llliWIiiiiliiltlDHHis'llSl'l '")iit3illlllftlliH{i!in'ili JJWjm i M IllllJllliS!::!)!!)!!!;!!!!!!!!]!!!!!!!!!!:!!!!!!;!!!!,,,,;,,,, 'J(/m|Wi.i.Mfl(i!f|ltlltll-212) . While hydrogen in fuel adds materially to its heating value, it also increases the necessary loss due to the escape of super- heated steam and thereby lowers the efficiency. Other factors being equal, a fuel with low hydrogen content would be desir- able from the standpoint of most efficient combustion. In spite of the fact that the moisture content is also responsi- ble for a loss of heat, many fuels can be more satisfactorily burned by the addition of from 3% to 5% surface moisture. This is not due to any chemical action of the moisture but to its effect on the nature of the fuel bed. This matter will be referred to in detail later. Combustible Discharged at the Ash Pit. The heat loss due to the presence of combustible in the ash pit is usually over estimated. A comparatively small percentage of unburned carbon is plainly visible and may appear to represent a much 14 MECHANICAL STOKERS larger loss than actually exists. The loss per pound of coal as fired may be calculated from the following formula : , _ (% refuseX% Gin refuse) 100 ~~' in which H = calorific value of carbon and h = heat loss per pound of coal as fired. Sensible Heat in the Ash Pit Refuse. The hot ash and refuse carry a certain amount of sensible heat away from the furnace. The specific heat of the refuse is about .28 and the loss from this source would be represented by the follow- ing equation: T X.28X% refuse per Ib. of coal 100 The temperature at which the refuse is discharged varies considerably with different methods of firing but in most cases, averages from 1500 to 2000 F. Soot and Cinders Deposited in the Gas Passages or Carried Away by the Chimney Gases. In a well designed and properly operated furnace, the fuel loss due to soot accumulations is negligible. With poor design and improper operation, dense clouds of black smoke may be discharged and a small amount of carbon in the form of soot is thus lost but it is doubtful if this loss ever reaches 1% of the fuel. The large loss of which dense smoke is the visible sign, is not due to the particles of soot discharged but to the incomplete combustion of the hydro- carbons. It is well known that a rapidly moving current of air or gas will carry in suspension particles heavier than air, espe- cially if they are small. In this manner cinders are carried over into the boiler passes and breeching and are deposited at points where there is a sudden change in the direction of flow or a reduction in velocity due to increased crossed section of the gas passage. . The lighter particles being held in suspen- sion the longest, are discharged to the atmosphere with the chimney gases. PRINCIPLES OF COMBUSTION 15 The loss due to cinders may be as high as 2% of the total coal fired, especially when furnaces are operated at high capacities and gases are traveling at high velocity. Radiation and Miscellaneous. The radiation from furnace and boiler brickwork depends very largely upon the construc- tion of the furnace walls. At one time it was believed that this loss could be materially reduced by leaving an air space in the center of the walls but it has been found by careful experi- ments that the radiation across this air space actually increased the loss, and that filling the air spaces with sand or cinders resulted in a substantial decrease. The temperature of a furnace wall will not increase in direct proportion to the rate of burning fuel and since the area of radiating surface is constant, the per cent of the total heat which is lost by radiation thereby decreases as the rating is increased. When a boiler is banked the amount of fuel required to keep it in a standard condition is sometimes referred to as radiation loss, but this is not correct for the reason that under such conditions the fuel required to maintain the banked con- dition is burned very inefficiently and only a small part of the heat apparently generated is actually available. The leakage of cold air through cracks in brickwork and through the brick itself is often a source of considerable loss, especially where the brickwork is unprotected and the boilers are operated with a high draft throughout the setting. CHAPTER II MECHANICAL STOKERS From the time that coal was first fired on a grate, there seemed to be a pretty good understanding that the factors effecting the proper burning of coal were : (a) A continuous feed of coal. (b) Proper proportion of air and a mixture of air and gases. (c) High temperatures. It was, therefore, the ambition of most inventors in the early history of coal-burning devices, to conceive of some combination of things that would provide these conditions and thus lead to the burning of coal without smoke. D. K. Clark, in his excellent treatise "The Steam Engine," gives some very interesting history of smoke contrivances that came from ambitious inventors in the early days a review of some of the most important ones is interesting, as leading up to the mechanical feeding of fuel to furnaces, SMOKE-PREVENTION CONTRIVANCES Watt 1785 (English}. James Watt, the inventor of the steam engine, conceived the idea that the volatile gases of coal should be distilled slowly, and in one of his first furnaces (Fig. 1), the coal was piled up at the front of the grate and then gradually pushed farther towards the rear, giving the volatile gases a chance to distill slowly. The coal piled up in front served to shut off excess air admittance to the furnace. Robertson 1800 (English}. J. and J. Robertson thought it was necessary to admit air over the fire in order to completely burn the volatile gases. Their invention covered the admission of a sheet of air immediately over the coking part of the fuel 16 MECHANICAL STOKERS 17 bed (Fig. 2). It is interesting to note that this patent involves a coal hopper, a fuel-burning structure and a refuse disposal space; these are fundamental ideas and were later worked out FIG. 1. Watt's Smokeless Furnace. and developed in connection with the design of mechanical stokers. Wakefield1810 (English). John Wakefield had the same general idea that air was required over the fuel bed for smoke prevention and worked out the idea of passing air through a FIG. 2. Robertson's System, hollow bridgewall, thus heating the air before admitting it (Fig. 3). This appears to be the first idea of admitting air over the fire at a point near the bridgewall. Gregson 1816 (English) Gregson, in 1816, used piers or bridges in a furnace, in order to obtain a mixture of the gases 18 MECHANICAL STOKERS (Fig. 4). By the installation of two bridgewalls, the gases from the fuel bed were made to separate, part passing over the bridge and part underneath, and then coming in contact again with FIG, 3, Wakefield's System. an air admission before passing underneath the second bridge- wall. This is probably the first idea of using bridges or piers for mixing and intermingling gases, and was used quite success- FIG. 4. Gregson's System. fully in later years in hand-fired furnaces for smoke prevention. Witty 1828 (English). R. Witty, it appears, had the first idea of using the gas-producer effect in burning coal. Coal was MECHANICAL STOKERS 19 admitted slowly, and a deep well provided in which, the fuel was burned (Fig. 5). The volatile gases were made to pass upward over an incandescent fuel bed and, in this way, main- tained high temperatures. It is said that this system failed on account of lack of air supply for the volatile gases. Shanter 1834 (English}. John Shanter, following a similar idea of Gregson, used an inverted arch back of the bridgewall, and in combination with this, admitted air back of the bridge- wall endeavoring to obtain a proper mixture of air and gases. FIG. 5. Witty's System of Furnace. Gray and Shanter 1835 (English). Gray & Shanter patented a system of two grates, one inclined for coking the coal, and the other for burning the fixed carbon. The coal, when the gases were distilled, was pushed back on the second grate. This is probably the fundamental idea of a down draft furnace that was used quite successfully in later years. Rodda 1838 (English). R. Rodda followed the same idea as Gregson, using an inverted arch in the center of the grate. In order to obtain a proper mixture, the air and gases were forced underneath this bridge. 20 MECHANICAL STOKERS Williams 1839 (English}. C. "Wye Williams used an Argand blower to obtain a mixture of air and gases (Fig. 6). Air was introduced behind the bridgewall in finely divided streams, either by driving air through perforated pipes, or through perforated plates. In some of his patents, an ingenious idea for admitting air over the fire was obtained by taking out the center grate bars of a furnace and installing a perforated plate so that air could be admitted about 3 in. over the fire. This was very effective and streams of fire seemed to come from the orifices of this plate. FIG. 6. Williams' System. Prideaux 1853 (English}. T. S. Prideaux is probably the first one who conceived the idea of automatically admitting air through the fire doors after each charge of fuel. In the fire front, valves were used and controlled by hand levers, so that when opened, a full charge of air was admitted, and, by means of water cylinders, the system of valves and levers gradually fell and shut off the air. Langen 1862 (English). Langen developed the idea of an inclined stepped grate wherein the coal was pushed from one grate to another until completely burned (Fig. 7). This is a fundamental idea that probably led to the development of a stepped grate mechanical stoker. Barber 1881 (English). From the present knowledge of the requirements for burning coal without smoke, the early inventors were working under a serious handicap since all of MECHANICAL STOKERS 21 the contrivances were installed in connection with internally- fired boilers. FIG. 7. Langen's Stepped Grate. FIG. 8. Barber's Stepped Furnace. Barber's stepped furnace (Fig. 8), seems to be the first instance where an extended firebrick combustion chamber is used providing proper distance between the fuel bed and the 22 MECHANICAL STOKERS cool surfaces of the boiler. In all previous contrivances up to this time, the grate was placed very close to the cool surfaces of the boiler, and the gases had very little time in which to burn. No doubt, this application feature was the reason for so many of the early contrivances failing insofar as smoke abate- ment was concerned. MECHANICAL FEEDING OF COAL TO FURNACES The many attempts to fire coal by hand, and to burn it with- out producing smoke led to an endeavor to mechanically produce the conditions necessary for proper combustion. This development work seemed to be along the lines of pro- ducing these conditions by means of a traveling grate, an inclined grate or a screw conveyor. Thus, the fundamental principles of the present forms of traveling grate, overfeed and underfeed stokers, were established. The principle of the traveling grate stoker is to deposit the fuel from suitable hoppers on a grate that moves slowly inward. The coal is first ignited and the volatiles driven off and progres- sing farther inward on the same grate, the fixed carbon is con- sumed. Air is admitted through the grates. At the end of the grate travel, at the rear of the furnace, the ash is dumped into a pit. In the overfeed stokers, the coal from suitable hoppers is pushed in by mechanical means onto a coking plate where the volatile gases are distilled. The grate bars are inclined and given a movement and, aided by gravity, the fuel progresses over the grate and the fixed carbon is consumed. Air is admitted through the grates. The ash is collected at the bottom of the incline and there dumped into the ash pit periodically or crushed by ash grinders. In the underfeed type of stoker, the coal is forced by mechani- cal means into a magazine or retort extending into the furnace. The coal is then pushed upwards into the incandescent fuel bed. Air under pressure is forced through the fuel bed. Ash is collected on plates at the side of the retorts or on dump grates at the rear of the furnace and periodically dropped into the ash pit. MECHANICAL STOKERS 23 TRAVELING GRATE STOKERS Brunton 1819 (English). The first mechanical stoker was brought out in England in 1819 by Wm. Brunton. This was a traveling grate stoker consisting of a circular grate revolving on a vertical spindle. The coal was fed to the grate from a suitable hopper, and as the grate gradually revolved, the volatile gases were distilled slowly, and finally the fixed carbon was consumed and ash and refuse pulled from the grate. FIG. 9. Jukes' Chain Grate Stoker of 1841. Bodmer 1834 (English). The first traveling grate that moved from the front of the boiler inward to the bridgewall was brought out by Bodmer in 1834. The grates moved slowly inward and were then dropped and returned to the front on rails or by means of screws. In the forward movement, the bars by setting in spiral screws were given a reciprocating move- ment, the aim being to break up the caking fuel bed. Jukes 1841 (English). The original traveling chain grate stoker was brought out in England by Jukes in 1841 (Fig. 9). The principle of this stoker was a number of longitudinal bars connected together to form an endless chain. This moved slowly 24 MECHANICAL STOKERS from the front of the furnace inward towards the rear, the coal being deposited on the grate from a suitable hopper and moving inward on the grate, the volatile gases were distilled slowly. The ash was dropped over the rear of the grate. Weller 1871 (American). The earliest record of a travel- ing grate stoker in America was that brought out by Royal F. Weller in 1871 (Fig. 10). In this grate, the Jukes principle was used with the exception that the arrangement of the bars 1 1 )4r' L _ L. _. L J_ n rH- - T-; : rf " *! 9\ t=i. r r' V T - ^ ; 3 -M- u FIG. 10. Weller Traveling Grate Stoker. were made transversely instead of longitudinally. Each of the bars strung transversely across the furnace were fastened to- gether by links and, in this way, an endless chain was made. Coxe 1893 (American). E. B. Coxe employed many novel features in a chain grate stoker, the most important of which were the method of air distribution and the design of the grates for burning small sizes of anthracite coals. MECHANICAL STOKERS 25 OVERFEED STOKER Hall 1845 (English). Probably the first attempt to mechanically feed a furnace fire by means of inclined grate bars was brought out by Hall in 1845 (Fig. 11). Fuel was supplied from a hopper, in back of which channels were left for admitting air over the fire. The fuel was pushed onto inclined reciprocat- ing grate bars. This original inclined overfeed stoker had the same general design principles as the present-day types, namely, a hopper for feeding fuel, an inclined grate for burning the fuel, and a sliding shelf for disposing of ash and refuse. Vicars 1867 (English) .This development of the inclined grate stoker is interesting in that coal was fed onto grate bars FIG. 11. Samuel Hall's Smoke-preventing Apparatus. by means of plungers (Fig. 12), and the inclined grate bars were given a reciprocating motion to slowly advance the fuel. This stoker was used extensively in England. McDougall 1880 (English). This stoker covered the most complete combinations of the elements making up an inclined grate stoker. The coal was fed from suitable hoppers, being pushed onto a coking plate which projected somewhat into the furnace. Air was admitted over the fire at this point. The stroke of the rams feeding fuel into the furnace could be varied. The grate bars were given a reciprocating movement that gradually fed the fuel from the front of the stoker inwards. An arch was used for ignition purposes. Ash and refuse were collected on grates at the bottom of the furnace. 26 MECHANICAL STOKERS Murphy 1878 (American). Thomas Murphy brought out a complete new design of an inclined grate stoker (Fig. 13). This was probably the first American stoker that did not have some resemblance to former English patents. It, therefore, stands distinct as a combination of elements necessary for pro- FIG. 12. Vicar's Reciprocating Bar Stoker. ducing conditions for proper combustion of coal. In this stoker, the fuel was fed onto grates from each side of the furnace, the grates being inclined towards the middle of the furnace so as to form a V-shaped cross section. A combustion arch was used extending across the grates above the end of the V. Arch chan- nels were provided above the coking portion of the fuel bed for air admission for combustion of volatile gases. The grate bars MECHANICAL STOKERS 27 were given a reciprocating motion for breaking up the caking fuel bed. Ash and refuse were disposed of by means of a grinder located at the bottom of the V-shaped bars. Honey 1885 (American}. Win. R. Roney brought out a front inclined grate stoker which, although having the basic principles of some of the early English patents, was distinctive as to construction details (Fig. 14). In this stoker, coal was fed from a hopper to a coking plate, and from there, by means of FIG. 13. Murphy's Patent Smokeless Furnace. gravity and rocking of the grate bars, the fuel bed progressed to the bottom of the furnace, depositing the ash on the dumping grates. At certain intervals, these dumping grates were dropped and the ash and refuse deposited in a pit. Bright man 1885 (American). About the same time that the Roney stoker was brought out, "William Brightman patented a front inclined stoker which was distinctive as regards to the construction of the grate bars, but had the fundamental prin- ciples of the earlier forms of the inclined stoker. 28 MECHANICAL STOKERS Wilkinson 1890 (American). Wilkinson brought out .a dis- tinctive, front inclined, stoker in that air was drawn in by steam jets, through hollow grate bars. It was designed par- ticularly to burn small sizes anthracite coals. Coal was fed onto the grates by a pusher from a suitable hopper. The grate bars were inclined and given a reciprocating movement. FIG. 14 William R. Honey's Original Stoker, UNDERFEED STOKER Holyrod-Smith (English). The first English patent which brough forth the underfeed principle was that of Holyrod- Smith. The fuel was fed from a hopper into a horizontal trough lying across the front of the furnace. From this trough, the coal fell into three longitudinal troughs, placed at right angles and passing into the furnace. By certain construction of the screw conveyors in the troughs, the coal was lifted up into the burning fuel and onto perforated side castings through which air was admitted. Jukes 1838 (English). The same inventor of the traveling grate stoker also brought out a stoker involving the principle of underfeeding (Fig. 15). Coal from a hopper dropped in front of a ram. A forward movement forced the coal into a retort and underneath the burning fuel. During this process, the volatile MECHANICAL STOKERS 29 gases were distilled, and the fixed carbon burned on fuel sup- porting grates. Frisbie 1844 (American). Following the underfeed prin- ciple, Frisbie patented an underfeed stoker in which fuel was FIG. 15. Jukes' Underfeed Stoker of 1838. fed from beneath through a central aperture. The coal was fed into a hopper or box swinging on pivots. When the box was in place, a vertical movement of a plunger pushed the coal upward into the center of the fuel bed. When the box was FIG. 16. The First Coal-burning Jones' Underfeed Stoker. empty and placed aside for refilling, a sliding plate closed the central aperture. Jones 1889 (American). Evan Jones brought out a success- ful underfeed stoker which, with development changes in details, is still being used successfully (Fig. 16). 30 MECHANICAL STOKERS This stoker consisted of a hopper and plunger for feeding coal, and a retort extending into the furnace. Coal was forced forward, by means of the piston or ram, carrying a portion of the coal in the hopper to the furnace, and underneath the fuel bed. Air under pressure was forced into a sealed ash pit from there through tuyeres to the incandescent portion of the fuel bed. Wood 1898 (American}. W. R. Wood brought out the American stoker. In principle, it was of the single retort type FIG. 17. Early Form of the Taylor Underfeed Stoker. but used a spiral screw for feeding coal from the hopper to the retort and forcing it up into the fuel bed. Taylor 1903 (American). Most of the early underfeed stoker inventions provided a single retort where the coal from the retort was distributed on dead plates and the ash and clinker pulled from the fire, through suitable doors in the front. Taylor brought out an underfeed stoker, which was distinct, in that a series of inclined retorts were used, being placed about 22 in. apart (Fig. 17). Gravity was resorted to in the MECHANICAL STOKERS 31 progress of the fuel from the coal hopper to the refuse disposal plate at the bottom of the inclined retorts. Coal was forced into the furnace by plungers, and air admitted at pressure through tuyeres. DEVELOPMENT OF MECHANICAL STOKERS All of the early forms of mechanical stokers showed progress in mechanically burning fuel, but still there were many operat- ing faults and, consequently, some skepticism as to the advis- ability of installing them. Many of the earlier forms of stokers were applied to internally-fired boilers, and there were many application problems. In the United States, the development of the steam engine, turbines and other prime movers naturally required an improvement in the character of firing coal in order to obtain better results. In the application of stokers, a proper conception of their scope, benefits and limitation must be known, but in the device itself there are five good reasons for their extended use and development, these being (1) To prevent smoke; (2) To conserve coal; (3) To produce conditions neces- sary for the most economical combustion of coal; (4) To save labor, and (5) To save equipment and investment. (1) Smoke Prevention. The factors effecting smoke pre- vention are : (a) Continuous feed of coal. (b) Volatile gases to be distilled slowly. (c) Mixture of gases and air. (d) Proper firebrick combustion chamber for maintaining proper temperature. The mechanical stoker now does all of these things well and uniformly. It feeds the coal with mechanical regularity to a coking zone of the fuel bed. The volatile gases are distilled slowly. It is not necessary to feed coal to the fires by open- ing doors as in hand-firing, resulting in a reduction of furnace temperatures. The elimination of smoke by hand-firing de- pends too much on the human element. The character of manual labor that is now commercially available in boiler 32 MECHANICAL STOKERS rooms falls considerably short of the expertness required for smoke abatement when coal is fired by hand. (2) Coal Conservation. The principle of coal conservation is the transforming into useful work every pound of coal that is mined. The mechanical stoker now does this better than hand-firing, "With the proper stoker, a poorer and lower grade of fuel can be burned. Years ago, fine slack coal was without a market, because it could not be used successfully on a hand-fired grate. The stoker has been developed and now handles this coal suc- cessfully. Many plants in the United States today are using the richest coal (i. e., high in heat value, low in ash and sulphur), for industrial purposes on hand-fired grates, when low-grade coal should be used and the richest coal saved for other pur- poses where the poorer grade fuel cannot be used. (3) Producing Conditions Necessary for the most Eco- nomical Combustion of Coal. The factors effecting the proper burning of coal are : (1) Fuel feed. (2) Fuel burning. (a) Structure. (b) Air admission. (3) Ash disposal. The mechanical stoker has been developed to feed the fuel to the furnace by means of plungers or pushers with mechani- cal regularity. In this way, the volatile gases are distilled slowly, and there is sufficient time to admit the proper air for combustion. In a properly-designed stoker, the fuel bed has a progressive movement by means of traveling grates or mov- able grates, and it is not necessary to open doors to rake the fires. Air can be admitted at different zones of the fuel bed to burn the remaining combustibles. The mechanical stoker meets load conditions better than hand-firing, for the reasons that the air admission can be adjusted to suit fuel bed conditions, and the rate of fuel feeding can be altered to meet rapid required changes n steam demands. In the stoker, the fires are either cleaned continuously or by dropping ash at the rear of the grates periodically. MECHANICAL STOKERS 33 (4) Labor Saving. The factors effecting labor saving are : (a) Installation of machinery. (b) Intelligent supervision. In any industry, labor is saved by the introduction of machinery. With the introduction of mechanical stokers, labor is saved just as soon as the requirements of the plant exceed the amount of coal that one man can fire by hand. The amount that labor can be reduced depends on the size of the plant. A greater saving is made possible by the introduction of stokers, together with coal and ash-handling machinery. In one installation, twelve boilers were hand-fired by eight fire- men and a water tender. With the installation of stokers, coal and ash-handling machinery, this was reduced to two men and a water tender. The installation of mechanical stokers generally results in the use of a better class of labor in the boiler room, and con- sequently, a more intelligent supervision of that labor. (5) Saving in Equipment and Investment. The factors effecting a saving in boiler-room equipment are : (a) Capacity of equipment. (b) Flexibility of equipment. (c) Economy of equipment. With the introduction of modern mechanical stokers, coal can be burned at rates of 60 to 70 Ibs. per sq. ft. of grate area per hour, and this can be done with little loss in efficiency. This is impractical with hand-firing which rarely exceeds 25 Ibs. per sq. ft. per hour and means that with the installation of stokers, the number of boilers in a particular installation can be reduced when compared with a hand-fired installation. In order to meet the sudden demands for steam, it is only necessary to increase the coal-burning rate of the stoker equipment already in service. With hand-firing which does not have this degree of flexibility, it is necessary to put additional boilers on the line, and this cannot be done in time to meet sudden demands for steam. With modern stokers, boilers can be operated from 50% to 300 % of boiler rating within a range of 15% efficiency. This flexibility is not obtained with hand-firing. 34 MECHANICAL STOKERS PRESENT TYPES OF MECHANICAL STOKERS IN THE UNITED STATES The principal stokers now in use in the United States can be divided into the Chain Crate, Overfeed and Underfeed types. The names of the most prominent stokers are : Traveling or Chain Grate B. & W Manufactured by Babcock & Wilcox Co. Burke " " Burke Furnace Co. Coxe " ' ' Combustion Engineering Corp. Green ' ' " Green Engineering Co. Harrington ' ' " James A. Brady Foundry Co. Illinois " " Illinois Stoker Co. LaClede-Christy ' ' ' ' LaClede Christy Clay Prod. Co. McKenzie " ' ' McKenzie Furnace Co. Playf ord " " Eosedale Foundry & Mach. Co. Stowe " " LaClede Christy Clay Prod. Co. Westinghouse " " Westinghouse Elec. & Mfg. Co. Overfeed Detroit Manufactured by Detroit Stoker Co. Model ' ' " Automatic Furnace Co. Murphy " " Murphy Iron Works Eoney ' ' " Westinghouse Elec. & Mfg. Co. Wetzel " " Wetzel Stoker Co. Underfeed (Multiple Retort) Jones A. C Manufactured by Underfeed Stoker Co. of America Eiley " ' ' Sanf ord-Eiley Stoker Co. Taylor " American Engineering Co. Westinghouse " ' ' Westinghouse Elec. & Mfg. Co. Underfeed (Single Eetort) Jones Manufactured by Underfeed Stoker Co. of America. Type ' ' E " " " Combustion Engineering Corp. Eoach ' ' " Eoach Stoker Co. Detroit " " Detroit Stoker Co. Sturtevant < < B. F. Sturtevant Co. CHAIN GRATE STOKERS Babcock & Wilcox Chain Grate. This stoker operates on natural draft. The chain (Fig. 18) is made up of common and MECHANICAL STOKERS 35 driving links about 9 in. long with vertical air spaces. The links are spaced and held together by a steel rod passing through solid hubs. The chain passes over sprocket wheels at the front and rear of the grate, these being keyed to steel shafts. The shafts run in cast-iron bearings mounted in rectangular guides at the rear of the cast-iron side frames. Adjustment is pro- vided by means of screws for both front and rear bearings. Such adjustment makes possible the taking up of sag in the chain. The upper part of the chain is supported on rollers spaced 9 inches apart, and the lower portion on rollers spaced 18 inches FiG. 18. Babcock & Wilcox Chain Grate Stoker. apart. These rollers are of wrought-iron pipe, to the ends of which cast-iron bushings are fitted. The bushings run on stationary wrought-steel axles extending from side to side on the grate and supported by the cast-iron frames. The side frames are flush with the top of the grate. The inner sides of the flush portions form a guide against which the side links of the chain rub. At the outer edges of the side frames, side seals are provided for exclusion of air at the sides of the furnace. These seals are held by weighted levers against the under surface of cast-iron side plates which are built into the brickwork and overhang the side frames of the stoker. The side frames are maintained at a proper distance from each other by means of steel spacing bolts front and rear, and 36 MECHANICAL STOKERS a cast-iron cross beam at the front, a wrought-steel channel at the front, a second wrought-steel channel between the chains at the front, and a third wrought-steel channel between the chains at the rear. Diagonal rods from side to side maintain the frames at right angles to the cross ties and shafts. The frame is mounted on four track wheels of cast iron, 18 inches in diameter, running on steel axles so that the stoker can be withdrawn from the furnace. The chain is about level from front to rear. This last wrought-steel channel forms a part of the baffle at the rear of the stoker for excluding the air from this space. Below the channel a steel plate baffle forms an additional spacing piece. Hinged to the bottom of this stationary baffle plate a swinging steel plate, stiffened by angles, extends to the bottom of the ashpit between the stoker rails, completing the seal at the rear. A coal hopper is formed at the front by the cast-iron hopper ends and by an inclined steel plate. A coal gate, sliding vertically in removable guides bolted to the inner surface of the cast-iron hopper end pieces, furnishes a method of regulating the thickness of the fuel bed as fed to the forward end of the grate. The height of this gate is regulated by a hand wheel through a worm wheel and cross shaft, which raises or lowers the chains from which the gate is hung. The inner surface of this gate is lined with special shaped firebrick. The front sprocket shaft is driven by a cast-iron worm wheel. This worm wheel engages a cast-iron worm secured to a worm shaft on the inner end of which is keyed one of a pair of mitre gears. Another mitre gear which engages this is actuated by a ratchet wheel. Long and short tool steel pawls drive this ratchet wheel from a cast-iron ratchet arm. A second pair of tool steel pawls prevents the ratchet wheel from mov- ing backward. The driving mechanism is encased with a cast-iron hous- ing. The ratchet arm is driven from an eccentric rod, the radius of whose attachment to the ratchet arm may be changed to increase or decrease the amount of feed for each revolution MECHANICAL STOKERS 37 of the eccentric. A spring safety stop in the eccentric rod limits the power which may be transmitted from the eccentric, to prevent breakage in case any foreign object blocks the motion of the stoker. A stoker water box is a part of the standard stoker equip- ment. At the bridgewall, a bridgewall water box of forged steel T 1 /^ in. square outside, is carried transversely across the end of the stoker. The water box acts as an air seal at this point. The water box is connected into the circulation of the boiler by boiler tubes expanded into counterbored seats. A sprung arch, made up of standard firebrick shapes, is generally used in connection with this stoker. Burke Traveling Grate. This stoker uses natural draft for its operation. The grates are made up on a bar which are connected at the end to endless chains that operate around sprockets at the front and rear of the stoker. The hopper ends are supported in front. An adjustable gate at front gives the desired thickness of fuel bed. The front sprockets are driven by a nest of spur gears which are operated from a line shaft. Ignition arches are used with this stoker as well as water backs at the rear. Coxe Traveling Grate. This Stoker is designed to burn the small sizes of anthracite coal. (Fig. 19.) The fuel supporting surface consists of a number of parallel grate bars which are connected to endless chains forming an endless moving grate. Provision is made for introducing air under pressure under the grate with means for proportioning the volume and pressure of air under different parts of the fire as may be necessary. Ignition and combustion arches are used over the grate to insure ignition. Coal is fed to a hopper extending across the front end of the stoker above the grate from which it is deposited on the grate, the thickness of the fuel in the grate being regulated by an adjustable coal gate. Ignition takes place and combus- tion is supported by forced draft under the grates. There are three or four air compartments (Fig. 20) each extending cross- 38 MECHANICAL STOKERS wise of the furnace, in each of which the air pressure may be independently regulated. The stoker weighs approximately 450 Ibs. per square foot of active grate surface. The side frames on which practically FIG. 19. End View of Coxe Traveling Grate Stoker. FIG. 20. Elevation and Perspective of Coxe Traveling Grate Stoker. the entire weight of the stoker is carried are iron castings of channel cross-section about 34 inches high with four-inch flanges. These frames carry on each end the shaft bearings or boxes for the driving shaft at the rear end and idler shaft at the front end. MECHANICAL STOKERS 39 Access to each tuyere box is made through a cast iron door located outside of boiler setting. The fuel supporting surface is made up of keys or grate tops which are small castings approximately %" wide, 8" long and 2" deep. The top surface is curved, and the front end of each key matches the real end of the next key. The chains are made of drop forgings held by steel pins. The chains are carried over sprockets at the front and rear ends of stoker returning under the floor of the air compart- ments. The rear shaft is the driving shaft and extends through FIG, 21. Green's " K " Type Chain Grate Stoker. the side wall of boiler where it is keyed to a cast iron worm wheel mounted in a cast iron enclosed gear case. Green Chain Grate. Open hub links with vertical air spaces are used on this stoker type "K" (Fig. 21) in making up the chain except those links which hold the chain together. Flat- tened cross bars are used instead of round and the link designed so that if the rod is turned on its edge the links can be removed individually. The chain passes over sprockets at the front and rear; adjustment for the chain being provided for at the rear. The upper part of the chain is supported by pipe rollers which, in turn, are supported by the side frames. The upper edges of these frames are set well below the top of the links, 40 MECHANICAL STOKERS this design being used to keep the frame away from the high furnace temperatures. Air seals are provided at the rear by accumulation of ashes on the rear girder. This girder, in connection with the pipe rollers, form the air seal. The side frames are maintained in their proper position by spacing beams, one at the front and one at the rear. In all wide stokers, a center support is used for the front and rear sprocket shafts and the upper roll shafts. Diagonal bars are used to keep the frames at right angles. The frame is mounted on four track wheels so the stoker can be withdrawn from the furnace. The coal hopper is formed of cast iron hopper ends and a sheet steel front plate. The feed gate is supported from a square shaft and moves between vertical guides, and is adjusted by a worm and sector attachment on the hopper end. The inner surface of the gate is lined with firebrick tile of special shape, and designed so that each tile can be removed individu- ally. The front sprocket shaft is driven by a ratchet, cast steel pawl and cast steel gear train, babbitted in a self-contained frame which is bolted to the stoker front side frames. The ratchet is operated from an eccentric on the main driving shaft, the eccentric rod being provided with a safety spring in case the grate is blocked for any reason in its motion. A high pressure water box is used with the stoker at the bridgewall. The water box is connected into the circulation of the boiler by boiler tubes. An ignition arch of the suspended type is used at the front of the stoker; specially formed firebrick tile being suspended from I-beams. The stoker operates on natural draft. "L" TYPE GREEN STOKER This company also make the "L" Type stoker (Fig. 23) the important difference from the "K" Type being a fuel pusher and inclined coking plates in front of the chain grate. These inclined plates are designed to keep fuel broken up MECHANICAL STOKERS 41 during the first period of burning, and delivering it to the chain without large, unmanageable masses of coke. After the coal is coked on the front part of the stoker then combustion is completed upon the plain chain grates. The Fuel Pusher is made as wide as the hopper. It is operated through an adjustable stroke giving a positive means of controlling the fuel bed. In this way the fuel bed is varied. The driving mechanism of the pusher plates is independent of the chain drive and of the coking plate agitators. FIG. 22. Front View Green " L " Type Chain Grate Stoker, To maintain uniform density in the fuel bed during the coking process, the fuel pushers are provided with small adjust- able sections each 12" wide. The inclined coking plates form an inclined grate area between the fuel hopper and the chain grate. Agitation is given to the coking plates to keep the fuel particles in motion. The rear cross girder of this stoker is a semi-steel box maintained at low temperature by water circulation. It is de- signed to hold the stoker frame square and true. The chain is kept at tension by worm gearing in cast iron 42 MECHANICAL STOKERS casings. These are interconnected and can be adjusted from the side. A water cooled surface is placed in the wall adjacent to the coking plates to prevent clinker adhesions and erosion of brick work. A coking or ignition arch is used over the front part of the stoker. This arch is of special design of suspended type. High pressure water backs are used at the rear connected up to the boiler circulation. The stoker can be operated on either natural or forced draft. FIG, 23, Green's " L " Type Chain Grate Stoker. Illinois Chain Grate. Natural draft is used with this Type "A" stoker (Fig. 24). The links are about 9" long, solid, and held together by link rods. The spaces in the link through which air passes to the fuel bed are placed at an angle and when the chain is assembled the angles of adjacent links cross each other. This design has been used in an attempt to reduce the sifting of fine coal, through the air spaces, to a minimum. The chain is slightly inclined from front to rear. The chain passes over sprocket wheels at the front and rear. The rear sprockets are loose on the shaft. The front driving sprockets engage small rollers that are placed in between the MECHANICAL STOKERS 43 links. This construction differs from designs where the driv- ing sprockets engage the links. Adjustment of the chain is provided by means of take-up screws at the front of the stoker. The rollers upon which the chains travel are spaced about 12 in. apart, the roller rods being supported by side frames which are cast in a single piece, that is, the hopper supports and rear frames are one piece. The frames are held together by two cast-iron girders, one at each end, and diagonal tie rods from side to side maintain the frames at right angles. Air seals are placed at the rear of the frames. FIG. 24. Type " A " Illinois Chain Grate Stoker. The hopper ends are supported from the side frames, as shown in Fig. 25. The adjustable gate to give the desired thickness of fuel bed, is operated by a hand wheel at the side of the stoker which is connected to a shaft extending across the stoker by means of a worm and gear design. The gate is gradually raised or lowered. The inner surface of the gate is lined with special-shape firebrick. The front sprockets are driven by a worm which engages a pawl and ratchet wheel operated by the eccentric on the drive shafting. The speed of the grate is varied from one to five inches per minute by moving a hand lever forward or back- ward, thus controlling the number of teeth on the ratchet wheel that the pawl engages at each stroke. 44 MECHANICAL STOKERS A low pressure water box made up of wrought iron pipe is generally used at the bridgewall. A suspended fire brick arch is used, made up of special shaped blocks and suspended over the stoker. This company also manufactures a Type "G" (Fig. 25) forced draft chain grate stoker. The important feature of which is the system of dampered air control. Air required for combustion is delivered to a wind box which is incor- porated in the side wall of the setting. The dampers for air admission to different parts of the grate surface are operated J FIG. 25. Type " G ' ; Illinois Forced Draft Chain Grate Stoker. from the side. The wind box is usually made of concrete and is the base of the side wall. Baffles are used so that air cannot pass through to the end of the grate. The mechanical opera- tion of this stoker is practically like the Type "A" stoker, having sprockets in front which are connected to a worm wheel and worm attached to the end of the front sprocket shaft. Rear drums are used similar to the Type "A" stoker. An arch is used for ignition purposes. Laclede- Christy Chain Grate. The links of this stoker (Fig. 26), are all of the same design with the exception of the side links. They are about 9" long with the air spaces at an angle. Cast iron rollers are placed on the link rods in MECHANICAL STOKERS 45 between the links and act as spreaders, and also engage the front sprockets. The chain in slightly inclined from front to rear. The chain is driven by the front sprockets, keyed onto the shaft. The rear end of the chain passes over idler pulleys which are loose on the shaft. Take-up boxes are located at the front of the stoker. The side frames are made of two pieces, the front part being bolted to the rear part. These side frames are held together by rods and pipe spacers and diagonal bracing, the FIG. 26. Laclede-Christy Chain Grate Stoker. chain being supported on the pipe rollers, one at the top of the frame and one at the bottom. The entire frame is sup- ported on four cast-iron flanged wheels which fit T-rails so that the stoker can be withdrawn. The feed gate is adjusted by two hand wheels, one on each side of the stoker, and regulate the thickness of the fuel bed from V to 10". The inner surface of the gate is lined with special shape firebrick blocks having rounded ends where the coal is admitted. Air seals are placed near the rear idler wheels and a second damper which can be regulated, placed 24" to the front of the rear seal. 46 MECHANICAL STOKERS The driving mechanism consists of a worm gear operated by a pawl and ratchet which can be regulated to control the speed of the grate. The pawl is operated by an eccentric placed on the driving shaft. A low pressure water box at the bridgewall and a sus- pended arch of special firebrick shapes is generally used. Natural draft is used with this stoker. Continental Traveling Grate. The chain of this stoker (Fig. 27), is distinctive in that grates are not interlocking as the ordinary link design. Natural draft is used. The grates are designed and constructed of small units, with dovetail and semicircle for locking each grate, this dovetail FIG. 27. Continental Chain Grate Stoker. being inserted into the openings in the links and bars, a rod passing through the cored hole locks each grate into its proper position. The grate can be removed and replaced, there being one rod which locks each section of grate in its position. This rod acts as a key to each grate. The grates are interchange- able and of one size. An independent chain is used of links separated and bolted to cast-iron bars. These bars act as supports for grates. The frame consists of two cast-iron side frames connected to two hopper frames, braced by four cross beams transversely to the frames, and two steel shafts upon which are mounted and keyed the sprocket wheels which impart the traveling MECHANICAL STOKERS 47 motion to the chain. The frame is mounted upon flanged wheels which rest upon rails set under the furnace so that the stoker can be withdrawn from the furnace. The driving mechanism utilizes the double acting upward stroke of cams. The spur gear, consisting of a train of gears, is enclosed in a casing. The gears are driven by ratchet wheels and pawls, the ratchet wheels being operated by pawl levers connected to the speed adjustment links by rods which contain the relief springs. The adjustment links are connected to the roller levers and these levers ride on the cams of the line shaft. A low pressure water box is used at the bridgewall and a flat suspended arch at the front of the stoker. McKenzie Traveling- Grate. This stoker is of the traveling grate class, having the entire grate surface detachable and fastened to bars in small sections. This design has been worked out so as to make it possible to remove any grate bar inde- pendent of the others. The entire stoker is built up with side frames which are supported on four wheels so that the stoker can be removed from the furnace. The driving mechanism is made up of what is termed double-acting, giving a continuous travel to the grate surface, the speed of the grate being controlled by operating mechanism fastened to the side of the stoker part. The stoker is also equipped with a clinker apron at the rear and a horizontal dumping grate, this dumping grate form- ing an ash receiver, this design being used to prevent, as much as possible, excess air at the rear of the grate. The stoker is also equipped with a flat suspended ignition arch at the front and a low-pressure water box at the rear. Natural draft is used for the operation of the stoker. Harrington Traveling Grate. This stoker consists of cast- iron side frames, carrying the driving gear, hopper front shaft and feed gate in the usual manner (Fig. 28}. The side girders are formed of structural-steel members, built like a truss. Transverse members of structural steel support a series of tracks, on which run semi-steel chains, which carry and support the grate surface and take up the stress and tension of the 48 MECHANICAL STOKERS chain. These are provided with V-rollers to insure alignment both horizontally and vertically, and to reduce the power required for driving the stoker. An inclosed double worm drive is provided at the rear of the stoker. Attached to the chains is a series of transverse racks or beams on which the clips or bars forming the grate surface are attached. The grate bars are sufficiently loose to slide over the ends of the racks. The straight under-surface of these racks make an air-tight diaphragm of seal between the adjacent compart- FIG. 28. Front View, Showing Hopper Parts of Harrington Forced Draft Traveling Grate Stoker. ments. These compartments occupy the space between the chains communicating on one or both sides to the air duct in the boiler side walls, or below the floor of the boiler room. An adjustable damper serves to control the air pressure in the respective compartments. Each communicating passage through the side wall terminates in a removable door, which, when taken off, allows free access to the chamber. The clos- ing of the damper and the removal of this door serves to put the stoker on a natural-draft basis. MECHANICAL STOKERS 49 The grate bars fit close together, and the air in passing through them makes two right-angle turns. The lower shoulder at the joint is designed to prevent the falling of fuel through the grate. Projections hold the adjacent surfaces apart so that an air space of approximately 15% is attained. Fig. 29 is a view of the stoker partly assembled. It has four compartments, the one under the central part of the grate having double the width of any one of the others. Under- FIG. 29. Harrington Forced Draft Traveling Grate Stoker .Partly Assembled. neath the lower run of the grate an extension is built out over the ashpit to protect the bars from radiated heat, and a seal under the rear cross baffle is carried up as close as possible to the moving surface. These provisions obviate the need for a water-back or an overhang to the bridge-wall. The chambers communicating between the compartments and the common air duct from the fan are shown in Fig. 29. The duct passes immediately below and a common damper plate in the bottom of each chamber controls the volume of air 50 MECHANICAL STOKERS to each compartment. The dampers are operated manually by means of the lever and hand-wheel shown. Each damper is set in accordance with requirements while the total air supply is controlled through the fan serving the stoker. Playford Chain Grate. This stoker (Fig. 30) operates on natural draft. The chain consists of a number of driving and standard links with vertical air spaces, traveling in the form of an endless chain over supporting rollers at the rear. The motion is imparted by the sprocket wheels which are mounted on the front driving shaft, and engage with the rods support- ing the grate links, which form the chain. Adjustment of the chain is provided by screws at the front of the stoker. ^i^^Ajgp^^^^^^ ^IHHHHHHi FIG. 30. Playford Chain Grate Stoker. The chain is supported by pipe rollers fastened to the side frames which are spaced by the usual cross beams. Air seals are provided at the rear of the stoker. The frame is mounted on wheels so it can be removed from the furnace. The motion of the driving shaft is derived from a ratchet, worm and gear, located at the side of the stoker, and is trans- mitted through an eccentric from the line shaft. The coal feed is regulated by raising or lowering a sheet steel water gate by means of a hand wheel located at the side of the stoker. A low pressure water box at the bridgewall and an ignition arch, built of standard size firebrick and located immediately at the front of the stoker. MECHANICAL STOKERS 51 Stowe Traveling Grate. This stoker (Fig. 31) consists of traveling grates alternating with stationary tuyeres. The grate surface is inclined towards the bridge wall at an angle of twenty degrees. The stoker essentially is made up of coal hopper in f ron t where the coal is allowed to feed with the grate accord- ing to a thickness set by a feed gate. The chain grates are about 4" wide and the tuyeres in between are about 3" wide. The top of the tuyeres are depressed slightly below the chain. Near the bridge wall the grates rise to form a more horizontal grate FIG. 31. Stowe Conveyor Feed Stoker. surface this being designed to retard or hold back the fuel bed, if necessary, to burn all combustible matter left. The chain elements are driven by sprockets keyed to a single shaft extending across the stoker in front. The main sprocket shaft is driven by an eccentric and ratchet arrange- ment through a nest of spur gears. As the chain grates move down in the furnace and around the sprockets as in an ordinary chain grate stoker they are supported by cast iron skids. These skids also serve as a sup- port for the tuyeres. A complete tuyere unit extends from the 52 MECHANICAL STOKERS dead plates in between the chain grates at the top to retarding bars in between the chain grates at the rear. Air for the stoker is admitted from a chamber extending beneath the entire grate that serves as a wind box; at the rear is a concrete wall on which is mounted a series of cast-iron tunnels through which the returning chain grates pass. A suspended arch is used with this stoker for ignition pur- poses as coal is burned by the over feed method the same as a standard chain grate. A water back is not used however but if the ash pit is not sealed it would be necessary in order to FIG. 32. Westinghouse Chain Grate Stoker. eliminate air leakage between the rear of the stoker and bridge wall. Westinghouse Chain Grate. The chain (Fig. 32} is made up of standard and driving links with solid hubs 9" long weighing 6 Ibs. and 8 Ibs., respectively. They are spaced and held together by steel rods. The chain passes over sprockets at the front and rear. The front sprockets are keyed to the shaft. The rear sprockets are all connected together by pipe spacers and through bolts, and the entire unit revolves on a steel shaft supported by cast- iron bearings mounted in the side frames. The upper part of the chain is supported on pipe rollers with cast-iron ends or bushings. These bushings run on steel MECHANICAL STOKERS 53 cross rods, spaced about 9 inches apart. The lower portion of the grate is supported on pipe rollers spaced about 18 inches apart. The side frames are in one piece with removable top pieces that come flush with the top of the links. The frames are held together by a cast-iron beam at the front and a wrought-iron channel at the rear. Diagonal rods are also used. The frame is mounted on four wheels of cast iron, so the stoker can be withdrawn from the furnace. The chain is level from the front to rear. Air seals are provided at the reai* cross beam. The hopper is made up of hopper ends bolted to the side frames and a steel front plate. The coal gate is supended from a channel supported on the hopper ends and adjusted by two hand wheels on each side of the gate. The inner surface of the gate is lined with standard arch and straight firebrick held together by cast iron clamps. The chain is driven by a cast-iron worm gear which engages a cast-iron worm. Two mitre gears are actuated by a ratchet which, in turn, is driven by a pawl placed between two rods making up the ratchet arm. The ratchet arm is driven from an eccentric placed on the driving shaft. A safety spring is placed in the eccentric rod to prevent breakage. A 4" wrought-iron low-pressure water box is used at the bridge wall, and a sprung arch of standard firebrick at the front of the stoker. Natural draft is used with this stoker. OVERFEED TYPE STOKERS Cox-Fulton Stoker. This stoker is of the front feed class operating on natural draft (Fig. 33). The coal hopper extends across the front of the stoker. The coal is fed to the coking plate and onto the inclined grate bars by a reciprocating pusher, operated by a sector on the hopper shaft. Motion is given to the hopper shaft by means of an eccentric on the main shaft. The motion of the pusher is adjustable. The grate supports are inclined to the rear about 39. The grate bars are water-cooled on their inner edges, steel MECHANICAL STOKERS tubing being used to connect the grates to the water supply. Movable and stationary grates are used, giving a forward- upward-inward motion to the movable grates. Motion to the grates is obtained from a main shaft located in front of the stoker through eccentrics connected to inclined grate bar bearers. The movement of the grates forces the fuel bed to the bottom of the furnace on the dump grate. FIG. 33. Cox-Fulton Inclined Overfeed Stoker. Dump grates and guards are operated from the front, and thus the ash and refuse is dumped into the ash-pit periodically. An ignition arch of the sprung or suspended type is used. Model Stoker. This stoker is of the side feed class having the coal hoppers on the side and operated on natural draft of from .25" to .6" in the furnace. The grates are ar- ranged in pairs inclined from the sides to the center in a V-shape, one of each pair on each side being stationary and the other movable. When in operation, the movable grate is moved by the rocker bar up so its fire edge is a little above the fire edge of the stationary grate and then down a little below. The stationary grates rest at the lower end on the MECHANICAL STOKERS 55 bearer and at the upper end against the edge of the bottom plate of the magazine over which the coal is fed into the furnace. The movable grates are hinged to the stationary grates by a pin lug which fits into a hole in the stationary grate near its upper end, the lower end of the movable grate being held to place and rocked by the rocker bar as indicated. FIG. 34. Murphy Automatic Furnace. The grate bearer located in the center of the furnace sup- ports the grates and forms a box-like receptacle into which the clinkers and ash pass and are ground out into the ash pit. A sprung arch is used over the V-shaped grates, and air admitted at the point where the volatiles are distilled from the coal as it comes from the stoker coal hoppers. Murphy Stoker. The Murphy stoker is of the side feed class, having the coal hoppers on the sides with inclined fires 56 MECHANICAL STOKERS on both sides of the furnace and the observation door and operating mechanism in the front (Fig. 34). This stoker uses natural draft. At either side of the furnace, extending from front to rear, is a coal magazine into which the coal is introduced by conveyors. At the bottom of this magazine is the coking plate against which the inclined grates rest at their upper ends. The stoker boxes, operated by segment gear shaft and racks, push the coal out over the coking plate and onto the grates. The grates are made in pairs, one fixed, the other movable. The movable grates, pinioned at their upper ends, are moved by a rocker bar at their- lower ends, alternately above and below the surface of the stationary grates. The stationary grates rest upon the grate bearer which also contains the clinker or ash grinder. This grate bearer is cast hollow and receives the exhaust steam from the stoker engine. This steam escapes through small openings spaced at regular intervals on either side of the clinker grinder and lower ends of the grates to soften the clinker and to assist the cleaning process. As the coal leaves the magazine, it rests upon the coking plate. The volatile gases are driven off and mixed with the heated air admitted through the air ducts in the arch plate. The coal, having been coked, travels down the inclined grates toward the clinker grinder, receiving air in the ordinary way through the grates to complete the burning process. The speed at which the stoker boxes push the coal on the grates can be regulated to conform to the duty required. Like- wise, the clinker grinder can be turned slower or faster accord- ing to the amount of ash in the coal. A sprung arch is used extending from one hopper to the other. Detroit Stoker. This stoker uses natural draft and is of the side feed class having the coal hoppers on the sides of the stoker front (Fig. 35). From the hopper, the coal is fed into the magazines by a worm coal conveyor. The gears operating the worm conveyors are lubricated by running in oil, and are covered with shields. The coal conveyors are operated by the upper shaft in front at a slow speed and distribute the coal at the upper end of the inclined grates on a coking plate. MECHANICAL STOKERS 57 Inclined grates of two kinds are used, i.e., stationary and moving, each alternate grate being operated by the driving shaft in front. The vibrating or operating grates have a motion forward and backward, moving the bed of fire down toward the center of the furnace. The vibrating grates are operated by upper and lower rocker bars connected to the lower driving shaft by links, FIG. 35 Detroit " V " Type Overfeed Stoker. which can be unhooked during the operation, thereby discon- tinuing the grate movement entirely when desired. In the center of the stoker, and at the bottom of the inclined bars, is a clinker crusher composed of a row of cast-iron discs, ten inches in diameter, which rotate alternately toward and from each other by the reverse gear and is connected with the front driving shaft. This serves to crush the clinkers and deposits them in the ash pit. 58 MECHANICAL STOKERS A sprung or suspended arch is used with this stoker and air admitted through channels forming the support for the arch skewbacks, this air being admitted where the volatile gases are distilled. An observation door is placed in the stoker front to observe conditions of the furnace. Roney Stoker. The Roney stoker (Fig. 36) operates on natural draft and belongs to the front-feed class, the coal being fed from a hopper at the front of the furnace. FIG. 36. Westinghouse lloney Stoker. From the hopper, the coal is pushed by an adjustable pusher onto a coking plate where the volatiles are distilled. From the coking plate the fuel passes to the grates. The grates con- sist of cast-iron webs on which are placed narrow grate bar tops. In the upper part of the furnace, flat overlapping bars are used to prevent sifting of fine coal. Each web is sup- ported at its ends by trunnions and is connected by an arm to a rocker bar which is slowly moved to and fro by an eccentric on the shaft on the stoker front so as to rock the grates back and forth between a horizontal position and an inclination MECHANICAL STOKERS 59 towards the back of the furnace. The grates thus gradually move the burning coke downwards. The ashes and clinkers are deposited onto the dumping grate which can be lowered by means of rods from the front of the stoker so as to drop the ash into the ash-pit below. A guard may be raised so as to prevent coke or coal on the grate bars from falling into the ash-pit when the dumping grate is lowered. Air for the volatile gases is admitted in small jets at the front of the stoker. A firebrick arch is used at the front made up of standard firebrick shapes. The stoker shaft on the front of the stoker is operated at 7 to 14 B. P. M. by a small engine through a worm and gear reduction. Doors are provided on each side of the hopper for observation of furnace conditions. Wetzel Stoker. This stoker operates on natural draft and is of the front-feed class, since the coal is placed in a hopper at the front of the furnace (Fig. 37). From this hopper, the fuel is pushed over the dead plate and onto the coking grate by the feeder, moved by an eccentric on the shaft. The cokr ing grate driven by a link connection to the feeder moves the coal onto the main grate. The main grate consists of a series of movable, and a series of stationary bars, the bars of one series being alternately arranged with respect to those of the other. The grates are mounted on a stationary cast-iron frame, the stationary grates being directly attached thereto and the movable grates sup- ported by rock shafts. The movable bars are driven by an eccentric on the shaft operating through a bell crank. The motion of the bars moves the fuel down the main grate which is inclined at about 30, and discharges the ash onto the dump- ing grate. When sufficient ash has been accumulated on the dumping grate, a lever is thrown from the front of the furnace and the ash is discharged into the ash pit. The coking grate contains an extremely large percentage of air spaces, the upper part of the main grate a somewhat smaller percentage, the lower part of the main grate still less, and the dumping grate a very small percentage. 60 MECHANICAL STOKERS Above the dead plate, coking grate and the upper part of the main grate is sprung a firebrick ignition arch. The amount of motion of the feeder of the coal and motion FIG. 37. Wetzel Front Inclined Overfeed Stoker. of the grates is adjusted from the front of the stoker by means of hand-wheels on the eccentric rods. An inspection door is provided at the front on each side of the hopper enabling the operator to view the condition of the fire. The main shaft which runs along the stoker front below MECHANICAL STOKERS 61 the hopper is driven by a steam engine operating through a worm gearing. Wilkinson Stoker. The Wilkinson stoker (Fig. 38) is of the front-feed class and designed more particularly for the burning of fine anthracite coal. The coal hopper extends across the front of the stoker. A pusher fastened to the upper end of each grate bar pushes the coal from the hopper through the opening in the furnace front onto the bars. The grates are inclined about 30 and the motion of the bars gradually FIG. 38. Wilkinson Front Inclined Overfeed Stoker. moves the coal downwards, and deposits the ashes and clinkers on the clinker grates, from which they are finally pushed into the ash pit. The grate bars are cast hollow with nearly horizontal openings leading from the interior of the bars through the risers of the steps that form the upper surface of the bars. Each grate bar is given a to-and-from motion in a horizontal direction by the rock shaft and links, the ends of the bars being supported by, and sliding on, the hollow cast-iron bearing bars. Practically all the air from the com- bustion of the coal is drawn into the upper ends of the hollow 62 MECHANICAL STOKERS grate bars by the steam jets, and forced into the fire from the openings in the tops of the bars. A sprung or suspended arch is used with this stoker at the front. UNDERFEED STOKERS (Multiple Retort) Riley Stoker. The Riley stoker (Fig. 39) is of the multiple inclined retort class, using forced draft for its operation. Essentially, it is made up of individual retorts each having horizontal plungers for feeding the coal (about 12 to 15 pounds of coal being fed per stroke), reciprocating retorts, inclined about 20 degrees, moving overfeed grates, and adjustable FIG. 39. Riley Multiple Retort Underfeed Stoker. apron refuse supporting plates, each retort weighing about 4,000 pounds. The fuel-feeding mechanism is made up of cylindrical horizontal rams, 9" in diameter, set about 19" centers. These rams or plungers are connected to the crank shaft by connect- ing rods. All ram boxes are set in line and bolted to angles. The crank shaft bearing brackets are bolted to the ram boxes and tie them together. Crank shafts are made in sections, each section being driven by a gear box. Eeduction gearing is used to drive the main crank shaft. The main worm on the crank shaft is driven by a worm mounted on a supported shaft. This shaft carries a cut worm MECHANICAL STOKERS 63 wheel which is driven by a hardened steel worm mounted on the speed shaft of the stoker. The reduction through the gears, that is, the ratio of speed shaft to crank shaft, is 330 to 1. The speed shaft drive may be taken from any convenient source, usually from a line shafting running about 400 R. P. M. A y 2 " shearing pin is used in the connecting rod to provide against breakage of parts, should the rams become obstructed in any position of its stroke. The retorts of the underfeed section are inclined about 20, and the reciprocating movement is obtained by side rods driven by extension of the main plunger wrist pins. The side FIG. 40. Rear View Riley Multiple Retort Underfeed Stoker. rod bolts withdraw the side bars to the same position 011 each return stroke. The travel towards the bridge wall is varied by changing the amount of lost motion between the wrist pins and side rod by adjusting blocks. The retorts move a maxi- mum of V. On top of the retort sides are placed tuyere blocks with openings for air admission to the fuel bed. These tuyeres inter- lock and are bolted together. The overfeed grates (Fig. 40) extend the full width of the stoker, and are made up of unit retort width. They reciprocate back and forth practically the same as the reciprocating retorts. The refuse supporting plates are hinged together by chains to form an apron, which hangs down over the ends of adjust- 64 MECHANICAL STOKERS able racks. These racks are set by hand to the size of the opening. Air is admitted under the front of the stoker and forced through the tuyeres to the fuel bed. A damper is placed between the main air chamber underneath the front of the stoker and the overfeed reciprocating grates so that air can be regulated for this part of the stoker. Jones A-C-Stoker. The Jones A-C-Stoker is a gradual development from the original single retort Jones-Stoker. The A-C stoker is of the inclined, multiple retort class using forced draft for its operation. The stoker is essentially made up of horizontal rams inclined retorts stationary overfeed sections, and single dumping grates (Fig. 41). The fuel is fed to the furnace from the hopper located directly in front of the stoker by horizontal steam operated rams. In the underfeed section the volatile gases are distilled and the fuel bed progresses onto dead plates at the rear of the retort and then onto the dump grates. The fuel feeding mechanism consist of a steam cylinder for each retort. A ram is connected to the piston of this cylinder. "When steam is admitted into the cylinder through an automatic control valve the ram is drawn outward and a charge of coal falls into the ram case. The automatic con- trol valve reverses the stoke and the charge is forced into the retort. A rod is connected to the ram and travels through the front end of the retort below the ram with each operation of the steam piston. On this rod inside the retort are bolted two pusher blocks so that the coal is carried upward and rear- ward with each stroke of the ram. The dump plates are made in sections and are hinged to a shaft located at the rear of the overfeed sections. The dump plates projects towards the bridge wall, and are balanced and operated from the side of the furnace. The standard tuyeres are fitted to the retort sides and so formed so as to make a continuation of the retort, rounding off on top. Special side tuyeres are used reaching quite high above the side wall air is circulated through these tuyeres and they are so designed to keep the fuel bed away from the MECHANICAL STOKERS 65 brickwork of the side wall and in this way prevent clinker formation and bridging over the retort. A distinct feature of this stoker is the control valve. It is installed in the steam line to each stoker cylinder and has eight rates of operation. The length of the stroke of the pusher FIG. 41. Jones' " A-C " Multiple Retort Underfeed Stoker. blocks can be adjusted by changing a pin on the connecting bars below the rams. Air is admitted to an air chamber below the retorts from the main air duct ; from this chamber the air goes through the main tuyeres, the side tuyeres and the overfeed section. Air distribution boxes are used at the front above the mouth of the retort. 66 MECHANICAL STOKERS Taylor Stoker. The Taylor stoker (Fig. 42) was the first of the multiple retort class using forced draft for its opera- tion. The stoker is made up of two horizontal plungers or rams, one above the other, and connected together by links for feed- ing the coal; stationary retorts inclined about 22; an oscillat- ing overfeed section; and a single leaf dumping grate, each single retort weighing about 5,000 pounds. The coal from the hopper discharges into a cylindrical chamber in which the 9" diameter upper ram works. This ram is operated by a crank shaft at right angles which is driven by a worm and gear. The distance from center to FIG. 42. Type " A A " Taylor Multiple Retort Underfeed Stoker. center of each ram is 20%", this being a unit retort width. A single speed shaft drives the series of worms and gears enclosed in a gear box. The ratio of speed shaft to the main crank shaft is 352 to 1. The lower horizontal plunger or ram is con- nected to the upper one by means of links, and its lost motion is adjustable. Bearing brackets for the main crank shafts are bolted to the ram boxes and serve to tie them rigidly together. These bearings are babbitted and provided for lubrication. This shaft operates clockwise (looking from the right side of the stoker at the end of the shaft), the shaft operating from one revolution in 45 seconds to one revolution in a minute and a half. MECHANICAL STOKERS 67 In order to provide against damage due to any foreign substances that might block the action of the rams, a shearing pin is provided in the speed shaft and the parts so designed that stresses are transmitted to this part of the mechanism. In the standard stoker, 17 tuyere blocks are used, set immediately on top of the tuyere boxes. Each tuyere block hooks into recesses and interlock with each other, thus hold- ing them in place. The air for combustion is forced from the wind box through the tuyeres to the fuel bed and controlled by suitable dampers. FIG. 43. Rear View Taylor Type " A A " Multiple Retort Underfeed Stoker. The air for the oscillating overfeed section is alsa controlled by dampers. The dumping grates (Fig 43) are made up of frames to which are fitted interchangeable grate bar tops, these being of the unit retort width. The dumping grate is operated by means of levers in front of the stoker. The stokers for different size furnace widths are built up by a number of retorts. For example, the furnace for a 500- H. P. boiler might be made up of six retorts. Different lengths from the front wall to the bridge wall are used. In some cases, the dump grates are operated by power 68 MECHANICAL STOKERS and in special installations a clinker grinder is used for ash disposal. Westinghouse Stoker. The Westinghouse stoker (Fig. 44} is a multiple retort inclined about 20, and uses forced draft for its operation. The stoker is essentially made up of downward inclined rams, inclined retorts, a reciprocating overfeed section and double dumping grates. The fuel is fed to the furnace from the hopper proper by downward inclined rams equal in number to the retorts in FIG. 44. Westinghouse Multiple Retort Underfeed Stoker. the furnace. In the underfeed section, the volatile gases are distilled and the fuel bed progresses on to the overfeed section and then on to the dumping grates. About 18 Ibs. of coal is pushed into the underfeed section with each stroke of the ram. The fuel-feeding mechanism consists of a 9" plunger or ram operating in an inclined cylinder forming part of the ram box, these rams being set 21" centers. These rams obtain their motion through connecting rods to cast steel crank shafts 3y 2 " diameter, these being made up of units and connected together with bolts. Bearing brackets for the crank shafts are bolted to the ram boxes and, in this way, tie them together. These bearings in MECHANICAL STOKERS 69 the brackets are babbitted and provided with grease cups for lubrication. This shaft operates from one revolution in 45 seconds to one revolution in a minute and a half. The reduction worm gearing is used to drive the crank shaft. The main power worm gear is connected by bolts to the flanges of the crank shaft, and is driven by a worm mounted on a cross shaft supported in the gear box. This shaft, in turn, is driven by a bronze worm gear and hardened steel worm fitted to the speed shaft. One gear set is used to drive a maximum of four retorts. A hinged cover on the gear case is provided to make inspection. The speed reduction in the gear box is 352 to 1. A protective device, consisting of a 3/32" shearing pin, is provided in connection with the speed shaft to guard against damage of stoker parts, should foreign substances be acci- dentally admitted with the coal and block the movement of the rams. The lower ram is operated by means of connecting rods, through lost-motion mechanism, to the upper ram. It recipro- cates along the bottom of the retort, and in the same plane as the main ram. Above the upper end of the tuyere boxes, and extending laterally across the furnace, are air distributing boxes which are bolted to the ram boxes. These are made of unit retort width, cast hollow, and designed to transmit part of the load of the front wall to the tuyere boxes. A fuel deflecting plate is provided in the retort for varying the thickness and outline of the fuel bed. The forward and rear dumping grates are made up of frames to which are fitted interchangeable corrugated grate bar tops, and in this way a passage for air is formed. These are made of the unit retort width, the lower grate bar top being bolted so as to lock the other tops in place. The forward dump- ing grate is pivotally connected to the dump grate brackets, and projects towards the bridgewall, and the rear dumping grate is supported in a similar manner and projects towards the front of the stoker. Both dump grates are operated from the side of the furnace. The overfeed grate is of unit (Fig. 45) retort width, and is 70 MECHANICAL STOKERS operated by the upper ram through rods and lost-motion con- nection. The rods return the overfeed grate to the same posi- tion on each stroke. The travel forward is adjusted by chang- ing the amount of lost-motion by means of collars. These are placed on the rods from the front of the stoker. The furnace is sealed from the stoker front to the rear of tuyere boxes by means of a reinforced concrete floor. Dampers are provided and set in the floor to control the air from the main air ducts. Auxiliary dampers divide the wind box trans- versely. Doors are placed in the front for access to the wind box and for air admission when the stokers are being operated on natural draft. FIG. 45. Rear View Westinghouse Multiple Retort Underfeed Stoker. The tuyere boxes used with the stokers are of the box girder type. Their front ends are bolted to the ram boxes and rest on angles supported from the floor. Their rear ends are tied together. The ribs on the sides of the tuyere boxes are used for supporting the retort bottoms. The tuyeres are of corrugated construction and hooked into the recesses in the top of the tuyere boxes and interlock with each other, thus holding them in place. In a stoker 10 ft. from the front wall to the bridge wall of the double dump grate type, 17 tuyeres are used. They are laid, one upon the other, and the entire block is locked by means of the upper tuyere. Air admission to all parts of the furnace is controlled from the front or side of the stoker. Air is admitted to air distrib- uting boxes located at the front for air above the fuel bed. The air through the underfeed section is forced from the MECHANICAL STOKERS 71 wind box through the tuyeres to the fuel bed, and controlled bj dampers. Air admission to the overfeed section and dump grates is also controlled by dampers. Frederick Stoker. The Frederick Underfeed Stoker is of the general inclined multiple retort type, having horizontal rams; stationary underfeed sections, and air admitting dump- ing grates. The retorts are spaced 21 inches apart and have a main feeding ram O 1 /^ inches diameter, feeding approximately 20 pounds of Eastern fuel per stroke. The underfeed section is inclined 20 degrees from the hori- zontal and the usual extension grate common to this type of stoker is eliminated. The secondary rams are operated by suitable connection to the main ram mechanism and the stroke of this ram is controlled by means of a shaft located above the retorts in front which engages or disengages the dogs fastened to the moving rod ; thus increasing the stroke of the secondary ram to a maximum of 6 inches or allowing it to operate at normal stroke. The shearing pin arrangement is located in the speed shaft mechanism as is common with other stokers of this type. In order to obtain two sets of speeds for the rams, there are two sprockets placed on the speed shaft and by operating these through a clutch arrangement one or the other ratio of speeds can be used. Kefractory blocks are used in the front wail and bridge wall immediately over the stoker parts. UNDERFEED STOKERS (Single Retort) Jones Stoker. The Jones stoker (Figs. 46 and 47) is of the single retort class essentially consisting of one horizontal retort with plates on the side for supporting a fuel bed as it is pushed out of the retort. Forced draft is used with this equipment. The fuel feeding mechanism consists of a small hopper bolted onto the ram case, which, in turn, is bolted to a steam cylinder, all of this mechanism being outside of the furnace. Steam is admitted behind the piston which forces the piston and ram forward carrying a portion of the coal in the hopper 72 MECHANICAL STOKERS to the retort. Pusher rods are provided in the retort to carry a portion of the coal forward in the retort. FIG. 4b'. Sectional Front View Jones Single Retort Underfeed Stoker with Side Plates. The retort consists of a fuel magazine with tuyere blocks attached to the top of the retort. These tuyere blocks are made in unit sections and are fastened to the retort by one single rod. FIG. 47. Jones Single Retort Side-dump Underfeed Stoker. Air from the blower is forced into a sealed ash pit from which the air passes through the hollow tuyeres to the fuel bed. The dead plates on the side are ribbed and the air circulates under them and through the tuyere blocks. No air is admitted through them. MECHANICAL STOKERS 73 The operation of the steam rams are controlled by means of automatic valves, each ram being adjusted independently of the other. The rate of feed can also be adjusted within a certain range of operation. Doors are placed in the stoker front for use in cleaning the fires as the ash is separated from the incandescent fuel bed and pulled out of these doors. Moloch Stoker. This stoker is of the single retort class using forced draft. A retort runs lengthwise of the furnace into which the fuel is pushed by a steam ram. Above the retorts FIG. 48. Moloch Single Retort Underfeed Stoker. are tuyeres to supply the air to the fuel bed, and on either side is a rotary grinder disposing of the refuse. The fresh fuel is fed underneath the zone of combustion, there being no moving or stationary grates to provide for overfeed burning. Fig. 48 is a perspective of a two-retort equipment. The retorts are inclosed by cast-iron air boxes with the air supply for each controlled independently by an air gate operated from the front of the boiler. Each stoker unit is supported at the front and at the bridgewall. The retort has a horizontal top on which are mounted tuyere blocks to provide air under pressure, the fuel being fed to 74 MECHANICAL STOKERS the retort by a steam operated ram supplied from the hopper attached to the ram cage. The operation of the ram is inter- mittent and automatically regulated, each charge delivering coal to the retort. The tuyere openings supply the air for com- bustion below the fire and above the fresh fuel. The heat of the fire above drives off the volatile matter, and these gases FIG. 49. Type " E " Single Retort Underfeed Stoker. mix with the air supply passing through the zone of com- bustion. The coke passes upward and out of the retort and above the grinders, the refuse passing over the tuyere blocks to the rotary grinders. Type "E" Stoker. The Type "E" stoker is of the single reton class and uses forced draft. The coal is fed into a hopper on the outside of the furnace. From this hopper (Fig. 49) the fuel is delivered by gravity to the front end of the bottom of the retort, and is then pushed MECHANICAL STOKERS 75 into the furnace by a steam-driven feeder block until the retort, which runs the length of the furnace, is filled. FIG. 60. Cross Section Type " E " Single Retort Underfeed Stoker. As the coal rises in the retort, it is flooded on the fire-bars (Fig. 50) by the movement of auxiliary pushers. The grate bars are arranged alternately moving and fixed and reciprocate with the movement of the pusher / spreading the coked fuel toward 76 MECHANICAL STOKERS the side or dump plates. The movement of the fire-bars also conveys the clinker and ashes to the dump trays. The bars are slightly inclined, but not enough to cause a gravity travel of the coal. The fire is kept moving by the mechanical movements of the bars, obtained by means of two helices and nuts placed outside the furnace. These cause the moving bars to rock to and fro. Each stoker has an individual drive, but by means of auto- matic control all are run at a uniform speed. A stoker may FIG. 51. Detroit Single Retort Underfeed Stoker. be cut in or out of service by throttling the driving engine and shutting off the air. Detroit Underfeed Stoker. This stoker (Fig. 51) is of the single retort type and uses forced draft for its operation. It consists of a horizontal retort with side grates for supporting the fuel bed as it is pushed out of the retort, and dumping grates on each side for cleaning purposes. It has mechanically operated plungers, or rams, connected through a reduction gear to a shaft located in front of the stoker. All the gears, worms MECHANICAL STOKERS 77 and moving parts are enclosed in a gear box. This gear box is similar in construction to the gear box used on the multiple inclined underfeed stokers. The stoker consists of a coal hopper in front, and the retort proper, extending into the furnace. Connected to the ram or plunger is a pusher block located in the bottom of the retort and is used to feed the coal the entire length of the fuel bed. FIG. 52. Rear View Detroit Single Retort Underfeed Stoker. Tuyere blocks for distribution of the air to the fuel bed are made of unit sections, and are fitted to both sides of the retort. Air from a blower is forced into sealed compartments from which it is directed by the tuyeres to the fuel bed. The grates on each side (Fig. 52) of the retort are ribbed, and are made to extend from the tuyere blocks to the dumping grates, located at the sides. The dumping grates are solid, without air admission, and are operated from the front of the stoker. The operation of the mechanical rams is taken from the crank shaft and controlled by lengthening or shortening the 78 MECHANICAL STOKERS stroke of the connecting rod, each rod being adjusted inde- pendently. The rate of feed can be adjusted within a certain range of operation. Doors are placed in the stoker front for use in cleaning fires, these doors are located immediately in front of the dump grates and a view of the fires can be had at all times from the front. Ash pit doors are also located in the stoker front, so that ashes can be cleaned out from the front of the stoker. Roach Stoker. This stoker is of the single retort type with side grates and dump grates next to the furnace wall. FIG. 53. Roach Single Retort Underfeed Stoker. Coal is conveyed from a hopper located in front by the action of a plunger operated from a steam cylinder. This plunger pushes the coal into the retort where it is distributed to the inclined side grates, which have a reciprocating motion. The fuel bed progresses over the side grates to the dump grates which are made up in sections. The ash and refuse is dumped into the ash pit, and removed from the front of the stoker or from a tunnel below. The motion of the side grates can be adjusted so that a certain movement of the bars can be obtained. The air distribution is controlled from a central air cham- ber; from this chamber air is directed to the ends of the MECHANICAL STOKERS 79 grate bars next to the dump grates and then travels through the bars and enters the furnace or fuel bed through the head of the bars. Air is also directed to a chamber immediately under the retort, being controlled with a valve, shutting this chamber off from the main wind box. The air taken from this so-called low-pressure air chamber and travels upwards and passes through the interstices between the grate bars. An ignition arch is not necessary with this stoker unless the boiler and stoker application requires it. The stoker op- erates on forced draft the same as other stokers of this class. CHAPTER III COAL AND COAL-PRODUCING FIELDS OF THE UNITED STATES COAL DEFINITIONS General. According to the general meaning, coal is a solid fuel and it is something which enters combustion and produces heat. Ash- and Moisture-Free Coal is that part of the fuel, minus ash and moisture, as neither of these take part in the combus- tion processes, nor do they develop heat. Clean Coal. Properly prepared lump coal; for example, consisting of fuel in which there is no visible ash, or, in other words, consisting of clean, black pieces accompanied by no slate or other dirt, the inference being that there are no in- visible impurities with the coal. Dirty Coal. A fuel mixture containing a large amount of foreign matter, such as slate, fire clay, rock, etc. Size of Coal. This term is used to denote the sizes .of coal pieces. An example of this application would be "1^4" screenings." Kind of Coal. This expression is used in the classification of coals, such as the following examples : Anthracite, Semi-Anthracite, Bituminous, Semi-Bituminous, Lignite, Coking Coal, Gas Coal, Dry Coal, Moist Coal, etc. Grade of Coal. As an example, anthracite or bituminous are not grades of coal, but kinds. The application of the term grade is shown by the following examples: Mine run, lump, egg, nut, washed coal, washed slack, washed screenings, etc. Caking Coal. Some coals tend to form a solid mass when heated in a retort or furnace. This characteristic makes the coal difficult to burn by any means which does not provide an agitation to break up the cake during its processes of f orma- 80 COAL AND COAL-PRODUCING FIELDS 81 tion. This action is due to the peculiarity of the volatile matter but after the volatile has been driven off and the caked mass broken up, there is no further tendency for the fuel to again cake in this manner. Such coal will be known as caking coal. Coals which are most suitable for making coke possess this property. Clinker. Clinker is ash which has been fused. These coals containing ash having a low fusing temperature are commonly referred to as clinkering coals because when they are burned in the ordinary furnace, a considerable percentage of the ash is reduced to clinker. Those coals whose ash has a high fusing temperature are commonly referred to as non-clinkering. It is apparent, however, that if fuel is being burned economically a comparatively small amount of excess air is being introduced into the furnace and high combustion temperatures must result. The actual temperature of a particle of coal under such condi- tions is considerably in excess of the fusing temperature of ash even in the so-called non-clinkering coal. It therefore fol- lows that if coal is being burned economically, a large per- centage of the ash will be fused. If the method of burning coal is such that large masses of incandescent fuel in the latter stages of combustion are agitated there is a tendency to produce large clinkers, whereas if the fuel is not disturbed, smaller masses of clinker will result. Clinker becomes troublesome only when it adheres to furnace brickwork or accumulates in such quantities that it interferes with the operation of the furnace, and where clinker troubles are hereafter referred to it will be understood to refer to these large accumulations. Coal having ash of low fusing temperature will not necessarily cause clinker troubles. If the percentage of ash be low, the stoking mechan- ism will usually be able to accumulate and discharge the clinker from the. furnace without interfering with operation. On the other hand, a coal comparatively high in ash which has a high fusing temperature can usually be handled without trouble be- cause all of the ash will not be reduced to clinker and the accumulations will not be large enough to interfere with opera- tion. Coking Coal. Some kinds of coal, when heated, give off the volatile constituents at relatively low temperatures, and 82 MECHANICAL STOKERS leave the carbon in a compact solid mass. This is generally known as coking coal. USE OF COALS Coal is used in the United States to a greater extent than any other one material, and the supply is^of general importance to the industries. Coal is essential to the small enterprise as well as the public utility that develops and sells power (Fig. 54). 55 Wafer Purification Labor Water Purification Supplies Mainf. Boiler Planf Bldg. and Grounds \ Mainf. Wafer Purification Equipment-' FIG. 54. "Relation of Coal Expenses to Other Operating Expenses of the Generating Plant in Public Utility Operation." For the year of 1915 the Geological Survey obtained data which show the relative importance of the ways in which bituminous coal is used. The percentage of the total consump- tion in 1915 was as follows : COAL AND COAL-PRODUCING FIELDS 83 Exports 4% Steamship bunkers at tidewater. 2% Used at mines for steam and heat. 2% Manufacture of coal gas 1% Industrial steam trade 33% Railroad fuel 28% Domestic and small steam trade. 16% Manufacture of beehive coke. . . 9% Manufacture of by-product coke 4% Other statistics by manufacturers were computed by the Bureau of the Census for 1914. Bituminous coal was then, ac- cording to these figures, used most largely in the manufacture of the following articles (the figures represent net tons) : Coke 50,457,000 Steel works and rolling mills 20,343,000 Brick, tile and other clay products 8,566,000 Cement 6,731,000 Chemicals 2,667,000 Glass 2,252,000 Petroleum refining 2,045,000 Blast furnace 1,892,000 Flour-mill and grist-mill products. . .. 1,809,000 Woolen and worsted goods. 1,544,000 Oil, cottonseed and cake. . . 1,232,000 Leather, tanned, curried and finished 1,124,000 Zinc smelting and refining. . 1,066,000 Rubber goods 919,000 Paper and wood pulp 6,268,000 Gas, illuminating and heat- ing 6,078,000 Car and general shop con- struction and repair by steam railways 5,486,000 Distilled liquors 909,000 Dyeing and finishing tex- tiles 896,000 Lumber and timber prod- ucts 885,000 Sugar refining 875,000 Copper smelting and refin- ing 812,000 Electrical machinery, appa- ratus, etc 769,000 Furniture 751,000 Salt 714,000 Steam-railway cars, private bunders 698,000 Beet sugar 682,000 Cotton goods 3,579,000 Ice, manufactured 3,386,000 Foundry and machine-shop products 2,913,000 Slaughtering and meat packing 2,786,000 Malt liquors 2,749,000 Lime 677,000 Paving materials 665,000 Glucose and starch pottery . 577,000 Agricultural implements. . . 555,000 Wire 523,000 Soap 515,000 Marble and stone work 485,000 Hosiery and knit goods .... 484,000 Automobiles 464,000 Planing-mill products, not including mills connected with saw mills 457,000 Fertilizers 433,000 WORLD'S RESERVE On account of the many unknown factors, an estimate on the world's coal supply is more or less speculative. According to an inquiry made in 1913, the coal reserves of the world available in the principal coal-producing countries, stand as follows : 84 MECHANICAL STOKERS Short Tons United States, including Alaska 4,231,352,000,000 Canada 1,360,535,000,000 China 1,097,436,000,000 Germany 466,665,000,000 Great Britain and Ireland 208,922,000,000 Siberia 191,667,000,000 Australia 182,510,000,000 India 87,083,000,000 Russia in Europe 66,255,000,000 Union of South Africa 61,949,000,000 Austria 59,387,000,000 Colombia 29,762,000,000 Indo-China 22,048,000,000 France 19,382,000,000 Other countries 69,369,500,000 8,154,322,500,000 WORLD'S PRODUCTION The latest statistics available with a degree of completeness are for the year 1914. In that year, in a world production in the neighborhood of 1,345,000,000 net tons, the United States contributed 38 per cent, Great Britain 22 per cent, and Ger- many 20 per cent. In the year 1913, for which estimates are more complete, the production of all kinds of coal by the more important countries was approximately as follows: Net Tons United States 569,000,000 Great Britain 321,000,000 Germany 305,000,000 Austria-Hungary 59,000,000 Net Tons France 45,000,000 Russia 35,000,000 Belgium 25,000,000 Japan 23,000,000 COAL PRODUCTION IN THE UNITED STATES In 1916, the United States produced over a half million tons of bituminous coal, and, as the demand for coal is now unprecedented, there is no question but what the fields will produce more than ever before. The coal produced in the United States in 1807 (the date of the earliest record) to the end of 1915 is shown in the following table: COAL AND COAL-PRODUCING FIELDS 85 Year Pennsylvania Anthracite Bituminous Total 1807-1820 12,000 3,000 15,000 1821 1,322 1,322 1822 4,583 54,000 58,583 1823 8,563 60,000 68,563 1824 13,685 67,040 80,725 1825 42,988 75,000 117,988 1826 59,194 88,720 149,914 1827 78,151 94,000 172,151 1828 95,500 100,408 195,908 1829 138,086 102,000 240,086 1830 215,272 104,800 320,072 1831 217,842 120,100 337,942 1832 447,550 146,500 594,050 1833 600,907 133,750 734,657 1834 464,015 136,500 600,515 1835 690,854 134,000 824,854 1836 842,832 142,000 984,832 1837 1,071,151 182,500 1,253,651 1838 910,075 445,452 1,355,527 1839 1,008,322 552,038 1,560,360 1840 967,108 1,102,931 2,070,039 1841 1,182,441 1,108,700 2,291,141 1842 1,365,563 1,244,494 2,610,057 1843 1,556,753 1,504,121 3,060,874 1844 2,009,207 1,672,045 3,681,252 1845 2,480,032 1,829,872 4,309,904 1846 2,887,815 1,977,707 4,865,522 1847 3,551,005 1,735,062 5,286,067 1848 3,805,942 1,968,032 5,773,974 1849 3,995,334 2,453,497 6,448,831 1850 4,138,164 2,880,017 7,018,181 1851 5,481,065 3,253,460 8,734,525 1852 6,151,957 3,664,707 9,816,664 1853 6,400,426 4,169,862 10,570,288 1854 7,394,875 4,582,227 11,977,102 18-55 8,141,754 4,784,919 12,926,673 86 MECHANICAL STOKERS Year Pennsylvania Anthracite Bituminous Total 1856 8,534,779 5,012,146 13,546,925 1857 8,186,567 5,153,622 13,340,189 1858 8,426,102 5,548,376 13,974,478 1859 9,619,771 6,013,404 15,633,175 1860 8,115,842 6,494,200 14,610,042 1861 9,799,654 6,688,358 16,488,012 1862 9,695,110 7,790,725 17,485,835 1863 11,785,320 9,533,742 21,319,062 1864 12,538,649 11,066,474 23,605,123 1865 11,891,746 11,900,427 23,792,173 1866 15,651,183 13,352,400 29,003,583 1867 16,002,109 14,722,313 30,724,422 1868 17,003,405 15,858,555 32,861,960 1869 17,083,134 15,821,226 32,904,360 1870 15,664,275 17,371,305 33,035,580 1871 19,342,057 27,543,023 46,885,080 1872 24,233,166 27,220,233 51,453,399 1873 26,152,837 31,449,643 57,602,480 1874 24,818,790 27,787,130 52,605,920 1875 22,485,766 29,862,554 52,348,320 1876 22,793,245 30,486,755 53,280,000 1877. 25,660,316 34,841,444 60,501,760 1878 21,689,682 36,245,918 57,935,600 1879 30,207,793 37,898,006 68,105,799 1880 28,649,812 42,831,758 71,481,570 1881 31,920,018 53,961,012 85,881,030 1882 35,121,256 68,429,933 103,551,189 1883 38,456,845 77,250,680 115,707,525 1884 37,156,847 82,998,704 120,155,551 1885 38,335,974 72,824,321 111,160,295 1886 39,035,446 74,644,981 113,680,427 1887 42,088,197 88,562,314 130,650,511 1888 46,619,564 ' 102,040,093 148,659,657 1889 45,546,970 95,682,543 141,229,513 1890 46,468,641 111,302,322 157,770,963 COAL AND COAL-PRODUCING FIELDS 87 Year Pennsylvania Anthracite Bituminous Total 1891 50,665,431 117,901,238 168,566,669 1892 52,472,504 126,856,567 179,329,071 1893 53,967,543 128,385,231 182,352,774 1894 51,921,121 118,820,405 170,741,526 1895 57,999,337 135,118,193 193,117,530 1896 54,346,081 137,640,276 191,986,357 1897 52,611,680 147,617,519 200,229,199 1898 53,382,644 166,593,623 219,976,267 1899 60,418,005 193,323,187 253,741,192 1900 57,367,915 212,316,112 269,684,027 1901 67,471,667 225,828,149 293,299,816 1902 41,373,595 260,216,844 301,590,439 1903 74,607,068 282,749,348 357,356,416 1904 73,156,709 278,659,689 351,816,398 1905 77,659,850 315,062,785 392,722,635 1906 71,282,411 342,874,867 414,157,278 1907 85,604,312 394,759,112 480,363,424 1908 83,268,754 332,573,944 415,842,698 1909 81,070,359 379,744,257 460,814,616 1910 84,485,236 417,111,142 501,596,378 1911 90,464,067 405,907,059 496,371,126 1912 84,361,598 450,104,982 534,466,580 1913 91,524,922 478,435,297 569,960,219 1914 90,821,507 422,703,970 513,525,477 1915 88,995,061 442,624,426 531,619,487 2,626,512,578 8,262,792,323 10,889,304,901 COAL PRODUCING STATES Coal is produced in thirty states, but almost eighty (80%) per cent, is produced west of the Mississippi river. The relative importance of the states was expressed by the Geological Sur- vey in percentage of all coal produced (bituminous and anthra- cite) as follows, for 1915: 88 MECHANICAL STOKERS Pennsylvania : Anthracite 16.8% Bituminous 29.7% West Virginia 14.5% Illinois 11.1% Ohio 4.2% Kentucky 4.0% Indiana 3.2% Alabama 2.8% Colorado 1.6% Virginia 1.5% Maryland 8% Oklahoma 8% Missouri 8% New Mexico 7% Utah 6% Washington 6% Montana 5% Texas 4% Arkansas 3% Michigan 2% Iowa 1.4% Kansas 1.3% Wyoming 1.2% North Dakota 1% Georgia, Oregon, California, Idaho, Nevada, South Dakota. . .1% COMPOSITION OF COALS To some extent, the analysis of a coal will give some indi- cation of how successfully it can be handled on a grate or stoker. These analyses can be made with proper facilities, and are not too technical for boiler-room work. The two analyses generally used are the Proximate analysis and Ultimate analysis. Proximate Analysis. The proximate analysis of coal de- termines the moisture, volatile matter, fixed carbon, percentage of ash, and sulphur (separately determined). The fixed carbon is the carbon remaining after distillation. Volatile matter is the total combustible, less the carbon contents, and includes hydric carbons, etc. Ash is the residue remaining after the moisture and volatile contents have been driven off and the carbon consumed. Moisture is that percentage of the weight of the coal when dried at a given temperature. COAL AND COAL-PRODUCING FIELDS 89 Ultimate Analysis. The ultimate analysis is a more compli- cated chemical analysis giving the percentages of carbon (C), hydrogen (H), nitrogen (N), Sulphur (S), and ash (A). This analysis is used, and is necessary for making the heat balance on any given boiler test. The ultimate analysis does not dis- tinguish between the carbon and hydrogen derived from the combustible matter of coal. Heating Value. The heating value, sometimes called the calorific value of coal, is the number of units of heat liberated by the perfect combustion of a unit weight of the coal. The British Thermal Unit (B.T.U.) is used to designate the heating value, and is the quantity of heat required to raise the tem- perature of one pound of water 1 F. A bomb calorimeter, many of which are on the market, is used to determine the heating value of coal, and can easily be used in connection with boiler-room equipment. Heating Value from Analysis. A number of equations have been derived to give the heating value of coal from the analy- sis. The one most commonly used is DuLong's formula, which is as follows : B.T.U. per Ib. of coal = 14,544 C + 62,028 (H-^ +4050 S. C, H, and S are the percentages of carbon, hydrogen, oxygen and sulphur, respectively, in the combustible. For western coals, DuLong's formula gives heating values a little too low, but for eastern coals, is sufficiently close for estimating purposes. CLASSIFICATION OF COALS U. S. Geological Survey. Coals can be classified in many different ways, namely, according to the chemical composition, the ratio of volatile and carbon, location of mines, etc. The United States Geological Survey method of classifying coals is part chemical and part physical, the same being as follows: Anthracite is generally defined as hard coal, most of it being mined in Eastern Pennsylvania. Small areas of anthracite occur in the West. Anthracite is an almost ideal domestic fuel, but largely on account of its low heating power, it is not an 90 MECHANICAL STOKERS economical fuel for steam raising or for use in general manu- facturing. Semi- Anthracite is also a hard coal, but it is not so hard as true anthracite. It is high in fixed carbon, but not so high as anthracite. The change of -ordinary soft coal to semi-anthra- cite is due to the same causes that produced anthracite, except that the process has not been carried so far in semi-anthracite. There is very little semi-anthracite in this country, so it is only a small factor in the coal trade. Such semi-anthracite as is mined reaches the consumer generally under the name ' ' anthra- cite." Semi-Bituminous. The name "semi-bituminous" is exceed- ingly unfortunate, as literally it implies that this coal is half the rank of bituminous, whereas, it is applied to a kind of coal that is of higher rank than bituminous really super- bituminous. Its relatively high percentage of fixed carbon makes it nearly smokeless when it is burned properly, and con- sequently, most of these coals go into the market as ' ' smokeless OO rH rH (N rH Tfl IO rH t^ rH t^. CO 00 iO t^- OOOi O rH f* fe CO CO CO O5 O (M CD rH 00 O H ca co b- 1O CD rH Thl 1> rH CD O rJH 1C CO 00 O I-H .J^ . .t|_H . * .o> . .0 . ^ . .11 .-fj .11 . . .o3 .0 .o3-.. a ' e llfi terminations of Jan. Moisture assumed. Volume obtained by sh Dete COAL AND COAL-PRODUCING FIELDS 99 .11 M o fl III % I' S 5 2 > "S 3 & ^) OJ M ?! O 85 O 'H' 3 a Is c .2 .2 i S 8* 8 -2 J: 0) G si 11 O iO 10 O e eoeodcoTHco't-ic^ '.-I ddciw coi-i^Ji-! -H^H 02 OOCC^J* OO5 d -OCO t^OO5OiCOiO(N -OO 1 : a : -2 j bo 11! Hi! OOOOO O il OQ 66 i 00 . 11 m mil QQQQQ i COAL AND COAL-PRODUCING FIELDS 101 eo o" M" c : | i-H (N O -* I" CO ^C CO O O C5 O O ' CO 00 rH C O CSCOCO'COCO'COCOCO TH. OOCOCOCOCO. COCO 3 2 cococo -coo -t^oeo O O O O CD T-H O T^l CD CO CO OS IO <9 IQ IQ lo^^iOT^Tjn O O o o o OS CO cO ^ IO Tt< O 1C 15-5 * OO (M iO 1-1 C^ >O 00 O O O *0 O5 O5 GO rH O5 3 2 t*1 IS l-g b HIM | H o < bC 'd o I I co S i a a-fl 1~.l 03 03 O O o K & PH 1 1 I 2 : o 11 1 1 : 1 ij O O O P Z M u Q ffi M l > * Q o O) O Appanoose Leavenwor |.=i ;.s O cj o3 " /> ! 3 a a c3 1 o| W M : .3 ^ i 111111 03 ase of Stack- Inches Water 0.1 02 OA 0.4 0.5 0.6 0.1 0.8 0.9 1.0 I.I 1000 Escaping Gasjemp >TSl For Stack Heights other than 100 Ft. - Multiply tne Curves Value by the Rrfio { of Height to 100 ~ i 120,000 180,000 240,000 300,000 Lbs. of Flue Gas per Hr. 90,000 FIG. 55. Performance of 100' Stacks from 36" to 90" Diameter. As an illustration of the use of these curves, assume that it is desired to determine the correct chimney size for 2,000 boiler H.P. output. It is first necessary to establish values for weight of gas per H.P. and exit temperature. Sixty Ibs. of gas per H.P. represents good operation and from seventy to seventy-five Ibs. if fair. First, locate the intersection of the horizontal line for 2,000 H.P. with the diagonal line represent- ing weight of gas per H.P., then project vertically to the curved lines of chimney diameter. A horizontal line through this intersection will in turn intersect the diagonal lines repre- senting escaping gas temperature. A vertical line is then drawn through this latter intersection to the scale of chimney 134 MECHANICAL STOKERS draft at the top of the diagram and the draft that would be produced by a chimney of the given diameter and 100 ft. high is read from this scale. For example, a 60" chimney 100" high would produce a draft of only .39" with a load of 2,000 H.P. In general it may be said that a chimney that will not produce at least .55" draft with gases at 500 F., for each 100 ft., in height, is overloaded and the frictional resistance is too great due to excessive velocities. The 60" chimney would therefore be too small. The selection would lie between the Draff df Base of Stack- Inches of Water .10 .15 .25 35 .45 .55 .65 .15 .85 .95 1.05 US t.25> eooo HOTE: For Stack Heights of her than ' 100 Ft- Multiply the Curves Value by the Ratio ofHewht to 100 I I I ill 1 s- S s < s" s sf g x ucu^^m Lbs.of Flue Gas per Hr FIG. 56. Performance of 100' Stacks from 96" to 144" Diameter. 72" size which will produce .59" draft per 100 ft. and the 78" which will produce .62" per 100 ft. It is apparent that for a given draft at the base of the stack, a lesser height will be required with the greater diameter. Assume that 1.10" must be available at the base of the stack, the 72" size must be X 100 =187 ft. high, while the 78" size must be X 100 =177 ft. high. \)Z The choice between these two sizes will depend upon first cost and such local conditions as may effect the selection. DRAFT 135 In the case of natural draft, the static draft must overcome all resistances to flow which are as follows : 1. Loss through fuel bed and grate 2. Loss through boiler 3. Pressure required to create velocity of gases leaving the boiler 4. Damper loss 5. Breeching loss 6. Friction loss in chimney A number of formulae have been developed for determining certain of these amounts but they depend to such an extent upon the values selected for certain constants that their ap- plication is of doubtful value. It is known that the temperature of gases in a chimney is less near the top than at the point where the gases enter, due to radiation and to leakage of cold air into the chimney, but no data are available from which the amount of this difference can be determined accurately. The relation between static draft and that available for any given operating condition will depend upon a number of variables, the principal ones being the diameter of the chimney, the nature of its surface, and the velocity of the gases. Of the above losses, the first and second are most important and of greatest amount. The method of analyzing these losses can best be explained by reference to Pig. 57, which shows a cross section through boiler and stoker. Provision should be made to take draft readings at the points indicated and connections to the draft gauges should be carefully made to insure an absence of leaks which affect the accuracy of the readings. If these readings are to be of any value, they must be taken under operating conditions, with a good fire on the grates and gas analyses should be made to determine the com- bustion conditions. Notes should be made recording the fuel bed conditions, gas analyses and ratings developed. These data arc necessary as they affect the draft losses and no conclusions can be drawn from draft readings unless accompanied by such information. In case an unusual loss is encountered between any two points, such as B and C, the draft gauge can be corrected as shown to read this loss directly and the effect of 138 MECHANICAL STOKERS any change in conditions will be detected immediately. The values given represent actual results of an investigation but are used merely for purposes of illustration and not to establish standard values for the type of boiler shown. The performance of a chimney was first presented in con- venient form by William Kent in 1884 and the table of chimney sizes calculated from the formula given has been almost uni- versally used by engineers since that time. This table is based 4th. Pass 8.24 ' Ratio 1 to &38 2nd. Pass 14.13 Ratio 1 to 4.82 Total .46" NOTES:- fuel Bed about 6 M thick CO Z -I2.4%, 2 -5.97o,C.O-0% RatinafrornFlow Meter Readings 145% Ignition Good No Holes in Fire eideWalls'underArch Will Bum the Bare Hand FIG. 57. Analyzing Draft Losses through Boilers. on the use of five pounds of coal per boiler H.P., and twenty pounds of air per pound of coal. The height of the chimney must be determined independently of this table by the draft which must be available at the base of the chimney to overcome the various losses of fuel bed, boiler, damper and breeching at the ratings for which the installation is designed and many mistakes have been made by engineers due to their failure to make proper allowance for these losses. DRAFT 137 A chimney which would be of the proper size to produce draft for two five hundred horsepower boilers operating at rating, would be entirely unsuitable for one of these boilers operating at 200% rating for the reason that the draft loss through the fuel bed and the boiler is very much greater at 200% rating than at rating and the chimney which was right for two 500 H.P. boilers at rating would not produce the draft intensity required to overcome these losses. In the ordinary chimney calculations, sea level conditions of atmosphere are assumed. The error due to this assumption is slight for elevations up to 1,000' and it is not customary to make corrections but when plants are located at greater alti- tudes, it is necessary to make allowance for the existing at- mospheric conditions. Owing to the lower atmospheric pres- sure at high altitudes, the draft intensity produced by a chim- ney under a given set of conditions is less than at sea level and an increase in height is necessary. The density of the air and flue gases being less at the higher altitudes, an increase in cross sectional area is necessary to handle the same weight of gas at a given velocity. Due to the lower density, there is slightly less friction for a given velocity but this is so small that it can be disregarded. In proportioning a chimney for high altitudes, one is first selected which would be used under sea level conditions and the height and diameter are then increased by the amount required to correct for the given altitude as shown in Fig. 58. Since the height of the chimney depends upon the draft which will be required at its base, it is obviously very im- portant that the various losses which must be overcome be carefully considered and accurately estimated. Failure to do this, may result in a serious mistake and one which is very difficult to correct. The various losses outlined above will be considered separately. First, "Loss through fuel bed and grate." In the de- sign of a stoker installation, one of the first things which must be determined is the combustion rate as outlined in Chapter VIII. This combustion rate being known, the fuel bed resistance can be approximately determined for natural 138 MECHANICAL STOKERS draft stokers from Fig. 59 and for forced draft underfeed stokers from Fig. 60. 1000 2000 3000 4000 5000 6000 Altitude, Feet Above Sea level OOO 8000 9000 10000 FIG. 58. Altitude Corrections for Chimney Dimensions. It should be understood that these curves are only ap- proximate and that actual performances may differ consider- \ PerC enl- Solids 1 AH r;c.+Ash)/ V V M ^D ^ \ A -40 B-50 /, / / X x^ \ "C-60 D-70 Z '/ /\ x \ rE- U i // /, / \ / /\ / \ /// y\ 3 \ / ///, / i \ I Y 1 \ i \ j 50 45 40 35 30 25 20 15 Coal per Sq.ft. per Hr.- Pounds 10 5 .10 '.20 .30 .40 .50 .60 .10 .80 .90 1.0 Draft-Inches of Water FIG. 59. Furnace Draft Required for Natural Draft Stokers. ably from the values given. The reason for this is that the curves fail to take into account two of the principal factors affecting fuel bed resistance, namely the dust and moisture DRAFT 139 contents of the fuel. Commercial screenings will vary in size approximately as follows: Overl Maximum ....... 50% Minimum ....... 2% Over" Over J" Over |" Through \" 25% 15% 7% 3% 20% 25% 15% 38% Hundreds of draft readings have been taken on tests where the combustion rates were being carefully recorded but no information has been secured as to the percentage of dust in the fuel. The relation of draft to combustion rate is affected to such an extent by the percentage of fine dust in coal that without this information the draft readings and combustion \ Per Cent Solids(F.C.+ Ash) -A -40 9t ;A .-B -C 100 90 80 70 60 50 40 30 20 Coal per Sq. Ft. per Hr -Pounds 10 12345678 Wind Box Pressure -Inches of Water FIG. 60. Windbox Pressure Required for Underfeed Stokers. rates are of little value. A fuel containing 40% of dust that will pass through a %" round screen can be burned at only about 60% of the rate which can be secured with the same draft from coal containing only 5 or 10% of dust. It is for this reason that such wide discrepancies exist in the drafts required to burn fuel. It has been found that by adding a sufficient amount of moisture to agglomerate this dust, the fuel bed resistance can be materially re'duced and the combustion rate with the given amount of draft correspondingly increased. This explains the improved combustion which often results from adding moisture to fuel and which is often ascribed to chemical action of the moisture. The action is entirely mechanical and is due to reduced fuel bed resistance. 140 MECHANICAL STOKERS The percentage of solids (F. C. and ash) in coal also affect the draft required for combustion. A coal high in volatile can be burned at a given rate with less draft than a low volatile coal, not because less air is required but because it is the solid matter and not the volatile that determines the character of the fuel bed and the amount of air that can be drawn in with a given draft. The curves (Fig. 59) show to what extent this factor influences the draft required. As an example, a thirty-pound combustion rate with coal having F. C. w +. ash = 50% will require .21" furnace draft while a 1.10 1.00 0.90 0.80 O.TO 0.60f 0.50 040 tt30 020 0.10 A 4 Pass Vertical Baffle 14 Tubes High _B 3 16 > w C 3 ' >' 14 D 3 E 3 -I ! Sterling or Vertical Heine Type 100 140 160 180 200 220 Per Cent Boiler Rating 260 280 300 FIG. 61. Draft Losses through Boilers. coal having F. C. + ash = 70% will require .38" draft for the same combustion rate. Second: "Loss through boiler." The draft loss through boilers varies through wide limits. With the great number of boilers of different designs and the variety of baffle arrange- ments, installed to meet particular local conditions, it is impos- sible to establish values for draft losses which can be of general application and it is advisable to secure from, the manufacturer, figures for the particular boiler and baffle ar- rangements which may be under consideration. The curves shown on Fig. 61 may be used, however, for preliminary calculations. DRAFT 141 Third: "Pressure required to create velocity of gases leaving the boiler. ' ' The draft required to create velocity of the gases leaving the boiler is not an important item. At a velocity of the 20' per second, the draft required is about .05" at a temperature of 550 and for 30' per second, the draft required is about .11". There is, however, a certain chimney effect in the boiler itself due to the vertical height from the fuel bed to the damper which is usually sufficient to offset the loss required to create the velocity. This is clearly shown in the case of some large boilers operating on forced draft running with practically atmospheric pressure in the furnace which can be operated at rating with atmospheric pressure or a slight pressure above atmosphere just below the boiler damper. In this case, the chimney effect of the boiler is sufficient not only to create the velocity, which is low, but also to overcome the boiler draft loss, Fourth: "Restriction at damper." There should be no re- striction at the boiler damper if it were wide open but the areas through boiler dampers are often inadequate especially when the boilers are operated at high ratings. As dampers are often installed there is a sudden change of direction either when the gases enter the damper opening or just as they leave which is responsible for a certain amount of draft loss. When boilers are operated at high ratings, the gas velocity through the average damper will exceed 30' per second and there will be a draft loss of about .1". In many cases, however, dampers are installed in such a manner that the loss is two or three times this amount, due to the fact that the path of the gases through the damper opening is such that when the damper is wide open it interferes with the free flow of gases through the opening on both sides of the damper itself. The location of the damper and the path of the gases both entering and leaving should be carefully considered to insure a free passage if unnecessary draft losses at this point are to be avoided. Fifth: "Breeching losses." Accurate data upon which draft losses through a given breeching may be determined are not available. The effect of changes in cross section of the breech- ing, disturbances in the flow caused by successive boilers dis- charging into the breeching, the shape of the gas passage and 142 MECHANICAL STOKERS the nature of its surface cannot be determined with a degree of accuracy which permits of general application. The best posible guide in the design of a breeching is an accurate record of draft losses in a similar breeching where gas velocities are approximately the same as those for which the breeching is being designed. There are a number of " thumb rules" for proportioning breeches in accordance with boiler H.P., grate area, or some other known unit, but they all neglect one or more factors which have an important bearing on the correct design. It is necessary, therefore, to analyze the conditions in sufficient detail to determine the gas volumes to be handled and the breeching areas proportioned to give the desired velocity. Formula A (page 132) for friction losses in chimneys is ap- plicable to breechings but is less accurate due to the disturbances created by successive boilers discharging into the breeching with consequent sudden changes in the direction and velocity of flow. In general, it may be said that there will be a loss of .1" for every 50' of straight breeching for breechings having not less than 25 sq. ft. cross sectional area and a velocity not exceeding 30' per second. The draft loss in a right angled bend will also be about .1" for a velocity not exceeding 30' per second. If the area of the breeching is small, the draft loss is increased and in such cases, it is usually preferable that the velocity be reduced rather than that the chimney be made high enough to overcome the additional friction. A good rule to follow in this connection is that the velocity in feet per second should not be greater than the area of the breeching in square feet. This of course becomes absurd for very small breechings but can be followed for areas as small as twelve to fifteen square feet. For larger breechings, a velocity of from twenty-five to thirty feet per second will be found satis- factory and this can be increased to thirty-five feet for short distances. A circular breeching offers less resistance to the flow of gas than one of square or rectangular section. A breeching of a given diameter has about the same draft loss for a given condition as a square breeching whose sides equal the diameter of the round breeching. In the case of rectangular breechings, DRAFT 143 the ratio of surface to cross sectional area is greater than for either the round or square breeching and the carrying capacity for a given draft loss becomes less. By the use of curve (Fig. 62) a rectangular breeching may be directly compared to its equivalent circular or square section of equal carrying capacity. Sharp turns or sudden changes in cross section are to be avoided and a construction should be employed that is air- tight when new and can easily be kept tight. Suitable doors should be provided for inspection and cleaning and where 40 50 60 Diameter of Circle 100 FIG. 62. Circular Equivalents of Rectangles for Equal Friction per Unit of Length, radiation will cause excessive temperatures in places where repair men may be required to work, the breeching should be insulated. Underground flues are almost invariably unsatis- factory and should be avoided wherever possible. It is sometimes difficult to secure a simple straight breech- ing on account of local conditions but if the importance of such construction is fully appreciated, the necessary changes can usually be made to permit of a suitable layout. Construc- tion difficulties are soon forgotten after operation has begun but the operating engineer who has to contend with a poor breeching, works at a disadvantage as long as the plant 144 MECHANICAL STOKERS operates. In one extreme case of bad design, two 90 turns and twenty feet of length were added to avoid moving a 16" steam line which could be cut out over the week end and changed without affecting the plant operation. Fig. 63 shows the method of analyzing draft conditions in a breeching and incidentally brings out some defects in the design shown although the areas were ample and the gas velocity at no point greater than twenty-five feet per second. The dampers when open project into the breeching and seriously interfere with the gas flow both by restricting the Boiler No. 1 Boiler No.2 Boiler No.3 BoilerNo.4 BoilerNo.5 BoilerNo.& NOTE'. Letters Show Location of Draft Readings A-.44" B-.62" C-.G8" D-.85" E-.5S" F-.SO" G'.45" H-.92 1 ' FIG. 63. Analyzing Draft Losses in Breechings. breeching area and by improperly directing the gas. At A, the gas passing through the left side of the damper opening is directed against the top of the breeching and must make a sudden change in direction resulting in an unnecessary draft loss. At B y the same condition exists and in addition, the net breeching area is reduced to about two-thirds of the full area, resulting in a gas velocity at this point considerably greater than that for which the breeching was designed. This condition exists at all boiler dampers and is a serious defect. Where the two branches meet and go to the chimney, there is a sudden DRAFT 145 change in direction and a serious disturbance to flow by the manner in which the two streams of gas come together. This is shown by the large draft loss between points C and H. The sudden reduction in width between point H and the entrance to the chimney is also responsible for an unnecessary loss which could easily have been avoided. This breeching would be a good design instead of a very poor one if the following changes had been made: First, raise the breeching enough to bring the top of the boiler dampers when wide open down to the bottom of the breeching, thereby allowing the full area for gas passage; second, eliminate the right angle turn where the two branches meet the connection to the chimney; third, reduce the width of this chimney con- nection gradually instead of suddenly. The changes could have been made with only a slight increase in cost and no structural difficulties would have been encountered in this par- ticular case. The sum of losses one to five inclusive, is the actual draft which must be available at the base of the chimney and when determining the chimney height necessary to produce this draft, the maximum temperature of the atmosphere in the given locality must be used because the draft depends not upon the temperature of the gases in the chimney but upon the difference between this temperature and that of the outside air. There has been much discussion of the merits of individual chimneys as compared with one large chimney for several boilers. The individual unit has the advantage of being pro- portioned for only one boiler and no allowance must be made for leakage through dampers of idle boilers. Repairs can be made when necessary without interfering with plant operation, there is no breeching loss to consider and close fitting boiler dampers are not necessary. Where boiler units are small, how- ever, the cost is excessive and this consideration will result in the selection of one chimney for a number of units. A similar selection is sometimes made for the sake of appearance. In general it may be said that while the chimney serving a group of boilers must be made higher to take care of breeching losses and damper leakage there are no controlling factors except cost and appearance. 146 MECHANICAL STOKERS The efficiency of a chimney will depend upon the basis on which the calculations are made. Since the flow of gases is maintained due to temperature difference inside and outside the chimney, the efficiency is measured by the amount of heat expended for this purpose. The foot pounds of energy required to handle a given weight of gas represents a very small per- centage of the energy delivered to the chimney in the form of heat and on this basis, the efficiency would not exceed .06% under average conditions. While the actual efficiency is very low, the chimney has many advantages as a draft producer. It has no moving parts and does not require daily attention. The cost of upkeep is low and the possibility of failure is remote. The heat necessary to produce the draft has been rejected by the boilers and might be considered a waste product. With these advantages, the chimney would appear to be ideal for producing draft but the fact that other methods are often employed, shows that there are conditions which the chimney cannot meet. Induced Draft. With the draft requirements in many plants and the temperatures at which the gases leave the boiler heating surface, a chimney of less than 200' in height is suffi- cient. Many of the smaller installations require chimneys of not over 100' in height and except in unusual cases, chimneys of over 250' are not built. The use of an economizer has two very important effects on the draft producing apparatus : first, it lowers the tempera- ture of the gases, and since the ability of the chimney to produce draft depends upon the difference of temperature be- tween the air and gas, it reduces the effectiveness of the chim- ney, requiring a much greater height to produce a given draft intensity; second, the economizer offers a certain amount of resistance to the flow of gases which must be overcome by the chimney draft. A greater draft intensity at the base of the stack is therefore required when the economizer is used. Considering the decreased temperature and the increased gas resistance, it would often require a chimney 400 or 500' in height to produce the necessary draft. This, of course, is im- practical on account of the great cost and some other means for producing draft must be employed. I47 J A number of years ago many installations were made in which one economizer served all the boilers in the plant and delivered the gases to a chimney. The installation of economiz- ers under such circumstances often resulted in an actual loss in economy instead of in a substantial gain which should have been realized, and in addition, decreased the capacity on ac- count of the large reduction in draft available for burning fuel. The induced draft fan which takes the gases from the breeching at a pressure below the atmospheric pressure and discharges them to the atmosphere is commonly employed where the chimney is not able to meet the conditions. With this arrangement, any draft intensity required in even the most unusual cases is easily secured. Induced draft is also employed in many plants where a high chimney would detract from the appearance of the building or its surroundings. The increasing tendency to operate boilers at higher ratings introduces two conditions tending to make induced draft de- sirable if not absolutely necessary: first, the temperature of escaping gases increases with the rating and it is found desir- able to install economizers to reclaim the large amount of heat that would otherwise be lost; second, the draft loss through a boiler increases rapidly with the rating and at ratings now developed in many plants, chimneys of commercial sizes do not produce sufficient draft to overcome these high losses. Induced draft fans to fulfill any set of conditions met with in practice can be selected from standard designs and it is therefore not necessary in the selection of induced draft equip- ment to go further than to determine the service which the fan must perform. The procedure so far as the suction at the fan inlet is concerned is practically the same as in the case of chimney design. To determine the volume of gas to be handled, it is necessary to know the maximum horse power which the boilers served by the fans will deliver, the heating value of the coal, the percentage of excess air in the gases entering the fan and the temperature. The percentage of excess air must be determined from a knowledge of operating conditions and the gas temperatures can be stated with a fair degree of accuracy by the builders of the boilers and economiz- 148 MECHANICAL STOKERS may be used to de- handled per unit of ers. With this information, Fig. 64 termine the cubic feet of gas to be time. Induced draft fans are of two general types : the steel plate and multi-vane. Steel plate fans run at relatively low rotative speeds and are usually engine driven, the engines being direct connected. The multi-vane fans run at higher speeds and are suitable for turbine or motor drive. The type of fan selected will depend upon local conditions and individual preference. Where units of large size are installed, space limitations often & 40 10 II 12, 13 14 15 16 n 18 19 20 21 22 23 24 25 Cubic Feet of Air per Minute FIG. 64. Volume of Air per Developed Boiler Horsepower. make the multi-vane fan the only one which can be conveniently installed. The fan drive must be selected with a clear understanding of the nature of the service it must perform and the drive should be of sufficient power to operate the fan at maximum capacity under the most unfavorable conditions. In the case of a steam-driven unit, the engine or turbine should be of sufficient size to carry the full load with an abnormal drop in steam pressure. When steam is low, the fan must handle the maximum amount of gas if normal pressure conditions are to be re-established and if the fan drive is not of sufficient power, the fan will slow down thereby crippling the entire plant. The drive should, therefore, be designed to operate on DRAFT 149 a pressure somewhat below the lowest pressure which may ever exist. The exhaust from the steam unit should be used for heating feed water or for other useful work around the plant. In case exhaust steam is not required, the fan should be motor driven. In the case of turbine drives, the fan may be direct connected to a low speed turbine if a large amount of exhaust steam can be utilized but where only a limited amount of steam is desired, the high speed geared turbine is preferable on account of its lower water rate. This matter should be carefully studied in connection with the heat balance of the plant and in no case should a steam driven unit be installed if any of the exhaust steam is to be wasted. If the exhaust is properly utilized, the net reduction from the overall efficiency of the boiler unit will be only a fraction of one per cent but if the exhaust is to be discharged to the atmosphere, the loss may be as high as five per cent. A chimney which is properly designed for a given plant condition where economizers are not installed, would be unable to meet the requirements if economizers were added, due to the fact that it would not be able to produce sufficient draft intensity to overcome the various resistances. In the case of an induced draft fan, however, it usually is the case that the same fan will do the work whether economizers are installed or not. In either case practically the same weight of gas must be handled. The installation of economizers merely re- duces the temperature and volume and increases the resistance to be overcome. The induced draft fan operating in connection with economizers would have a smaller volume to handle than would be the case without economizers and due to this decrease in volume, and increase in density the fan would naturally produce a higher suction. The one just about offsets the other and the fan is therefore able to meet both conditions, requiring almost exactly the same horse power in either case. Forced draft is required for those stokers carrying heavy fuel beds and designed for operation at high rates of combus- tion. Pressures under the grates of such stokers vary from V to 6" and the increasing use of such stokers has brought about the development of a number of fans particularly well 150 MECHANICAL STOKERS suited to this class of work. The pressure required for dif- ferent combustion rates on stokers using forced draft is subject to the same correction for the dust content of the fuel that applies to natural draft stoker work and (Fig. 60) showing the relation of wind box pressures to combustion rates are approximate only although the effect of the dust content is less marked than in the case of natural draft stokers. Where forced draft is employed it is necessary to make calculations of the amount of air that will be required. It is pos- sible to calculate the theoretical amount of air required for combustion as outlined in Chapter I and to make an allowance for excess air entering the combustion process and for leakage from the air duct. Fig. 64 shows the volume of air in C.F.M. per boiler H.P. developed for various efficiencies and grades of coal. For example, if 13,000 B.T.U. coal were being burned at a combined efficiency of 70%, there would be required 12.8 cubic feet of air per minute per H.P. This allows about 60% excess air which is more than that required for good operation and will be found to provide ample for all reasonable conditions. Forced draft fans should be selected of ample capacity for the maximum demand which they may be required to meet in case of emergency. The data available on forced draft stoker work indicate that in almost every installation, the limiting capacity is determined by the ability to force air through the fuel bed. In the case of natural draft stokers an abnormally high draft draws such quantities of air through the fuel bed near the zone of ignition that the temperatures will fall and ignition become sluggish, thus limiting the capacity which can be secured. Stokers of this type are there- fore provided with arch constructions which are designed with a view to providing sufficient ignition effect for the ratings which are desired. In the case of the heavy fuel beds carried on forced draft stokers there is probably a similar limitation but it has never been reached in practice. The limiting factor is either the ability to supply air or to discharge the refuse and since for short peak loads the stokers can be operated without discharging refuse, the ability to supply air is the DRAFT 151 limiting factor, and the importance of ample fan capacity is apparent. In selecting a fan for high altitudes, the density of the air must be taken into account. The static pressure developed by a fan at any given speed will decrease with increased altitude and it is therefore necessary to make a correction as fan performances are based on sea level conditions. It is also necessary to correct the volume of air to give a weight of air equal to the weight at sea level. It will be found, however, that the power required to drive the fan will be less than that calculated for sea level conditions and an additional correc- tion must be made for this condition. Fig. 65 can be 115 85 500 2500 1000 1500 Altitude in Feet FIG. 65. Altitude Corrections for Fan Performance. 3000 used for this purpose. It will be seen that at an altitude of 3,000 ft. the volume and pressure determined for sea level con- ditions must be increased 12% and that the power will be decreased 10%. As an example, assume a condition requir- ing 25,000 C.F.M. at 6" static pressure at sea level. At an altitude of 3,000', the volume and pressure must be increased 32%, making 28,000 C.F.M. against a static pressure of 6.72 inches. If a fan were selected that would deliver 28,000 C.F.M. against 6.72 inches at sea-level and required 50 H.P. for its operation, the power required at an elevation of 3,000 ft. would be (.9 X 50) or 45 H.P. A forced draft fan to be suitable for stoker work must have certain characteristics. Fans are designed to deliver a given volume 'of air against a given static pressure when run- ning at a specified speed. In case the resistance be increased 152 MECHANICAL STOKERS and the speed maintained constant, some designs will deliver against this increased resistance only a small percentage of their rated volume. Such fans are evidently not suitable for forced draft stoker work. In case of careless operation, abnormally heavy fires may be built up increasing the pressure against which the fan must operate and the design should be such that the fan will operate against this increased resistance with only a slight decrease in volume. The steel plate fan has the correct characteristics for such performance and mul- tivane designs have also been developed which fulfill this requirement very satisfactorily. There are multivane fans designed for different service which do not have this charac- teristic and they should not be used for forced draft service. The selection of a fan drive depends largely upon local conditions. Where exhaust steam can be used, steam driven units are often installed. In the case of small installations where the pressure need never exceed three or four inches of water, the slow moving steel plate fan direct driven by a steam engine is often used. Larger installations usually con- sist of multivane fans turbine driven with or without reduc- tion gears, depending upon the amount of exhaust which can be used. It is sometimes desirable to install some steam driven and some electrically driven fans in a large installation in order to assist in maintaining a correct station heat balance. In plants where exhaust steam can be utilized, the net charge against the forced draft equipment represents from .25 to .6 of 1% of the steam generated. Where motor driven fans are used, the net deduction will be from .75 of 1% to l l / 2 % but will always be less than 1% where efficient generating equip- ment is installed. Boiler units of 800 H.P. and larger, equipped with forced draft stokers, are suitably served by individual fans. This arrangement has the advantage of short connections from fan to stoker wind box and simplifies the regulation of the air supply to the individual units. It also eliminates the resistance which is encountered in long air ducts requiring less power to operate the fans. Smaller units are usually served from a common air duct suplied by one or more fans conveniently located. Owing to the fact that air is delivered to the stokers DRAFT 153 at atmospheric temperature, ducts of large cross section are usually not required. Air velocities of from 30 to 50' per second are usually employed, although in case of space limita- tions considerably higher velocities can be used if proper allowance be made for the friction in the duct. For steel ducts there will be a pressure drop equal to the pressure required to create the given velocity for every twenty diameters of duct and a right angled turn will cause a drop of one half this amount. For construction reasons, ducts are usually made square or rectangular and the equivalent round duct may be readily determined from Fig. 62. It has been pointed out that the plant heat balance affects the selection of fan drives. Another factor which must be considered is the nature of the boiler plant load. In the case of an electric generating station, any accident which affects the electrical system seriously will throw the load off the boiler house. In such plants motor drives can be safely employed but if part of the steam goes to the electric generat- ing apparatus and a considerable amount goes into process work, a failure in the electrical ends of the plant will throw only part of the load off the boilers. In such cases, it is desir- able either to install some steam driven fan units or to secure the necessary electric power from an independent steam driven house generating set. CHAPTER VI FACTORS AFFECTING SELECTION OF STOKER EQUIPMENT When stokers are applied to steam generating apparatus, the individual features of the different types of stokers and their influences are taken into account. Especially is this necessary for proper selection of stoker equipment to attain certain ultimate results of the complete generating unit includ- ing the stoker, the furnace and the boiler. A plan to investigate the stoker for a special combination requires primarily an exact definition of the terms used in connection with the units making up the complete steam generating apparatus. For example, the word "boiler," is employed indiscriminately to designate either the boiler proper or the combination of it with other apparatus. The brick walls which enclose the boiler, the stoker or the furnace, are not recognized as being in any way a part of the metal structure. The stoker is that portion of the combination which pro- vides means for feeding the fuel as required, supplying the air in such relative proportions as to cause a balancing of the quantities of air and combustible, and causing the air and gases to mix and burn without smoke, also providing means for burning the coke and discharging the ashes. The furnace is the intermediate element located between and connecting the stoker and boiler, wherein the process of combustion which begins at the grate is finished, and where a sufficient mixture between air and combustible may be secured. In selecting stoker equipment, four factors are considered. These, in the order of their importance, are 1. Load to be carried. 2. Fuel to be used. 154 SELECTION OF STOKER EQUIPMENT 155 3. Draft requirements. 4. Application characteristics. LOAD CONDITIONS The character of the load to be carried, that is, the boiler horse power that must be developed and the time element in connection with increases in the load, is of prime importance because this factor is generally beyond control; that is, the characteristic load is generally established by the particular industry. It is the function of the stoker and boiler unit to carry the horse power requirements through the many varia- tions, at a minimum cost, and above all, in a reliable way. The problem of a manufacturer who has a steady load and a comparatively continuous output of his product, is entirely different, insofar as stokers are concerned, from that of the Central Station operator who is called upon to meet almost instantaneous demands for steam which require opera- tion of boilers at from 100% to 400% of boiler rating. When the load that is to be carried is determined, a study is made of the characteristic curves of the different types of stokers showing the relation between the load and the com- bined efficiency of the boiler and stoker. Stoker performance follows quite closely a certain curve, and this varies accord- ing to the proportions of the apparatus. Fig. 66 shows the relation between the coal burned and the combined efficiency of boiler and grate of an underfeed stoker. It has a wide range on each side of the peak of the curve, and is relatively flat. A range in combustion rate of 3 to 1, and, in some cases, 4% to 1, is possible on this type of stoker without decreasing the efficiency very much. This corresponds roughly from 70% to 200% of boiler rating for some sizes of underfeed stokers, and 70% to 300% for larger sizes. Fig. 67 shows the ability of the underfeed type of stoker to handle sudden demands for steam without very much preparation. Without forced draft, sudden changes in fuel-burning rate would not be pos- sible. The deep fuel bed provides a reserved capacity so that jumps from 50% to 200% of rating can be made without much change in the fuel-feeding speed. 156 MECHANICAL STOKERS SELECTION OF STOKER EQUIPMENT 157 158 MECHANICAL STOKERS Fig. 68 shows the relation of load to combined boiler and stoker efficiency of the overfeed stoker. This characteristic curve has about the same shape as the underfeed but does not have the same range. The most efficient point for this condi- tion was at 79% of boiler rating, and the maximum horsepower was 225% of boiler rating, which was probably the maximum reserve capacity for the local conditions under which the equip- ment was designed. 84 LU O Roney Stoker Red Jacket Coal except where marked -lL n is & 10 80 90 100 110 120 130 140 150 160 110 180 190 200 210. 220 Per Cent of Rating on Basis of 10 Sq. Ft. of Boiler Heating Surface =1 hp. FIG. 68. Relation between Load and Combined Efficiency of Boiler and Stoker, Front Inclined Overfeed Stoker. Fig. 69 shows the relation of load to the combined boiler and stoker efficiency for different fuel bed thickness of the chain grate stoker. The chain grate embodies the automatic principle of ash disposal more completely than any other type, because coal is fed to a hopper in the front and ash discharged at the rear automatically. Both of these functions are per- formed by mechanical means, and it is for this reason that the characteristic curve drops off so rapidly at low ratings. A chain grate stoker 10 ft. long, and feeding a fuel bed 6 inches thick to burn 25 Ibs. of coal per square ft. of grate surface per hour, would require a speed of the grate of 2~y 2 " P er minute. If the fire were carried thinner, a corresponding increase in the grate speed would be required, but, in any case, grate speeds of over 4" per minute, are unusual, and the wear SELECTION OF STOKER EQUIPMENT 159 ISO 250 300 35O 400 450 500 5SO 6OO 65O 700 Lood (Horse -pomr) Relation between Load Efficiency of Boiler, Furnace, and Grate. JW 350 400 450 500 550 6M 650 700 7fO Load (Horse power) Relation between Load and Efficiency of Boiler and Furnace, Excluding Grate. 110 / o 6V7/J? ff o rfire IS A O'fire ff Sffirf \90 1 80 60 200 & JOO 350 400 45O SOO 550 $00 650 700 Load (Horse- poner) Relation between Load and Efficiency of Boiler, Excluding Furnace and Grate. FIG. 69. Efficiency Chain Grate Stoker, 160 MECHANICAL STOKERS and tear on the stoker at grate speeds of 4" or over, is very rapid. When carrying a light load with the damper partly shut, the last two or three feet of the grate surface contains only a small amount of fixed carbon, and the fire is more or less dead at this part of the grate surface. If, in this condition, it becomes necessary to pick up a load suddenly, and the boiler dampers are opened wide, it is only a few minutes until the small amount of coke at the rear of the furnace is burned out, and there is nothing but dead ash remaining. COAL CONDITIONS The coals best adapted to the different types of stokers, in general, are pretty well defined in Chapter IV. For all coals having coking or caking tendency, that type of stoker so designed that it agitates the fuel bed and, in some cases, uses forced draft, is most suitable for these fuels. This takes in the front and side feed stokers, and some underfeed types. Coking coals must be agitated in order to obtain a thorough air distribution through the fuel bed. If coking fuels are not agitated, they ball up into large masses and the air admission is faulty because it only enters the fuel bed through the inter- stices between the large masses. The result is that a large percentage of carbon is dumped in the ash pit unconsumed. Most of the eastern coals are coking or caking coals, and it is for this reason that the front and side feed and underfeed stokers have been very successful in handling this kind of coal. There are, however, some eastern coals that do not require agitation when being burned, and in using this grade of coal, the stoker that agitates the fuel bed does not operate success- fully. For free burning coal, the chain grate type of stoker is most successful. This coal does not require agitation and, in fact, when it is agitated, it causes trouble on account of its high ash content. This is the most prominent characteristic of middle western coals, and it is for this reason that the chain grate stoker has been so successful with this fuel. The forced draft underfeed stoker, however, is burning this coal very satisfactorily, and on account of a better control of air SELECTION OF STOKER EQUIPMENT 161 a g a a s s s K g w O CD i i CD TH rH Z5O 300 450 500 550 Looct (Horse-potter) 600 650 FIG. 71. Relation between Load and Draft for Chain Grate Stokers when Burning Illinois Coals. 164 MECHANICAL STOKERS of the necessity for this ignition arch, and also on account of the length of the stokers usually installed, a furnace extension beyond the front line of the boiler wall is, in most cases, required. In some types of large Stirling boilers, not more than 18" to 24" is required. In the case of B. & W. and other vertically baffled boilers, this extension varies from 3' to 5'. It is almost necessary to provide sufficient space in front of the furnace fronts, to completely withdraw the stoker from the furnace. It is, therefore, necessary to provide the proper distance in the firing space from the front of the furnace to the building wall or coal bunker. It is true that a great many chain grate stokers are installed in less space than this, but it makes repairs difficult and tedious when the stoker cannot be entirely withdrawn from the furnace for repairs. Another characteristic feature of the chain grate which must be considered is that considerable coal fired sifts through the grates. Where the coal contains only a small percentage of dust and sufficient amount of surface moisture to make the coal stick togther, the sifting is very low. On the other hand, where there is a large percentage of fine dust and the coal is dry, it is not uncommon to get considerable siftings. This falls through the lower part of the chain to a slab or pan located slightly below the floor. Where basement construc- tion is installed, it is desirable to provide hoppers under the stoker chains in which siftings can be collected and returned by means of conveyor, or otherwise, to the coal bunkers. Since the ash is deposited at the rear of the stoker, it is best to install an underground pit or tunnel, or provide a drag to pull the ash to the front, or where it can be readily handled. To protect the links of the chain at the rear where the ash is discharged from the furnace, an overhanging self-sup- ported firebrick wall is provided, or a firebrick wall supported on a water cooled pipe, commonly called a water back. This water back, or firebrick wall, is set at the proper height above the chain to permit the free discharge of ash. If the brick- work is allowed to burn off or become broken off, a consider- able amount of air leaks around the rear of the sto"ker into the SELECTION OF STOKER EQUIPMENT 165 furnace. If the water back is supplied with water from, a cold water supply, considerable heat is lost unless this water is returned to a hot well. To overcome this loss, it is best to connect the water back into the boiler circulation and under boiler pressure. This construction is generally recommended. Side Feed Stoker. Side feed stokers present some problems in their application on account of peculiar construction features. Since the coal is supplied at both sides of the stoker and the coal magazine runs from the front to rear, it is sometimes difficult to get coal to the rear of the coal magazine. There are two ways in which this can be done. Either set the stoker in a full " dutch oven" so that the rear of the magazine comes in front of the front wall of the boiler, or have the boilers set singly so that the coal can be supplied to the coal magazine from the sides. If installations do not provide either one of these con- ditions, it is necessary to admit coal to the front part of the coal magazine and push it back to the rear with a bar, or by mechanical means. The entire grate area is covered by a firebrick arch, either supported from structural work or sprung arch shape and supported by skewbacks. Ash disposal is not a serious matter since a grinder is usually located at, or slightly above, the floor line and the ash can be deposited in a small pit and raked into a conveyor or brought out on the floor and shoveled into wheel barrows. The siftings of coal through the grate surface is not serious if the coal contains only a small percentage of dust and the grate bars are kept in first-class condition. Since a full "dutch oven" is required, this means a long furnace extension and provision is made for sufficient space in front of the furnace fronts for proper operation. Front Feed Stoker. Front feed stokers are built on a con- siderable incline, and all depend, to a greater extent, on the force of gravity for movement of the fuel bed. Stokers of this kind generally employ a dumping grate and also use a fuel guard of some kind to prevent the fuel from dropping into the ash pit when the dump grates are dropped. When the dump grates have finally been cleaned and are brought back to their operating position, the guards are then lowered and the fuel bed moved downward. 166 MECHANICAL STOKERS This type of stoker does not, due to its construction, require an extension furnace, but in obtaining a proper furnace design, an extension might be necessary. Ordinarily, the stoker hopper is 6' or 7' from the floor, and if coal is to be shoveled into the hoppers from the floor line, the stoker front is depressed so that the top of the hopper is not over 5' from the floor line. Ashes can be raked out into a pit at the front of the stoker and from there shoveled into wheel barrows. The best arrange- ment, however, is to provide hoppers underneath the dump- ing grates and remove the ashes by cars or conveyors in a tunnel below the boiler room floor. The arch construction used with this type of stoker is very important. In general, it may be said that the ignition arch, or arch placed directly over the front part of the stoker, should be not less than 5' long in order to secure proper igni- tion of the particular fuel to be burned. Underfeed Stoker. The multiple retort underfeed stoker is generally applied to boilers only in battery or single settings with alley-ways at least 8 ft. wide, so that access to the furnace can be made either at the sides or at the rear. High speed forced draft fans are used with underfeed stokers, and these are located in a place where they are access- ible and easily cleaned. Care is generally taken not to place them in a dark corner where it is difficult to get at them. There should also be a sufficient supply of air for the fans if they are placed in basement. Often there is not sufficient air connections Between the basement and the outside air to provide the air required. The line shafting used to drive the stoker is also best placed above the boiler room floor, if possible, so that attention can be given to oiling and maintaining the bearings. The design of ash pits for underfeed stokers requires special consideration. When operating at high ratings, the pits must be of sufficient volume to hold a reasonable supply of ash and refuse. They should also be air-tight and provided with doors. When the stoker is cleaned, if open pits are used, spark from the dropping ash is liable to injure the attendants. The doors on the ash pits should be of sufficient area so that ash can be SELECTION OF STOKER EQUIPMENT 167 taken from the pits without difficulty. An underfeed stoker requires roomy ash pit facilities, and is not adapted to applica- tions where these facilities cannot be procured. On account of the high temperatures of underfeed furnaces, i.e., from 2500 F. to 3000 F., the very best firebrick should be used. Arches are not generally used with underfeed stokers when applied to boilers where the proper setting can be obtained. FlG. 72. Relation between Speed of Crank Shaft and Amount of Coal Multiple Retort Underfeed Stokers. Each feeding ram will displace from 13 to 18 pounds of coal per stroke, depending upon the size and kind of coal, therefore the approximate amount of coal used can be determined by the number of strokes multiplied by the number of rams or retorts per stoker. The approximate weights are 13 Ibs. for lignite coal, 16 Ibs. for western coal and 18 Ibs. for eastern coal. With some types of the underfeed stoker, dumping grates are used for discharging ash and clinker. These dumping grates are either operated by hand; mechanically operated by 168 MECHANICAL STOKERS steam and hydraulic cylinders ; or an electric motor. It gener- ally requires 45 second to 1% minutes to operate these dump- ing grates, depending upon the type installed and the character of the fuel. For higher ratings over long periods, a continuous method of ash disposal is sometimes used in the form of rotary clinker grinders. These have been applied to large stokers installed under boilers rated at 1500 H.P. and above. Single Retort Underfeed Stoker. The single retort underfeed stoker with side grates generally does not require ignition arches unless the furnace design makes such a connecting medium advisable. With reference to the disposal of ashes, inasmuch as the accumulation of ashes is at the sides of the stoker, the same is accessible from the fire doors in the stoker front. The dump^ ing grates are manually operated from the front and the ash discharged into the low ash pits at the side of the stoker. This ash can be raked to the front of the stoker and shoveled in the wheel barrows, or hoppers can be provided underneath the dump grates and the ashes taken out from a tunnel below the floor. Almost everything in connection with this type of stoker is accessible from the front, so that it presents no exact requirements insofar as accessibility at the sides or the rear of the stoker is concerned. FURNACE DESIGN The real economy in boiler rooms comes from good judg- ment used in making the combination of various boiler room apparatus fulfill their proper function. The individual charac- teristics of stokers have been given first, because the design- ing of furnaces require first the knowledge of the individual features of stokers. Brickwork and Arches. A furnace arch is made of refractory material and forms the roof of a furnace, or it is an arch located within the furnace for the purpose of aiding combustion. The combustion or ignition arch used for chain grate stokers is given considerable attention, because it has been found that the burn- ing of different kinds of fuel depend to a great extent on the length of these arches and their height above the fuel bed. SELECTION OF STOKER EQUIPMENT 169 In the chain grate type of stoker complete combustion of coal involves series of events, which can be briefly outlined as follows: The fresh fuel, containing some moisture, enters the furnace where it is subjected to the influence of the furnace tempera- ture. The moisture is first driven off, which is accomplished by the time the temperature of the particle of coal under con- sideration reaches the temperature of 212 F., and as the tem- perature continues to increase, the volatile constituents begin to come off. If the temperature at the point of ignition is sufficient, these burn in the space above, and approximately as fast as they are distilled. The burning of this portion of the fuel forms one source of the heat required for the ignition of the succeeding charge or unit of fresh coal. The volatile contents are not all driven off at the same temperature, so this portion of the process continues during an appreciable time or until the fuel has traveled some distance in the furnace. Temperature readings taken at the point of ignition indicate that about 1100 deg. must be obtained before the volatile will properly ignite and 1300 deg. must be had if the ignition is to be prompt and bright. About the time that the volatile is all gone the particle of coal has reached a quite high temperature and the fixed car- bon begins to burn. It is obvious that this particular stage must be begun as early as possible, in order that the end may be within the time limit of the chain-grate travel. Early and rapid ignition, therefore, by means of an arch, becomes, as a consequence, vitally necessary to the proper completion of the entire process. With an arch having the front end 10 in. from the surface of the grate and elevated to 34 in., the ignition is slow and the coal will pull several inches away from the gate at the front of the grate before burning, thus losing the effect of a portion of the grate surface. Many experiments in suspending the arch for the purpose of getting ignition close up to the gate have been made, and found that by having the arch more nearly horizontal and elevating it more at the front, the coal 170 MECHANICAL STOKERS will take fire right at the edge of the gate. The effect from the arch suspended in this manner is probably due to decreasing the opening at the back end of the arch, thus holding the fire towards the front, and to increasing the opening at the front and reducing the velocity of the incoming air at this point. In addition to producing quicker ignition, this arch adds to the capacity of the boiler. An ignition arch for an overfeed stoker, when fuel is fed from the front, is made, generally, so that the crown of the arch is horizontal. The length of the arch depends con- siderably on the type of boiler and the extension of the stoker in front of the boiler. For Eastern coals, the arch is generally made about 4' long the stoker front extending in front of the boiler about 3'. As the gases move along the underside of this arch, it is well to have sufficient combustion space above the rear end of the arch so that there will be some travel for the gases to complete combustion before they reach the cold surface of the boiler, such as shown in Fig. 73. When sufficient height cannot be obtained and the proper distance allowed between the grates and the cold surface of the boiler, a longer arch is used, such as shown in Fig. 74. These arches are sometimes made of the suspended type where special firebrick blocks are suspended from supporting struc- ture over the stoker, each block being suspended independently. In this design arch, the difficulty with expansion and contraction of the refractory material have no deteriorating effects. The sprung type of arch, as shown in Fig. 73, is often used where the arch is made of standard square and wedge firebrick, and the skewbacks supported by means of structural angles set in the side walls. Proper buckstays are provided so that the skewback angles cannot move outwards. First grade firebrick is generally used throughout the furnace setting. Firebrick in the side walls are placed 9" headers, 18" above the grate line, and above this line every fifth course is a stretcher course and tied in with the red brick. The furnace arch, which is also an aid to combustion, is used with the double inclined side feed stoker. This arch is SELECTION OF STOKER EQUIPMENT 171 either made of the flat suspended type or the sprung type supported by skewbacks. The design of the multiple retort underfeed stoker is such that ignition or furnace arches are not used. Straight front, side and bridge walls are designed wherever it is possible to do so. Considerable trouble has been experienced with the brick FIG. 73. Overfeed Stoker Applied to B. & W. Boiler, Showing Extension of Furnace in Front of Boiler. lining of the front or bridge walls due to the 'fact that they bulge out and eventually fall into the furnace. The front wall immediately over the throat opening of the stoker is con- structed as shown in Fig. 94. The brickwork in the furnace, in general cases, is made of 9" firebrick lining, and, in some cases, 13" firebrick is used. If it is necessary to use arches, they are either of the sprung or suspended type, and, where very high ratings are expected, arrangements are made to place a slight pressure over the arches so that air is pulled from the outside into the 172 MECHANICAL STOKERS furnace instead of having the flames lap backward between the blocks of the arches. Location of Observation Doors. It is always necessary to obtain complete observation of furnace conditions, so that, with the multiple retort underfeed, the front feed, and chain grate types of stokers, it should be made possible to install one door at FIG. 74. Stoker and Boiler Application, Showing Distance Required between Dumping Grates and Lower End of Tubes. least in each side of the furnace. Stoker installations, where it is not possible to do this, make operation very difficult. One door should be placed near the throat opening where the fuel enters the furnace, and the other placed near the ash disposal mechan- ism. With large furnaces, observation door (Fig. 85), located in the bridge wall, are very convenient. Clinker ing of Coal. The formation of clinker at the side walls of furnaces and the difficulty of removing them when formed SELECTION OF STOKER EQUIPMENT 173 is one of the most troublesome experiences of stoker operation, besides being a serious factor in high maintenance cost on settings. To reduce trouble of this kind, cast-iron air boxes have been built into the side walls of the furnace. A 4-in. pipe is connected to one of the air boxes, which are all connected together. Into this 4-in. pipe a 1%-in. steam line is led to act as an inspirator; the steam jet, discharging into the 4-in. pipe, draws air into Part* Section -through Furnace Walls A,B,0,D,E&F P/an \ * &
$ r t r ,o Siafe Frorrf- Detail of Block FIG. 75. Application and Details of Drake Furnace Blocks. the open end of that pipe. Three-quarter inch holes are drilled into the side of the box facing the furnace. To prevent the formation of clinkers on the side walls of furnaces a method has been used consisting of an arrange- ment of firebrick in the furnace walls whereby air is ad- mitted into the fuel bed between the bricks of the side set- ting. By supplying forced draft through these air passes, the face of the brick in the furnace wall is kept comparatively cool, the idea being that the clinker will not then adhere to 174 MECHANICAL STOKERS the brick surface. The combustion at these points is stimulated and increased. Where forced draft is applied to the fires, a branch conduit is connected to the air passage back of the side walls and the same forced draft is applied through the brick spaces in the side wall. The circulation of air passing directly into the fire from the furnace walls supplies draft at a point where it seems to be needed, A damper or valve operated from the outside con- FIG. 76. Interior View of Stoker, Showing Side Plates for Prevention of Clinker Adhesion to Side-walls. trols the amount of air thus supplied. No more forced draft is used than that supplied to the fire through the grate. In some cases steam jets are installed along the side tuyere boxes of underfeed stokers. This steam tends to rot the clinker so that it is more easily removed from the side walls. Specially designed firebrick blocks are sometimes installed in the side walls of the furnace and arranged for air to enter the furnace through these blocks. This system is shown in Fig. 75. Where the furnace will allow it, very often side plates are SELECTION OF STOKER EQUIPMENT 175 used next to the retorts of the stoker, as shown in Fig. 76, which serves to keep the fuel bed away from the walls. The accumulation of clinker on the bridge walls of under- feed stoker installations is partly overcome in the design. In one case the stoker is equipped with dump grate operating mechanism that is designed to knock loose the clinker adhesion from the bridge wall. This method as used, is shown in Fig. 77. High and low pressure water backs are also sometimes placed in the bridge wall to overcome the adhesion of clinker. Second operation with Taylor Power Dump. Dump plate is raised to loosen the clinker masses on lower grate, and to knock off slag adhesions on bridge-wall. If desired, it may be dropped a second time to get rid of them. f\ FIG. 77. Dump Grate Operation Designed to Loosen the Clinker Adhesion from Bridge-wall. ! '' ' f : f '* Another scheme is shown in Fig. 78, where a series of tubes is set into the lower part of the bridge wall to assist in draw- ing heat from the ashes and preventing the clinker formation. These tubes are made to extend out through the bridge wall and connect to headers. In some designs of the front inclined overfeed type of stoker, where clinkering coal is used, the exhaust steam from the stoker engines is used in connection with steam jets placed under the grates similar to that shown in Fig. 79. The small holes in the steam outlets are directed downward and the 176 MECHANICAL STOKERS draft pulling the steam up through the fuel bed tends to moisten and break up the clinker formation. The dump grates of this type of stoker are supported in such a manner that, when the ash and refuse is dumped, the rear part of the dump grate travels through an arc and tends to pull the clinker away from the bridge wall (Fig. 80). piG. 78. Water Tubes Set in Lower Half of Bridge-wall to Prevent Clinker Formation on the Wall. Air Over the Fire. The Bureau of Mines, U. S. Geological Survey, have shown that air taken through ordinary hand-fired grates is completely used up and the oxygen in the air combined with the carbon in the coal before it has a chance to get entirely through the fuel bed. Although this is not exactly similar to stoker fired furnace operation, on account of the more even distribution of air, nevertheless with certain high volatile coals, SELECTION OF STOKER EQUIPMENT 177 even with some stokers, air over the fire is necessary. This has been accomplished in many cases by taking air from a channel built in the front wall of the stoker, as shown in Fig. 81. \ v X^- ' J ' O-TV FIG. 79. Steam Jets Placed under Stoker Grates to Assist in Loosening Clinker Formation. Mixture of Gases in the Furnace. In order to obtain an intermingling of gases in the furnace to complete combustion at the earliest possible time, steam jets are installed at the front of the front inclined overfeed stoker and three or four jets of steam sprayed into the volatile gases, as they are distilled from the fuel bed (Fig. 82). These jets of steam tend to mix the gases with air coming down through the channels in the front 178 MECHANICAL STOKERS of the stoker, and is so designed to mix the gases in the furnace and complete combustion before the gases reach the boiler tubes. Ash Pit Construction. The design and construction of ash pits for underfeed stokers is very important so that the entire installation will not be limited as to the amount of ash and refuse that can be stored or removed in a certain time. For proper size of ash pits, etc., basements under underfeed stokers should be at least 20 ft. high. This will then give ample room for installation FIG. 80. Dumping Grate and Guard of Overfeed Front Inclined Stoker, Showing Method of Breaking off Clinker Adhesion to Bridge-wall. of fans, ash hoppers, ash cars and air ducts. Such a basement is shown in Fig. 89. Draft. The maintenance of brickwork in an underfeed furnace becomes increasingly difficult with low draft pressure. The result of low draft in an underfeed furnace is to start a puddling condition in the furnace which directs the flames back into the cracks in the brickwork. In one installation, experi- ments demonstrated that, by pulling the gases through the boiler at a higher velocity, the capacity of the boiler was increased from 80,000 Ibs. of steam to 120,000 Ibs of steam. In the first instant, considerable trouble was experienced with firebrick, and after the draft was increased and the gases SELECTION OF STOKER EQUIPMENT 179 pulled through the boiler and from the furnace at a higher velocity, this trouble ceased. FIG. 81. Magazine Construction, Showing Method of Admitting Air over the Fire in " V " Type Overfeed Stoker. COMBUSTION SPACE Underfeed Stokers. Considerable effect is realized from the incandescent fuel bed of an underfeed stoker fire. For the same rate of combustion, the same combustion space is not required for this type of stoker, compared with other types. On account, how- 180 MECHANICAL STOKERS SELECTION OF STOKER EQUIPMENT 181 ever, of the fact that higher rates of combustion are possible, and generally used with this stoker, the combustion space should be as much as is required for other types of stokers. For Eastern Bituminous coal not less than 10 cubic ft. com- bustion space should be used per sq. ft. of grate surface, when a rate of combustion does not exceed 75 Ibs. of coal per sq. ft. of grate surface per hour. For Pittsburgh, Illinois and Middle Western coals, at least 12 cubic ft. of combustion space should be used. This would require setting B. & W., Heine and similar types of boilers, from 10' to 14' from the floor line to the front header. When this stoker is installed in connection with the Stirling, Connelly, Ladd, Erie City or similar types of boilers, the dump grates of the stoker should be not less than 7' from the tubes where they enter the lower drum. Front and Side Feed Stokers. For Eastern Bituminous coal, the front inclined overfeed stoker, should be set with at least an extension of 4' in front of the boiler, with an arch at least 5' 6" long. When this stoker is combined with the B. & W., Heine and similar types of boilers, the front headers should be set 11' from the floor line. For Pittsburgh, Illinois and other high volatile coals, this stoker should have an arch at least T long with the stoker extended 5' in front of the boiler. The front header of the B. & W., Heine or similar type boiler should be set at least 12' from the floor line for this stoker. For the Stirling, Connelly, Wicks and similar types of boilers, the dump grates of this stoker should be at least T from the tubes where they enter the lower drum. For the side feed stokers, on account of the Dutch Oven extension, considerable combustion space is obtained by the mere construction of this stoker, but there should be at least 6' from the rear grates of this stoker to any boiler tubes. The reason for this, is that there is green coal fed to that part of the grate surface nearest to the boiler and there should be sufficient flame travel from that part of the grate surface to the tubes of the boiler. Chain Grate Stokers. Chain grate stokers have been used more than any other in connection with Middle West High Vola- tile coals and for this reason, considerable development work has 182 MECHANICAL STOKERS been done in connection with the combustion space when this stoker is applied to different types of boilers. As previously out- lined, the arch in connection with the furnace design of this stoker has considerable effect on combustion, and naturally this effects the type of combustion chamber required. When burning Indiana coals the furnace volume should be from 11 to 15 cubic ft. per sq. ft of grate surface. Arches varying from 4' to 6' in length, are also used as a factor in designing the combustion space. When burning Iowa coals, the combustion space and length of arch, is again of great importance, since the poorer grades of coal, as hereinbefore mentioned, are of low heat value and therefore difficult to burn. These coals require an arch covering Yz of the entire grate surface, and there should be provided at least 12' between tubes of a B. & W., Heine or similar type of boiler and the grate surface, and at least 7' between the rear of the grate and the tubes of a Stirling, Connelly or similar type boiler, where they enter the lower drum. When this stoker is used for burning lignite fuel, the design of the arch is again of utmost importance, because these coals contain from 25 to 40% moisture and it is necessary to provide a drying out process before they can be burned. There should be provided at least 10' between the boiler tubes of a B. & W., Heine or similar type boiler and the grate, and at least 7' when this stoker is applied to the Stirling, Connelly, or similar type of boiler between the rear of the grate and the tubes where they enter the bottom drums. THE FLOW OF HEAT THROUGH FURNACE WALLS After careful investigations and research work, by the Bureau of Mines, U. S. Geological Survey, bulletin number 8, gives the following conclusions regarding the heat flow through furnace walls. In the case of the furnace wall, where the quantity of heat passing between any two planes which are parallel to the surfaces of the walls is the same, the temperature difference between any two planes indicates the resistance which the material or space between the two planes offers to the flow of heat. For example, if the temperature difference between SELECTION OF STOKER EQUIPMENT 183 the faces of the firebrick wall is high, it may be said that the resistance to the heat flow of the firebrick wall is high; or, if the temperature difference between the two surfaces on each side of the air space is low, it may be inferred that the resist- ance to the heat passage across the air space is low. Thus it is possible to rely on the temperature difference as being a true indicator of "high or low resistance to heat flow between any two planes which are parallel to the surface of the wall. With this knowledge the reader can turn to the charts and study the resistance of the firebrick, the air space, the asbestos layer, and the common brick, and the relative value of these materials as heat insulators in the construction of furnace walls. Fig. 83 gives the temperature drops through the side wall as recorded by the set of couples placed at &, and through the roof as recorded by the set of couples placed at c. At the foot of the figure is shown diagrammatically the thickness of the side wall, and at the top of the figure is shown thickness of the roof ; in each case the measurements of thickness are used as abscissae in the chart. The temperatures at the various points are platted as ordinates. The figure shows three tem- perature gradients or drops through the wall and through the roof, one at 11 a. m., April 12, when the test was started, one at 4 p. m. the same day, and one at 2 p. m. the next day. The first two gradients give the relation of the temperatures before the equilibrium is reached, and are interesting only when com- pared with one another to show how the temperatures change with respect to each other while the walls are being heated. The last gradient represents the equilibrium and is most of interest. The striking feature concerning the side wall thermocouples, set 6, is the large temperature drop through the firebrick wall, the very small drop through the air space, and, again, the large temperature drop through the common brick wall. These drops plainly indicate that the resistance to heat pas- sage of the air space is very low compared with that of either brick wall, only about one-fourth as much. The last tempera- ture gradient through the roof, as given by the set of thermo- couples c, show a rather low temperature drop through the 184 MECHANICAL STOKERS THICKNESS OP ARCH ROOF, INCHES. 8 10 12 14 2 4 6 8 10 12 14 16 18 20 THICKNESS OF SIDE WALL, INCHES. FIG. 83. Temperature Drops through Furnace Walls. SELECTION OF STOKER EQUIPMENT 185 firebrick, a high drop through the 1 inch layer of asbestos, and a rather small drop through the common brick. These temperature drops indicate that the resistance to heat flow of the 1 inch asbestos layer is higher than that of 7 inches of firebrick. By comparing the last gradient of couples- b with that of couples c, it is easy to see that 1 inch of asbestos is much more effective as a heat insulator under the existing con- ditions than a 2 inch air space. Although the total thickness of the roof is 5 inches less than that of the side wall, a smaller quantity of heat per sq. ft. is lost through it than through the side wall. The results of the investigation as outlined in this bulletin justify the following conclusions: In furnace construction a solid wall is a better heat insulator than a wall of the same total thickness containing an air space. This statement is particulary true if the air space is close to the furnace side of the wall, and if the furnace is operated at high temperatures. If it is desirable in furnace construction to build the walls in two parts, so as to prevent cracks being formed by the expansion of the brickwork on the furnace side of the walls, it is preferable to fill the space between the two walls with some " solid'* (not firm, but loose) insulating material. Any such easily obtainable materials as ash, crushed brick, or sand offer higher resistance to heat flow through the walls than an air space. Furthermore, any such loose material by its plasticity reduces air leakage, which is an important feature deserving consideration. CHAPTER VII STOKER EQUIPMENT OF MODERN STEAM POWER STATIONS A study of the fuel burning equipment of the most modern plants will show that every consideration is being given to those details which provide for a balancing of the economic results that come from a careful selection of equipment, good supervision and correct operation. It will be found that elaborate means are being provided so that the boiler room organization can do things easily. It is no longer necessary for firemen to climb ladders and crawl over the boiler tops to change the position of dampers, although such methods are still common in many old plants. Mechanisms are being placed at the hands of the operators so that it is not necessary for them to go to inconvenient places in order to control operating conditions. The most generally used fuel burning equipment in the modern stations is the "inclined multiple retort" underfeed and the "chain grate" stoker, designed for large boiler units, ranging from 1200 to 1500 H.P. up. A number of boilers contain- ing 12,500 sq. ft. of heating surface have been used and are furnish- ing steam for 7000 to 8000 kw. in the prime mover. It is not at all improbable that this unit will be further developed to furnish steam for at least 10,000 kw., in the prime mover for continuous operation. These units are set singly with large alley ways between each setting, so that the boiler and fuel- burning equipment are accessible on all sides. The stokers are designed for a flexible operation of 50 to 300 per cent rating. Clinker grinders are used in a number of cases for discharging the ash and refuse automatically from underfeed stokers. The following brief description of the fuel-burning equip- ment installed in a number of modern power stations covers 186 EQUIPMENT OF MODERN STEAM POWER STATIONS 187 a wide range in the character of load and fuel used. Some of these plants are completely new stations, while others are extensions to old stations, and still others are old stations in which inadequate fuel-burning equipment has been replaced by more modern equipment. EDISON ELECTRIC ILLUMINATING COMPANY. Boston, Mass. This company replaced old fuel-burning equipment under eight 512 horse power boilers with inclined underfeed stokers. One of these stokers was equipped with a clinker grinder, the idea being to try this out under regular operating conditions and with the fuel available, this being a part of a study for the new extension to the station. Although the stoker was of small size (five retorts), the clinker grinder operated satis- factorily and it was decided to use this design in connection with the equipment for the new extension consisting of four cross-drum boilers, 42 sections wide, 14 tubes high and 18 ft. long, rated at 1232 H.P., at 300 Ibs. gauge pressure equipped with a superheater designed to give 150 superheat. These stokers, as shown in Fig. 84, are of the Westing- house underfeed type, having 13 retorts installed under the back end of the boiler, under the mud drums, and equipped with rotary clinker grinders (Fig. 55) for removing the ash and clinker continuously. The stoker drives (Fig. 86) are divided with not over four retorts to a motor; also, the wind boxes and dampers are so arranged that they can be con- trolled on the same basis, this provision being made so as to give a complete control of coal and air across the entire furnace width. The coal used is New River, of approximately the following analysis : Fixed carbon 73.50 Volatile 20.75 Ash 5.75 Moisture 3.25 Sulphur 1.05 B.T.U 14,700 188 MECHANICAL STOKERS The average per cent of combustible in the ash and refuse is not to exceed 15 per cent. The stoker equipment, when supplied with the above fuel, is designed to develop 300 per cent of normal rating of the boilers for periods of short dura- tion. FIG. 84. Boston Edison Stoker Setting, Showing Clinker Grinder and Furnace Control Mechanism Located at the Front of the Boiler. Doors are placed in the bridge wall and all controlling mechanism placed at the end opposite the stoker (Fig. 84) so that when the operator views the furnace fires through the bridge wall doors, he will have the controlling mechanism at hand. EQUIPMENT OF MODERN STEAM POWER STATIONS 189 UNITED ELECTRIC LIGHT AND POWER COMPANY, HELL GATE New York City The fuel burning equipment at this station consists of twelve 28-retort, type AA7 Taylor Stokers, each installed under FIG. 85. Interior View of Boston Edison Furnace, Showing Clinker Grinder and Front-wall Construction. 1890 horse power boilers. This type of Taylor Stoker has seventeen tuyeres and two feeding rams per retort. It is pro- vided with double rotary clinker crushers of the same general design as those used on the Taylor Stokers at the Delray Plant of the Detroit Edison Company. 190 MECHANICAL STOKERS The combined boiler and furnace efficiencies of these units will range from 76% at 150% of rating to approximately 63% at 360% of rating, when burning Eastern Bituminous coal of approximately 13,000 B.T.U. per pound as fired. FIG. 86. Front View of Boston Edison Stokers, Showing Motor Driving Equipment. The ashes will be discharged directly into a flume from which they will be removed by water. This stoker and boiler arrangement is shown in Fig. 87. PUBLIC SERVICE ELECTRIC COMPANY, Newark, NJ. The " Essex" station of the above company, located on the Passaic Eiver about two and one-half miles from Newark, N. J., was placed in operation in 1915. The boiler room equipment consists of B. & W. Cross Drum boilers of 1373 horse power each with an operating pressure of 225 pounds and superheat of EQUIPMENT OF MODERN STEAM POWER STATIONS 191 FIG. 87. Setting of Stokers and Boilers of the Hell Gate Plant, United Electric Light & Power Company. 192 MECHANICAL STOKERS 100 F. Each boiler is equipped with 16 retorts, Riley Under- feed stokers, in a Duplex setting (Fig. 88). The stoker equip- ment was designed to burn up to 15,000 pounds per hour, when burning Pittsburgh coal of about 13,500 B.T.U. (as fired) and to develop about 500% and 600% of boiler rating for short periods. FIG. 88. Stoker Installation Public Service Electric, Showing Stoker Operating Board. PHILADELPHIA ELECTRIC COMPANY, Philadelphia, Pa. Delaware Avenue Station At this Station special type Stirling boilers of 1508 horse power each are equipped with fifteen retort type BAT Taylor Stokers (Fig. 89). These stokers have twenty-two tuyeres and three rams per retort. They are provided with double roll clinker crushers and are capable of operating the boilers up to 330% of rating, when burning Eastern coal of approximately 13,800 B.T.U. per pound as fired, and having the following proximate analysis: EQUIPMENT OF MODERN STEAM POWER STATIONS 193 Moisture 2.3 Volatile 22.5 Fixed Carbon 65.0 Ash 10.2 Sulphur 1.83 FIG. 89. Setting of Stokers at Philadelphia Electric Delaware Avenue Station. The efficiencies of the combined unit (boiler, furnace and economizer) will range from 82% at rating to 70% at 250% rating. 194 MECHANICAL STOKERS CONSOLIDATED GAS AND ELECTRIC CO., Baltimore, Md. At the Westport Station of the Consolidated Gas & Electric Company, Baltimore, 11-retort 22-tuyere type Taylor Stokers, similar to Fig. 91, are in service under 1074 horse power Water- tube boilers. FIG. 90. Interior View Delaware Avenue Station, Philadelphia Electric, Showing Stoker Operating Board. These stokers are of the 22-tuyere type, and are equipped with power operated dump plates, which are designed to swing above the horizontal to clear the bridge wall of clinkers. This installation is designed to burn Eastern coals of the following characteristics : Moisture 2.00 Volatile 18.00 Fixed Carbon 62.00 Ash 16.00 Sulphur 2.00 B.T.U. per pound (as fired) 12,600 EQUIPMENT OF MODERN STEAM POWER STATIONS 195 This installation will burn sufficient of the above coal to develop 350% of boiler rating. The efficiency through the normal range will run from ap- proximately 72% at 250% of rating to 77% at 150% of rating. FIG. 91. Setting of EdgeMoor Boilers and Taylor Stokers at Consolidated Gas & Electric Company. BUFFALO GENERAL ELECTRIC COMPANY, Buffalo, N. Y. The Niagara Eiver station of this company was built in 1916 with an ultimate total capacity of 200,000 K.W. The fuel burning equipment consists of ten 1140 horse power cross drum boilers of the B. & W. type. The stoker equipment was designed for burning Pittsburgh coals of the following analysis: 196 MECHANICAL STOKERS Moisture 3.00 Ash 10.00 Sulphur 2.00 B.T.U. (as fired) 13,500 To eliminate, as much as possible, the formation of clinkers, air boxes were designed for installation in the sidewalls. Each boiler is served by two 15-retorts, Standard Riley Underfeed stokers (Fig. 92) arranged in a Duplex setting. The furnace width is 24 ft. and the depth about 17 ft. 6 inches. The total grate area under each boiler is 417.8 square feet. The stokers are set so that there is a height of 10 ft. 10 inches from the top of the grate to the front header and 6 ft. from the top of grate to rear header. When the boilers are operating at normal rating at 275 pounds working pressure and 275 super- heat, the rate of coal feed by the plungers is 127 pounds per retort per hour. When feeding 700 pounds of coal per retort per hour the boilers will operate at about 500% of boiler rating. Estimating the average thickness of the fuel bed as two feet there would be in the furnace at all times about twenty-three tons of green coal and coal in process of combustion. The equipment is designed to operate between 500% and 600% of boiler rating for short periods. CLEVELAND ELECTRIC ILLUMINATING COMPANY, Cleveland, Ohio The Lake Shore station of the above company is a large central station furnishing electricity for the community in and around Cleveland. The boiler-room equipment consists of class M-25 685 horse power Stirling Boilers, equipped with 12 ft. wide by 15 ft. long Green Chain Grate stokers. These stokers are of the combination KLM type Green design for handling free burning coal. The boilers are set with what is known as a rear end setting. The central line of the mud drum being 15' 8" above the floor line (Fig. 93). This gives an unusually large combustion space, there being 16 cubic feet furnace volume per square foot of grate surface. The coal generally used at this station comes from South- EQUIPMENT OF MODERN STEAM POWER STATIONS 197 FIG. 92. Setting of Buffalo General Electric Stokers, Showing Duplex Setting of Riley Stokers. 198 MECHANICAL STOKERS . I 16 "x?/ 'Opening in Side Wall Opening in Side Girder l<-3-6*--> Longitudinal Section FIG. 93. Setting of Green Chain Grate Stokers with Stirling Boilers, Cleveland Electric Illuminating Company. EQUIPMENT OF MODERN STEAM POWER STATIONS 199 eastern Ohio, which is free burning coal. The analysis running about as follows: Moisture 2.90 Volatile Matter 31.4 Fixed Carbon 55.0 Ash 13.6 Sulphur 4.4 B.T.U. (dry) 12,350 B.T.U. (as fired) 11,992 The stoker equipment was designed for a range of operation from 100% to 300% of boiler rating. The average operating rating being about 175%. The stoker equipment is designed to give from 70% to 75% combined boiler and stoker efficiency when operating at this rating. DUQUESNE LIGHT COMPANY, Pittsburgh, Pa. The " Coif ax Station" of the above company located at Springdale, Pa., on the Allegheny River was designed for an ultimate capacity of 300,000 K.W. The location of this station makes several sources of coal supply available. The stoker equipment consists of 17 retorts, Westinghouse Underfeed stokers applied to B. & "W. Cross Drum boilers, each having heating surface of 20,706 square feet. The ratio of furnace volume to boiler rating is 3.45 cubic feet. The boilers are 18 tubes high by 15 tubes wide (Fig. 94). The stoker equipment was designed for burning high volatile Pittsburgh coals of the following analysis: Fixed Carbon 54.00 Volatile 34.00 Moisture 3.00 Ash 9.00 Sulphur 1.23 B.T.U. (as fired) 13,500 Double roll clinker grinders were installed, the same being cooled by a continuous water spray. To eliminate as much as 200 MECHANICAL STOKERS possible the formation of clinkers, air boxes were designed and installed in the side and bridge walls. The boiler and stoker efficiency of the plant under regular operating conditions were FIG. 94. Setting of Westinghouse Stokers and B. & W. Boilers, Coif ax Station Duquesne Light Company. designed for 78% at 100% of boiler rating and 65% at 300% of boiler rating. The entire stoker equipment was designed for 250% of boiler rating. EQUIPMENT OF MODERN STEAM POWER STATIONS 201 WEST PENN POWER COMPANY, Pittsburgh, Pa. The design of the new plant of the West Penn Power Com- pany, on the Allegheny river above Pittsburgh, contemplated some decidedly novel features in the boiler and stoker equip- ment. The initial installation was designed for six boilers of FIG. 95. Stoker and Boiler Installation, West Penn Power Company. the cross-drum vertical-header type, 42 sections wide, 16 tubes high, 20 ft. long, set with the front header 16 ft. above the floor, each boiler being rated at 1,529 H.P. and equipped with superheaters designed to give 200 degrees superheat. Westing- house Underfeed stokers are installed at the front and rear ends of the boilers (Fig. 95) 14 retorts under the mud drum, and 14 retorts under the front of the boiler. The operating conditions being a maximum of 300 pounds gauge pressure, 200 degrees superheat. 202 MECHANICAL STOKERS The boilers are set in two rows with aisles about 15 ft. between, thus giving plenty of room around each boiler for proper operating facilities. The stoker drives are so divided that there are 7 or 14 retorts driven by one prime mover, and the wind box dampers are arranged to control separately the air for units for three or four retorts. The stokers are equipped with clinker grinders for continuously removing the ash and clinker. Pittsburgh coals with approximately the following analyses, are used: Coal "A" Coal "B" Coal"C" Fixed carbon 57 38 49 56 56 55 Volatile 34 81 32 84 32 80 Ash 7 81 13 26 10 10 Moisture 5 52 94 55 Sulphur B.T.U. fas fired). . 1.50 13.500 1.20 11.748 0.79 12.713 The boiler equipment is designed so that the flue gas tem- peratures will range from 500 degrees at 150 per cent rating to 700 degrees at 300 per cent rating, the combined efficiency ranging from 75 per cent at 150 per cent rating, to 65 per cent at 350 per cent rating. Each stoker, when burning fuel as mentioned above, is designed to develop 350 per cent of boiler rating continuous with the clinker grinder in operation, and 400 per cent of boiler rating for peaks of short duration. Under these operating conditions, the combustible in ash is not to exceed 14 per cent. AMERICAN GAS & ELECTRIC CO., Windsor, W. Va. The plant of this company, located in the coal fields of Pittsburgh, is one of the largest power plant developments. The present boiler-room equipment, either installed or provided for, consists of 14 boilers with underfeed stokers similar to the equipment mentioned for the Union Gas & Electric Co. The setting of the stokers is shown in Fig. 96. EQUIPMENT OF MODERN STEAM POWER STATIONS 203 DETROIT EDISON COMPANY, Detroit, Mich. The first installation of double set underfeed stokers under large boilers was made at the Delray Plant of the Detroit Fn and Motor Drive (f) Dampers In Fan Outlet (F) FIG. 96. Stoker and Boiler Setting American Gas & Electric Co. Edison Company. This consisted of two 13-retort Taylor Stokers, under each of the 2365 horse power water tube boilers, as shown in Fig. 97. Roll clinker grinders were developed for these stokers and have been installed on the eight Taylor Stokered boilers of this type at Delray. 204 MECHANICAL STOKERS EQUIPMENT OF MODERN STEAM POWER STATIONS 205 This equipment was duplicated for the ten units compris- ing the boiler and stoker equipment at the Connors Creek Station of this Company. On test the efficiencies of these units have run from 80% at slightly above rating to approximately 77% at 200% of rating, when burning coal of approximately the following analysis : Moisture 2.00 Volatile 33.00 Fixed Carbon / 61.00 Ash 6.00 B. T. U. per pound (as fired) 14,000 The Congress Street, Willis Avenue and Farmer Street Stations have similar double set Taylor Stoker installations, but with a smaller number of retorts per unit. The Marysville Plant will have twelve-retorts, twenty-two tuyeres, double set Taylor Stokers under 2365 horse power boilers. This equipment will burn sufficient coal of 14,000 B.T.U. per pound as fired to develop 350% of boiler rating. The efficiencies will range from 80% at 150% of rating to 75% at 250% of rating. UNION GAS & ELECTRIC CO., Cincinnati, Ohio. In the new plant of this company there are installed cross- drum type boilers containing approximately 12,625 sq. ft. of water heating surface, with superheaters to produce 250 degrees superheat. Each boiler was made up of 42 sections each, 13 tubes high and 20 ft. long, the furnace width being 24 ft. inside the setting walls. Each boiler is equipped with econo- mizers over the boiler and each boiler, with its economizer, is designed for evaporating 100,000 pounds of water per hour continuously from 100 degrees to steam at 250 pounds pressure, and superheated 250 degrees. The entire equipment is capable of evaporating 120,000 of water under the same conditions for short periods. The fuel-burning equipment is designed for burning West Virginia coal from the Kanawha district, con- taining approximately 12,500 B.T.U. per Ib. as fired. The setting of these stokers is shown in Fig. 96. 206 MECHANICAL STOKERS The stoker equipment is of the Westinghouse & Riley under- fed type, each stoker containing 14 retorts placed under the rear of the boiler under the mud drum. The stokers consist of double dumping grates with arrangements for admitting air to them. The fuel-burning equipment is designed for com- bined efficiency ranging from 75 per cent, with a boiler capacity of 35,000 Ibs. of water, to 65 per cent with a capacity of 100,000 Ibs. of water. Each stoker is driven independently by direct- current motors connected by silent chain drives to the line shaft of the stokers. Instrument boards are installed to indicate to the operators the exact furnace conditions. MERCHANTS HEAT & LIGHT CO., Indianapolis, Ind. The above company replaced their former coal-burning equipment with Westinghouse underfeed stokers and, at the same time, added additional 800 horse power units to their plant, the entire work consisting as follows : Twelve 500 H.P. Stirling boilers equipped with twelve 5- retort Westinghouse underfeed stokers. Two 800 H.P. vertical boilers equipped with two 9-retort Westinghouse underfeed stokers. Two 800 H.P. Badenhausen boilers equipped with two 8- retort Westinghouse underfeed stokers. In the new settings, the lower drum of the boiler has been raised considerably so that doors could be placed in the bridge- wall. The fuel-burning equipment was laid out to burn Indiana screenings of the following analysis, and when burning this fuel the operating performance ranges from 100% boiler rating to 300% boiler rating for short durations: Fixed Carbon 43.89 Volatile 40.27 Moisture 15.23 Ash 15.84 Sulphur . 3.99 B.T.U 12,053 EQUIPMENT OF MODERN STEAM POWER STATIONS 207 UNION ELECTRIC LIGHT & POWER CO., St. Louis, Mo. The boiler plant of this company has been entirely re- vamped and a change made in the type of fuel-burning equip- ment formerly used. Careful study was made in regard to the installation of stokers, and it was finally decided to install underfeed stokers for use with good Illinois coal of the follow- ing analysis: Fixed Carbon 48.9 Volatile 27.3 Ash 14.9 Moisture 9.0 B.T.U. (as fired) 11,112 The main problem at the start was that of designing the equipment to eliminate, as much as possible, trouble due to clinker formation on the side walls. After the equipment was in operation, and when using the coal that was originally contemplated, very little difficulty was encountered with clinkers. Performance results are shown in Fig. 98, when a grade of coal with the following analysis was used: Fixed Carbon 41.0 Volatile 29.0 Moisture 9.0 Ash 21.7 B.T.U. (dry) 12,000 With this coal considerable more attention was required to keep the fires uniform and cleaned properly in order to decrease clinker trouble to a minimum. COMMONWEALTH EDISON COMPANY, Chicago, 111. The Northwest Station of the above company located on the Chicago River is one of the largest central stations using chain grate type of stokers. 208 MECHANICAL STOKERS The first section of this plant included 580 horse power B. & W. boilers operated at a pressure of 250 Ibs. with super- heat of 125. The stoker equipment consisted of B. & W. chain grate stokers, twenty of which have 150 sq. ft. of grate surface each and twenty, 136 sq. ft. grate surface. The last boilers installed were 1220 horse power cross drum B. & W. type, pressure 250 Ibs. superheat 220. 140 150 160 170 IbO ISO 200 2 220 230 240 250 260 2 280 290 300 310 320 FIG. 98. Performance of Underfeed Stoker when Burning Carterville Illinois Coal. Illinois coal is used at this plant averaging about 10,000 B.T.U. as fired. MINNEAPOLIS GENERAL ELECTRIC COMPANY, Minneapolis, Minn. In re-designing the fuel-burning equipment of the plant of the Minneapolis General Electric Company (Fig. 99), there were installed 12 Westinghouse underfeed stokers under twelve 600 H.P. boilers. A recent extension to this contemplated EQUIPMENT OF MODERN STEAM POWER STATIONS 209 the installation of five 14-retort underfeed stokers under five 1300 H.P. boilers. On account of the coal conditions prevailing at this plant, it was necessary to design equipment for two grades of coal of the following proximate analyses: Coal "A" Coal "B" Fixed carbon Volatile 56.48 30 81 43.49 32 59 Ash 11 03 20 44 Moisture 7 00 10.00 Sulphur 1 70 3 48 B.T.U 13,400 dry 11,200 dry FIG. 99. Underfeed Stoker Equipment of the Minneapolis General Electric Company. Under the above conditions, the operating performance of fuel "A" ranged from 1800 to 3000 H.P. continuous and 4500 H.P. for short durations. With the poorer grade of coal, the Maximum capacity was reduced to 3600 H.P. for short duration. 210 MECHANICAL STOKERS DENVER GAS & ELECTRIC COMPANY Denver, Colo. Recent developments in the West have brought about the installation of underfeed stokers for burning coals found in Denver markets. The above company 's new extensions included the installation of four 750 H.P. boilers and four nine retort Westinghouse stokers. The stoker application setting, worked out gives sufficient combustion space for any high volatile coals, including lignite, that are liable to be used at this plant. The fuel-burning equipment is designed for the following coals: Fixed Carbon 39.00 Volatile 35.85 Moisture 19.70 Ash 5.37 Sulphur 0.42 B.T.U. (dry) 12,000 When using the above fuel, the operating performance ranges from 140% boiler rating to 200% boiler rating for short duration, with approximately 70% combined boiler and furnace efficiency. CHAPTER VIII APPLICATION OF STOKERS DETERMINATION OF SIZE While it is true that economy in fuel burning is largely the result of good operation it is necessary that the apparatus be properly proportioned to the work to be done. A poorly proportioned installation if skillfully operated may give as good or better results than one correctly proportioned and carelessly operated, but this does not relieve the engineer of responsibility for correct design and proportions. Under best conditions, the range of efficient combustion rates is not great and under average operating conditions, this range is even smaller. As combustion rates are increased above the most efficient point, the amount of excess air will remain constant or may decrease slightly, indicating an increase in efficiency but this is more than offset by increased ash pit loss and the possibility of incomplete combustion. Below the point of best efficiency the ash pit loss should decrease but the loss due to excess air will increase more than enough to offset the decreased ash pit loss and the net efficiency decreases. The rate of this decrease depends upon the skill and care of the operators and in many plants is so rapid that the range of efficient combustion rates is very small. Fig. 100 shows the range for best conditions, the efficiency curve indicating what actually happens in many plants. It is apparent that the engineer who selects the stoker and boiler must carefully consider the plant load conditions and select the correct proportions in order that the operators may be able to secure the best results. If the plant has a substantially uniform load throughout the twenty-four hours, the best results so far as the boiler is 211 212 MECHANICAL STOKERS concerned will be secured at between 125% and 175% of rating. Variations within this range will depend upon local conditions such as cost of real estate, price and quality of fuel and necessity of providing future development. For plants carrying a uniform load for from eight to twelve hours a day and banked the balance of the time, the fixed charges per unit of output will be greater and it is necessary to operate at higher ratings to secure the lowest operating cost. Under such conditions, the most economical rating will be between 150 and 200%, the exact figure being determined by local conditions. r W -TA "~" fc^^^^^ta o ( * f-,S 3? ^X> \ X % -TQ /^ / s fc "- 08 f# s -0 o j_ / / \ \ _ 01 ( 37 N / \ -o V n f* 1 r \ <-> 60 / ^\ ) 5 1C 1! JO ZC )0 25 30( Per Cent Boiler Rating FIG. 100. Typical Capacity-efficiency Curve. The twenty-four hour variable load of the central station plant presents additional difficulties. The maximum capacity must be ample for the peak load and since the maximum peak occurs only a few times each year, the efficiency at which this peak can be carried is of little importance. The best results will be secured by proportioning the apparatus to carry the day load most economically and providing the necessary over- load capacity to meet the peaks. If the day load can be carried at between 150% and 200% rating and the peaks by increas- ing to 250% or 300%, which represents the average condition, a satisfactory combination can be secured. If a greater peak load capacity is necessary, it is advisable to install stokers of APPLICATION OF STOKERS 213 sufficient capacity to meet this demand rather than to increase the size and number of boilers, provided the peak load is not more than twice the day load. In general, it is not wise to design for a peak load on any unit of more than twice the average day load because at ratings below 50% of the maximum capacity, the efficiency will fall rapidly unless the best of operation can be depended upon. Tlie intermittent load of some industrial plants presents a particularly difficult problem. Sudden and unexpected steam demands must be met, in some cases without a large drop in steam pressure, and .the equipment must be able to satisfy these demands regardless of economy. The selection of equip- ment must be such that the maximum demand can be supplied and the flexibility should enable the periods of low load to be carried economically, while the change from one condition to the other should be made quickly and automatically. Such a combination of requirements cannot always be met and the economy of operation will necessarily be lower than in a plant having a better load condition. The selection of boiler equipment should never be made without at the same time considering the stokers, because the boiler proportions are determined largely by the size of stoker selected. A typical example will make this clear: Assume a plant being designed to carry a steady load of 3000 B.H.P. burning coal having 13,500 B.T.U. per Ib. on underfeed stokers, and that a rating of about 150% has been decided upon as the most economical rating. This load could be carried on four 500 H.P. units, each developing 150% rating and the plant should contain five units, allowing one spare. The stokers should be of such size that three units could carry the load in case of a forced shut down of one unit. This requires 200% rating from each of the remaining units and it might be neces- sary to carry this rating for twenty-four hours. The stokers must therefore be of sufficient size to operate the boilers at 200% rating for twenty-four hours. Assuming 72% combined efficiency, the coal consumption per boiler per hour at 200% rating will be 214 MECHANICAL STOKERS at 150% rating and 75% efficiency, the coal burned per boiler per hour will be 34.5X970.4 13,500 X. 75 X A stoker must be selected that will burn 3440 Ibs. of coal per hour for twenty-four hours, but the most important requirement is high economy when burning 2483 Ibs. per hour. For the given condition a combustion rate of 35 Ibs. per square foot per hour should give the best results and the stoker size will be 2,483 .. . - = 71. sq.ft., at 200% rating this stoker would have a combustion rate of 3,440 71 48.5 Ibs. per square foot per hour, which is well within the reserve capacity of the type of stoker selected. These stokers are made in lengths of 9 ft. or more and it is therefore unnecessary to make the stoker more than ^ = 7.9 ft. wide, y In order to allow for the variations in dimensions employed by different manufacturers, it would be desirable to select a boiler having a furnace width of 9' 0" or the nearest standard width. Standard boiler designs for units of 500 H.P. can be secured in furnace widths up to 14' 0" and it is obvious that if such a design had been purchased without considering the stoker proportions, a serious mistake would have been made. In general, it may be said that any given size or type of boiler will give better results if made as narrow as possible because the narrow unit gives a better distribution of the heat- ing surface and will be a more efficient heat absorber. The stoker should be proportioned with this fact in mind and where several combinations of width and length are available, the narrow long one should be selected and the boiler pro- portioned accordingly. In order that the best stoker size may be selected for any given condition, it is necessary that the best combustion rates APPLICATION OF STOKERS 215 for the various grades of coal be known. Figs. 101, 102 and 103 give these values for several typical fuels. The minimum combustion rate recommended for continuous operation represents the lower limit for actual operation although good test results can be secured at lower rates. This requires careful operation and constant attention such as fires receive during tests or in regular operation in a few excep- tionally well managed plants. Under average operating con- ditions, however, the efficiency will drop off rapidly at com- bustion rates below this minimum and unless it is absolutely Combustion Rate per Sq. Ft. per Hour Dry Coal EASTERN COAL FC. 73 vol. n Ash 6 BT.U.(Dry) 14300 PITTSBURGH COAL EC. 57 Vol. 30 Ash 7 S Z Moisture 4 B.T.U.(Dry) 13500 ILLINOIS COAL FC. 48 Vol. 30 Ash 12 Moisture 10 BIlWDry) 12200 IOWA COAL FC. 33 Vol. Zl %" ? Moisture 15 &T.U.(Dry) 10400 LIGNITE FC. 34 Vol. 33 Ash 10 S>. 1 Moisture 23 B.T.U.(Dru) 11500 Mmimunrfbr Continuous Operation 20-25 25-28 25-28 25-28 25-28 Recommended for Continuous Operation 30-38 32-40 30-38 28 -35 30-35 Maximum for Continuous Operation 40-45 40-45 38-42 35-42 38-45 Recommended for 3 to 4 Hr. Peaks 50-60 50-60 45-50 42-45 45-50 Maximum for 3 to 4 Hn Peaks 60 -65 60-65 50-55 45-47 50-55 Maximum for One Hr. Peaks 10 70 60 50 60 FIG. 101. Combustion Rates Recommended for Various Fuel Conditions for Forced Draft Underfeed Stokers. necessary, provision should not be made for such operation. Some industrial plants having an intermittent load may be required to operate below this minimum but cannot reduce the number of units in service on account of the periods of heavy load which alternate with the low load periods, and such plants are at a definite disadvantage so far as economy is concerned. The continuous combustion rates recommended for best results apply especially to plants having steady loads. It is usually necessary, however, to effect a compromise between this combustion rate and the maximum continuous rate. In the case cited above it is desired to carry a given load on four 216 MECHANICAL STOKERS boilers which in an emergency can be carried on three of the units. The most efficient combustion rate was thirty-five Ibs. per sq. ft. of grate surface per hour and four units at this Combustion Rate per Sq. Ft. per Hour Dry Coal EASTERN UAL F.C. 73 vol. n I st1 ? Moisture 4 B.T.U(Dry) 14300 PITTSBURGH COAL FC. 5T Vol. 30 f I Moisture 4 B.T.U.(OryV 13500 ILLINOIS COAL F.C. 48 Vol. 30 gi. 3 Moisture 10 B.T.U.(Dru) 12200 IOWA COAL F.C. 33 Vol. 27 , Moisture 15 BJ.U.(Dry) 10400 LIGNITE Vol'. 33 Ash 10 & 1 Moisture ZT> B.T.U.(Ory) 11500 Minimum for Continuous Operation 15- ia 18 -20 18-20 18-20 18-20 Recommended for Continuous Operation 20 -25 23-26 23-26 20-23 72-26 Maximum for Continuous Operation 25 -t8 "50-35 50-32 25-27 26-32 Recommended for3to4Hr. Peaks 50-35 35-40 32-35 27-30 32-35 Maximum for 3to4Hr. Peaks 1)5-40 40-42 35-40 30 35 Maximum for One Hr. Peaks 40 42 40 30 35 FIG. 102. Combustion Rates Recommended for Various Fuel Conditions for Natural Draft, Overfeed Stokers. Combustion Rate perSq. Ft. per Hour Dry Coal EASTERN COAL vol. n Ash 6 S . 1 Moisture 4 BJ.U(Dru) 14500 PITTSBURGH COAL Vol. 30 A l h Moisture 4 B.T.U.(Ory) 13500 ILLINOIS COAL F.C. 48 Vol. 30 Ash 12 Moisture 10 B.T.U.(Ory) 12200 IOWA COAL F.C. 33 Vol. 87 Ash 25 S 4 Moisture 15 B.T.U.(Ory) 10400 LI6NJTE F.C. 34 Vol. 33 Ash 10 Moisture 23 B.T.U.(Dr) H500 Minimum for Continuous Operation 20-22 ZO-22 20-22 20-22 Recommended for Continuous Operation 23-26 23-26 22-25 25-30 Maximum for Continuous Operation 30-33 32-35 25-30 35-40 Recommended for3to4Hr. Peaks 35-40 40-45 30-35 42-45 Maximum for 3to4Hr. Peaks 40 45 35 45 [Maximum for One Hr. Peaks 40 45 35 45 FIG. 103. Combustion Rates Recommended for Various Fuel Conditions for Natural Draft, Chain Grates and Traveling Grate Stokers. rate would carry the load, while with three in service, the combustion rate would increase to 48.5 Ibs. If 45 Ibs. was the maximum for continuous operation it would be necessary to increase the grate area to 76.5 sq. ft. thereby reducing the APPLICATION OF STOKERS 217 combustion rate to 32.5 Ibs. when four units were in service. This condition does not enter into the design of a large plant but is important in installations of three, four or five boilers. In the selection of new apparatus, it is possible to propor- tion both boilers and stokers for best results but in the case of an old installation, this cannot always be done. Many boilers which are still in condition to give good service for years and therefore cannot be discarded, are not proportioned for stoker firing. The hand fired grate is limited to a length of about seven feet and it has been common practice in the past to make the boilers wide enough to permit of the installa- tion of the desired grate area, based on a length of six or seven feet. These boilers are wider than would be selected today for stoker firing, but it is often necessary to equip them with stokers. In such cases it is important that the stoker be proportioned to suit the boiler furnace if best results are to be secured. The stoker should be made as wide as the furnace if possible and long enough to give the desired grate area. Some types of stokers are made in a variety of lengths and widths and are therefore more easily applied to these special cases than those designs which vary only in width. The * ' grate area " of a stoker is a rather indefinite unit and depends upon the type of stoker and the methods of determina- tion employed by different manufacturers but it makes little difference how this unit is determined because it does not affect the fuel burning capacity of a given stoker. If a manu- facturer chooses to designate dump grates, coking plates, or dead plates as "grate area" thereby apparently increasing the size of the stoker, he must decrease the allowable combustion rate per sq. ft, while on the other hand, if these be eliminated from the calculations, the unit combustion rate will be cor- respondingly increased. It is desirable, however, for purposes of comparison that the same standard of measurement be applied to stokers of the same type in order that their com- parative fuel burning capacities can be compared. Overfeed stokers of the front feed type usually figure the area to be the product of the stoker width multiplied by the length measured along the line of fuel travel from the point where the fuel enters the furnace to the bridgewall. In some 218 MECHANICAL &TOKERS cases, the dump grates are not included and in others they are given partial values. It is, therefore, desirable with stokers of this type to determine exactly how the grate area has been determined, especially when a comparison is to be made with some other type of stoker. Side feed stokers are calculated on the basis of the dis- tance from the inside of front wall to face of bridgewall, mul- tiplied by the length of actual grate area measured along the Each ring of this arch must be thoroughly bonded to the adjacent rings FIG. 104. Dimensions of Westinghouse Roney Stoker. grates. For convenience, in making calculations, the projected area can be multiplied by 1.4. Multiple retort underfeed stokers have generally employed the retort as a unit but this is not a satisfactory unit of grate area because no two manufacturers have adopted the same retort dimensions and the situation is further complicated because the same manufacturer has more than one retort size. It is now generally accepted that the area in square feet should be specified and this is determined by multiplying the actual width by the horizontal distance from the inside of front wall to the face of the bridgewall. This includes dump grates or APPLICATION OF STOKERS 219 other ash disposal devices but does not take into account the angle of the retorts. Center feed underfeed stokers are figured on the basis of projected area enclosed by the four furnace walls. Traveling grates are based on projected area enclosed by the side walls, feed gate, and water box. Forced draft stokers of this type do not employ the water box and the length should be measured from the inside of the feed regulating gate to the rear of the last wind compartment. In the determination of correct stoker size for a given set of conditions, the following procedure will be found con- venient Assume the following conditions: Boiler size, 500 H.P. Continuous rating desired 150% Maximum rating for four hours 200% Maximum rating for one hour 275% Coal Volatile 32% Fixed Carbon 54% Moisture 5% Ash 9% Sulphur 1% B.T.U. dry 13,500 Efficiency at 150% 75% Efficiency at 200% 72% Efficiency at 275% 65% The calculations can be arranged as follows: Per Cent Rating Horse power Developed Efficiency Coal per Horse power Total Coal per Hour 150 750 75 3.31 2483 200 1000 72 3.44 3440 275 1375 65 3.82 5253 For convenience in determing the pounds of coal required per boiler H.P., a diagram such as Fig. 105 may be used in 220 MECHANICAL STOKERS the following manner: locate the intersection of the vertical line of B.T.U. in the coal with the diagonal line representing the combined efficiency then project horizontally from this point to the heavy curved line. From this second intersection, project vertically to the scale representing pounds of coal per boiler H.P. The same diagram may be used to determine the equivalent evaporation per pound of coal by locating the inter- section of the vertical line of B.T.U. in the coal with the Pounds of fuel or Combustible Per B.H.P Per flout 4 35 of & i.oVv ti& &' / / J- IXri/^lfVi /Tnoislf^ STANDARD HOPPER SPECIAL HOPPER No. Retorts Wiatn ^inside; Capacity, Pounds Capacity Pounds, 2 2' 6" 281 735 3 4' 3" 478 1250 4 6' 0" 675 1765 5 7' 9" 872 2280 6 9' 6" 1069 2795 7 11' 3" 1266 3310 8 13' 0" 1463 3825 9 14' 9" 1660 4340 10 16' 6" 1857 4855 11 18' 3" 2054 5370 12 20' 0" 2251 5885 13 21' 9" 2448 6400 14 23' 6" 2645 6915 15 25' 3" 2842 7430 CHAPTER IX INSTALLATION OF STOKERS SPECIFICATIONS CON- TRACTS GUARANTEES BOILER ROOM LOG There has been some improvements in recent years in the matter of boiler and stoker combinations. Boilers have been raised, stokers have been set differently; more attention has been given to the breeching design and higher stacks are being used. Still there has never been anything like the thought on this subject that there should be and the standardization of the practice that is necessary. There is no reason for doing exactly the same things that were done years ago, still installations are going on nowdays the same as they did fifteen years ago. It is also not necessary to present exactly the same standard. When changes are made, however, there is need of an analysis of the installation and the information translated into some definite grasp of the subject, into some real data that can be distributed with con- fidence. Whenever a stoker is installed in combination with a boiler, there are many things that must be considered and decided jointly by the purchaser, the boiler and stoker manufacturer. A definite conclusion must be reached on the following: 1. Height of the boiler header above the floor line or height of boiler setting. 2. Setting of the stoker. 3. Combustion space necessary for the coal to be used. 4. Design and location of the breeching. 5. Size and location of the stack. 6. Area of gas passages through the boiler. 7. Area of damper openings. 8. Facilities for cleaning soot off boiler baffles and boiler tubes. 9. Grade of firebrick to be used in the furnace construction. 226 INSTALLATION OF STOKERS 227 10. Size of walls of boiler and furnace setting. 11. Size and grade of firebrick for arches. 12. Method used to control dampers. 13. Construction of ash pit and facilities for disposing of the ash. 14. Method of conveying coal to the stoker hoppers. 15. Locations of fans, etc. 16. Design and location of air ducts. FIG. 109. Typical Underfeed Stoker Application. 228 MECHANICAL STOKERS If the purchaser failed to install the height of stack that was necessary, he would be the one that was responsible for the failure. If the stoker manufacturer did not take a firm stand and hold out for the correct setting of the stoker, he would be responsible for the failure. If the boiler manufac- turer failed to provide the correct areas for the passage of the furnace gases and arrange to set the boiler at a height required for the particular stoker selected, he would be responsible for the failure. Of course, some of the items mentioned are more important than others. Slighting some of them would not ruin an installa- tion entirely, while slighting others would make an installation absolutely a failure. The question arises as to how those interested are to know to what degree installations will be successful. One can hardly plan an installation for the future unless he has some concep- tion of past installations. One must be capable of recognizing the strong points of installations and ascertaining the weak ones. Great care must be taken to see that the weak ones are not unduly attributed to other causes than the real ones. Names sometimes mislead. Very often when discussing a satis- factory installation the first question asked is What is the name of the boiler and stoker? In most cases this has very little to do with the results obtained. It is true that some stokers adapt themselves more easily than others to particular boilers; and it may be true that some boilers are more easily set than others, but one cannot come to any definite con- clusion as to the cause for a satisfactory or unsatisfactory boiler and stoker combination unless he knows, and has de- termined by careful analysis, the cause. It is not intended that one should not be exact and resource- ful in the handling of various materials that go to make up a good boiler and stoker combination. If it is not necessary to raise boilers, use higher stacks, etc., the reason why these things are not necessary should be known. It is right, how- ever, to assert what we actually know in the planning of new work. Installations are always being made that do not follow the principles that are commonly known to be right. One fre- INSTALLATION OF STOKERS 229 quently hears that boilers cannot be set higher because the contract for the masonry work has been included with the boilers; or, that the contract has already been let and the purchaser will not pay the extra cost of setting the boilers the way they should be set with the particular stoker selected. Again, we frequently hear that the boilers cannot be set right because the architect has previously provided so much room for the boiler and stoker and they must go within the limit provided, whether a good combination or a bad one is obtained. Plans continue to be made in the wrong way and unsatisfactory installations result. There is another phase of this problem that seems to interfere with obtaining good installations ; that is, the cost of the installation. Of course, boilers being raised, stokers extended, higher stacks, etc., cost more money. The boiler and stoker manufacturers must take a sufficiently firm stand for the combinations that are known to be right and be sure that money is expended to make them right. A case is recalled where the contract had been closed for boilers, stokers and the brickwork. The boilers were to be set a certain height and the contract was let with the masonry figure on this type of setting. The setting did not agree with what the stoker manufacture thought was right and he took a firm stand that the boiler should be raised. If the purchaser, the boiler and stoker manufacturers, in this case, had cooperated and definitely decided the points mentioned in the forepart of this Chapter enough money would have been expended to obtain the right kind of a combination. It does not seem possible that the plans and methods adopted in one section of the United States could be followed with the same degree of exactness and success in another, quite remote, or any other place where coal and installation con- ditions are different. It would seem that each community where coal conditions are about the same should obtain their own data. The time has not come when a combination can be standardized in the west and be adapted to the conditions in. the east, or vice versa, with success. Conditions are daily encountered that are prejudical to good furnace performance. One plant that was investigated 230 MECHANICAL STOKERS will present a typical example of conditions to be found in many other plants. This plant operated twenty-four hours a day and had six water tube boilers installed, each of 250 horse power rated capacity. The boilers were served by one stack, 9 ft. in diameter by 150 ft. high. There was one long breeching connecting all the boilers. A short breeching con- nected the main breeching to the stack. The complaints were excessive labor and great difficulty in maintaining the steam pressure necessary to operate the plant. Considerable money was spent in sending engineers to the plant with instructions to assist in every possible way to better the operating con- ditions. It was immediately found that the draft available in each furnace was low and insufficient to burn the coal required. Arrangements were made to carefully analyze this draft condition and find the cause of the troubles. There was an available draft in the stack of about .90", and in the short breeching, about .83". At points in the main breechings, how- ever, only a few feet away, the draft dropped to about .53", indicating a loss of .3" draft in the right angle turn to the main breeching. The investigating engineers reported the boilers dirty and on several occasions 3/16" scale was removed from the tubes. It was also found that the boilers were only cleaned every six months and the soot blown from the tubes every week. There was a heater installed and owing to the piping construction it could only be cleaned once a year. An inspection of the blow-off valves of the boiler proved that they all leaked. In this particular case, the purchaser was at fault in not operating the plant properly and maintaining the equipment in good condition. "Whoever put the breeching in was respon- sible for its faulty design. The stoker manufacturer was at fault if he knew of the breeching design; he should have cautioned the purchaser regarding draft losses. A peculiar situation arose in analyzing the conditions of this plant. The owner's operating engineer reported the boiler free from scale. The investigating engineer reported the boilers badly scaled. It was finally necessary to have the manager of the company personally inspect the boiler on which reports were being made. In his personal investigations small INSTALLATION OF STOKERS 231 spots of scale in the tubes were noted which the turbine had skipped. The operating engineer claimed that this was a trivial matter. The manager, however, insisted on having all of the scale removed. This was done and five wheel barrow loads of scale were removed from this one boiler this scale being removed after the owner's operating engineer had re- ported the boiler clean. After all the causes of the troubles at this plant were determined, it was arranged to correct them. The results obtained were astonishing after everything was fixed up and a better practice established in cleaning boilers. The important part of the analysis is this : The matter had to be sifted down and the causes of the troubles determined without question and presented to the management of the company. This cost money who was to pay for it ? If someone had not found the troubles and expended the money necessary to find them, the result would have been dissatisfaction with the entire equip- ment; the stoker would have been thrown out; boilers con- demned; probably money unnecessarily expended on a new stack and the owner convinced that some one made a mistake in the original purchase of the equipment. In this kind of work there is always a question of whether or not the trouble is due to the stoker and boiler equipment; the operating conditions, or the design of the breeching and stack. It is necessary, therefore, to make a careful analysis and obtain sufficient engineering facts that will properly place the reponsibility. There are many things that effect a boiler and stoker com- bination and unfortunately the purchaser or user cannot appre- ciate how anything wrong with a part of the equipment can effect another part. A few years ago the stoker manufacturer had very little control over the things that determined whether a stoker installation would be a success. As an example of this, a combination was installed, where the stoker manufacturer inquired as to the height of stack selected for the 500 H.P. boiler to obtain the %" draft specified for the furnace. He was told by the architect that the stack would be 100 ft. above the grates. The stoker manufacturer claimed that 100 ft. was 232 MECHANICAL STOKERS not enough and insisted on 150 ft. The architect was greatly astonished that such a height for this one boiler was necessary he finally agreed, however, to make it 125 ft. The stoker manufacturer still insisted that a 125 ft. stack was not sufficient and nothing less than 150 ft. would do. Everything possible was done to convince the architect that this size stack was needed. It was finally decided, however, to build the 125 ft. stack, the purchaser approving the architect's opinion. The stack was built and sufficient draft was not obtained for the amount of coal it was necessary to burn consequently the installation was a failure. One stoker manufacturer cannot alone take a firm stand and hold out for a better practice in installations, neither can one boiler manufacturer, but there must be cooperation among all, in order to obtain the type of installation that is required. Better practice could be obtained if the purchaser gave more thought to the whole combination of boilers, stokers, breechings and stacks. The purchase of a stoker requires more thought than it is generally given. If a boiler and stoker combination is to be purchased to burn bituminous coal, the type of boiler and stoker should be determined first. It will not be attempted here to outline the things that must be considered in deciding this matter. There are all kinds of combinations that can be inspected. Time can be used to a good advantage by finding the good and bad points of local installations and thereby be assured that contemplated combinations will not duplicate faulty ones. After the boiler and stoker has been selected, it is not yet time to finally decide whether or not these particular types should be purchased it is not the time to sign the contracts. The purchaser should arrange a conference between the manu- facturer of the boiler selected, and the manufacturer of the stoker selected. The whole combination and the things men- tioned in the forepart of this chapter should be discussed in detail and a decision made on each matter, final decision to be based on good engineering judgement and experience. The purchaser should not obtain an opinion from the boiler manu- facturer as to how the boiler should set, unless he gives the INSTALLATION OF STOKERS 233 stoker manufacturer an opportunity to present his opinions. If all points are settled on a good engineering basis, there will be no question but what the best combination known will be obtained and the customer can well afford to expend the money necessary for it. This practice of buying stokers and boilers has proved its effectiveness. Many boilers and stokers are purchased by this method. One case is recalled where the purchaser decided on the boiler and stoker that he had in mind purchasing; he then called the boiler manufacturer, the stoker manufacturer and his consult- ing engineer who was designing the breeching, stacks, etc., in conference with him. He made the statement that he wanted the best combination of this type of boiler and stoker that he could get and wanted all conditions right for its proper opera- tion. At this meeting the size of the stack was decided on, the setting of the stoker in combination with the boiler was arranged, the grade of firebrick that was to be used in the arches was selected; in fact, all matters, even to the minutest detail pertaining to this combination, was discussed and decided upon. After it was thoroughly understood between those present that in their opinion no changes could be made from those decided that would better the installation, the purchaser signed the contracts. It is a fact that this installation is very satisfactory in every way. The purchaser of the equipment knew of other combinations of this same type of boiler and stoker that were failures. He also knew and was capable of determining the weak points of those installations and he made sure that the conditions were going to be right for the equipment he was purchasing. The purchaser must expend the money necessary to obtain the best combination known; he must operate the equipment properly and keep it in good condition. The stoker manu- facturer must take a firm stand for the proper setting of the stoker ; he must hold out for the draft that is required to burn the coal and he must insist on the proper operation of the stokers. The boiler manufacturer must provide ample damper areas and gas passages so there will be no restriction to the flow of gases through the boiler to the breeching. If these areas 234 MECHANICAL STOKERS must be changed to suit local conditions, then the boiler manu- facturer should advise the purchaser how they should be changed. The boiler manufacturer must also provide easy means for removing the soot from the boiler tubes and baffles ; and he must arrange to set the boiler according to the require- ments of the particular stoker in combination. This kind of cooperation is necessary for every installation. Those installations that obtain it will have very little chance of failure. STOKER ENGINEERING DATA Prom the forgoing it will be clear that a stoker manufacturer must have certain pertinent engineering data, from the pur- chaser in order to study all conditions surrounding the installa- tion. In general the following data cover a typical boiler room case and this information should be given in any specifications that are proposed covering stoker apparatus: Name and address of Purchaser. Location of Plant. Stoker: (What type of stoker are you considering?) 1. Type. Boiler: 2. Type Eated H.P Tubes high, or class, or Dia. (H.K.T ) Tube width tube length 3. Center wall dimension Alleyway dimension Sidewall dimension Furnace dimension Floor line to: Mud drum (center line) or Header, or shell (center line) Stack: 4. No. of stacks brick or steel 5. Ht. above present boiler room floor. Inside Dia. at top. Boilers served Total H.P. served (each stack) (each stack) 6. Connected to boiler by: Breeching or direct. Stoker setting and application. 7. Old or new boiler? If old, can they be reset? Can floor be lowered ? INSTALLATION OF STOKERS 235 8. What local conditions prevent the best application? 9. Will ashes be taken out: Floor or Basement? Conveyor or Car? 10. Do you contemplate installing future stokers? How many? Eela- tion to this installation? 11. What drawings do you want for preliminary study? Fuel to be used: 12. Name Where mined 13. F.C Vol Moist Ash Sulphur B.T.U. (as fired). Operating service: 14. Best economy desired at rating. What will be maximum rating? Duration (hrs.) Avg. daily rating. 15. Eemarks regarding the character of service and plant organization. 16. Steam pressure of plant Superheat Back pressure Stoker Drive: (Do you want stoker driven by) 17. Engine Turbine and Gear Motor Forced Draft Fan Equipment: (How many fans do you want, and how driven?) 18. Number of Fans ( ) Driven by ( ) Turbine and Gear. ( ) Motor. ( ) Engine. Deliveries Required: 19. Stokers and Equipment Months. Drawings : 20. If possible, furnish the following drawings with specification: (1) Boilers and boiler settings as installed. (2) Beams and columns adjacent to boilers. (3) Details of auxiliary equipment, piping, etc., that may inter- fere with stoker settings. In drawing specifications for stokers it is quite essential that they be specific and contain the engineering data required. Following is a good type of specification in general use. 236 MECHANICAL STOKERS SPECIFICATIONS for MECHANICAL STOKING EQUIPMENT for the PITTSBURGH ELECTRIC COMPANY PITTSBURGH, PA. Pittsburgh, Aug. 16, 1920. General Data. These specifications are intended to cover the requirements for Mechanical Stoking and Forced Draft Equipment to be constructed, delivered, and erected complete with all appurtenances and otherwise ready for service, started and put in successful operating condition by Contractor in the DuQuesne Station, located at First Avenue and Forty- Sixth Street, Pittsburgh, Pa., of the Pittsburgh Electric Com- pany, Pittsburgh, Pa., hereinafter called the Purchaser. Contractor may deliver his material to the station over a siding from the P. R. R., which enters the boiler room. Boiler. The twelve boilers under which Contractor shall erect the stokers are A. & C. Company's all wrought steel con- struction, arranged two in battery, each boiler containing approximately 6000 sq. ft. of water heating surface. The boilers are 21 tubes wide and 14 tubes high with 3-42" drums, are 12' 1" wide inside of setting walls, are set 10 ft. high from floor line to bottom of front header and are equipped with 125 F. Atlas Superheaters. Working Pressure. Under normal operating conditions the boilers will deliver steam at 200 Ibs. per sq. inch gauge pressure and superheated at 125 F. Stacks. Boilers number 2, 4, 6, 8, 10 and 12 are served by a brick stack 13' 6" clear diameter by 193' above boiler room floor and located adjacent to the East side of the boiler room. Boilers number 1, 3, 5, 7, 9 and 11 will be served by a brick lined steel stack 15' 6" clear diameter by 200' above boiler room floor and located immediately over future boilers number 13 and 15. Soot Blowers. Each boiler will be equipped with soot blowers. INSTALLATION OF STOKERS 237 Coal. The stoking equipment furnished hereunder shall be constructed and guaranteed by Contractor to burn success- fully and economically at all rates within and including the maximum safe operating capacity of its feeding mechanism, steam coals common to the Pittsburgh market, among which the principal is Youghiougheny screenings of approximately the following analysis : Volatile combustible matter 30.81% Fixed carbon 56.46% Sulphur 1.70% Ash 11.03% B.T.U 13,400% Operation. After the first two stoking equipments are erected and ready for operation, Contractor shall furnish and shall maintain daily at the Station for a period, of six weeks, a competent firemen thoroughly experienced and skilled in the operation of the stoker equipment furnished by him. Said fireman shall direct the operation of said stoking equipment and shall carefully and thoroughly instruct Purchaser's employes in the proper care, manipulation and operation there- of, to the end that Purchaser may derive the greatest benefit from the installation. Stoking Equipment. Apparatus to be furnished and erected hereunder by Contractor consist of the following: Twelve mechanical stokers of identical construction, except that six will be left hand and six will be right hand. The necessary new lower half boiler fronts, stoker bearing bars, anchor bolts, buck stays, driving gear regulators, clean- out and inspection doors and all other appliances, attachments and apparatus necessary to make the installation complete and ready for commercial service. Purchaser will remove lower half fronts and grates on boilers now in place and will furnish and set in place all necessary structural steel work and other foundations for carrying the stoker framework under the direction of the Contractor's erecting superintendent. Purchaser will do all necessary cutting away and rebuild- ing of boiler settings and furnace brickwork. 238 MECHANICAL STOKERS Purchaser will provide suitable foundations and foundation bolts for forced draft equipments. Purchaser will furnish all steam and exhaust piping out- side of the stop valves and exhaust openings on Contractor's apparatus. Purchaser will furnish and erect the air ducts and con- nections to the stoker wind boxes of ample area which will be arranged as indicated on drawing, attached to and forming part of these specifications. Capacity and Efficiency. Contractor shall state in his pro- posal the following: 1. The safe continuous maximum coal feeding capacity per hour of each stoker offered by him. 2. When burning Youghiougheny screenings of approxi- mately the heating value specified above, the maximum capacity and corresponding combined efficiency each equipment will develop continuously from the boiler under which it is installed. (a) For a period of 36 consecutive hours. This capacity must not be less than 1200 boiler horse power. (b) For a period of 8 consecutive hours. (c) For a period of 2 consecutive hours. This capacity must not be less than 1800 boiler horse power. 3. The combined efficiency when developing continuously the following capacities: (a) 600 boiler horse power. (b) 900 " 4. The pounds of coal per hour or B.T.U. per hour required to be fed to stoker to maintain on a banked boiler a steam pressure of 190 Ibs. per sq. inch with steam stop valve closed. 5. Time required to develop from a boiler so banked for a period of 48 hours a capacity of (a) 600 boiler horse power (b) 1200 boiler horse power. 6. Steam consumption in pounds per hour of the stokers and of the forced draft apparatus when the boilers served by it are operating at : (a) 600 boiler horse power. (b) 1200 " (c) Maximum (2-hour rate). INSTALLATION OF STOKERS 239 Mechanical Stokers. Stokers shall be of the inclined under- feed type and shall be provided with adequate blast boxes, air openings and tuyeres for conducting the air required for com- bustion properly to all parts of the bed of fuel and discharging it into the bed of fuel from beneath. The blast boxes and air openings shall be so proportioned and separated into sections, each provided with suitable damper, that the air pressure in the fuel bed can be adjusted as may be required for best combus- tion and most satisfactory manipulation of the fire. These dampers shall be arranged to be conveniently operated from the front or side of the stokers and so provided with suitable locking device that they will remain in position when set. Hoppers. Each stoker shall be provided with a suitable coal hopper extending its entire width and made of sheet steel rigidly braced. These hoppers shall be designed to receive coal from an overhead chute and deliver it to the feeding plungers. Hoppers shall have ample capacity to contain the quantity of coal required for a period of not less than 10 minutes when the stokers are feeding coal at the maximum rate. Retort and Feeding Mechanism. The plungers shall be arranged for receiving coal from the hoppers and delivering it to the retorts. Retorts shall be of cast-iron, of substantial con- struction and so designed as to be free from warping or defor- mation under the normal conditions of service and free from roughness or ridges which might obstruct the passage of the coal. Suitable ram blocks shall be provided in the retorts to insure even distribution of the coal. Travel of ram blocks and moving grates shall be adjustable while stokers are in opera- tion. Operating Shafts and Auxiliary Mechanism. The plungers, ram blocks and moving grates shall be given a reciprocat- ing motion by suitable rods connecting with cranks on the drive shaft. The rod ends which connect with the cranks shall be of the marine type and fitted with genuine babbitted bush- ings. The drive shaft shall be of cast steel with journals turned true and accurately in line. Shaft bearings shall be rigidly attached to the stoker front by suitable brackets of ample strength and free from deflection. Shaft bearing boxes 240 MECHANICAL STOKERS shall be genuine babbitt lined. Shaft bearings and connecting rod bearings shall be arranged for grease lubrication and grease cups shall be furnished. Power shall be transmitted to the drive shaft by a suitable cut worm and cut gear mechanism running in oil in a dust and oil tight cast-iron box having removable cover for inspection and adequate means for removing and renewing oil. Dumping Grates. Each stoker shall be equipped with an adequate dumping grate. Dumping grate shall be easily operated by levers suitably located in front of the boilers. Dumping grate shall be arranged to prevent the accumulation of clinkers on the bridge wall or on other parts that might choke or hinder the proper dumping of ashes, etc. The ashes and clinkers will fall into an ash hopper located below the furnace from which they will be delivered by gravity into the ash conveying equipment for removal. The discharge openings on the ash hoppers will be about 24" square. Adequate provision must be made by Contractor in the construction and arrangement of the dumping grates so that the clinkers dis- charged by his stoker when properly operated shall be small enough to discharge freely and easily from the ash hoppers in the manner described without the necessity for continual punching, raking, stirring or breaking up clinkers in the ash pit. Smoke. The stoking equipment furnished hereunder shall operate under all conditions of load and fuel so as to conform to the smoke ordinances of the City of Pittsburgh. Forced Draft Equipment. Contractor shall furnish four sets of forced draft equipment, any three of which shall be easily capable of delivering continuously a sufficient quantity of air at a sufficient pressure, including ample allowance for friction losses in air ducts, damper boxes, etc., to develop from the twelve boilers simultaneously the maximum capacity at the 2-hour rate guaranteed by him for each boiler. The forced draft equipments shall be of similar construction and shall be driven by steam turbines of manufacture approved by the purchaser. Turbines shall operate non-condensing with normal steam pressure of 200 Ibs. per sq. inch, superheated about 140 F., but they shall be designed and arranged with suitable by-pass valves hand operated, as to be easily capable INSTALLATION OF STOKERS 241 of developing the maximum capacity specified above when supplied with steam at 150 Ibs. per sq. inch by gauge and superheated 100 F. The exhaust pressure will not exceed one pound per square inch above atmospheric pressure. Each turbine shall be equipped with safety governor ade- quate to prevent development of a dangerous speed, also a suitable governor to maintain a practically uniform speed under all conditions and changes of load. Speed governors shall be capable of adjustment so that there will be no interference or "bucking" when two or more fan units are operating together feeding into the main air ducts. Contractor shall state and guarantee the maximum con- tinuous capacity and blast pressure of each of the forced draft equipments offered by him and the speed of the equipment when operating under such maximum conditions. Air Ducts. Purchaser will furnish and erect the necessary air duct (a) between the fans and the main air duct and (b) between the main air duct and the blast boxes on the stokers. All air ducts will be constructed of No. 16 Birmingham wire gauge galvanized iron; joints will be substantially riveted together and soldered air tight after riveted. Air ducts between fans and main air duct will be fitted with hand operated butterfly dampers with suitable lever handle and provided with suitable locking device that they will remain in position when set. Air ducts between main air duct and stoker blast boxes will be fitted with butterfly dampers operated by suitable regulating devices specified below. Driving Mechanism. Contractor shall furnish suitable driv- ing mechanism for stokers. Stokers shall be driven either by belt or chain from 2 line shafts furnished and erected by Con- tractor, one for each side of the boiler room, complete with all necessary hangers, brackets, bearings, etc. Each stoker line shaft shall be arranged with jaw clutch between each battery of boilers and shall be driven through jaw clutches by two engines of manufacture and construction approved by the Purchaser. Each engine shall be of ample capacity to drive all stokers 242 MECHANICAL STOKERS on its line shaft at maximum capacity when supplied with steam at 150 Ibs. per sq. inch gauge, and exhausting against 1 Ib. back-pressure by gauge, but shall be designed for normal operation at the normal operating steam pressure of the station. Each engine shall be fitted with adequate governor arranged to operate to prevent over-speed only. Speed of the engine in normal operation shall be controlled by regulating devices specified below. Regulating Devices. Contractor shall furnish suitable auto- matic devices for regulating the supply of coal and air to the stokers in accordance with the demand for steam. The regulat- ing devices shall be adjusted to maintain at all times such a proportion between the coal and air as will develop the highest practicable combustion efficiency and maintain the steam pressure within 2% Ibs. of the normal operating pressure at all capacities including the maximum. It is proposed to operate the fans at constant pressure and control the air supply to the fuel bed by automatically operat- ing the butterfly dampers in the air ducts between the main air duct and the stoker blast boxes. Contractor shall furnish for this purpose a damper regulator approved by the Purchaser, said regulator being operated directly by the change of steam pressure due to the demand for steam. It is proposed to control the supply of fuel to the furnace by regulating the speed of the engine operating the stoker line shaft. For this purpose Contractor shall furnish suitable regulating device of type approved by the Purchaser, said regulator being operated by the steam pressure on the station, by the air pressure in the stoker blast boxes, or by such other means approved by the Purchaser as Contractor may recom- mend. The regulating devices shall be of simple and substantial construction easily adjusted, arranged to maintain adjustments when once set, and connected so that they may be easily and rapidly thrown into and out of operation should it at any time be desirable to regulate by hand. Contractor shall include in his proposal complete descrip- tion of the regulating devices he proposes to use for these INSTALLATION OF STOKERS 243 purposes and show therein how change in the resistance of the fuel bed due to varying size of coal is provided for. Description and Drawing's. Contractor shall include with his proposal a complete detailed description and completely dimensioned general arrangement drawings of the apparatus offered by him. After the contract is let Contractor shall furnish promptly complete detailed drawings of the apparatus to be furnished by him hereunder. Tests. At a convenient time not more than six months after completion by Contractor of his work hereunder, Pur- chaser will make such service and running tests as considered necessary to determine whether the equipment furnished here- ander conforms to the requirements of these specifications. Contractor shall be notified in advance of such tests and may have a representative present. Should the tests show that the equipment furnished by him does not meet the requirements of these specifications, Contractor shall promptly and at his own expense make the necessary changes to make it conform thereto. STOKER GUARANTEES A stoker primarily is for burning fuel and delivering the resultant heat to a boiler or other kind of vessels. How well a stoker does its work is theoretically based on the following: (1) Pounds of coal burned per hour. (2) Percent of combustible in ash. (3) Percent of CO 2 in furnace gases. (4) Percent of CO in furnace gases. (5) Draft required in the furnace. The purchaser however, wants to know how many pounds of steam can be obtained from a pound of coal. Consequently, stoker manufacturers are asked to make guarantees that are affected by the following: (1) Type of boiler. (2) Condition of brick setting. (3) Layout and design of breeching and stack. Stoker manufacturers therefore do not approve of making an overall guarantee, but in order to specify performances it is important that they be given all the engineering data pre- 244 MECHANICAL STOKERS viously asked for. For general purposes, the following per- formances are generally given to Purchasers : (1) Maximum percent of rating that can be obtained from the boilers for 24 hours duration. (2) Maximum percent of rating that can be obtained from the boilers for short duration to carry over peaks. (3) Combined boiler and grate efficiency at the boiler rating that boilers will be operated at the greatest number of hours during the day. TYPICAL STOKER CONTRACT FORMS Most stoker manufacturers sell their product on a proposal form, which is submitted to the purchaser and if accepted by him and approved by the manufacturer becomes a contract. The typical form used is as follows : THE IDEAL STOKER COMPANY. CONTRACT PROPOSAL No Detroit, Mich., 192. . To Hereinafter called the Purchaser. P. O. Address Shipping Address For Stoker equipment for use in connection with the following: (A rated boiler horse power being taken as 10 sq. ft. of effective water- heating surface) (1) THE IDEAL STOKER COMPANY (hereinafter called the contractor) proposes to furnish the Purchaser, f.o.b. cars point of shipment, apparatus as specified below: (a) Stokers: (&) Actuation: (c) Stoker companies arrange A, B, C, etc., for their individual equip- < ment requirements. (2) FURNISHED BY THE PURCHASER: The Purchaser agrees to unload all mechanical stoker equipment and accessories herein specified to be furnished by the contractor, and to place same adjacent to the foundations upon which the said equipment and accessories are to be erected. All materials, boxed or otherwise, are to be protected from the weather. The Purchaser will furnish labor and tackle for erecting all equipment. INSTALLATION OF STOKERS 245 The Purchaser will furnish, in place, all foundations, anchorage and anchor bolts; steel and concrete pits, air duct, ash-pit doors, supports for line shaft hangers, boilers and boiler-setting walls, draft gauges, all steam piping, electric wiring, and all other equipment not otherwise specified herein. (3) SUPEEINTENDENCE: Unless otherwise stipulated, all materials shall be installed by and at the expense of the purchaser and under the supervision and direction of a Superintendent, to be furnished by the Contractor, for whose services the Purchaser agrees to pay the Contractor the sum of ($ ) dollars per calendar day (which shall include time traveling) plus living and traveling expenses, all of which shall be paid by the Purchaser as invoices are presented; it being understood and agreed that during the term of such services, the Superintendent shall be the Pur- chaser's employee. (4) PEEFOEMANCE CONDITIONS: It is understood and agreed that any guarantees are based upon the Purchaser providing the following conditions: (a) That the stoker equipment has been erected in accordance with the Company's plans and specifications, and is properly operated. (b) That the boilers shall be of type with a minimum distance from heating surface of boiler to grate of ft. (c) That the boilers are in good condition and heating surface clean, inside and out. (d) That the baffling is tight and so arranged that the temperature of the flue gases at boiler outlet shall not exceed 550 degrees F. when the boiler is operated at 150% of nominal rating. (e) That the boiler setting and furnace brickwork are in first-class condition and free from excessive air leaks, as determined by candle flame, in accordance with A. S. M. E. Boiler Test Code. (/) That the draft (negative pressure) provided by the Purchaser and available in the furnace of each stoker, shall not be less than inches water column when boiler is operating at maximum rating specified. (#) There shall be available for each stoker, when boiler is operating at maximum rating specified, not less than cubic feet of air per minute referred to barometer, and 70 degrees Fahr. at inches water column static pressure at stoker forced-draft inlet. (ft) That fuel, known commercially as size and of the following proximate analysis shall be used: % Fixed Carbon % Volatile Matter % Ash % Moisture % Sulphur (Sep. Det.) 246 MECHANICAL STOKERS B.T.U. per pound as fired not less than Fusing temperature of ash not less than Fahr. (5) DATE OF SHIPMENT: The Contractor agrees (unless delayed by the Purchaser) that shipments will be made days after acceptance of this proposal. The Purchaser shall furnish the Contractor, within ten days from date of acceptance of this proposal, all data necessary to enable the Contractor to Complete his drawings. The Contractor shall be privileged to extend date of shipment specified without notice, in case the Purchaser delays furnishing information necessary to complete the Contractor's drawings, or delays in approving same. The Contractor shall be granted reasonable time after final drawings are approved to complete material lists and arrange for shipment. The acceptance, when delivered, of the mechanical stoker equipment herein specified to be supplied by Contractor, shall con- stitute a waiver of all claims for damages caused by any delay. (6) CONSEQUENTIAL DAMAGE: The Contractor shall not be held liable for any loss, damage, detention or delay caused by fires, strike, civil or military authority, or by insurrection or riot, or by any other cause which is unavoidable or beyond its reasonable control, or, in any event, for consequential damages. (7) EEPLACEMENT OF DEFECTIVE PAKTS: The Contractor agrees to correct, and shall have the right to correct, by supplying new parts at its own expense, f.o.b. Point of Shipment, any defects in the apparatus furnished by the Contractor which may develop under normal and proper use, within one year from the shipment thereof provided the Purchaser gives the Contractor immediate written notice of such defects, and correction of such defect, by supplying such parts by the Contractor, shall constitute a fulfillment of all his obligations to the Purchaser hereunder. Acceptance by Purchaser IDEAL STOKEE COMPANY The foregoing proposal is hereby g y accepted and agreed to this. . . .day Approved at This day of 192... (Purchaser to sign 'here')' ' IDEAL STOKER COMPANY? By By. SPECIFICATIONS FORMS Every stoker builder has certain specifications for the par- ticular type of stoker sold, but in general these forms cover about the same items as follows : INSTALLATION OF STOKERS 247 CHAIN GRATE STOKERS The following items are 'named in that part of the proposal covering materials required. 1. General description of stoker. 2. Equipment furnished by Contractor. (1) Number and size of stokers. (Sq. Ft. grate surface and weight within 5%) (2) Number and size of ignition arches. (3) Number and size of upper arches. (4) Type of water backs. (5) Inspection doors. (6) Kails. (7) Ledge Plates. (8) Arch cover Plates. 3. Stoker drive furnished by: (1) Number, size, types of prime movers, pulleys, shafts, hangers and boxes. 4. Forced draft furnished by: (1) Description and method of operation. (2) Eegulation. 5. Purchaser will furnish. (1) All masonry, foundations, grouting foundation, bolts and sup- porting structure. (2) All labor for unloading and erection of stoker equipment. (3) All ash pits and ash pit construction. (4) Complement of gauges, for draft, air pressure, etc. (5) All piping, valves, wiring and other connections. 6. Optional Equipment. (1) Curtain wall supports furnished by purchaser or contractor. (2) Lower boiler fronts furnished by purchaser or contractor. (3) Drip pans for header furnished by purchaser or contractor. 7. Boilers. (1) Number and type. (2) Horse power. (3) Sq. Ft. heating surface. (4) Width and length furnace. (5) Setting height, single or battery setting. (6) Steam pressure and superheat. 248 MECHANICAL STOKERS BOILEK BOOM LOG I. Installation Data: 1. Plan of Boiler room. 2. Setting Details. 3. Breeching Details. 4. Stack Details. 5. Coal handling Machinery Capacities. 6. Ash handling Machinery Capacities. 7. Oil burning equipment details. 8. Stoker details. 9. Piping details. 10. Heater details. II. Labor Data Boiler Koom: 1. Engineers Numbers Hrs. Eates Schedules Field. 2. Firemen 3. Water Tenders " 4. Coal Passers 5. Ash Handlers " " " " 6. Boiler Washers 7. Janitors 8. Specialists " " " " " 9. Apprentices " " " " " 10. Chart showing responsibility and authority. Sec. III. 10. III. Labor Data Engine Koom: 1. Engineers Numbers Hrs. Eates Schedules Field. 2. Oilers " " " " 3. Electricians 4. Janitors 5. Eepairmen 6. Apprentices 7. 8. 9. 10. Chart showing responsibility and authority. Sec. II, 10. IV. Maintenance Data Boiler Eoom One Year: 1. Brickwork Men Hrs. Eates Materials 2. Boiler Tubes " " " (individual Boilers) 3. Boiler Trimmings " " " 4. Auxiliaries " " " " 5. Stokers 6. Oil Equipment " " ll " 7. Feed Water Heaters " " " " 8. Ash Handling " " " " 9. Coal Handling 10. Building Eepairs INSTALLATION OF STOKERS 249 V. Coal Data: 1. Quantities by days, months, year. Curve. 2. Daily consumption curve by hrs. Add VI 2 on heat equiv. 3. Heat values per Ib. 4. Proximate analyses. 5. Bate of combustion per sq. ft. per hr. Max.-Min. Sec. VII, 6, 7, 8. VI. Oil Data: 1. Quantities by days, months, year. Curve. 2. Daily consumption curve by hours. Add V 2 on heat equiv. 3. Heat values per Ib. 4. Proximate or Ultimate analyses. 5. Bate of combustion combine with V 5 on heat equiv. basis in curves. VII. Boilers in Service 1. Total number in service daily Chart for mo. Averages per yr. 2. Maximum capacity (B.H.P.) per boiler unit. 3. Minimum capacity (B.H.P.) per boiler unit. 4. Number units operating max. cap. on peak load. 5. Number units operating min. cap. on valley load. 6. Total max. B.H.P. developed at peak load Bate of combus- tion. Sec. VII 8. 7. Total min. B.H.P. developed at valley load Bate of combus- tion. Sec. VII 8. 8. Total grate area in service daily Chart per mo. Avgs. per yr. 9. Time in hours to get up steam from cold boiler. 10. Description of banked fire. 11. When and how is oil used. VIII. Electrical Output Data: 1. Characteristic Load (K.W.H.) Curves Daily. 2. Characteristic Load (K.W.H.) Curves Monthly. IX. Water Data: 1. Purification System and Methods Baw Water Analyses. 2. Meter Monthly Beadings Daily Monthly Charts. 3. Steam charts Daily Monthly. X. Temperature Data Boiler Boom: 1. Feed Water. 2. Furnace. 3. Uptake. 4. Before and after economizer Gas side. 5. Before and after economizer Water side. 6. Superheat actual and increase. 7. Stack Base. 8. Boiler Settings Charts. 9. Boiler Boom. 10. Breeching at various points. 250 MECHANICAL STOKERS XI. Pressure Data: 1. Steam at Boiler charts. 2. Fall through superheaters. 3. Fall to engines. 4. Draft. a. Stack Base. fe. Breeching at various points. c. Boiler Setting throughout chart. To be studied in con- junction with X 2, 3, 10. d. Between interior and exterior boiler rooms. e. Source of air supply. 5. Oil Equip. a. Steam pressure at burner, fc. Oil presure at burner. XII. Flue Gas Data: 1. Continuous C.O. charts. 2. Flue Gas analyses at uptakes. 3. Flue Gas throughout setting simultaneous with XII, 2. 4. Determinations of air leakages based on XII, 3. XIII. Eoutine Service Boiler Boom: 1. Soot blowing, Manner, Time, Duration, By Whom Effective- ness. 2. Soot deposits. a. Frequency of removal, fe. Quantity of removal. c. Inspected by whom. 3. Boiler Washing. a. Schedule. fc. Time taken for each boiler unit. c. Method. d. By whom inspected. 4. Setting Overhauling. a. Air leakage tests. fc. Baffle leakage tests. c. Boiler covering. d. Inspected by whom. 5. Blow Downs. a. Frequency Time of Day By Whom. 5. Duration. XIV. Smoke Data: 1. Continuous records. 2. Method used in judging smoke density. 3. Causes of smoke production. 4. Meaning of periods when smoke is absent Sec. XII, 2. 5. Time when most prevalent. INSTALLATION OF STOKERS 251 XV. 1. Heat value chart showing total supply daily for 30 days. 2. Heat value chart showing total supply monthly for 12 months. 3. Heat absorption showing total supply daily for 30 days. 4. Heat absorption showing total supply monthly for 12 months. 5. Heat chart by several furnaces factors shown graphically. 6. Heat chart by several boiler setting factors shown graphically. 7. Heat chart by several breeching and stack factors shown graphically. 8. Heat reclaimed from exhaust shown graphically. 9. Heat delivered to engines after subtracting B.E. auxiliaries. 10 4 Heat delivered to switch board as electric energy. 11. 12. Chart showing combination of all above month by month. XVI. Cost of Power Production on K.W.H. basis: 1. Coal 2. B.E. Labor. 3. B.K. Maintenance. 4. Engine Eoom Labor. 5. Engine Boom Maintenance. 6. 7. 8. 9. Chart combining all XVI items month by month. INDEX Air, composition of, 2 leakage in ducts, 152 percent excess required, 7 required for combustion, (table), 4 spaces in boiler walls, 185 supplied for combustion, 3 volume required per developed horsepower, (table), 148 Alabama coals, 95-118 Altitude corrections for fans, (table), 151 Altitude corrections for stacks, (table), 138 American Gas & Electric Co., Windsor plant, 202 American stoker, 30 Analyses of coals, proximate, 88 table, 99 ultimate, 89 Anthracite, culm, 97-125 Colorado, 121 Application characteristics of stokera, 162 Application of stokers, 211 Arches, 168 chain grates, 162-169 overfeed stoker, 165-169 sprung, 170 supsended, 163-169 underfeed stoker, 166-169 Arkansas coals, analyses, 95-99 characteristics, 119 Ash, sensible heat in, 14 Ash pits, chain grate stokers, 193 overfeed stokers, 178 underfeed stokers, 193 Auxiliaries, (stoker) engines, 153 fans, 150 turbines, 152 Babcock & Wilcox stoker, 34 Baffles, restriction of, 140, 233 Bodmer stoker, 23 Boiler, boiler room log, 248 draft loss through, 140 Bone coal, analyses, 97 characteristics, 128 type of stoker to burn, 128 Boston Edison plant, 187 Breechings, analyzing losses, 136- 144 losses, 136 Brightman stoker, 27 Brunton stoker, 23 Buffalo General Electric Co., Niagara River Station, 195 Burke stoker, 37 Carbon, burning of, 1 dioxide, 3 Central Station plants, stoker equip- ment installed, 187 Chain grate stoker, 34 Babcock & Wilcox, 34 Green, 39 Illinois, 42 Laclede-Christy, 44 Playford, 50 Westinghouse, 52 Chimneys, capacity, sizes, (table), 133 corrections for altitude, 138 draft table, 134 formula for sizes, 132 friction loss, (table), 132 temperature of gases, 131 Cleveland Electric Illuminating Co., Lake Shore Station, 196 253 254 INDEX Clinkering of coal, 81-172 adhesions to walls, 173 methods to avoid, 173 Coal, caking, 81 changes in weight and volume by wetting, 98 characteristics of, 106 classifications of, 89 clinkering of, 81 coking, 81 commercial classification, 94 anthracite culm, 97-125 bone coal, 97-128 Colorado, 95-121 Eastern bituminous, 94-108 Eastern Kentucky, Tennes- see, and Alabama, 95-1 18 Middle West, 94 North Dakota lignite, 96- 124 Pittsburgh, 94-110 Texas, Oklahoma and Arkansas, 95-119 Washington, Wyoming, and Montana, 96-124 composition of, 88-93 conservation, 32 definitions, 80 dust in coals, 139 heating value, 89-99 Kent's classification, 92 producing states, 87 proximate analysis, 88 ultimate analysis, 89 uses of, 82 used by Central Station plants in United States, 99 U. S. geological survey classifi- cation, 89 U. S. production, 84 World's production, 84 World's reserve, 83 Coal hoppers, capacity of, 225 Coke breeze, analyses, 96 characteristics, 127 Colorado coals, analyses, 95-99 characteristics, 121-123 Combustion characteristics of coal, 106 Combustion, principles of, 1 temperature of, 8 Combustion rates, 108, 114, 116, 118, 120, 122, 123, 125, 126 chain grate stoker, 112, 113, 121, 216 overfeed stoker, 108, 110, 113, 115, 116, 118, 120, 122, 123, 126, 128, 216 underfeed stoker, 111, 113, 114, 115, 118, 119, 123, 126, 215 Combustion space, chain grate stoker, 181 overfeed stoker, 181 underfeed stoker, 179 Commonwealth Edison Co. North- west Station, 207 Conditions necessary for burning coal, 32 Continental stoker, 46 Contract forms, used by stoker manufacturers, 244 Consolidated Gas & Electric Co., Westport Station, 194 Coxe stoker, 24, 37, 53 Cox-Fulton stoker, 53 Dakota coal, analyses, 96 characteristics, 124 lignite, 124 Dampers, friction losses, 141 sizes, 141 Detroit stoker, 56-76 Detroit Edison Co., Delray Station, 203 Denver Gas & Electric Co., 210 Development of mechanical stokers, 31 Draft, 129 effects on brickwork, 178 forced, 150 formula for stacks, 132 induced, 146 losses, through fuel bed, 137 through boiler, 140 through breeching, 141 through damper, 141 INDEX 255 Draft, through stack, 142 natural, 130 required for, chain grate stoker, 163 overfeed stoker, 138 underfeed stoker, 139 Drake fire brick blocks, 173 Duquesne Light Co., Colfax Station, 199 E Early forms of stokers, 22 Eastern coals, analyses, 94-99 characteristics, 108 Efficiency, typical capacity, effi- ciency curve, 212 of chain grate stoker, 159 of combustion, 10 of overfeed stoker, 158 of underfeed stoker, 156 Engineering data, required for stoker installations, 234 Evaporation chart, 220 Fans, corrections for altitude, (table), 151 forced draft, 150 induced draft, 148 Feeding of coal to furnaces, 22 Flexibility of, chain grate stokers, 159 overfeed stoker, 158 underfeed stokers, 157 Flue gas, analyses, 10 Frederick stoker, 71 Frisbie stoker, 29 Fuel, definition, 80 Furnace design, 168 G Gases, flue, 10 mixture of furnace gases, 177 velocity, (formula), 131 Grate areas of stokers, chain grate, 223 overfeed, 217 underfeed, 223 Grate speeds, chain grate stoker, 161 Green stoker, 39 Guarantees, stoker performance, 243 H Hall stoker, 25 Harrington stoker, 47 Heat, flow through furnace walls, 182 loss in flue gases, 10 loss in unburned gases, 11 loss due to superheated steam, 13 Heating value of coals, Kent's table, 92 table, 93-99 Holyrod-Smith stoker, 28 Hydrocarbons, 1 Illinois coals, analyses, 93-99 characteristics, 113 Illinois stoker, 42 Indiana coals, analyses, 93-99 characteristics, 113 Installation of stokers, things to provide for, 226 Iowa coals, analyses, 93-99 characteristics, 115 Jukes stoker, 64-71 K Gases, density of, 4 dry gas per Ib. of carbon, (for- mula), 3 Kentucky coals, analyses, 93-94- dry gas per Ib. of fuel, (for- 95-99 mula), 4 characteristics, 110-118 256 INDEX Labor saved by mechanical stokers, 33 Laclede-Christy stoker, 44 Lignite, Dakota, characteristics of, 93-96-99-124 Denver, characteristics of, 121 Texas, characteristics of, 92-95 M McDougal stoker, 25 McKenzie stoker, 34-47 Mechanical stokers, 16 Merchants Heat & Light Co. station, 206 Michigan coal, analyses of, 93-99 characteristics of, 112 Middle West coals, 94 Minneapolis General Electric Co., Riverside station, 208 Missouri coals, analyses of, 93-99 characteristics of, 113 Mixture of gases, methods, 180 requirements for, 177 Model stoker, 54 Moloch stoker, 73 Moisture in coals, effect on combus- tion, 106 Montana coals, analyses of, 96 characteristics of, 124 Murphy stoker, 26-34-55 N Overfeed stokers, Detroit, 34-56 Hall, 25 McDougal, 25 . Model, 54 Murphy, 26-34-55 Roney, 27-34-58 Vicars, 25 Wetzel, 59 Wilkinson, 28-61 Oxygen, 2 Pennsylvania coals, analyses, 94-99 characteristics, 106-110 Philadelphia Electric Co., Delaware Ave. station, 192 Pittsburgh coals, analyses of, 93- 94-99 characteristics, 110 Playford stoker, 50 Present types of stokers in U. S., 34 Principles of combustion, 1 Proximate analyses, 88 Public Service Electric Co., Essex Station, 180 R Radiation losses, 15 Riley stoker, 62 Roach stoker, 78 Roney stoker, 58 Nitrogen, 2 Ohio coals, analyses, 93-94-99 characteristics, 110 Oklahoma coals, analyses of, 99 characteristics, 119 Oregon coals, analyses of, 93-99 characteristics, 124 Overfeed stokers, 25 Brightman, 27 Cox-Fulton, 53 Selection of stoker equipment, 106- 154 application conditions, 162 draft conditions, 162 load conditions, 155 Sizes and dimensions of stokers, 211 chain grate stokers, 223 coal hoppers, 224 overfeed stokers, 218-222 underfeed stokers, 221-223 Smoke prevention devises, historical, Barber, 20 Gray, 19 INDEX 257 Smoke prevention devices, Greyson, Stokers, Stowe, 34, 51 17 Sturtevant, 34 Langen, 20 Taylor, 30, 34, 66 Predeaux, 20 Type, "E", 34-74 Robertson, 16 Vicars, 25 Rodda, 19 Weller, 24 Shanter, 19 Westinghouse, 34, 52, 68, 224 Wakefield, 17 Wetzel, 34-59 Watt, 16 Wilkinson, 28-61 Williams, 20 Stowe stoker, 51 Witty, 18 Sturtevant stoker, 34 Smoke abatement, 31 Sulphur in coal, 2 Soot deposited in gas passages, 14 effect on clinkers, 81 Specific heat of flue gases, 8 Specifications for stokers, typical T specification, 236 Speed of, chain grate, 158-161 on ox AA verfeed 59 Taylor stoker, 30-34-66 j ., - Temperature, of combustion, 8 underfeed, 167 f f Q Stoker equipment of modern steam ol lurnace > y Tennessee coals, analyses of, 93-95- plants, 186 Stokers, mechanical, American, 30 . ' IP 1*7-1 o/i characteristics, 118 Babcock & Wilcox, 34 Texas coals, analyses of, 93, 95, Bodmer, 26 __ Brightman, 27 ' characteristics, 119 Brunton 23 Traveling grate stokers, 23 Burke, 34-37 _ , e ' _ , A Bodmer, 73 Continental, 46 00 ', ' Brunton, 23 Cox-Fulton, 53 ' BurKe, d/ 7fi Continental, 46 84, 56, 76 37 Fnsbie, 29 TT . 0/1 . Green, 34-39 Hamngton, 34, 47 Hall 2-i JU B8 ' Hdyrod-Srnith^S Ilhno,s 34-42 gtoke H . Laclede-Christy, 34-44 McDougal, 3-25 McKenzie, 34-47 Model, 34-54 Ultimate analyses, 89 Moloch, 73 Underfeed stokers, 28 Murphy, 25, 34, 55 American, 30 Playford, 34-50 Detroit, 34^56-76 Riley, 34, 62, 221 Frederick, 71 Roach, 34-78 Frisbie, 29 Roney, 27, 34, 58, 218, 222 Holyrod-Smith, 28 17 258 INDEX Underfeed stokers, Jones, 29-34- 64-71 Jukes, 28 Moloch, 73 Riley, 34-62-221 Roach, 34, 78 Taylor, 30, 34, 66 Type "E," 34, 74 Westinghouse, 34, 52, 68, 224 Union Electric Light & Power Co., 207 United Electric Light & Power Co., Hellgate plant, 189 United Gas & Electric Co., 205 Use of coals, 82 Virginia coals, analyses, 94 characteristics, 106 Volatile matter, 88 Volume of air per developed boiler horsepower, 148 W Washington coals, analyses of, 46, 93, 99 characteristics, 124 Weights of, products of combustion, (table), 7 of coals, (table), 104 stokers, 62, 66 Weller stoker, 24 Westinghouse stoker, 52, 68 West Penn Power Co., Springdale plant, 201 West Virginia coals, analyses, 93, 94, 99 characteristics, 106-110 Wetzel stoker, 59 Wilkinson stoker, 61 Wind box pressure, underfeed stokers, 139 Wyoming coals, analyses of, 46, 93, 99 characteristics, 124 UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. ENGINEERING LIBHAHY LD 21-100m-9,'48(B399sl6)476 581216 Engineering Library* UNIVERSITY OF CALIFORNIA LIBRARY