CA1158099A - Rotary continuous ash discharge stoker - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A rotary continuous ash discharge stoker having a circular grate which is designed to support burning fuel as it dis-tributes the fuel from the feedpoint over the entire grate, and at the same time provides for the controlled admission of air for combustion of the fuel and also automatically removes from the furnace the remaining ash. The upper grate surface consists of two zones, a central stationary section and an outer rotating sec-tion or ring. The central section is inclined and is the main air admitting zone. The outer rotating ring serves to distribute the fuel in the furnace with the aid of a stationary spreader arm, admits the air necessary to complete combustion of the fuel and removes the burned out ash from the furnace with the aid of a stationary ash plow. This rotating ring is supported and guided on rails and rollers which allow for the complete rotation of this section of the grate, and has an improved wear-resistant furnace wall seal at the interface between the outer periphery of the ring and the inner periphery of the furnace wall.

Description

1 1580~9 ROTARY CONTINUOUS AS~ Dl~C~ARCE STOKER

BACKGPlOUND AND SI~MMARY OF THE INVENTION

The present invention relates generally to mechanlcal stokers, and partlcularly to an Improved constructlon of a rotary grate continuous ash discharge stoker. This irnproved construction may be used in either an overfeed or underfeed n-.echanlcal stoker design. Numerous other possible designs and comb}nations thereof are includible in the scope of the inventlon.
More particularly~ the present invention relates to a rotary contEnuous ash dlscharge stoker having a clrcular grate which 0 i9 designed to support burning fuel as it distributes the fuel from the feedpolnt over the entire grate, and at the same time provldes for the controlled admission of air for combustion of the fuel and also auto-matically removes from the furnace the remainlng ash. The upper grate surface consLsts of two zones, a central stationary section and an outer rotating sectlon or ring. The central section Is Inclined and is the main alr admLtting zone. The outer rotatlng ring serYes to distribute the fuel in the furnace with the aid of a statlonary spreader arrn, admlts the air necessary to complete combustlon of the fuel and removes the burned out ash from the furnace wlth the ald of a etationary ash plow. Thls rotating ring Is supported and gulded on rails and rollers whlch allow for the complete rotatlon of thls sectlon of the grate. Any of several drlve mechanlsms can be employed to drlve the rotatlng rlng.

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The present invention provides many advantages in combustion o~ wood, bagasse, bark, municipal refuse, coal, or any other cellulose or by-product waste fuel.
A grate surface having a substantial number of controls for fuel and air to provide for complete combustion of the fuel at a wide variety oE load demands is one object of the present invention. The grate provides for movement of the fuel as it burns, moving from the feedpoint to -the ash dischàrge point. The present invention includes various air compartments providing for control of air flow to the fuel at various points along the path of movement of the fuel. Control of air flow controls the rate of combustion of the fuel.
Also, with a spreader in com~ination with this grate design the ash will not build up to create blow holes or dead islands, but will be burned e~enly.
According to the present invention there lS
provided a rotary stoker having a housing with an inner wall forming a furnace combustion chamber and a circular grate having a central stationary section and an outer rotating ring, each having means to supply pressurized air to burn fuel supported on both sections of the grate. Means is also provided to supply pressurized air into the housing below the grate.
~ The circular grate surface design, furthermore, along wlth the~combustion air control system, is not limited significantly by size and will provide an efficient mechanical stoker of any reasonable diameter having the advantages of the present lnvention.
Another object of the present invention is to

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~rovide contirluous ~sh dischar~e from a sin~le point.
This allows for a simple ash rernoval and disposal system with all the ash deposited through a single chute.
If the grate is not completely covered and protected ~rom furnace and combustion temperatures, waxping or other damage to the grate can result from overheating.
The present invention has the object of having a grate design in which fuel can be fed to the center feed point in such a manner that the grate is always covered by unburned fuel or ash and protected from furnace and combustion temperatures.
Substantial fuel or ash in the air chamber would significant~y decrease the quality and efficiency of the combustion process. A further object of the present invention is to prevent fuel and ash from sifting into the air chamber.
When the usage situation permits, a specific embodiment of the present invention has a further advantage of reducing or eliminating clinkers or slag adhesion on the refractory by having a row of air-cooled tuyeres at the outer circumference of the grate, along the furnace wall, to provide further air for combustion. The tuyeres on the outer wall also are useful, as another air supply controlj in obtaining sufficient overfire air turbulence to maintain combustion at low loads while also completing combustion at high loads, and also to reduce stratification of air and combustion products at the. radially outer extreme of the grate. In some instances, however, such as when the ,

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~ 158~99 grate is part of a yasifier unit or the like, air-cooled tuyeres on the furnace wall would not be used since such a construction would interfere with the efficient performance of the gasifier unit by diluting the desired gaseous product of combustion.

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l l ~ 8d99 Other objects arld advantages of the instant invention will be apparent in the following specification, claitns and drawlngs.

BRIEF DESCRIPTION OF T~ DRAWINGS

Figure 1 is a vertical sectional view of a boiler iDCOrpOrating a ~toker of the present invention with certain portions broken away, the stoker being shown 60tnewhat diagrammatically.
Figure 2 is a plan view of the grate portion of the stoker of Figure 1, with half of the view cut away ~howing the air supply cystetn arld drive mechanism below the grate.
~igure 3 is a side view taken along line 3-3 in Figure 2, Figure 4 is a diagratnmatic vertical sectional view along the line 4-4 of Figure 2.
Figure 5 is an et~arged view of a portion of the apparatus 6hown in Figure 3.
Figure 6 is a diagrammatic view similar to Figure 4 showing alternative means for control of air flow.
Figure 7 is a fragmentary sectional view ~imilar to Figure 3 illustrating alternative fuel feed means.
Figure 8 i~ a ~ide elevational view of a furnace wall tuyere grate fortning a part of the stolcer of the present invention.
DESCRIPTION 01? THE P~EFER!RED EMBODIME NT
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P~eferring now to Figure 1, M itnproved overfeed continuous ash discharge stoker 101~ illustrated. The stoker 10

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Includes generally a furnace area 12, a fuel feed 14, a clrcular grate 16, air plenums or wIrldboxes 18, l9 and 20, an ash collec-tion box 22, a ~uperheater area 24, and a collection area 26 to collect ash particles carried outside of thP furnace area by the heated gases, The collected particles from the collection area 26 may or may not be directly reinjected Into the furnace for further burning of any combustible that they may contain. Various other areas and devices would be Included downstream of the fur-nace area 12 beyond the broken away portion of Figure 1 as known in the art and not included withln the scope of the invention. Not shown Ln Figure 1 is the air supply unit whlch will be discussed infra.
Various types of conventlonal fuel feeders may be employed at the feedpoint 14. The fuel feeder utilized may depend on the fuel used in the stoXer 10. Typical fuels utilized are bLtu-minous and lignite coal, wood, coke bree3e, bagasse, bark, munici-pal refuse, spent coffee grounds, or any other cellulose or by-product waste fuel. The feed 14 directs the fuel to the center cap 76 of the grate 16. The feed 14 in the preferred embodiment Is directly above the ash collection box 22 to provide the optimum fuel distributLon pattern and maximum residence tLme on the grate 16 for complete combustion of any fuel that does not reach the center cap 76 target pos itlon.
Referrlng to Figures 2 and 3, the grate 16 15 shown ln detaU. The upper grate æurface of the grate 16 conslsts of two zones, a central stationary sectIon 30 and an outer rotatlng sectIon .

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or ring 40. The central section 30 ls inclined and is the maIn alr admittin~ ~one. The outer rotating ring 40 serves to distribute the fuel in the furrlace 12 wlth the ald of a stationary spreader arrn 42 and admits air necessary to cornplete combustion of the fuel S The outer ring 40 also removes the burned out ash from the fur-nace 12 with the aId of an adjustable stationary ash plow 44.
The outer rotating ring 40 is made up of several grate sections 40a which are fixedly attached to an annular rail 46 and guided by rollers, generally designated 48. The rollers 48 are supported by shafts 50 in C-brackets 52. The C-brackets 52 are attached to jolsts 54 supported at circurnferentially spaced intervals by the outer plenum wall S6 of air plenum 18 and the inner plenum wall 58 separating air plenum 18 and air plenum 20.
The stationary central 6ection 30 of said grate 16 Is of a generally conlcal or frusto-conical configuration and comprises an Inclined circular grate 60 having a nurlber of layers of circum-ferentially spaced tuyeres, generally designated 62, Inset throughout the grate 60. Sald tuyeres 62 are inclined downwardly, as shown in Figure 3, to prevent fuel and ash from sifting into the air plenurn 20.
~ The inner~air plenum 20 is a cylinder and has joists 66 attached across the upper portion thereto as shown in Figures 2 and 3, A second stationary central support cylinder 68 i8 attached to said jolsts 66 by buttressed support brackets 70. Attached to the upper portlon of cyllnder 68 and Integral thereto 18 an annular support as n}ng,e 7a. -6-.

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The inner plenum wall 58 and the annular support nange 7Z jointly support the ~tatlonary central section 30 s~f saId grate 16 at support groove~ 64 and 74 respectively, as shown In Figure 3. A cap 76 is ffxedly seated upon the top of cyllnder 68 to separate the air plenum ~0 from the furnace area 12.
The outer ring 40 has a radially Inwardly Incllned ~ection 78 and an outer horizontal portlon 80, as demonstrated in Figure 3. The inclined section 78 has a radially Inner edge 82 ~hich is situated below the radially outer overhang 84 of the central stationary section 42. Both the outer ring 40 and the overhang 84 are located above the aLr plenum 18 radially outwardl~ of alr plenum 20. The overhang 81 and the inclined section 78 each have rows o~
circumferentially spaced tuyeres, generally designated 86, com~
~nunlcating with air plenum 18 as air passages to the ~uel on the grate 16 in the furnace area 12. I`he tuyeres B6 are downwardly dErected to prevent fuel and ash from siftlng into the air plenum 18.
Referring to Figure 5, the hori~ontal portion 80 of the ring 40 e~ctends radially outwardly to a downwardly extending ~ nange 88. The nange 88 i8 operably associated with a furnace wall seal 90. Thls seal 90 comprises an annular trough 91 extending along and secured to the inner perlphery of the outer plenum wall 56, filled originally wIth sand, ash residue or the lL~ce 92 from the combustlon process to provlde an effectlve and wear-resl8tant seal.
During operation oi the stoker 10, the a8h re~idue of the 8toker 10 refIlls the trough 91, The seal 90 reduces alr lealcage to provlde a hlgher combustlon efflclency per amount of alr and fuel used.

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'rhe drlve means 100 of the outer rlng 40 comprlses a drlve ratchet 10~ driv~rl by two hydraullc cylinders 104 and 108.
As shown in Figure 2, hydraullc c~llnder 104 ha8 a drlve piston 106 havlng a head 110 which engages the drlve ratchet 102. The drlve plston 106 Is gllidet by a guide bracket 112 secured to a c~oss rall 114. The cross rail 114 is attached between two roller support joists 54 in a conventional manner. Hydraulic cylinder 108 ls operably secureù and assoclated wIth the drlve ratchet 102 at the opposSte drive point of the ratchet 102 such that the hydraullc cyllnders 104 and 108 operate in unison to rotate the ratchet 102, although sequentlal operation Is al60 wlthln the scope of the invention.
The ratchet 102 and the outer rlng 40 are interconnected by cylinder 116 and support jolsts 118. The drive ratchet lQ2 16 secured to the cyllnder 116 at the lower portlon of said cyllnder 116.
IS The support joists 118 are attached to the cylinder 116 at circum-ferentlally spaced intervals at an inte~ediate axial positlon of the cylinder 116 by buttressed support brackets 117. The radlally outer : ~ portlon of ~aid jolsts 118 are con:ected to the annular support rail ~: 46 of the outer rlng 40. I~e axially upper portion of said cylinder 116 has a nange 119 which i6 inserted into groove 120 of each rlng grate section 40a to laterally: support the Inclined sectlon 78 of the rlng ~40, F'uel 18 fed from above In the Illu8trated embodiment from the fe~edpoint ~4 and l~ directed toward the cap 76 of the central 25; 6tationary ~ectlon 42 of the grate 16. The fuel subsequently follows a generally splral path down the lncllned grate 60 of the central 8tatlonary 8ectlon 30 to the rotatlng ~Incllned 8ection q8 o the outer ~ .

, ,' .. , ' 1 15~0~9 ring 40 onward to the outer horlzontal portion 80 and Is spread evenly by the spreader arm 42. Eventually the fuel i5 combusted Into ash by the time it reaches the adjustable ash plow 44. 'rhe ash plow 44 dIrects the ash to the ash collection box 22. The ash plow 44 has a handle extending outward}y from the ash collectlon box 22 at the axis of rotation 132 of the ash plow 44 to adjust the rake of the plow.
The ash collectlon box is operably associated wIth a chute 130 and an ash treatment system tnot shown), such as a clinker grinder in combination with a Dense-A-Matic unit as manufactured by the Detroit Stoker Company. The chute 130 includes a manual knife grate 134 in order to control the flow of ash into the ash treatment system and an access door 136 for manual access to the furnace 12 for manual removal of ash or other operation deemed necessary during the operation of the ~toker 10.
The ash removal system formed by the ash plow 44, collection box 22, and chute 130 (to an ash treatment system) allows for continuous discharge of ash, provlding for higher combustion efficiency because of the reduction in carbon loss and lower excess air requirements. The single point disposal further acts to make the overal] system more co~t-efiective since the sye-tem allows for single ~tation ash removal and disposal In a verg complete m anner. Stoker ash itself is a readily saleable ltem ln great demand for use as aggregate ln clnder block manufacture and for fill.

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1 15~09g The alr supply system IS0 provides the forced draff alr utili~ed in the combustion process whlch is passed through the fuel from the underside of the grate 16. The Illustrated alr supply duct 152 is dlvided intothree ducts 155 160 and 165 as it approaches the stoker houslng 11. Control dampers 1~6 161 and 166 are oper^
ably associated with each duct 155 160 165 respectively at the inlet port of each duct as shown in Figure 3. The dampers are con-trolled by adjustment knobs 157 162 and 167.
As seen in Figure 4 the lower duct 155 is operably associated with air plenum 20 to provide high pressure air to the underside of the central stationary section 30 of the grate 16. The high pressure air is passed to the fuel through the tuyeres 62 as shown in Figure 3.
The middle duct 160 is operably associated with air plenum 18 to provide the relatively lower pressure alr to the under-side of the overhang section 84 of the central stationary section 30 aod the inclined section 78 of the outer rotating ring 40.
The upper duct 165 is operably associated with thè
~ optional furnace wall air plenum 19 to provide high pressure air to an annular duct 170 at the periphery of the refractory portion 180 of the housing 11 posltioned axially above the 6urface of tbe circular grat 16. The radially inner portion of 6ald annular duct 170 Is comprised of a serles of grates 17Z havlng rows of tuyeres 174 8paced clrcumferentlally along the extent of the periphery of the furnace area 12 ae shown In Figure6 2 and 3.

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1 15~0gg An alternative alr supply system Is shown In ~igure 6.
ln this alternatlve embodiment, the air ~upply duct 152 Is divIded lnto only two ducts 153 and 163, having control dampers 154 and 16~, and adjustment knobs 158 and 168.
The lower duct 153 Is operably assoclated wlth alr plenum 20 to provlde high pressure air to the underside of the cen-tral stationary section 30 of the grate 16, as detailed above.
The upper duct 163 is operably assoclated with the optional furnace wall air plenum 19 to provide high pressure air to the annular duct 170 at the perlphery of the refractory 180 as detailed above.
The furnace wall Qir plenum 19 is optional based upon the type of unit with whlch the rotary continuous ash discharge stoker of the present invention is used. When the grate is part of ~15 a gasifler unit or the like, where it is not desirable to dilute thegas resulting from the combustion process with air, the furnace wall air plenum 19 and the air supply duct attached thereto (16S in Flgure 4 or 163 in Figure 6) would not be lncluded in the construc-tion o~ the present invention.
Air flow to air plenum 18 is controlled by butterfly valves 159 and 169, operably attached eO the inner plenum wall 58.
The rotation of the valves 159 and 169 Is controlled by a rotatable rod (not shown) which extends through a seal Ln the houslng 11 to a control knob outaide the housing 11, as Is known In the art. The valves lS9 and 169 provide tbe relaeIvely lower pressure alr to the underside of the overhang ~ection 84 o~ the central stationary sec tion 30 and the Incllned sectlon ~8 Or the outer rotatlng rtng 40.
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If the furnace wall alr p]enum is used, each furnace wall grate 172 Is supported wlthln the duct 19 along the furnace wall as shown In Figure 2. Each grate 172 has a C-shsped con-fIguration when viewed from the ~Ide. ~eferring to Figure 5, the base of the grate 172 is retalned by an annular support flange 176 ~velded to the outer wall 56. The grate 172 also has an extended portion 173 which fits ~ecurely lnto a 6econd annular &upport nange 182 welded to the outer wall 56. A grate cap 178 is seated at the top of the grate 172 anù is also 6upported by annular flange 179, After the grate cap 178 and grate 172 are installed, a heat resistant, compres6ible materIal 184, such as ceramlc flber or rock ~1vool, is packed above the grate cap 178.
The tuyeres 174 are downwardly directed to prevent fuel and ash from sifting into the furnace wall air plenum 19. The outer wall 56 has passages 186 so that the alr plenum 19 can direct air into the Inner air plenum l9a communlcating directly with the tuyeres 174 to admlt hlgh pressure air Into the furnace area 12 above the surface of the circuSar grate 16. The admission of addi-tional air along the sidewa11 in this manner permits a further con-20 trol and ooordination of fuel and air with respect to load demand toobtain complete combustSon of the fuel both on the grate 16 and In ~uspension above the grate 16 at any particular combination of load demand, air and fuel. This is particularly ir.nportant to malntaIn combustion at law. loads and 18 essentIal for an approach to complete 25 combu6tlon at hlgh loads, although, as stated previously, Sn ~ome Instances, such as when the grate S~ part of a gaslfler unltj alr-cooled tuyeres on the rurnace wall would not be used, .
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~ , 09g The sidewall air also provldes a great deal of turbulence whlch, In combination with the furnace ~vall seal 90, wLIl red~lce stratUication of ~ir along the furnace walls where it could not be efficlently uti~lzed In the combustlon process. Further-more, the flow of air will cool the sidewall to eliminate cllnlcer formation or slag adheslon to the refractory or the furnace wall in this area of the furnace 12.
The rotary continuous ash discharge stoker lO as described herein has numerous advantages as recited above. An overfeed stoker with a substantial variety of controls and admlsslon areas for the forced dra~t alr of varying pressures wIll provlde for ~nore efficient combustion of fuel at various load requirements and fuel/air combinatlons, The present invention further allows flexi-bllity to have addltIonal air admitting zones either concentrically lS wIth the present zones or sllced at intervals clrcumferentlally at different stages ot combustlon as the fuel traverses an expan[iing spiral path around the grate 16. Various feeder arrangements either from above or below are totally compatible wLth the present Inve nt lon.
An underfeed embod~nent i~ illustrated In Figure 7O
A feed tube 200 extends axlally through the inner alr plenurn 20 and the central stationary section 30 of the grate 16, concentric wlth the Inner plenum wall 58. She central cap 76a Is an annulus, separatlng of the Inner alr plenum 20 from the furnace area 12 and the feed area 202. The central statlonary sectlon 30 Is atlll jolntly supported at support groovea 64 and 74 by the lnner plenum wall 58 1~8099 and annular 6UppO~ flange 72 respectlvely. Annular support flange 72 is fixedly attached to cylinder 68, which in turn Is s~pported by and attached to jolsts 204, JoLsts 204 extend from the inner plenum wall 58 to the feed tube 200 and are fixedly attached thereto by con-ventional fasteners 206 and 208. Further details of construction can be gleaned from Figures 2 and 3 as descrEbed above.
A drive screw, a ram, or other feed means as known In the art may be utilized within the feed tube 200 to feed fuel to the grate d;rectly at the outlet point 210 of the feed tube 200 or at a higher discharge point released above the grate.
Thus, there is disclosed in the above description and in the drawlngs an illustratlve embodiment of the invention which fully and effectively accomplishes the objects thereof. However, it will be apparent that variations in the details of the apparatus may be indulged in without departing from the sphere of the invention herein described, or the scope of the appended claims, .. . .. Y .. , . .. .. , . ~ .. . .. . .
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Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A rotary stoker comprising:
a housing having an inner wall forming a furnace combustion chamber;
a circular grate having a central stationary section and an outer rotating ring section, each having means to supply pressurized air to burn fuel supported on both sections of said grate; and means to supply pressurized air into said housing below said grate.

2. A stoker in accordance with claim 1, further comprising feed means directing fuel to said circular grate and ash discharge means operably associated with said outer rotating ring section whereby said grate provides movement of the fuel as it burns, from a feedpoint to an ash discharge point.

3. A stoker in accordance with claim 2, wherein said fuel moves in a generally spiral path relative to said central stationary section from said feedpoint to said ash discharge point.

4. A stoker in accordance with claim 1, wherein said air supply means includes at least two compartments formed below said circular grate wherein at least one of said compart-ments communicates with said central stationary section and at least one other compartment communicates with said outer ring section, and said air supply means further includes means to separately control the air pressure in each of said compartments.

5. A stoker in accordance with claim 4, wherein an air compartment is included along the inner wall of said housing located above said grate having means to admit air into the furnace chamber and connected to said pressurized air supply means.

6. A stoker in accordance with claim 5, wherein said outer rotating ring section has a downwardly extending flange at its radially outward periphery and said stoker further comprises sealing means, comprising an annular trough extending along and secured to the inner wall of said housing, and filler means disposed in said trough and operably associated with said outer ring flange to provide an effective, wear-resistant seal.

7. A rotary stoker comprising:

a housing having an inner wall forming a furnace combustion chamber;

support means located within said housing to support burning fuel, comprising a circular grate having a central stationary section and an outer rotating ring, said central stationary section being of a generally hollow frusto-conical configuration, having a plurality of tuyeres disposed in said section, said tuyeres being directed generally radially outwardly, and said outer rotating ring concentric with said central section and located radially outwardly of said central section;

means to supply pressurized air into said housing below said circular grate;

a plurality of compartments formed below said circular grate, connected to said air supply means, to supply pressurized air to said tuyeres; and drive means to drive said outer ring of said circular grate.

8. A stoker in accordance with claim 7, wherein at least one of said compartments communicates with said central stationary section and at least one other compartment communicates with said outer ring, and said outer ring has means to admit air from said compartment to the grate surface.

9. A stoker in accordance with claim 8, further comprising means to separately control the pressure of the air in the central stationary section compartment and the air in the said outer ring compartment.

10. A stoker in accordance with claim 9, wherein the air pressure in the outer ring compartment is lower than the air pressure in the central section compartment,

11. A stoker in accordance with claim 8, wherein a plurality of compartments are located under said central stationary section.

12. A stoker in accordance with claim 7, wherein a plurality of compartments are formed under said central stationary section.

13. A stoker in accordance with claim 12, wherein said stationary central section has at least one set of tuyeres near the base portion of said section.

14. A stoker in accordance with claim 13, wherein at least one compartment communicates with the base portion of the central stationary section in which the tuyeres are located and at least one other compartment communicates with the other portion of the central stationary section.

15. A stoker in accordance with claim 14, wherein the base portion of said central stationary section overlaps the radially inner portion of said outer rotating ring.

16. A stoker in accordance with claim 7, further compris-ing an air compartment along said inner wall of the housing, located above the outer portion of said grate, having means to admit air into said furnace chamber, and connected to said pressurized air supply.

17. A stoker in accordance with claim 16, wherein said air admission means comprises grates having a multiplicity of tuyeres operably connected to said inner wall air compartment.

18. A stoker in accordance with claim 7, wherein said tuyeres are directed downwardly to prevent fuel and ash from sifting into the corresponding air compartment.

19. A stoker in accordance with claim 7, wherein said outer rotating ring has sealing means at the inner wall of the housing to reduce air leakage along said wall.

20. A stoker in accordance with claim 19, wherein said outer rotating ring has a downwardly extending flange at its outer periphery and said sealing means comprises an annular trough extending along and secured to the inner wall of said hous-ing, and filler means disposed in said trough and operably associated with said outer ring flange to provide an effective, wear-resistant seal.

21. A stoker in accordance with claim 7, wherein said circular grate is supported by roller means and said roller means comprises:

a rail attached to the underside of said outer rotating ring; and rollers spaced circumferentially along the underside of said outer rotating ring to rotatably support said outer retaining ring.

22. A stoker in accordance with claim 7, wherein said stoker further comprises ash discharge means operably associated with said outer rotating ring at a single ash discharge point.

23. A stoker in accordance with claim 22, wherein said ash discharge means includes an adjustable stationary ash plow located transversely across the upper surface of said outer rotat-ing ring, a chute located outside said housing, and passage means through which ash is directed by said plow into said chute.

24. A stoker in accordance with claim 7, further comprising a spreader attached to said inner wall of said housing to distribute the fuel evenly over said grate.