 1.90 | 35.31 | 57.34 | 7.35 | 14198 | U. S. Geo. S.| +181 | 0.68 | 31.89 | 63.48 | 4.63 | 14126 | Hill | +182 | 3.02 | 33.81 | 59.45 | 6.74 | 14414 | U. S. Geo. S.| +183 | 4.14 | 29.09 | 63.50 | 7.41 | 14546 | U. S. Geo. S.| +184 | 7.41 | 32.84 | 53.96 | 13.20 | 12568 | B. & W. Co. | +185 | 2.11 | 29.57 | 59.93 | 10.50 | 13854 | U. S. Geo. S.| +____|__________|__________|________|_________|________|______________| + | | | | | | | + | | | | | | | +____|__________|__________|________|_________|________|______________| + | | | | | | | +186 | 16.05 | 42.12 | 47.97 | 9.91 | 10678 | B. & W. Co. | +187 | 23.25 | 42.11 | 49.38 | 8.51 | 11090 | B. & W. Co. | +188 | 23.77 | 48.70 | 41.47 | 9.83 | 10629 | B. & W. Co. | +189 | 20.38 | 46.38 | 47.50 | 6.12 | | | +190 | 16.74 | 47.90 | 44.60 | 7.50 | |Col. Sc. of M.| +191 | 18.30 | 45.29 | 44.67 | 10.04 | | | +192 | 29.65 | 45.56 | 47.05 | 7.39 | 10553 | Lord | +193 | 35.96 | 49.84 | 38.05 | 12.11 | 11036 | U. S. Geo. S.| +194 | 29.65 | 46.56 | 38.70 | 14.74 | | Lord | +195 | 35.84 | 43.84 | 39.59 | 16.57 | 10121 | U. S. Geo. S.| +196 | 41.76 | 39.37 | 48.09 | 12.54 | 10121 | B. & W. Co. | +197 | 42.74 | 40.83 | 47.79 | 11.38 | 10271 | B. & W. Co. | +198 | 32.77 | 42.76 | 36.88 | 20.36 | 8958 | B. & W. Co. | +199 | 23.27 | 40.95 | 38.37 | 20.68 | 10886 | U. S. Geo. S.| +200 | 31.48 | 46.93 | 34.40 | 18.87 | 10176 | B. & W. Co. | + | | | | | | | +201 | 32.48 | 43.04 | 41.14 | 15.82 | 10021 | B. & W. Co. | +202 | 32.01 | 43.70 | 43.08 | 13.22 | 10753 | B. & W. Co. | +203 | 33.98 | 46.97 | 41.40 | 11.63 | 10600 | U. S. Geo. S.| + | | | | | | | +204 | 30.25 | 43.27 | 41.46 | 15.27 | 10597 | | +205 | 3.71 | 48.72 | 46.56 | 4.72 | | Gale | +206 | 6.44 | 51.32 | 43.00 | 5.68 | 11607 | B. & W. Co. | +207 | 19.08 | 45.21 | 46.42 | 8.37 | 12641 | U. S. Geo. S.| + | | | | | | | +208 | 21.18 | 51.87 | 40.43 | 7.70 | 12316 | U. S. Geo. S.| +209 | 7.70 | 38.57 | 56.99 | 4.44 | 12534 | B. & W. Co. | +210 | 19.15 | 45.50 | 48.11 | 6.39 | 9868 | U. S. Geo. S.| +____|__________|__________|________|_________|________|______________| + +[Illustration: Portion of 12,080 Horse-power Installation of Babcock & +Wilcox Boilers and Superheaters at the Potomac Electric Co., Washington, +D. C.] + + TABLE 39 + + SHOWING RELATION BETWEEN PROXIMATE AND ULTIMATE ANALYSES OF COAL + +========================================================================= +| | | | Common in | +| | | |Proximate &| +| | Proximate | | Ultimate | +| | Analysis | Ultimate Analysis | Analysis | +|--------------------|-----------|--------------------------|-----------| +| | | | V | | | H | | N | | | M | +| | | | o | | | y | | i | S | | o | +| | | | l M | C | C | d | O | t | u | | i | +| S | | | a a | F a | a | r | x | r | l | | s | +| t | | | t t | i r | r | o | y | o | p | | t | +| a | Field | | i t | x b | b | g | g | g | h | A | u | +| t | or | | l e | e o | o | e | e | e | e | s | r | +| e | Bed | Mine | e r | d n | n | n | n | n | r | h | e | +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| | |Icy Coal| | | | | | | | | | +| | | & Iron | | | | | | | | | | +| | Horse | Co. | | | | | | | | | | +|Ala| Creek | No. 8 |31.81|53.90|72.02|4.78| 6.45|1.66| .80|14.29| 2.56| +|---|----------------|-----|-----|-----|----|-----|----|----|-----|-----| +| | |Central | | | | | | | | | | +| | |C. & C. | | | | | | | | | | +| | Hunt- | Co. | | | | | | | | | | +|Ark|ington | No. 3 |18.99|67.71|76.37|3.90| 3.71|1.49|1.23|13.30| 1.99| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| | Pana | Clover | | | | | | | | | | +| | or | Leaf, | | | | | | | | | | +|Ill| No. 5 | No. 1 |37.22|45.64|63.04|4.49|10.04|1.28|4.01|17.14|13.19| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |No. 5, | | | | | | | | | | | +| |Warrick| | | | | | | | | | | +|Ind| Co. |Electric|41.85|44.45|68.08|4.78| 7.56|1.35|4.53|13.70| 9.11| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |No. 11,| St. | | | | | | | | | | +| |Hopkins|Bernard,| | | | | | | | | | +|Ky | Co. | No. 11 |41.10|49.60|72.22|5.06| 8.44|1.33|3.65| 9.30| 7.76| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |"B" or | | | | | | | | | | | +| |Lower | | | | | | | | | | | +| |Kittan-| Eureka,| | | | | | | | | | +|Pa | ning | No. 31 |16.71|77.22|84.45|4.25| 3.04|1.28| .91| 6.07| .56| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +| |Indiana| | | | | | | | | | | +|Pa | Co. | |29.55|62.64|79.86|5.02| 4.27|1.86|1.18| 7.81| 2.90| +|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| +|W. | Fire | Rush | | | | | | | | | | +|Va | Creek | Run |22.87|71.56|83.71|4.64| 3.67|1.70| .71| 5.57| 2.14| +========================================================================= + +Table 39 gives for comparison the ultimate and proximate analyses of +certain of the coals with which tests were made in the coal testing +plant of the United States Geological Survey at the Louisiana Purchase +Exposition at St. Louis. + +The heating value of a fuel cannot be directly computed from a proximate +analysis, due to the fact that the volatile content varies widely in +different fuels in composition and in heating value. + +Some methods have been advanced for estimating the calorific value of +coals from the proximate analysis. William Kent[38] deducted from +Mahler's tests of European coals the approximate heating value dependent +upon the content of fixed carbon in the combustible. The relation as +deduced by Kent between the heat and value per pound of combustible and +the per cent of fixed carbon referred to combustible is represented +graphically by Fig. 23. + +Goutal gives another method of determining the heat value from a +proximate analysis, in which the carbon is given a fixed value and the +heating value of the volatile matter is considered as a function of its +percentage referred to combustible. Goutal's method checks closely with +Kent's determinations. + +All the formulae, however, for computing the calorific value of coals +from a proximate analysis are ordinarily limited to certain classes of +fuels. Mr. Kent, for instance, states that his deductions are correct +within a close limit for fuels containing more than 60 per cent of fixed +carbon in the combustible, while for those containing a lower +percentage, the error may be as great as 4 per cent, either high or low. + +While the use of such computations will serve where approximate results +only are required, that they are approximate should be thoroughly +understood. + +Calorimetry--An ultimate or a proximate analysis of a fuel is useful in +determining its general characteristics, and as described on page 183, +may be used in the calculation of the approximate heating value. Where +the efficiency of a boiler is to be computed, however, this heating +value should in all instances be determined accurately by means of a +fuel calorimeter. + +[Graph: B.T.U. per Pound of Combustible +against Per Cent of Fixed Carbon in Combustible + +Fig. 23. Graphic Representation of Relation between Heat Value Per Pound +of Combustible and Fixed Carbon in Combustible as Deduced by Wm. Kent.] + +In such an apparatus the fuel is completely burned and the heat +generated by such combustion is absorbed by water, the amount of heat +being calculated from the elevation in the temperature of the water. A +calorimeter which has been accepted as the best for such work is one in +which the fuel is burned in a steel bomb filled with compressed oxygen. +The function of the oxygen, which is ordinarily under a pressure of +about 25 atmospheres, is to cause the rapid and complete combustion of +the fuel sample. The fuel is ignited by means of an electric current, +allowance being made for the heat produced by such current, and by the +burning of the fuse wire. + +A calorimeter of this type which will be found to give satisfactory +results is that of M. Pierre Mahler, illustrated in Fig. 24 and +consisting of the following parts: + +A water jacket A, which maintains constant conditions outside of the +calorimeter proper, and thus makes possible a more accurate computation +of radiation losses. + +The porcelain lined steel bomb B, in which the combustion of the fuel +takes place in compressed oxygen. + +[Illustration: Fig. 24. Mahler Bomb Calorimeter] + +The platinum pan C, for holding the fuel. + +The calorimeter proper D, surrounding the bomb and containing a definite +weighed amount of water. + +An electrode E, connecting with the fuse wire F, for igniting the fuel +placed in the pan C. + +A support G, for a water agitator. + +A thermometer I, for temperature determination of the water in the +calorimeter. The thermometer is best supported by a stand independent of +the calorimeter, so that it may not be moved by tremors in the parts of +the calorimeter, which would render the making of readings difficult. To +obtain accuracy of readings, they should be made through a telescope or +eyeglass. + +A spring and screw device for revolving the agitator. + +A lever L, by the movement of which the agitator is revolved. + +A pressure gauge M, for noting the amount of oxygen admitted to the +bomb. Between 20 and 25 atmospheres are ordinarily employed. + +An oxygen tank O. + +A battery or batteries P, the current from which heats the fuse wire +used to ignite the fuel. + +This or a similar calorimeter is used in the determination of the heat +of combustion of solid or liquid fuels. Whatever the fuel to be tested, +too much importance cannot be given to the securing of an average +sample. Where coal is to be tested, tests should be made from a portion +of the dried and pulverized laboratory sample, the methods of obtaining +which have been described. In considering the methods of calorimeter +determination, the remarks applied to coal are equally applicable to any +solid fuel, and such changes in methods as are necessary for liquid +fuels will be self-evident from the same description. + +Approximately one gram of the pulverized dried coal sample should be +placed directly in the pan of the calorimeter. There is some danger in +the using of a pulverized sample from the fact that some of it may be +blown out of the pan when oxygen is admitted. This may be at least +partially overcome by forming about two grams into a briquette by the +use of a cylinder equipped with a plunger and a screw press. Such a +briquette should be broken and approximately one gram used. If a +pulverized sample is used, care should be taken to admit oxygen slowly +to prevent blowing the coal out of the pan. The weight of the sample is +limited to approximately one gram since the calorimeter is proportioned +for the combustion of about this weight when under an oxygen pressure of +about 25 atmospheres. + +A piece of fine iron wire is connected to the lower end of the plunger +to form a fuse for igniting the sample. The weight of iron wire used is +determined, and if after combustion a portion has not been burned, the +weight of such portion is determined. In placing the sample in the pan, +and in adjusting the fuse, the top of the calorimeter is removed. It is +then replaced and carefully screwed into place on the bomb by means of a +long handled wrench furnished for the purpose. + +The bomb is then placed in the calorimeter, which has been filled with a +definite amount of water. This weight is the "water equivalent" of the +apparatus, _i. e._, the weight of water, the temperature of which would +be increased one degree for an equivalent increase in the temperature of +the combined apparatus. It may be determined by calculation from the +weights and specific heats of the various parts of the apparatus. Such a +determination is liable to error, however, as the weight of the bomb +lining can only be approximated, and a considerable portion of the +apparatus is not submerged. Another method of making such a +determination is by the adding of definite weights of warm water to +definite amounts of cooler water in the calorimeter and taking an +average of a number of experiments. The best method for the making of +such a determination is probably the burning of a definite amount of +resublimed naphthaline whose heat of combustion is known. + +The temperature of the water in the water jacket of the calorimeter +should be approximately that of the surrounding atmosphere. The +temperature of the weighed amount of water in the calorimeter is made by +some experimenters slightly greater than that of the surrounding air in +order that the initial correction for radiation will be in the same +direction as the final correction. Other experimenters start from a +temperature the same or slightly lower than the temperature of the room, +on the basis that the temperature after combustion will be slightly +higher than the room temperature and the radiation correction be either +a minimum or entirely eliminated. + +While no experiments have been made to show conclusively which of these +methods is the better, the latter is generally used. + +After the bomb has been placed in the calorimeter, it is filled with +oxygen from a tank until the pressure reaches from 20 to 25 atmospheres. +The lower pressure will be sufficient in all but exceptional cases. +Connection is then made to a current from the dry batteries in series so +arranged as to allow completion of the circuit with a switch. The +current from a lighting system should not be used for ignition, as there +is danger from sparking in burning the fuse, which may effect the +results. The apparatus is then ready for the test. + +Unquestionably the best method of taking data is by the use of +co-ordinate paper and a plotting of the data with temperatures and time +intervals as ordinates and abscissae. Such a graphic representation is +shown in Fig. 25. + +[Graph: Temperature--deg. C. against Time--Hours and Minutes + +Fig. 25. Graphic Method of Recording Bomb Calorimeter Results] + +After the bomb is placed in the calorimeter, and before the coal is +ignited, readings of the temperature of the water should be taken at one +minute intervals for a period long enough to insure a constant rate of +change, and in this way determine the initial radiation. The coal is +then ignited by completing the circuit, the temperature at the instant +the circuit is closed being considered the temperature at the beginning +of the combustion. After ignition the readings should be taken at +one-half minute intervals, though because of the rapidity of the +mercury's rise approximate readings only may be possible for at least a +minute after the firing, such readings, however, being sufficiently +accurate for this period. The one-half minute readings should be taken +after ignition for five minutes, and for, say, five minutes longer at +minute intervals to determine accurately the final rate of radiation. + +Fig. 25 shows the results of such readings, plotted in accordance with +the method suggested. It now remains to compute the results from this +plotted data. + +The radiation correction is first applied. Probably the most accurate +manner of making such correction is by the use of Pfaundler's method, +which is a modification of that of Regnault. This assumes that in +starting with an initial rate of radiation, as represented by the +inclination of the line AB, Fig. 25, and ending with a final radiation +represented by the inclination of the line CD, Fig. 25, that the rate of +radiation for the intermediate temperatures between the points B and C +are proportional to the initial and final rates. That is, the rate of +radiation at a point midway between B and C will be the mean between the +initial and final rates; the rate of radiation at a point three-quarters +of the distance between B and C would be the rate at B plus +three-quarters of the difference in rates at B and C, etc. This method +differs from Regnault's in that the radiation was assumed by Regnault to +be in each case proportional to the difference in temperatures between +the water of the calorimeter and the surrounding air plus a constant +found for each experiment. Pfaundler's method is more simple than that +of Regnault, and the results by the two methods are in practical +agreement. + +Expressed as a formula, Pfaundler's method is, though not in form given +by him: + + _ _ + | R' - R | +C = N|R + ------ (T" - T)| (19) + |_ T' - T _| + +Where C = correction in degree centigrade, + N = number of intervals over which correction is made, + R = initial radiation in degrees per interval, + R' = final radiation in degrees per interval, + T = average temperature for period through which initial radiation + is computed, + T" = average temperature over period of combustion[39], + T' = average temperature over period through which final radiation + is computed.[39] + +The application of this formula to Fig. 25 is as follows: + +As already stated, the temperature at the beginning of combustion is the +reading just before the current is turned on, or B in Fig. 25. The point +C or the temperature at which combustion is presumably completed, should +be taken at a point which falls well within the established final rate +of radiation, and not at the maximum temperature that the thermometer +indicates in the test, unless it lies on the straight line determining +the final radiation. This is due to the fact that in certain instances +local conditions will cause the thermometer to read higher than it +should during the time that the bomb is transmitting heat to the water +rapidly, and at other times the maximum temperature might be lower than +that which would be indicated were readings to be taken at intervals of +less than one-half minute, _i. e._, the point of maximum temperature +will fall below the line determined by the final rate of radiation. With +this understanding AB, Fig. 25, represents the time of initial +radiation, BC the time of combustion, and CD the time of final +radiation. Therefore to apply Pfaundler's correction, formula (19), to +the data as represented by Fig. 25. + +N = 6, R = 0, R' = .01, T = 20.29, T' = 22.83, + + 20.29 + 22.54 + 22.84 + 22.88 + 22.87 + 22.86 +T" = --------------------------------------------- = 22.36 + 6 + + _ _ + | .01 - 0 | +C = 6|0 + -------------(22.36 - 20.29)| + |_ 22.85 - 20.29 _| + + = 6 x .008 = .048 + +Pfaundler's formula while simple is rather long. Mr. E. H. Peabody has +devised a simpler formula with which, under proper conditions, the +variation from correction as found by Pfaundler's method is negligible. + +It was noted throughout an extended series of calorimeter tests that the +maximum temperature was reached by the thermometer slightly over one +minute after the time of firing. If this period between the time of +firing and the maximum temperature reported was exactly one minute, the +radiation through this period would equal the radiation per one-half +minute _before firing_ plus the radiation per one-half minute _after the +maximum temperature is reached_; or, the radiation through the one +minute interval would be the average of the radiation per minute before +firing and the radiation per minute after the maximum. A plotted chart +of temperatures would take the form of a curve of three straight lines +(B, C', D) in Fig. 25. Under such conditions, using the notation as in +formula (19) the correction would become, + + 2R + 2R' +C = ------- + (N - 2)R', or R + (N - 1)R' (20) + 2 + +This formula may be generalized for conditions where the maximum +temperature is reached after a period of more than one minute as +follows: + +Let M = the number of intervals between the time of firing and the +maximum temperature. Then the radiation through this period will be an +average of the radiation for M intervals before firing and for M +intervals after the maximum is recorded, or + + MR + MR' M M +C = ------- + (N - M)R' = - R + (N - -)R' (21) + 2 2 2 + +In the case of Mr. Peabody's deductions M was found to be approximately +2 and formula (21) becomes directly, C = R + (N - 1)R' or formula (20). + +The corrections to be made, as secured by the use of this formula, are +very close to those secured by Pfaundler's method, where the point of +maximum temperature is not more than five intervals later than the point +of firing. Where a longer period than this is indicated in the chart of +plotted temperatures, the approximate formula should not be used. As the +period between firing and the maximum temperature is increased, the +plotted results are further and further away from the theoretical +straight line curve. Where this period is not over five intervals, or +two and a half minutes, an approximation of the straight line curve may +be plotted by eye, and ordinarily the radiation correction to be applied +may be determined very closely from such an approximated curve. + +Peabody's approximate formula has been found from a number of tests to +give results within .003 degrees Fahrenheit for the limits within which +its application holds good as described. The value of M, which is not +necessarily a whole number, should be determined for each test, though +in all probability such a value is a constant for any individual +calorimeter which is properly operated. + +The correction for radiation as found on page 188 is in all instances to +be added to the range of temperature between the firing point and the +point chosen from which the final radiation is calculated. This +corrected range multiplied by the water equivalent of the calorimeter +gives the heat of combustion in calories of the coal burned in the +calorimeter together with that evolved by the burning of the fuse wire. +The heat evolved by the burning of the fuse wire is found from the +determination of the actual weight of wire burned and the heat of +combustion of one milligram of the wire (1.7 calories), _i. e._, +multiply the weight of wire used by 1.7, the result being in gram +calories or the heat required to raise one gram of water one degree +centigrade. + +Other small corrections to be made are those for the formation of nitric +acid and for the combustion of sulphur to sulphuric acid instead of +sulphur dioxide, due to the more complete combustion in the presence of +oxygen than would be possible in the atmosphere. + +To make these corrections the bomb of the calorimeter is carefully +washed out with water after each test and the amount of acid determined +from titrating this water with a standard solution of ammonia or of +caustic soda, all of the acid being assumed to be nitric acid. Each +cubic centimeter of the ammonia titrating solution used is equivalent to +a correction of 2.65 calories. + +As part of acidity is due to the formation of sulphuric acid, a further +correction is necessary. In burning sulphuric acid the heat evolved per +gram of sulphur is 2230 calories in excess of the heat which would be +evolved if the sulphur burned to sulphur dioxide, or 22.3 calories for +each per cent of sulphur in the coal. One cubic centimeter of the +ammonia solution is equivalent to 0.00286 grams of sulphur as sulphuric +acid, or to 0.286 x 22.3 = 6.38 calories. It is evident therefore that +after multiplying the number of cubic centimeters used in titrating by +the heat factor for nitric acid (2.65) a further correction of +6.38 - 2.65 = 3.73 is necessary for each cubic centimeter used in +titrating sulphuric instead of nitric acid. This correction will be +3.73/0.297 = 13 units for each 0.01 gram of sulphur in the coal. + +The total correction therefore for the aqueous nitric and sulphuric acid +is found by multiplying the ammonia by 2.65 and adding 13 calories for +each 0.01 gram of sulphur in the coal. This total correction is to be +deducted from the heat value as found from the corrected range and the +amount equivalent to the calorimeter. + +After each test the pan in which the coal has been burned must be +carefully examined to make sure that all of the sample has undergone +complete combustion. The presence of black specks ordinarily indicates +unburned coal, and often will be found where the coal contains bone or +slate. Where such specks are found the tests should be repeated. In +testing any fuel where it is found difficult to completely consume a +sample, a weighed amount of naphthaline may be added, the total weight +of fuel and naphthaline being approximately one gram. The naphthaline +has a known heat of combustion, samples for this purpose being +obtainable from the United States Bureau of Standards, and from the +combined heat of combustion of the fuel and naphthaline that of the +former may be readily computed. + +The heat evolved in burning of a definite weight of standard naphthaline +may also be used as a means of calibrating the calorimeter as a whole. + + + + +COMBUSTION OF COAL + + +The composition of coal varies over such a wide range, and the methods +of firing have to be altered so greatly to suit the various coals and +the innumerable types of furnaces in which they are burned, that any +instructions given for the handling of different fuels must of necessity +be of the most general character. For each kind of coal there is some +method of firing which will give the best results for each individual +set of conditions. General rules can be suggested, but the best results +can be obtained only by following such methods as experience and +practice show to be the best suited to the specific conditions. + +The question of draft is an all important factor. If this be +insufficient, proper combustion is impossible, as the suction in the +furnace will not be great enough to draw the necessary amount of air +through the fuel bed, and the gases may pass off only partially +consumed. On the other hand, an excessive draft may cause losses due to +the excess quantities of air drawn through holes in the fire. Where coal +is burned however, there are rarely complaints from excessive draft, as +this can be and should be regulated by the boiler damper to give only +the draft necessary for the particular rate of combustion desired. The +draft required for various kinds of fuel is treated in detail in the +chapter on "Chimneys and Draft". In this chapter it will be assumed that +the draft is at all times ample and that it is regulated to give the +best results for each kind of coal. + + + TABLE 40 + + ANTHRACITE COAL SIZES + + _________________________________________________________________ +| | | | +| | | Testing Segments | +| | Round Mesh | Standard Square | +| | | Mesh | +| Trade Name |__________________|__________________| +| | | | | | +| | Through | Over | Through | Over | +| | Inches | Inches | Inches | Inches | +|___________________________|_________|________|_________|________| +| | | | | | +| Broken | 4-1/2 | 3-1/4 | 4 | 2-3/4 | +| Egg | 3-1/4 | 2-3/8 | 2-3/4 | 2 | +| Stove | 2-3/8 | 1-5/8 | 2 | 1-3/8 | +| Chestnut | 1-5/8 | 7/8 | 1-3/8 | 3/4 | +| Pea | 7/8 | 5/8 | 3/4 | 1/2 | +| No. 1 Buckwheat | 5/8 | 3/8 | 1/2 | 1/4 | +| No. 2 Buckwheat or Rice | 3/8 | 3/16 | 1/4 | 1/8 | +| No. 3 Buckwheat or Barley | 3/16 | 3/32 | 1/8 | 1/16 | +|___________________________|_________|________|_________|________| + +Anthracite--Anthracite coal is ordinarily marketed under the names and +sizes given in Table 40. + +The larger sizes of anthracite are rarely used for commercial steam +generating purposes as the demand for domestic use now limits the +supply. In commercial plants the sizes generally found are Nos. 1, 2 and +3 buckwheat. In some plants where the finer sizes are used, a small +percentage of bituminous coal, say, 10 per cent, is sometimes mixed with +the anthracite and beneficial results secured both in economy and +capacity. + +Anthracite coal should be fired evenly, in small quantities and at +frequent intervals. If this method is not followed, dead spots will +appear in the fire, and if the fire gets too irregular through burning +in patches, nothing can be done to remedy it until the fire is cleaned +as a whole. After this grade of fuel has been fired it should be left +alone, and the fire tools used as little as possible. Owing to the +difficulty of igniting this fuel, care must be taken in cleaning fires. +The intervals of cleaning will, of course, depend upon the nature of the +coal and the rate of combustion. With the small sizes and moderately +high combustion rates, fires will have to be cleaned twice on each +eight-hour shift. As the fires become dirty the thickness of the fuel +bed will increase, until this depth may be 12 or 14 inches just before a +cleaning period. In cleaning, the following practice is usually +followed: The good coal on the forward half of the grate is pushed to +the rear half, and the refuse on the front portion either pulled out or +dumped. The good coal is then pulled forward onto the front part of the +grate and the refuse on the rear section dumped. The remaining good coal +is then spread evenly over the whole grate surface and the fire built up +with fresh coal. + +A ratio of grate surface to heating surface of 1 to from 35 to 40 will +under ordinary conditions develop the rated capacity of a boiler when +burning anthracite buckwheat. Where the finer sizes are used, or where +overloads are desirable, however, this ratio should preferably be 1 to +25 and a forced blast should be used. Grates 10 feet deep with a slope +of 1-1/2 inches to the foot can be handled comfortably with this class of +fuel, and grates 12 feet deep with the same slope can be successfully +handled. Where grates over 8 feet in depth are necessary, shaking grates +or overlapping dumping grates should be used. Dumping grates may be +applied either for the whole grate surface or to the rear section. Air +openings in the grate bars should be made from 3/16 inch in width for +No. 3 buckwheat to 5/16 inch for No. 1 buckwheat. It is important that +these air openings be uniformly distributed over the whole surface to +avoid blowing holes in the fire, and it is for this reason that +overlapping grates are recommended. + +No air should be admitted over the fire. Steam is sometimes introduced +into the ashpit to soften any clinker that may form, but the quantity of +steam should be limited to that required for this purpose. The steam +that may be used in a steam jet blower for securing blast will in +certain instances assist in softening the clinker, but a much greater +quantity may be used by such an apparatus than is required for this +purpose. Combustion arches sprung above the grates have proved of +advantage in maintaining a high furnace temperature and in assisting in +the ignition of fresh coal. + +Stacks used with forced blast should be of such size as to insure a +slight suction in the furnace under any conditions of operation. A blast +up to 3 inches of water should be available for the finer sizes supplied +by engine driven fans, automatically controlled by the boiler pressure. +The blast required will increase as the depth of the fuel bed increases, +and the slight suction should be maintained in the furnace by damper +regulation. + +The use of blast with the finer sizes causes rapid fouling of the +heating surfaces of the boiler, the dust often amounting to over 10 per +cent of the total fuel fired. Economical disposal of dust and ashes is +of the utmost importance in burning fuel of this nature. Provision +should be made in the baffling of the boiler to accommodate and dispose +of this dust. Whenever conditions permit, the ashes can be economically +disposed of by flushing them out with water. + +Bituminous Coals--There is no classification of bituminous coal as to +size that holds good in all localities. The American Society of +Mechanical Engineers suggests the following grading: + + +_Eastern Bituminous Coals_-- + +(A) Run of mine coal; the unscreened coal taken from the mine. + +(B) Lump coal; that which passes over a bar-screen with openings 1-1/4 + inches wide. + +(C) Nut coal; that which passes through a bar-screen with 1-1/4-inch + openings and over one with 3/4-inch openings. + +(D) Slack coal; that which passes through a bar-screen with 3/4-inch + openings. + + +_Western Bituminous Coals_-- + +(E) Run of mine coal; the unscreened coal taken from the mine. + +(F) Lump coal; divided into 6-inch, 3-inch and 1-1/4-inch lump, according + to the diameter of the circular openings over which the respective + grades pass; also 6 x 3-inch lump and 3 x 1-1/4-inch lump, according as + the coal passes through a circular opening having the diameter of + the larger figure and over that of the smaller diameter. + +(G) Nut coal; divided into 3-inch steam nut, which passes through an + opening 3 inches diameter and over 1-1/4 inches; 1-1/4 inch nut, which + passes through a 1-1/4-inch diameter opening and over a 3/4-inch + diameter opening; 3/4-inch nut, which passes through a 3/4-inch + diameter opening and over a 5/8-inch diameter opening. + +(H) Screenings; that which passes through a 1-1/4-inch diameter opening. + + +As the variation in character of bituminous coals is much greater than +in the anthracites, any rules set down for their handling must be the +more general. The difficulties in burning bituminous coals with economy +and with little or no smoke increases as the content of fixed carbon in +the coal decreases. It is their volatile content which causes the +difficulties and it is essential that the furnaces be designed to +properly handle this portion of the coal. The fixed carbon will take +care of itself, provided the volatile matter is properly burned. + +Mr. Kent, in his "Steam Boiler Economy", described the action of +bituminous coal after it is fired as follows: "The first thing that the +fine fresh coal does is to choke the air spaces existing through the bed +of coke, thus shutting off the air supply which is needed to burn the +gases produced from the fresh coal. The next thing is a very rapid +evaporation of moisture from the coal, a chilling process, which robs +the furnace of heat. Next is the formation of water-gas by the chemical +reaction, C + H_{2}O = CO + 2H, the steam being decomposed, its oxygen +burning the carbon of the coal to carbonic oxide, and the hydrogen being +liberated. This reaction takes place when steam is brought in contact +with highly heated carbon. This also is a chilling process, absorbing +heat from the furnaces. The two valuable fuel gases thus generated would +give back all the heat absorbed in their formation if they could be +burned, but there is not enough air in the furnace to burn them. +Admitting extra air through the fire door at this time will be of no +service, for the gases being comparatively cool cannot be burned unless +the air is highly heated. After all the moisture has been driven off +from the coal, the distillation of hydrocarbons begins, and a +considerable portion of them escapes unburned, owing to the deficiency +of hot air, and to their being chilled by the relatively cool heating +surfaces of the boiler. During all this time great volumes of smoke are +escaping from the chimney, together with unburned hydrogen, +hydrocarbons, and carbonic oxide, all fuel gases, while at the same time +soot is being deposited on the heating surface, diminishing its +efficiency in transmitting heat to the water." + +To burn these gases distilled from the coal, it is necessary that they +be brought into contact with air sufficiently heated to cause them to +ignite, that sufficient space be allowed for their mixture with the air, +and that sufficient time be allowed for their complete combustion before +they strike the boiler heating surfaces, since these surfaces are +comparatively cool and will lower the temperature of the gases below +their ignition point. The air drawn through the fire by the draft +suction is heated in its passage and heat is added by radiation from the +hot brick surfaces of the furnace, the air and volatile gases mixing as +this increase in temperature is taking place. Thus in most instances is +the first requirement fulfilled. The element of space for the proper +mixture of the gases with the air, and of time in which combustion is to +take place, should be taken care of by sufficiently large combustion +chambers. + +Certain bituminous coals, owing to their high volatile content, require +that the air be heated to a higher temperature than it is possible for +it to attain simply in its passage through the fire and by absorption +from the side walls of the furnace. Such coals can be burned with the +best results under fire brick arches. Such arches increase the +temperature of the furnace and in this way maintain the heat that must +be present for ignition and complete combustion of the fuels in +question. These fuels too, sometimes require additional combustion +space, and an extension furnace will give this in addition to the +required arches. + +As stated, the difficulty of burning bituminous coals successfully will +increase with the increase in volatile matter. This percentage of +volatile will affect directly the depth of coal bed to be carried and +the intervals of firing for the most satisfactory results. The variation +in the fuel over such wide ranges makes it impossible to definitely +state the thickness of fires for all classes, and experiment with the +class of fuel in use is the best method of determining how that +particular fuel should be handled. The following suggestions, which are +not to be considered in any sense hard and fast rules, may be of service +for general operating conditions for hand firing: + +Semi-bituminous coals, such as Pocahontas, New River, Clearfield, etc., +require fires from 10 to 14 inches thick; fresh coal should be fired at +intervals of 10 to 20 minutes and sufficient coal charged at each firing +to maintain a uniform thickness. Bituminous coals from Pittsburgh Region +require fires from 4 to 6 inches thick, and should be fired often in +comparatively small charges. Kentucky, Tennessee, Ohio and Illinois +coals require a thickness from 4 to 6 inches. Free burning coals from +Rock Springs, Wyoming, require from 6 to 8 inches, while the poorer +grades of Montana, Utah and Washington bituminous coals require a depth +of about 4 inches. + +In general as thin fires are found necessary, the intervals of firing +should be made more frequent and the quantity of coal fired at each +interval smaller. As thin fires become necessary due to the character of +the coal, the tendency to clinker will increase if the thickness be +increased over that found to give the best results. + +There are two general methods of hand firing: 1st, the spreading method; +and 2nd, the coking method. + +[Illustration: Babcock & Wilcox Chain Grate Stoker] + +In the spreading method but little fuel is fired at one time, and is +spread evenly over the fuel bed from front to rear. Where there is more +than one firing door the doors should be fired alternately. The +advantage of alternate firing is the whole surface of the fire is not +blanketed with green coal, and steam is generated more uniformly than if +all doors were fired at one time. Again, a better combustion results due +to the burning of more of the volatile matter directly after firing than +where all doors are fired at one time. + +In the coking method, fresh coal is fired at considerable depth at the +front of the grate and after it is partially coked it is pushed back +into the furnace. The object of such a method is the preserving of a bed +of carbon at the rear of the grate, in passing over which the volatile +gases driven off from the green coal will be burned. This method is +particularly adaptable to a grate in which the gases are made to pass +horizontally over the fire. Modern practice for hand firing leans more +and more toward the spread firing method. Again the tendency is to work +bituminous coal fires less than formerly. A certain amount of slicing +and raking may be necessary with either method of firing, but in +general, the less the fire is worked the better the results. + +Lignites--As the content of volatile matter and moisture in lignite is +higher than in bituminous coal, the difficulties encountered in burning +them are greater. A large combustion space is required and the best +results are obtained where a furnace of the reverberatory type is used, +giving the gases a long travel before meeting the tube surfaces. A fuel +bed from 4 to 6 inches in depth can be maintained, and the coal should +be fired in small quantities by the alternate method. Above certain +rates of combustion clinker forms rapidly, and a steam jet in the ashpit +for softening this clinker is often desirable. A considerable draft +should be available, but it should be carefully regulated by the boiler +damper to suit the condition of the fire. Smokelessness with hand firing +with this class of fuel is a practical impossibility. It has a strong +tendency to foul the heating surfaces rapidly and these surfaces should +be cleaned frequently. Shaking grates, intelligently handled, aid in +cleaning the fires, but their manipulation must be carefully watched to +prevent good coal being lost in the ashpit. + +Stokers--The term "automatic stoker" oftentimes conveys the erroneous +impression that such an apparatus takes care of itself, and it must be +thoroughly understood that any stoker requires expert attention to as +high if not higher degree than do hand-fired furnaces. + +Stoker-fired furnaces have many advantages over hand firing, but where a +stoker installation is contemplated there are many factors to be +considered. It is true that stokers feed coal to the fire automatically, +but if the coal has first to be fed to the stoker hopper by hand, its +automatic advantage is lost. This is as true of the removal of ash from +a stoker. In a general way, it may be stated that a stoker installation +is not advantageous except possibly for diminishing smoke, unless the +automatic feature is carried to the handling of the coal and ash, as +where coal and ash handling apparatus is not installed there is no +saving in labor. In large plants, however, stokers used in conjunction +with the modern methods of coal storage and coal and ash handling, make +possible a large labor saving. In small plants the labor saving for +stokers over hand-fired furnaces is negligible, and the expense of the +installation no less proportionately than in large plants. Stokers are, +therefore, advisable in small plants only where the saving in fuel will +be large, or where the smoke question is important. + +Interest on investment, repairs, depreciation and steam required for +blast and stoker drive must all be considered. The upkeep cost will, in +general, be higher than for hand-fired furnaces. Stokers, however, make +possible the use of cheaper fuels with as high or higher economy than is +obtainable under operating conditions in hand-fired furnaces with a +better grade of fuel. The better efficiency obtainable with a good +stoker is due to more even and continuous firing as against the +intermittent firing of hand-fired furnaces; constant air supply as +against a variation in this supply to meet varying furnace conditions in +hand-fired furnaces; and the doing away to a great extent with the +necessity of working the fires. + +Stokers under ordinary operating conditions will give more nearly +smokeless combustion than will hand-fired furnaces and for this reason +must often be installed regardless of other considerations. While a +constant air supply for a given power is theoretically secured by the +use of a stoker, and in many instances the draft is automatically +governed, the air supply should, nevertheless, be as carefully watched +and checked by flue gas analyses as in the case of hand-fired furnaces. + +There is a tendency in all stokers to cause the loss of some good fuel +or siftings in the ashpit, but suitable arrangements may be made to +reclaim this. + +In respect to efficiency of combustion, other conditions being equal, +there will be no appreciable difference with the different types of +stokers, provided that the proper type is used for the grade of fuel to +be burned and the conditions of operation to be fulfilled. No stoker +will satisfactorily handle all classes of fuel, and in making a +selection, care should be taken that the type is suited to the fuel and +the operating conditions. A cheap stoker is a poor investment. Only the +best stoker suited to the conditions which are to be met should be +adopted, for if there is to be a saving, it will more than cover the +cost of the best over the cheaper stoker. + +Mechanical Stokers are of three general types: 1st, overfeed; 2nd, +underfeed; and 3rd, traveling grate. The traveling grate stokers are +sometimes classed as overfeed but properly should be classed by +themselves as under certain conditions they are of the underfeed rather +than the overfeed type. + +Overfeed Stokers in general may be divided into two classes, the +distinction being in the direction in which the coal is fed relative to +the furnaces. In one class the coal is fed into hoppers at the front end +of the furnace onto grates with an inclination downward toward the rear +of about 45 degrees. These grates are reciprocated, being made to take +alternately level and inclined positions and this motion gradually +carries the fuel as it is burned toward the rear and bottom of the +furnace. At the bottom of the grates flat dumping sections are supplied +for completing the combustion and for cleaning. The fuel is partly +burned or coked on the upper portion of the grates, the volatile gases +driven off in this process for a perfect action being ignited and burned +in their passage over the bed of burning carbon lower on the grates, or +on becoming mixed with the hot gases in the furnace chamber. In the +second class the fuel is fed from the sides of the furnace for its full +depth from front to rear onto grates inclined toward the center of the +furnace. It is moved by rocking bars and is gradually carried to the +bottom and center of the furnace as combustion advances. Here some type +of a so-called clinker breaker removes the refuse. + +Underfeed Stokers are either horizontal or inclined. The fuel is fed +from underneath, either continuously by a screw, or intermittently by +plungers. The principle upon which these stokers base their claims for +efficiency and smokelessness is that the green fuel is fed under the +coked and burning coal, the volatile gases from this fresh fuel being +heated and ignited in their passage through the hottest portion of the +fire on the top. In the horizontal classes of underfeed stokers, the +action of a screw carries the fuel back through a retort from which it +passes upward, as the fuel above is consumed, the ash being finally +deposited on dead plates on either side of the retort, from which it can +be removed. In the inclined class, the refuse is carried downward to the +rear of the furnace where there are dumping plates, as in some of the +overfeed types. + +Underfeed stokers are ordinarily operated with a forced blast, this in +some cases being operated by the same mechanism as the stoker drive, +thus automatically meeting the requirements of various combustion rates. + +Traveling Grates are of the class best illustrated by chain grate +stokers. As implied by the name these consist of endless grates composed +of short sections of bars, passing over sprockets at the front and rear +of the furnace. Coal is fed by gravity onto the forward end of the +grates through suitable hoppers, is ignited under ignition arches and is +carried with the grate toward the rear of the furnace as its combustion +progresses. When operated properly, the combustion is completed as the +fire reaches the end of the grate and the refuse is carried over this +rear end by the grate in making the turn over the rear sprocket. In some +cases auxiliary dumping grates at the rear of the chain grates are used +with success. + +Chain grate stokers in general produce less smoke than either overfeed +or underfeed types, due to the fact that there are no cleaning periods +necessary. Such periods occur with the latter types of stokers at +intervals depending upon the character of the fuel used and the rate of +combustion. With chain grate stokers the cleaning is continuous and +automatic, and no periods occur when smoke will necessarily be produced. + +In the earlier forms, chain grates had an objectionable feature in that +the admission of large amounts of excess air at the rear of the furnace +through the grates was possible. This objection has been largely +overcome in recent models by the use of some such device as the bridge +wall water box and suitable dampers. A distinct advantage of chain +grates over other types is that they can be withdrawn from the furnace +for inspection or repairs without interfering in any way with the boiler +setting. + +This class of stoker is particularly successful in burning low grades of +coal running high in ash and volatile matter which can only be burned +with difficulty on the other types. The cost of up-keep in a chain +grate, properly constructed and operated, is low in comparison with the +same cost for other stokers. + +The Babcock & Wilcox chain grate is representative of this design of +stoker. + +Smoke--The question of smoke and smokelessness in burning fuels has +recently become a very important factor of the problem of combustion. +Cities and communities throughout the country have passed ordinances +relative to the quantities of smoke that may be emitted from a stack, +and the failure of operators to live up to the requirements of such +ordinances, resulting as it does in fines and annoyance, has brought +their attention forcibly to the matter. + +The whole question of smoke and smokelessness is to a large extent a +comparative one. There are any number of plants burning a wide variety +of fuels in ordinary hand-fired furnaces, in extension furnaces and on +automatic stokers that are operating under service conditions, +practically without smoke. It is safe to say, however, that no plant +will operate smokelessly under any and all conditions of service, nor is +there a plant in which the degree of smokelessness does not depend +largely upon the intelligence of the operating force. + +[Illustration: Fig. 26. Babcock & Wilcox Boiler and Superheater Equipped +with Babcock & Wilcox Chain Grate Stoker. This Setting has been +Particularly Successful in Minimizing Smoke] + +When a condition arises in a boiler room requiring the fires to be +brought up quickly, the operatives in handling certain types of stokers +will use their slice bars freely to break up the green portion of the +fire over the bed of partially burned coal. In fact, when a load is +suddenly thrown on a station the steam pressure can often be maintained +only in this way, and such use of the slice bar will cause smoke with +the very best type of stoker. In a certain plant using a highly volatile +coal and operating boilers equipped with ordinary hand-fired furnaces, +extension hand-fired furnaces and stokers, in which the boilers with the +different types of furnaces were on separate stacks, a difference in +smoke from the different types of furnaces was apparent at light loads, +but when a heavy load was thrown on the plant, all three stacks would +smoke to the same extent, and it was impossible to judge which type of +furnace was on one or the other of the stacks. + +In hand-fired furnaces much can be accomplished by proper firing. A +combination of the alternate and spreading methods should be used, the +coal being fired evenly, quickly, lightly and often, and the fires +worked as little as possible. Smoke can be diminished by giving the +gases a long travel under the action of heated brickwork before they +strike the boiler heating surfaces. Air introduced over the fires and +the use of heated arches, etc., for mingling the air with the gases +distilled from the coal will also diminish smoke. Extension furnaces +will undoubtedly lessen smoke where hand firing is used, due to the +increase in length of gas travel and the fact that this travel is +partially under heated brickwork. Where hand-fired grates are +immediately under the boiler tubes, and a high volatile coal is used, if +sufficient combustion space is not provided the volatile gases, +distilled as soon as the coal is thrown on the fire, strike the tube +surfaces and are cooled below the burning point before they are wholly +consumed and pass through as smoke. With an extension furnace, these +volatile gases are acted upon by the radiant heat from the extension +furnace arch and this heat, together with the added length of travel +causes their more complete combustion before striking the heating +surfaces than in the former case. + +Smoke may be diminished by employing a baffle arrangement which gives +the gases a fairly long travel under heated brickwork and by introducing +air above the fire. In many cases, however, special furnaces for smoke +reduction are installed at the expense of capacity and economy. + +From the standpoint of smokelessness, undoubtedly the best results are +obtained with a good stoker, properly operated. As stated above, the +best stoker will cause smoke under certain conditions. Intelligently +handled, however, under ordinary operating conditions, stoker-fired +furnaces are much more nearly smokeless than those which are hand fired, +and are, to all intents and purposes, smokeless. In practically all +stoker installations there enters the element of time for combustion, +the volatile gases as they are distilled being acted upon by ignition or +other arches before they strike the heating surfaces. In many instances +too, stokers are installed with an extension beyond the boiler front, +which gives an added length of travel during which, the gases are acted +upon by the radiant heat from the ignition or supplementary arches, and +here again we see the long travel giving time for the volatile gases to +be properly consumed. + +To repeat, it must be emphatically borne in mind that the question of +smokelessness is largely one of degree, and dependent to an extent much +greater than is ordinarily appreciated upon the handling of the fuel and +the furnaces by the operators, be these furnaces hand fired or +automatically fired. + +[Illustration: 3520 Horse-power Installation of Babcock & Wilcox Boilers +at the Portland Railway, Light and Power Co., Portland, Ore. These +Boilers are Equipped with Wood Refuse Extension Furnaces at the Front +and Oil Burning Furnaces at the Mud Drum End] + + + + +SOLID FUELS OTHER THAN COAL AND THEIR COMBUSTION + + +Wood--Wood is vegetable tissue which has undergone no geological change. +Usually the term is used to designate those compact substances +familiarly known as tree trunks and limbs. When newly cut, wood contains +moisture varying from 30 per cent to 50 per cent. When dried for a +period of about a year in the atmosphere, the moisture content will be +reduced to 18 or 20 per cent. + + TABLE 41 + +ULTIMATE ANALYSES AND CALORIFIC VALUES OF DRY WOOD (GOTTLIEB) + + _______________________________________________________ +| | | | | | | | +| Kind | | | | | | B. t. u.| +| of | C | H | N | O | Ash | per | +| Wood | | | | | | Pound | +|________|_______|______|______|_______|______|_________| +| | | | | | | | +| Oak | 50.16 | 6.02 | 0.09 | 43.36 | 0.37 | 8316 | +| Ash | 49.18 | 6.27 | 0.07 | 43.91 | 0.57 | 8480 | +| Elm | 48.99 | 6.20 | 0.06 | 44.25 | 0.50 | 8510 | +| Beech | 49.06 | 6.11 | 0.09 | 44.17 | 0.57 | 8391 | +| Birch | 48.88 | 6.06 | 0.10 | 44.67 | 0.29 | 8586 | +| Fir | 50.36 | 5.92 | 0.05 | 43.39 | 0.28 | 9063 | +| Pine | 50.31 | 6.20 | 0.04 | 43.08 | 0.37 | 9153 | +| Poplar | 49.37 | 6.21 | 0.96 | 41.60 | 1.86 | 7834[40]| +| Willow | 49.96 | 5.96 | 0.96 | 39.56 | 3.37 | 7926[40]| +|________|_______|______|______|_______|______|_________| + +Wood is usually classified as hard wood, including oak, maple, hickory, +birch, walnut and beech; and soft wood, including pine, fir, spruce, +elm, chestnut, poplar and willow. Contrary to general opinion, the heat +value per pound of soft wood is slightly greater than the same value per +pound of hard wood. Table 41 gives the chemical composition and the heat +values of the common woods. Ordinarily the heating value of wood is +considered equivalent to 0.4 that of bituminous coal. In considering the +calorific value of wood as given in this table, it is to be remembered +that while this value is based on air-dried wood, the moisture content +is still about 20 per cent of the whole, and the heat produced in +burning it will be diminished by this amount and by the heat required to +evaporate the moisture and superheat it to the temperature of the gases. +The heat so absorbed may be calculated by the formula giving the loss +due to moisture in the fuel, and the net calorific value determined. + +In designing furnaces for burning wood, the question resolves itself +into: 1st, the essential elements to give maximum capacity and +efficiency with this class of fuel; and 2nd, the construction which will +entail the least labor in handling and feeding the fuel and removing the +refuse after combustion. + +Wood, as used commercially for steam generating purposes, is usually a +waste product from some industrial process. At the present time refuse +from lumber and sawmills forms by far the greater part of this class of +fuel. In such refuse the moisture may run as high as 60 per cent and the +composition of the fuel may vary over wide ranges during different +portions of the mill operation. The fuel consists of sawdust, "hogged" +wood and slabs, and the percentage of each of these constituents may +vary greatly. Hogged wood is mill refuse and logs that have been passed +through a "hogging machine" or macerator. This machine, through the +action of revolving knives, cuts or shreds the wood into a state in +which it may readily be handled as fuel. + +Table 42 gives the moisture content and heat value of typical sawmill +refuse from various woods. + + TABLE 42 + + MOISTURE AND CALORIFIC VALUE OF SAWMILL REFUSE + _____________________________________________________________________ +| | | | | +| | | Per Cent | B. t. u. | +| Kind of Wood | Nature of Refuse | Moisture | per Pound | +| | | | Dry Fuel | +|_____________________|_______________________|__________|____________| +| | | | | +| Mexican White Pine | Sawdust and Hog Chips | 51.90 | 9020 | +| Yosemite Sugar Pine | Sawdust and Hog Chips | 62.85 | 9010 | +| Redwood 75%, | Sawdust, Box Mill | | | +| Douglas Fir 25% | Refuse and Hog | 42.20 | 8977[41] | +| Redwood | Sawdust and Hog Chips | 52.98 | 9040[41] | +| Redwood | Sawdust and Hog Chips | 49.11 | 9204[41] | +| Fir, Hemlock, | | | | +| Spruce and Cedar | Sawdust | 42.06 | 8949[41] | +|_____________________|_______________________|__________|____________| + +It is essential in the burning of this class of fuel that a large +combustion space be supplied, and on account of the usually high +moisture content there should be much heated brickwork to radiate heat +to the fuel bed and thus evaporate the moisture. Extension furnaces of +the proper size are usually essential for good results and when this +fuel is used alone, grates dropped to the floor line with an ashpit +below give additional volume for combustion and space for maintaining a +thick fuel bed. A thick fuel bed is necessary in order to avoid +excessive quantities of air passing through the boiler. Where the fuel +consists of hogged wood and sawdust alone, it is best to feed it +automatically into the furnace through chutes on the top of the +extension. The best results are secured when the fuel is allowed to pile +up in the furnace to a height of 3 or 4 feet in the form of a cone under +each chute. The fuel burns best when not disturbed in the furnace. Each +fuel chute, when a proper distance from the grates and with the piles +maintained at their proper height, will supply about 30 or 35 square +feet of grate surface. While large quantities of air are required for +burning this fuel, excess air is as harmful as with coal, and care must +be taken that such an excess is not admitted through fire doors or fuel +chutes. A strong natural draft usually is preferable to a blast with +this fuel. The action of blast is to make the regulation of the furnace +conditions more difficult and to blow over unconsumed fuel on the +heating surfaces and into the stack. This unconsumed fuel settling in +portions of the setting out of the direct path of the gases will have a +tendency to ignite provided any air reaches it, with results harmful to +the setting and breeching connection. This action is particularly +objectionable if these particles are carried over into the base of a +stack, where they will settle below the point at which the flue enters +and if ignited may cause the stack to become overheated and buckle. + +Whether natural draft or blast is used, much of the fuel is carried onto +the heating surfaces and these should be cleaned regularly to maintain a +good efficiency. Collecting chambers in various portions of the setting +should be provided for this unconsumed fuel, and these should be kept +clean. + +With proper draft conditions, 150 pounds of this fuel containing about +30 to 40 per cent of moisture can be burned per square foot of grate +surface per hour, and in a properly designed furnace one square foot of +grate surface can develop from 5 to 6 boiler horse power. Where the wood +contains 50 per cent of moisture or over, it is not usually safe to +figure on obtaining more than 3 to 4 horse power per square foot of +grate surface. + +Dry sawdust, chips and blocks are also used as fuel in many wood-working +industries. Here, as with the wet wood, ample combustion space should be +supplied, but as this fuel is ordinarily kiln dried, large brickwork +surfaces in the furnace are not necessary for the evaporation of +moisture in the fuel. This fuel may be burned in extension furnaces +though these are not required unless they are necessary to secure an +added furnace volume, to get in sufficient grate surface, or where such +an arrangement must be used to allow for a fuel bed of sufficient +thickness. Depth of fuel bed with the dry fuel is as important as with +the moist fuel. If extension furnaces are used with this dry wood, care +must be taken in their design that there is no excessive throttling of +the gases in the furnace, or brickwork trouble will result. In Babcock & +Wilcox boilers this fuel may be burned without extension furnaces, +provided that the boilers are set at a sufficient height to provide +ample combustion space and to allow for proper depth of fuel bed. +Sometimes this is gained by lowering the grates to the floor line and +excavating for an ashpit. Where the fuel is largely sawdust, it may be +introduced over the fire doors through inclined chutes. The old methods +of handling and collecting sawdust by means of air suction and blast +were such that the amount of air admitted through such chutes was +excessive, but with improved methods the amount of air so admitted may +be reduced to a negligible quantity. The blocks and refuse which cannot +be handled through chutes may be fired through fire doors in the front +of the boiler, which should be made sufficiently large to accommodate +the larger sizes of fuel. As with wet fuel, there will be a quantity of +unconsumed wood carried over and the heating surfaces must be kept +clean. + +In a few localities cord wood is burned. With this as with other classes +of wood fuel, a large combustion space is an essential feature. The +percentage of moisture in cord wood may make it necessary to use an +extension furnace, but ordinarily this is not required. Ample combustion +space is in most cases secured by dropping the grates to the floor line, +large double-deck fire doors being supplied at the usual fire door level +through which the wood is thrown by hand. Air is admitted under the +grates through an excavated ashpit. The side, front and rear walls of +the furnace should be corbelled out to cover about one-third of the +total grate surface. This prevents cold air from laneing up the sides of +the furnace and also reduces the grate surface. Cord wood and slabs form +an open fire through which the frictional loss of the air is much less +than in the case of sawdust or hogged material. The combustion rate with +cord wood is, therefore, higher and the grate surface may be +considerably reduced. Such wood is usually cut in lengths of 4 feet or 4 +feet 6 inches, and the depth of the grates should be kept approximately +5 feet to get the best results. + +Bagasse--Bagasse is the refuse of sugar cane from which the juice has +been extracted by pressure between the rolls of the mill. From the start +of the sugar industry bagasse has been considered the natural fuel for +sugar plantations, and in view of the importance of the industry a word +of history relative to the use of this fuel is not out of place. + +When the manufacture of sugar was in its infancy the cane was passed +through but a single mill and the defecation and concentration of the +saccharine juice took place in a series of vessels mounted one after +another over a common fire at one end and connected to a stack at the +opposite end. This primitive method was known in the English colonies as +the "Open Wall" and in the Spanish-American countries as the "Jamaica +Train". + +The evaporation and concentration of the juice in the open air and over +a direct fire required such quantities of fuel, and the bagasse, in +fact, played such an important part in the manufacture of sugar, that +oftentimes the degree of extraction, which was already low, would be +sacrificed to the necessity of obtaining a bagasse that might be readily +burned. + +The furnaces in use with these methods were as primitive as the rest of +the apparatus, and the bagasse could be burned in them only by first +drying it. This naturally required an enormous quantity of handling of +the fuel in spreading and collecting and frequently entailed a shutting +down of the mill, because a shower would spoil the supply which had been +dried. + +The difficulties arising from the necessity of drying this fuel caused a +widespread attempt on the part of inventors to the turning out of a +furnace which would successfully burn green bagasse. Some of the designs +were more or less clever, and about the year 1880 several such green +bagasse furnaces were installed. These did not come up to expectations, +however, and almost invariably they were abandoned and recourse had to +be taken to the old method of drying in the sun. + +From 1880 the new era in the sugar industry may be dated. Slavery was +almost universally abolished and it became necessary to pay for labor. +The cost of production was thus increased, while growing competition of +European beet sugar lowered the prices. The only remedy for the new +state of affairs was the cheapening of the production by the increase of +extraction and improvement in manufacture. The double mill took the +place of the single, the open wall method of extraction was replaced by +vacuum evaporative apparatus and centrifugal machines were introduced to +do the work of the great curing houses. As opposed to these +improvements, however, the steam plants remained as they started, +consisting of double flue boilers externally fired with dry bagasse. + +On several of the plantations horizontal multitubular boilers externally +fired were installed and at the time were considered the acme of +perfection. Numerous attempts were made to burn the bagasse green, among +others the step grates imported from Louisiana and known as the Leon +Marie furnaces, but satisfactory results were obtained in none of the +appliances tried. + +The Babcock & Wilcox Co. at this time turned their attention to the +problem with the results which ultimately led to its solution. Their New +Orleans representative, Mr. Frederick Cook, invented a hot forced blast +bagasse furnace and conveyed the patent rights to this company. This +furnace while not as efficient as the standard of to-day, and expensive +in its construction, did, nevertheless, burn the bagasse green and +enabled the boilers to develop their normal rated capacity. The first +furnace of this type was installed at the Southwood and Mt. Houmas +plantations and on a small plantation in Florida. About the year 1888 +two furnaces were erected in Cuba, one on the plantation Senado and the +other at the Central Hormiguero. The results obtained with these +furnaces were so remarkable in comparison with what had previously been +accomplished that the company was overwhelmed with orders. The expense +of auxiliary fuel, usually wood, which was costly and indispensable in +rainy weather, was done away with and as the mill could be operated on +bagasse alone, the steam production and the factory work could be +regulated with natural increase in daily output. + +Progress and improvement in the manufacture itself was going on at a +remarkable rate, the single grinding had been replaced by a double +grinding, this in turn by a third grinding, and finally the maceration +and dilution of the bagasse was carried to the extraction of practically +the last trace of sugar contained in it. The quantity of juice to be +treated was increased in this way 20 or 30 per cent but was accompanied +by the reduction to a minimum of the bagasse available as a fuel, and +led to demands upon the furnace beyond its capacity. + +With the improvements in the manufacture, planters had been compelled to +make enormous sacrifices to change radically their systems, and the +heavy disbursement necessary for mill apparatus left few in a financial +position to make costly installations of good furnaces. The necessity of +turning to something cheap in furnace construction but which was +nevertheless better than the early method of burning the fuel dry led to +the invention of numerous furnaces by all classes of engineers +regardless of their knowledge of the subject and based upon no +experience. None of the furnaces thus produced were in any sense +inventions but were more or less barefaced infringements of the patents +of The Babcock & Wilcox Co. As the company could not protect its rights +without hurting its clients, who in many cases against their own will +were infringing upon these patents, and as on the other hand they were +anxious to do something to meet the wants of the planters, a series of +experiments were started, at their own rather than at their customers' +expense, with a view to developing a furnace which, without being as +expensive, would still fulfill all the requirements of the manufacturer. +The result was the cold blast green bagasse furnace which is now +offered, and it has been adopted as standard for this class of work +after years of study and observation in our installations in the sugar +countries of the world. Such a furnace is described later in considering +the combustion of bagasse. + +Composition and Calorific Value of Bagasse--The proportion of fiber +contained in the cane and density of the juice are important factors in +the relation the bagasse fuel will have to the total fuel necessary to +generate the steam required in a mill's operation. A cane rich in wood +fiber produces more bagasse than a poor one and a thicker juice is +subject to a higher degree of dilution than one not so rich. + +Besides the percentage of bagasse in the cane, its physical condition +has a bearing on its calorific value. The factors here entering are the +age at which the cane must be cut, the locality in which it is grown, +etc. From the analysis of any sample of bagasse its approximate +calorific value may be calculated from the formula, + + 8550F + 7119S + 6750G - 972W +B. t. u. per pound bagasse = ---------------------------- (22) + 100 + +Where F = per cent of fiber in cane, S = per cent sucrose, G = per cent +glucose, W = per cent water. + +This formula gives the total available heat per pound of bagasse, that +is, the heat generated per pound less the heat required to evaporate its +moisture and superheat the steam thus formed to the temperature of the +stack gases. + +Three samples of bagasse in which the ash is assumed to be 3 per cent +give from the formula: + +F = 50 S and G = 4.5 W = 42.5 B. t. u. = 4183 +F = 40 S and G = 6.0 W = 51.0 B. t. u. = 3351 +F = 33.3 S and G = 7.0 W = 56.7 B. t. u. = 2797 + +A sample of Java bagasse having F = 46.5, S = 4.50, G = 0.5, W = 47.5 +gives B. t. u. 3868. + +These figures show that the dryer the bagasse is crushed, the higher the +calorific value, though this is accompanied by a decrease in sucrose. +The explanation lies in the fact that the presence of sucrose in an +analysis is accompanied by a definite amount of water, and that the +residual juice contains sufficient organic substance to evaporate the +water present when a fuel is burned in a furnace. For example, assume +the residual juice (100 per cent) to contain 12 per cent organic matter. +From the constant in formula, + +12x7119 (100-12)x972 +------- = 854.3 and ------------ = 855.4. + 100 100 + +That is, the moisture in a juice containing 12 per cent of sugar will be +evaporated by the heat developed by the combustion of the contained +sugar. It would, therefore, appear that a bagasse containing such juice +has a calorific value due only to its fiber content. This is, of course, +true only where the highest products of oxidization are formed during +the combustion of the organic matter. This is not strictly the case, +especially with a bagasse of a high moisture content which will not burn +properly but which smoulders and produces a large quantity of products +of destructive distillation, chiefly heavy hydrocarbons, which escape +unburnt. The reasoning, however, is sufficient to explain the steam +making properties of bagasse of a low sucrose content, such as are +secured in Java, as when the sucrose content is lower, the heat value is +increased by extracting more juice, and hence more sugar from it. The +sugar operations in Java exemplify this and show that with a high +dilution by maceration and heavy pressure the bagasse meets all of the +steam requirements of the mills without auxiliary fuel. + +A high percentage of silica or salts in bagasse has sometimes been +ascribed as the reason for the tendency to smoulder in certain cases of +soft fiber bagasse. This, however, is due to the large moisture content +of the sample resulting directly from the nature of the cane. Soluble +salts in the bagasse has also been given as the explanation of such +smouldering action of the fire, but here too the explanation lies solely +in the high moisture content, this resulting in the development of only +sufficient heat to evaporate the moisture. + + TABLE 43 + + ANALYSES AND CALORIFIC VALUES OF BAGASSE ++---------------------------------------------------------------------+ +|+----------+--------+-------+-------+-------+-------+-------+-------+| +|| | | | | | | |B.t.u. || +|| | | | | | | | per || +|| Source |Moisture| C | H | O | N | Ash | Pound || +|| | | | | | | | Dry || +|| | | | | | | |Bagasse|| +|+----------+--------+-------+-------+-------+-------+-------+-------+| +||Cuba | 51.50 | 43.15 | 6.00 | 47.95 | | 2.90 | 7985 || +||Cuba | 49.10 | 43.74 | 6.08 | 48.61 | | 1.57 | 8300 || +||Cuba | 42.50 | 43.61 | 6.06 | 48.45 | | 1.88 | 8240 || +||Cuba | 51.61 | 46.80 | 5.34 | 46.35 | | 1.51 | || +||Cuba | 52.80 | 46.78 | 5.74 | 45.38 | | 2.10 | || +||Porto Rico| 41.60 | 44.28 | 6.66 | 47.10 | 0.41 | 1.35 | 8359 || +||Porto Rico| 43.50 | 44.21 | 6.31 | 47.72 | 0.41 | 1.35 | 8386 || +||Porto Rico| 44.20 | 44.92 | 6.27 | 46.50 | 0.41 | 1.90 | 8380 || +||Louisiana | 52.10 | | | | | 2.27 | 8230 || +||Louisiana | 54.00 | | | | | | 8370 || +||Louisiana | 51.80 | | | | | | 8371 || +||Java | | 46.03 | 6.56 | 45.55 | 0.18 | 1.68 | 8681 || +|+----------+--------+-------+-------+-------+-------+-------+-------+| ++---------------------------------------------------------------------+ + +Table 43 gives the analyses and heat values of bagasse from various +localities. Table 44 gives the value of mill bagasse at different +extractions, which data may be of service in making approximations as to +its fuel value as compared with that of other fuels. + + TABLE 44 + + VALUE OF ONE POUND OF MILL BAGASSE AT DIFFERENT EXTRACTIONS + + 1: Per Cent Extraction of Weight of Cane + 2: Per Cent Moisture in Bagasse + 3: Per Cent in Bagasse + 4: Fuel Value, B. t. u. + 5: Per Cent in Bagasse + 6: Fuel Value, B. t. u. + 7: Per Cent in Bagasse + 8: Fuel Value, B. t. u. + 9: Total Heat Developed per Pound of Bagasse +10: Heat Required to Evaporate Moisture[42] +11: Heat Available for Steam Generation +12: Pounds of Bagasse Equivalent to one Pound of Coal of 14,000 B. t. u. + ++----------------------------------------------------------------+ +|+---+-----+----------+---------+---------+----------------+----+| +|| | | | | |B.t.u. Value per| || +|| | | Fiber | Sugar |Molasses |Pound of Bagasse| || +|| | +-----+----+----+----+----+----+-----+----+-----+ || +|| | | | | | | | | | | | || +|| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 || +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +|| BASED UPON CANE OF 12 PER CENT FIBER AND JUICE CONTAINING || +||18 PER CENT OF SOLID MATTER. REPRESENTING TROPICAL CONDITIONS || +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +||75 |42.64|48.00|3996|6.24|451 |3.12|217 |4664 |525 |4139 |3.38|| +||77 |39.22|52.17|4343|5.74|414 |2.87|200 |4958 |483 |4475 |3.13|| +||79 |35.15|57.14|4757|5.14|371 |2.57|179 |5307 |433 |4874 |2.87|| +||81 |30.21|63.16|5258|4.42|319 |2.21|154 |5731 |372 |5359 |2.61|| +||83 |24.12|70.59|5877|3.53|256 |1.76|122 |6255 |297 |5958 |2.35|| +||85 |16.20|80.00|6660|2.40|173 |1.20| 83 |6916 |200 |6716 |2.08|| +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +|| BASED UPON CANE OF 10 PER CENT FIBER AND JUICE CONTAINING || +||15 PER CENT OF SOLID MATTER. REPRESENTING LOUISIANA CONDITIONS|| +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +||75 |51.00|40.00|3330|6.00|433 |3.00|209 |3972 |678 |3294 |4.25|| +||77 |48.07|43.45|3617|5.66|409 |2.82|196 |4222 |592 |3630 |3.86|| +||79 |44.52|47.62|3964|5.24|378 |2.62|182 |4524 |548 |3976 |3.52|| +||81 |40.18|52.63|4381|4.73|342 |2.36|164 |4887 |495 |4392 |3.19|| +||83 |35.00|58.82|4897|4.12|298 |2.06|143 |5436 |431 |5005 |2.80|| +||85 |28.33|66.67|5550|3.33|241 |1.67|116 |5907 |349 |5558 |2.52|| +|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| ++----------------------------------------------------------------+ + +Furnace Design and the Combustion of Bagasse--With the advance in sugar +manufacture there came, as described, a decrease in the amount of +bagasse available for fuel. As the general efficiency of a plant of this +description is measured by the amount of auxiliary fuel required per ton +of cane, the relative importance of the furnace design for the burning +of this fuel is apparent. + +In modern practice, under certain conditions of mill operation, and with +bagasse of certain physical properties, the bagasse available from the +cane ground will meet the total steam requirements of the plant as a +whole; such conditions prevail, as described, in Java. In the United +States, Cuba, Porto Rico and like countries, however, auxiliary fuel is +almost universally a necessity. The amount will vary, depending to a +great extent upon the proportion of fiber in the cane, which varies +widely with the locality and with the age at which it is cut, and to a +lesser extent upon the degree of purity of the manufactured sugar, the +use of the maceration water and the efficiency of the mill apparatus as +a whole. + +[Illustration: Fig. 27. Babcock & Wilcox Boiler Set with Green Bagasse +Furnace] + +Experience has shown that this fuel may be burned with the best results +in large quantities. A given amount of bagasse burned in one furnace +between two boilers will give better results than the same quantity +burned in a number of smaller furnaces. An objection has been raised +against such practice on the grounds that the necessity of shutting down +two boiler units when it is necessary for any reason to take off a +furnace, requires a larger combined boiler capacity to insure continuity +of service. As a matter of fact, several small furnaces will cost +considerably more than one large furnace, and the saving in original +furnace cost by such an installation, taken in conjunction with the +added efficiency of the larger furnace over the small, will probably +more than offset the cost of additional boiler units for spares. + +The essential features in furnace design for this class of fuel are +ample combustion space and a length of gas travel sufficient to enable +the gases to be completely burned before the boiler heating surfaces are +encountered. Experience has shown that better results are secured where +the fuel is burned on a hearth rather than on grates, the objection to +the latter method being that the air for combustion enters largely +around the edges, where the fuel pile is thinnest. When burned on a +hearth the air for combustion is introduced into the furnace through +several rows of tuyeres placed above and symmetrically around the +hearth. An arrangement of such tuyeres over a grate, and a proper +manipulation of the ashpit doors, will overcome largely the objection to +grates and at the same time enable other fuel to be burned in the +furnace when necessary. This arrangement of grates and tuyeres is +probably the better from a commercially efficient standpoint. Where the +air is admitted through tuyeres over the grate or hearth line, it +impinges on the fuel pile as a whole and causes a uniform combustion. +Such tuyeres connect with an annular space in which, where a blast is +used, the air pressure is controlled by a blower. + +All experience with this class of fuel indicates that the best results +are secured with high combustion rates. With a natural draft in the +furnace of, say, three-tenths inch of water, a combustion rate of from +250 to 300 pounds per square foot of grate surface per hour may be +obtained. With a blast of, say, five-tenths inch of water, this rate can +be increased to 450 pounds per square foot of grate surface per hour. +These rates apply to bagasse as fired containing approximately 50 per +cent of moisture. It would appear that the most economical results are +secured with a combustion rate of approximately 300 pounds per square +foot per hour which, as stated, may be obtained with natural draft. +Where a natural draft is available sufficient to give such a rate, it is +in general to be preferred to a blast. + +Fig. 27 shows a typical bagasse furnace with which very satisfactory +results have been obtained. The design of this furnace may be altered to +suit the boilers to which it is connected. It may be changed slightly in +its proportions and in certain instances in its position relative to the +boiler. The furnace as shown is essentially a bagasse furnace and may be +modified somewhat to accommodate auxiliary fuel. + +The fuel is ignited in a pit A on a hearth which is ordinarily +elliptical in shape. Air for combustion is admitted through the tuyeres +B connected to an annular space C through which the amount of air is +controlled. Above the pit the furnace widens out to form a combustion +space D which has a cylindrical or spherical roof with its top +ordinarily from 11 to 13 feet above the floor. The gases pass from this +space horizontally to a second combustion chamber E from which they are +led through arches F to the boiler. The arrangement of such arches is +modified to suit the boiler or boilers with which the furnace is +operated. A furnace of such design embodies the essential features of +ample combustion space and long gas travel. + +The fuel should be fed to the furnace through an opening in the roof +above the pit by some mechanical means which will insure a constant fuel +feed and at the same time prevent the inrush of cold air into the +furnace. + +This class of fuel deposits a considerable quantity of dust, which if +not removed promptly will fuse into a hard glass-like clinker. Ample +provision should be made for the removal of such dust from the furnace, +the gas ducts and the boiler setting, and these should be thoroughly +cleaned once in 24 hours. + +Table 45 gives the results of several tests on Babcock & Wilcox boilers +using fuel of this character. + + TABLE 45 + + TESTS OF BABCOCK & WILCOX BOILERS WITH GREEN BAGASSE + ____________________________________________________________________ +| Duration of Test | Hours | 12 | 10 | 10 | 10 | +| Rated Capacity of Boiler |Horse Power| 319 | 319 | 319 | 319 | +| Grate Surface |Square Feet| 33 | 33 | 16.5 | 16.5 | +| Draft in Furnace | Inches | .30 | .28 | .29 | .27 | +| Draft at Damper | Inches | .47 | .45 | .46 | .48 | +| Blast under Grates | Inches | ... | ... | ... | .34 | +| Temperature of Exit Gases | Degrees F.| 536 | 541 | 522 | 547 | +| /CO_{2} | Per Cent | 13.8 | 12.6 | 11.7 | 12.8 | +| Flue Gas Analysis { O | Per Cent | 5.9 | 7.6 | 8.2 | 6.9 | +| \CO | Per Cent | 0.0 | 0.0 | 0.0 | 0.0 | +| Bagasse per Hour as Fired | Pounds | 4980 | 4479 | 5040 | 5586 | +| Moisture in Bagasse | Per Cent |52.39 |52.93 |51.84 |51.71 | +| Dry Bagasse per Hour | Pounds | 2371 | 2108 | 2427 | 2697 | +| Dry Bagasse per Square Foot| | | | | | +| of Grate Surface per Hour| Pounds | 71.9 | 63.9 |147.1 |163.4 | +| Water per Hour from and at | | | | | | +| 212 Degrees | Pounds |10141 | 9850 |10430 |11229 | +| Per Cent of Rated Capacity | | | | | | +| Developed | Per Cent | 92.1 | 89.2 | 94.7 |102.0 | +|____________________________|___________|______|______|______|______| + +Tan Bark--Tan bark, or spent tan, is the fibrous portion of bark +remaining after use in the tanning industry. It is usually very high in +its moisture content, a number of samples giving an average of 65 per +cent or about two-thirds of the total weight of the fuel. The weight of +the spent tan is about 2.13 times as great as the weight of the bark +ground. In calorific value an average of 10 samples gives 9500 B. t. u. +per pound dry.[43] The available heat per pound as fired, owing to the +great percentage of moisture usually found, will be approximately 2700 +B. t. u. Since the weight of the spent tan as fired is 2.13 as great as +the weight of the bark as ground at the mill, one pound of ground bark +produces an available heat of approximately 5700 B. t. u. Relative to +bituminous coal, a ton of bark is equivalent to 0.4 ton of coal. An +average chemical analysis of the bark is, carbon 51.8 per cent, hydrogen +6.04, oxygen 40.74, ash 1.42. + +Tan bark is burned in isolated cases and in general the remarks on +burning wet wood fuel apply to its combustion. The essential features +are a large combustion space, large areas of heated brickwork radiating +to the fuel bed, and draft sufficient for high combustion rates. The +ratings obtainable with this class of fuel will not be as high as with +wet wood fuel, because of the heat value and the excessive moisture +content. Mr. D. M. Meyers found in a series of experiments that an +average of from 1.5 to 2.08 horse power could be developed per square +foot of grate surface with horizontal return tubular boilers. This horse +power would vary considerably with the method in which the spent tan was +fired. + +[Illustration: 686 Horse-power Babcock & Wilcox Boiler and Superheater +in Course of Erection at the Quincy, Mass., Station of the Bay State +Street Railway Co.] + + + + +LIQUID FUELS AND THEIR COMBUSTION + + +Petroleum is practically the only liquid fuel sufficiently abundant and +cheap to be used for the generation of steam. It possesses many +advantages over coal and is extensively used in many localities. + +There are three kinds of petroleum in use, namely those yielding on +distillation: 1st, paraffin; 2nd, asphalt; 3rd, olefine. To the first +group belong the oils of the Appalachian Range and the Middle West of +the United States. These are a dark brown in color with a greenish +tinge. Upon their distillation such a variety of valuable light oils are +obtained that their use as fuel is prohibitive because of price. + +To the second group belong the oils found in Texas and California. These +vary in color from a reddish brown to a jet black and are used very +largely as fuel. + +The third group comprises the oils from Russia, which, like the second, +are used largely for fuel purposes. + +The light and easily ignited constituents of petroleum, such as naphtha, +gasolene and kerosene, are oftentimes driven off by a partial +distillation, these products being of greater value for other purposes +than for use as fuel. This partial distillation does not decrease the +value of petroleum as a fuel; in fact, the residuum known in trade as +"fuel oil" has a slightly higher calorific value than petroleum and +because of its higher flash point, it may be more safely handled. +Statements made with reference to petroleum apply as well to fuel oil. + +In general crude oil consists of carbon and hydrogen, though it also +contains varying quantities of moisture, sulphur, nitrogen, arsenic, +phosphorus and silt. The moisture contained may vary from less than 1 to +over 30 per cent, depending upon the care taken to separate the water +from the oil in pumping from the well. As in any fuel, this moisture +affects the available heat of the oil, and in contracting for the +purchase of fuel of this nature it is well to limit the per cent of +moisture it may contain. A large portion of any contained moisture can +be separated by settling and for this reason sufficient storage capacity +should be supplied to provide time for such action. + +A method of obtaining approximately the percentage of moisture in crude +oil which may be used successfully, particularly with lighter oils, is +as follows. A burette graduated into 200 divisions is filled to the 100 +mark with gasolene, and the remaining 100 divisions with the oil, which +should be slightly warmed before mixing. The two are then shaken +together and any shrinkage below the 200 mark filled up with oil. The +mixture should then be allowed to stand in a warm place for 24 hours, +during which the water and silt will settle to the bottom. Their +percentage by volume can then be correctly read on the burette +divisions, and the percentage by weight calculated from the specific +gravities. This method is exceedingly approximate and where accurate +results are required it should not be used. For such work, the +distillation method should be used as follows: + +Gradually heat 100 cubic centimeters of the oil in a distillation flask +to a temperature of 150 degrees centigrade; collect the distillate in a +graduated tube and measure the resulting water. Such a method insures +complete removal of water and reduces the error arising from the slight +solubility of the water in gasolene. Two samples checked by the two +methods for the amount of moisture present gave, + + _Distillation_ _Dilution_ + _Per Cent_ _Per Cent_ + 8.71 6.25 + 8.82 6.26 + + TABLE 46 + + COMPOSITION AND CALORIFIC VALUE OF VARIOUS OILS + ++-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ +| Kind of Oil | %C | %H | %S | %O |S.G.|FP | %H2O |Btu |Authority | ++-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ +|California, Coaling | | | | |.927|134| |17117|Babcock & Wilcox Co. | +|California, Bakersfield | | | | |.975| | |17600|Wade | +|California, Bakersfield | | |1.30| |.992| | |18257|Wade | +|California, Kern River | | | | |.950|140| |18845|Babcock & Wilcox Co. | +|California, Los Angeles | | |2.56| | | | |18328|Babcock & Wilcox Co. | +|California, Los Angeles | | | | |.957|196| |18855|Babcock & Wilcox Co. | +|California, Los Angeles | | | | |.977| | .40 |18280|Babcock & Wilcox Co. | +|California, Monte Christo| | | | |.966|205| |18878|Babcock & Wilcox Co. | +|California, Whittier | | | .98| |.944| |1.06 |18507|Wade | +|California, Whittier | | | .72| |.936| |1.06 |18240|Wade | +|California |85.04|11.52|2.45| .99[44]| | |1.40 |17871|Babcock & Wilcox Co. | +|California |81.52|11.51| .55|6.92[44]| |230| |18667|U.S.N. Liquid Fuel Board| +|California | | | .87| | | | .95 |18533|Blasdale | +|California | | | | |.891|257| |18655|Babcock & Wilcox Co. | +|California | | |2.45| |.973| |1.50[45]|17976|O'Neill | +|California | | |2.46| |.975| |1.32 |18104|Shepherd | +|Texas, Beaumont |84.6 |10.9 |1.63|2.87 |.924|180| |19060|U.S.N. Liquid Fuel Board| +|Texas, Beaumont |83.3 |12.4 | .50|3.83 |.926|216| |19481|U.S.N. Liquid Fuel Board| +|Texas, Beaumont |85.0 |12.3 |1.75| .92[44]| | | |19060|Denton | +|Texas, Beaumont |86.1 |12.3 |1.60| |.942| | |20152|Sparkes | +|Texas, Beaumont | | | | |.903|222| |19349|Babcock & Wilcox Co. | +|Texas, Sabine | | | | |.937|143| |18662|Babcock & Wilcox Co. | +|Texas |87.15|12.33|0.32| |.908|370| |19338|U. S. N. | +|Texas |87.29|12.32|0.43| |.910|375| |19659|U. S. N. | +|Ohio |83.4 |14.7 |0.6 |1.3 | | | |19580| | +|Pennsylvania |84.9 |13.7 | |1.4 |.886| | |19210|Booth | +|West Virginia |84.3 |14.1 | |1.6 |.841| | |21240| | +|Mexico | | | | |.921|162| |18840|Babcock & Wilcox Co. | +|Russia, Baku |86.7 |12.9 | | |.884| | |20691|Booth | +|Russia, Novorossick |84.9 |11.6 | |3.46 | | | |19452|Booth | +|Russia, Caucasus |86.6 |12.3 | |1.10 |.938| | |20138| | +|Java |87.1 |12.0 | | .9 |.923| | |21163| | +|Austria, Galicia |82.2 |12.1 |5.7 | |.870| | |18416| | +|Italy, Parma |84.0 |13.4 |1.8 | |.786| | | | | +|Borneo |85.7 |11.0 | |3.31 | | | |19240|Orde | ++-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ + +%C = Per Cent Carbon +%H = Per Cent Hydrogen +%S = Per Cent Sulphur +%O = Per Cent Oxygen +S.G. = Specific Gravity +FP = Degrees Flash Point +%H_{2}O = Per Cent Moisture +Btu = B. t. u. Per Pound + +Calorific Value--A pound of petroleum usually has a calorific value of +from 18,000 to 22,000 B. t. u. If an ultimate analysis of an average +sample be, carbon 84 per cent, hydrogen 14 per cent, oxygen 2 per cent, +and assuming that the oxygen is combined with its equivalent of hydrogen +as water, the analysis would become, carbon 84 per cent, hydrogen 13.75 +per cent, water 2.25 per cent, and the heat value per pound including +its contained water would be, + +Carbon .8400 x 14,600 = 12,264 B. t. u. +Hydrogen .1375 x 62,100 = 8,625 B. t. u. + ------[**Should be .1375 x 62,000 = 8,525] + Total 20,889 B. t. u.[**Would be Total = 20,789] + +The nitrogen in petroleum varies from 0.008 to 1.0 per cent, while the +sulphur varies from 0.07 to 3.0 per cent. + +Table 46, compiled from various sources, gives the composition, +calorific value and other data relative to oil from different +localities. + +The flash point of crude oil is the temperature at which it gives off +inflammable gases. While information on the actual flash points of the +various oils is meager, it is, nevertheless, a question of importance in +determining their availability as fuels. In general it may be stated +that the light oils have a low, and the heavy oils a much higher flash +point. A division is sometimes made at oils having a specific gravity of +0.85, with a statement that where the specific gravity is below this +point the flash point is below 60 degrees Fahrenheit, and where it is +above, the flash point is above 60 degrees Fahrenheit. There are, +however, many exceptions to this rule. As the flash point is lower the +danger of ignition or explosion becomes greater, and the utmost care +should be taken in handling the oils with a low flash point to avoid +this danger. On the other hand, because the flash point is high is no +justification for carelessness in handling those fuels. With proper +precautions taken, in general, the use of oil as fuel is practically as +safe as the use of coal. + +Gravity of Oils--Oils are frequently classified according to their +gravity as indicated by the Beaume hydrometer scale. Such a +classification is by no means an accurate measure of their relative +calorific values. + +Petroleum as Compared with Coal--The advantages of the use of oil fuel +over coal may be summarized as follows: + +1st. The cost of handling is much lower, the oil being fed by simple +mechanical means, resulting in, + +2nd. A general labor saving throughout the plant in the elimination of +stokers, coal passers, ash handlers, etc. + +3rd. For equal heat value, oil occupies very much less space than coal. +This storage space may be at a distance from the boiler without +detriment. + +4th. Higher efficiencies and capacities are obtainable with oil than +with coal. The combustion is more perfect as the excess air is reduced +to a minimum; the furnace temperature may be kept practically constant +as the furnace doors need not be opened for cleaning or working fires; +smoke may be eliminated with the consequent increased cleanliness of the +heating surfaces. + +5th. The intensity of the fire can be almost instantaneously regulated +to meet load fluctuations. + +6th. Oil when stored does not lose in calorific value as does coal, nor +are there any difficulties arising from disintegration, such as may be +found when coal is stored. + +7th. Cleanliness and freedom from dust and ashes in the boiler room with +a consequent saving in wear and tear on machinery; little or no damage +to surrounding property due to such dust. + +The disadvantages of oil are: + +1st. The necessity that the oil have a reasonably high flash point to +minimize the danger of explosions. + +2nd. City or town ordinances may impose burdensome conditions relative +to location and isolation of storage tanks, which in the case of a plant +situated in a congested portion of the city, might make use of this fuel +prohibitive. + +3rd. Unless the boilers and furnaces are especially adapted for the use +of this fuel, the boiler upkeep cost will be higher than if coal were +used. This objection can be entirely obviated, however, if the +installation is entrusted to those who have had experience in the work, +and the operation of a properly designed plant is placed in the hands of +intelligent labor. + + TABLE 47 + + RELATIVE VALUE OF COAL AND OIL FUEL + ++------+--------+-------+-----------------------------------------------+ +|Gross | Net | Net | Water Evaporated from and at | +|Boiler| Boiler |Evap- | 212 Degrees Fahrenheit per Pound of Coal | +|Effic-|Effici- |oration+-----+-----+-----+-----+-----+-----+-----+-----+ +| iency|ency[46]| from | | | | | | | | | +| with | with |and at | | | | | | | | | +| Oil | Oil | 212 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | +| Fuel | Fuel |Degrees| | | | | | | | | +| | |Fahren-| | | | | | | | | +| | | heit +-----+-----+-----+-----+-----+-----+-----+-----+ +| | | per | | +| | | Pound | Pounds of Oil Equal to One Pound of Coal | +| | |of Oil | | ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ +| 73 | 71 | 13.54 |.3693|.4431|.5170|.5909|.6647|.7386|.8124|.8863| +| 74 | 72 | 13.73 |.3642|.4370|.5099|.5827|.6556|.7283|.8011|.8740| +| 75 | 73 | 13.92 |.3592|.4310|.5029|.5747|.6466|.7184|.7903|.8621| +| 76 | 74 | 14.11 |.3544|.4253|.4961|.5670|.6378|.7087|.7796|.8505| +| 77 | 75 | 14.30 |.3497|.4196|.4895|.5594|.6294|.6993|.7692|.8392| +| 78 | 76 | 14.49 |.3451|.4141|.4831|.5521|.6211|.6901|.7591|.8281| +| 79 | 77 | 14.68 |.3406|.4087|.4768|.5450|.6131|.6812|.7493|.8174| +| 80 | 78 | 14.87 |.3363|.4035|.4708|.5380|.6053|.6725|.7398|.8070| +| 81 | 79 | 15.06 |.3320|.3984|.4648|.5312|.5976|.6640|.7304|.7968| +| 82 | 80 | 15.25 |.3279|.3934|.4590|.5246|.5902|.6557|.7213|.7869| +| 83 | 81 | 15.44 |.3238|.3886|.4534|.5181|.5829|.6447|.7125|.7772| ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ +| | | Net | | +| | |Evap- | | +| | |oration| | +| | | from | | +| | |and at | | +| | | 212 | Barrels of Oil Equal to One Ton of Coal | +| | |Degrees| | +| | |Fahren-| | +| | | heit | | +| | | per | | +| | |Barrel | | +| | |of Oil | | ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ +| 73 | 71 | 4549 |2.198|2.638|3.077|3.516|3.955|4.395|4.835|5.275| +| 74 | 72 | 4613 |2.168|2.601|3.035|3.468|3.902|4.335|4.769|5.202| +| 75 | 73 | 4677 |2.138|2.565|2.993|3.420|3.848|4.275|4.703|5.131| +| 76 | 74 | 4741 |2.110|2.532|2.954|3.376|3.798|4.220|4.642|5.063| +| 77 | 75 | 4807 |2.082|2.498|2.914|3.330|3.746|4.162|4.578|4.994| +| 78 | 76 | 4869 |2.054|2.465|2.876|3.286|3.697|4.108|4.518|4.929| +| 79 | 77 | 4932 |2.027|2.433|2.838|3.243|3.649|4.054|4.460|4.865| +| 80 | 78 | 4996 |2.002|2.402|2.802|3.202|3.602|4.003|4.403|4.803| +| 81 | 79 | 5060 |1.976|2.371|2.767|3.162|3.557|3.952|4.348|4.743| +| 82 | 80 | 5124 |1.952|2.342|2.732|3.122|3.513|3.903|4.293|4.683| +| 83 | 81 | 5187 |1.927|2.313|2.699|3.085|3.470|3.856|4.241|4.627| ++------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ + +[Illustration: City of San Francisco, Cal., Fire Fighting Station. No. +1. 2800 Horse Power of Babcock & Wilcox Boilers, Equipped for Burning +Oil Fuel] + +Many tables have been published with a view to comparing the two fuels. +Such of these as are based solely on the relative calorific values of +oil and coal are of limited value, inasmuch as the efficiencies to be +obtained with oil are higher than that obtainable with coal. Table 47 +takes into consideration the variation in efficiency with the two fuels, +but is based on a constant calorific value for oil and coal. This table, +like others of a similar nature, while useful as a rough guide, cannot +be considered as an accurate basis for comparison. This is due to the +fact that there are numerous factors entering into the problem which +affect the saving possible to a much greater extent than do the relative +calorific values of two fuels. Some of the features to be considered in +arriving at the true basis for comparison are the labor saving possible, +the space available for fuel storage, the facilities for conveying the +oil by pipe lines, the hours during which a plant is in operation, the +load factor, the quantity of coal required for banking fires, etc., etc. +The only exact method of estimating the relative advantages and costs of +the two fuels is by considering the operating expenses of the plant with +each in turn, including the costs of every item entering into the +problem. + +Burning Oil Fuel--The requirements for burning petroleum are as follows: + +1st. Its atomization must be thorough. + +2nd. When atomized it must be brought into contact with the requisite +quantity of air for its combustion, and this quantity must be at the +same time a minimum to obviate loss in stack gases. + +3rd. The mixture must be burned in a furnace where a refractory material +radiates heat to assist in the combustion, and the furnace must stand up +under the high temperatures developed. + +4th. The combustion must be completed before the gases come into contact +with the heating surfaces or otherwise the flame will be extinguished, +possibly to ignite later in the flue connection or in the stack. + +5th. There must be no localization of the heat on certain portions of +the heating surfaces or trouble will result from overheating and +blistering. + +The first requirement is met by the selection of a proper burner. + +The second requirement is fulfilled by properly introducing the air into +the furnace, either through checkerwork under the burners or through +openings around them, and by controlling the quantity of air to meet +variations in furnace conditions. + +The third requirement is provided for by installing a furnace so +designed as to give a sufficient area of heated brickwork to radiate the +heat required to maintain a proper furnace temperature. + +The fourth requirement is provided for by giving ample space for the +combustion of the mixture of atomized oil and air, and a gas travel of +sufficient length to insure that this combustion be completed before the +gases strike the heating surfaces. + +The fifth requirement is fulfilled by the adoption of a suitable burner +in connection with the furnace meeting the other requirements. A burner +must be used from which the flame will not impinge directly on the +heating surface and must be located where such action cannot take place. +If suitable burners properly located are not used, not only is the heat +localized with disastrous results, but the efficiency is lowered by the +cooling of the gases before combustion is completed. + +Oil Burners--The functions of an oil burner is to atomize or vaporize +the fuel so that it may be burned like a gas. All burners may be +classified under three general types: 1st, spray burners, in which the +oil is atomized by steam or compressed air; 2nd, vapor burners, in which +the oil is converted into vapor and then passed into the furnace; 3rd, +mechanical burners, in which the oil is atomized by submitting it to a +high pressure and passing it through a small orifice. + +Vapor burners have never been in general use and will not be discussed. + +Spray burners are almost universally used for land practice and the +simplicity of the steam atomizer and the excellent economy of the better +types, together with the low oil pressure and temperature required makes +this type a favorite for stationary plants, where the loss of fresh +water is not a vital consideration. In marine work, or in any case where +it is advisable to save feed water that otherwise would have to be added +in the form of "make-up", either compressed air or mechanical means are +used for atomization. Spray burners using compressed air as the +atomizing agent are in satisfactory operation in some plants, but their +use is not general. Where there is no necessity of saving raw feed +water, the greater simplicity and economy of the steam spray atomizer is +generally the most satisfactory. The air burners require blowers, +compressors or other apparatus which occupy space that might be +otherwise utilized and require attention that is not necessary where +steam is used. + +Steam spray burners of the older types had disadvantages in that they +were so designed that there was a tendency for the nozzle to clog with +sludge or coke formed from the oil by the heat, without means of being +readily cleaned. This has been overcome in the more modern types. + +Steam spray burners, as now used, may be divided into two classes: 1st, +inside mixers; and 2nd, outside mixers. In the former the steam and oil +come into contact within the burner and the mixture is atomized in +passing through the orifice of the burner nozzle. + +[Illustration: Fig. 28. Peabody Oil Burner] + +In the outside mixing class the steam flows through a narrow slot or +horizontal row of small holes in the burner nozzle; the oil flows +through a similar slot or hole above the steam orifice, and is picked up +by the steam outside of the burner and is atomized. Fig. 28 shows a type +of the Peabody burner of this class, which has given eminent +satisfaction. The construction is evident from the cut. It will be noted +that the portions of the burner forming the orifice may be readily +replaced in case of wear, or if it is desired to alter the form of the +flame. + +Where burners of the spray type are used, heating the oil is of +advantage not only in causing it to be atomized more easily, but in +aiding economical combustion. The temperature is, of course, limited by +the flash point of the oil used, but within the limit of this +temperature there is no danger of decomposition or of carbon deposits on +the supply pipes. Such heating should be done close to the boiler to +minimize radiation loss. If the temperature is raised to a point where +an appreciable vaporization occurs, the oil will flow irregularly from +the burner and cause the flame to sputter. + +On both steam and air atomizing types, a by-pass should be installed +between the steam or air and the oil pipes to provide for the blowing +out of the oil duct. Strainers should be provided for removing sludge +from the fuel and should be so located as to allow for rapid removal, +cleaning and replacing. + +Mechanical burners have been in use for some time in European countries, +but their introduction and use has been of only recent occurrence in the +United States. Here as already stated, the means for atomization are +purely mechanical. The most successful of the mechanical atomizers up to +the present have been of the round flame type, and only these will be +considered. Experiments have been made with flat flame mechanical +burners, but their satisfactory action has been confined to instances +where it is only necessary to burn a small quantity of oil through each +individual burner. + +This system of oil burning is especially adapted for marine work as the +quantity of steam for putting pressure on the oil is small and the +condensed steam may be returned to the system. + +The only method by which successful mechanical atomization has been +accomplished is one by which the oil is given a whirling motion within +the burner tip. This is done either by forcing the oil through a passage +of helical form or by delivering it tangentially to a circular chamber +from which there is a central outlet. The oil is fed to these burners +under a pressure which varies with the make of the burner and the rates +at which individual burners are using oil. The oil particles fly off +from such a burner in straight lines in the form of a cone rather than +in the form of a spiral spray, as might be supposed. + +With burners of the mechanical atomizing design, the method of +introducing air for combustion and the velocity of this air are of the +greatest importance in securing good combustion and in the effects on +the character and shape of the flame. Such burners are located at the +front of the furnace and various methods have been tried for introducing +the air for combustion. Where, in the spray burners, air is ordinarily +admitted through a checkerwork under the burner proper, with the +mechanical burner, it is almost universally admitted around the burner. +Early experiments with these air distributors were confined largely to +single or duplicate cones used with the idea of directing the air to the +axis of the burner. A highly successful method of such air introduction, +developed by Messrs. Peabody and Irish of The Babcock & Wilcox Co., is +by means of what they term an "impeller plate". This consists of a +circular metal disk with an opening at the center for the oil burner and +with radial metal strips from the center to the periphery turned at an +angle which in the later designs may be altered to give the air supply +demanded by the rate of combustion. + +The air so admitted does not necessarily require a whirling motion, but +experiments show that where the air is brought into contact with the oil +spray with the right "twist", better combustion is secured and lower air +pressures and less refinement of adjustment of individual burners are +required. + +Mechanical burners have a distinct advantage over those in which steam +is used as the atomizing agent in that they lend themselves more readily +to adjustment under wider variations of load. For a given horse power +there will ordinarily be installed a much greater number of mechanical +than steam atomizing burners. This in itself is a means to better +regulation, for with the steam atomizing burner, if one of a number is +shut off, there is a marked decrease in efficiency. This is due to the +fact that with the air admitted under the burner, it is ordinarily +passing through the checkerwork regardless of whether it is being +utilized for combustion or not. With a mechanical burner, on the other +hand, where individual burners are shut off, air that would be admitted +for such burner, were it in operation, may also be shut off and there +will be no undue loss from excess air. + +Further adjustment to meet load conditions is possible by a change in +the oil pressure acting on all burners at once. A good burner will +atomize moderately heavy oil with an oil pressure as low as 30 pounds +per square inch and from that point up to 200 pounds or above. The +heating of the oil also has an effect on the capacity of individual +burners and in this way a third method of adjustment is given. Under +working conditions, the oil pressure remaining constant, the capacity of +each burner will decrease as the temperature of the oil is increased +though at low temperatures the reverse is the case. Some experiments +with a Texas crude oil having a flash point of 210 degrees showed that +the capacity of a mechanical atomizing burner of the Peabody type +increased from 80 degrees Fahrenheit to 110 degrees Fahrenheit, from +which point it fell off rapidly to 140 degrees and then more slowly to +the flash point. + +The above methods, together with the regulation possible through +manipulation of the boiler dampers, indicate the wide range of load +conditions that may be handled with an installation of this class of +burners. + +As has already been stated, results with mechanical atomizing burners +that may be considered very successful have been limited almost entirely +to cases where forced blast of some description has been used, the high +velocity of the air entering being of material assistance in securing +the proper mixture of air with the oil spray. Much has been done and is +being done in the way of experiment with this class of apparatus toward +developing a successful mechanical atomizing burner for use with natural +draft, and there appears to be no reason why such experiments should not +eventually produce satisfactory results. + +Steam Consumption of Burners--The Bureau of Steam Engineering, U. S. +Navy, made in 1901 an exhaustive series of tests of various oil burners +that may be considered as representing, in so far as the performance of +the burners themselves is concerned, the practice of that time. These +tests showed that a burner utilizing air as an atomizing agent, required +for compressing the air from 1.06 to 7.45 per cent of the total steam +generated, the average being 3.18 per cent. Four tests of steam +atomizing burners showed a consumption of 3.98 to 5.77 per cent of the +total steam, the average being 4.8 per cent. + +Improvement in burner design has largely reduced the steam consumption, +though to a greater degree in steam than in air atomizing burners. +Recent experiments show that a good steam atomizing burner will require +approximately 2 per cent of the total steam generated by the boiler +operated at or about its rated capacity. This figure will decrease as +the capacity is increased and is so low as to be practically negligible, +except in cases where the question of loss of feed water is all +important. There are no figures available as to the actual steam +consumption of mechanical atomizing burners but apparently this is small +if the requirement is understood to be entirely apart from the steam +consumption of the apparatus producing the forced blast. + +Capacity of Burners--A good steam atomizing burner properly located in a +well-designed oil furnace has a capacity of somewhat over 400 horse +power. This question of capacity of individual burners is largely one of +the proper relation between the number of burners used and the furnace +volume. In some recent tests with a Babcock & Wilcox boiler of 640 rated +horse power, equipped with three burners, approximately 1350 horse power +was developed with an available draft of .55 inch at the damper or 450 +horse power per burner. Four burners were also tried in the same furnace +but the total steam generated did not exceed 1350 horse power or in this +instance 338 horse power per burner. + +From the nature of mechanical atomizing burners, individual burners have +not as large a capacity as the steam atomizing class. In some tests on a +Babcock & Wilcox marine boiler, equipped with mechanical atomizing +burners, the maximum horse power developed per burner was approximately +105. Here again the burner capacity is largely one of proper relation +between furnace volume and number of burners. + +Furnace Design--Too much stress cannot be laid on the importance of +furnace design for the use of this class of fuel. Provided a good type +of burner is adopted the furnace arrangement and the method of +introducing air for combustion into the furnace are the all important +factors. No matter what the type of burner, satisfactory results cannot +be secured in a furnace not suited to the fuel. + +The Babcock & Wilcox Co. has had much experience with the burning of oil +as fuel and an extended series of experiments by Mr. E. H. Peabody led +to the development and adoption of the Peabody furnace as being most +eminently suited for this class of work. Fig. 29 shows such a furnace +applied to a Babcock & Wilcox boiler, and with slight modification it +can be as readily applied to any boiler of The Babcock & Wilcox Co. +manufacture. In the description of this furnace, its points of advantage +cover the requirements of oil-burning furnaces in general. + +The atomized oil is introduced into the furnace in the direction in +which it increases in height. This increase in furnace volume in the +direction of the flame insures free expansion and a thorough mixture of +the oil with the air, and the consequent complete combustion of the +gases before they come into contact with the tube heating surfaces. In +such a furnace flat flame burners should be used, preferably of the +Peabody type, in which the flame spreads outward toward the sides in the +form of a fan. There is no tendency of the flames to impinge directly on +the heating surfaces, and the furnace can handle any quantity of flame +without danger of tube difficulties. The burners should be so located +that the flames from individual burners do not interfere nor impinge to +any extent on the side walls of the furnace, an even distribution of +heat being secured in this manner. The burners are operated from the +boiler front and peepholes are supplied through which the operator may +watch the flame while regulating the burners. The burners can be +removed, inspected, or cleaned and replaced in a few minutes. Air is +admitted through a checkerwork of fire brick supported on the furnace +floor, the openings in the checkerwork being so arranged as to give the +best economic results in combustion. + +[Illustration: Fig. 29. Babcock & Wilcox Boiler, Equipped with a Peabody +Oil Furnace] + +With steam atomizing burners introduced through the front of the boiler +in stationary practice, it is usually in the direction in which the +furnace decreases in height and it is with such an arrangement that +difficulties through the loss of tubes may be expected. With such an +arrangement, the flame may impinge directly upon the tube surfaces and +tube troubles from this source may arise, particularly where the feed +water has a tendency toward rapid scale formation. Such difficulties may +be the result of a blowpipe action on the part of the burner, the over +heating of the tube due to oil or scale within, or the actual erosion of +the metal by particles of oil improperly atomized. Such action need not +be anticipated, provided the oil is burned with a short flame. The +flames from mechanical atomizing burners have a less velocity of +projection than those from steam atomizing burners and if introduced +into the higher end of the furnace, should not lead to tube difficulties +provided they are properly located and operated. This class of burner +also will give the most satisfactory results if introduced so that the +flames travel in the direction of increase in furnace volume. This is +perhaps best exemplified by the very good results secured with +mechanical atomizing burners and Babcock & Wilcox marine boilers in +which, due to the fact that the boilers are fired from the low end, the +flames from burners introduced through the front are in this direction. + +Operation of Burners--When burners are not in use, or when they are +being started up, care must be taken to prevent oil from flowing and +collecting on the floor of the furnace before it is ignited. In starting +a burner, the atomized fuel may be ignited by a burning wad of oil-soaked +waste held before it on an iron rod. To insure quick ignition, the steam +supply should be cut down. But little practice is required to become an +adept at lighting an oil fire. When ignition has taken place and the +furnace brought to an even heat, the steam should be cut down to the +minimum amount required for atomization. This amount can be determined +from the appearance of the flame. If sufficient steam is not supplied, +particles of burning oil will drop to the furnace floor, giving a +scintillating appearance to the flame. The steam valves should be opened +just sufficiently to overcome this scintillating action. + +Air Supply--From the nature of the fuel and the method of burning, the +quantity of air for combustion may be minimized. As with other fuels, +when the amount of air admitted is the minimum which will completely +consume the oil, the results are the best. The excess or deficiency of +air can be judged by the appearance of the stack or by observing the +gases passing through the boiler settings. A perfectly clear stack +indicates excess air, whereas smoke indicates a deficiency. With +properly designed furnaces the best results are secured by running near +the smoking point with a slight haze in the gases. A slight variation in +the air supply will affect the furnace conditions in an oil burning +boiler more than the same variation where coal is used, and for this +reason it is of the utmost importance that flue gas analysis be made +frequently on oil-burning boilers. With the air for combustion properly +regulated by adjustment of any checkerwork or any other device which may +be used, and the dampers carefully set, the flue gas analysis should +show, for good furnace conditions, a percentage of CO_{2} between 13 and +14 per cent, with either no CO or but a trace. + +In boiler plant operation it is difficult to regulate the steam supply +to the burners and the damper position to meet sudden and repeated +variations in the load. A device has been patented which automatically +regulates by means of the boiler pressure the pressure of the steam to +the burners, the oil to the burners and the position of the boiler +damper. Such a device has been shown to give good results in plant +operation where hand regulation is difficult at best, and in many +instances is unfortunately not even attempted. + +Efficiency with Oil--As pointed out in enumerating the advantages of oil +fuel over coal, higher efficiencies are obtainable with the former. With +boilers of approximately 500 horse power equipped with properly designed +furnaces and burners, an efficiency of 83 per cent is possible or making +an allowance of 2 per cent for steam used by burners, a net efficiency +of 81 per cent. The conditions under which such efficiencies are to be +secured are distinctly test conditions in which careful operation is a +prime requisite. With furnace conditions that are not conductive to the +best combustion, this figure may be decreased by from 5 to 10 per cent. +In large properly designed plants, however, the first named efficiency +may be approached for uniform running conditions, the nearness to which +it is reached depending on the intelligence of the operating crew. It +must be remembered that the use of oil fuel presents to the careless +operator possibilities for wastefulness much greater than in plants +where coal is fired, and it therefore pays to go carefully into this +feature. + +Table 48 gives some representative tests with oil fuel. + + TABLE 48 + + TESTS OF BABCOCK AND WILCOX BOILERS WITH OIL FUEL + + _______________________________________________________________________ +| | | | | +| |Pacific Light|Pacific Light|Miami Copper | +| | and Power | and Power | Company | +| Plant | Company | Company | | +| |Los Angeles, | | Miami, | +| | Cal. |Redondo, Cal.| Arizona | +|_____________________________|_____________|_____________|_____________| +| | | | | | +| Rated Capacity | Horse | | | | +| of Boiler | Power | 467 | 604 | 600 | +|__________________|__________|_____________|_____________|_____________| +| | | | | | | | | +| Duration of Test | Hours | 10 | 10 | 7 | 7 | 10 | 4 | +| | | | | | | | | +| Steam Pressure | | | | | | | | +| by Gauge | Pounds | 156.4| 156.9| 184.7| 184.9| 183.4| 189.5| +| | | | | | | | | +| Temperature of | Degrees | | | | | | | +| Feed Water | F. | 62.6| 61.1| 93.4| 101.2| 157.7| 156.6| +| | | | | | | | | +| Degrees of | Degrees | | | | | | | +| Superheat | F. | | | 83.7| 144.3| 103.4| 139.6| +| | | | | | | | | +| Factor of | | | | | | | | +| Evaporation | |1.2004|1.2020|1.2227|1.2475|1.1676|1.1886| +| | | | | | | | | +| Draft in Furnace | Inches | .02 | .05 | .014| .19 | .12 | .22 | +| | | | | | | | | +| Draft at Damper | Inches | .08 | .15 | .046| .47 | .19 | .67 | +| | | | | | | | | +| Temperature of | Degrees | | | | | | | +| Exit Gases | F. | 438 | 525 | 406 | 537 | 430 | 612 | +| _ | | | | | | | | +| Flue | CO_{2} | Per Cent | | | 14.3 | 12.1 | | | +| Gas | O | Per Cent | | | 3.8 | 6.8 | | | +| Analysis|_CO | Per Cent | | | 0.0 | 0.0 | | | +| | | | | | | | | +| Oil Burned | | | | | | | | +| per Hour | Pounds | 1147 | 1837 | 1439 | 2869 | 1404 | 3214 | +| | | | | | | | | +| Water Evaporated | | | | | | | | +| per Hour from | | | | | | | | +| from and at | Pounds | 18310| 27855| 22639| 40375| 21720| 42863| +| 212 Degrees | | | | | | | | +| | | | | | | | | +| Evaporation from | | | | | | | | +| and at 212 | | | | | | | | +| Degrees per | Pounds | 15.96| 15.16| 15.73| 14.07| 15.47| 13.34| +| Pound of Oil | | | | | | | | +| | | | | | | | | +| Per Cent of | | | | | | | | +| Rated Capacity | Pounds | 113.6| 172.9| 108.6| 193.8| 104.9| 207.1| +| Developed | | | | | | | | +| | | | | | | | | +| B. t. u. per | | | | | | | | +| Pound of Oil | B. t. u. | 18626| 18518| 18326| 18096| 18600| 18600| +| | | | | | | | | +| Efficiency | Per Cent | 83.15| 79.46| 83.29| 76.02| 80.70| 69.6 | +|__________________|__________|______|______|______|______|______|______| + +Burning Oil in Connection with Other Fuels--Considerable attention has +been recently given to the burning of oil in connection with other +fuels, and a combination of this sort may be advisable either with the +view to increasing the boiler capacity to assist over peak loads, or to +keep the boiler in operation where there is the possibility of a +temporary failure of the primary fuel. It would appear from experiments +that such a combination gives satisfactory results from the standpoint +of both capacity and efficiency, if the two fuels are burned in separate +furnaces. Satisfactory results cannot ordinarily be obtained when it is +attempted to burn oil fuel in the same furnace as the primary fuel, as +it is practically impossible to admit the proper amount of air for +combustion for each of the two fuels simultaneously. The Babcock & +Wilcox boiler lends itself readily to a double furnace arrangement and +Fig. 30 shows an installation where oil fuel is burned as an auxiliary +to wood. + +[Illustration: Fig. 30. Babcock & Wilcox Boiler Set with Combination Oil +and Wood-burning Furnace] + +Water-gas Tar--Water-gas tar, or gas-house tar, is a by-product of the +coal used in the manufacture of water gas. It is slightly heavier than +crude oil and has a comparatively low flash point. In burning, it should +be heated only to a temperature which makes it sufficiently fluid, and +any furnace suitable for crude oil is in general suitable for water-gas +tar. Care should be taken where this fuel is used to install a suitable +apparatus for straining it before it is fed to the burner. + +[Illustration: Babcock & Wilcox Boilers Fired with Blast Furnace Gas at +the Bethlehem Steel Co., Bethlehem, Pa. This Company Operates 12,900 +Horse Power of Babcock & Wilcox Boilers] + + + + +GASEOUS FUELS AND THEIR COMBUSTION + + +Of the gaseous fuels available for steam generating purposes, the most +common are blast furnace gas, natural gas and by-product coke oven gas. + +Blast furnace gas, as implied by its name, is a by-product from the +blast furnace of the iron industry. This gasification of the solid fuel +in a blast furnace results, 1st, through combustion by the oxygen of the +blast; 2nd, through contact with the incandescent ore (Fe_{2}O_{3} + C += 2 FeO + CO and FeO + C = Fe + CO); and 3rd, through the agency of +CO_{2} either formed in the process of reduction or driven from the +carbonates charged either as ore or flux. + +Approximately 90 per cent of the fuel consumed in all of the blast +furnaces of the United States is coke. The consumption of coke per ton +of iron made varies from 1600 to 3600 pounds per ton of 2240 pounds of +iron. This consumption depends upon the quality of the coal, the nature +of the ore, the quality of the pig iron produced and the equipment and +management of the plant. The average consumption, and one which is +approximately correct for ordinary conditions, is 2000 pounds of coke +per gross ton (2240 pounds) of pig iron. The gas produced in a gas +furnace per ton of pig iron is obtained from the weight of fixed carbon +gasified, the weight of the oxygen combined with the material of charge +reduced, the weight of the gaseous constituents of the flux and the +weight of air delivered by the blowing engine and the weight of volatile +combustible contained in the coke. Ordinarily, this weight of gas will +be found to be approximately five times the weight of the coke burned, +or 10,000 pounds per ton of pig iron produced. + +With the exception of the small amount of carbon in combination with +hydrogen as methane, and a very small percentage of free hydrogen, +ordinarily less than 0.1 per cent, the calorific value of blast furnace +gas is due to the CO content which when united with sufficient oxygen +when burned under a boiler, burns further to CO_{2}. The heat value of +such gas will vary in most cases from 85 to 100 B. t. u. per cubic foot +under standard conditions. In modern practice, where the blast is heated +by hot blast stoves, approximately 15 per cent of the total amount of +gas is used for this purpose, leaving 85 per cent of the total for use +under boilers or in gas engines, that is, approximately 8500 pounds of +gas per ton of pig iron produced. In a modern blast furnace plant, the +gas serves ordinarily as the only fuel required. Table 49 gives the +analyses of several samples of blast furnace gas. + + TABLE 49 + + TYPICAL ANALYSES OF BLAST FURNACE GAS + ++----------------------------------------------------------------+ +|+-----------------------+------+----+-----+----+------+--------+| +|| |CO_{2}| O | CO | H |CH_{4}| N || +|+-----------------------+------+----+-----+----+------+--------+| +||Bessemer Furnace | 9.85|0.36|32.73|3.14| .. |53.92 || +||Bessemer Furnace | 11.4 | .. |27.7 |1.9 | 0.3 |58.7 || +||Bessemer Furnace | 10.0 | .. |26.2 |3.1 | 0.2 |60.5 || +||Bessemer Furnace | 9.1 | .. |28.7 |2.7 | 0.2 |59.3 || +||Bessemer Furnace | 13.5 | .. |25.2 |1.43| .. |59.87 || +||Bessemer Furnace[47] | 10.9 | .. |27.8 |2.8 | 0.2 |58.3 || +||Ferro Manganese Furnace| 7.1 | .. |30.1 | .. | .. |62.8[48]|| +||Basic Ore Furnace | 16.0 |0.2 |23.6 | .. | .. |60.2[48]|| +|+-----------------------+------+----+-----+----+------+--------+| ++----------------------------------------------------------------+ + +Until recently, the important consideration in the burning of blast +furnace gas has been the capacity that can be developed with practically +no attention given to the aspect of efficiency. This phase of the +question is now drawing attention and furnaces especially designed for +good efficiency with this class of fuel are demanded. The essential +feature is ample combustion space, in which the combustion of gases may +be practically completed before striking the heating surfaces. The gases +have the power of burning out completely after striking the heating +surfaces, provided the initial temperature is sufficiently high, but +where the combustion is completed before such time, the results secured +are more satisfactory. A furnace volume of approximately 1 to 1.5 cubic +feet per rated boiler horse power will give a combustion space that is +ample. + +Where there is the possibility of a failure of the gas supply, or where +steam is required when the blast furnace is shut down, coal fired grates +of sufficient size to get the required capacity should be installed. +Where grates of full size are not required, ignition grates should be +installed, which need be only large enough to carry a fire for igniting +the gas or for generating a small quantity of steam when the blast +furnace is shut down. The area of such grates has no direct bearing on +the size of the boiler. The grates may be placed directly under the gas +burners in a standard position or may be placed between two bridge walls +back of the gas furnace and fired from the side of the boiler. An +advantage is claimed for the standard grate position that it minimizes +the danger of explosion on the re-ignition of gas after a temporary +stoppage of the supply and also that a considerable amount of dirt, of +which there is a good deal with this class of fuel and which is +difficult to remove, deposits on the fire and is taken out when the +fires are cleaned. In any event, regardless of the location of the +grates, ample provision should be made for removing this dust, not only +from the furnace but from the setting as a whole. + +Blast furnace gas burners are of two general types: Those in which the +air for combustion is admitted around the burner proper, and those in +which this air is admitted through the burner. Whatever the design of +burner, provision should be made for the regulation of both the air and +the gas supply independently. A gas opening of .8 square inch per rated +horse power will enable a boiler to develop its nominal rating with a +gas pressure in the main of about 2 inches. This pressure is ordinarily +from 6 to 8 inches and in this way openings of the above size will be +good for ordinary overloads. The air openings should be from .75 to .85 +square inch per rated horse power. Good results are secured by inclining +the gas burners slightly downward toward the rear of the furnace. Where +the burners are introduced over coal fired grates, they should be set +high enough to give headroom for hand firing. + +Ordinarily, individual stacks of 130 feet high with diameters as given +in Kent's table for corresponding horse power are large enough for this +class of work. Such a stack will give a draft sufficient to allow a +boiler to be operated at 175 per cent of its rated capacity, and beyond +this point the capacity will not increase proportionately with the +draft. When more than one boiler is connected with a stack, the draft +available at the damper should be equivalent to that which an individual +stack of 130 feet high would give. The draft from such a stack is +necessary to maintain a suction under all conditions throughout all +parts of the setting. If the draft is increased above that which such a +stack will give, difficulties arise from excess air for combustion with +consequent loss in efficiency. + +A poor mixing or laneing action in the furnace may result in a pulsating +effect of the gases in the setting. This action may at times be remedied +by admitting more air to the furnace. On account of the possibility of a +pulsating action of the gases under certain conditions and the puffs or +explosions, settings for this class of work should be carefully +constructed and thoroughly buckstayed and tied. + +Natural Gas--Natural gas from different localities varies considerably +in composition and heating value. In Table 50 there is given a number of +analyses and heat values for natural gas from various localities. + +This fuel is used for steam generating purposes to a considerable extent +in some localities, though such use is apparently decreasing. It is best +burned by employing a large number of small burners, each being capable +of handling 30 nominal rated horse power. The use of a large number of +burners obviates the danger of any laneing or blowpipe action, which +might be present where large burners are used. Ordinarily, such a gas, +as it enters the burners, is under a pressure of about 8 ounces. For the +purpose of comparison, all observations should be based on gas reduced +to the standard conditions of temperature and pressure, namely 32 +degrees Fahrenheit and 14.7 pounds per square inch. When the temperature +and pressure corresponding to meter readings are known, the volume of +gas under standard conditions may be obtained by multiplying the meter +readings in cubic feet by 33.54 P/T, in which P equals the absolute +pressure in pounds per square inch and T equals the absolute temperature +of the gas at the meter. In boiler testing work, the evaporation should +always be reduced to that per cubic foot of gas under standard +conditions. + + TABLE 50 + + TYPICAL ANALYSES (BY VOLUME) AND CALORIFIC VALUES OF NATURAL + GAS FROM VARIOUS LOCALITIES + ++----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ +|Locality of Well| H |CH_{4}| CO |CO_{2}| N | O | Heavy |H_{2}S|B. t. u.| +| | | | | | | |Hydro- | | per | +| | | | | | | |carbons| | Cubic | +| | | | | | | | | | Foot | +| | | | | | | | | |Calcul- | +| | | | | | | | | |ated[49]| +|----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ +|Anderson, Ind. | 1.86|93.07| 0.73| 0.26| 3.02|0.42| 0.47 | 0.15 | 1017 | +|Marion, Ind. | 1.20|93.16| 0.60| 0.30| 3.43|0.55| 0.15 | 0.20 | 1009 | +|Muncie, Ind. | 2.35|92.67| 0.45| 0.25| 3.53|0.35| 0.25 | 0.15 | 1004 | +|Olean, N. Y. | |96.50| 0.50| | |2.00| 1.00 | | 1018 | +|Findlay, O. | 1.64|93.35| 0.41| 0.25| 3.41|0.39| 0.35 | 0.20 | 1011 | +|St. Ive, Pa. | 6.10|75.54|Trace| 0.34| | | 18.12 | | 1117 | +|Cherry Tree, Pa.|22.50|60.27| | 2.28| 7.32|0.83| 6.80 | | 842 | +|Grapeville, Pa. |24.56|14.93|Trace|Trace|18.69|1.22| 40.60 | | 925 | +|Harvey Well, | | | | | | | | | | +| Butler Co., Pa.|13.50|80.00|Trace| 0.66| | | 5.72 | | 998 | +|Pittsburgh, Pa. | 9.64|57.85| 1.00| |23.41|2.10| 6.00 | | 748 | +|Pittsburgh, Pa. |20.02|72.18| 1.00| 0.80| |1.10| 4.30 | | 917 | +|Pittsburgh, Pa. |26.16|65.25| 0.80| 0.60| |0.80| 6.30 | | 899 | ++----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ + +[Illustration: 1600 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters at the Carnegie Natural Gas Co., Underwood, W. Va. +Natural Gas is the Fuel Burned under these Boilers] + +When natural gas is the only fuel, the burners should be evenly +distributed over the lower portion of the boiler front. If the fuel is +used as an auxiliary to coal, the burners may be placed through the fire +front. A large combustion space is essential and a volume of .75 cubic +feet per rated horse power will be found to give good results. The +burners should be of a design which give the gas and air a rotary motion +to insure a proper mixture. A checkerwork wall is sometimes placed in +the furnace about 3 feet from the burners to break up the flame, but +with a good design of burner this is unnecessary. Where the gas is +burned alone and no grates are furnished, good results are secured by +inclining the burner downward to the rear at a slight angle. + +By-product Coke Oven Gas--By-product coke oven gas is a product of the +destructive distillation of coal in a distilling or by-product coke +oven. In this class of apparatus the gases, instead of being burned at +the point of their origin, as in a beehive or retort coke oven, are +taken from the oven through an uptake pipe, cooled and yield as +by-products tar, ammonia, illuminating and fuel gas. A certain portion +of the gas product is burned in the ovens and the remainder used or sold +for illuminating or fuel purposes, the methods of utilizing the gas +varying with plant operation and locality. + +Table 51 gives the analyses and heat value of certain samples of +by-product coke oven gas utilized for fuel purposes. + +This gas is nearer to natural gas in its heat value than is blast +furnace gas, and in general the remarks as to the proper methods of +burning natural gas and the features to be followed in furnace design +hold as well for by-product coke oven gas. + + TABLE 51 + + TYPICAL ANALYSES OF BY-PRODUCT + COKE OVEN GAS + ++----------------------------------------------+ +|+------+-------------------------------------+| +||CO_{2}| O |CO |CH_{4}| H | N |B.t.u. per|| +|| | | | | | |Cubic Foot|| +|+------+-----+---+------+----+----+----------+| +|| 0.75 |Trace|6.0|28.15 |53.0|12.1| 505 || +|| 2.00 |Trace|3.2|18.80 |57.2|18.0| 399 || +|| 3.20 | 0.4 |6.3|29.60 |41.6|16.1| 551 || +|| 0.80 | 1.6 |4.9|28.40 |54.2|10.1| 460 || +|+------+-----+---+------+----+----+----------+| ++----------------------------------------------+ + +The essential difference in burning the two fuels is the pressure under +which it reaches the gas burner. Where this is ordinarily from 4 to 8 +ounces in the case of natural gas, it is approximately 4 inches of water +in the case of by-product coke oven gas. This necessitates the use of +larger gas openings in the burners for the latter class of fuel than for +the former. + +By-product coke oven gas comes to the burners saturated with moisture +and provision should be made for the blowing out of water of +condensation. This gas too, carries a large proportion of tar and +hydrocarbons which form a deposit in the burners and provision should be +made for cleaning this out. This is best accomplished by an attachment +which permits the blowing out of the burners by steam. + + + + +UTILIZATION OF WASTE HEAT + + +While it has been long recognized that the reclamation of heat from the +waste gases of various industrial processes would lead to a great saving +in fuel and labor, the problem has, until recently, never been given the +attention that its importance merits. It is true that installations have +been made for the utilization of such gases, but in general they have +consisted simply in the placing of a given amount of boiler heating +surface in the path of the gases and those making the installations have +been satisfied with whatever power has been generated, no attention +being given to the proportioning of either the heating surface or the +gas passages to meet the peculiar characteristics of the particular +class of waste gas available. The Babcock & Wilcox Co. has recently gone +into the question of the utilization of what has been known as waste +heat with great thoroughness, and the results secured by their +installations with practically all operations yielding such gases are +eminently successful. + + TABLE 52 + + TEMPERATURE OF WASTE GASES FROM + VARIOUS INDUSTRIAL PROCESSES + ++-----------------------------------------------------+ +|+-----------------------------------+---------------+| +||Waste Heat From |Temperature[50]|| +|| | Degrees || +|+-----------------------------------+---------------+| +||Brick Kilns | 2000-2300 || +||Zinc Furnaces | 2000-2300 || +||Copper Matte Reverberatory Furnaces| 2000-2200 || +||Beehive Coke Ovens | 1800-2000 || +||Cement Kilns | 1200-1600[51]|| +||Nickel Refining Furnaces | 1500-1750 || +||Open Hearth Steel Furnaces | 1100-1400 || +|+-----------------------------------+---------------+| ++-----------------------------------------------------+ + +The power that can be obtained from waste gases depends upon their +temperature and weight, and both of these factors vary widely in +different commercial operations. Table 52 gives a list of certain +processes yielding waste gases the heat of which is available for the +generation of steam and the approximate temperature of such gases. It +should be understood that the temperatures in the table are the average +of the range of a complete cycle of the operation and that the minimum +and maximum temperatures may vary largely from the figures given. + +The maximum available horse power that may be secured from such gases is +represented by the formula: + + W(T-t)s +H. P. = ------- (23) + 33,479 + + +Where W = the weight of gases passing per hour, + T = temperature of gases entering heating surface, + t = temperature leaving heating surface, + s = specific heat of gases. + +The initial temperature and the weight or volume of gas will depend, as +stated, upon the process involved. The exit temperature will depend, to +a certain extent, upon the temperature of the entering gases, but will +be governed mainly by the efficiency of the heating surfaces installed +for the absorption of the heat. + +Where the temperature of the gas available is high, approaching that +found in direct fired boiler practice, the problem is simple and the +question of design of boiler becomes one of adapting the proper amount +of heating surface to the volume of gas to be handled. With such +temperatures, and a volume of gas available approximately in accordance +with that found in direct fired boiler practice, a standard boiler or +one but slightly modified from the standard will serve the purpose +satisfactorily. As the temperatures become lower, however, the problem +is more difficult and the departure from standard practice more radical. +With low temperature gases, to obtain a heat transfer rate at all +comparable with that found in ordinary boiler practice, the lack of +temperature must be offset by an added velocity of the gases in their +passage over the heating surfaces. In securing the velocity necessary to +give a heat transfer rate with low temperature gases sufficient to make +the installation of waste heat boilers show a reasonable return on the +investment, the frictional resistance to the gases through the boiler +becomes greatly in excess of what would be considered good practice in +direct fired boilers. Practically all operations yielding waste gases +require that nothing be done in the way of impairing the draft at the +furnace outlet, as this might interfere with the operation of the +primary furnace. The installation of a waste heat boiler, therefore, +very frequently necessitates providing sufficient mechanical draft to +overcome the frictional resistance of the gases through the heating +surfaces and still leave ample draft available to meet the maximum +requirements of the primary furnace. + +Where the temperature and volume of the gases are in line with what are +found in ordinary direct fired practice, the area of the gas passages +may be practically standard. With the volume of gas known, the draft +loss through the heating surfaces may be obtained from experimental data +and this additional draft requirement met by the installation of a stack +sufficient to take care of this draft loss and still leave draft enough +for operating the furnace at its maximum capacity. + +Where the temperatures are low, the added frictional resistance will +ordinarily be too great to allow the draft required to be secured by +additional stack height and the installation of a fan is necessary. Such +a fan should be capable of handling the maximum volume of gas that the +furnace may produce, and of maintaining a suction equivalent to the +maximum frictional resistance of such volume through the boiler plus the +maximum draft requirement at the furnace outlet. Stacks and fans for +this class of work should be figured on the safe side. Where a fan +installation is necessary, the loss of draft in the fan connections +should be considered, and in figuring conservatively it should be +remembered that a fan of ample size may be run as economically as a +smaller fan, whereas the smaller fan, if overloaded, is operated with a +large loss in efficiency. In practically any installation where low +temperature gas requires a fan to give the proper heat transfer from the +gases, the cost of the fan and of the energy to drive it will be more +than offset by the added power from the boiler secured by its use. +Furthermore, the installation of such a fan will frequently increase the +capacity of the industrial furnace, in connection with which the waste +heat boilers are installed. + +In proportioning heating surfaces and gas passages for waste heat work +there are so many factors bearing directly on what constitutes the +proper installation that it is impossible to set any fixed rules. Each +individual installation must be considered by itself as well as the +particular characteristics of the gases available, such as their +temperature and volume, and the presence of dust or tar-like substances, +and all must be given the proper weight in the determination of the +design of the heating surfaces and gas passages for the specific set of +conditions. + +[Graph: Per Cent of Water Heating Surface passed over by Gases/Per Cent +of the Total Amount of Steam Generated in the Boiler +against Temperature in Degrees Fahrenheit of Hot Gases Sweeping Heating +Surface + +Fig. 31. Curve Showing Relation Between Gas Temperature, Heating Surface +passed over, and Amount of Steam Generated. Ten Square Feet of Heating +Surface are Assumed as Equivalent to One Boiler Horse Power] + +Fig. 31 shows the relation of gas temperatures, heating surface passed +over and work done by such surface for use in cases where the +temperatures approach those found in direct fired practice and where the +volume of gas available is approximately that with which one horse power +may be developed on 10 square feet of heating surface. The curve assumes +what may be considered standard gas passage areas, and further, that +there is no heat absorbed by direct radiation from the fire. + +Experiments have shown that this curve is very nearly correct for the +conditions assumed. Such being the case, its application in waste heat +work is clear. Decreasing or increasing the velocity of the gases over +the heating surfaces from what might be considered normal direct fired +practice, that is, decreasing or increasing the frictional loss through +the boiler will increase or decrease the amount of heating surface +necessary to develop one boiler horse power. The application of Fig. 31 +to such use may best be seen by an example: + +Assume the entering gas temperatures to be 1470 degrees and that the +gases are cooled to 570 degrees. From the curve, under what are assumed +to be standard conditions, the gases have passed over 19 per cent of +the heating surface by the time they have been cooled 1470 degrees. +When cooled to 570 degrees, 78 per cent of the heating surface has been +passed over. The work done in relation to the standard of the curve is +represented by (1470 - 570) / (2500 - 500) = 45 per cent. (These +figures may also be read from the curve in terms of the per cent of the +work done by different parts of the heating surfaces.) That is, 78 per +cent - 19 per cent = 59 per cent of the standard heating surface has +done 45 per cent of the standard amount of work. 59 / 45 = 1.31, which +is the ratio of surface of the assumed case to the standard case of the +curve. Expressed differently, there will be required 13.1 square feet +of heating surface in the assumed case to develop a horse power as +against 10 square feet in the standard case. + +The gases available for this class of work are almost invariably very +dirty. It is essential for the successful operation of waste-heat +boilers that ample provision be made for cleaning by the installation of +access doors through which all parts of the setting may be reached. In +many instances, such as waste-heat boilers set in connection with cement +kilns, settling chambers are provided for the dust before the gases +reach the boiler. + +By-passes for the gases should in all cases be provided to enable the +boiler to be shut down for cleaning and repairs without interfering with +the operation of the primary furnace. All connections from furnace to +boilers should be kept tight to prevent the infiltration of air, with +the consequent lowering of gas temperatures. + +Auxiliary gas or coal fired grates must be installed to insure +continuity in the operation of the boiler where the operation of the +furnace is intermittent or where it may be desired to run the boiler +with the primary furnace not in operation. Such grates are sometimes +used continuously where the gases available are not sufficient to +develop the required horse power from a given amount of heating surface. + +Fear has at times been expressed that certain waste gases, such as those +containing sulphur fumes, will have a deleterious action on the heating +surface of the boiler. This feature has been carefully watched, however, +and from plants in operation it would appear that in the absence of +water or steam leaks within the setting, there is no such harmful +action. + +[Illustration: Fig. 32. Babcock & Wilcox Boiler Arranged for Utilizing +Waste Heat from Open Hearth Furnace. This Setting may be Modified to +Take Care of Practically any Kind of Waste Gas] + + + + +CHIMNEYS AND DRAFT + + +The height and diameter of a properly designed chimney depend upon the +amount of fuel to be burned, its nature, the design of the flue, with +its arrangement relative to the boiler or boilers, and the altitude of +the plant above sea level. There are so many factors involved that as +yet there has been produced no formula which is satisfactory in taking +them all into consideration, and the methods used for determining stack +sizes are largely empirical. In this chapter a method sufficiently +comprehensive and accurate to cover all practical cases will be +developed and illustrated. + +Draft is the difference in pressure available for producing a flow of +the gases. If the gases within a stack be heated, each cubic foot will +expand, and the weight of the expanded gas per cubic foot will be less +than that of a cubic foot of the cold air outside the chimney. +Therefore, the unit pressure at the stack base due to the weight of the +column of heated gas will be less than that due to a column of cold air. +This difference in pressure, like the difference in head of water, will +cause a flow of the gases into the base of the stack. In its passage to +the stack the cold air must pass through the furnace or furnaces of the +boilers connected to it, and it in turn becomes heated. This newly +heated gas will also rise in the stack and the action will be +continuous. + +The intensity of the draft, or difference in pressure, is usually +measured in inches of water. Assuming an atmospheric temperature of 62 +degrees Fahrenheit and the temperature of the gases in the chimney as +500 degrees Fahrenheit, and, neglecting for the moment the difference in +density between the chimney gases and the air, the difference between +the weights of the external air and the internal flue gases per cubic +foot is .0347 pound, obtained as follows: + +Weight of a cubic foot of air at 62 degrees Fahrenheit = .0761 pound +Weight of a cubic foot of air at 500 degrees Fahrenheit = .0414 pound + ------------------------ + Difference = .0347 pound + +Therefore, a chimney 100 feet high, assumed for the purpose of +illustration to be suspended in the air, would have a pressure exerted +on each square foot of its cross sectional area at its base of .0347 x +100 = 3.47 pounds. As a cubic foot of water at 62 degrees Fahrenheit +weighs 62.32 pounds, an inch of water would exert a pressure of 62.32 / +12 = 5.193 pounds per square foot. The 100-foot stack would, therefore, +under the above temperature conditions, show a draft of 3.47 / 5.193 or +approximately 0.67 inches of water. + +The method best suited for determining the proper proportion of stacks +and flues is dependent upon the principle that if the cross sectional +area of the stack is sufficiently large for the volume of gases to be +handled, the intensity of the draft will depend directly upon the +height; therefore, the method of procedure is as follows: + + +1st. Select a stack of such height as will produce the draft required by +the particular character of the fuel and the amount to be burned per +square foot of grate surface. + + +2nd. Determine the cross sectional area necessary to handle the gases +without undue frictional losses. + + +The application of these rules follows: + +Draft Formula--The force or intensity of the draft, not allowing for the +difference in the density of the air and of the flue gases, is given by +the formula: + + / 1 1 \ +D = 0.52 H x P |--- - -----| (24) + \ T T_{1}/ + +in which + + D = draft produced, measured in inches of water, + H = height of top of stack above grate bars in feet, + P = atmospheric pressure in pounds per square inch, + T = absolute atmospheric temperature, + T_{1} = absolute temperature of stack gases. + +In this formula no account is taken of the density of the flue gases, it +being assumed that it is the same as that of air. Any error arising from +this assumption is negligible in practice as a factor of correction is +applied in using the formula to cover the difference between the +theoretical figures and those corresponding to actual operating +conditions. + +The force of draft at sea level (which corresponds to an atmospheric +pressure of 14.7 pounds per square inch) produced by a chimney 100 feet +high with the temperature of the air at 60 degrees Fahrenheit and that +of the flue gases at 500 degrees Fahrenheit is, + + / 1 1 \ +D = 0.52 x 100 x 14.7 | --- - --- | = 0.67 + \ 521 961 / + +Under the same temperature conditions this chimney at an atmospheric +pressure of 10 pounds per square inch (which corresponds to an altitude +of about 10,000 feet above sea level) would produce a draft of, + + / 1 1 \ +D = 0.52 x 100 x 10 | --- - --- | = 0.45 + \ 521 961 / + +For use in applying this formula it is convenient to tabulate values of +the product + + / 1 1 \ + 0.52 x 14.7|--- - -----| + \ T T_{1}/ + +which we will call K, for various values of T_{1}. With these values +calculated for assumed atmospheric temperature and pressure (24) becomes + + D = KH. (25) + +For average conditions the atmospheric pressure may be considered 14.7 +pounds per square inch, and the temperature 60 degrees Fahrenheit. For +these values and various stack temperatures K becomes: + +_Temperature Stack Gases_ _Constant K_ + 750 .0084 + 700 .0081 + 650 .0078 + 600 .0075 + 550 .0071 + 500 .0067 + 450 .0063 + 400 .0058 + 350 .0053 + +Draft Losses--The intensity of the draft as determined by the above +formula is theoretical and can never be observed with a draft gauge or +any recording device. However, if the ashpit doors of the boiler are +closed and there is no perceptible leakage of air through the boiler +setting or flue, the draft measured at the stack base will be +approximately the same as the theoretical draft. The difference existing +at other times represents the pressure necessary to force the gases +through the stack against their own inertia and the friction against the +sides. This difference will increase with the velocity of the gases. +With the ashpit doors closed the volume of gases passing to the stack +are a minimum and the maximum force of draft will be shown by a gauge. + +As draft measurements are taken along the path of the gases, the +readings grow less as the points at which they are taken are farther +from the stack, until in the boiler ashpit, with the ashpit doors open +for freely admitting the air, there is little or no perceptible rise in +the water of the gauge. The breeching, the boiler damper, the baffles +and the tubes, and the coal on the grates all retard the passage of the +gases, and the draft from the chimney is required to overcome the +resistance offered by the various factors. The draft at the rear of the +boiler setting where connection is made to the stack or flue may be 0.5 +inch, while in the furnace directly over the fire it may not be over, +say, 0.15 inch, the difference being the draft required to overcome the +resistance offered in forcing the gases through the tubes and around the +baffling. + +One of the most important factors to be considered in designing a stack +is the pressure required to force the air for combustion through the bed +of fuel on the grates. This pressure will vary with the nature of the +fuel used, and in many instances will be a large percentage of the total +draft. In the case of natural draft, its measure is found directly by +noting the draft in the furnace, for with properly designed ashpit doors +it is evident that the pressure under the grates will not differ +sensibly from atmospheric pressure. + +Loss in Stack--The difference between the theoretical draft as +determined by formula (24) and the amount lost by friction in the stack +proper is the available draft, or that which the draft gauge indicates +when connected to the base of the stack. The sum of the losses of draft +in the flue, boiler and furnace must be equivalent to the available +draft, and as these quantities can be determined from record of +experiments, the problem of designing a stack becomes one of +proportioning it to produce a certain available draft. + +The loss in the stack due to friction of the gases can be calculated +from the following formula: + + f W*W C H +[Delta]D = --------- (26) + A*A*A + +in which + +[Delta]D = draft loss in inches of water, + W = weight of gas in pounds passing per second, + C = perimeter of stack in feet, + H = height of stack in feet, + f = a constant with the following values at sea level: + .0015 for steel stacks, temperature of gases 600 degrees + Fahrenheit. + .0011 for steel stacks, temperature of gases 350 degrees + Fahrenheit. + .0020 for brick or brick-lined stacks, temperature of gases + 600 degrees Fahrenheit. + .0015 for brick or brick-lined stacks, temperature of gases + 350 degrees Fahrenheit. + A = Area of stack in square feet. + +[Illustration: 24,420 Horse-power Installation of Babcock & Wilcox +Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate +Stokers in the Quarry Street Station of the Commonwealth Edison Co., +Chicago, Ill.] + +This formula can also be used for calculating the frictional losses for +flues, in which case, C = the perimeter of the flue in feet, H = the +length of the flue in feet, the other values being the same as for +stacks. + +The available draft is equal to the difference between the theoretical +draft from formula (25) and the loss from formula (26), hence: + + f W*W C H +d^{1} = available draft = KH - --------- (27) + A*A*A + +Table 53 gives the available draft in inches that a stack 100 feet high +will produce when serving different horse powers of boilers with the +methods of calculation for other heights. + + TABLE 53 + + AVAILABLE DRAFT + + CALCULATED FOR 100-FOOT STACK OF DIFFERENT DIAMETERS ASSUMING STACK +TEMPERATURE OF 500 DEGREES FAHRENHEIT AND 100 POUNDS OF GAS PER HORSE POWER + + FOR OTHER HEIGHTS OF STACK MULTIPLY DRAFT BY HEIGHT / 100 + ++-----+-------------------------------------------------------------------+ +|Horse| | +|Power| Diameter of Stack in Inches | ++-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +| |36 |42 |48 |54 |60 |66 |72 |78 |84 |90 |96 |102|108|114|120|132|144| ++-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +| 100 |.64| | | | | | | | | | | | | | | | | +| 200 |.55|.62| | | | | | | | | | | | | | | | +| 300 |.41|.55|.61| | | | | | | | | | | | | | | +| 400 |.21|.46|.56|.61| | | | | | | | | | | | | | +| 500 | |.34|.50|.57|.61| | | | | | | | | | | | | +| 600 | |.19|.42|.53|.59| | | | | | | | | | | | | +| 700 | | |.34|.48|.56|.60|.63| | | | | | | | | | | +| 800 | | |.23|.43|.52|.58|.61|.63| | | | | | | | | | +| 900 | | | |.36|.49|.56|.60|.62|.64| | | | | | | | | +|1000 | | | |.29|.45|.53|.58|.61|.63|.64| | | | | | | | +|1100 | | | | |.40|.50|.56|.60|.62|.63|.64| | | | | | | +|1200 | | | | |.35|.47|.54|.58|.61|.63|.64|.65| | | | | | +|1300 | | | | |.29|.44|.52|.57|.60|.62|.63|.64|.65| | | | | +|1400 | | | | | |.40|.49|.55|.59|.61|.63|.64|.65|.65| | | | +|1500 | | | | | |.36|.47|.53|.58|.60|.62|.63|.64|.65|.65| | | +|1600 | | | | | |.31|.43|.52|.56|.59|.62|.63|.64|.65|.65| | | +|1700 | | | | | | |.41|.50|.55|.58|.61|.62|.64|.64|.65| | | +|1800 | | | | | | |.37|.47|.54|.57|.60|.62|.63|.64|.65| | | +|1900 | | | | | | |.34|.45|.52|.56|.59|.61|.63|.64|.64| | | +|2000 | | | | | | | |.43|.50|.55|.59|.61|.62|.63|.64| | | +|2100 | | | | | | | |.40|.49|.54|.58|.60|.62|.63|.64| | | +|2200 | | | | | | | |.38|.47|.53|.57|.59|.61|.62|.64| | | +|2300 | | | | | | | |.35|.45|.52|.56|.59|.61|.62|.63| | | +|2400 | | | | | | | |.32|.43|.50|.55|.58|.60|.62|.63| | | +|2500 | | | | | | | | |.41|.49|.54|.57|.60|.61|.63| | | +|2600 | | | | | | | | | |.47|.53|.56|.59|.61|.62|.64|.65| +|2700 | | | | | | | | | |.45|.52|.55|.58|.60|.62|.64|.65| +|2800 | | | | | | | | | |.44|.59|.55|.58|.60|.61|.64|.65| +|2900 | | | | | | | | | |.42|.49|.54|.57|.59|.61|.63|.65| +|3000 | | | | | | | | | |.40|.48|.53|.56|.59|.61|.63|.64| +|3100 | | | | | | | | | |.38|.47|.52|.56|.58|.60|.63|.64| +|3200 | | | | | | | | | | |.45|.51|.55|.58|.60|.63|.64| +|3300 | | | | | | | | | | |.44|.50|.54|.57|.59|.62|.64| +|3400 | | | | | | | | | | |.42|.49|.53|.56|.59|.62|.64| +|3500 | | | | | | | | | | |.40|.48|.52|.56|.58|.62|.64| +|3600 | | | | | | | | | | | |.47|.52|.55|.58|.61|.63| +|3700 | | | | | | | | | | | |.45|.51|.55|.57|.61|.63| +|3800 | | | | | | | | | | | |.44|.50|.54|.57|.61|.63| +|3900 | | | | | | | | | | | |.43|.49|.53|.56|.60|.63| +|4000 | | | | | | | | | | | |.42|.48|.52|.56|.60|.62| +|4100 | | | | | | | | | | | |.40|.47|.52|.55|.60|.62| +|4200 | | | | | | | | | | | |.39|.46|.51|.55|.59|.62| +|4300 | | | | | | | | | | | | |.45|.50|.54|.59|.62| +|4400 | | | | | | | | | | | | |.44|.49|.53|.59|.62| +|4500 | | | | | | | | | | | | |.43|.49|.53|.58|.61| +|4600 | | | | | | | | | | | | |.42|.48|.52|.58|.61| +|4700 | | | | | | | | | | | | |.41|.47|.51|.57|.61| +|4800 | | | | | | | | | | | | |.40|.46|.51|.57|.60| +|4900 | | | | | | | | | | | | | |.45|.50|.57|.60| +|5000 | | | | | | | | | | | | | |.44|.49|.56|.60| ++-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ + +FOR OTHER STACK TEMPERATURES ADD OR DEDUCT BEFORE MULTIPLYING BY +HEIGHT / 100 AS FOLLOWS[52] + +For 750 Degrees F. Add .17 inch. +For 700 Degrees F. Add .14 inch. +For 650 Degrees F. Add .11 inch. +For 600 Degrees F. Add .08 inch. +For 550 Degrees F. Add .04 inch. +For 450 Degrees F. Deduct .04 inch. +For 400 Degrees F. Deduct .09 inch. +For 350 Degrees F. Deduct .14 inch. + +[Graph: Horse Power of Boilers against Diameter of Stack in Inches + +Fig. 33. Diameter of Stacks and Horse Power they will Serve + +Computed from Formula (28). For brick or brick-lined stacks, increase +the diameter 6 per cent] + +Height and Diameter of Stacks--From this formula (27) it becomes evident +that a stack of certain diameter, if it be increased in height, will +produce the same available draft as one of larger diameter, the +additional height being required to overcome the added frictional loss. +It follows that among the various stacks that would meet the +requirements of a particular case there must be one which can be +constructed more cheaply than the others. It has been determined from +the relation of the cost of stacks to their diameters and heights, in +connection with the formula for available draft, that the minimum cost +stack has a diameter dependent solely upon the horse power of the +boilers it serves, and a height proportional to the available draft +required. + +Assuming 120 pounds of flue gas per hour for each boiler horse power, +which provides for ordinary overloads and the use of poor coal, the +method above stated gives: + +For an unlined steel stack-- + +diameter in inches = 4.68 (H. P.)^{2/5} (28) + +For a stack lined with masonry-- + +diameter in inches = 4.92 (H. P.)^{2/5} (29) + +In both of these formulae H. P. = the rated horse power of the boiler. + +From this formula the curve, Fig. 33, has been calculated and from it +the stack diameter for any boiler horse power can be selected. + +For stoker practice where a large stack serves a number of boilers, the +area is usually made about one-third more than the above rules call for, +which allows for leakage of air through the setting of any idle boilers, +irregularities in operating conditions, etc. + +Stacks with diameters determined as above will give an available draft +which bears a constant ratio of the theoretical draft, and allowing for +the cooling of the gases in their passage upward through the stack, this +ratio is 8. Using this factor in formula (25), and transposing, the +height of the chimney becomes, + + + d^{1} +H = ----- (30) + .8 K + +Where H = height of stack in feet above the level of the grates, + d^{1} = available draft required, + K = constant as in formula. + +Losses in Flues--The loss of draft in straight flues due to friction and +inertia can be calculated approximately from formula (26), which was +given for loss in stacks. It is to be borne in mind that C in this +formula is the actual perimeter of the flue and is least, relative to +the cross sectional area, when the section is a circle, is greater for a +square section, and greatest for a rectangular section. The retarding +effect of a square flue is 12 per cent greater than that of a circular +flue of the same area and that of a rectangular with sides as 1 and 1-1/2, +15 per cent greater. The greater resistance of the more or less uneven +brick or concrete flue is provided for in the value of the constants +given for formula (26). Both steel and brick flues should be short and +should have as near a circular or square cross section as possible. +Abrupt turns are to be avoided, but as long easy sweeps require valuable +space, it is often desirable to increase the height of the stack rather +than to take up added space in the boiler room. Short right-angle turns +reduce the draft by an amount which can be roughly approximated as equal +to 0.05 inch for each turn. The turns which the gases make in leaving +the damper box of a boiler, in entering a horizontal flue and in turning +up into a stack should always be considered. The cross sectional areas +of the passages leading from the boilers to the stack should be of ample +size to provide against undue frictional loss. It is poor economy to +restrict the size of the flue and thus make additional stack height +necessary to overcome the added friction. The general practice is to +make flue areas the same or slightly larger than that of the stack; +these should be, preferably, at least 20 per cent greater, and a safe +rule to follow in figuring flue areas is to allow 35 square feet per +1000 horse power. It is unnecessary to maintain the same size of flue +the entire distance behind a row of boilers, and the areas at any point +may be made proportional to the volume of gases that will pass that +point. That is, the areas may be reduced as connections to various +boilers are passed. + +[Illustration: 6000 Horse-power Installation of Babcock & Wilcox Boilers +at the United States Navy Yard, Washington, D. C.] + +With circular steel flues of approximately the same size as the stacks, +or reduced proportionally to the volume of gases they will handle, a +convenient rule is to allow 0.1 inch draft loss per 100 feet of flue +length and 0.05 inch for each right-angle turn. These figures are also +good for square or rectangular steel flues with areas sufficiently large +to provide against excessive frictional loss. For losses in brick or +concrete flues, these figures should be doubled. + +Underground flues are less desirable than overhead or rear flues for the +reason that in most instances the gases will have to make more turns +where underground flues are used and because the cross sectional area of +such flues will oftentimes be decreased on account of an accumulation of +dirt or water which it may be impossible to remove. + +In tall buildings, such as office buildings, it is frequently necessary +in order to carry spent gases above the roofs, to install a stack the +height of which is out of all proportion to the requirements of the +boilers. In such cases it is permissible to decrease the diameter of a +stack, but care must be taken that this decrease is not sufficient to +cause a frictional loss in the stack as great as the added draft +intensity due to the increase in height, which local conditions make +necessary. + +In such cases also the fact that the stack diameter is permissibly +decreased is no reason why flue sizes connecting to the stack should be +decreased. These should still be figured in proportion to the area of +the stack that would be furnished under ordinary conditions or with an +allowance of 35 square feet per 1000 horse power, even though the cross +sectional area appears out of proportion to the stack area. + +Loss in Boiler--In calculating the available draft of a chimney 120 +pounds per hour has been used as the weight of the gases per boiler +horse power. This covers an overload of the boiler to an extent of 50 +per cent and provides for the use of poor coal. The loss in draft +through a boiler proper will depend upon its type and baffling and will +increase with the per cent of rating at which it is run. No figures can +be given which will cover all conditions, but for approximate use in +figuring the available draft necessary it may be assumed that the loss +through a boiler will be 0.25 inch where the boiler is run at rating, +0.40 inch where it is run at 150 per cent of its rated capacity, and +0.70 inch where it is run at 200 per cent of its rated capacity. + +Loss in Furnace--The draft loss in the furnace or through the fuel bed +varies between wide limits. The air necessary for combustion must pass +through the interstices of the coal on the grate. Where these are large, +as is the case with broken coal, but little pressure is required to +force the air through the bed; but if they are small, as with bituminous +slack or small sizes of anthracite, a much greater pressure is needed. +If the draft is insufficient the coal will accumulate on the grates and +a dead smoky fire will result with the accompanying poor combustion; if +the draft is too great, the coal may be rapidly consumed on certain +portions of the grate, leaving the fire thin in spots and a portion of +the grates uncovered with the resulting losses due to an excessive +amount of air. + +[Graph: Force of Draft between Furnace and Ash Pit--Inches of Water +against Pounds of Coal burned per Square Foot of Grate Surface per Hour + +Fig. 34. Draft Required at Different Combustion Rates for Various Kinds +of Coal] + +Draft Required for Different Fuels--For every kind of fuel and rate of +combustion there is a certain draft with which the best general results +are obtained. A comparatively light draft is best with the free burning +bituminous coals and the amount to use increases as the percentage of +volatile matter diminishes and the fixed carbon increases, being highest +for the small sizes of anthracites. Numerous other factors such as the +thickness of fires, the percentage of ash and the air spaces in the +grates bear directly on this question of the draft best suited to a +given combustion rate. The effect of these factors can only be found by +experiment. It is almost impossible to show by one set of curves the +furnace draft required at various rates of combustion for all of the +different conditions of fuel, etc., that may be met. The curves in Fig. +34, however, give the furnace draft necessary to burn various kinds of +coal at the combustion rates indicated by the abscissae, for a general +set of conditions. These curves have been plotted from the records of +numerous tests and allow a safe margin for economically burning coals of +the kinds noted. + +Rate of Combustion--The amount of coal which can be burned per hour per +square foot of grate surface is governed by the character of the coal +and the draft available. When the boiler and grate are properly +proportioned, the efficiency will be practically the same, within +reasonable limits, for different rates of combustion. The area of the +grate, and the ratio of this area to the boiler heating surface will +depend upon the nature of the fuel to be burned, and the stack should be +so designed as to give a draft sufficient to burn the maximum amount of +fuel per square foot of grate surface corresponding to the maximum +evaporative requirements of the boiler. + +Solution of a Problem--The stack diameter can be determined from the +curve, Fig. 33. The height can be determined by adding the draft losses +in the furnace, through the boiler and flues, and computing from formula +(30) the height necessary to give this draft. + +Example: Proportion a stack for boilers rated at 2000 horse power, +equipped with stokers, and burning bituminous coal that will evaporate 8 +pounds of water from and at 212 degrees Fahrenheit per pound of fuel; +the ratio of boiler heating surface to grate surface being 50:1; the +flues being 100 feet long and containing two right-angle turns; the +stack to be able to handle overloads of 50 per cent; and the rated horse +power of the boilers based on 10 square feet of heating surface per +horse power. + +The atmospheric temperature may be assumed as 60 degrees Fahrenheit and +the flue temperatures at the maximum overload as 550 degrees Fahrenheit. +The grate surface equals 400 square feet. + + 2000 x 34-1/2 +The total coal burned at rating = ------------- = 8624 pounds. + 8 + +The coal per square foot of grate surface per hour at rating = + +8624 +---- = 22 pounds. + 400 + +For 50 per cent overload the combustion rate will be approximately 60 +per cent greater than this or 1.60 x 22 = 35 pounds per square foot of +grate surface per hour. The furnace draft required for the combustion +rate, from the curve, Fig. 34, is 0.6 inch. The loss in the boiler will +be 0.4 inch, in the flue 0.1 inch, and in the turns 2 x 0.05 = 0.1 inch. +The available draft required at the base of the stack is, therefore, + + _Inches_ +Boiler 0.4 +Furnace 0.6 +Flues 0.1 +Turns 0.1 + --- + Total 1.2 + +Since the available draft is 80 per cent of the theoretical draft, this +draft due to the height required is 1.2 / .8 = 1.5 inch. + +The chimney constant for temperatures of 60 degrees Fahrenheit and 550 +degrees Fahrenheit is .0071 and from formula (30), + + 1.5 +H = ----- = 211 feet. + .0071 + +Its diameter from curve in Fig. 33 is 96 inches if unlined, and 102 +inches inside if lined with masonry. The cross sectional area of the +flue should be approximately 70 square feet at the point where the total +amount of gas is to be handled, tapering to the boiler farthest from the +stack to a size which will depend upon the size of the boiler units +used. + +Correction in Stack Sizes for Altitudes--It has ordinarily been assumed +that a stack height for altitude will be increased inversely as the +ratio of the barometric pressure at the altitude to that at sea level, +and that the stack diameter will increase inversely as the two-fifths +power of this ratio. Such a relation has been based on the assumption of +constant draft measured in inches of water at the base of the stack for +a given rate of operation of the boilers, regardless of altitude. + +If the assumption be made that boilers, flues and furnace remain the +same, and further that the increased velocity of a given weight of air +passing through the furnace at a higher altitude would have no effect on +the combustion, the theory has been advanced[53] that a different law +applies. + +Under the above assumptions, whenever a stack is working at its maximum +capacity at any altitude, the entire draft is utilized in overcoming the +various resistances, each of which is proportional to the square of the +velocity of the gases. Since boiler areas are fixed, all velocities may +be related to a common velocity, say, that within the stack, and all +resistances may, therefore, be expressed as proportional to the square +of the chimney velocity. The total resistance to flow, in terms of +velocity head, may be expressed in terms of weight of a column of +external air, the numerical value of such head being independent of the +barometric pressure. Likewise the draft of a stack, expressed in height +of column of external air, will be numerically independent of the +barometric pressure. It is evident, therefore, that if a given boiler +plant, with its stack operated with a fixed fuel, be transplanted from +sea level to an altitude, assuming the temperatures remain constant, the +total draft head measured in height of column of external air will be +numerically constant. The velocity of chimney gases will, therefore, +remain the same at altitude as at sea level and the weight of gases +flowing per second with a fixed velocity will be proportional to the +atmospheric density or inversely proportional to the normal barometric +pressure. + +To develop a given horse power requires a constant weight of chimney gas +and air for combustion. Hence, as the altitude is increased, the density +is decreased and, for the assumptions given above, the velocity through +the furnace, the boiler passes, breeching and flues must be +correspondingly greater at altitude than at sea level. The mean +velocity, therefore, for a given boiler horse power and constant weight +of gases will be inversely proportional to the barometric pressure and +the velocity head measured in column of external air will be inversely +proportional to the square of the barometric pressure. + +For stacks operating at altitude it is necessary not only to increase +the height but also the diameter, as there is an added resistance within +the stack due to the added friction from the additional height. This +frictional loss can be compensated by a suitable increase in the +diameter and when so compensated, it is evident that on the assumptions +as given, the chimney height would have to be increased at a ratio +inversely proportional to the square of the normal barometric pressure. + +In designing a boiler for high altitudes, as already stated, the +assumption is usually made that a given grade of fuel will require the +same draft measured in inches of water at the boiler damper as at sea +level, and this leads to making the stack height inversely as the +barometric pressures, instead of inversely as the square of the +barometric pressures. The correct height, no doubt, falls somewhere +between the two values as larger flues are usually used at the higher +altitudes, whereas to obtain the ratio of the squares, the flues must be +the same size in each case, and again the effect of an increased +velocity of a given weight of air through the fire at a high altitude, +on the combustion, must be neglected. In making capacity tests with coal +fuel, no difference has been noted in the rates of combustion for a +given draft suction measured by a water column at high and low +altitudes, and this would make it appear that the correct height to use +is more nearly that obtained by the inverse ratio of the barometric +readings than by the inverse ratio of the squares of the barometric +readings. If the assumption is made that the value falls midway between +the two formulae, the error in using a stack figured in the ordinary way +by making the height inversely proportional to the barometric readings +would differ about 10 per cent in capacity at an altitude of 10,000 +feet, which difference is well within the probable variation of the size +determined by different methods. It would, therefore, appear that ample +accuracy is obtained in all cases by simply making the height inversely +proportional to the barometric readings and increasing the diameter so +that the stacks used at high altitudes have the same frictional +resistance as those used at low altitudes, although, if desired, the +stack may be made somewhat higher at high altitudes than this rule calls +for in order to be on the safe side. + +The increase of stack diameter necessary to maintain the same friction +loss is inversely as the two-fifths power of the barometric pressure. + +Table 54 gives the ratio of barometric readings of various altitudes to +sea level, values for the square of this ratio and values of the +two-fifths power of this ratio. + + TABLE 54 + + STACK CAPACITIES, CORRECTION FACTORS FOR + ALTITUDES + + _______________________________________________________________________ +| | | | | | +| Altitude | | R | | R^{2/5} | +| Height in Feet | Normal | Ratio Barometer | | Ratio Increase | +| Above | Barometer | Reading | R*R | in Stack | +| Sea Level | | Sea Level to | | Diameter | +| | | Altitude | | | +|________________|___________|_________________|_______|________________| +| | | | | | +| 0 | 30.00 | 1.000 | 1.000 | 1.000 | +| 1000 | 28.88 | 1.039 | 1.079 | 1.015 | +| 2000 | 27.80 | 1.079 | 1.064 | 1.030 | +| 3000 | 26.76 | 1.121 | 1.257 | 1.047 | +| 4000 | 25.76 | 1.165 | 1.356 | 1.063 | +| 5000 | 24.79 | 1.210 | 1.464 | 1.079 | +| 6000 | 23.87 | 1.257 | 1.580 | 1.096 | +| 7000 | 22.97 | 1.306 | 1.706 | 1.113 | +| 8000 | 22.11 | 1.357 | 1.841 | 1.130 | +| 9000 | 21.28 | 1.410 | 1.988 | 1.147 | +| 10000 | 20.49 | 1.464 | 2.144 | 1.165 | +|________________|___________|_________________|_______|________________| + +These figures show that the altitude affects the height to a much +greater extent than the diameter and that practically no increase in +diameter is necessary for altitudes up to 3000 feet. + +For high altitudes the increase in stack height necessary is, in some +cases, such as to make the proportion of height to diameter +impracticable. The method to be recommended in overcoming, at least +partially, the great increase in height necessary at high altitudes is +an increase in the grate surface of the boilers which the stack serves, +in this way reducing the combustion rate necessary to develop a given +power and hence the draft required for such combustion rate. + + TABLE 55 + + STACK SIZES BY KENT'S FORMULA + + ASSUMING 5 POUNDS OF COAL PER HORSE POWER + + + ____________________________________________________________________ +| | | | | +| | | Height of Stack in Feet |Side of| +| | |______________________________________________|Equiva-| +| Dia- | Area | | | | | | | | | | | lent | +| meter|Square| 50| 60| 70| 80 | 90 | 100| 110| 125| 150| 175|Square | +|Inches| Feet |___|___|___|____|____|____|____|____|____|____| Stack | +| | | |Inches | +| | | Commercial Horse Power | | +|______|______|______________________________________________|_______| +| | | | | | | | | | | | | | +| 33 | 5.94|106|115|125| 133| 141| 149| | | | | 30 | +| 36 | 7.07|129|141|152| 163| 173| 182| | | | | 32 | +| 39 | 8.30|155|169|183| 196| 208| 219| 229| 245| | | 35 | +| 42 | 9.62|183|200|216| 231| 245| 258| 271| 289| 316| | 38 | +| 48 | 12.57|246|269|290| 311| 330| 348| 365| 389| 426| 460| 43 | +| 54 | 15.90|318|348|376| 402| 427| 449| 472| 503| 551| 595| 48 | +| 60 | 19.64|400|437|473| 505| 536| 565| 593| 632| 692| 748| 54 | +| 66 | 23.76|490|537|580| 620| 658| 694| 728| 776| 849| 918| 59 | +| 72 | 28.27|591|646|698| 747| 792| 835| 876| 934|1023|1105| 64 | +| 78 | 33.18|700|766|828| 885| 939| 990|1038|1107|1212|1310| 70 | +| 84 | 38.48|818|896|968|1035|1098|1157|1214|1294|1418|1531| 75 | +|______|______|___|___|___|____|____|____|____|____|____|____|_______| +| | | | | +| | | Height of Stack in Feet |Side of| +| | |______________________________________________|Equiva-| +| Dia- | Area | | | | | | | | | lent | +| meter|Square| 100| 110 | 125 | 150 | 175 | 200 | 225 | 250 |Square | +|Inches| Feet |____|_____|_____|_____|_____|_____|_____|_____| Stack | +| | | |Inches | +| | | Commercial Horse Power | | +|______|______|______________________________________________|_______| +| | | | | | | | | | | | +| 90 | 44.18|1338| 1403| 1496| 1639| 1770| 1893| 2008| 2116| 80 | +| 96 | 50.27|1532| 1606| 1713| 1876| 2027| 2167| 2298| 2423| 86 | +| 102 | 56.75|1739| 1824| 1944| 2130| 2300| 2459| 2609| 2750| 91 | +| 108 | 63.62|1959| 2054| 2190| 2392| 2592| 2770| 2939| 3098| 98 | +| 114 | 70.88|2192| 2299| 2451| 2685| 2900| 3100| 3288| 3466| 101 | +| 120 | 78.54|2438| 2557| 2726| 2986| 3226| 3448| 3657| 3855| 107 | +| 126 | 86.59|2697| 2829| 3016| 3303| 3568| 3814| 4046| 4265| 112 | +| 132 | 95.03|2970| 3114| 3321| 3637| 3929| 4200| 4455| 4696| 117 | +| 144 |113.10|3554| 3726| 3973| 4352| 4701| 5026| 5331| 5618| 128 | +| 156 |132.73|4190| 4393| 4684| 5131| 5542| 5925| 6285| 6624| 138 | +| 168 |153.94|4878| 5115| 5454| 5974| 6454| 6899| 7318| 7713| 150 | +|______|______|____|_____|_____|_____|_____|_____|_____|_____|_______| + +Kent's Stack Tables--Table 55 gives, in convenient form for approximate +work, the sizes of stacks and the horse power of boilers which they will +serve. This table is a modification of Mr. William Kent's stack table +and is calculated from his formula. Provided no unusual conditions are +encountered, it is reliable for the ordinary rates of combustion with +bituminous coals. It is figured on a consumption of 5 pounds of coal +burned per hour per boiler horse power developed, this figure giving a +fairly liberal allowance for the use of poor coal and for a reasonable +overload. When the coal used is a low grade bituminous of the Middle or +Western States, it is strongly recommended that these sizes be increased +materially, such an increase being from 25 to 60 per cent, depending +upon the nature of the coal and the capacity desired. For the coal +burned per hour for any size stack given in the table, the values should +be multiplied by 5. + +A convenient rule for large stacks, 200 feet high and over, is to +provide 30 square feet of cross sectional area per 1000 rated horse +power. + +Stacks for Oil Fuel--The requirements of stacks connected to boilers +under which oil fuel is burned are entirely different from those where +coal is used. While more attention has been paid to the matter of stack +sizes for oil fuel in recent years, there has not as yet been gathered +the large amount of experimental data available for use in designing +coal stacks. + +In the case of oil-fired boilers the loss of draft through the fuel bed +is partially eliminated. While there may be practically no loss through +any checkerwork admitting air to the furnace when a boiler is new, the +areas for the air passage in this checkerwork will in a short time be +decreased, due to the silt which is present in practically all fuel oil. +The loss in draft through the boiler proper at a given rating will be +less than in the case of coal-fired boilers, this being due to a +decrease in the volume of the gases. Further, the action of the oil +burner itself is to a certain extent that of a forced draft. To offset +this decrease in draft requirement, the temperature of the gases +entering the stack will be somewhat lower where oil is used than where +coal is used, and the draft that a stack of a given height would give, +therefore, decreases. The factors as given above, affecting as they do +the intensity of the draft, affect directly the height of the stack to +be used. + +As already stated, the volume of gases from oil-fired boilers being less +than in the case of coal, makes it evident that the area of stacks for +oil fuel will be less than for coal. It is assumed that these areas will +vary directly as the volume of the gases to be handled, and this volume +for oil may be taken as approximately 60 per cent of that for coal. + +In designing stacks for oil fuel there are two features which must not +be overlooked. In coal-firing practice there is rarely danger of too +much draft. In the burning of oil, however, this may play an important +part in the reduction of plant economy, the influence of excessive draft +being more apparent where the load on the plant may be reduced at +intervals. The reason for this is that, aside from a slight decrease in +temperature at reduced loads, the tendency, due to careless firing, is +toward a constant gas flow through the boiler regardless of the rate of +operation, with the corresponding increase of excess air at light loads. +With excessive stack height, economical operation at varying loads is +almost impossible with hand control. With automatic control, however, +where stacks are necessarily high to take care of known peaks, under +lighter loads this economical operation becomes less difficult. For this +reason the question of designing a stack for a plant where the load is +known to be nearly a constant is easier than for a plant where the load +will vary over a wide range. While great care must be taken to avoid +excessive draft, still more care must be taken to assure a draft suction +within all parts of the setting under any and all conditions of +operation. It is very easily possible to more than offset the economy +gained through low draft, by the losses due to setting deterioration, +resulting from such lack of suction. Under conditions where the suction +is not sufficient to carry off the products of combustion, the action of +the heat on the setting brickwork will cause its rapid failure. + +[Illustration: 7800 Horse-power Installation of Babcock & Wilcox +Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the +Metropolitan West Side Elevated Ry. Co., Chicago, Ill.] + +It becomes evident, therefore, that the question of stack height for +oil-fired boilers is one which must be considered with the greatest of +care. The designer, on the one hand, must guard against the evils of +excessive draft with the view to plant economy, and, on the other, +against the evils of lack of draft from the viewpoint of upkeep cost. +Stacks for this work should be proportioned to give ample draft for the +maximum overload that a plant will be called upon to carry, all +conditions of overload carefully considered. At the same time, where +this maximum overload is figured liberally enough to insure a draft +suction within the setting under all conditions, care must be taken +against the installation of a stack which would give more than this +maximum draft. + + TABLE 56 + + STACK SIZES FOR OIL FUEL + + ADAPTED FROM C. R. WEYMOUTH'S TABLE (TRANS. + A. S. M. E. VOL. 34) + ++----------------------------------------------------+ +|+--------+-----------------------------------------+| +|| | Height in Feet Above Boiler Room Floor || +||Diameter+------+------+------+-----+--------------+| +|| Inches | 80 | 90 | 100 | 120 | 140 | 160 || +|+--------+------+------+------+------+------+------+| +|| 33 | 161 | 206 | 233 | 270 | 306 | 315 || +|| 36 | 208 | 253 | 295 | 331 | 363 | 387 || +|| 39 | 251 | 303 | 343 | 399 | 488 | 467 || +|| 42 | 295 | 359 | 403 | 474 | 521 | 557 || +|| 48 | 399 | 486 | 551 | 645 | 713 | 760 || +|| 54 | 519 | 634 | 720 | 847 | 933 | 1000 || +|| 60 | 657 | 800 | 913 | 1073 | 1193 | 1280 || +|| 66 | 813 | 993 | 1133 | 1333 | 1480 | 1593 || +|| 72 | 980 | 1206 | 1373 | 1620 | 1807 | 1940 || +|| 84 | 1373 | 1587 | 1933 | 2293 | 2560 | 2767 || +|| 96 | 1833 | 2260 | 2587 | 3087 | 3453 | 3740 || +|| 108 | 2367 | 2920 | 3347 | 4000 | 4483 | 4867 || +|| 120 | 3060 | 3660 | 4207 | 5040 | 5660 | 6160 || +|+--------+------+------+------+------+------+------+| ++----------------------------------------------------+ + +Figures represent nominal rated horse power. Sizes as given good for 50 +per cent overloads. + +Based on centrally located stacks, short direct flues and ordinary +operating efficiencies. + +Table 56 gives the sizes of stacks, and horse power which they will +serve for oil fuel. This table is, in modified form, one calculated by +Mr. C. R. Weymouth after an exhaustive study of data pertaining to the +subject, and will ordinarily give satisfactory results. + +Stacks for Blast Furnace Gas Work--For boilers burning blast furnace +gas, as in the case of oil-fired boilers, stack sizes as suited for coal +firing will have to be modified. The diameter of stacks for this work +should be approximately the same as for coal-fired boilers. The volume +of gases would be slightly greater than from a coal fire and would +decrease the draft with a given stack, but such a decrease due to volume +is about offset by an increase due to somewhat higher temperatures in +the case of the blast furnace gases. + +Records show that with this class of fuel 175 per cent of the rated +capacity of a boiler can be developed with a draft at the boiler damper +of from 0.75 inch to 1.0 inch, and it is well to limit the height of +stacks to one which will give this draft as a maximum. A stack of proper +diameter, 130 feet high above the ground, will produce such a draft and +this height should ordinarily not be exceeded. Until recently the +question of economy in boilers fired with blast furnace gas has not been +considered, but, aside from the economical standpoint, excessive draft +should be guarded against in order to lower the upkeep cost. + +Stacks should be made of sufficient height to produce a draft that will +develop the maximum capacity required, and this draft decreased +proportionately for loads under the maximum by damper regulation. The +amount of gas fed to a boiler for any given rating is a fixed quantity +and if a draft in excess of that required for that particular rate of +operation is supplied, economy is decreased and the wear and tear on the +setting is materially increased. Excess air which is drawn in, either +through or around the gas burners by an excessive draft, will decrease +economy, as in any other class of work. Again, as in oil-fired practice, +it is essential on the other hand that a suction be maintained within +all parts of the setting, in this case not only to provide against +setting deterioration but to protect the operators from leakage of gas +which is disagreeable and may be dangerous. Aside from the intensity of +the draft, a poor mixture of the gas and air or a "laneing" action may +lead to secondary combustion with the possibility of dangerous +explosions within the setting, may cause a pulsating action within the +setting, may increase the exit temperatures to a point where there is +danger of burning out damper boxes, and, in general, is hard on the +setting. It is highly essential, therefore, that the furnace be properly +constructed to meet the draft which will be available. + +Stacks for Wood-fired Boilers--For boilers using wood as fuel, there is +but little data upon which to base stack sizes. The loss of draft +through the bed of fuel will vary over limits even wider than in the +case of coal, for in this class of fuel the moisture may run from +practically 0.0 per cent to over 60 per cent, and the methods of +handling and firing are radically different for the different classes of +wood (see chapter on Wood-burning Furnaces). As economy is ordinarily of +little importance, high stack temperatures may be expected, and often +unavoidably large quantities of excess air are supplied due to the +method of firing. In general, it may be stated that for this class of +fuel the diameter of stacks should be at least as great as for coal-fired +boilers, while the height may be slightly decreased. It is far the best +plan in designing a stack for boilers using wood fuel to consider each +individual set of conditions that exist, rather than try to follow any +general rule. + +One factor not to be overlooked in stacks for wood burning is their +location. The fine particles of this fuel are often carried unconsumed +through the boiler, and where the stack is not on top of the boiler, +these particles may accumulate in the base of the stack below the point +at which the flue enters. Where there is any air leakage through the +base of such a stack, this fuel may become ignited and the stack burned. +Where there is a possibility of such action taking place, it is well to +line the stack with fire brick for a portion of its height. + +Draft Gauges--The ordinary form of draft gauge, Fig. 35, which consists +of a U-tube, containing water, lacks sensitiveness in measuring such +slight pressure differences as usually exist, and for that reason gauges +which multiply the draft indications are more convenient and are much +used. + +[Illustration: Fig. 35. U-tube Draft Gauge] + +[Illustration: Fig. 36. Barrus Draft Gauge] + +An instrument which has given excellent results is one introduced by Mr. +G. H. Barrus, which multiplies the ordinary indications as many times as +desired. This is illustrated in Fig. 36, and consists of a U-tube made +of one-half inch glass, surmounted by two larger tubes, or chambers, +each having a diameter of 2-1/2 inches. Two different liquids which will +not mix, and which are of different color, are used, usually alcohol +colored red and a certain grade of lubricating oil. The movement of the +line of demarcation is proportional to the difference in the areas of +the chambers and the U-tube connecting them. The instrument is +calibrated by comparison with the ordinary U-tube gauge. + +In the Ellison form of gauge the lower portion of the ordinary U-tube +has been replaced by a tube slightly inclined to the horizontal, as +shown in Fig. 37. By this arrangement any vertical motion in the +right-hand upright tube causes a very much greater travel of the liquid +in the inclined tube, thus permitting extremely small variation in the +intensity of the draft to be read with facility. + +[Illustration: Fig. 37. Ellison Draft Gauge] + +The gauge is first leveled by means of the small level attached to it, +both legs being open to the atmosphere. The liquid is then adjusted +until its meniscus rests at the zero point on the left. The right-hand +leg is then connected to the source of draft by means of a piece of +rubber tubing. Under these circumstances, a rise of level of one inch in +the right-hand vertical tube causes the meniscus in the inclined tube to +pass from the point 0 to 1.0. The scale is divided into tenths of an +inch, and the sub-divisions are hundredths of an inch. + +The makers furnish a non-drying oil for the liquid, usually a 300 +degrees test refined petroleum. + +A very convenient form of the ordinary U-tube gauge is known as the +Peabody gauge, and it is shown in Fig. 38. This is a small modified +U-tube with a sliding scale between the two legs of the U and with +connections such that either a draft suction or a draft pressure may be +taken. The tops of the sliding pieces extending across the tubes are +placed at the bottom of the meniscus and accurate readings in hundredths +of an inch are obtained by a vernier. + +[Illustration: Fig. 38. Peabody Draft Gauge] + + + + +EFFICIENCY AND CAPACITY OF BOILERS + + +Two of the most important operating factors entering into the +consideration of what constitutes a satisfactory boiler are its +efficiency and capacity. The relation of these factors to one another +will be considered later under the selection of boilers with reference +to the work they are to accomplish. The present chapter deals with the +efficiency and capacity only with a view to making clear exactly what is +meant by these terms as applied to steam generating apparatus, together +with the methods of determining these factors by tests. + +Efficiency--The term "efficiency", specifically applied to a steam +boiler, is the ratio of heat absorbed by the boiler in the generation of +steam to the total amount of heat available in the medium utilized in +securing such generation. When this medium is a solid fuel, such as +coal, it is impossible to secure the complete combustion of the total +amount fed to the boiler. A portion is bound to drop through the grates +where it becomes mixed with the ash and, remaining unburned, produces no +heat. Obviously, it is unfair to charge the boiler with the failure to +absorb the portion of available heat in the fuel that is wasted in this +way. On the other hand, the boiler user must pay for such waste and is +justified in charging it against the combined boiler and furnace. Due to +this fact, the efficiency of a boiler, as ordinarily stated, is in +reality the combined efficiency of the boiler, furnace and grate, and + + Efficiency of boiler,} Heat absorbed per pound of fuel + furnace and grate } = ------------------------------- (31) + Heat value per pound of fuel + + +The efficiency will be the same whether based on dry fuel or on fuel as +fired, including its content of moisture. For example: If the coal +contained 3 per cent of moisture, the efficiency would be + + Heat absorbed per pound of dry coal x 0.97 + ------------------------------------------ + Heat value per pound of dry coal x 0.97 + +where 0.97 cancels and the formula becomes (31). + +The heat supplied to the boiler is due to the combustible portion of +fuel which is actually burned, irrespective of what proportion of the +total combustible fired may be.[54] This fact has led to the use of a +second efficiency basis on combustible and which is called the +efficiency of boiler and furnace[55], namely, + + Efficiency of boiler and furnace[55] + + Heat absorbed per pound of combustible[56] + = -------------------------------------- (32) + Heat value per pound of combustible + + +The efficiency so determined is used in comparing the relative +performance of boilers, irrespective of the type of grates used under +them. If the loss of fuel through the grates could be entirely overcome, +the efficiencies obtained by (31) and (32) would obviously be the same. +Hence, in the case of liquid and gaseous fuels, where there is +practically no waste, these efficiencies are almost identical. + +As a matter of fact, it is extremely difficult, if not impossible, to +determine the actual efficiency of a boiler alone, as distinguished from +the combined efficiency of boiler, grate and furnace. This is due to the +fact that the losses due to excess air cannot be correctly attributed to +either the boiler or the furnace, but only to a combination of the +complete apparatus. Attempts have been made to devise methods for +dividing the losses proportionately between the furnace and the boiler, +but such attempts are unsatisfactory and it is impossible to determine +the efficiency of a boiler apart from that of a furnace in such a way as +to make such determination of any practical value or in a way that might +not lead to endless dispute, were the question to arise in the case of a +guaranteed efficiency. From the boiler manufacturer's standpoint, the +only way of establishing an efficiency that has any value when +guarantees are to be met, is to require the grate or stoker manufacturer +to make certain guarantees as to minimum CO_{2}, maximum CO, and that +the amount of combustible in the ash and blown away with the flue gases +does not exceed a certain percentage. With such a guarantee, the +efficiency should be based on the combined furnace and boiler. + +General practice, however, has established the use of the efficiency +based upon combustible as representing the efficiency of the boiler +alone. When such an efficiency is used, its exact meaning, as pointed +out on opposite page, should be realized. + +The computation of the efficiencies described on opposite page is best +illustrated by example. + +Assume the following data to be determined from an actual boiler trial. + +Steam pressure by gauge, 200 pounds. +Feed temperature, 180 degrees. +Total weight of coal fired, 17,500 pounds. +Percentage of moisture in coal, 3 per cent. +Total ash and refuse, 2396 pounds. +Total water evaporated, 153,543 pounds. +Per cent of moisture in steam, 0.5 per cent. +Heat value per pound of dry coal, 13,516. +Heat value per pound of combustible, 15,359. + +The factor of evaporation for such a set of conditions is 1.0834. The +actual evaporation corrected for moisture in the steam is 152,775 and +the equivalent evaporation from and at 212 degrees is, therefore, +165,516 pounds. + +The total dry fuel will be 17,500 x .97 = 16,975, and the evaporation +per pound of dry fuel from and at 212 degrees will be 165,516 / 16,975 = +9.75 pounds. The heat absorbed per pound of dry fuel will, therefore, be +9.75 x 970.4 = 9461 B. t. u. Hence, the efficiency by (31) will be 9461 +/ 13,516 = 70.0 per cent. The total combustible burned will be 16,975 +- 2396 = 14,579, and the evaporation from and at 212 degrees per pound +of combustible will be 165,516 / 14,579 = 11.35 pounds. Hence, the +efficiency based on combustible from (32) will be (11.35 x 97.04) / +15,359 = 71.79.[**should be 71.71] + +For approximate results, a chart may be used to take the place of a +computation of efficiency. Fig. 39 shows such a chart based on the +evaporation per pound of dry fuel and the heat value per pound of dry +fuel, from which efficiencies may be read directly to within one-half of +one per cent. It is used as follows: From the intersection of the +horizontal line, representing the evaporation per pound of fuel, with +the vertical line, representing the heat value per pound, the efficiency +is read directly from the diagonal scale of efficiencies. This chart may +also be used for efficiency based upon combustible when the evaporation +from and at 212 degrees and the heat values are both given in terms of +combustible. + +[Graph: Evaporation from and at 212deg. per Pound of Dry Fuel +against B.T.U. per Pound of Dry Fuel + +Fig. 39. Efficiency Chart. Calculated from Marks and Davis Tables + +Diagonal Lines Represent Per Cent Efficiency] + +Boiler efficiencies will vary over a wide range, depending on a great +variety of factors and conditions. The highest efficiencies that have +been secured with coal are in the neighborhood of 82 per cent and from +that point efficiencies are found all the way down to below 50 per cent. +Table 59[57] of tests of Babcock & Wilcox boilers under varying +conditions of fuel and operation will give an idea of what may be +obtained with proper operating conditions. + +The difference between the efficiency secured in any boiler trial and +the perfect efficiency, 100 per cent, includes the losses, some of which +are unavoidable in the present state of the art, arising in the +conversion of the heat energy of the coal to the heat energy in the +steam. These losses may be classified as follows: + +1st. Loss due to fuel dropped through the grate. + +2nd. Loss due to unburned fuel which is carried by the draft, as small +particles, beyond the bridge wall into the setting or up the stack. + +3rd. Loss due to the utilization of a portion of the heat in heating the +moisture contained in the fuel from the temperature of the atmosphere to +212 degrees; to evaporate it at that temperature and to superheat the +steam thus formed to the temperature of the flue gases. This steam, of +course, is first heated to the temperature of the furnace but as it +gives up a portion of this heat in passing through the boiler, the +superheating to the temperature of the exit gases is the correct degree +to be considered. + +4th. Loss due to the water formed and by the burning of the hydrogen in +the fuel which must be evaporated and superheated as in item 3. + +5th. Loss due to the superheating of the moisture in the air supplied +from the atmospheric temperature to the temperature of the flue gases. + +6th. Loss due to the heating of the dry products of combustion to the +temperature of the flue gases. + +7th. Loss due to the incomplete combustion of the fuel when the carbon +is not completely consumed but burns to CO instead of CO_{2}. The CO +passes out of the stack unburned as a volatile gas capable of further +combustion. + +8th. Loss due to radiation of heat from the boiler and furnace settings. + +Obviously a very elaborate test would have to be made were all of the +above items to be determined accurately. In ordinary practice it has +become customary to summarize these losses as follows, the methods of +computing the losses being given in each instance by a typical example: + +(A) Loss due to the heating of moisture in the fuel from the atmospheric +temperature to 212 degrees, evaporate it at that temperature and +superheat it to the temperature of the flue gases. This in reality is +the total heat above the temperature of the air in the boiler room, in +one pound of superheated steam at atmospheric pressure at the +temperature of the flue gases, multiplied by the percentage of moisture +in the fuel. As the total heat above the temperature of the air would +have to be computed in each instance, this loss is best expressed by: + +Loss in B. t. u. per pound = W(212-t+970.4+.47(T-212)) (33) + +Where W = per cent of moisture in coal, + t = the temperature of air in the boiler room, + T = temperature of the flue gases, + .47 = the specific heat of superheated steam at the atmospheric + pressure and at the flue gas temperature, + (212-t) = B. t. u. necessary to heat one pound of water from the + temperature of the boiler room to 212 degrees, + 970.4 = B. t. u. necessary to evaporate one pound of water at 212 + degrees to steam at atmospheric pressure, +.47(T-212) = B. t. u. necessary to superheat one pound of steam at + atmospheric pressure from 212 degrees to temperature T. + +[Illustration: Portion of 15,000 Horse-power Installation of Babcock & +Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Northumberland, Pa., Plant of the Atlas Portland Cement Co. This +Company Operates a Total of 24,000 Horse Power of Babcock & Wilcox +Boilers in its Various Plants] + +(B) Loss due to heat carried away in the steam produced by the burning +of the hydrogen component of the fuel. In burning, one pound of hydrogen +unites with 8 pounds of oxygen to form 9 pounds of steam. Following the +reasoning of item (A), therefore, this loss will be: + +Loss in B. t. u. per pound = 9H((212-t)+970.4+.47(T-212)) (34) + +where H = the percentage by weight of hydrogen. + +This item is frequently considered as a part of the unaccounted for +loss, where an ultimate analysis of the fuel is not given. + +(C) Loss due to heat carried away by dry chimney gases. This is +dependent upon the weight of gas per pound of coal which may be +determined by formula (16), page 158. + +Loss in B. t. u. per pound = (T-t)x.24xW. + +Where T and t have values as in (33), + +.24 = specific heat of chimney gases, + + W = weight of dry chimney gas per pound of coal. + +(D) Loss due to incomplete combustion of the carbon content of the fuel, +that is, the burning of the carbon to CO instead of CO_{2}. + + 10,150 CO +Loss in B. t. u. per pound = Cx--------- (35) + CO_{2}+CO + +C = per cent of carbon in coal by ultimate analysis, + +CO and CO_{2} = per cent of CO and CO_{2} by volume from flue gas +analysis. + +10,150 = the number of heat units generated by burning to CO_{2} one +pound of carbon contained in carbon monoxide. + +(E) Loss due to unconsumed carbon in the ash (it being usually assumed +that all the combustible in the ash is carbon). + +Loss in B. t. u. per pound = +per cent C x per cent ash x B. t. u. per pound of combustible in the ash +(usually taken as 14,600 B. t. u.) (36) + +The loss incurred in this way is, directly, the carbon in the ash in +percentage terms of the total dry coal fired, multiplied by the heat +value of carbon. + +To compute this item, which is of great importance in comparing the +relative performances of different designs of grates, an analysis of the +ash must be available. + +The other losses, namely, items 2, 5 and 8 of the first classification, +are ordinarily grouped under one item, as unaccounted for losses, and +are obviously the difference between 100 per cent and the sum of the +heat utilized and the losses accounted for as given above. Item 5, or +the loss due to the moisture in the air, may be readily computed, the +moisture being determined from wet and dry bulb thermometer readings, +but it is usually disregarded as it is relatively small, averaging, say, +one-fifth to one-half of one per cent. Lack of data may, of course, make +it necessary to include certain items of the second and ordinary +classification in this unaccounted for group. + + TABLE 57 + + DATA FROM WHICH HEAT BALANCE + (TABLE 58) IS COMPUTED + ++------------------------------------------------------+ +|+----------------------------------------------------+| +||Steam Pressure by Gauge, Pounds | 192 || +||Temperature of Feed, Degrees Fahrenheit | 180 || +||Degrees of Superheat, Degrees Fahrenheit |115.2|| +||Temperature of Boiler Room, Degrees Fahrenheit| 81 || +||Temperature of Exit Gases, Degrees Fahrenheit | 480 || +||Weight of Coal Used per Hour, Pounds | 5714|| +||Moisture, Per Cent | 1.83|| +||Dry Coal Per Hour, Pounds | 5609|| +||Ash and Refuse per Hour, Pounds | 561|| +||Ash and Refuse (of Dry Coal), Per Cent |10.00|| +||Actual Evaporation per Hour, Pounds |57036|| +|| .- C, Per Cent |78.57|| +|| | H, Per Cent | 5.60|| +||Ultimate | O, Per Cent | 7.02|| +||Analysis -+ N, Per Cent | 1.11|| +||Dry Coal | Ash, Per Cent | 6.52|| +|| '- Sulphur, Per Cent | 1.18|| +||Heat Value per Pound Dry Coal, B. t. u. |14225|| +||Heat Value per Pound Combustible, B. t. u. |15217|| +||Combustible in Ash by Analysis, Per Cent | 17.9|| +|| .- CO_{2}, Per Cent |14.33|| +||Flue Gas -+ O, Per Cent | 4.54|| +||Analysis | CO, Per Cent | 0.11|| +|| '- N, Per Cent |81.02|| +|+----------------------------------------------+-----+| ++------------------------------------------------------+ + +A schedule of the losses as outlined, requires an evaporative test of +the boiler, an analysis of the flue gases, an ultimate analysis of the +fuel, and either an ultimate or proximate analysis of the ash. As the +amount of unaccounted for losses forms a basis on which to judge the +accuracy of a test, such a schedule is called a "heat balance". + +A heat balance is best illustrated by an example: Assume the data as +given in Table 57 to be secured in an actual boiler test. + +From this data the factor of evaporation is 1.1514 and the evaporation +per hour from and at 212 degrees is 65,671 pounds. Hence the evaporation +from and at 212 degrees per pound of dry coal is 65,671/5609 = 11.71 +pounds. The efficiency of boiler, furnace and grate is: + +(11.71x970.4)/14,225 = 79.88 per cent. + +The heat losses are: + +(A) Loss due to moisture in coal, + += .01831 ((212-81)+970.4+.47(480-212)) += 22. B. t. u., += 0.15 per cent. + +(B) The loss due to the burning of hydrogen: + += 9x.0560((212-81)+970.4+.47(480-212)) += 618 B. t. u., += 4.34 per cent. + +(C) To compute the loss in the heat carried away by dry chimney gases +per pound of coal the weight of such gases must be first determined. +This weight per pound of coal is: + +(11CO_{2}+8O+7(CO+N)) +(-------------------)C +( 3(CO_{2}+CO) ) + +where CO_{2}, O, CO and H are the percentage by volume as determined by +the flue gas analysis and C is the percentage by weight of carbon in the +dry fuel. Hence the weight of gas per pound of coal will be, + +(11x14.33+8x4.54+7(0.11+81.02)) +(-----------------------------)x78.57 = 13.7 pounds. +( 3(14.33+0.11) ) + +Therefore the loss of heat in the dry gases carried up the chimney = + +13.7x0.24(480-81) = 1311 B. t. u., + = 9.22 per cent. + +(D) The loss due to incomplete combustion as evidenced by the presence +of CO in the flue gas analysis is: + + 0.11 +----------x.7857x10,150 = 61. B. t. u., +14.33+0.11 = .43 per cent. + +(E) The loss due to unconsumed carbon in the ash: + +The analysis of the ash showed 17.9 per cent to be combustible matter, +all of which is assumed to be carbon. The test showed 10.00 of the total +dry fuel fired to be ash. Hence 10.00x.179 = 1.79 per cent of the total +fuel represents the proportion of this total unconsumed in the ash and +the loss due to this cause is + +1.79 per cent x 14,600 = 261 B. t. u., + = 1.83 per cent. + +The heat absorbed by the boilers per pound of dry fuel is 11.71x970.4 = +11,363 B. t. u. This quantity plus losses (A), (B), (C), (D) and (E), or +11,363+22+618+1311+61+261 = 13,636 B. t. u. accounted for. The heat +value of the coal, 14,225 B. t. u., less 13,636 B. t. u., leaves 589 +B. t. u., unaccounted for losses, or 4.15 per cent. + +The heat balance should be arranged in the form indicated by Table 58. + + TABLE 58 + + HEAT BALANCE + + B. T. U. PER POUND DRY COAL 14,225 + ++----------------------------------------------------------------------+ +|+--------------------------------------------------------------------+| +|| |B. t. u.|Per Cent|| +|+--------------------------------------------------+--------+--------+| +||Heat absorbed by Boiler | 11,363 | 79.88 || +||Loss due to Evaporation of Moisture in Fuel | 22 | 0.15 || +||Loss due to Moisture formed by Burning of Hydrogen| 618 | 4.34 || +||Loss due to Heat carried away in Dry Chimney Gases| 1311 | 9.22 || +||Loss due to Incomplete Combustion of Carbon | 61 | 0.43 || +||Loss due to Unconsumed Carbon in the Ash | 261 | 1.83 || +||Loss due to Radiation and Unaccounted Losses | 589 | 4.15 || +|+--------------------------------------------------+--------+--------+| +||Total | 14,225 | 100.00 || +|+--------------------------------------------------+--------+--------+| ++----------------------------------------------------------------------+ + +Application of Heat Balance--A heat balance should be made in connection +with any boiler trial on which sufficient data for its computation has +been obtained. This is particularly true where the boiler performance +has been considered unsatisfactory. The distribution of the heat is thus +determined and any extraordinary loss may be detected. Where accurate +data for computing such a heat balance is not available, such a +calculation based on certain assumptions is sometimes sufficient to +indicate unusual losses. + +The largest loss is ordinarily due to the chimney gases, which depends +directly upon the weight of the gas and its temperature leaving the +boiler. As pointed out in the chapter on flue gas analysis, the lower +limit of the weight of gas is fixed by the minimum air supplied with +which complete combustion may be obtained. As shown, where this supply +is unduly small, the loss caused by burning the carbon to CO instead of +to CO_{2} more than offsets the gain in decreasing the weight of gas. + +The lower limit of the stack temperature, as has been shown in the +chapter on draft, is more or less fixed by the temperature necessary to +create sufficient draft suction for good combustion. With natural draft, +this lower limit is probably between 400 and 450 degrees. + +Capacity--Before the capacity of a boiler is considered, it is necessary +to define the basis to which such a term may be referred. Such a basis +is the so-called boiler horse power. + +The unit of motive power in general use among steam engineers is the +"horse power" which is equivalent to 33,000 foot pounds per minute. +Stationary boilers are at the present time rated in horse power, though +such a basis of rating may lead and has often led to a misunderstanding. +_Work_, as the term is used in mechanics, is the overcoming of +resistance through space, while _power_ is the _rate_ of work or the +amount done per unit of time. As the operation of a boiler in service +implies no motion, it can produce no power in the sense of the term as +understood in mechanics. Its operation is the generation of steam, which +acts as a medium to convey the energy of the fuel which is in the form +of heat to a prime mover in which that heat energy is converted into +energy of motion or work, and power is developed. + +If all engines developed the same amount of power from an equal amount +of heat, a boiler might be designated as one having a definite horse +power, dependent upon the amount of engine horse power its steam would +develop. Such a statement of the rating of boilers, though it would +still be inaccurate, if the term is considered in its mechanical sense, +could, through custom, be interpreted to indicate that a boiler was of +the exact capacity required to generate the steam necessary to develop a +definite amount of horse power in an engine. Such a basis of rating, +however, is obviously impossible when the fact is considered that the +amount of steam necessary to produce the same power in prime movers of +different types and sizes varies over very wide limits. + +To do away with the confusion resulting from an indefinite meaning of +the term boiler horse power, the Committee of Judges in charge of the +boiler trials at the Centennial Exposition, 1876, at Philadelphia, +ascertained that a good engine of the type prevailing at the time +required approximately 30 pounds of steam per hour per horse power +developed. In order to establish a relation between the engine power and +the size of a boiler required to develop that power, they recommended +that an evaporation of 30 pounds of water from an initial temperature of +100 degrees Fahrenheit to steam at 70 pounds gauge pressure be +considered as _one boiler horse power_. This recommendation has been +generally accepted by American engineers as a standard, and when the +term boiler horse power is used in connection with stationary +boilers[58] throughout this country,[59] without special definition, it +is understood to have this meaning. + +Inasmuch as an equivalent evaporation from and at 212 degrees Fahrenheit +is the generally accepted basis of comparison[60], it is now customary +to consider the standard boiler horse power as recommended by the +Centennial Exposition Committee, in terms of equivalent evaporation from +and at 212 degrees. This will be 30 pounds multiplied by the factor of +evaporation for 70 pounds gauge pressure and 100 degrees feed +temperature, or 1.1494. 30 x 1.1494 = 34.482, or approximately 34.5 +pounds. Hence, _one boiler horse power is equal to an evaporation of +34.5 pounds of water per hour from and at 212 degrees Fahrenheit_. The +term boiler horse power, therefore, is clearly a measure of evaporation +and not of power. + +A method of basing the horse power rating of a boiler adopted by boiler +manufacturers is that of heating surfaces. Such a method is absolutely +arbitrary and changes in no way the definition of a boiler horse power +just given. It is simply a statement by the manufacturer that his +product, under ordinary operating conditions or conditions which may be +specified, will evaporate 34.5 pounds of water from and at 212 degrees +per definite amount of heating surface provided. The amount of heating +surface that has been considered by manufacturers capable of evaporating +34.5 pounds from and at 212 degrees per hour has changed from time to +time as the art has progressed. At the present time 10 square feet of +heating surface is ordinarily considered the equivalent of one boiler +horse power among manufacturers of stationary boilers. In view of the +arbitrary nature of such rating and of the widely varying rates of +evaporation possible per square foot of heating surface with different +boilers and different operating conditions, such a basis of rating has +in reality no particular bearing on the question of horse power and +should be considered merely as a convenience. + +The whole question of a unit of boiler capacity has been widely +discussed with a view to the adoption of a standard to which there would +appear to be a more rational and definite basis. Many suggestions have +been offered as to such a basis but up to the present time there has +been none which has met with universal approval or which would appear +likely to be generally adopted. + +With the meaning of boiler horse power as given above, that is, a +measure of evaporation, it is evident that the capacity of a boiler is a +measure of the power it can develop expressed in boiler horse power. +Since it is necessary, as stated, for boiler manufacturers to adopt a +standard for reasons of convenience in selling, the horse power for +which a boiler is sold is known as its normal rated capacity. + +The efficiency of a boiler and the maximum capacity it will develop can +be determined accurately only by a boiler test. The standard methods of +conducting such tests are given on the following pages, these methods +being the recommendations of the Power Test Committee of the American +Society of Mechanical Engineers brought out in 1913.[61] Certain changes +have been made to incorporate in the boiler code such portions of the +"Instructions Regarding Tests in General" as apply to boiler testing. +Methods of calculation and such matter as are treated in other portions +of the book have been omitted from the code as noted. + +[Illustration: Portion of 2600 Horse-power Installation of Babcock & +Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Peter Schoenhofen Brewing Co., Chicago, Ill.] + + + +1. OBJECT + + +Ascertain the specific object of the test, and keep this in view not +only in the work of preparation, but also during the progress of the +test, and do not let it be obscured by devoting too close attention to +matters of minor importance. Whatever the object of the test may be, +accuracy and reliability must underlie the work from beginning to end. + +If questions of fulfillment of contract are involved, there should be a +clear understanding between all the parties, preferably in writing, as +to the operating conditions which should obtain during the trial, and as +to the methods of testing to be followed, unless these are already +expressed in the contract itself. + +Among the many objects of performance tests, the following may be noted: + + Determination of capacity and efficiency, and how these compare + with standard or guaranteed results. + + Comparison of different conditions or methods of operation. + + Determination of the cause of either inferior or superior + results. + + Comparison of different kinds of fuel. + + Determination of the effect of changes of design or proportion + upon capacity or efficiency, etc. + + + +2. PREPARATIONS + + +_(A) Dimensions:_ + +Measure the dimensions of the principal parts of the apparatus to be +tested, so far as they bear on the objects in view, or determine these +from correct working drawings. Notice the general features of the same, +both exterior and interior, and make sketches, if needed, to show +unusual points of design. + + The dimensions of the heating surfaces of boilers and + superheaters to be found are those of surfaces in contact with + the fire or hot gases. The submerged surfaces in boilers at the + mean water level should be considered as water-heating surfaces, + and other surfaces which are exposed to the gases as + superheating surfaces. + + +_(B) Examination of Plant:_ + +Make a thorough examination of the physical condition of all parts of +the plant or apparatus which concern the object in view, and record the +conditions found, together with any points in the matter of operation +which bear thereon. + + In boilers, examine for leakage of tubes and riveted or other + metal joints. Note the condition of brick furnaces, grates and + baffles. Examine brick walls and cleaning doors for air leaks, + either by shutting the damper and observing the escaping smoke + or by candle-flame test. Determine the condition of heating + surfaces with reference to exterior deposits of soot and + interior deposits of mud or scale. + + See that the steam main is so arranged that condensed and + entrained water cannot flow back into the boiler. + +If the object of the test is to determine the highest efficiency or +capacity obtainable, any physical defects, or defects of operation, +tending to make the result unfavorable should first be remedied; all +foul parts being cleaned, and the whole put in first-class condition. +If, on the other hand, the object is to ascertain the performance under +existing conditions, no such preparation is either required or desired. + + +_(C) General Precautions against Leakage:_ + +In steam tests make sure that there is no leakage through blow-offs, +drips, etc., or any steam or water connections of the plant or apparatus +undergoing test, which would in any way affect the results. All such +connections should be blanked off, or satisfactory assurance should be +obtained that there is leakage neither out nor in. This is a most +important matter, and no assurance should be considered satisfactory +unless it is susceptible of absolute demonstration. + + + +3. FUEL + + +Determine the character of fuel to be used.[62] For tests of maximum +efficiency or capacity of the boiler to compare with other boilers, the +coal should be of some kind which is commercially regarded as a standard +for the locality where the test is made. + + In the Eastern States the standards thus regarded for + semi-bituminous coals are Pocahontas (Va. and W. Va.) and New + River (W. Va.); for anthracite coals those of the No. 1 + buckwheat size, fresh-mined, containing not over 13 per cent ash + by analysis; and for bituminous coals, Youghiogheny and + Pittsburgh coals. In some sections east of the Allegheny + Mountains the semi-bituminous Clearfield (Pa.) and Cumberland + (Md.) are also considered as standards. These coals when of good + quality possess the essentials of excellence, adaptability to + various kinds of furnaces, grates, boilers, and methods of + firing required, besides being widely distributed and generally + accessible in the Eastern market. There are no special grades of + coal mined in the Western States which are widely and generally + considered as standards for testing purposes; the best coal + obtainable in any particular locality being regarded as the + standard of comparison. + +A coal selected for maximum efficiency and capacity tests, should be the +best of its class, and especially free from slagging and unusual +clinker-forming impurities. + +For guarantee and other tests with a specified coal containing not more +than a certain amount of ash and moisture, the coal selected should not +be higher in ash and in moisture than the stated amounts, because any +increase is liable to reduce the efficiency and capacity more than the +equivalent proportion of such increase. + +The size of the coal, especially where it is of the anthracite class, +should be determined by screening a suitable sample. + + + +4. APPARATUS AND INSTRUMENTS[63] + + +The apparatus and instruments required for boiler tests are: + + (A) Platform scales for weighing coal and ashes. + + (B) Graduated scales attached to the water glasses. + + (C) Tanks and platform scales for weighing water (or water + meters calibrated in place). Wherever practicable the feed water + should be weighed, especially for guarantee tests. The most + satisfactory and reliable apparatus for this purpose consists of + one or more tanks each placed on platform scales, these being + elevated a sufficient distance above the floor to empty into a + receiving tank placed below, the latter being connected to the + feed pump. Where only one weighing tank is used the receiving + tank should be of larger size than the weighing tank, to afford + sufficient reserve supply to the pump while the upper tank is + filling. If a single weighing tank is used it should preferably + be of such capacity as to require emptying not oftener than + every 5 minutes. If two or more are used the intervals between + successive emptyings should not be less than 3 minutes. + + (D) Pressure gauges, thermometers, and draft gauges. + + (E) Calorimeters for determining the calorific value of fuel and + the quality of steam. + + (F) Furnaces pyrometers. + + (G) Gas analyzing apparatus. + + + +5. OPERATING CONDITIONS + + +Determine what the operating conditions and method of firing should be +to conform to the object in view, and see that they prevail throughout +the trial, as nearly as possible. + + Where uniformity in the rate of evaporation is required, + arrangement can be usually made to dispose of the steam so that + this result can be attained. In a single boiler it may be + accomplished by discharging steam through a waste pipe and + regulating the amount by means of a valve. In a battery of + boilers, in which only one is tested, the draft may be regulated + on the remaining boilers to meet the varying demands for steam, + leaving the test boiler to work under a steady rate of + evaporation. + + + +6. DURATION + + +The duration of tests to determine the efficiency of a hand-fired +boiler, should be 10 hours of continuous running, or such time as may be +required to burn a total of 250 pounds of coal per square foot of grate. + +In the case of a boiler using a mechanical stoker, the duration, where +practicable, should be at least 24 hours. If the stoker is of a type +that permits the quantity and condition of the fuel bed at beginning and +end of the test to be accurately estimated, the duration may be reduced +to 10 hours, or such time as may be required to burn the above noted +total of 250 pounds per square foot. + + In commercial tests where the service requires continuous + operation night and day, with frequent shifts of firemen, the + duration of the test, whether the boilers are hand fired or + stoker fired, should be at least 24 hours. Likewise in + commercial tests, either of a single boiler or of a plant of + several boilers, which operate regularly a certain number of + hours and during the balance of the day the fires are banked, + the duration should not be less than 24 hours. + + The duration of tests to determine the maximum evaporative + capacity of a boiler, without determining the efficiency, should + not be less than 3 hours. + + + +7. STARTING AND STOPPING + + +The conditions regarding the temperature of the furnace and boiler, the +quantity and quality of the live coal and ash on the grates, the water +level, and the steam pressure, should be as nearly as possible the same +at the end as at the beginning of the test. + +To secure the desired equality of conditions with hand-fired boilers, +the following method should be employed: + + The furnace being well heated by a preliminary run, burn the + fire low, and thoroughly clean it, leaving enough live coal + spread evenly over the grate (say 2 to 4 inches),[64] to serve + as a foundation for the new fire. Note quickly the thickness of + the coal bed as nearly as it can be estimated or measured; also + the water level,[65] the steam pressure, and the time, and + record the latter as the starting time. Fresh coal should then + be fired from that weighed for the test, the ashpit throughly + cleaned, and the regular work of the test proceeded with. Before + the end of the test the fire should again be burned low and + cleaned in such a manner as to leave the same amount of live + coal on the grate as at the start. When this condition is + reached, observe quickly the water level,[65] the steam + pressure, and the time, and record the latter as the stopping + time. If the water level is not the same as at the beginning a + correction should be made by computation, rather than by feeding + additional water after the final readings are taken. Finally + remove the ashes and refuse from the ashpit. In a plant + containing several boilers where it is not practicable to clean + them simultaneously, the fires should be cleaned one after the + other as rapidly as may be, and each one after cleaning charged + with enough coal to maintain a thin fire in good working + condition. After the last fire is cleaned and in working + condition, burn all the fires low (say 4 to 6 inches), note + quickly the thickness of each, also the water levels, steam + pressure, and time, which last is taken as the starting time. + Likewise when the time arrives for closing the test, the fires + should be quickly cleaned one by one, and when this work is + completed they should all be burned low the same as the start, + and the various observations made as noted. In the case of a + large boiler having several furnace doors requiring the fire to + be cleaned in sections one after the other, the above directions + pertaining to starting and stopping in a plant of several + boilers may be followed. + +To obtain the desired equality of conditions of the fire when a +mechanical stoker other than a chain grate is used, the procedure should +be modified where practicable as follows: + + Regulate the coal feed so as to burn the fire to the low + condition required for cleaning. Shut off the coal-feeding + mechanism and fill the hoppers level full. Clean the ash or dump + plate, note quickly the depth and condition of the coal on the + grate, the water level,[66] the steam pressure, and the time, + and record the latter as the starting time. Then start the + coal-feeding mechanism, clean the ashpit, and proceed with the + regular work of the test. + + When the time arrives for the close of the test, shut off the + coal-feeding mechanism, fill the hoppers and burn the fire to + the same low point as at the beginning. When this condition is + reached, note the water level, the steam pressure, and the time, + and record the latter as the stopping time. Finally clean the + ashplate and haul the ashes. + + In the case of chain grate stokers, the desired operating + conditions should be maintained for half an hour before starting + a test and for a like period before its close, the height of the + throat plate and the speed of the grate being the same during + both of these periods. + + + +8. RECORDS + + +A log of the data should be entered in notebooks or on blank sheets +suitably prepared in advance. This should be done in such manner that +the test may be divided into hourly periods, or if necessary, periods of +less duration, and the leading data obtained for any one or more periods +as desired, thereby showing the degree of uniformity obtained. + +Half-hourly readings of the instruments are usually sufficient. If there +are sudden and wide fluctuations, the readings in such cases should be +taken every 15 minutes, and in some instances oftener. + + The coal should be weighed and delivered to the firemen in + portions sufficient for one hour's run, thereby ascertaining the + degree of uniformity of firing. An ample supply of coal should + be maintained at all times, but the quantity on the floor at the + end of each hour should be as small as practicable, so that the + same may be readily estimated and deducted from the total + weight. + + The records should be such as to ascertain also the consumption + of feed water each hour and thereby determine the degree of + uniformity of evaporation. + + + +9. QUALITY OF STEAM[67] + + +If the boiler does not produce superheated steam the percentage of +moisture in the steam should be determined by the use of a throttling or +separating calorimeter. If the boiler has superheating surface, the +temperature of the steam should be determined by the use of a +thermometer inserted in a thermometer well. + +For saturated steam construct a sampling pipe or nozzle made of one-half +inch iron pipe and insert it in the steam main at a point where the +entrained moisture is likely to be most thoroughly mixed. The inner end +of the pipe, which should extend nearly across to the opposite side of +the main, should be closed and interior portion perforated with not less +than twenty one-eighth inch holes equally distributed from end to end +and preferably drilled in irregular or spiral rows, with the first hole +not less than half an inch from the wall of the pipe. + + The sampling pipe should not be placed near a point where water + may pocket or where such water may effect the amount of moisture + contained in the sample. Where non-return valves are used, or + there are horizontal connections leading from the boiler to a + vertical outlet, water may collect at the lower end of the + uptake pipe and be blown upward in a spray which will not be + carried away by the steam owing to a lack of velocity. A sample + taken from the lower part of this pipe will show a greater + amount of moisture than a true sample. With goose-neck + connections a small amount of water may collect on the bottom of + the pipe near the upper end where the inclination is such that + the tendency to flow backward is ordinarily counterbalanced by + the flow of steam forward over its surface; but when the + velocity momentarily decreases the water flows back to the lower + end of the goose-neck and increases the moisture at that point, + making it an undesirable location for sampling. In any case it + must be borne in mind that with low velocities the tendency is + for drops of entrained water to settle to the bottom of the + pipe, and to be temporarily broken up into spray whenever an + abrupt bend or other disturbance is met. + +If it is necessary to attach the sampling nozzle at a point near the end +of a long horizontal run, a drip pipe should be provided a short +distance in front of the nozzle, preferably at a pocket formed by some +fitting and the water running along the bottom of the main drawn off, +weighed, and added to the moisture shown by the calorimeter; or, better, +a steam separator should be installed at the point noted. + +In testing a stationary boiler the sampling pipe should be located as +near as practicable to the boiler, and the same is true as regards the +thermometer well when the steam is superheated. In an engine or turbine +test these locations should be as near as practicable to throttle valve. +In the test of a plant where it is desired to get complete information, +especially where the steam main is unusually long, sampling nozzles or +thermometer wells should be provided at both points, so as to obtain +data at either point as may be required. + + + +10. SAMPLING AND DRYING COAL + + +During the progress of test the coal should be regularly sampled for the +purpose of analysis and determination of moisture. + +Select a representative shovelful from each barrow-load as it is drawn +from the coal pile or other source of supply, and store the samples in a +cool place in a covered metal receptacle. When all the coal has thus +been sampled, break up the lumps, thoroughly mix the whole quantity, and +finally reduce it by the process of repeated quartering and crushing to +a sample weighing about 5 pounds, the largest pieces being about the +size of a pea. From this sample two one-quart air-tight glass fruit +jars, or other air-tight vessels, are to be promptly filled and +preserved for subsequent determinations of moisture, calorific value, +and chemical composition. These operations should be conducted where the +air is cool and free from drafts. + +[Illustration: 3460 Horse-power Installation of Babcock & Wilcox Boilers +at the Chicago, Ill., Shops of the Chicago and Northwestern Ry. Co.] + +When the sample lot of coal has been reduced by quartering to, say, 100 +pounds, a portion weighing, say, 15 to 20 pounds should be withdrawn for +the purpose of immediate moisture determination. This is placed in a +shallow iron pan and dried on the hot iron boiler flue for at least 12 +hours, being weighed before and after drying on scales reading to +quarter ounces. + +The moisture thus determined is approximately reliable for anthracite +and semi-bituminous coals, but not for coals containing much inherent +moisture. For such coals, and for all absolutely reliable determinations +the method to be pursued is as follows: + + Take one of the samples contained in the glass jars, and subject + it to a thorough air drying, by spreading it in a thin layer and + exposing it for several hours to the atmosphere of a warm room, + weighing it before and after, thereby determining the quantity + of surface moisture it contains.[68] Then crush the whole of it + by running it through an ordinary coffee mill or other suitable + crusher adjusted so as to produce somewhat coarse grains (less + than 1/16 inch), thoroughly mix the crushed sample, select from + it a portion of from 10 to 50 grams,[69] weigh it in a balance + which will easily show a variation as small as 1 part in 1000, + and dry it for one hour in an air or sand bath at a temperature + between 240 and 280 degrees Fahrenheit. Weigh it and record the + loss, then heat and weigh again until the minimum weight has + been reached. The difference between the original and the + minimum weight is the moisture in the air-dried coal. The sum of + the moisture thus found and that of the surface moisture is the + total moisture. + + + +11. ASHES AND REFUSE + + +The ashes and refuse withdrawn from the furnace and ashpit during the +progress of the test and at its close should be weighed so far as +possible in a dry state. If wet the amount of moisture should be +ascertained and allowed for, a sample being taken and dried for this +purpose. This sample may serve also for analysis and the determination +of unburned carbon and fusing temperature. + +The method above described for sampling coal may also be followed for +obtaining a sample of the ashes and refuse. + + + +12. CALORIFIC TESTS AND ANALYSES OF COAL + + +The quality of the fuel should be determined by calorific tests and +analysis of the coal sample above referred to.[70] + + + +13. ANALYSES OF FLUE GASES + + +For approximate determinations of the composition of the flue gases, the +Orsat apparatus, or some modification thereof, should be employed. If +momentary samples are obtained the analyses should be made as frequently +as possible, say, every 15 to 30 minutes, depending on the skill of the +operator, noting at the time the sample is drawn the furnace and firing +conditions. If the sample drawn is a continuous one, the intervals may +be made longer. + + + +14. SMOKE OBSERVATIONS[71] + + +In tests of bituminous coals requiring a determination of the amount of +smoke produced, observations should be made regularly throughout the +trial at intervals of 5 minutes (or if necessary every minute), noting +at the same time the furnace and firing conditions. + + + +15. CALCULATION OF RESULTS + + +The methods to be followed in expressing and calculating those results +which are not self-evident are explained as follows: + + (A) _Efficiency._ The "efficiency of boiler, furnace and + grate" is the relation between the heat absorbed per pound of + coal fired, and the calorific value of one pound of coal. + + The "efficiency of boiler and furnace" is the relation between + the heat absorbed per pound of combustible burned, and the + calorific value of one pound of combustible. This expression of + efficiency furnishes a means for comparing one boiler and + furnace with another, when the losses of unburned coal due to + grates, cleanings, etc., are eliminated. + + The "combustible burned" is determined by subtracting from the + weight of coal supplied to the boiler, the moisture in the coal, + the weight of ash and unburned coal withdrawn from the furnace + and ashpit, and the weight of dust, soot, and refuse, if any, + withdrawn from the tubes, flues, and combustion chambers, + including ash carried away in the gases, if any, determined from + the analysis of coal and ash. The "combustible" used for + determining the calorific value is the weight of coal less the + moisture and ash found by analysis. + + The "heat absorbed" per pound of coal, or combustible, is + calculated by multiplying the equivalent evaporation from and at + 212 degrees per pound of coal or combustible by 970.4. + +Other items in this section which have been treated elsewhere are: + + (B) Corrections for moisture in steam. + + (C) Correction for live steam used. + + (D) Equivalent evaporation. + + (E) Heat balance. + + (F) Total heat of combustion of coal. + + (G) Air for combustion and the methods recommended for + calculating these results are in accordance with those described + in different portions of this book. + + + +16. DATA AND RESULTS + + +The data and results should be reported in accordance with either the +short form or the complete form, adding lines for data not provided for, +or omitting those not required, as may conform to the object in view. + + + +17. CHART + + +In trials having for an object the determination and exposition of the +complete boiler performance, the entire log of readings and data should +be plotted on a chart and represented graphically. + + + +18. TESTS WITH OIL AND GAS FUELS + + +Tests of boilers using oil or gas for fuel should accord with the rules +here given, excepting as they are varied to conform to the particular +characteristics of the fuel. The duration in such cases may be reduced, +and the "flying" method of starting and stopping employed. + + The table of data and results should contain items stating + character of furnace and burner, quality and composition of oil + or gas, temperature of oil, pressure of steam used for + vaporizing and quantity of steam used for both vaporizing and + for heating. + + TABLE DATA AND RESULTS OF EVAPORATIVE TEST + SHORT FORM, CODE OF 1912 + + 1 Test of.................boiler located at................................ + to determine...............conducted by.............................. + 2 Kind of furnace.......................................................... + 3 Grate surface.................................................square feet + 4 Water-heating surface.........................................square feet + 5 Superheating surface..........................................square feet + 6 Date..................................................................... + 7 Duration............................................................hours + 8 Kind and size of coal.................................................... + +AVERAGE PRESSURES, TEMPERATURES, ETC. + + 9 Steam pressure by gauge............................................pounds +10 Temperature of feed water entering boiler.........................degrees +11 Temperature of escaping gases leaving boiler......................degrees +12 Force of draft between damper and boiler...........................inches +13 Percentage of moisture in steam, + or number degrees of superheating..................per cent or degrees + +TOTAL QUANTITIES + +14 Weight of coal as fired[72]........................................pounds +15 Percentage of moisture in coal...................................per cent +16 Total weight of dry coal consumed..................................pounds +17 Total ash and refuse...............................................pounds +18 Percentage of ash and refuse in dry coal.........................per cent +19 Total weight of water fed to the boiler[73]........................pounds +20 Total water evaporated, corrected for moisture in steam............pounds +21 Total equivalent evaporation from and at 212 degrees...............pounds + +HOURLY QUANTITIES AND RATES + +22 Dry coal consumed per hour.........................................pounds +23 Dry coal per square feet of grate surface per hour.................pounds +24 Water evaporated per hour corrected for quality of steam...........pounds +25 Equivalent evaporation per hour from and at 212 degrees............pounds +26 Equivalent evaporation per hour from and at 212 degrees + per square foot of water-heating surface........................pounds + +CAPACITY + +27 Evaporation per hour from and at 212 degrees (same as Line 25).....pounds +28 Boiler horse power developed (Item 27/34-1/2)...........boiler horse power +29 Rated capacity, in evaporation from and at 212 degrees per hour....pounds +30 Rated boiler horse power...............................boiler horse power +31 Percentage of rated capacity developed...........................per cent + +ECONOMY RESULTS + +32 Water fed per pound of coal fired (Item 19/Item 14)................pounds +33 Water evaporated per pound of dry coal (Item 20/Item 16)...........pounds +34 Equivalent evaporation from and at 212 degrees per pound + of dry coal (Item 21/Item 16)...................................pounds +35 Equivalent evaporation from and at 212 degrees per pound + of combustible [Item 21/(Item 16-Item 17)]......................pounds + +EFFICIENCY + +36 Calorific value of one pound of dry coal.........................B. t. u. +37 Calorific value of one pound of combustible......................B. t. u. + + ( Item 34x970.4) +38 Efficiency of boiler, furnace and grate (100 x -------------)....per cent + ( Item 36 ) + + ( Item 35x970.4) +39 Efficiency of boiler and furnace (100 x -------------)...........per cent + ( Item 37 ) + +COST OF EVAPORATION + +40 Cost of coal per ton of......pounds delivered in boiler room......dollars +41 Cost of coal required for evaporating 1000 pounds of water + from and at 212 degrees........................................dollars + +[Illustration: Portion of 3600 Horse-power Installation of Babcock & +Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Loomis Street Plant of the Peoples Gas Light & Coke Co., Chicago, +Ill. This Company has Installed 7780 Horse Power of Babcock & Wilcox +Boilers] + + + + +THE SELECTION OF BOILERS WITH A CONSIDERATION OF THE FACTORS DETERMINING +SUCH SELECTION + + +The selection of steam boilers is a matter to which the most careful +thought and attention may be well given. Within the last twenty years, +radical changes have taken place in the methods and appliances for the +generation and distribution of power. These changes have been made +largely in the prime movers, both as to type and size, and are best +illustrated by the changes in central station power-plant practice. It +is hardly within the scope of this work to treat of power-plant design +and the discussion will be limited to a consideration of the boiler end +of the power plant. + +As stated, the changes have been largely in prime movers, the steam +generating equipment having been considered more or less of a standard +piece of apparatus whose sole function is the transfer of the heat +liberated from the fuel by combustion to the steam stored or circulated +in such apparatus. When the fact is considered that the cost of steam +generation is roughly from 65 to 80 per cent of the total cost of power +production, it may be readily understood that the most fruitful field +for improvement exists in the boiler end of the power plant. The +efficiency of the plant as a whole will vary with the load it carries +and it is in the boiler room where such variation is largest and most +subject to control. + +The improvements to be secured in the boiler room results are not simply +a matter of dictation of operating methods. The securing of perfect +combustion, with the accompanying efficiency of heat transfer, while +comparatively simple in theory, is difficult to obtain in practical +operation. This fact is perhaps best exemplified by the difference +between test results and those obtained in daily operation even under +the most careful supervision. This difference makes it necessary to +establish a standard by which operating results may be judged, a +standard not necessarily that which might be possible under test +conditions but one which experiment shows can be secured under the very +best operating conditions. + +The study of the theory of combustion, draft, etc., as already given, +will indicate that the question of efficiency is largely a matter of +proper relation between fuel, furnace and generator. While the +possibility of a substantial saving through added efficiency cannot be +overlooked, the boiler design of the future must, even more than in the +past, be considered particularly from the aspect of reliability and +simplicity. A flexibility of operation is necessary as a guarantee of +continuity of service. + +In view of the above, before the question of the selection of boilers +can be taken up intelligently, it is necessary to consider the subjects +of boiler efficiency and boiler capacity, together with their relation +to each other. + +The criterion by which the efficiency of a boiler plant is to be judged +is the cost of the production of a definite amount of steam. Considered +in this sense, there must be included in the efficiency of a boiler +plant the simplicity of operation, flexibility and reliability of the +boiler used. The items of repair and upkeep cost are often high because +of the nature of the service. The governing factor in these items is +unquestionably the type of boiler selected. + +The features entering into the plant efficiency are so numerous that it +is impossible to make a statement as to a means of securing the highest +efficiency which will apply to all cases. Such efficiency is to be +secured by the proper relation of fuel, furnace and boiler heating +surface, actual operating conditions, which allow the approaching of the +potential efficiencies made possible by the refinement of design, and a +systematic supervision of the operation assisted by a detailed record of +performances and conditions. The question of supervision will be taken +up later in the chapter on "Operation and Care of Boilers". + +The efficiencies that may be expected from the combination of +well-designed boilers and furnaces are indicated in Table 59 in which +are given a number of tests with various fuels and under widely +different operating conditions. + +It is to be appreciated that the results obtained as given in this table +are practically all under test conditions. The nearness with which +practical operating conditions can approach these figures will depend +upon the character of the supervision of the boiler room and the +intelligence of the operating crew. The size of the plant will +ordinarily govern the expense warranted in securing the right sort of +supervision. + +The bearing that the type of boiler has on the efficiency to be expected +can only be realized from a study of the foregoing chapters. + +Capacity--Capacity, as already defined, is the ability of a definite +amount of boiler-heating surface to generate steam. Boilers are +ordinarily purchased under a manufacturer's specification, which rates a +boiler at a nominal rated horse power, usually based on 10 square feet +of heating surface per horse power. Such a builders' rating is +absolutely arbitrary and implies nothing as to the limiting amount of +water that this amount of heating surface will evaporate. It does not +imply that the evaporation of 34.5 pounds of water from and at 212 +degrees with 10 square feet of heating surface is the limit of the +capacity of the boiler. Further, from a statement that a boiler is of a +certain horse power on the manufacturer's basis, it is not to be +understood that the boiler is in any state of strain when developing +more than its rated capacity. + +Broadly stated, the evaporative capacity of a certain amount of heating +surface in a well-designed boiler, that is, the boiler horse power it is +capable of producing, is limited only by the amount of fuel that can be +burned under the boiler. While such a statement would imply that the +question of capacity to be secured was simply one of making an +arrangement by which sufficient fuel could be burned under a definite +amount of heating surface to generate the required amount of steam, +there are limiting features that must be weighed against the advantages +of high capacity developed from small heating surfaces. Briefly stated, +these factors are as follows: + +1st. Efficiency. As the capacity increases, there will in general be a +decrease in efficiency, this loss above a certain point making it +inadvisable to try to secure more than a definite horse power from a +given boiler. This loss of efficiency with increased capacity is treated +below in detail, in considering the relation of efficiency to capacity. + +2nd. Grate Ratio Possible or Practicable. All fuels have a maximum rate +of combustion, beyond which satisfactory results cannot be obtained, +regardless of draft available or which may be secured by mechanical +means. Such being the case, it is evident that with this maximum +combustion rate secured, the only method of obtaining added capacity +will be through the addition of grate surface. There is obviously a +point beyond which the grate surface for a given boiler cannot be +increased. This is due to the impracticability of handling grates above +a certain maximum size, to the enormous loss in draft pressure through a +boiler resulting from an attempt to force an abnormal quantity of gas +through the heating surface and to innumerable details of design and +maintenance that would make such an arrangement wholly unfeasible. + +3rd. Feed Water. The difficulties that may arise through the use of poor +feed water or that are liable to happen through the use of practically +any feed water have already been pointed out. This question of feed is +frequently the limiting factor in the capacity obtainable, for with an +increase in such capacity comes an added concentration of such +ingredients in the feed water as will cause priming, foaming or rapid +scale formation. Certain waters which will give no trouble that cannot +be readily overcome with the boiler run at ordinary ratings will cause +difficulties at higher ratings entirely out of proportion to any +advantage secured by an increase in the power that a definite amount of +heating surface may be made to produce. + +Where capacity in the sense of overload is desired, the type of boiler +selected will play a large part in the successful operation through such +periods. A boiler must be selected with which there is possible a +furnace arrangement that will give flexibility without undue loss in +efficiency over the range of capacity desired. The heating surface must +be so arranged that it will be possible to install in a practical +manner, sufficient grate surface at or below the maximum combustion rate +to develop the amount of power required. The design of boiler must be +such that there will be no priming or foaming at high overloads and that +any added scale formation due to such overloads may be easily removed. +Certain boilers which deliver commercially dry steam when operated at +about their normal rated capacity will prime badly when run at overloads +and this action may take place with a water that should be easily +handled by a properly designed boiler at any reasonable load. Such +action is ordinarily produced by the lack of a well defined, positive +circulation. + +Relation of Efficiency and Capacity--The statement has been made that in +general the efficiency of a boiler will decrease as the capacity is +increased. Considering the boiler alone, apart from the furnace, this +statement may be readily explained. + +Presupposing a constant furnace temperature, regardless of the capacity +at which a given boiler is run; to assure equal efficiencies at low and +high ratings, the exit temperature in the two instances would +necessarily be the same. For this temperature at the high rating, to be +identical with that at the low rating, the rate of heat transfer from +the gases to the heating surfaces would have to vary directly as the +weight or volume of such gases. Experiment has shown, however, that this +is not true but that this rate of transfer varies as some power of the +volume of gas less than one. As the heat transfer does not, therefore, +increase proportionately with the volume of gases, the exit temperature +for a given furnace temperature will be increased as the volume of gases +increases. As this is the measure of the efficiency of the heating +surface, the boiler efficiency will, therefore, decrease as the volume +of gases increases or the capacity at which the boiler is operated +increases. + +Further, a certain portion of the heat absorbed by the heating surface +is through direct radiation from the fire. Again, presupposing a +constant furnace temperature; the heat absorbed through radiation is +solely a function of the amount of surface exposed to such radiation. +Hence, for the conditions assumed, the amount of heat absorbed by +radiation at the higher ratings will be the same as at the lower ratings +but in proportion to the total absorption will be less. As the added +volume of gas does not increase the rate of heat transfer, there are +therefore two factors acting toward the decrease in the efficiency of a +boiler with an increase in the capacity. + + TABLE 59 + + TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS + + ______________________________________________________________________ +|Number| | | | Rated | +| of | Name and Location | Kind of Coal | Kind of | Horse | +| Test | of Plant | | Furnace |Power of| +| | | | | Boiler | +| | | | | | +|______|___________________________|________________|_________|________| +| |Susquehanna Coal Co., |No. 1 Anthracite|Hand | | +| 1 |Shenandoah, Pa. |Buckwheat |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Balbach Smelting & |No. 2 Buckwheat |Wilkenson| | +| 2 |Refining Co., Newark, N. J.|and Bird's-eye | Stoker | 218 | +|______|___________________________|________________|_________|________| +| |H. R. Worthington, |No. 2 Anthracite|Hand | | +| 3 |Harrison N. J. |Buckwheat |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Raymond Street Jail, |Anthracite Pea |Hand | | +| 4 |Brooklyn, N. Y. | |Fired | 155 | +|______|___________________________|________________|_________|________| +| |R. H. Macy & Co., |No. 3 Anthracite|Hand | | +| 5 |New York, N. Y. |Buckwheat |Fired | 293 | +|______|___________________________|________________|_________|________| +| |National Bureau of |Anthracite Egg |Hand | | +| 6 |Standards, Washington, D.C.| |Fired | 119 | +|______|___________________________|________________|_________|________| +| |Fred. Loeser & Co., |No. 1 Anthracite|Hand | | +| 7 |Brooklyn, N. Y. |Buckwheat |Fired | 300 | +|______|___________________________|________________|_________|________| +| |New York Edison Co., |No. 2 Anthracite|Hand | | +| 8 |New York City |Buckwheat |Fired | 374 | +|______|___________________________|________________|_________|________| +| |Sewage Pumping Station, |Hocking Valley |Hand | | +| 9 |Cleveland, O. |Lump, O. |Fired | 150 | +|______|___________________________|________________|_________|________| +| |Scioto River Pumping Sta., |Hocking Valley, |Hand | | +| 10 |Cleveland, O. |O. |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Consolidated Gas & Electric|Somerset, Pa. |Hand | | +| 11 |Co., Baltimore, Md. | |Fired | 640 | +|______|___________________________|________________|_________|________| +| |Consolidated Gas & Electric|Somerset, Pa. |Hand | | +| 12 |Co., Baltimore, Md. | |Fired | 640 | +|______|___________________________|________________|_________|________| +| |Merrimac Mfg. Co., |Georges Creek, |Hand | | +| 13 |Lowell, Mass. |Md. |Fired | 321 | +|______|___________________________|________________|_________|________| +| |Great West'n Sugar Co., |Lafayette, Col.,|HandFired| | +| 14 |Ft. Collins, Col. |Mine Run |Extension| 351 | +|______|___________________________|________________|_________|________| +| |Baltimore Sewage Pumping |New River |Hand | | +| 15 | Station | |Fired | 266 | +|______|___________________________|________________|_________|________| +| |Tennessee State Prison, |Brushy Mountain,|Hand | | +| 16 |Nashville, Tenn. |Tenn. |Fired | 300 | +|______|___________________________|________________|_________|________| +| |Pine Bluff Corporation, |Arkansas Slack |Hand | | +| 17 |Pine Bluff, Ark. | |Fired | 298 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Valley, Pa., |Roney | | +| 18 |of N. J., Hoboken |Mine Run |Stoker | 520 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Valley, Pa., |Roney | | +| 19 |of N. J., Hoboken |Mine Run |Stoker | 520 | +|______|___________________________|________________|_________|________| +| |Frick Building, |Pittsburgh Nut |American | | +| 20 |Pittsburgh, Pa. |and Slack |Stoker | 300 | +|______|___________________________|________________|_________|________| +| |New York Edison Co., |Loyal Hanna, Pa.|Taylor | | +| 21 |New York City | |Stoker | 604 | +|______|___________________________|________________|_________|________| +| |City of Columbus, O., |Hocking Valley, |Detroit | | +| 22 |Dept. Lighting |O. |Stoker | 300 | +|______|___________________________|________________|_________|________| +| |Edison Elec. Illum. Co., |New River |Murphy | | +| 23 |Boston, Mass. | |Stoker | 508 | +|______|___________________________|________________|_________|________| +| |Colorado Springs & |Pike View, Col.,|Green Chn| | +| 24 |Interurban Ry., Col. |Mine Run |Grate | 400 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Lancashire, Pa. |B&W.Chain| | +| 25 |of N. J., Marion | |Grate | 600 | +|______|___________________________|________________|_________|________| +| |Pub. Serv. Corporation |Lancashire, Pa. |B&W.Chain| | +| 26 |of N. J., Marion | |Grate | 600 | +|______|___________________________|________________|_________|________| +| |Erie County Electric Co., |Mercer County, |B&W.Chain| | +| 27 |Erie, Pa. |Pa. |Grate | 508 | +|______|___________________________|________________|_________|________| +| |Union Elec. Lt. & Pr. Co., |Mascouth, Ill. |B&W.Chain| | +| 28 |St. Louis, Mo. | |Grate | 508 | +|______|___________________________|________________|_________|________| +| |Union Elec. Lt. & Pr. Co., |St. Clair |B&W.Chain| | +| 29 |St. Louis, Mo. |County, Ill. |Grate | 508 | +|______|___________________________|________________|_________|________| +| |Commonwealth Edison Co., |Carterville, |B&W.Chain| | +| 30 |Chicago, Ill. |Ill., Screenings|Grate | 508 | +|______|___________________________|________________|_________|________| + + ________________________________________________________________ +|Number|Grate |Dura-|Steam |Temper-|Degrees|Factor| Draft | +| of |Surf. | tion|Pres. | ature | Super | of | In | At | +| Test |Square|Test | By | Water | -heat |Evapo-|Furnace|Boiler| +| | Feet |Hours|Gauge |Degrees|Degrees|ration|Inches |Damper| +| | | |Pounds| Fahr. | Fahr. | |Upr/Lwr|Inches| +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 1 | 84 | 8 | 68 | 53.9 | |1.1965| +.41 | .21 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.65 | | +| 2 | 51.6 | 7 | 136.3| 203 | 150 |1.1480| .47 | .56 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 3 | 67.6 | 8 | 139 | 139.6 | 139 |1.1984| .70 | .96 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 4 | 40 | 8 | 110.2| 137 | |1.1185| .33 | .43 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 5 | 59.5 | 10 | 133.2| 75.2 | |1.1849| .19 | .40 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 6 | 26.5 | 18 | 132.1| 70.5 | |1.1897| .33 | | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.51 | | +| 7 | 48.9 | 7 | 101. | 121.3 | |1.1333| -.20 | .30 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 8 | 59.5 | 6 | 191.8| 88.3 | |1.1771| .50 | | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 9 | 27 | 24 | 156.3| 58 | |1.2051| .10 | .24 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 10 | | 24 | 145 | 75 | |1.1866| .26 | .46 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 11 | 118 | 8 | 170 | 186.1 | 66.7 |1.1162| .34 | .42 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 12 | 118 | 7.92| 173 | 180.2 | 75.2 |1.1276| .44 | .58 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 13 | 52 | 24 | 75 | 53.3 | |1.1987| .25 | .35 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 14 | 59.5 | 8 | 105 | 35.8 | |1.2219| .17 | .38 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 15 | 59.5 | 24 | 170.1| 133 | |1.1293| .12 | .43 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 16 | 51.3 | 10 | 105 | 75.1 | |1.1814| .21 | .42 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 17 | 59.5 | 8 | 149.2| 71 | |1.1910| .35 | .59 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 18 | 103.2| 10 | 133.2| 65.3 | 65.9 |1.2346| .05 | .49 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 19 | 103.2| 9 | 139 | 64 | 80.2 |1.2358| .18 | .57 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 20 | 53 | 9 | 125 | 76.6 | |1.1826| +1.64 | .64 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 21 | 75 | 8 | 198.5| 165.1 | 104 |1.1662| +3.05 | .60 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 22 | | 9 | 140 | 67 | 180 |1.2942| .22 | .35 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 23 | 90 |16.25| 199 | 48.4 | 136.5 |1.2996| .23 | 1.27 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 24 | 103 | 8 | 129 | 56 | |1.2002| .23 | .30 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.52 | | +| 25 | 132 | 8 | 200 | 57.2 | 280.4 |1.3909| +.19 | .52 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | +.15 | | +| 26 | 132 | 8 | 199 | 60.7 | 171.0 |1.3191| .04 | .52 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 27 | 90 | 8 | 120 | 69.9 | |1.1888| .31 | .58 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 28 | 103.5| 8 | 180 | 46 | 113 |1.2871| .62 | 1.24 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 29 | 103.5| 8 | 183 | 53.1 | 104 |1.2725| .60 | 1.26 | +|______|______|_____|______|_______|_______|______|_______|______| +| | | | | | | | | | +| 30 | 90 | 7 | 184 | 127.1 | 180 |1.2393| .68 | 1.15 | +|______|______|_____|______|_______|_______|______|_______|______| + ______________________________________________________________ +|Number|Temper-| Coal | +| of | ature | Total | Moist-| Total |Ash and| Total |DryCoal| +| Test |FlueGas|Weight:| ure | dry | Refuse|Combus-|/sq.ft.| +| |Degrees| Fired | Per | Coal | Per | tible | Grate | +| | Fahr. |Pounds | Cent | Pounds| Cent | Pounds|/Hr.Lb.| +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 1 | | 11670 | 4.45 | 11151 | 26.05 | 8248 | 16.6 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 2 | 487 | 8800 | 7.62 | 8129 | 29.82 | 5705 | 19.71 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 3 | 559 | 10799 | 6.42 | 10106 | 20.02 | 8081 | 21.77 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 4 | 427 | 5088 | 4.00 | 4884 | 19.35 | 3939 | 15.26 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 5 | 414 | 9440 | 2.14 | 9238 | 11.19 | 8204 | 15.52 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 6 | 410 | 8555 | 3.62 | 8245 | 15.73 | 6948 | 17.28 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 7 | 480 | 7130 | 7.38 | 6604 | 18.35 | 5392 | 19.29 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 8 | 449 | 7500 | 2.70 | 7298 | 27.94 | 5259 | 14.73 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 9 | 410 | 15087 | 7.50 | 13956 | 11.30 | 12379 | 21.5 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 10 | 503 | 29528 | 7.72 | 27248 | | | 24.7 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 11 | 487 | 20400 | 2.84 | 19821 | 7.83 | 18269 | 21.00 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 12 | 494 | 21332 | 2.29 | 20843 | 8.23 | 19127 | 22.31 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 13 | 516 | 24584 | 4.29 | 23529 | 7.63 | 21883 | 18.85 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 14 | 523 | 15540 | 18.64 | 12643 | | | 28.59 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 15 | 474 | 18330 | 2.03 | 17958 | 16.36 | 16096 | 12.57 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 16 | 536 | 12243 | 2.14 | 11981 | | | 23.40 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 17 | 534 | 10500 | 3.04 | 10181 | | | 21.40 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 18 | 458 | 18600 | 3.40 | 17968 | 18.38 | 14665 | 17.41 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 19 | 609 | 23400 | 2.56 | 22801 | 16.89 | 18951 | 24.55 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 20 | 518 | 10500 | 1.83 | 10308 | 12.22 | 9048 | 21.56 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 21 | 536 | 25296 | 2.20 | 24736 | | | 41.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 22 | 511 | 14263 | 8.63 | 13032 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 23 | 560 | 39670 | 4.22 | 37996 | 4.32 | 36355 | 25.98 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 24 | 538 | 23000 | 23.73 | 17542 | | | 21.36 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 25 | 590 | 32205 | 4.03 | 30907 | 15.65 | 26070 | 29.26 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 26 | 529 | 24243 | 4.09 | 23251 | 12.33 | 20385 | 22.01 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 27 | 533 | 22328 | 4.42 | 21341 | 16.88 | 17739 | 29.64 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 28 | 523 | 32163 | 13.74 | 27744 | | | 33.50 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 29 | 567 | 36150 | 14.62 | 30865 | | | 37.28 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 30 | | 30610 | 11.12 | 27206 | 14.70 | 23198 | 43.20 | +|______|_______|_______|_______|_______|_______|_______|_______| + + ______________________________________________________________ +|Number| Water | | Flue Gas Analysis | +| of |Actual | Equiv.|ditto /|% Rated|CO_{2} | O | CO | +| Test |Evapor-|Evap. @|sq.ft. |Cap'ty.| Per | Per | Per | +| | ation |>212deg|Heating|Develpd| Cent | Cent | Cent | +| |/Hr.Lb.|/Hr.Lb.|Surface|PerCent| | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 1 | 10268 | 12286 | 4.10 | 118.7 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 2 | 8246 | 9466 | 4.34 | 125.7 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 3 | 9145 | 10959 | 3.65 | 105.9 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 4 | 5006 | 5599 | 3.61 | 104.7 | 12.26 | 7.88 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 5 | 7434 | 8809 | 3.06 | 87.2 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 6 | 2903 | 3454 | 2.91 | 84.4 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 7 | 7464 | 8459 | 2.82 | 81.7 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 8 | 9164 | 10787 | 2.88 | 83.5 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 9 | 4374 | 5271 | 3.51 | 101.8 | 11.7 | 7.3 | 0.07 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 10 | 8688 | 10309 | 3.44 | 99.6 | 12.9 | 5.0 | 0.2 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 11 | 24036 | 26829 | 4.19 | 121.5 | 12.5 | 6.4 | 0.5 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 12 | 25313 | 28544 | 4.46 | 129.3 | 13.3 | 5.1 | 0.5 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 13 | 9168 | 10990 | 3.42 | 99.3 | 9.6 | 8.8 | 0.4 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 14 | 11202 | 13689 | 3.91 | 113.5 | 9.1 | 9.9 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 15 | 7565 | 8543 | 3.21 | 93.1 | 10.71 | 9.10 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 16 | 9512 | 11237 | 3.74 | 108.6 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 17 | 9257 | 11025 | 3.70 | 107.2 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 18 | 15887 | 19614 | 3.77 | 108.7 | 11.7 | 7.7 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 19 | 21320 | 26347 | 5.06 | 146.7 | 11.9 | 7.8 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 20 | 9976 | 11978 | 3.93 | 112.0 | 11.3 | 7.5 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 21 | 28451 | 33066 | 5.47 | 158.6 | 12.3 | 6.4 | 0.7 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 22 | 10467 | 13526 | 4.51 | 130.7 | 11.9 | 7.2 | 0.04 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 23 | 20700 | 26902 | 5.30 | 153.5 | 11.1 | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 24 | 14650 | 17583 | 4.40 | 127.4 | | | | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 25 | 28906 | 40205 | 6.70 | 194.2 | 10.5 | 8.3 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 26 | 23074 | 30437 | 5.07 | 147.0 | 10.1 | 9.0 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 27 | 20759 | 24678 | 4.85 | 140.8 | 10.1 | 9.1 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 28 | 21998 | 28314 | 5.67 | 161.5 | 8.7 | 10.6 | 0.0 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 29 | 24386 | 31031 | 6.11 | 177.1 | 8.9 | 10.7 | 0.2 | +|______|_______|_______|_______|_______|_______|_______|_______| +| | | | | | | | | +| 30 | 30505 | 37805 | 7.43 | 215.7 | 10.4 | 9.4 | 0.2 | +|______|_______|_______|_______|_______|_______|_______|_______| + +_______________________________________________________ +|Number| Proximate Analysis Dry Coal | Equiv.|Combnd.| +| of |Volatl.| Fixed | Ash |B.t.u./|Evap. @|Efficy.| +| Test |Matter |Carbon | Per | Pound |>212deg|Boiler | +| | Per | Per | Cent | Dry | /Pound|& Grate| +| | Cent | Cent | | Coal |DryCoal|PerCent| +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 1 | | | 26.05 | 11913 | 8.81 | 71.8 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 2 | | | | 11104 | 8.15 | 72.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 3 | 5.55 | 80.60 | 13.87 | 12300 | 8.67 | 68.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 4 | 7.74 | 77.48 | 14.78 | 12851 | 9.17 | 69.2 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 5 | | | | 13138 | 9.53 | 69.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 6 | 6.13 | 84.86 | 9.01 | 13454 | 9.57 | 69.0 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 7 | | | | 12224 | 8.97 | 71.2 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 8 | 0.55 | 86.73 | 12.72 | 12642 | 8.87 | 68.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 9 | 39.01 | 48.08 | 12.91 | 12292 | 9.06 | 71.5 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 10 | 38.33 | 46.71 | 14.96 | 12284 | 9.08 | 71.7 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 11 | 19.86 | 73.02 | 7.12 | 14602 | 10.83 | 72.0 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 12 | 20.24 | 72.26 | 7.50 | 14381 | 10.84 | 73.2 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 13 | | | | 14955 | 11.21 | 72.7 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 14 | 39.60 | 54.46 | 5.94 | 11585 | 8.66 | 72.5 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 15 | 17.44 | 76.42 | 5.84 | 15379 | 11.42 | 72.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 16 | 33.40 | 54.73 | 11.87 | 12751 | 9.38 | 71.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 17 | 15.42 | 62.48 | 22.10 | 12060 | 8.66 | 69.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 18 | 14.99 | 75.13 | 9.88 | 14152 | 10.92 | 74.88 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 19 | 14.40 | 74.33 | 11.27 | 14022 | 10.40 | 71.97 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 20 | 32.44 | 56.71 | 10.85 | 13510 | 10.30 | 74.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 21 | 19.02 | 72.09 | 8.89 | 14105 | 10.69 | 73.5 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 22 | 32.11 | 53.93 | 13.96 | 12435 | 9.41 | 73.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 23 | 19.66 | 75.41 | 4.93 | 14910 | 11.51 | 74.9 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 24 | 43.57 | 46.22 | 10.21 | 11160 | 8.02 | 69.7 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 25 | 22.84 | 69.91 | 7.25 | 13840 | 10.41 | 72.6 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 26 | 32.36 | 60.67 | 6.97 | 14027 | 10.47 | 72.1 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 27 | 33.26 | 54.03 | 12.71 | 12742 | 9.25 | 70.4 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 28 | 28.96 | 46.88 | 24.16 | 10576 | 8.16 | 74.9 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 29 | 36.50 | 41.20 | 22.30 | 10849 | 8.04 | 71.9 | +|______|_______|_______|_______|_______|_______|_______| +| | | | | | | | +| 30 | | | 10.24 | 13126 | 9.73 | 71.9 | +|______|_______|_______|_______|_______|_______|_______| + +[Illustration: 15400 Horse-power Installation of Babcock & Wilcox +Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate +Stokers at the Plant of the Twin City Rapid Transit Co., Minneapolis, +Minn.] + +This increase in the efficiency of the boiler alone with the decrease in +the rate at which it is operated, will hold to a point where the +radiation of heat from the boiler setting is proportionately large +enough to be a governing factor in the total amount of heat absorbed. + +The second reason given above for a decrease of boiler efficiency with +increase of capacity, viz., the effect of radiant heat, is to a greater +extent than the first reason dependent upon a constant furnace +temperature. Any increase in this temperature will affect enormously the +amount of heat absorbed by radiation, as this absorption will vary as +the fourth power of the temperature of the radiating body. In this way +it is seen that but a slight increase in furnace temperature will be +necessary to bring the proportional part, due to absorption by +radiation, of the total heat absorbed, up to its proper proportion at +the higher ratings. This factor of furnace temperature more properly +belongs to the consideration of furnace efficiency than of boiler +efficiency. There is a point, however, in any furnace above which the +combustion will be so poor as to actually reduce the furnace temperature +and, therefore, the proportion of heat absorbed through radiation by a +given amount of exposed heating surface. + +Since it is thus true that the efficiency of the boiler considered alone +will increase with a decreased capacity, it is evident that if the +furnace conditions are constant regardless of the load, that the +combined efficiency of boiler and furnace will also decrease with +increasing loads. This fact was clearly proven in the tests of the +boilers at the Detroit Edison Company.[74] The furnace arrangement of +these boilers and the great care with which the tests were run made it +possible to secure uniformly good furnace conditions irrespective of +load, and here the maximum efficiency was obtained at a point somewhat +less than the rated capacity of the boilers. + +In some cases, however, and especially in the ordinary operation of the +plant, the furnace efficiency will, up to a certain point, increase with +an increase in power. This increase in furnace efficiency is ordinarily +at a greater rate as the capacity increases than is the decrease in +boiler efficiency, with the result that the combined efficiency of +boiler and furnace will to a certain point increase with an increase in +capacity. This makes the ordinary point of maximum combined efficiency +somewhat above the rated capacity of the boiler and in many cases the +combined efficiency will be practically a constant over a considerable +range of ratings. The features limiting the establishing of the point of +maximum efficiency at a high rating are the same as those limiting the +amount of grate surface that can be installed under a boiler. The +relative efficiency of different combinations of boilers and furnaces at +different ratings depends so largely upon the furnace conditions that +what might hold for one combination would not for another. + +In view of the above, it is impossible to make a statement of the +efficiency at different capacities of a boiler and furnace which will +hold for any and all conditions. Fig. 40 shows in a general form the +relation of efficiency to capacity. This curve has been plotted from a +great number of tests, all of which were corrected to bring them to +approximately the same conditions. The curve represents test conditions. +The efficiencies represented are those which may be secured only under +such conditions. The general direction of the curve, however, will be +found to hold approximately correct for operating conditions when used +only as a guide to what may be expected. + +[Graph: Combined Efficiency of Boiler and Furnace Per Cent +against Per Cent of Boiler's Rated Capacity Developed + +Fig. 40. Approximate Variation of Efficiency with Capacity under Test +Conditions] + +Economical Loads--With the effect of capacity on economy in mind, the +question arises as to what constitutes the economical load to be +carried. In figuring on the economical load for an individual plant, the +broader economy is to be considered, that in which, against the boiler +efficiency, there is to be weighed the plant first cost, returns on such +investment, fuel cost, labor, capacity, etc., etc. This matter has been +widely discussed, but unfortunately such discussion has been largely +limited to central power station practice. The power generated in such +stations, while representing an enormous total, is by no means the +larger proportion of the total power generated throughout the country. +The factors determining the economic load for the small plant, however, +are the same as in a large, and in general the statements made relative +to the question are equally applicable. + +The economical rating at which a boiler plant should be run is dependent +solely upon the load to be carried by that individual plant and the +nature of such load. The economical load for each individual plant can +be determined only from the careful study of each individual set of +conditions or by actual trial. + +The controlling factor in the cost of the plant, regardless of the +nature of the load, is the capacity to carry the maximum peak load that +may be thrown on the plant under any conditions. + +While load conditions, do, as stated, vary in every individual plant, in +a broad sense all loads may be grouped in three classes: 1st, the +approximately constant 24-hour load; 2nd, the steady 10 or 12-hour load +usually with a noonday period of no load; 3rd, the 24-hour variable +load, found in central station practice. The economical load at which +the boiler may be run will vary with these groups: + +1st. For a constant load, 24 hours in the day, it will be found in most +cases that, when all features are considered, the most economical load +or that at which a given amount of steam can be produced the most +cheaply will be considerably over the rated horse power of the boiler. +How much above the rated capacity this most economic load will be, is +dependent largely upon the cost of coal at the plant, but under ordinary +conditions, the point of maximum economy will probably be found to be +somewhere between 25 and 50 per cent above the rated capacity of the +boilers. The capital investment must be weighed against the coal saving +through increased thermal efficiency and the labor account, which +increases with the number of units, must be given proper consideration. +When the question is considered in connection with a plant already +installed, the conditions are different from where a new plant is +contemplated. In an old plant, where there are enough boilers to operate +at low rates of capacity, the capital investment leads to a fixed +charge, and it will be found that the most economical load at which +boilers may be operated will be lower than where a new plant is under +consideration. + +2nd. For a load of 10 or 12 hours a day, either an approximately steady +load or one in which there is a peak, where the boilers have been banked +over night, the capacity at which they may be run with the best economy +will be found to be higher than for uniform 24-hour load conditions. +This is obviously due to original investment, that is, a given amount of +invested capital can be made to earn a larger return through the higher +overload, and this will hold true to a point where the added return more +than offsets the decrease in actual boiler efficiency. Here again the +determining factors of what is the economical load are the fuel and +labor cost balanced against the thermal efficiency. With a load of this +character, there is another factor which may affect the economical plant +operating load. This is from the viewpoint of spare boilers. That such +added capacity in the way of spares is necessary is unquestionable. +Since they must be installed, therefore, their presence leads to a fixed +charge and it is probable that for the plant, as a whole, the economical +load will be somewhat lower than if the boilers were considered only as +spares. That is, it may be found best to operate these spares as a part +of the regular equipment at all times except when other boilers are off +for cleaning and repairs, thus reducing the load on the individual +boilers and increasing the efficiency. Under such conditions, the added +boiler units can be considered as spares only during such time as some +of the boilers are not in operation. + +Due to the operating difficulties that may be encountered at the higher +overloads, it will ordinarily be found that the most economical ratings +at which to run boilers for such load conditions will be between 150 and +175 per cent of rating. Here again the maximum capacity at which the +boilers may be run for the best plant economy is limited by the point at +which the efficiency drops below what is warranted in view of the first +cost of the apparatus. + +3rd. The 24-hour variable load. This is a class of load carried by the +central power station, a load constant only in the sense that there are +no periods of no load and which varies widely with different portions of +the 24 hours. With such a load it is particularly difficult to make any +assertion as to the point of maximum economy that will hold for any +station, as this point is more than with any other class of load +dependent upon the factors entering into the operation of each +individual plant. + +The methods of handling a load of this description vary probably more +than with any other kind of load, dependent upon fuel, labor, type of +stoker, flexibility of combined furnace and boiler etc., etc. + +In general, under ordinary conditions such as appear in city central +power station work where the maximum peaks occur but a few times a year, +the plant should be made of such size as to enable it to carry these +peaks at the maximum possible overload on the boilers, sufficient margin +of course being allowed for insurance against interruption of service. +With the boilers operating at this maximum overload through the peaks a +large sacrifice in boiler efficiency is allowable, provided that by such +sacrifice the overload expected is secured. + +[Illustration: Portion of 4890 Horse-power Installation of Babcock & +Wilcox Boilers at the Billings Sugar Co., Billings, Mont. 694 Horse +Power of these Boilers are Equipped with Babcock and Wilcox Chain Grate +Stokers] + +Some methods of handling a load of this nature are given below: + +Certain plant operating conditions make it advisable, from the +standpoint of plant economy, to carry whatever load is on the plant at +any time on only such boilers as will furnish the power required when +operating at ratings of, say, 150 to 200 per cent. That is, all boilers +which are in service are operated at such ratings at all times, the +variation in load being taken care of by the number of boilers on the +line. Banked boilers are cut in to take care of increasing loads and +peaks and placed again on bank when the peak periods have passed. It is +probable that this method of handling central station load is to-day the +most generally used. + +Other conditions of operation make it advisable to carry the load on a +definite number of boiler units, operating these at slightly below their +rated capacity during periods of light or low loads and securing the +overload capacity during peaks by operating the same boilers at high +ratings. In this method there are no boilers kept on banked fires, the +spares being spares in every sense of the word. + +A third method of handling widely varying loads which is coming somewhat +into vogue is that of considering the plant as divided, one part to take +care of what may be considered the constant plant load, the other to +take care of the floating or variable load. With such a method that +portion of the plant carrying the steady load is so proportioned that +the boilers may be operated at the point of maximum efficiency, this +point being raised to a maximum through the use of economizers and the +general installation of any apparatus leading to such results. The +variable load will be carried on the remaining boilers of the plant +under either of the methods just given, that is, at the high ratings of +all boilers in service and banking others, or a variable capacity from +all boilers in service. + +The opportunity is again taken to indicate the very general character of +any statements made relative to the economical load for any plant and to +emphasize the fact that each individual case must be considered +independently, with the conditions of operations applicable thereto. + +With a thorough understanding of the meaning of boiler efficiency and +capacity and their relation to each other, it is possible to consider +more specifically the selection of boilers. + +The foremost consideration is, without question, the adaptability of the +design selected to the nature of the work to be done. An installation +which is only temporary in its nature would obviously not warrant the +first cost that a permanent plant would. If boilers are to carry an +intermittent and suddenly fluctuating load, such as a hoisting load or a +reversing mill load, a design would have to be selected that would not +tend to prime with the fluctuations and sudden demand for steam. A +boiler that would give the highest possible efficiency with fuel of one +description, would not of necessity give such efficiency with a +different fuel. A boiler of a certain design which might be good for +small plant practice would not, because of the limitations in +practicable size of units, be suitable for large installations. A +discussion of the relative value of designs can be carried on almost +indefinitely but enough has been said to indicate that a given design +will not serve satisfactorily under all conditions and that the +adaptability to the service required will be dependent upon the fuel +available, the class of labor procurable, the feed water that must be +used, the nature of the plant's load, the size of the plant and the +first cost warranted by the service the boiler is to fulfill. + + TABLE 60 + + ACTUAL EVAPORATION FOR DIFFERENT PRESSURES AND TEMPERATURES OF FEED + WATER CORRESPONDING TO ONE HORSE POWER (34-1/2 POUNDS PER HOUR FROM AND AT 212 DEGREES FAHRENHEIT) + +----------------------------------------------------------------------------------------------------------------------------------------- +Temperature| | + of | Pressure by Gauge--Pounds per Square Inch | + Feed | | + Degrees | | +Fahrenheit | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 210 | 220 | 230 | 240 | 250 | +-----------+-----------------------------------------------------------------------------------------------------------------------------| + 32 |28.41|28.36|28.29|28.24|28.20|28.16|28.13|28.09|28.07|28.04|28.02|27.99|27.97|27.95|27.94|27.92|27.90|27.89|27.87|27.86|27.83| + 40 |28.61|28.54|28.49|28.44|28.40|28.35|28.32|28.29|28.26|28.23|28.21|28.18|28.16|28.14|28.12|28.11|28.09|28.07|28.06|28.05|28.03| + 50 |28.85|28.79|28.73|28.68|28.64|28.60|28.56|28.53|28.50|28.47|28.45|28.43|28.40|28.38|28.36|28.35|28.33|28.31|28.30|28.28|28.27| + 60 |29.10|29.04|28.98|28.93|28.88|28.84|28.81|28.77|28.74|28.72|28.69|28.67|28.65|28.62|28.60|28.59|28.57|28.55|28.54|28.52|28.51| + 70 |29.36|29.29|29.23|29.18|29.14|29.09|29.06|29.02|28.99|28.96|28.94|28.92|28.89|28.87|28.85|28.83|28.82|28.80|28.78|28.77|28.76| + 80 |29.62|29.55|29.49|29.44|29.39|29.35|29.31|29.27|29.24|29.22|29.19|29.17|29.14|29.12|29.10|29.08|29.07|29.05|29.03|29.02|29.00| + 90 |29.88|29.81|29.75|29.70|29.65|29.61|29.57|29.53|29.50|29.47|29.45|29.42|29.40|29.38|29.36|29.34|29.32|29.30|29.29|29.27|29.25| +100 |30.15|30.08|30.02|29.96|29.91|29.87|29.83|29.80|29.76|29.73|29.71|29.68|29.66|29.63|29.61|29.60|29.58|29.56|29.54|29.53|29.51| +110 |30.42|30.35|30.29|30.23|30.18|30.14|30.10|30.06|30.03|30.00|29.97|29.95|29.92|29.90|29.88|29.86|29.84|29.82|29.81|29.79|29.77| +120 |30.70|30.63|30.56|30.51|30.46|30.41|30.37|30.33|30.30|30.27|30.24|30.22|30.19|30.17|30.15|30.13|30.11|30.09|30.07|30.06|30.04| +130 |30.99|30.91|30.84|30.79|30.73|30.69|30.65|30.61|30.57|30.54|30.52|30.49|30.47|30.44|30.42|30.40|30.38|30.36|30.35|30.33|30.31| +140 |31.28|31.20|31.13|31.07|31.02|30.97|30.93|30.89|30.86|30.83|30.80|30.77|30.75|30.72|30.70|30.68|30.66|30.64|30.62|30.61|30.59| +150 |31.58|31.49|31.42|31.36|31.31|31.26|31.22|31.18|31.14|31.11|31.08|31.06|31.03|31.01|30.98|30.96|30.94|30.92|30.91|30.89|30.87| +160 |31.87|31.79|31.72|31.66|31.61|31.56|31.51|31.47|31.44|31.40|31.37|31.35|31.32|31.29|31.27|31.25|31.23|31.21|31.19|31.18|31.16| +170 |32.18|32.10|32.02|31.96|31.91|31.86|31.81|31.77|31.73|31.70|31.67|31.64|31.62|31.59|31.57|31.54|31.52|31.50|31.49|31.47|31.46| +180 |32.49|32.41|32.33|32.27|32.22|32.16|32.12|32.08|32.04|32.00|31.97|31.95|31.92|31.89|31.87|31.84|31.82|31.80|31.79|31.77|31.75| +190 |32.81|32.72|32.65|32.59|32.53|32.47|32.43|32.38|32.35|32.32|32.29|32.26|32.23|32.20|32.17|32.15|32.13|32.11|32.09|32.07|32.05| +200 |33.13|33.05|32.97|32.91|32.85|32.79|32.75|32.70|32.66|32.63|32.60|32.57|32.54|32.51|32.49|32.46|32.44|32.42|32.40|32.38|32.36| +210 |33.47|33.38|33.30|33.24|33.18|33.13|33.08|33.03|32.99|32.95|32.92|32.89|32.86|32.83|32.81|32.79|32.76|32.74|32.72|32.70|32.68| +----------------------------------------------------------------------------------------------------------------------------------------- + +The proper consideration can be given to the adaptability of any boiler +for the service in view only after a thorough understanding of the +requirements of a good steam boiler, with the application of what has +been said on the proper operation to the special requirements of each +case. Of almost equal importance to the factors mentioned are the +experience, the skill and responsibility of the manufacturer. + +With the design of boiler selected that is best adapted to the service +required, the next step is the determination of the boiler power +requirements. + +The amount of steam that must be generated is determined from the steam +consumption of the prime movers. It has already been indicated that such +consumption can vary over wide limits with the size and type of the +apparatus used, but fortunately all types have been so tested that +manufacturers are enabled to state within very close limits the actual +consumption under any given set of conditions. It is obvious that +conditions of operation will have a bearing on the steam consumption +that is as important as the type and size of the apparatus itself. This +being the case, any tabular information that can be given on such steam +consumption, unless it be extended to an impracticable size, is only of +use for the most approximate work and more definite figures on this +consumption should in all cases be obtained from the manufacturer of the +apparatus to be used for the conditions under which it will operate. + +To the steam consumption of the main prime movers, there is to be added +that of the auxiliaries. Again it is impossible to make a definite +statement of what this allowance should be, the figure depending wholly +upon the type and the number of such auxiliaries. For approximate work, +it is perhaps best to allow 15 or 20 per cent of the steam requirements +of the main engines, for that of auxiliaries. Whatever figure is used +should be taken high enough to be on the conservative side. + +When any such figures are based on the actual weight of steam required, +Table 60, which gives the actual evaporation for various pressures and +temperatures of feed corresponding to one boiler horse power (34.5 +pounds of water per hour from and at 212 degrees), may be of service. + +With the steam requirements known, the next step is the determination of +the number and size of boiler units to be installed. This is directly +affected by the capacity at which a consideration of the economical load +indicates is the best for the operating conditions which will exist. The +other factors entering into such determination are the size of the plant +and the character of the feed water. + +The size of the plant has its bearing on the question from the fact that +higher efficiencies are in general obtained from large units, that labor +cost decreases with the number of units, the first cost of brickwork is +lower for large than for small size units, a general decrease in the +complication of piping, etc., and in general the cost per horse power of +any design of boiler decreases with the size of units. To illustrate +this, it is only necessary to consider a plant of, say, 10,000 boiler +horse power, consisting of 40-250 horse-power units or 17-600 +horse-power units. + +The feed water available has its bearing on the subject from the other +side, for it has already been shown that very large units are not +advisable where the feed water is not of the best. + +The character of an installment is also a factor. Where, say, 1000 horse +power is installed in a plant where it is known what the ultimate +capacity is to be, the size of units should be selected with the idea of +this ultimate capacity in mind rather than the amount of the first +installation. + +Boiler service, from its nature, is severe. All boilers have to be +cleaned from time to time and certain repairs to settings, etc., are a +necessity. This makes it necessary, in determining the number of boilers +to be installed, to allow a certain number of units or spares to be +operated when any of the regular boilers must be taken off the line. +With the steam requirements determined for a plant of moderate size and +a reasonably constant load, it is highly advisable to install at least +two spare boilers where a continuity of service is essential. This +permits the taking off of one boiler for cleaning or repairs and still +allows a spare boiler in the event of some unforeseen occurrence, such +as the blowing out of a tube or the like. Investment in such spare +apparatus is nothing more nor less than insurance on the necessary +continuity of service. In small plants of, say, 500 or 600 horse power, +two spares are not usually warranted in view of the cost of such +insurance. A large plant is ordinarily laid out in a number of sections +or panels and each section should have its spare boiler or boilers even +though the sections are cross connected. In central station work, where +the peaks are carried on the boilers brought up from the bank, such +spares are, of course, in addition to these banked boilers. From the +aspect of cleaning boilers alone, the number of spare boilers is +determined by the nature of any scale that may be formed. If scale is +formed so rapidly that the boilers cannot be kept clean enough for good +operating results, by cleaning in rotation, one at a time, the number of +spares to take care of such proper cleaning will naturally increase. + +In view of the above, it is evident that only a suggestion can be made +as to the number and size of units, as no recommendation will hold for +all cases. In general, it will be found best to install units of the +largest possible size compatible with the size of the plant and +operating conditions, with the total power requirements divided among +such a number of units as will give proper flexibility of load, with +such additional units for spares as conditions of cleaning and insurance +against interruption of service warrant. + +In closing the subject of the selection of boilers, it may not be out of +place to refer to the effect of the builder's guarantee upon the +determination of design to be used. Here in one of its most important +aspects appears the responsibility of the manufacturer. Emphasis has +been laid on the difference between test results and those secured in +ordinary operating practice. That such a difference exists is well known +and it is now pretty generally realized that it is the responsible +manufacturer who, where guarantees are necessary, submits the +conservative figures, figures which may readily be exceeded under test +conditions and which may be closely approached under the ordinary plant +conditions that will be met in daily operation. + + + + +OPERATION AND CARE OF BOILERS + + +The general subject of boiler room practice may be considered from two +aspects. The first is that of the broad plant economy, with a suggestion +as to the methods to be followed in securing the best economical results +with the apparatus at hand and procurable. The second deals rather with +specific recommendations which should be followed in plant practice, +recommendations leading not only to economy but also to safety and +continuity of service. Such recommendations are dictated from an +understanding of the nature of steam generating apparatus and its +operation, as covered previously in this book. + +It has already been pointed out that the attention given in recent years +to steam generating practice has come with a realization of the wide +difference existing between the results being obtained in every-day +operation and those theoretically possible. The amount of such attention +and regulation given to the steam generating end of a power plant, +however, is comparatively small in relation to that given to the balance +of the plant, but it may be safely stated that it is here that there is +the greatest assurance of a return for the attention given. + +In the endeavor to increase boiler room efficiency, it is of the utmost +importance that a standard basis be set by which average results are to +be judged. With the theoretical efficiency obtainable varying so widely, +this standard cannot be placed at the highest efficiency that has been +obtained regardless of operating conditions. It is better set at the +best obtainable results for each individual plant under its conditions +of installation and daily operation. + +With an individual standard so set, present practice can only be +improved by a systematic effort to approach this standard. The degree +with which operating results will approximate such a standard will be +found to be directly proportional to the amount of intelligent +supervision given the operation. For such supervision to be given, it is +necessary to have not only a full realization of what the plant can do +under the best operating conditions but also a full and complete +knowledge of what it is doing under all of the different conditions that +may arise. What the plant is doing should be made a matter of continuous +record so arranged that the results may be directly compared for any +period or set of conditions, and where such results vary from the +standard set, steps must be taken immediately to remedy the causes of +such failings. Such a record is an important check in the losses in the +plant. + +As the size of the plant and the fuel consumption increase, such a check +of losses and recording of results becomes a necessity. In the larger +plants, the saving of but a fraction of one per cent in the fuel bill +represents an amount running into thousands of dollars annually, while +the expense of the proper supervision to secure such saving is small. +The methods of supervision followed in the large plants are necessarily +elaborate and complete. In the smaller plants the same methods may be +followed on a more moderate scale with a corresponding saving in fuel +and an inappreciable increase in either plant organization or expense. + +There has been within the last few years a great increase in the +practicability and reliability of the various types of apparatus by +which the records of plant operation may be secured. Much of this +apparatus is ingenious and, considering the work to be done, is +remarkably accurate. From the delicate nature of some of the apparatus, +the liability to error necessitates frequent calibration but even where +the accuracy is known to be only within limits of, say, 5 per cent +either way, the records obtained are of the greatest service in +considering relative results. Some of the records desirable and the +apparatus for securing them are given below. + +[Illustration: 2400 Horse-power Installation of Cross Drum Babcock & +Wilcox Boilers and Superheaters at the Westinghouse Electric and +Manufacturing Co., East Pittsburgh, Pa.] + +Inasmuch as the ultimate measure of the efficiency of the boiler plant +is the cost of steam generation, the important records are those of +steam generated and fuel consumed Records of temperature, analyses, +draft and the like, serve as a check on this consumption, indicating the +distribution of the losses and affording a means of remedying conditions +where improvement is possible. + +Coal Records--There are many devices on the market for conveniently +weighing the coal used. These are ordinarily accurate within close +limits, and where the size or nature of the plant warrants the +investment in such a device, its use is to be recommended. The coal +consumption should be recorded by some other method than from the +weights of coal purchased. The total weight gives no way of dividing the +consumption into periods and it will unquestionably be found to be +profitable to put into operation some scheme by which the coal is +weighed as it is used. In this way, the coal consumption, during any +specific period of the plant's operation, can be readily seen. The +simplest of such methods which may be used in small plants is the actual +weighing on scales of the fuel as it is brought into the fire room and +the recording of such weights. + +Aside from the actual weight of the fuel used, it is often advisable to +keep other coal records, coal and ash analyses and the like, for the +evaporation to be expected will be dependent upon the grade of fuel used +and its calorific value, fusibility of its ash, and like factors. + +The highest calorific value for unit cost is not necessarily the +indication of the best commercial results. The cost of fuel is governed +by this calorific value only when such value is modified by local +conditions of capacity, labor and commercial efficiency. One of the +important factors entering into fuel cost is the consideration of the +cost of ash handling and the maintenance of ash handling apparatus if +such be installed. The value of a fuel, regardless of its calorific +value, is to be based only on the results obtained in every-day plant +operation. + +Coal and ash analyses used in connection with the amount of fuel +consumed, are a direct indication of the relation between the results +being secured and the standard of results which has been set for the +plant. The methods of such analyses have already been described. The +apparatus is simple and the degree of scientific knowledge necessary is +only such as may be readily mastered by plant operatives. + +The ash content of a fuel, as indicated from a coal analysis checked +against ash weights as actually found in plant operation, acts as a +check on grate efficiency. The effect of any saving in the ashes, that +is, the permissible ash to be allowed in the fuel purchased, is +determined by the point at which the cost of handling, combined with the +falling off in the evaporation, exceeds the saving of fuel cost through +the use of poorer coal. + +Water Records--Water records with the coal consumption, form the basis +for judging the economic production of steam. The methods of securing +such records are of later introduction than for coal, but great advances +have been made in the apparatus to be used. Here possibly, to a greater +extent than in any recording device, are the records of value in +determining relative evaporation, that is, an error is rather allowable +provided such an error be reasonably constant. + +The apparatus for recording such evaporation is of two general classes: +Those measuring water before it is fed to the boiler and those measuring +the steam as it leaves. Of the first, the venturi meter is perhaps the +best known, though recently there has come into considerable vogue an +apparatus utilizing a weir notch for the measuring of such water. Both +methods are reasonably accurate and apparatus of this description has an +advantage over one measuring steam in that it may be calibrated much +more readily. Of the steam measuring devices, the one in most common use +is the steam flow meter. Provided the instruments are selected for a +proper flow, etc., they are of inestimable value in indicating the steam +consumption. Where such instruments are placed on the various engine +room lines, they will immediately indicate an excessive consumption for +any one of the units. With a steam flow meter placed on each boiler, it +is possible to fix relatively the amount produced by each boiler and, +considered in connection with some of the "check" records described +below, clearly indicate whether its portion of the total steam produced +is up to the standard set for the over-all boiler room efficiency. + +Flue Gas Analysis--The value of a flue gas analysis as a measure of +furnace efficiency has already been indicated. There are on the market a +number of instruments by which a continuous record of the carbon dioxide +in the flue gases may be secured and in general the results so recorded +are accurate. The limitations of an analysis showing only CO_{2} and the +necessity of completing such an analysis with an Orsat, or like +apparatus, and in this way checking the automatic device, have already +been pointed out, but where such records are properly checked from time +to time and are used in conjunction with a record of flue temperatures, +the losses due to excess air or incomplete combustion and the like may +be directly compared for any period. Such records act as a means for +controlling excess air and also as a check on individual firemen. + +Where the size of a plant will not warrant the purchase of an expensive +continuous CO_{2} recorder, it is advisable to make analyses of samples +for various conditions of firing and to install an apparatus whereby a +sample of flue gas covering a period of, say, eight hours, may be +obtained and such a sample afterwards analyzed. + +Temperature Records--Flue gas temperatures, feed water temperatures and +steam temperatures are all taken with recording thermometers, any number +of which will, when properly calibrated, give accurate results. + +A record of flue temperatures is serviceable in checking stack losses +and, in general, the cleanliness of the boiler. A record of steam +temperatures, where superheaters are used, will indicate excessive +fluctuations and lead to an investigation of their cause. Feed +temperatures are valuable in showing that the full benefit of the +exhaust steam is being derived. + +Draft Regulation--As the capacity of a boiler varies with the combustion +rate and this rate with the draft, an automatic apparatus satisfactorily +varying this draft with the capacity demands on the boiler will +obviously be advantageous. + +As has been pointed out, any fuel has some rate of combustion at which +the best results will be obtained. In a properly designed plant where +the load is reasonably steady, the draft necessary to secure such a rate +may be regulated automatically. + +Automatic apparatus for the regulation of draft has recently reached a +stage of perfection which in the larger plants at any rate makes its +installation advisable. The installation of a draft gauge or gauges is +strongly to be recommended and a record of such drafts should be kept as +being a check on the combustion rates. + +An important feature to be considered in the installing of all recording +apparatus is its location. Thermometers, draft gauges and flue gas +sampling pipes should be so located as to give as nearly as possible an +average of the conditions, the gases flowing freely over the ends of the +thermometers, couples and sampling pipes. With the location permanent, +there is no security that the samples may be considered an average but +in any event comparative results will be secured which will be useful in +plant operation. The best permanent location of apparatus will vary +considerably with the design of the boiler. + +It may not be out of place to refer briefly to some of the shortcomings +found in boiler room practice, with a suggestion as to a means of +overcoming them. + +1st. It is sometimes found that the operating force is not fully +acquainted with the boilers and apparatus. Probably the most general of +such shortcomings is the fixed idea in the heads of the operatives that +boilers run above their rated capacity are operating under a state of +strain and that by operating at less than their rated capacity the most +economical service is assured, whereas, by determining what a boiler +will do, it may be found that the most economical rating under the +conditions of the plant will be considerably in excess of the builder's +rating. Such ideas can be dislodged only by demonstrating to the +operatives what maximum load the boilers can carry, showing how the +economy will vary with the load and the determining of the economical +load for the individual plant in question. + +2nd. Stokers. With stoker-fired boilers, it is essential that the +operators know the limitations of their stokers as determined by their +individual installation. A thorough understanding of the requirements of +efficient handling must be insisted upon. The operatives must realize +that smokeless stacks are not necessarily the indication of good +combustion for, as has been pointed out, absolute smokelessness is +oftentimes secured at an enormous loss in efficiency through excess air. + +Another feature in stoker-fired plants is in the cleaning of fires. It +must be impressed upon the operatives that before the fires are cleaned +they should be put into condition for such cleaning. If this cleaning is +done at a definite time, regardless of whether the fires are in the best +condition for cleaning, there will be a great loss of good fuel with the +ashes. + +3rd. It is necessary that in each individual plant there be a basis on +which to judge the cleanliness of a boiler. From the operative's +standpoint, it is probably more necessary that there be a thorough +understanding of the relation between scale and tube difficulties than +between scale and efficiency. It is, of course, impossible to keep +boilers absolutely free from scale at all times, but experience in each +individual plant determines the limit to which scale can be allowed to +form before tube difficulties will begin or a perceptible falling off in +efficiency will take place. With such a limit of scale formation fixed, +the operatives should be impressed with the danger of allowing it to be +exceeded. + +4th. The operatives should be instructed as to the losses resulting from +excess air due to leaks in the setting and as to losses in efficiency +and capacity due to the by-passing of gases through the setting, that +is, not following the path of the baffles as originally installed. In +replacing tubes and in cleaning the heating surfaces, care must be taken +not to dislodge baffle brick or tile. + +[Illustration: 2000 Horse-power Installation of Babcock & Wilcox +Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the +Sunnyside Plant of the Pennsylvania Tunnel and Terminal Railroad Co., +Long Island City, N. Y.] + +5th. That an increase in the temperature of the feed reduces the amount +of work demanded from the boiler has been shown. The necessity of +keeping the feed temperature as high as the quantity of exhaust steam +will allow should be thoroughly understood. As an example of this, there +was a case brought to our attention where a large amount of exhaust +steam was wasted simply because the feed pump showed a tendency to leak +if the temperature of feed water was increased above 140 degrees. The +amount wasted was sufficient to increase the temperature to 180 degrees +but was not utilized simply because of the slight expense necessary to +overhaul the feed pump. + +The highest return will be obtained when the speed of the feed pumps is +maintained reasonably constant for should the pumps run very slowly at +times, there may be a loss of the steam from other auxiliaries by +blowing off from the heaters. + +6th. With a view to checking steam losses through the useless blowing of +safety valves, the operative should be made to realize the great amount +of steam that it is possible to get through a pipe of a given size. +Oftentimes the fireman feels a sense of security from objections to a +drop in steam simply because of the blowing of safety valves, not +considering the losses due to such a cause and makes no effort to check +this flow either by manipulation of dampers or regulation of fires. + +The few of the numerous shortcomings outlined above, which may be found +in many plants, are almost entirely due to lack of knowledge on the part +of the operating crew as to the conditions existing in their own plants +and the better performances being secured in others. Such shortcomings +can be overcome only by the education of the operatives, the showing of +the defects of present methods, and instruction in better methods. Where +such instruction is necessary, the value of records is obvious. There is +fortunately a tendency toward the employment of a better class of labor +in the boiler room, a tendency which is becoming more and more marked as +the realization of the possible saving in this end of the plant +increases. + +The second aspect of boiler room management, dealing with specific +recommendations as to the care and operation of the boilers, is dictated +largely by the nature of the apparatus. Some of the features to be +watched in considering this aspect follow. + +Before placing a new boiler in service, a careful and thorough +examination should be made of the pressure parts and the setting. The +boiler as erected should correspond in its baffle openings, where +baffles are adjustable, with the prints furnished for its erection, and +such baffles should be tight. The setting should be so constructed that +the boiler is free to expand without interfering with the brickwork. +This ability to expand applies also to blow-off and other piping. After +erection all mortar and chips of brick should be cleaned from the +pressure parts. The tie rods should be set up snug and then slacked +slightly until the setting has become thoroughly warm after the first +firing. The boiler should be examined internally before starting to +insure the absence of dirt, any foreign material such as waste, and +tools. Oil and paint are sometimes found in the interior of a new boiler +and where such is the case, a quantity of soda ash should be placed +within it, the boiler filled with water to its normal level and a slow +fire started. After twelve hours of slow simmering, the fire should be +allowed to die out, the boiler cooled slowly and then opened and washed +out thoroughly. Such a proceeding will remove all oil and grease from +the interior and prevent the possibility of foaming and tube +difficulties when the boiler is placed in service. + +The water column piping should be examined and known to be free and +clear. The water level, as indicated by the gauge glass, should be +checked by opening the gauge cocks. + +The method of drying out a brick setting before placing a boiler in +operation is described later in the discussion of boiler settings. + +A boiler should not be cut into the line with other boilers until the +pressure within it is approximately that in the steam main. The boiler +stop valve should be opened very slowly until it is fully opened. The +arrangement of piping should be such that there can be no possibility of +water collecting in a pocket between the boiler and the main, from which +it can be carried over into the steam line when a boiler is cut in. + +In regular operation the safety valve and steam gauge should be checked +daily. In small plants the steam pressure should be raised sufficiently +to cause the safety valves to blow, at which time the steam gauge should +indicate the pressure at which the valve is known to be set. If it does +not, one is in error and the gauge should be compared with one of known +accuracy and any error at once rectified. + +In large plants such a method of checking would result in losses too +great to be allowed. Here the gauges and valves are ordinarily checked +at the time a boiler is cut out, the valves being assured of not +sticking by daily instantaneous opening through manipulation by hand of +the valve lever. The daily blowing of the safety valve acts not only as +a check on the gauge but insures the valve against sticking. + +The water column should be blown down thoroughly at least once on every +shift and the height of water indicated by the glass checked by the +gauge cocks. The bottom blow-offs should be kept tight. These should be +opened at least once daily to blow from the mud drum any sediment that +may have collected and to reduce the concentration. The amount of +blowing down and the frequency is, of course, determined by the nature +of the feed water used. + +In case of low water, resulting either from carelessness or from some +unforeseen condition of operation, the essential object to be obtained +is the extinguishing of the fire in the quickest possible manner. Where +practicable, this is best accomplished by the playing of a heavy stream +of water from a hose on the fire. Another method, perhaps not so +efficient, but more generally recommended, is the covering of the fire +with wet ashes or fresh fuel. A boiler so treated should be cut out of +line after such an occurrence and a thorough inspection made to +ascertain what damage, if any, has been done before it is again placed +in service. + +The efficiency and capacity depend to an extent very much greater than +is ordinarily realized upon the cleanliness of the heating surfaces, +both externally and internally, and too much stress cannot be put upon +the necessity for systematic cleaning as a regular feature in the plant +operation. + +The outer surfaces of the tubes should be blown free from soot at +regular intervals, the frequency of such cleaning periods being +dependent upon the class of fuel used. The most efficient way of blowing +soot from the tubes is by means of a steam lance with which all parts of +the surfaces are reached and swept clean. There are numerous soot +blowing devices on the market which are designed to be permanently fixed +within the boiler setting. Where such devices are installed, there are +certain features that must be watched to avoid trouble. If there is any +leakage of water of condensation within the setting coming into contact +with the boiler tubes, it will tend toward corrosion, or if in contact +with the heated brickwork will cause rapid disintegration of the +setting. If the steam jets are so placed that they impinge directly +against the tubes, erosion may take place. Where such permanent soot +blowers are installed, too much care cannot be taken to guard against +these possibilities. + +Internally, the tubes must be kept free from scale, the ingredients of +which a study of the chapter on the impurities of water indicates are +present in varying quantities in all feed waters. Not only has the +presence of scale a direct bearing on the efficiency and capacity to be +obtained from a boiler but its absence is an assurance against the +burning out of tubes. + +In the absence of a blow-pipe action of the flames, it is impossible to +burn a metal surface where water is in intimate contact with that +surface. + +In stoker-fired plants where a blast is used, and the furnace is not +properly designed, there is a danger of a blow-pipe action if the fires +are allowed to get too thin. The rapid formation of steam at such points +of localized heat may lead to the burning of the metal of the tubes. + +Any formation of scale on the interior surface of a boiler keeps the +water from such a surface and increases its tendency to burn. Particles +of loose scale that may become detached will lodge at certain points in +the tubes and localize this tendency at such points. It is because of +the danger of detaching scale and causing loose flakes to be present +that the use of a boiler compound is not recommended for the removal of +scale that has already formed in a boiler. This question is covered in +the treatment of feed waters. If oil is allowed to enter a boiler, its +action is the same as that of scale in keeping the water away from the +metal surfaces. + +[Illustration: Fig. 41] + +It has been proven beyond a doubt that a very large percentage of tube +losses is due directly to the presence of scale which, in many +instances, has been so thin as to be considered of no moment, and the +importance of maintaining the boiler heating surfaces in a clean +condition cannot be emphasized too strongly. + +The internal cleaning can best be accomplished by means of an air or +water-driven turbine, the cutter heads of which may be changed to handle +various thicknesses of scale. Fig. 41 shows a turbine cleaner with +various cutting heads, which has been found to give satisfactory +service. + +Where a water-driven turbine is used, it should be connected to a pump +which will deliver at least 120 gallons per minute per cleaner at 150 +pounds pressure. This pressure should never be less than 90 pounds if +satisfactory results are desired. Where an air-driven turbine is used, +the pressure should be at least 100 pounds, though 150 pounds is +preferable, and sufficient water should be introduced into the tube to +keep the cutting head cool and assist in washing down the scale as it is +chipped off. + +Where scale has been allowed to accumulate to an excessive thickness, +the work of removal is difficult and tedious. Where such a heavy scale +is of sulphate formation, its removal may be assisted by filling the +boiler with water to which there has been added a quantity of soda ash, +a bucketful to each drum, starting a low fire and allowing the water to +boil for twenty-four hours with no pressure on the boiler. It should be +cooled slowly, drained, and the turbine cleaner used immediately, as the +scale will tend to harden rapidly under the action of the air. + +Where oil has been allowed to get into a boiler, it should be removed +before placing the boiler in service, as described previously where +reference is made to its removal by boiling out with soda ash. + +Where pitting or corrosion is noted, the parts affected should be +carefully cleaned and the interior of the drums should be painted with +white zinc if the boiler is to remain idle. The cause of such action +should be immediately ascertained and steps taken to apply the proper +remedy. + +When making an internal inspection of a boiler or when cleaning the +interior heating surfaces, great care must be taken to guard against the +possibility of steam entering the boiler in question from other boilers +on the same line either through the careless opening of the boiler stop +valve or some auxiliary valve or from an open blow-off. Bad accidents +through scalding have resulted from the neglect of this precaution. + +Boiler brickwork should be kept pointed up and all cracks filled. The +boiler baffles should be kept tight to prevent by-passing of any gases +through the heating surfaces. + +Boilers should be taken out of service at regular intervals for cleaning +and repairs. When this is done, the boiler should be cooled slowly, and +when possible, be allowed to stand for twenty-four hours after the fire +is drawn before opening. The cooling process should not be hurried by +allowing cold air to rush through the setting as this will invariably +cause trouble with the brickwork. When a boiler is off for cleaning, a +careful examination should be made of its condition, both external and +internal, and all leaks of steam, water and air through the setting +stopped. If water is allowed to come into contact with brickwork that is +heated, rapid disintegration will take place. If water is allowed to +come into contact with the metal of the boiler when out of service, +there is a likelihood of corrosion. + +If a boiler is to remain idle for some time, its deterioration may be +much more rapid than when in service. If the period for which it is to +be laid off is not to exceed three months, it may be filled with water +while out of service. The boiler should first be cleaned thoroughly, +internally and externally, all soot and ashes being removed from the +exterior of the pressure parts and any accumulation of scale removed +from the interior surfaces. It should then be filled with water, to +which five or six pails of soda ash have been added, a slow fire started +to drive the air from the boiler, the fire drawn and the boiler pumped +full. In this condition it may be kept for some time without bad +effects. + +If the boiler is to be out of service for more than three months, it +should be emptied, drained and thoroughly dried after being cleaned. A +tray of quick lime should be placed in each drum, the boiler closed, the +grates covered and a quantity of quick lime placed on top of the +covering. Special care should be taken to prevent air, steam or water +leaks into the boiler or onto the pressure parts to obviate danger of +corrosion. + +[Illustration: 3000 Horse-power Installation of Babcock & Wilcox Boilers +in the Main Power Plant, Chicago & Northwestern Ry. Depot, Chicago, +Ill.] + + + + +BRICKWORK BOILER SETTINGS + + +A consideration of the losses in boiler efficiency, due to the effects +of excess air, clearly indicates the necessity of maintaining the brick +setting of a boiler tight and free from air leaks. In view of the +temperatures to which certain portions of such a setting are subjected, +the material to be used in its construction must be of the best +procurable. + +Boiler settings to-day consist almost universally of brickwork--two +kinds being used, namely, red brick and fire brick. + +The red brick should only be used in such portions of the setting as are +well protected from the heat. In such location, their service is not so +severe as that of fire brick and ordinarily, if such red brick are +sound, hard, well burned and uniform, they will serve their purpose. + +The fire brick should be selected with the greatest care, as it is this +portion of the setting that has to endure the high temperatures now +developed in boiler practice. To a great extent, the life of a boiler +setting is dependent upon the quality of the fire brick used and the +care exercised in its laying. + +The best fire brick are manufactured from the fire clays of +Pennsylvania. South and west from this locality the quality of fire clay +becomes poorer as the distance increases, some of the southern fire +clays containing a considerable percentage of iron oxide. + +Until very recently, the important characteristic on which to base a +judgment of the suitability of fire brick for use in connection with +boiler settings has been considered the melting point, or the +temperature at which the brick will liquify and run. Experience has +shown, however, that this point is only important within certain limits +and that the real basis on which to judge material of this description +is, from the boiler man's standpoint, the quality of plasticity under a +given load. This tendency of a brick to become plastic occurs at a +temperature much below the melting point and to a degree that may cause +the brick to become deformed under the stress to which it is subjected. +The allowable plastic or softening temperature will naturally be +relative and dependent upon the stress to be endured. + +With the plasticity the determining factor, the perfect fire brick is +one whose critical point of plasticity lies well above the working +temperature of the fire. It is probable that there are but few brick on +the market which would not show, if tested, this critical temperature at +the stress met with in arch construction at a point less than 2400 +degrees. The fact that an arch will stand for a long period under +furnace temperatures considerably above this point is due entirely to +the fact that its temperature as a whole is far below the furnace +temperature and only about 10 per cent of its cross section nearest the +fire approaches the furnace temperature. This is borne out by the fact +that arches which are heated on both sides to the full temperature of an +ordinary furnace will first bow down in the middle and eventually fall. + +A method of testing brick for this characteristic is given in the +Technologic Paper No. 7 of the Bureau of Standards dealing with "The +testing of clay refractories with special reference to their load +carrying capacity at furnace temperatures." Referring to the test for +this specific characteristic, this publication recommends the following: +"When subjected to the load test in a manner substantially as described +in this bulletin, at 1350 degrees centigrade (2462 degrees Fahrenheit), +and under a load of 50 pounds per square inch, a standard fire brick +tested on end should show no serious deformation and should not be +compressed more than one inch, referred to the standard length of nine +inches." + +In the Bureau of Standards test for softening temperature, or critical +temperature of plasticity under the specified load, the brick are tested +on end. In testing fire brick for boiler purposes such a method might be +criticised, because such a test is a compression test and subject to +errors from unequal bearing surfaces causing shear. Furthermore, a +series of samples, presumably duplicates, will not fail in the same way, +due to the mechanical variation in the manufacture of the brick. Arches +that fail through plasticity show that the tensile strength of the brick +is important, this being evidenced by the fact that the bottom of a +wedge brick in an arch that has failed is usually found to be wider than +the top and the adjacent bricks are firmly cemented together. + +A better method of testing is that of testing the brick as a beam +subjected to its own weight and not on end. This method has been used +for years in Germany and is recommended by the highest authorities in +ceramics. It takes into account the failure by tension in the brick as +well as by compression and thus covers the tension element which is +important in arch construction. + +The plastic point under a unit stress of 100 pounds per square inch, +which may be taken as the average maximum arch stress, should be above +2800 degrees to give perfect results and should be above 2400 degrees to +enable the brick to be used with any degree of satisfaction. + +The other characteristics by which the quality of a fire brick is to be +judged are: + +Fusion point. In view of the fact that the critical temperature of +plasticity is below the fusion point, this is only important as an +indication from high fusion point of a high temperature of plasticity. + +Hardness. This is a relative quality based on an arbitrary scale of 10 +and is an indication of probable cracking and spalling. + +Expansion. The lineal expansion per brick in inches. This characteristic +in conjunction with hardness is a measure of the physical movement of +the brick as affecting a mass of brickwork, such movement resulting in +cracked walls, etc. The expansion will vary between wide limits in +different brick and provided such expansion is not in excess of, say, +.05 inch in a 9-inch brick, when measured at 2600 degrees, it is not +particularly important in a properly designed furnace, though in general +the smaller the expansion the better. + +Compression. The strength necessary to cause crushing of the brick at +the center of the 4-1/2 inch face by a steel block one inch square. The +compression should ordinarily be low, a suggested standard being that a +brick show signs of crushing at 7500 pounds. + +Size of Nodules. The average size of flint grains when the brick is +carefully crushed. The scale of these sizes may be considered: Small, +size of anthracite rice; large, size of anthracite pea. + +Ratio of Nodules. The percentage of a given volume occupied by the flint +grains. This scale may be considered: High, 90 to 100 per cent; medium, +50 to 90 per cent; low, 10 to 50 per cent. + +The statement of characteristics suggested as desirable, are for arch +purposes where the hardest service is met. For side wall purposes the +compression and hardness limit may be raised considerably and the +plastic point lowered. + +Aside from the physical properties by which a fire brick is judged, it +is sometimes customary to require a chemical analysis of the brick. Such +an analysis is only necessary as determining the amount of total basic +fluxes (K_{2}O, Na_{2}O, CaO, MgO and FeO). These fluxes are ordinarily +combined into one expression, indicated by the symbol RO. This total +becomes important only above 0.2 molecular equivalent as expressed in +ceramic empirical formulae, and this limit should not be exceeded.[75] + +From the nature of fire brick, their value can only be considered from a +relative standpoint. Generally speaking, what are known as first-grade +fire brick may be divided into three classes, suitable for various +conditions of operation, as follows: + +Class A. For stoker-fired furnaces where high overloads are to be +expected or where other extreme conditions of service are apt to occur. + +Class B. For ordinary stoker settings where there will be no excessive +overloads required from the boiler or any hand-fired furnaces where the +rates of driving will be high for such practice. + +Class C. For ordinary hand-fired settings where the presumption is that +the boilers will not be overloaded except at rare intervals and for +short periods only. + +Table 61 gives the characteristics of these three classes according to +the features determining the quality. This table indicates that the +hardness of the brick in general increases with the poorer qualities. +Provided the hardness is sufficient to enable the brick to withstand its +load, additional hardness is a detriment rather than an advantage. + + TABLE 61 + + APPROXIMATE CLASSIFICATION OF FIRE BRICK + + ________________________________________________________________________ +| | | | | +| Characteristics | Class A | Class B | Class C | +|_____________________|________________|________________|________________| +| | | | | +| Fuse Point, Degrees | Safe at Degrees| Safe at Degrees| Safe at Degrees| +| Fahrenheit | 3200-3300 | 2900-3200 | 2900-3000 | +| | | | | +| Compression Pounds | 6500-7500 | 7500-11,000 | 8500-15,000 | +| | | | | +| Hardness Relative | 1-2 | 2-4 | 4-6 | +| | | | | +| Size of Nodules | Medium | Medium to |Medium to Large | +| | | Medium Large | | +| | | | | +| Ratio of Nodules | High | Medium to High | Medium Low | +| | | | to Medium | +|_____________________|________________|________________|________________| + +An approximate determination of the quality of a fire brick may be made +from the appearance of a fracture. Where such a fracture is open, clean, +white and flinty, the brick in all probability is of a good quality. If +this fracture has the fine uniform texture of bread, the brick is +probably poor. + +In considering the heavy duty of brick in boiler furnaces, experience +shows that arches are the only part that ordinarily give trouble. These +fail from the following causes: + +Bad workmanship in laying up of brick. This feature is treated below. + +The tendency of a brick to become plastic at a temperature below the +fusing point. The limits of allowable plastic temperature have already +been pointed out. + +Spalling. This action occurs on the inner ends of combustion arches +where they are swept by gases at a high velocity at the full furnace +temperature. The most troublesome spalling arises through cold air +striking the heated brickwork. Failure from this cause is becoming rare, +due to the large increase in number of stoker installations in which +rapid temperature changes are to a great degree eliminated. Furthermore, +there are a number of brick on the market practically free from such +defects and where a new brick is considered, it can be tried out and if +the defect exists, can be readily detected and the brick discarded. + +Failures of arches from the expansive power of brick are also rare, due +to the fact that there are a number of brick in which the expansion is +well within the allowable limits and the ease with which such defects +may be determined before a brick is used. + +Failures through chemical disintegration. Failure through this cause is +found only occasionally in brick containing a high percentage of iron +oxide. + +With the grade of brick selected best suited to the service of the +boiler to be set, the other factor affecting the life of the setting is +the laying. It is probable that more setting difficulties arise from the +improper workmanship in the laying up of brick than from poor material, +and to insure a setting which will remain tight it is necessary that the +masonry work be done most carefully. This is particularly true where the +boiler is of such a type as to require combustion arches in the furnace. + +Red brick should be laid in a thoroughly mixed mortar composed of one +volume of Portland cement, 3 volumes of unslacked lime and 16 volumes of +clear sharp sand. Not less than 2-1/2 bushels of lime should be used in the +laying up of 1000 brick. Each brick should be thoroughly embedded and +all joints filled. Where red brick and fire brick are both used in the +same wall, they should be carried up at the same time and thoroughly +bonded to each other. + +All fire brick should be dry when used and protected from moisture until +used. Each brick should be dipped in a thin fire clay wash, "rubbed and +shoved" into place, and tapped with a wooden mallet until it touches the +brick next below it. It must be recognized that fire clay is not a +cement and that it has little or no holding power. Its action is that of +a filler rather than a binder and no fire-clay wash should be used which +has a consistency sufficient to permit the use of a trowel. + +All fire-brick linings should be laid up four courses of headers and one +stretcher. Furnace center walls should be entirely of fire brick. If the +center of such walls are built of red brick, they will melt down and +cause the failure of the wall as a whole. + +Fire-brick arches should be constructed of selected brick which are +smooth, straight and uniform. The frames on which such arches are built, +called arch centers, should be constructed of batten strips not over 2 +inches wide. The brick should be laid on these centers in courses, not +in rings, each joint being broken with a bond equal to the length of +half a brick. Each course should be first tried in place dry, and +checked with a straight edge to insure a uniform thickness of joint +between courses. Each brick should be dipped on one side and two edges +only and tapped into place with a mallet. Wedge brick courses should be +used only where necessary to keep the bottom faces of the straight brick +course in even contact with the centers. When such contact cannot be +exactly secured by the use of wedge brick, the straight brick should +lean away from the center of the arch rather than toward it. When the +arch is approximately two-thirds completed, a trial ring should be laid +to determine whether the key course will fit. When some cutting is +necessary to secure such a fit, it should be done on the two adjacent +courses on the side of the brick away from the key. It is necessary that +the keying course be a true fit from top to bottom, and after it has +been dipped and driven it should not extend below the surface of the +arch, but preferably should have its lower ledge one-quarter inch above +this surface. After fitting, the keys should be dipped, replaced +loosely, and the whole course driven uniformly into place by means of a +heavy hammer and a piece of wood extending the full length of the keying +course. Such a driving in of this course should raise the arch as a +whole from the center. The center should be so constructed that it may +be dropped free of the arch when the key course is in place and removed +from the furnace without being burned out. + +[Illustration: A Typical Steel Casing for a Babcock & Wilcox Boiler +Built by The Babcock & Wilcox Co.] + +Care of Brickwork--Before a boiler is placed in service, it is essential +that the brickwork setting be thoroughly and properly dried, or +otherwise the setting will invariably crack. The best method of starting +such a process is to block open the boiler damper and the ashpit doors +as soon as the brickwork is completed and in this way maintain a free +circulation of air through the setting. If possible, such preliminary +drying should be continued for several days before any fire is placed in +the furnace. When ready for the drying out fire, wood should be used at +the start in a light fire which may be gradually built up as the walls +become warm. After the walls have become thoroughly heated, coal may be +fired and the boiler placed in service. + +As already stated, the life of a boiler setting is dependent to a large +extent upon the material entering into its construction and the care +with which such material is laid. A third and equally important factor +in the determining of such life is the care given to the maintaining of +the setting in good condition after the boiler is placed in operation. +This feature is discussed more fully in the chapter dealing with general +boiler room management. + +Steel Casings--In the chapter dealing with the losses operating against +high efficiencies as indicated by the heat balance, it has been shown +that a considerable portion of such losses is due to radiation and to +air infiltration into the boiler setting. These losses have been +variously estimated from 2 to 10 per cent, depending upon the condition +of the setting and the amount of radiation surface, the latter in turn +being dependent upon the size of the boiler used. In the modern efforts +after the highest obtainable plant efficiencies much has been done to +reduce such losses by the use of an insulated steel casing covering the +brickwork. In an average size boiler unit the use of such casing, when +properly installed, will reduce radiation losses from one to two per +cent., over what can be accomplished with the best brick setting without +such casing and, in addition, prevent the loss due to the infiltration +of air, which may amount to an additional five per cent., as compared +with brick settings that are not maintained in good order. Steel plate, +or steel plate backed by asbestos mill-board, while acting as a +preventative against the infiltration of air through the boiler setting, +is not as effective from the standpoint of decreasing radiation losses +as a casing properly insulated from the brick portion of the setting by +magnesia block and asbestos mill-board. A casing which has been found to +give excellent results in eliminating air leakage and in the reduction +of radiation losses is clearly illustrated on page 306. + +Many attempts have been made to use some material other than brick for +boiler settings but up to the present nothing has been found that may be +considered successful or which will give as satisfactory service under +severe conditions as properly laid brickwork. + + + + +BOILER ROOM PIPING + + +In the design of a steam plant, the piping system should receive the +most careful consideration. Aside from the constructive details, good +practice in which is fairly well established, the important factors are +the size of the piping to be employed and the methods utilized in +avoiding difficulties from the presence in the system of water of +condensation and the means employed toward reducing radiation losses. + +Engineering opinion varies considerably on the question of material of +pipes and fittings for different classes of work, and the following is +offered simply as a suggestion of what constitutes good representative +practice. + +All pipe should be of wrought iron or soft steel. Pipe at present is +made in "standard", "extra strong"[76] and "double extra strong" +weights. Until recently, a fourth weight approximately 10 per cent +lighter than standard and known as "Merchants" was built but the use of +this pipe has largely gone out of practice. Pipe sizes, unless otherwise +stated, are given in terms of nominal internal diameter. Table 62 gives +the dimensions and some general data on standard and extra strong +wrought-iron pipe. + + TABLE 62 + + DIMENSIONS OF STANDARD AND EXTRA STRONG[76] + WROUGHT-IRON AND STEEL PIPE + + _______________________________________________________________ +| | | | +| | Diameter | Circumference | +| |__________________________|__________________________| +| | | | | | +| |External| Internal |External| Internal | +| |Standard|_________________|Standard|_________________| +| | and | | | and | | | +| Nominal | Extra |Standard| Extra | Extra |Standard| Extra | +| Size | Strong | | Strong | Strong | | Strong | +|_________|________|________|________|________|________|________| +| | | | | | | | +| 1/8 | .405 | .269 | .215 | 1.272 | .848 | .675 | +| 1/4 | .540 | .364 | .302 | 1.696 | 1.144 | .949 | +| 3/8 | .675 | .493 | .423 | 2.121 | 1.552 | 1.329 | +| 1/2 | .840 | .622 | .546 | 2.639 | 1.957 | 1.715 | +| 3/4 | 1.050 | .824 | .742 | 3.299 | 2.589 | 2.331 | +| 1 | 1.315 | 1.049 | .957 | 4.131 | 3.292 | 3.007 | +| 1-1/4 | 1.660 | 1.380 | 1.278 | 5.215 | 4.335 | 4.015 | +| 1-1/2 | 1.900 | 1.610 | 1.500 | 5.969 | 5.061 | 4.712 | +| 2 | 2.375 | 2.067 | 1.939 | 7.461 | 6.494 | 6.092 | +| 2-1/2 | 2.875 | 2.469 | 2.323 | 9.032 | 7.753 | 7.298 | +| 3 | 3.500 | 3.068 | 2.900 | 10.996 | 9.636 | 9.111 | +| 3-1/2 | 4.000 | 3.548 | 3.364 | 12.566 | 11.146 | 10.568 | +| 4 | 4.500 | 4.026 | 3.826 | 14.137 | 12.648 | 12.020 | +| 4-1/2 | 5.000 | 4.506 | 4.290 | 15.708 | 14.162 | 13.477 | +| 5 | 5.563 | 5.047 | 4.813 | 17.477 | 15.849 | 15.121 | +| 6 | 6.625 | 6.065 | 5.761 | 20.813 | 19.054 | 18.099 | +| 7 | 7.625 | 7.023 | 6.625 | 23.955 | 22.063 | 20.813 | +| 8 | 8.625 | 7.981 | 7.625 | 27.096 | 25.076 | 23.955 | +| 9 | 9.625 | 8.941 | 8.625 | 30.238 | 28.089 | 27.096 | +| 10 | 10.750 | 10.020 | 9.750 | 33.772 | 31.477 | 30.631 | +| 11 | 11.750 | 11.000 | 10.750 | 36.914 | 34.558 | 33.772 | +| 12 | 12.750 | 12.000 | 11.750 | 40.055 | 37.700 | 36.914 | +|_________|________|________|________|________|________|________| + + + __________________________________________________________ +| | | | | +| | | Length | | +| | Internal | of | Nominal Weight | +| | Transverse |Pipe in | Pounds per | +| | Area |Feet per| Foot | +| |_____________________| Square |_________________| +| | | |Foot of | | | +| Nominal | Standard | Extra |External|Standard| Extra | +| Size | | Strong |Surface | | Strong | +|_________|__________|__________|________|________|________| +| | | | | | | +| 1/8 | .0573 | .0363 | 9.440 | .244 | .314 | +| 1/4 | .1041 | .0716 | 7.075 | .424 | .535 | +| 3/8 | .1917 | .1405 | 5.657 | .567 | .738 | +| 1/2 | .3048 | .2341 | 4.547 | .850 | 1.087 | +| 3/4 | .5333 | .4324 | 3.637 | 1.130 | 1.473 | +| 1 | .8626 | .7193 | 2.904 | 1.678 | 2.171 | +| 1-1/4 | 1.496 | 1.287 | 2.301 | 2.272 | 2.996 | +| 1-1/2 | 2.038 | 1.767 | 2.010 | 2.717 | 3.631 | +| 2 | 3.356 | 2.953 | 1.608 | 3.652 | 5.022 | +| 2-1/2 | 4.784 | 4.238 | 1.328 | 5.793 | 7.661 | +| 3 | 7.388 | 6.605 | 1.091 | 7.575 | 10.252 | +| 3-1/2 | 9.887 | 8.888 | .955 | 9.109 | 12.505 | +| 4 | 12.730 | 11.497 | .849 | 10.790 | 14.983 | +| 4-1/2 | 15.961 | 14.454 | .764 | 12.538 | 17.611 | +| 5 | 19.990 | 18.194 | .687 | 14.617 | 20.778 | +| 6 | 28.888 | 26.067 | .577 | 18.974 | 28.573 | +| 7 | 38.738 | 34.472 | .501 | 23.544 | 38.048 | +| 8 | 50.040 | 45.664 | .443 | 28.544 | 43.388 | +| 9 | 62.776 | 58.426 | .397 | 33.907 | 48.728 | +| 10 | 78.839 | 74.662 | .355 | 40.483 | 54.735 | +| 11 | 95.033 | 90.763 | .325 | 45.557 | 60.075 | +| 12 | 113.098 | 108.43 | .299 | 49.562 | 65.415 | +|_________|__________|__________|________|________|________| + +Dimensions are nominal and except where noted are in inches. + +In connection with pipe sizes, Table 63, giving certain tube data may be +found to be of service. + + TABLE 63 + + TUBE DATA, STANDARD OPEN HEARTH OR LAP WELDED STEEL TUBES + ++-----+--+----+-----+------+------+------+------+-------+-------+-------+ +|S E D|B | T | I D |Circumference| Transverse |Square |Length |Nominal| +|i x i|. | h | n i | | Area | Feet |in Feet|Weight | +|z t a|W | i | t a | |Square Inches| of | per |Pounds | +|e e m|. | c | e m +------+------+------+------+ Exter |Square | per | +| r e| | k | r e |Exter-|Inter-|Exter-|Inter-| -nal |Foot of| Foot | +| n t|G | n | n t | nal | nal | nal | nal |Surface| Exter | | +| a e|a | e | a e | | | | | per | -nal | | +| l r|u | s | l r | | | | |Foot of|Surface| | +| |g | s | | | | | |Length | | | +| |e | | | | | | | | | | ++-----+--+----+-----+------+------+------+------+-------+-------+-------+ +|1-1/2|10|.134|1.232| 4.712| 3.870|1.7671|1.1921| .392 | 2.546 | 1.955 | +|1-1/2| 9|.148|1.204| 4.712| 3.782|1.7671|1.1385| .392 | 2.546 | 2.137 | +|1-1/2| 8|.165|1.170| 4.712| 3.676|1.7671|1.0751| .392 | 2.546 | 2.353 | +| 2 |10|.134|1.732| 6.283| 5.441|3.1416|2.3560| .523 | 1.909 | 2.670 | +| 2 | 9|.148|1.704| 6.283| 5.353|3.1416|2.2778| .523 | 1.909 | 2.927 | +| 2 | 8|.165|1.670| 6.283| 5.246|3.1416|2.1904| .523 | 1.909 | 3.234 | +|3-1/4|11|.120|3.010|10.210| 9.456|8.2958|7.1157| .850 | 1.175 | 4.011 | +|3-1/4|10|.134|2.982|10.210| 9.368|8.2958|6.9840| .850 | 1.175 | 4.459 | +|3-1/4| 9|.148|2.954|10.210| 9.280|8.2958|6.8535| .850 | 1.175 | 4.903 | +| 4 |10|.134|3.732|12.566|11.724|12.566|10.939| 1.047 | .954 | 5.532 | +| 4 | 9|.148|3.704|12.566|11.636|12.566|10.775| 1.047 | .954 | 6.000 | +| 4 | 8|.165|3.670|12.566|11.530|12.566|10.578| 1.047 | .954 | 6.758 | ++-----+--+----+-----+------+------+------+------+-------+-------+-------+ + +Dimensions are nominal and except where noted are in inches. + +Pipe Material and Thickness--For saturated steam pressures not exceeding +160 pounds, all pipe over 14 inches should be 3/8 inch thick O. D. pipe. +All other pipe should be standard full weight, except high pressure +feed[77] and blow-off lines, which should be extra strong. + +For pressures above 150 pounds up to 200 pounds with superheated steam, +all high pressure feed and blow-off lines, high pressure steam lines +having threaded flanges, and straight runs and bends of high pressure +steam lines 6 inches and under having Van Stone joints should be extra +strong. All piping 7 inches and over having Van Stone joints should be +full weight soft flanging pipe of special quality. Pipe 14 inches and +over should be 3/8 inch thick O. D. pipe. All pipes for these pressures +not specified above should be full weight pipe. + +Flanges--For saturated steam, 160 pounds working pressure, all flanges +for wrought-iron pipe should be cast-iron threaded. All high pressure +threaded flanges should have the diameter thickness and drilling in +accordance with the "manufacturer's standard" for "extra heavy" flanges. +All low pressure flanges should have diameter, thickness and drilling in +accordance with "manufacturer's standard" for "standard flanges." + +The flanges on high pressure lines should be counterbored to receive +pipe and prevent the threads from shouldering. The pipe should be +screwed through the flange at least 1/16 inch, placed in machine and +after facing off the end one smooth cut should be taken over the face of +the flange to make it square with the axis of the pipe. + +[Illustration: 2000 Horse-power Installation of Babcock & Wilcox Boilers +and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers at +the Kentucky Electric Co., Louisville, Ky.] + +For pressures above 160 pounds, where superheated steam is used, all +high pressure steam lines 4 inches and over should have solid rolled +steel flanges and special upset lapped joints. In the manufacture of +such joints, the ends of the pipe are heated and upset against the face +of a holding mandrel conforming to the shape of the flange, the lapped +portion of the pipe being flattened out against the face of the mandrel, +the upsetting action maintaining the desired thickness of the lap. When +cool, both sides of the lap are faced to form a uniform thickness and an +even bearing against flange and gasket. The joint, therefore, is a +strictly metal to metal joint, the flanges merely holding the lapped +ends of the pipe against the gasket. + +A special grade of soft flanging pipe is selected to prevent breaking. +The bending action is a severe test of the pipe and if it withstands the +bending process and the pressure tests, the reliability of the joint is +assured. Such a joint is called a Van Stone joint, though many +modifications and improvements have been made since the joint was +originally introduced. + +The diameter and thickness of such flanges should be special extra +heavy. Such flanges should be turned to diameter, their fronts faced and +the backs machined in lieu of spot facing. + +In lines other than given for pressures over 150 pounds, all flanges for +wrought-iron pipe should be threaded. All threaded flanges for high +pressure superheated lines 3-1/2 inches and under should be "semi-steel" +extra heavy. Flanges for other than steam lines should be manufacturer's +standard extra heavy. + +Welded flanges are frequently used in place of those described with +satisfactory results. + +Fittings--For saturated steam under pressures up to 160 pounds, all +fittings 3-1/2 inches and under should be screwed. Fittings 4 inches and +over should have flanged ends. Fittings for this pressure should be of +cast iron and should have heavy leads and full taper threads. Flanged +fittings in high pressure lines should be extra heavy, and in low +pressure lines standard weight. Where possible in high pressure flanges +and fittings, bolt surfaces should be spot faced to provide suitable +bearing for bolt heads and nuts. + +Fittings for superheated steam up to 70 degrees at pressures above 160 +pounds are sometimes of cast iron.[78] For superheat above 70 degrees +such fittings should be "steel castings" and in general these fittings +are recommended for any degree of superheat. Fittings for other than +high pressure work may be of cast iron, except where superheated steam +is carried, where they should be of "wrought steel" or "hard metal". +Fittings 3-1/2 inches and under should be screwed, 4 inches and over +flanged. + +Flanges for pressures up to 160 pounds in pipes and fittings for low +pressure lines, and any fittings for high pressure lines should have +plain faces, smooth tool finish, scored with V-shaped grooves for rubber +gaskets. High pressure line flanges should have raised faces, projecting +the full available diameter inside the bolt holes. These faces should be +similarly scored. + +All pipe 1/2 inch and under should have ground joint unions suitable for +the pressure required. Pipe 3/4 inch and over should have cast-iron +flanged unions. Unions are to be preferred to wrought-iron couplings +wherever possible to facilitate dismantling. + +Valves--For 150 pounds working pressure, saturated steam, all valves 2 +inches and under may have screwed ends; 2-1/2 inches and over should be +flanged. All high pressure steam valves 6 inches and over should have +suitable by-passes. All valves for use with superheated steam should be +of special construction. For pressures above 160 pounds, where the +superheat does not exceed 70 degrees, valve bodies, caps and yokes are +sometimes made of cast iron, though ordinarily semi-steel will give +better satisfaction. The spindles of such valves should be of bronze and +there should be special necks with condensing chambers to prevent the +superheated steam from blowing through the packing. For pressures over +160 pounds and degrees of superheat above 70, all valves 3 inches and +over should have valve bodies, caps and yokes of steel castings. +Spindles should be of some non-corrosive metal, such as "monel metal". +Seat rings should be removable of the same non-corrosive metal as should +the spindle seats and plug faces. + +All salt water valves should have bronze spindles, sleeves and packing +seats. + +The suggestions as to flanges for different classes of service made on +page 311 hold as well for valve flanges, except that such flanges are +not scored. + +Automatic stop and check valves are coming into general use with boilers +and such use is compulsory under the boiler regulations of certain +communities. Where used, they should be preferably placed directly on +the boiler nozzle. Where two or more boilers are on one line, in +addition to the valve at the boiler, whether this be an automatic valve +or a gate valve, there should be an additional gate valve on each boiler +branch at the main steam header. + +Relief valves should be furnished at the discharge side of each feed +pump and on the discharge side of each feed heater of the closed type. + +Feed Lines--Feed lines should in all instances be made of extra strong +pipe due to the corrosive action of hot feed water. While it has been +suggested above that cast-iron threaded flanges should be used in such +lines, due to the sudden expansion of such pipe in certain instances +cast-iron threaded flanges crack before they become thoroughly heated +and expand, and for this reason cast-steel threaded flanges will give +more satisfactory results. In some instances, wrought-steel and Van +Stone joints have been used in feed lines and this undoubtedly is better +practice than the use of cast-steel threaded work, though the additional +cost is not warranted in all stations. + +Feed valves should always be of the globe pattern. A gate valve cannot +be closely regulated and often clatters owing to the pulsations of the +feed pump. + +Gaskets--For steam and water lines where the pressure does not exceed +160 pounds, wire insertion rubber gaskets 1/16 inch thick will be found +to give good service. For low pressure lines, canvas insertion black +rubber gaskets are ordinarily used. For oil lines special gaskets are +necessary. + +For pressure above 160 pounds carrying superheated steam, corrugated +steel gaskets extending the full available diameter inside of the bolt +holes give good satisfaction. For high pressure water lines wire +inserted rubber gaskets are used, and for low pressure flanged joints +canvas inserted rubber gaskets. + +Size of Steam Lines--The factors affecting the proper size of steam +lines are the radiation from such lines and the velocity of steam within +them. As the size of the steam line increases, there will be an increase +in the radiation.[79] As the size decreases, the steam velocity and the +pressure drop for a given quantity of steam naturally increases. + +There is a marked tendency in modern practice toward higher steam +velocities, particularly in the case of superheated steam. It was +formerly considered good practice to limit this velocity to 6000 feet +per minute but this figure is to-day considered low. + +In practice the limiting factor in the velocity advisable is the +allowable pressure drop. In the description of the action of the +throttling calorimeter, it has been demonstrated that there is no loss +accompanying a drop in pressure, the difference in energy between the +higher and lower pressures appearing as heat, which, in the case of +steam flowing through a pipe, may evaporate any condensation present or +may be radiated from the pipe. A decrease in pipe area decreases the +radiating surface of the pipe and thus the possible condensation. As the +heat liberated by the pressure drop is utilized in overcoming or +diminishing the tendency toward condensation and the heat loss through +radiation, the steam as it enters the prime mover will be drier or more +highly superheated where high steam velocities are used than where they +are lower, and if enough excess pressure is carried at the boilers to +maintain the desired pressure at the prime mover, the pressure drop +results in an actual saving rather than a loss. The whole is analogous +to standard practice in electrical distributing systems where generator +voltage is adjusted to suit the loss in the feeder lines. + +In modern practice, with superheated steam, velocities of 15,000 feet +per minute are not unusual and this figure is very frequently exceeded. + +Piping System Design--With the proper size of pipe to be used +determined, the most important factor is the provision for the removal +of water of condensation that will occur in any system. Such +condensation cannot be wholly overcome and if the water of condensation +is carried to the prime mover, difficulties will invariably result. +Water is practically incompressible and its effect when traveling at +high velocities differs little from that of a solid body of equal +weight, hence impact against elbows, valves or other obstructions, is +the equivalent of a heavy hammer blow that may result in the fracture of +the pipe. If there is not sufficient water in the system to produce this +result, it will certainly cause knocking and vibration in the pipe, +resulting eventually in leaky joints. Where the water reaches the prime +mover, its effect will vary from disagreeable knocking to disruption. +Too frequently when there are disastrous results from such a cause the +boilers are blamed for delivering wet steam when, as a matter of fact, +the evil is purely a result of poor piping design, the most common cause +of such an action being the pocketing of the water in certain parts of +the piping from whence it is carried along in slugs by the steam. The +action is particularly severe if steam is admitted to a cold pipe +containing water, as the water may then form a partial vacuum by +condensing the steam and be projected at a very high velocity through +the pipes producing a characteristic sharp metallic knock which often +causes bursting of the pipe or fittings. The amount of water present +through condensation may be appreciated when it is considered that +uncovered 6-inch pipe 150 feet long carrying 3600 pounds of high +pressure steam per hour will condense approximately 6 per cent of the +total steam carried through radiation. It follows that efficient means +of removing condensation water are absolutely imperative and the +following suggestions as to such means may be of service: + +The pitch of all pipe should be in the direction of the flow of steam. +Wherever a rise is necessary, a drain should be installed. All main +headers and important branches should end in a drop leg and each such +drop leg and any low points in the system should be connected to the +drainage pump. A similar connection should be made to every fitting +where there is danger of a water pocket. + +Branch lines should never be taken from the bottom of a main header but +where possible should be taken from the top. Each engine supply pipe +should have its own separator placed as near the throttle as possible. +Such separators should be drained to the drainage system. + +Check valves are frequently placed in drain pipes to prevent steam from +entering any portion of the system that may be shut off. + +Valves should be so located that they cannot form water pockets when +either open or closed. Globe valves will form a water pocket in the +piping to which they are connected unless set with the stem horizontal, +while gate valves may be set with the spindle vertical or at an angle. +Where valves are placed directly on the boiler nozzle, a drain should be +provided above them. + +High pressure drains should be trapped to both feed heaters and waste +headers. Traps and meters should be provided with by-passes. Cylinder +drains, heater blow-offs and drains, boiler blow-offs and similar lines +should be led to waste. The ends of cylinder drains should not extend +below the surface of water, for on starting up or on closing the +throttle valve with the drains open, water may be drawn back into the +cylinders. + + TABLE 64 + + RADIATION FROM COVERED AND UNCOVERED STEAM PIPES + + CALCULATED FOR 160 POUNDS PRESSURE AND 60 DEGREES TEMPERATURE + ++---------------------------------------------------------------------+ +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| | | | | | | | || +|| Pipe | |1/2 |3/4 | 1 |1-1/4|1-1/2| || +||Inches| Thickness of Covering |inch|inch|inch|inch |inch |Bare || +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |149 |118 | 99 | 86 | 79 | 597 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |240 |190 |161 | 138 | 127 | 959 || +|| 2 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.770|.613|.519|.445 |.410 |3.198|| +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |247 |193 |160 | 139 | 123 |1085 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |210 |164 |136 | 118 | 104 | 921 || +|| 4 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.677|.592|.439|.381 |.335 |2.970|| +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |352 |269 |221 | 190 | 167 |1555 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |203 |155 |127 | 110 | 96 | 897 || +|| 6 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.655|.500|.410|.355 |.310 |2.89 || +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |443 |337 |276 | 235 | 207 |1994 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |196 |149 |122 | 104 | 92 | 883 || +|| 8 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.632|.481|.394|.335 |.297 |2.85 || +|+------+---------------------------+----+----+----+-----+-----+-----+| +|| |B. t. u. per lineal foot | | | | | | || +|| | per hour |549 |416 |337 | 287 | 250 |2468 || +|| |B. t. u. per square foot | | | | | | || +|| | per hour |195 |148 |120 | 102 | 89 | 877 || +|| 10 |B. t. u. per square foot | | | | | | || +|| | per hour per one degree | | | | | | || +|| | difference in temperature|.629|.477|.387|.329 |.287 |2.83 || +|+------+---------------------------+----+----+----+-----+-----+-----+| ++---------------------------------------------------------------------+ + +Covering--Magnesia, canvas covered. + +For calculating radiation for pressure and temperature other than 160 +pounds, and 60 degrees, use B. t. u. figures for one degree difference. + +Radiation from Pipes--The evils of the presence of condensed steam in +piping systems have been thoroughly discussed above and in some of the +previous articles. Condensation resulting from radiation, while it +cannot be wholly obviated, can, by proper installation, be greatly +reduced. + +Bare pipe will radiate approximately 3 B. t. u. per hour per square foot +of exposed surface per one degree of difference in temperature between +the steam contained and the external air. This figure may be reduced to +from 0.3 to 0.4 B. t. u. for the same conditions by a 1-1/2 inch insulating +covering. Table 64 gives the radiation losses for bare and covered pipes +with different thicknesses of magnesia covering. + +Many experiments have been made as to the relative efficiencies of +different kinds of covering. Table 65 gives some approximately relative +figures based on one inch covering from experiments by Paulding, +Jacobus, Brill and others. + + TABLE 65 + + APPROXIMATE + EFFICIENCIES OF VARIOUS + COVERINGS REFERRED TO + BARE PIPES ++--------------------------------+ +|+-------------------+----------+| +|| Covering |Efficiency|| +|+-------------------+----------+| +||Asbestocel | 76.8 || +||Gast's Air Cell | 74.4 || +||Asbesto Sponge Felt| 85.0 || +||Magnesia | 83.5 || +||Asbestos Navy Brand| 82.0 || +||Asbesto Sponge Hair| 86.0 || +||Asbestos Fire Felt | 73.5 || +|+-------------------+----------+| ++--------------------------------+ + +Based on one-inch covering. + +The following suggestions may be of service: + +Exposed radiating surfaces of all pipes, all high pressure steam +flanges, valve bodies and fittings, heaters and separators, should be +covered with non-conducting material wherever such covering will improve +plant economy. All main steam lines, engine and boiler branches, should +be covered with 2 inches of 85 per cent carbonate of magnesia or the +equivalent. Other lines may be covered with one inch of the same +material. All covering should be sectional in form and large surfaces +should be covered with blocks, except where such material would be +difficult to install, in which case plastic material should be used. In +the case of flanges the covering should be tapered back from the flange +in order that the bolts may be removed. + +All surfaces should be painted before the covering is applied. Canvas is +ordinarily placed over the covering, held in place by wrought-iron or +brass bands. + +Expansion and Support of Pipe--It is highly important that the piping be +so run that there will be no undue strains through the action of +expansion. Certain points are usually securely anchored and the +expansion of the piping at other points taken care of by providing +supports along which the piping will slide or by means of flexible +hangers. Where pipe is supported or anchored, it should be from the +building structure and not from boilers or prime movers. Where supports +are furnished, they should in general be of any of the numerous sliding +supports that are available. Expansion is taken care of by such a method +of support and by the providing of large radius bends where necessary. + +It was formerly believed that piping would actually expand under steam +temperatures about one-half the theoretical amount due to the fact that +the exterior of the pipe would not reach the full temperature of the +steam contained. It would appear, however from recent experiments that +such actual expansion will in the case of well-covered pipe be very +nearly the theoretical amount. In one case noted, a steam header 293 +feet long when heated under a working pressure of 190 pounds, the steam +superheated approximately 125 degrees, expanded 8-3/4 inches; the +theoretical amount of expansion under the conditions would be +approximately 9-35/64 inches. + +[Illustration: Bankers Trust Building, New York City, Operation 900 +Horse Power of Babcock & Wilcox Boilers] + + + + +FLOW OF STEAM THROUGH PIPES AND ORIFICES + + +Various formulae for the flow of steam through pipes have been advanced, +all having their basis upon Bernoulli's theorem of the flow of water +through circular pipes with the proper modifications made for the +variation in constants between steam and water. The loss of energy due +to friction in a pipe is given by Unwin (based upon Weisbach) as + + f 2 v*v W L + E_{f} = ----------- (37) + gd + +where E is the energy loss in foot pounds due to the friction of W units +of weight of steam passing with a velocity of v feet per second through +a pipe d feet in diameter and L feet long; g represents the acceleration +due to gravity (32.2) and f the coefficient of friction. + +Numerous values have been given for this coefficient of friction, f, +which, from experiment, apparently varies with both the diameter of pipe +and the velocity of the passing steam. There is no authentic data on the +rate of this variation with velocity and, as in all experiments, the +effect of change of velocity has seemed less than the unavoidable errors +of observation, the coefficient is assumed to vary only with the size of +the pipe. + +Unwin established a relation for this coefficient for steam at a +velocity of 100 feet per second, + + / 3 \ + f = K| 1 + --- | (38) + \ 10d / + +where K is a constant experimentally determined, and d the internal +diameter of the pipe in feet. + +If h represents the loss of head in feet, then + + + f 2 v*v W L + E_{f} = Wh = ----------- (39) + gd + + f 2 v*v L + and h = --------- (40) + gd + +If D represents the density of the steam or weight per cubic foot, and p +the loss of pressure due to friction in pounds per square inch, then + + hD + p = --- (41) + 144 + +and from equations (38), (40) and (41), + + D v*v L / 3 \ + p = --------- x K | 1 + --- | (42) + 72 g d \ 10d / + +To convert the velocity term and to reduce to units ordinarily used, let +d_{1} the diameter of pipe in inches = 12d, and w = the flow in pounds +per minute; then + + [pi] / d_{1}\ + w = 60v x --- | ---- |^{2} D + 4 \ 12 / + + 9.6 w + and v = -------------- + [pi] d_{1}^2 D + + +Substituting this value and that of d in formula (42) + + / 3.6 \ w^{2} L + p = 0.04839 K | 1 + ----- | ----------- (43) + \ d_{1} / D d_{1}^{5} + + Some of the experimental determinations for the value of K are: + K = .005 for water (Unwin). + K = .005 for air (Arson). + K = .0028 for air (St. Gothard tunnel experiments). + K = .0026 for steam (Carpenter at Oriskany). + K = .0027 for steam (G. H. Babcock). + +The value .0027 is apparently the most nearly correct, and substituting +in formula (43) gives, + + / 3.6 \ w^{2} L + p = 0.000131 | 1 + ---- | ----------- (44) + \ d_{1}/ D d_{1}^{5} + + + / pDd_{1}^{5} \ + w = 87 | -------------- |^{.5} (45) + | / 3.6 \ | + | | 1 + ---- | L | + \ \ d_{1}/ / + +Where w = the weight of steam passing in pounds per minute, + p = the difference in pressure between the two ends of the pipe in + pounds per square inch, + D = density of steam or weight per cubic foot,[80] + d_{1} = internal diameter of pipe in inches, + L = length of pipe in feet. + + TABLE 66 + + FLOW OF STEAM THROUGH PIPES ++---------------------------------------------------------------------------------------+ +|Initl|Diameter[81] of Pipe in Inches, Length of Pipe = 240 Diameters | +|Gauge|---------------------------------------------------------------------------------+ +|Press| .75| 1 | 1.5| 2 | 2.5 | 3 | 4 | 5 | 6 | 8 | 10 | 12 | 15 | 18 | +|Pound|---------------------------------------------------------------------------------+ +|/SqIn| Weight of Steam per Minute, in Pounds, With One Pound Loss of Pressure | ++-----+---------------------------------------------------------------------------------+ +| 1 |1.16|2.07| 5.7|10.27|15.45|25.38| 46.85| 77.3|115.9|211.4| 341.1| 502.4| 804|1177| +| 10 |1.44|2.57| 7.1|12.72|19.15|31.45| 58.05| 95.8|143.6|262.0| 422.7| 622.5| 996|1458| +| 20 |1.70|3.02| 8.3|14.94|22.49|36.94| 68.20|112.6|168.7|307.8| 496.5| 731.3|1170|1713| +| 30 |1.91|3.40| 9.4|16.84|25.35|41.63| 76.84|126.9|190.1|346.8| 559.5| 824.1|1318|1930| +| 40 |2.10|3.74|10.3|18.51|27.87|45.77| 84.49|139.5|209.0|381.3| 615.3| 906.0|1450|2122| +| 50 |2.27|4.04|11.2|20.01|30.13|49.48| 91.34|150.8|226.0|412.2| 665.0| 979.5|1567|2294| +| 60 |2.43|4.32|11.9|21.38|32.19|52.87| 97.60|161.1|241.5|440.5| 710.6|1046.7|1675|2451| +| 70 |2.57|4.58|12.6|22.65|34.10|56.00|103.37|170.7|255.8|466.5| 752.7|1108.5|1774|2596| +| 80 |2.71|4.82|13.3|23.82|35.87|58.91|108.74|179.5|269.0|490.7| 791.7|1166.1|1866|2731| +| 90 |2.83|5.04|13.9|24.92|37.52|61.62|113.74|187.8|281.4|513.3| 828.1|1219.8|1951|2856| +| 100 |2.95|5.25|14.5|25.96|39.07|64.18|118.47|195.6|293.1|534.6| 862.6|1270.1|2032|2975| +| 120 |3.16|5.63|15.5|27.85|41.93|68.87|127.12|209.9|314.5|573.7| 925.6|1363.3|2181|3193| +| 150 |3.45|6.14|17.0|30.37|45.72|75.09|138.61|228.8|343.0|625.5|1009.2|1486.5|2378|3481| ++---------------------------------------------------------------------------------------+ + +This formula is the most generally accepted for the flow of steam in +pipes. Table 66 is calculated from this formula and gives the amount of +steam passing per minute that will flow through straight smooth pipes +having a length of 240 diameters from various initial pressures with one +pound difference between the initial and final pressures. + +To apply this table for other lengths of pipe and pressure losses other +than those assumed, let L = the length and d the diameter of the pipe, +both in inches; l, the loss in pounds; Q, the weight under the +conditions assumed in the table, and Q_{1}, the weight for the changed +conditions. + +For any length of pipe, if the weight of steam passing is the same as +given in the table, the loss will be, + + L + l = ---- (46) + 240d + +If the pipe length is the same as assumed in the table but the loss is +different, the quantity of steam passing per minute will be, + + Q_{1} = Ql^{.5} (47) + +For any assumed pipe length and loss of pressure, the weight will be, + + /240dl\ + Q_{1} = Q|-----|^{.5} (48) + \ L / + + TABLE 67 + + FLOW OF STEAM THROUGH PIPES + LENGTH OF PIPE 1000 FEET + ++--------------------------------------------------++----------------------------------------+ +| Discharge in Pounds per Minute corresponding to || Drop in Pressure in | +| Drop in Pressure on Right for Pipe Diameters || Pounds per Square Inch corresponding | +| in Inches in Top Line || to Discharge on Left: Densities | +| || and corresponding Absolute Pressures | +| || per Square Inch in First Two Lines | ++--------------------------------------------------++----------------------------------------+ +| Diameter[82]--Discharge || Density--Pressure--Drop | ++--------------------------------------------------++----------------------------------------+ +| 12 | 10 | 8 | 6 | 4 | 3 | 2.5| 2 | 1.5| 1 ||.208 |.230|.284|.328|.401|.443|.506|.548| +| In | In | In | In | In | In | In | In | In | In || 90 | 100| 125| 150| 180| 200| 230| 250| ++--------------------------------------------------++-------+--------------------------------+ +|2328|1443| 799| 371|123. |55.9|28.8|18.1|6.81|2.52||18.10|16.4|13.3|11.1|9.39|8.50|7.44|6.87| +|2165|1341| 742| 344|114.6|51.9|27.6|16.8|6.52|2.34||15.60|14.1|11.4|9.60|8.09|7.33|6.41|5.92| +|1996|1237| 685| 318|106.0|47.9|26.4|15.5|6.24|2.16||13.3 |12.0|9.74|8.18|6.90|6.24|5.47|5.05| +|1830|1134| 628| 292| 97.0|43.9|25.2|14.2|5.95|1.98||11.1 |10.0|8.13|6.83|5.76|5.21|4.56|4.21| +|1663|1031| 571| 265| 88.2|39.9|24.0|12.9|5.67|1.80|| 9.25|8.36|6.78|5.69|4.80|4.34|3.80|3.51| +|1580| 979| 542| 252| 83.8|37.9|22.8|12.3|5.29|1.71|| 8.33|7.53|6.10|5.13|4.32|3.91|3.42|3.16| +|1497| 928| 514| 239| 79.4|35.9|21.6|11.6|5.00|1.62|| 7.48|6.76|5.48|4.60|3.88|3.51|3.07|2.84| +|1414| 876| 485| 226| 75.0|33.9|20.4|10.9|4.72|1.53|| 6.67|6.03|4.88|4.10|3.46|3.13|2.74|2.53| +|1331| 825| 457| 212| 70.6|31.9|19.2|10.3|4.43|1.44|| 5.91|5.35|4.33|3.64|3.07|2.78|2.43|2.24| +|1248| 873| 428| 199| 66.2|23.9|18.0|9.68|4.15|1.35|| 5.19|4.69|3.80|3.19|2.69|2.44|2.13|1.97| +|1164| 722| 400| 186| 61.7|27.9|16.8|9.03|3.86|1.26|| 4.52|4.09|3.31|2.78|2.34|2.12|1.86|1.72| +|1081| 670| 371| 172| 57.3|25.9|15.6|8.38|3.68|1.17|| 3.90|3.53|2.86|2.40|2.02|1.83|1.60|1.48| +| 998| 619| 343| 159| 52.9|23.9|14.4|7.74|3.40|1.08|| 3.32|3.00|2.43|2.04|1.72|1.56|1.36|1.26| +| 915| 567| 314| 146| 48.5|21.9|13.2|7.10|3.11|0.99|| 2.79|2.52|2.04|1.72|1.45|1.31|1.15|1.06| +| 832| 516| 286| 132| 44.1|20.0|12.0|6.45|2.83|0.90|| 2.31|2.09|1.69|1.42|1.20|1.08|.949|.877| +| 748| 464| 257| 119| 39.7|18.0|10.8|5.81|2.55|0.81|| 1.87|1.69|1.37|1.15| .97|.878|.769|.710| +| 665| 412| 228| 106| 35.3|16.0| 9.6|5.16|2.26|0.72|| 1.47|1.33|1.08|.905|.762|.690|.604|.558| +| 582| 361| 200|92.8| 30.9|14.0| 8.4|4.52|1.98|0.63|| 1.13|1.02|.828|.695|.586|.531|.456|.429| ++--------------------------------------------------++----------------------------------------+ + +To get the pressure drop for lengths other than 1000 feet, multiply by +lengths in feet / 1000. + +Example: Find the weight of steam at 100 pounds initial gauge pressure, +which will pass through a 6-inch pipe 720 feet long with a pressure drop +of 4 pounds. Under the conditions assumed in the table, 293.1 pounds +would flow per minute; hence, Q = 293.1, and + + _ _ + | 240x6x4 | +Q_{1} = 293.1 | ------- |^{.5} = 239.9 pounds + |_ 720x12_| + +Table 67 may be frequently found to be of service in problems involving +the flow of steam. This table was calculated by Mr. E. C. Sickles for a +pipe 1000 feet long from formula (45), except that from the use of a +value of the constant K = .0026 instead of .0027, the constant in the +formula becomes 87.45 instead of 87. + +In using this table, the pressures and densities to be considered, as +given at the top of the right-hand portion, are the mean of the initial +and final pressures and densities. Its use is as follows: Assume an +allowable drop of pressure through a given length of pipe. From the +value as found in the right-hand column under the column of mean +pressure, as determined by the initial and final pressures, pass to the +left-hand portion of the table along the same line until the quantity is +found corresponding to the flow required. The size of the pipe at the +head of this column is that which will carry the required amount of +steam with the assumed pressure drop. + +The table may be used conversely to determine the pressure drop through +a pipe of a given diameter delivering a specified amount of steam by +passing from the known figure in the left to the column on the right +headed by the pressure which is the mean of the initial and final +pressures corresponding to the drop found and the actual initial +pressure present. + +For a given flow of steam and diameter of pipe, the drop in pressure is +proportional to the length and if discharge quantities for other lengths +of pipe than 1000 feet are required, they may be found by proportion. + + TABLE 68 + + FLOW OF STEAM INTO THE ATMOSPHERE + __________________________________________________________________ +| | | | | | +| Absolute | Velocity | Actual | Discharge | Horse Power | +| Initial | of Outflow | Velocity | per Square | per Square | +| Pressure | at Constant | of Outflow | Inch of | Inch of | +| per Square | Density | Expanded | Orifice | Orifice if | +| Inch | Feet per | Feet per | per Minute | Horse Power | +| Pounds | Second | Second | Pounds | = 30 Pounds | +| | | | | per Hour | +|____________|_____________|____________|____________|_____________| +| | | | | | +| 25.37 | 863 | 1401 | 22.81 | 45.6 | +| 30. | 867 | 1408 | 26.84 | 53.7 | +| 40. | 874 | 1419 | 35.18 | 70.4 | +| 50. | 880 | 1429 | 44.06 | 88.1 | +| 60. | 885 | 1437 | 52.59 | 105.2 | +| 70. | 889 | 1444 | 61.07 | 122.1 | +| 75. | 891 | 1447 | 65.30 | 130.6 | +| 90. | 895 | 1454 | 77.94 | 155.9 | +| 100. | 898 | 1459 | 86.34 | 172.7 | +| 115. | 902 | 1466 | 98.76 | 197.5 | +| 135. | 906 | 1472 | 115.61 | 231.2 | +| 155. | 910 | 1478 | 132.21 | 264.4 | +| 165. | 912 | 1481 | 140.46 | 280.9 | +| 215. | 919 | 1493 | 181.58 | 363.2 | +|____________|_____________|____________|____________|_____________| + + +Elbows, globe valves and a square-ended entrance to pipes all offer +resistance to the passage of steam. It is customary to measure the +resistance offered by such construction in terms of the diameter of the +pipe. Many formulae have been advanced for computing the length of pipe +in diameters equivalent to such fittings or valves which offer +resistance. These formulae, however vary widely and for ordinary +purposes it will be sufficiently accurate to allow for resistance at the +entrance of a pipe a length equal to 60 times the diameter; for a right +angle elbow, a length equal to 40 diameters, and for a globe valve a +length equal to 60 diameters. + +The flow of steam of a higher toward a lower pressure increases as the +difference in pressure increases to a point where the external pressure +becomes 58 per cent of the absolute initial pressure. Below this point +the flow is neither increased nor decreased by a reduction of the +external pressure, even to the extent of a perfect vacuum. The lowest +pressure for which this statement holds when steam is discharged into +the atmosphere is 25.37 pounds. For any pressure below this figure, the +atmospheric pressure, 14.7 pounds, is greater than 58 per cent of the +initial pressure. Table 68, by D. K. Clark, gives the velocity of +outflow at constant density, the actual velocity of outflow expanded +(the atmospheric pressure being taken as 14.7 pounds absolute, and the +ratio of expansion in the nozzle being 1.624), and the corresponding +discharge per square inch of orifice per minute. + +Napier deduced an approximate formula for the outflow of steam into the +atmosphere which checks closely with the figures just given. This +formula is: + + pa +W = ---- (49) + 70 + +Where W = the pounds of steam flowing per second, + p = the absolute pressure in pounds per square inch, + and a = the area of the orifice in square inches. + +In some experiments made by Professor C. H. Peabody, in the flow of +steam through pipes from 1/4 inch to 1-1/2 inches long and 1/4 inch in +diameter, with rounded entrances, the greatest difference from Napier's +formula was 3.2 per cent excess of the experimental over the calculated +results. + +For steam flowing through an orifice from a higher to a lower pressure +where the lower pressure is greater than 58 per cent of the higher, the +flow per minute may be calculated from the formula: + +W = 1.9AK ((P - d)d)^{.5} (50) + +Where W = the weight of steam discharged in pounds per minute, + A = area of orifice in square inches, + P = the absolute initial pressure in pounds per square inch, + d = the difference in pressure between the two sides in pounds + per square inch, + K = a constant = .93 for a short pipe, and .63 for a hole in a + thin plate or a safety valve. + +[Illustration: Vesta Coal Co., California, Pa., Operating at this Plant +3160 Horse Power of Babcock & Wilcox Boilers] + + + + +HEAT TRANSFER + + +The rate at which heat is transmitted from a hot gas to a cooler metal +surface over which the gas is flowing has been the subject of a great +deal of investigation both from the experimental and theoretical side. A +more or less complete explanation of this process is necessary for a +detailed analysis of the performance of steam boilers. Such information +at the present is almost entirely lacking and for this reason a boiler, +as a physical piece of apparatus, is not as well understood as it might +be. This, however, has had little effect in its practical development +and it is hardly possible that a more complete understanding of the +phenomena discussed will have any radical effect on the present design. + +The amount of heat that is transferred across any surface is usually +expressed as a product, of which one factor is the slope or linear rate +of change in temperature and the other is the amount of heat transferred +per unit's difference in temperature in unit's length. In Fourier's +analytical theory of the conduction of heat, this second factor is taken +as a constant and is called the "conductivity" of the substance. +Following this practice, the amount of heat absorbed by any surface from +a hot gas is usually expressed as a product of the difference in +temperature between the gas and the absorbing surface into a factor +which is commonly designated the "transfer rate". There has been +considerable looseness in the writings of even the best authors as to +the way in which the gas temperature difference is to be measured. If +the gas varies in temperature across the section of the channel through +which it is assumed to flow, and most of them seem to consider that this +would be the case, there are two mean gas temperatures, one the mean of +the actual temperatures at any time across the section, and the other +the mean temperature of the entire volume of the gas passing such a +section in any given time. Since the velocity of flow will of a +certainty vary across the section, this second mean temperature, which +is one tacitly assumed in most instances, may vary materially from the +first. The two mean temperatures are only approximately equal when the +actual temperature measured across the section is very nearly a +constant. In what follows it will be assumed that the mean temperature +measured in the second way is referred to. In English units the +temperature difference is expressed in Fahrenheit degrees and the +transfer rate in B. t. u.'s per hour per square foot of surface. Pecla, +who seems to have been one of the first to consider this subject +analytically, assumed that the transfer rate was constant and +independent both of the temperature differences and the velocity of the +gas over the surface. Rankine, on the other hand, assumed that the +transfer rate, while independent of the velocity of the gas, was +proportional to the temperature difference, and expressed the total +amount of heat absorbed as proportional to the square of the difference +in temperature. Neither of these assumptions has any warrant in either +theory or experiment and they are only valuable in so far as their use +determine formulae that fit experimental results. Of the two, Rankine's +assumption seems to lead to formulae that more nearly represent actual +conditions. It has been quite fully developed by William Kent in his +"Steam Boiler Economy". Professor Osborne Reynolds, in a short paper +reprinted in Volume I of his "Scientific Papers", suggests that the +transfer rate is proportional to the product of the density and velocity +of the gas and it is to be assumed that he had in mind the mean +velocity, density and temperature over the section of the channel +through which the gas was assumed to flow. Contrary to prevalent +opinion, Professor Reynolds gave neither a valid experimental nor a +theoretical explanation of his formula and the attempts that have been +made since its first publication to establish it on any theoretical +basis can hardly be considered of scientific value. Nevertheless, +Reynolds' suggestion was really the starting point of the scientific +investigation of this subject and while his formula cannot in any sense +be held as completely expressing the facts, it is undoubtedly correct to +a first approximation for small temperature differences if the additive +constant, which in his paper he assumed as negligible, is given a +value.[83] + +Experimental determinations have been made during the last few years of +the heat transfer rate in cylindrical tubes at comparatively low +temperatures and small temperature differences. The results at different +velocities have been plotted and an empirical formula determined +expressing the transfer rate with the velocity as a factor. The exponent +of the power of the velocity appearing in the formula, according to +Reynolds, would be unity. The most probable value, however, deduced from +most of the experiments makes it less than unity. After considering +experiments of his own, as well as experiments of others, Dr. Wilhelm +Nusselt[84] concludes that the evidence supports the following formulae: + + _ _ + [lambda]_{w} | w c_{p} [delta] | +a = b ------------ | --------------- |^{u} + d^{1-u} |_ [lambda] _| + + Where a is the transfer rate in calories per hour per square meter + of surface per degree centigrade difference in temperature, + u is a physical constant equal to .786 from Dr. Nusselt's + experiments, + b is a constant which, for the units given below, is 15.90, + w is the mean velocity of the gas in meters per second, + c_{p} is the specific heat of the gas at its mean temperature + and pressure in calories per kilogram, + [delta] is the density in kilograms per cubic meter, + [lambda] is the conductivity at the mean temperature and pressure in + calories per hour per square meter per degree centigrade + temperature drop per meter, +[lambda]_{w} is the conductivity of the steam at the temperature of the + tube wall, + d is the diameter of the tube in meters. + +If the unit of time for the velocity is made the hour, and in the place +of the product of the velocity and density is written its equivalent, +the weight of gas flowing per hour divided by the area of the tube, this +equation becomes: + + _ _ + [lambda]_{w} | Wc_{p} | +a = .0255 ------------ | --------- |^{.786} + d^{.214} |_ A[lambda] _| + +where the quantities are in the units mentioned, or, since the constants +are absolute constants, in English units, + + a is the transfer rate in B. t. u. per hour per square foot + of surface per degree difference in temperature, + W is the weight in pounds of the gas flowing through the tube + per hour, + A is the area of the tube in square feet, + d is the diameter of the tube in feet, + c_{p} is the specific heat of the gas at constant pressure, + [lambda] is the conductivity of the gas at the mean temperature and + pressure in B. t. u. per hour per square foot of surface + per degree Fahrenheit drop in temperature per foot, +[lambda]_{w} is the conductivity of the steam at the temperature of the + wall of the tube. + +The conductivities of air, carbonic acid gas and superheated steam, as +affected by the temperature, in English units, are: + +Conductivity of air .0122 (1 + .00132 T) +Conductivity of carbonic acid gas .0076 (1 + .00229 T) +Conductivity of superheated steam .0119 (1 + .00261 T) + +where T is the temperature in degrees Fahrenheit. + +Nusselt's formulae can be taken as typical of the number of other +formulae proposed by German, French and English writers.[85] Physical +properties, in addition to the density, are introduced in the form of +coefficients from a consideration of the physical dimensions of the +various units and of the theoretical formulae that are supposed to +govern the flow of the gas and the transfer of heat. All assume that the +correct method of representing the heat transfer rate is by the use of +one term, which seems to be unwarranted and probably has been adopted on +account of the convenience in working up the results by plotting them +logarithmically. This was the method Professor Reynolds used in +determining his equation for the loss in head in fluids flowing through +cylindrical pipes and it is now known that the derived equation cannot +be considered as anything more than an empirical formula. It, therefore, +is well for anyone considering this subject to understand at the outset +that the formulae discussed are only of an empirical nature and +applicable to limited ranges of temperature under the conditions +approximately the same as those surrounding the experiments from which +the constants of the formula were determined. + +It is not probable that the subject of heat transfer in boilers will +ever be on any other than an experimental basis until the mathematical +expression connecting the quantity of fluid which will flow through a +channel of any section under a given head has been found and some +explanation of its derivation obtained. Taking the simplest possible +section, namely, a circle, it is found that at low velocities the loss +of head is directly proportional to the velocity and the fluid flows in +straight stream lines or the motion is direct. This motion is in exact +accordance with the theoretical equations of the motion of a viscous +fluid and constitutes almost a direct proof that the fundamental +assumptions on which these equations are based are correct. When, +however, the velocity exceeds a value which is determinable for any size +of tube, the direct or stream line motion breaks down and is replaced by +an eddy or mixing flow. In this flow the head loss by friction is +approximately, although not exactly, proportional to the square of the +velocity. No explanation of this has ever been found in spite of the +fact that the subject has been treated by the best mathematicians and +physicists for years back. It is to be assumed that the heat transferred +during the mixing flow would be at a much higher rate than with the +direct or stream line flow, and Professors Croker and Clement[86] have +demonstrated that this is true, the increase in the transfer being so +marked as to enable them to determine the point of critical velocity +from observing the rise in temperature of water flowing through a tube +surrounded by a steam jacket. + +The formulae given apply only to a mixing flow and inasmuch as, from +what has just been stated, this form of motion does not exist from zero +velocity upward, it follows that any expression for the heat transfer +rate that would make its value zero when the velocity is zero, can +hardly be correct. Below the critical velocity, the transfer rate seems +to be little affected by change in velocity and Nusselt,[87] in another +paper which mathematically treats the direct or stream line flow, +concludes that, while it is approximately constant as far as the +velocity is concerned in a straight cylindrical tube, it would vary from +point to point of the tube, growing less as the surface passed over +increased. + +It should further be noted that no account in any of this experimental +work has been taken of radiation of heat from the gas. Since the common +gases absorb very little radiant heat at ordinary temperatures, it has +been assumed that they radiate very little at any temperature. This may +or may not be true, but certainly a visible flame must radiate as well +as absorb heat. However this radiation may occur, since it would be a +volume phenomenon rather than a surface phenomenon it would be +considered somewhat differently from ordinary radiation. It might apply +as increasing the conductivity of the gas which, however independent of +radiation, is known to increase with the temperature. It is, therefore, +to be expected that at high temperatures the rate of transfer will be +greater than at low temperatures. The experimental determinations of +transfer rates at high temperatures are lacking. + +Although comparatively nothing is known concerning the heat radiation +from gases at high temperatures, there is no question but what a large +proportion of the heat absorbed by a boiler is received direct as +radiation from the furnace. Experiments show that the lower row of tubes +of a Babcock & Wilcox boiler absorb heat at an average rate per square +foot of surface between the first baffle and the front headers +equivalent to the evaporation of from 50 to 75 pounds of water from and +at 212 degrees Fahrenheit per hour. Inasmuch as in these experiments no +separation could be made between the heat absorbed by the bottom of the +tube and that absorbed by the top, the average includes both maximum and +minimum rates for those particular tubes and it is fair to assume that +the portion of the tubes actually exposed to the furnace radiations +absorb heat at a higher rate. Part of this heat was, of course absorbed +by actual contact between the hot gases and the boiler heating surface. +A large portion of it, however, must have been due to radiation. Whether +this radiant heat came from the fire surface and the brickwork and +passed through the gases in the furnace with little or no absorption, or +whether, on the other hand, the radiation were absorbed by the furnace +gases and the heat received by the boiler was a secondary radiation from +the gases themselves and at a rate corresponding to the actual gas +temperature, is a question. If the radiations are direct, then the term +"furnace temperature", as usually used has no scientific meaning, for +obviously the temperature of the gas in the furnace would be entirely +different from the radiation temperature, even were it possible to +attach any significance to the term "radiation temperature", and it is +not possible to do this unless the radiations are what are known as +"full radiations" from a so-called "black body". If furnace radiation +takes place in this manner, the indications of a pyrometer placed in a +furnace are hard to interpret and such temperature measurements can be +of little value. If the furnace gases absorb the radiations from the +fire and from the brickwork of the side walls and in their turn radiate +heat to the boiler surface, it is scientifically correct to assume that +the actual or sensible temperature of the gas would be measured by a +pyrometer and the amount of radiation could be calculated from this +temperature by Stefan's law, which is to the effect that the rate of +radiation is proportional to the fourth power of the absolute +temperature, using the constant with the resulting formula that has been +determined from direct experiment and other phenomena. With this +understanding of the matter, the radiations absorbed by a boiler can be +taken as equal to that absorbed by a flat surface, covering the portion +of the boiler tubes exposed to the furnace and at the temperature of the +tube surface, when completely exposed on one side to the radiations from +an atmosphere at the temperature in the furnace. With this assumption, +if S^{1} is the area of the surface, T the absolute temperature of the +furnace gases, t the absolute temperature of the tube surface of the +boiler, the heat absorbed per hour measured in B. t. u.'s is equal to + + _ _ + | / T \ / t \ | +1600 | |----|^{4} - |----|^{4}| S^{1} + |_\1000/ \1000/ _| + +In using this formula, or in any work connected with heat transfer, the +external temperature of the boiler heating surface can be taken as that +of saturated steam at the pressure under which the boiler is working, +with an almost negligible error, since experiments have shown that with +a surface clean internally, the external surface is only a few degrees +hotter than the water in contact with the inner surface, even at the +highest rates of evaporation. Further than this, it is not conceivable +that in a modern boiler there can be much difference in the temperature +of the boiler in the different parts, or much difference between the +temperature of the water and the temperature of the steam in the drums +which is in contact with it. + +If the total evaporation of a boiler measured in B. t. u.'s per hour is +represented by E, the furnace temperature by T_{1}, the temperature of +the gas leaving the boiler by T_{2}, the weight of gas leaving the +furnace and passing through the setting per hour by W, the specific heat +of the gas by C, it follows from the fact that the total amount of heat +absorbed is equal to the heat received from radiation plus the heat +removed from the gases by cooling from the temperature T_{1} to the +temperature T_{2}, that + + _ _ + | / T \ / t \ | +E = 1600 | |----|^{4} - |----|^{4}| S^{1} + WC(T_{1} - T_{2}) + |_\1000/ \1000/ _| + +This formula can be used for calculating the furnace temperature when E, +t and T_{2} are known but it must be remembered that an assumption +which is probably, in part at least, incorrect is implied in using it or +in using any similar formula. Expressed in this way, however, it seems +more rational than the one proposed a few years ago by Dr. Nicholson[88] +where, in place of the surface exposed to radiation, he uses the grate +surface and assumes the furnace gas temperature as equal to the fire +temperature. + +If the heat transfer rate is taken as independent of the gas temperature +and the heat absorbed by an element of the surface in a given time is +equated to the heat given out from the gas passing over this surface in +the same time, a single integration gives + + Rs +(T - t) = (T_{1} - t) e^{- --} + WC + +where s is the area of surface passed over by the gases from the furnace +to any point where the gas temperature T is measured, and the rate of +heat transfer is R. As written, this formula could be used for +calculating the temperature of the gas at any point in the boiler +setting. Gas temperatures, however, calculated in this way are not to be +depended upon as it is known that the transfer rate is not independent +of the temperature. Again, if the transfer rate is assumed as varying +directly with the weight of the gases passing, which is Reynolds' +suggestion, it is seen that the weight of the gases entirely disappears +from the formula and as a consequence if the formula was correct, as +long as the temperature of the gas entering the surface from the furnace +was the same, the temperatures throughout the setting would be the same. +This is known also to be incorrect. If, however, in place of T is +written T_{2} and in place of s is written S, the entire surface of the +boiler, and the formula is re-arranged, it becomes: + + _ _ + WC | T_{1} - t | +R = --- Log[89]| --------- | + S |_ T_{2} - t _| + +This formula can be considered as giving a way of calculating an average +transfer rate. It has been used in this way for calculating the average +transfer rate from boiler tests in which the capacity has varied from an +evaporation of a little over 3 pounds per square foot of surface up to +15 pounds. When plotted against the gas weights, it was found that the +points were almost exactly on a line. This line, however, did not pass +through the zero point but started at a point corresponding to +approximately a transfer rate of 2. Checked out against many other +tests, the straight line law seems to hold generally and this is true +even though material changes are made in the method of calculating the +furnace temperature. The inclination of the line, however, varied +inversely as the average area for the passage of the gas through the +boiler. If A is the average area between all the passes of the boiler, +the heat transfer rate in Babcock & Wilcox type boilers with ordinary +clean surfaces can be determined to a rather close approximation from +the formula: + + W +R = 2.00 + .0014 - + A + +The manner in which A appears in this formula is the same as it would +appear in any formula in which the heat transfer rate was taken as +depending upon the product of the velocity and the density of the gas +jointly, since this product, as pointed out above, is equivalent to W/A. +Nusselt's experiments, as well as those of others, indicate that the +ratio appears in the proper way. + +While the underlying principles from which the formula for this average +transfer rate was determined are questionable and at best only +approximately correct, it nevertheless follows that assuming the +transfer rate as determined experimentally, the formula can be used in +an inverse way for calculating the amount of surface required in a +boiler for cooling the gases through a range of temperature covered by +the experiments and it has been found that the results bear out this +assumption. The practical application of the theory of heat transfer, as +developed at present, seems consequently to rest on these last two +formulae, which from their nature are more or less empirical. + +Through the range in the production of steam met with in boilers now in +service which in the marine type extends to the average evaporation of +12 to 15 pounds of water from and at 212 degrees Fahrenheit per square +foot of surface, the constant 2 in the approximate formula for the +average heat transfer rate constitutes quite a large proportion of the +total. The comparative increase in the transfer rate due to a change in +weight of the gases is not as great consequently as it would be if this +constant were zero. For this reason, with the same temperature of the +gases entering the boiler surface, there will be a gradual increase in +the temperature of the gases leaving the surface as the velocity or +weight of flow increases and the proportion of the heat contained in the +gases entering the boiler which is absorbed by it is gradually reduced. +It is, of course, possible that the weight of the gases could be +increased to such an amount or the area for their passage through the +boiler reduced by additional baffles until the constant term in the heat +transfer formula would be relatively unimportant. Under such conditions, +as pointed out previously, the final gas temperature would be unaffected +by a further increase in the velocity of the flow and the fraction of +the heat carried by the gases removed by the boiler would be constant. +Actual tests of waste heat boilers in which the weight of gas per square +foot of sectional area for its passage is many times more than in +ordinary installations show, however, that this condition has not been +attained and it will probably never be attained in any practical +installation. It is for this reason that the conclusions of Dr. +Nicholson in the paper referred to and of Messrs. Kreisinger and Ray in +the pamphlet "The Transmission of Heat into Steam Boilers", published by +the Department of the Interior in 1912, are not applicable without +modification to boiler design. + +In superheaters the heat transfer is effected in two different stages; +the first transfer is from the hot gas to the metal of the superheater +tube and the second transfer is from the metal of the tube to the steam +on the inside. There is, theoretically, an intermediate stage in the +transfer of the heat from the outside to the inside surface of the tube. +The conductivity of steel is sufficient, however, to keep the +temperatures of the two sides of the tube very nearly equal to each +other so that the effect of the transfer in the tube itself can be +neglected. The transfer from the hot gas to the metal of the tube takes +place in the same way as with the boiler tubes proper, regard being paid +to the temperature of the tube which increases as the steam is heated. +The transfer from the inside surface of the tube to the steam is the +inverse of the process of the transfer of the heat on the outside and +seems to follow the same laws. The transfer rate, therefore, will +increase with the velocity of the steam through the tube. For this +reason, internal cores are quite often used in superheaters and actually +result in an increase in the amount of superheat obtained from a given +surface. The average transfer rate in superheaters based on a difference +in mean temperature between the gas on the outside of the tubes and the +steam on the inside of the tubes is if R is the transfer rate from the +gas to the tube and r the rate from the tube to the steam: + + Rr + ----- + R + r + +and is always less than either R or r. This rate is usually greater than +the average transfer rate for the boiler as computed in the way outlined +in the preceding paragraphs. Since, however, steam cannot, under any +imagined set of conditions, take up more heat from a tube than would +water at the same average temperature, this fact supports the contention +made that the actual transfer rate in a boiler must increase quite +rapidly with the temperatures. The actual transfer rates in superheaters +are affected by so many conditions that it has not so far been possible +to evolve any formula of practical value. + +[Illustration: Iron City Brewery of the Pittsburgh Brewing Co., +Pittsburgh, Pa, Operating in this Plant 2000 Horse Power of Babcock & +Wilcox Boilers] + + + + +INDEX + + PAGE + +Absolute pressure 117 +Absolute zero 80 +Accessibility of Babcock & Wilcox boiler 59 +Acidity in boiler feed water 106 +Actual evap. corresponding to boiler horse power 288 +Advantages of Babcock & Wilcox boilers 61 + Stoker firing 195 + Water tube over fire tube boilers 61 +Air, composition of 147 + In boiler feed water 106 + Properties of 147 + Required for combustion 152, 156 + Specific heat of 148 + Supplied for combustion 157 + Vapor in 149 + Volume of 147 + Weight of 147 +Alkalinity in boiler feed water 103 + Testing feed for 103 +Altitude, boiling point of water at 97 + Chimney sizes corrected for 248 +Alum in feed water treatment 106 +A. S. M. E. code for boiler testing 267 +Analyses, comparison of proximate and ultimate 183 + Proximate coal, and heating values 177 +Analysis, coal, proximate, methods of 176 + Coal, ultimate 173 + Determination of heating value from 173 +Analysis, Flue gas 155 + Flue gas, methods of 160 + Flue gas, object of 155 +Anthracite coal 166 + Combustion rates with 246 + Distribution of 167 + Draft required for 246 + Firing 190 + Grate ratio for 191 + Semi 166 + Sizes of 190 + Steam as aid to burning 191 + Thickness of fires with 191 +Arches, fire brick, as aid to combustion 190 + Fire brick, for 304 + Fire brick, laying 305 +Automatic stokers, advantages of 195 + Overfeed 196 + Traveling grate 197 + Traveling grate, Babcock & Wilcox 194 + Underfeed 196 +Auxiliaries, exhaust from, in heating feed water 113 + Superheated steam with 142 +Auxiliary grates, with blast furnace gas 228 + With oil fuel 225 + With waste heat 235 +Babcock, G. H., lecture on circulation of water in Boilers 28 + Lecture on theory of steam making 92 +Babcock & Wilcox Co., Works at Barberton, Ohio 7 + Works at Bayonne, N. J. 6 +Babcock & Wilcox boiler, accessibility of 59 + Advantages of 61 + Circulation of water in 57, 66 + Construction of 49 + Cross boxes 50 + Cross drum 53 + Cross drum, dry steam with 71 + Drumheads 49 + Drums 49 + Durability 75 + Evolution of 39 + Fittings 55 + Fixtures 55 + Fronts 53 + Handhole fittings 50, 51 + Headers 50, 51 + Inclined header, wrought steel 54 + Inspection 75 + Life of 76 + Materials entering into the construction of 59 + Mud drums 51 + Path of gases in 57 + Path of water in 57 + Rear tube doors of 53, 74 + Repairs 75 + Safety of 66 + Sections 50 + Set for utilizing waste heat 236 + Set with Babcock & Wilcox chain grate stoker 12 + Set with bagasse furnace 208 + Set with Peabody oil furnace 222 + Supports, cross drum 53 + Supports, longitudinal drum 52 + Tube doors 53 + Vertical header, cast iron 58 + Vertical header, wrought steel 48 +Babcock & Wilcox chain grate stoker 194 +Babcock & Wilcox superheater 136 +Bagasse, composition of 206 + Furnace 209 + Heat, value of 206 + Tests of Babcock & Wilcox boilers with 210 + Value of diffusion 207 +Barium carbonate in feed water treatment 106 +Barium hydrate in feed water treatment 106 +Barrus draft gauge 254 +Bituminous coal, classification of 167 + Combustion rates with 246 + Composition of 177 + Distribution of 168 + Firing methods 193 + Semi 166 + Sizes of 191 + Thickness of fire with 193 +Blast furnace gas, burners for 228 + Combustion of 228 + Composition of 227 + Stacks for 228 +Boiler, Blakey's 23 + Brickwork, care of 307 + Circulation of water in steam 28 + Compounds 109 + Development of water tube 23 + Eve's 24 + Evolution of Babcock & Wilcox 39 + Fire tube, compared with water tube 61 + Guerney's 24 + Horse power 263 + Loads, economical 283 + Perkins' 24 + Room piping 108 + Room practice 297 + Rumsey's 23 + Stevens', John 23 + Stevens', John Cox 23 + Units, number of 289 + Units, size of 289 + Wilcox's 25 + Woolf's 23 +Boilers, capacity of 278 + Care of 291 + Efficiency of 256 + Horse power of 265 + Operation of 291 + Requirements of steam 27 + Testing 267 +Boiling point 86 + Of various substances 86 + Of water as affected by altitude 97 +Brick, fire 304 + Arches 305 + Classification of 304 + Compression of 303 + Expansion of 303 + Hardness of 303 + Laying up 305 + Nodules, ratio of 303 + Nodules, size of 303 + Plasticity of 302 +Brick, red 302 +Brickwork, care of 307 +British thermal unit 83 +Burners, blast furnace gas 228 + By-product coke oven gas 231 + Natural gas 231 + Oil 217 + Oil, capacity of 221 + Oil, mechanical atomizing 219 + Oil, operation of 223 + Oil, steam atomizing 218 + Oil, steam consumption of 220 +Burning hydrogen, loss due to moisture formed in 261 +By-product coke oven gas burners 231 +By-product coke oven gas, combustion of 231 +By-product coke oven gas, composition and heat value of 231 +Calorie 83 +Calorific value (see Heat value). +Calorimeter, coal, Mahler bomb 184 + Mahler bomb, method of correction 187 + Mahler bomb, method of operation of 185 +Calorimeter, steam, compact type of throttling 132 + Correction for 131 + Location of nozzles for 134 + Normal reading 131 + Nozzles 134 + Separating 133 + Throttling 129 +Capacity of boilers 264, 278 + As affecting economy 276 + Economical loads 283 + With bagasse 210 + With blast furnace gas 228 + With coal 280 + With oil fuel 224 +Capacity of natural gas burners 229 +Capacity of oil burners 221 +Carbon dioxide in flue gases 154 + Unreliability of readings taken alone 162 +Carbon, fixed 165 + Incomplete combustion of, loss due to 158 + Monoxide, heat value of 151 + Monoxide, in flue gases 155 + Unconsumed in ash, loss due to 261 +Care of boilers when out of service 300 +Casings, boilers 307 +Causticity of feed water 103 + Testing for 105 +Celsius thermometer scale 79 +Centigrade thermometer scale 79 +Chain grate stoker, Babcock & Wilcox 194 +Chemicals required in feed water treatment 105 +Chimney gases, losses in 158, 159 +Chimneys (see Draft). + Correction in dimensions for altitude 248 + Diameter of 243 + Draft available from 241 + Draft loss in 239 + For blast furnace gas 253 + For oil fuel 251 + For wood fuel 254 + Height of 243 + Horse power they will serve 250 +Circulation of water in Babcock & Wilcox boilers 57, 66 + Of water in steam boilers 28 + Results of defective 62, 66, 67 +Classification of coals 166 + Fire brick 304 + Feed water difficulties 100 + Fuels 165 +Cleaners, turbine tube 299 +Cleaning, ease of, Babcock & Wilcox boilers 73 +Closed feed water heaters 111 +Coal, Alaska 169 + Analyses and heat value 177 + Analysis, proximate 176 + Analysis, ultimate 173 + Anthracite 166 + Bituminous 167 + Cannel 167 + Classification of 165, 166 + Combustion of 190 + Comparison with oil 214 + Consumption, increase due to superheat 139 + Distribution of 167 + Formation of 165 + Lignite 167 + Records 293 + Semi-anthracite 166 + Semi-bituminous 166 + Sizes of anthracite 190 + Sizes of bituminous 191 +Code of A. S. M. E. for boiler testing 267 +Coefficient of expansion of various substances 87 +Coke 171 + Oven gas, by-product, burners 231 + Oven gas, by-product, combustion of 231 + Oven gas, by-product, composition and heat value of 231 +Coking method of firing 195 +Color as indication of temperature 91 +Combination furnaces 224 +Combustible in fuels 150 +Combustion 150 + Air required for 152, 156 + Air supplied for 157 +Combustion of coal 190 + Of gaseous fuels 227 + Of liquid fuels 212 + Of solid fuels other than coal 201 +Composition of bagasse 205 + Blast furnace gas 227 + By-product coke oven gas 231 + Coals 177 + Natural gas 229 + Oil 213 + Wood 201 +Compounds, boiler 109 +Compressibility of water 97 +Compression of fire brick 303 +Condensation, effect of superheated steam on 140 + In steam pipes 313 +Consumption, heat, of engines 141 +Correction, stem, for thermometers 80 + For normal reading in steam calorimeter 131 + For radiation, bomb calorimeter 187 +Corrosion 101, 106 +Coverings, pipe 315 +Cross drum, Babcock & Wilcox boiler 52, 53, 60 + Dry steam with 71 +Draft area as affecting economy in Babcock & Wilcox boilers 70 + Available from chimneys 241 +Draft loss in chimneys 239 + Loss in boilers 245 + Loss in flues 243 + Loss in furnaces 245 +Draft required for anthracite 246 + Required for various fuels 246 +Drums, Babcock & Wilcox, cross 53 + Cross, boxes 50 + Heads 49 + Longitudinal 49 + Manholes 49 + Nozzles on 50 +Dry steam in Babcock & Wilcox boilers 71 +Density of gases 147 + Steam 115 +Dulong's formula for heating value 173 +Ebullition, point of 86 +Economizers 111 +Efficiency of boilers, chart of 258 + Combustible basis 256 + Dry coal basis 256 + Increase in, due to superheaters 139 + Losses in (see Heat balance) 259 + Testing 267 + Test _vs._ operating 278 + Variation in, with capacity 284 + With coal 288 + With oil 224 +Ellison draft gauge 254 +Engine, Hero's 13 +Engines, superheated steam with 141 +Equivalent evaporation from and at 212 degrees 116 +Eve's boiler 24 +Evolution of Babcock & Wilcox boiler 39 +Exhaust steam from auxiliaries 113 +Expansion, coefficient of 87 + Of fire brick 303 + Of pipe 315 + Pyrometer 89 +Factor of evaporation 117 +Fahrenheit thermometer scale 79 +Fans, use of, in waste heat work 233 +Feed water, air in 106 + As affecting capacity 279 + Boiler 100 +Feed water heaters, closed 111 + Economizers 111 + Open 111 +Feed water heating, methods of 111 + Saving by 110 +Feed water, impurities in 100 + Lines 312 + Method of feeding 110 +Feed water treatment 102 + Chemical 102 + Chemical, lime and soda process 102 + Chemical, lime process 102 + Chemical, soda process 102 + Chemicals used in lime and soda process 105 + Combined heat and chemical 105 + Heat 102 + Less usual reagents 106 +Firing, advantages of stoker 195 + Methods for anthracite 190 + Bituminous 193 + Lignite 195 +Fittings, handhole in Babcock & Wilcox boilers 50, 51 + Pipe 311 + Superheated steam 145 + With Babcock & Wilcox boilers 55 +Fixtures with Babcock & Wilcox boilers 55 +Flanges, pipe 309 +Flow of steam into pressure above atmosphere 317 + Into the atmosphere 328 + Through orifices 317 + Through pipes 317 +Flue gas analysis 155 + Conversion of volumetric to weight 161 + Methods of making 160 + Object of 155 + Orsat apparatus 159 +Flue gas, composition of 155 + Losses in 158, 159 + Weight per pound of carbon in fuel 158 + Weight per pound of fuel 158 + Weight resulting from combustion 157 +Foaming 102, 107 +Fuel analysis, proximate 176 + Ultimate 173 +Fuel calorimeter, Mabler bomb 184 +Tests, method of making 186 +Fuels, classification of 165 + Gaseous, and their combustion 227 +Fuels, liquid, and their combustion 212 + Solid, coal 190 + Solid, other than coal 201 +Furnace, bagasse 209 + Blast furnace gas 228 + By-product coke oven gas 231 + Combination wood and oil 225 + Efficiency of 283 + Natural gas 229 + Peabody oil 222 + Webster 55 + Wood burning 201, 202 +Galvanic action 107 +Gas, blast furnace, burners 228 + Combustion of 228 + Composition of 227 +Gas, by-product coke oven, burners 231 + Combustion of 231 + Composition of and heat value 231 +Gas, natural, burners 229 + Combustion of 229 + Composition and heat value of 229 +Gases, chimney, losses in 158, 159 + Density of 163 + Flue (see Flue gases). + Path of in Babcock & Wilcox boilers 57 + Waste (see Waste heat) 232 +Gaskets 312 +Gauges, draft, Barrus 254 + Ellison 255 + Peabody 255 + U-tube 254 +Gauges, vacuum 117 +Grate ratio for anthracite 191 +Gravity of oils 214 +Grooving 102 +Guerney's boiler 24 +Handhole fittings for Babcock & Wilcox boilers 50, 51 +Handholes in Babcock & Wilcox boilers 50, 51 +Hardness of boiler feed water 102 + Permanent 102 + Temporary 102 + Testing for 105 +Hardness of fire brick 303 +Heat and chemical methods of treating feed water 105 + And its measurement 79 + Balance 262 + Consumption of engines 141 + Latent 84 + Of liquid 120 + Sensible 84 + Specific (see Specific heat) 83 + Total 86 + Transfer 323 +Heat value of bagasse 205 + By-product coke oven gas 231 + Coal 177 +Heat value of fuels, determination of 173 + Determination of Kent's approximate method 183 + High and low 174 +Heat value of natural gas 229 + Oil 215 + Wood 201 +Heat waste (see Waste heat) 232 +Heaters, feed water, closed 111 + Economizers 111 + Open 111 +Heating feed water, saving by 110 +Hero's engine 13 +High and low heat value of fuels 174 +High pressure steam, advantages of use of 119 +High temperature measurements, accuracy of 89 +Horse power, boiler 265 + Evaporation (actual) corresponding to 288 + Rated boiler 265 + Stacks for various, of boilers 250 +Hydrogen in flue gases 156 +Ice, specific heat of 99 +"Idalia", tests with superheated steam on yacht 143 +Impurities in boiler feed water 100 +Incomplete combustion of carbon, loss due to 158 +Injectors, efficiency of 112 + Relative efficiency of, and pumps 112 +Iron alum in feed water treatment 106 +Kent, Wm., determination of heat value from analysis 183 + Stack table 250 +Kindling point 150 +Latent heat 84, 115 +Laying of fire brick 305 + Red brick 305 +Lignite, analyses of 181 + Combustion of 195 +Lime and soda treatment of boiler feed 102 + Used in chemical treatment of feed 105 +Lime treatment of boiler feed water 102 +Liquid fuels and their combustion 212 +Loads, economical boiler 283 +Losses due to excess air 158 + Due to unburned carbon 158 + Due to unconsumed carbon in the ash 261 +Losses in efficiency (see Heat balance). + In flue gases 158, 159 +Low water in boilers 298 +Melting points of metals 91 +Mercurial pyrometers 89 +Moisture in coal, determination of 176 + In fuels, losses due to 259 + In steam, determination of 129 +Mud drum of Babcock & Wilcox boiler 51 +Napier's formula for flow of steam 321 +Natural gas, burners for 229 + Combustion of 229 + Composition and heat value of 229 +Nitrate of silver in testing feed water 105 +Nitrogen, as indication of excess air 157 + In air 147 + In flue gases 157 +Nodules, fire brick, ratio of 303 + Size of 303 +Normal reading, throttling calorimeter 131 +Nozzles, steam sampling for calorimeter 134 + Location of 134 +Oil fuel, burners (see Burners). + Capacity with 224 + Combustion of 217 + Comparison with coal 214 + Composition and heat value of 213 + Efficiency with 224 + Furnaces for 221 + Gravity of 214 + In combination with other fuels 224 + Stacks for 251 + Tests with 224 +Open hearth furnace, Babcock & Wilcox boiler set + for utilizing waste heat from 236 +Open heaters, feed water 111 +Operation of boilers 291 +Optical pyrometers 91 +Orsat apparatus 160 +Oxalate of soda in feed water treatment 106 +Oxygen in air 147 + Flue gases 155 +Peabody draft gauge 255 + Formulae for coal calorimeter correction 188 + Furnace for oil fuel 221, 222 + Oil burner 218 +Peat 167 +Perkins' boiler 24 +Pfaundler's method of coal calorimeter radiation correction 187 +Pipe coverings 315 + Data 308 + Expansion of 315 +Pipe fittings 311 + Flanges 309 + Flow of steam through 317 + Radiation from bare and covered 314 + Sizes 312 + Supports for 315 +Piping, boiler room 308 +Pitting 102 +Plant records, coal 293 + Draft 294 + Temperature 294 + Water 293 +Plasticity of fire brick 302 +Pressed fuels 171 +Priming in boilers 102 + Methods of treating for 107 +Properties of water 96 +Proximate analyses of coal 177 +Proximate analysis 173 + Method of making 176 +Pulverized fuels 170 +Pump, efficiency of feed 112 +Pyrometers, expansion 89 + Mercurial 89 + Optical 91 + Radiation 90 + Thermo-electric 90 +Quality of steam 129 +Radiation correction for coal calorimeter 187, 188 + Correction for steam calorimeter 131 + Effect of superheated steam on 140 + From pipes 314 + Losses in efficiency due to 307 + Pyrometers 90 +Ratio of air supplied to that required for combustion 157 +Reagents, less usual in feed treatment 106 +Records, plant, coal 293 + Draft 294 + Temperature 294 + Water 293 +Requirements of steam boilers 27 + As indicated by evolution of Babcock & Wilcox 45 +Rumsey's boiler 23 +Safety of Babcock & Wilcox boilers 66 +Salts responsible for scale 101 + Solubility of 101 +Sampling coal 271 + Nozzles for steam 134 + Nozzles for steam, location of 134 + Steam 134 + Steam, errors in 135 +Saturated air 149 +Saving by heating feed 110 + With superheat in "Idalia" tests 143 + With superheat in prime movers 140, 142 +Scale (see Thermometers) 101 +Sea water, composition of 97 +Sections, Babcock & Wilcox boiler 50 +Selection of boilers 277 +Sensible heat 84 +Separating steam calorimeter 132 +Sizes of anthracite coal 190 + Bituminous coal 191 +Smoke, methods of eliminating 197 +Smokelessness, relative nature of 197 + With hand-fired furnaces 199 + With stoker-fired furnaces 199 +Soda, lime and, treatment of feed 103 + Oxalate of, in treatment of feed 106 + Removal of scale aided by 300 + Silicate of, in treatment of feed 106 + Treatment of boiler feed 103 +Space occupied by Babcock & Wilcox boilers 66 +Specific heat 83 +Specific heat of air 148 + Ice 99 + Saturated steam 99 +Specific heat of superheated steam 137 + Various solids, liquids and gases 85 + Water 99 +Spreading method of firing 193 +Stacks and draft (see Chimneys) 237 +Stacks for blast furnace gas 228 + Oil fuel 251 + Wood 202, 254 +Stayed surfaces, absence of, in Babcock & Wilcox boilers 69 + Difficulties arising from use of 67 +Steam 115 + As aid to combustion of anthracite 191 + As aid to combustion of lignite 195 + Consumption of prime movers 289 + Density of 115 + Flow of, into atmosphere 320 + Flow of, into pressure above atmosphere 318 + Flow of, through pipes 317 + High pressure, advantage of 119 + History of generation and use of 13 + Making, theory of 92 + Moisture in 129 + Properties of, for vacuum 119 + Properties of saturated 122 + Properties of superheated 125 + Quality of 129 + Saturated 115 + Specific heat of saturated 99 + Specific heat of superheated 137 + Specific volume of 115 + Superheated 137 + Superheaters (see Superheated steam). +Steaming, quick, with Babcock & Wilcox boilers 73 +Stem Correction, thermometer 80 +Stevens, John, boiler 23 +Stevens, John Cox, boiler 23 +Stokers, automatic, advantages of 195 + Babcock & Wilcox chain grate 194 + Overfeed 196 + Smokelessness with 199 + Traveling grate 197 + Underfeed 196 +Superheated steam 137 + Additional fuel for 139 + Effect on condensation 140 + Effect on radiation 140 + Fittings for use with 145 + "Idalia" tests with 143 + Specific heat of 137 + Variation in temperature of 145 + With turbines 142 +Superheater, Babcock & Wilcox 136 + Effect of on boiler efficiency 139 +Supports, Babcock & Wilcox boiler 52, 53 +Tan bark 210 +Tar, water gas 225 +Temperature, accuracy of high, measurements 89 + As indicated by color 91 + Of waste gases 232 + Records 294 +Test conditions _vs._ operating conditions 278 +Testing, boiler, A. S. M. E. code for 267 +Tests of Babcock & Wilcox boilers with bagasse 210 + Coal 280 + Oil 224 +Theory of steam making 92 +Thermo-electric pyrometers 90 +Thermometer scale, celsius 79 +Thermometer scale, centigrade 76 + Fahrenheit 79 + Reaumur 79 +Thermometer scales, comparison of 80 + Conversion of 80 +Thermometer stem correction for 80 +Thermometers, glass for 79 +Throttling calorimeter 129 +Total heat 86, 115 +Treatment of boiler feed water (see Feed water) 102 + Chemicals used in 105 + Less usual reagents in 106 +Tube data 309 + Doors in Babcock & Wilcox boilers 53 + Tubes in Babcock & Wilcox boilers 50 +Ultimate analyses of coal 183 + Analysis of fuels 173 +Unaccounted losses in efficiency 261 +Unconsumed carbon in ash 261 +Units, boiler, number of 289 + Size of 289 +Units, British thermal 83 +Unreliability of CO_{2} readings alone 162 +Vacuum gauges 117 + Properties of steam for 119 +Valves used with superheated steam 312 +Variation in properties of saturated steam 119 + Superheat from boilers 145 +Volume of air 147 + Water 96 +Volume, specific, of steam 115 +Waste heat, auxiliary grates with boilers for 235 + Babcock & Wilcox boilers set for use with 236 + Boiler design for 233 + Curve of temperature, heat absorption, and heating surface 235 + Draft for 233 + Fans for use with 233 + Power obtainable from 232 + Temperature of, from various processes 232 + Utilization of 232 +Water, air in boiler feed 106 + Boiling points of 97 + Compressibility of 97 +Water feed, impurities in 100 + Methods of feeding to boiler 132 + Saving by heating 110 + Treatment (see Feed water). +Water-gas tar 225 + Heat of the liquid 120 + Path of, in Babcock & Wilcox boilers 57 + Properties of 96 + Records 293 + Specific heat of 99 + Volume of 96 + Weight of 96, 120 +Watt, James 17 +Weathering of coal 169 +Webster furnace 55 +Weight of air 147 +Wilcox boiler 25 +Wood, combustion of dry 202 + Wet 203 + Composition and heat value of 201 + Furnace design for 201 + Moisture in 201 + Sawmill refuse 202 +Woolf s boiler 24 +Zero, absolute 81 + + + + +FOOTNOTES + + +[Footnote 1: See discussion by George H. Babcock, of Stirling's paper on +"Water-tube and Shell Boilers", in Transactions, American Society of +Mechanical Engineers, Volume VI., Page 601.] + +[Footnote 2: When one temperature alone is given the "true" specific +heat is given; otherwise the value is the "mean" specific heat for the +range of temperature given.] + +[Footnote 3: For variation, see Table 13.] + +[Footnote 4: Where range of temperature is given, coefficient is mean +over range.] + +[Footnote 5: Coefficient of cubical expansion.] + +[Footnote 6: Le Chatelier's Investigations.] + +[Footnote 7: Burgess-Le Chatelier.] + +[Footnote 8: For accuracy of high temperature measurements, see Table +7.] + +[Footnote 9: Messrs. White & Taylor Trans. A. S. M. E., Vol. XXI, 1900.] + +[Footnote 10: See Scientific American Supplement, 624, 625, December, +1887.] + +[Footnote 11: 460 degrees below the zero of Fahrenheit. This is the +nearest approximation in whole degrees to the latest determinations of +the absolute zero of temperature] + +[Footnote 12: Marks and Davis] + +[Footnote 13: See page 120.] + +[Footnote 14: See Trans., A. S. M. E., Vol. XIV., Page 79.] + +[Footnote 15: Some waters, not naturally acid, become so at high +temperatures, as when chloride of magnesia decomposes with the formation +of free hydrochloride acid; such phenomena become more serious with an +increase in pressure and temperature.] + +[Footnote 16: L. M. Booth Company.] + +[Footnote 17: Based on lime containing 90 per cent calcium oxide.] + +[Footnote 18: Based on soda containing 58 per cent sodium oxide.] + +[Footnote 19: See Stem Correction, page 80.] + +[Footnote 20: See pages 125 to 127.] + +[Footnote 21: The actual specific heat at a particular temperature and +pressure is that corresponding to a change of one degree one way or the +other and differs considerably from the average value for the particular +temperature and pressure given in the table. The mean values given in +the table give correct results when employed to determine the factor of +evaporation whereas the actual values at the particular temperatures and +pressures would not.] + +[Footnote 22: See page 117.] + +[Footnote 23: Ratio by weight of O to N in air.] + +[Footnote 24: 4.32 pounds of air contains one pound of O.] + +[Footnote 25: Per pound of C in the CO.] + +[Footnote 26: Ratio by volume of O to N in air.] + +[Footnote 27: Available hydrogen.] + +[Footnote 28: See Table 31, page 151.] + +[Footnote 29: This formula is equivalent to (10) given in chapter on +combustion. 34.56 = theoretical air required for combustion of one pound +of H (see Table 31).] + +[Footnote 30: For degree of accuracy of this formula, see Transactions, +A. S. M. E., Volume XXI, 1900, page 94.] + +[Footnote 31: For loss per pound of coal multiply by per cent of carbon +in coal by ultimate analysis.] + +[Footnote 32: For loss per pound of coal multiply by per cent of carbon +in coal by ultimate analysis.] + +[Footnote 33: The Panther Creek District forms a part of what is known +as the Southern Field; in the matter of hardness, however, these coals +are more nearly akin to Lehigh coals.] + +[Footnote 34: Sometimes called Western Middle or Northern Schuylkill +Field.] + +[Footnote 35: Geographically, the Shamokin District is part of the +Western Middle Mahanoy Field, but the coals found in this section +resemble more closely those of the Wyoming Field.] + +[Footnote 36: See page 161.] + +[Footnote 37: U. S. Geological Survey.] + +[Footnote 38: See "Steam Boiler Economy", page 47, First Edition.] + +[Footnote 39: To agree with Pfaundler's formula the end ordinates should +be given half values in determining T", _i. e._, T" = ((Temp. at B + +Temp. at C) / 2 + Temp. all other ordinates) / N] + +[Footnote 40: B. t. u. calculated.] + +[Footnote 41: Average of two samples.] + +[Footnote 42: Assuming bagasse temperature = 80 degrees Fahrenheit and +exit gas temperature = 500 degrees Fahrenheit.] + +[Footnote 43: Dr. Henry C. Sherman. Columbia University.] + +[Footnote 44: Includes N.] + +[Footnote 45: Includes silt.] + +[Footnote 46: Net efficiency = gross efficiency less 2 per cent for +steam used in atomizing oil. + +Heat value of oil = 18500 B. t. u. + +One ton of coal weighs 2000 pounds. One barrel of oil weighs 336 pounds. +One gallon of oil weighs 8 pounds.] + +[Footnote 47: Average of 20 samples.] + +[Footnote 48: Includes H and CH_{4}.] + +[Footnote 49: B. t. u. approximate. For method of calculation, see page +175.] + +[Footnote 50: Temperatures are average over one cycle of operation and +may vary widely as to maximum and minimum.] + +[Footnote 51: Dependant upon length of kiln.] + +[Footnote 52: Results secured by this method will be approximately +correct.] + +[Footnote 53: See "Chimneys for Crude Oil", C. R. Weymouth, Trans. +A. S. M. E., Dec. 1912.] + +[Footnote 54: To determine the portion of the fuel which is actually +burned, the weight of ashes should be computed from the total weight of +coal burned and the coal and ash analyses in order to allow for any ash +that may be blown away with the flue gases. In many cases the ash so +computed is considerably higher than that found in the test.] + +[Footnote 55: As distinguished from the efficiency of boiler, furnace +and grate.] + +[Footnote 56: To obtain the efficiency of the boiler as an absorber of +the heat contained in the hot gases, this should be the heat generated +per pound of combustible corrected so that any heat lost through +incomplete combustion will not be charged to the boiler. This, however, +does not eliminate the furnace as the presence of excess air in the +gases lowers the efficiency and the ability to run without excess air +depends on the design and operation of the furnace. The efficiency based +on the total heat value per pound of combustible is, however, ordinarily +taken as the efficiency of the boiler notwithstanding the fact that it +necessarily involves the furnace.] + +[Footnote 57: See pages 280 and 281.] + +[Footnote 58: Where the horse power of marine boilers is stated, it +generally refers to and is synonymous with the horse power developed by +the engines which they serve.] + +[Footnote 59: In other countries, boilers are ordinarily rated not in +horse power but by specifying the quantity of water they are capable of +evaporating from and at 212 degrees or under other conditions.] + +[Footnote 60: See equivalent evaporation from and at 212 degrees, page +116.] + +[Footnote 61: The recommendations are those made in the preliminary +report of the Committee on Power Tests and at the time of going to press +have not been finally accepted by the Society as a whole.] + +[Footnote 62: This code relates primarily to tests made with coal.] + +[Footnote 63: The necessary apparatus and instruments are described +elsewhere. No definite rules can be given for location of instruments. +For suggestions on location, see A. S. M. E. Code of 1912, Appendix 24. +For calibration of instruments, see Code, Vol. XXXIV, Trans., +A. S. M. E., pages 1691-1702 and 1713-14.] + +[Footnote 64: One to two inches for small anthracite coals.] + +[Footnote 65: Do not blow down the water-glass column for at least one +hour before these readings are taken. An erroneous indication may +otherwise be caused by a change of temperature and density of the water +within the column and connecting pipe.] + +[Footnote 66: Do not blow down the water-glass column for at least one +hour before these readings are taken. An erroneous indication may +otherwise be caused by a change of temperature and density of the water +within the column and connecting pipe.] + +[Footnote 67: For calculations relating to quality of steam, see page +129.] + +[Footnote 68: Where the coal is very moist, a portion of the moisture +will cling to the walls of the jar, and in such case the jar and fuel +together should be dried out in determining the total moisture.] + +[Footnote 69: Say 1/2 ounce to 2 ounces.] + +[Footnote 70: For methods of analysis, see page 176.] + +[Footnote 71: For suggestions relative to Smoke Observations, see +A. S. M. E. Code of 1912, Appendix 16 and 17.] + +[Footnote 72: The term "as fired" means actual condition including +moisture, corrected for estimated difference in weight of coal on the +grate at beginning and end.] + +[Footnote 73: Corrected for inequality of water level and steam pressure +at beginning and end.] + +[Footnote 74: See Transactions, A. S. M. E., Volume XXXIII, 1912.] + +[Footnote 75: For methods of determining, see Technologic Paper No. 7, +Bureau of Standards, page 44.] + +[Footnote 76: Often called extra heavy pipe.] + +[Footnote 77: See Feed Piping, page 312.] + +[Footnote 78: See Superheat Chapter, page 145.] + +[Footnote 79: See Radiation from Steam Lines, page 314.] + +[Footnote 80: D, the density, is taken as the mean of the density at the +initial and final pressures.] + +[Footnote 81: Diameters up to 5 inches, inclusive, are _actual_ +diameters of standard pipe, see Table 62, page 308.] + +[Footnote 82: Diameters up to 4 inches, inclusive, are _actual_ internal +diameters, see Table 62, page 308.] + +[Footnote 83: H. P. Jordan, "Proceedings of the Institute of Mechanical +Engineers", 1909.] + +[Footnote 84: "Zeitschrift des Vereines Deutscher Ingenieur", 1909, page +1750.] + +[Footnote 85: Heinrich Grober--Zeit. d. Ver. Ing., March 1912, December +1912. Leprince-Ringuet--Revue de Mecanique. July 1911. John Perry--"The +Steam Engine". T. E. Stanton--Philosophical Transactions, 1897. Dr. +J. T. Nicholson--Proceedings Institute of Engineers & Shipbuilders in +Scotland, 1910. W. E. Dally--Proceedings Institute of Mechanical +Engineers, 1909.] + +[Footnote 86: Proceedings Royal Society, Vol. LXXI.] + +[Footnote 87: Zeitschrift des Vereines Deutscher Ingenieur, 1910, page +1154.] + +[Footnote 88: Proceedings Institute of Engineers and Shipbuilders, +1910.] + +[Footnote 89: Natural or Hyperbolic Logarithm.] + + + + + + +End of the Project Gutenberg EBook of Steam, Its Generation and Use, by +Babcock & Wilcox Co. + +*** END OF THIS PROJECT GUTENBERG EBOOK STEAM, ITS GENERATION AND USE *** + +***** This file should be named 22657.txt or 22657.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/2/6/5/22657/ + +Produced by Juliet Sutherland, Tony Browne, and the Online +Distributed Proofreading Team at http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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