US2936725A - Moving bed stoker - Google Patents

Description

May 17, 1960 w. s. BLUNDIN ETAI- 2,936,725-

MOVING BED STOKER 2 Sheets-Sheet 1 Filed July 15, 1954 .fzrold TflaZ/mazz [Var Z. Zangz azzd L esterl. leach ATTORNEY filed in the name of W. S. Blundin, one of the co-in- United States Patent MOVING BED STOKER Warren S. Blundin, North Plainfield, N.J., and Harold T. Hallman and Ivar L. Langvand, Barberton, and Lester L. Leach, Akron, Ohio, assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Application July 15, 1954, Serial No. 443,654

5 Claims. (Cl. 110-40) The present invention relates to the combustion of solid fuels, and more particularly to an improved construction and arrangement of moving grate stokers for the combustion of solid fuels.

Moving grate stokers have proven to be an efficient tool in the combustion of many types of solid fuels, particularly in relatively small installations burning, for example, less than five or six tons of coal per hour per stoker. In a proper installation, a moving grate stoker is characterized by low carbon losses in the ash and low carryover of dust in the products of combustion. Heretofore, moving grate stokers have been sluggish in responding to sudden increases in firing rates, and have been limited in the type of fuel that could be successfully burned. These difficulties have been largely overcome by means of overfire air jets positioned abo e the burning fuel bed as disclosed and claimed in the copending application Serial No. 311,448, now Patent No. 2,876,716,

ventors of the present invention. 7

Other difliculties have heretofore been encounteredin moving grate stokers, both with respect to the control of combustion air through the fuel bed and to mechanical difficulties caused particularly by operational temperature changes in the stoker parts. Such difficulties included twisting of the chain, breakage of links and the like; some of these difliculties being the cause of further difliculties.

We have overcome the major portion of the previous mechanical difficulties encountered with moving grate type stokers, and have also improved the combustion characteristics of the stokers by the construction and arrangement of the hereinafter described stoker. The features of the stoker cooperating to improve operations thereof include a new stoker chain construction-where separate tension links transmit all of the forces applied in the movement of the chain across the lower portion of a furnace. The links supporting the, fuel bed are not subjected to tensile or compressive forces by reason of chain movement and are mounted on rollers to reduce the friction of chain movement. Chain tension is maintained by the dead weight of a portion of the return run of the chain, which takes the form of a catenary. 'Drive means are provided for chain movement whereby the driving force applied to-thechain issubstantially constant regardless of chain speed. t

Combustion air control is simplified by the use of seals which cooperate with air inlet regulating means to assure proper distribution of air to the fuel for efiicient combustion. The flow of air through the grate and the fuel bed thereon is zoned by air compartments positioned beneath the upper run of the fuel bed'supporting chain, with each compartment supplied with combustion air' as regulated by the opening of a poppet type control valve.

,Any siftings of solids accumulated in the compartments are discharged by a valve systems to the lower runof thevchain for deposition in a siftings bin positioned beneath the forward end of the stoker.

Thevarious features of novelty which characterized 2,936,725 Patented May 17, 1960 our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferredembodiment of the invention.

Of the drawings:

Fig. l is .an elevation, in section, of a moving bed stoker constructed in accordance with the present invention; 1

Fig. 2 is an enlarged fragmental view, in perspective, of a portion of the stoker shown in Fig. l;

Fig. 3 is an enlarged fragmental view inperspective,

of the stoker chain shown in Fig. 1;

Fig. 4 is an enlarged schematic view, partly in section, of the hydraulic drive for the stoker shown in Fig. 1.

In the embodiment of the invention shown in Fig. 1 a moving bed stoker constructed in accordance with the present invention is illustrated as installed in the lower end portion of a water cooled furnace or combustion chamber 10. The stoker is positioned to extend horizontally through the front wall 11 of the combustion chamber to a spaced location adjacent a bridge Wall 12. As shown, the front wall 11 of the furnace is provided with vapor generating tubes 13 opening upwardly from a horizontally disposed transverse header 14 which is spaced above the upper run 15 of the stoker; The bridge wall is likewise provided with vapor generating tubes 16 which are connected into horizontally disposed longitudinally extending headers 17 positioned on opposite sides of the stoker bed and in the walls of the furnace chamber 10.

The forward end of the stoker extends beyond the front wall 11 of the combustion chamber with the drive mechanism, hereinafter described, of the stoker positioned externally of the furnace. A fuel flow regulating gate 18 is positioned adjacent the front wall of the furnace chamber and arranged for vertical adjustment to regulate the depth of solid fuel deposited upon the supporting surface of the stoker. Fuel is delivered to the stoker from an overhead bin (not shown) by gravity, with the fuel passing downwardly over an inclined plate 20 which forms the bottom surface of a hopper 21. The outer end of the stoker, beyond the front wall 11, is enclosed by a dust-tight housing including an upright panel 22 which is attached to the inclined bottom of the hopper 21 and is provided with suitable access doors 23. As disclosed and claimed in the companion application of W. S. Blundin Serial No. 311,448, the vertically adjustable gate 18 not only provides a means for regulating the depth of the fuel bed on the stoker chain, but also provides an efiective seal against infiltration of the air into the forward portion of the stoker. As also disclosed and claimed in said application, overfire air jets are supplied to the combustion chamber through nozzles 24 projecting through the front wall 11. The lowermost row of nozzles 24 is illustrated in Fig. 1. The overfire jets of combustion air impact the volatile matter being distilled from the fuel bed adjacent the front wall of the combustion chamber, and burn the volatiles in a turbulent ball of fire without smoke at any load. The jets also create a low pressure zone which induces a flow of flame and hot gases from the intermediate length portion of the stoker fuel ,bed toward the front wall 11 with large quantities of heat radiated downwardly upon the incoming raw fuel to aid in ignition of the fuel.

The moving bed stoker of the present invention inv cludes a structural framework 25 of channels and I beams for directing controlled quantities of combustion air upwardly through longitudinally spaced zones of the stoker, as hereinafter described, and provides a support for a series of longitudinally extending bars 27 positioned on the upper surface of the framework 25. The bars 27 directly support the endless chain of the stoker, and are illustrated in the Figs. 1, 2, and 3.

The endless chain 28 of the present construction is constructed for movement along the upper surface of the framework 25 from front to rear of the combustion chamber as supported by rollers 30 riding along the longitudinally extending bars 27 of the framework. As shown particularly in Fig. 3, the rollers 30 are mounted upon transversely extending rods 31 which are spaced longitudinally of the chain 28 and form the supporting means for the moving chain. With this construction the frictional force opposing longitudinal movement of the endless chain 28 is reduced to a minimum so that the driving forces employed in stoker operation are likewise maintained at a minimum.

The transversely extending rods 31 are connected by pairs of driving or tensile links 32 which are made of steel and constructed to resist tensile forces. These connecting links are illustrated in Fig. 3 and each pair is positioned on an opposite side of each of the rollers 30 so that the driving force causing movement of the chain is transmitted directly from transverse rod to transverse rod by the connecting driving links 32. As an example of this construction, when the transverse rods are 1" in diameter, the links 32 are drilled to a 1%" diameter so that the fit between the driving links 32 and the rods 31 is suflicient to permit rotation of the rods under all operating temperature conditions.

The rollers 3d are each protected by cover links 33 which are constructed withan upper extended surface 34 so that companion pairs of links extend over the top of the rollers and provide a surface intended to support the fuel bed and to avoid fuel or ash deposition on the rollers 30 and the supporting bars 27.

As hereinafter more fully described, the control of combustion air movement to the furnace 10 is essential for efficient fuel combustion. Accordingly, to avoid air leakage along the edges of the moving chain 28, the chain is provided with side seal links 35 which engage a shelf member 36 forming a part of the stoker support frame 25. This construction is illustrated in Fig. 3 where the side seal links 35 are constructed with an overhanging upper lip portion 37 which extends beyond the end of the transverse rods 31. The corresponding member 36 of the stoker support frame is provided with a ledge 38'to engage the lip 37 of the seal links 35.

The common links 40 forming the fuel bed supporting surface of the chain 28 are constructed with sufficient depth to provide a greater surface for contact with combustion air flow than the surface of the link in-contact with the supported fuel bed. The links other than the tension links are cast of high-grade cast iron and are accurately drilled to provide an opening of, for example, 1 /4" in diameter to accommodate the 1" diameter transverse rods 31 of the example given above.

The endless chain 28 of the sto'ker is driven at a controlled lineal rate by the drive sprocket 26 which is provided with teeth 41 to engage the rollers 30 of the chain (see Fig. 1). Ordinarily, there will be from three to .five sprockets 26 mounted on a common drive shaft 42 with equal spacing between the sprockets. There will be a corresponding number of rows of both rollers 30 and roller support bars 27 in the stoker construction.

The rear end of the stoker is provided with a curved drag plate 43 over which the chain 28 moves to its lower or return run 44 with the ash from the fuel falling by gravity into an ash pit 4h. The drag plate is curved and is suitably mounted for longitudinal adjustment to regulate the tension on the chain 28. Adjustment of the drag .plate 43 is accomplished by means of screw jacks 45 which are horizontally disposed and shift the position of the drag plate assembly relative to the rear crossbeam 46 of the stoker support framework 25. When initially installed, the chain 28 is adjusted as to the length of the chain 28 by means of the jack screws. Usually, at least two jack screws 45 are installed, one on each side of the drag plate 43 so that the alignment of the chain 28 relative to the sprockets 26 can be established.

Referring to Fig. 1 the lower part of the stoker support structure or framework 25 is provided with a pair of drag seal plates 47 and 48 longitudinally spaced along the bottom of the structural framework. The rearmost drag. plate 47 is mounted on a framework 50 for vertical adjustment relative to the fixed support structure of the stoker frame. With'the rear drag plate 47 spaced forwardly of and below the drag plate 43, the return run 4-4- of the stoker chain between these two members is unsupported. The dead weight of the chain 28 will cause the chain to take the form of a catenary, as indicated at 51. The shape of this catenary will change with expansion and contraction of the chain 223, as will occur during stoker operation. By reason of the low drive friction of the chain roller supports, the dead weight of the chain in the catenary 51 portion thereof will maintain the tensio'n of the upper run 15 of the chain 28 generally uniform. When it is desired to change the form of a catenary, and thus change the tension on the chain 28, the rear drag seal plate 47 may be vertically adjusted by means of the wormgear jack 52. The forward drag seal plate 48 is fixed in position with respect to the supporting framework of the stoker. When initially installed, sand is inserted between the lower seal plates 47 and 48 to form a surface upon which the return run 44 of the stoker chain 28 rests.

As hereinafter described, the stoker is provided with a plurality of transversely extending compartments 53 for v the delivery of combustion air upwardly through the upper run 15 of the stoker chain. Each of these co'mpartments is formed of steel plates 54 with a vertical section through each compartment being in the general shape of an inverted truncated triangle. The base or upper portion 55 of each compartment 53 is open with upper edges 56 of the base positioned adjacent the lower surface of the chain 28. The lower or smaller section 57 of each compartment 53 is provided with a closure member 58 which, in vertical section, is in the shape of an angle. The closure member 58 is arranged to be periodically opened from a position at one side of the stoker to release any fuel or ash siftingswhich may accumulate in each compartment 53.

When the fuel or ash siftings are discharged from the compartments they fall upon the upper surface of the lower run 44 of the chain 28 and are dragged forwardly to be discharged into a sittings receiving bin 60 located beneath the drive sprocket 26. Advantageously, the siftings can be removed from the storage space of the bin and reintroduced into the combustion chamber 10 of the furnace for the combustion of any unburned carbon which may be present in the siftings.

The air compartments 53,as shown in Figs. 1 and 2, are substantially air tight except for air discharged therefrom upwardly through the stoker chain 28. Additionally, the structure of the compartments adds to the rigidity of the stoker. support-frame 25 and forms a part of the support structure for the roller support bars 27. The compartments 53 are spaced longitudinally of the stoker and are provided with cap members 61 connecting adjac'ent;,plate s 54 of the adjacent compartments and have their upper surface flush with the roller support bars 27.

The closure member 58 for each of the compartments 53 is provided with an operating mechanism which includes a strip 62 extending upwardly from the apex of the member-and which is attached to a clevis 63 having an upwardly extending threaded bolt 64. The bolt is connected to a'tnodified S shaped arm '65 which is pivotally gaseyss connected to a downwardly'extending link 66. The lower 7 end of the link is keyed to an operating shaft 67 which ter position relative to the operating shaft 67. Thus, when the operating shaft 67 is turned by the handle 68 the link 66 moves the 8 member 65 to one side to allow the closure member 58 to drop into a siftings discharge position. The member 58 extends transversely across each compartment and is provided with a plurality of spaced members 65 operated simultaneously by an individual shaft 67. Between adjacent operating mechanisms each compartment 53 is provided with gusset plates 69 in the lower portion thereof which strengthen'the compartment walls and increase the rigidity of the stoker framework.

As shown particularly in Fig. 2, the air supply to each compartment 53 is regulated by a poppet valve 71 POSI- tioned to cooperate with an opening in the top of a combustion air manifold 72 which extends longitudinally along one, or both sides of the stoker. Above the combustion air manifold is positioned a compartmentalized air duct 73 each compartment of which individually opens into a compartment 53 of the stoker. Thus, each compartment of the stoker is individually supplied with combustion air in quantities regulated by an individual poppet valve. Advantageously, the poppet valves are individually positioned through'an arm 108 by an external operating rod 74 having a handle which cooperates with an indicator gage 75 for ready identification of the amount of opening of the individual poppet valve 71. The poppet valve type of air control mechanism is particularly useful since the amount of air passing through the valve will be proportional to the amount of valve opening, and thus provides an accurate indication of the amount of air delivered to each compartment 53 of the stoker.

The stoker drive mechanism illustrated in Fig. 4 is of the hydraulic type wherein a hydraulic fluid is pumped at constant pressure for delivery to a reciprocating piston. As shown, a hydraulic fluid reservoir 76 is connected with the inlet of a pump 77 by a pipe 78. The pump 77 is of the vane type which is self-regulating to deliver only the quantity of fluid required to maintain a selected pressure in the hydraulic fluid header 80. The pump is driven by any suitable type of constant speed prime mover with the flow of fluid through the header regulated by means of a valve 81 which can be adjusted manually, or in response to a combustion control system.

The substantially constant pressure fluid is delivered to a slide valve mechanism 82 for alternate delivery of the pressure fluid to opposite sides of a power piston 83 mounted in the cylinder 84. The cylinder is pivotally supported as at 85 on the side of the. stoker housing, with the piston rod 86 from the piston 83 pivotally connected with an arm 87. The arm oscillates in response to movement of the piston rod 86 about an axis common with'the drive shaft 42 of the sprocket 26. The oscillating arm is provided with a pawl 88 which is spring-loaded and engages a ratchet 90 keyed to-the sprocket drive shaft 42.

' A keeper pawl 91 engages the ratchet 90 on the opposite side of the shaft 42. Oscillation of the arm 87 actuates the slide valve mechanism 82 through the connecting link 92. The slide valve mechanism 82 receives the discharged fiuid from the power piston cylinder 84 with the fluid passing through the discharge pipe 93 to the hydraulic fluid reservoir 76.

While in accordance with the provisions of the statutes we have illustrated and described herein a preferred embodiment of the invention, those skilled in the art will understand that changes may' b'e made in the method of operation and form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. In combination with a furnace, an endless chain moving bed stoker positioned in the lower portion of said furnace, said endless chain having .a plurality of transversely extending rods spaced longitudinally thereof, at least two rollers spaced axially on each of said rods, fixed beams supporting said rollers beneathv the upper run .of said stoker chain, tension links spaced'on each side of each of the rollers and connecting adjacent transverse rods, driving means including roller engaging sprockets positioned adjacent the fuel inlet end of said stoker whereby movement of said endless chain is transmitted solely through said tension links, roller shielding links connecting adjacent transverse rods and positioned between said rollers and an adjacent tension bar,.each of said shielding links having an overhangingedge portion projecting at least partially over the top of an adjacent roller, and a multiplicity of fuel bed supporting links supported upon adjacent transverse rods. r

2. In combination with a furnace, an endless chain moving bed stoker positioned in the lower portion of said furnace, said endless chain having a plurality of transversely extending rods spaced longitudinally thereof, at least'two rollers spaced axially on each of said rods, fixed beams supporting said rollers beneath the upper run of said stoker chain, tension links spaced on each side of each of the rollers and connecting adjacent transverse rods, driving -means including roller engaging sprockets positioned adjacent the fuel inlet end of said stoker whereby movement of said endless chain is transmitted solely through said tension links, roller shielding links connecting adjacent transverse rods and positioned between said rollers and an adjacent tension bar, each of said shielding links having an overhanging edge portion projecting at least partially over the top of an adjacent roller, and a multiplicity of cast iron links supported upon adjacent transverse rods and spaced transversely across said stoker, each of said cast iron links having a depth greater than their fuel supporting width.

3. In combination with a furnace, an endless chain moving bed stoker positioned in the lower portion of said furnace, said endless chain having a plurality of transversely extending rods spaced longitudinally thereof, at least two rollers spaced axially on each of said rods, fixed beams supporting said rollers beneath the upper run of said stoker, fixed members positioned on each side of said endless chain and laterally spaced from the ends of said rods, each member having a horizontal shelf portion extending outwardly of said chain to an upstanding flange portion, tension links spaced on each side of each of the rollers and connecting adjacent transverse rods, driving means including roller engaging sprockets positioned adjacent the feed inlet end only of said stoker whereby movement of said endless chain is transmitted solely through said tension bars, roller shielding links supported upon adjacent transverse rods and positioned between said rollers and an adjacent tension bar, each of said shielding links having an overhanging top edge portion projecting at least partially over the top of an adjacent roller, seal links supported upon adjacent rods and having outwardly extending top portions overhanging the shelf portion of said fixed side members, and a plurality of fuel bed supportinglinks supported upon adjacent transverse rods.

4. A stoker chain comprising a plurality of transversely extending rods equally spaced longitudinally of said chain, at least two rollers transversely spaced axially of and rotatable on each of said rods, tension bars positioned on opposite sides of each of said rollers and connecting adjacent rods, cast roller shielding links supported by adjacent rods and positioned on opposite sides of each roller, cast seal links supported'by adjacent rods on the sides of said chain with the outer upper edge of said seal links projecting outwardly of said chain; and a multiplicity of cast links connecting adjacent rods and arranged in rows extending transversely across said chain between said seal links and an adjacent tension bar, and between said tension bars inwardly adjacent said spaced rollers.

5. In combination with a furnace, an endless chain moving bed stoker positioned in the lower portion of said furnace, said stoker having a plurality of transversely extending rods spaced longitudinally thereof, at least two rollers spaced axially on each of said rods, fixed beams supporting saidrollers beneath the upper run of said stoker, said stoker also comprising longitudinal rows of transverslyspaced links loosely connected to adjacent rods and longitudinal side by side rows of tension links, the tension links in each row being arranged in end to end relationship and the links in one row being in staggered overlapping relation to the links of the next adjacent row and with each tension link of said one row being tightly connected respectively to successive pairs of said rods and each tension link of said adjacent row being tightly connected respectively to the adjacent rods of the successive pairs of rods, driving means including roller engaging sprockets positioned adjacent the fuel feed end of said stoker whereby movement of said endles's chain .is transmittedisolely through said tension links, and drive means for rotating said sprockets at a controlled speed.

References Cited in the file of this patent UNITED STATES PATENTS 446,059 Crawford Feb. 10, 1891 1,133,007 Church Mar. 23, 1915 1,608,728 Duncan Nov. 30, 1926 1,656,179 Duncan Ian. 17, 1928 1,808,479 Ritter June 2, 1931 1,832,459 Haniman Nov. 17, 1931 1,883,299 Kerr Oct. 18, 1932 2,294,441 Beers Sept. 1, 1942 2,471,983 Spahr May 31, 1944 2,506,569 Agnew May 9, 1950 2,511,935 Midgette et a1 June 20, 1950 FOREIGN. PATENTS 266,601 Germany Jan. 24, 1913 211,060

Great Britain Feb. 14, 1924

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