US2008446A - Apparatus for feeding powdered fuel - Google Patents

Description

2 Sheets-Sheet 1 A. J. GRINDLE APPARATUS FOR FEEDING POWDERED FUEL Filed Jan. 9, 1955 July 16, 1935.

s loQlTz/Uem'm ,Jhr/wey I Grind. le,

July 16, 1935. A. J. GRINDLE APPARATUS FOR FEEDING POWDERED FUEL 2 Sheets-Sheet 2 Filed Jan. 9, 1955 Mr/f InUeYZZE Jwbrey I Grnd Le,

Patented July 16, 1935 Aubrey J. Grindle, Chicago, Ill., assigner to Gaskoal Corporation, Chicago, Ill., a corporation of Delaware Application January 9, 1935, Serial No. 997

16 Claims.

The present invention relates to improvements in apparatus for feeding powdered fuel and adapted for domestic use and other small heating installations.

One of the objects of the invention resides in the provision of a new and improved fuel feeder adapted to supply a mixtureof fueland primary air under pressure, to the burner.

Other and more specific objects reside in the provision of a fuel feed-er comprising a novel sprocket or gear feed wheel `for delivering the fuel from a hopper to the suction of'a delivery blower, new and improved means for regulating the supply of fuel and air to the blower, and l5' novel means for agitating the fuel in the hopper to insure an adequate'supply of fuel aboutand to the'feed wheel at all times.

Another object sto `provide a novel powdered fuel feeder in which the fuel is entrained in a streamof air drawn from the hopper by the blower.

A general `"object is to provide -a new and improved powdered fuel feeding apparatus which is simple, compactand inexpensive in construction, which is reliable and capable of` accuratevcontrol, and which `is not likely to jam or clog in use.

f' `Further objects and advantages will become apparent as the description proceeds. Y f Y Inv the accompanying drawings, Figure 1 is a front elevational view, on a reduced scala-of a combustion apparatus embodying a feeding apparatus having'thefeatures of my invention.-

Fig. 2 is a vertical sectional view of the combustion apparatus.

Fig. `3 is `a fragmentary View, partially in front elevation and partially in vertical section along line 3-3of Fig. 4, ofthe fuel feeding apparatus.

Fig. 4 isa fragmentary horizontal view, partially in sectionalong line 4 4 'of Fig. 3.

'Figj5 is a' fragmentary vertical sectional view taken along line 5-"5 of Figs. `3 and a.

While the invention is susceptible of various modifications and alternative constructions, rI` have shown in the drawings and will herein describe in vdetail the preferred embodiment, but vit isto be understood that I do not thereby intendY to limit the invention tothe specific 4form dis closed,'but` intend to cover all vrifiodifications and alternative constructions falling withinthe spirit and scope of the invention as expressed in the appended claims. 1

Referring more .particularly to the drawings, thefuel feeding apparatus, constituting the eX- emplary embodiment of the invention, is shown i withacombustion apparatus comprising` gener ally a heater I having a combustion chamber 2, a fuel burner 3 discharging into the chamber, and power operable means 4 for feeding fuel to the burner.

The various units of the combustion apparatus are conveniently mounted, compactly arranged and substantially enclosed within an outer housing 5 which isk rectangular in shape, and which comprises a horizontal base plate 6, 'opstanding front, rear and end walls 1, 8, 9 and I D, anda top wall I I.

The heater l shown comprises an upright cylindrical outer shell I2 having upper and lower end walls I3 and I4, and resting on the base plate 6. A transverse vertical partition wall I5 serves to enclose the heater I within a compartment lined with a suitable heat insulating material I1. The` combustion chamber 2 is dened by `a plurality of vertically superimposed coaxial sections, namely upper and lower cylindrical inner shells 8 and i9, respectively of relatively small land large diameters, and-an intermediate truncated conical section 2i). The shell I8 extends through the upper end wall I3 to the wall- I I and, with thev shell I2, denes an: annular heating chamber 2| 25;,

- for water, steam or hot air, etc. V A lining 22 of `a suitable refractory. material is provided within the shell I8 andthe underside of the. circumscribed portion of Athe wall il. The lower shell I9 extends coaxially in closely peripheral spaced 30, relation to the shell I2 to denne an annular water leg 23 opening from the chamber 2|. The com-V bustion chamber 2 also has' abottom Wall 24 which extends in spaced relation to the lower end wall I4 of theshell I2 to form an inward annular 35 extension of the water leg 23, and which is formed with a central annular flange 26 closing the leg extension and defining an opening 2T in axial alinement with the upper -shell I8. Water or any other medium to be heated may be introduced through a line 28 opening tangentially to the water leg 23 about the flange 26, and the heated medium may be taken from the top of the chamber 2| through an opening (not shown) Located in the upper portion of the chamber 2! just below the normal water level and in spaced relation between the shells I2 and I8 is an annular exhaust header 30 adapted to be connected to a stack (not shown). A plurality of kvertical heating flues or passages 32 `extend through theV chamber 2l, and open `at their upper and lower ends respectively to the header 3U and the inter-` mediate section 26 of the combustion chamber). These passages are dened by al plurality of cof.v axially spaced shells 33 intermediate the shells I2 and I8. It will be seen that the shells I2, I8

and 33 define alternate annular passages for the water or medium to be heated and the gases oi' combustion. The water passages are brought into intercommunication at their ends by a plurality of connecting tubes 94 opening laterally through gas passages. The lower ends of the Water passage, exceptfor the water leg 2.3, are closed by annular Walls which denne the intern mediate section 28 of the combustion chamber 2.

A heating element 42, adapted to supply hot water for domestic use, is positioned in the hottest zone of the water chamber 2|.

The burner assembly 3 is mounted within a hood 44 on the top wall II of the housingv 5. Opening at its upper end to the hood 44 is a vertical air duct 45 extending to the lower portion of the housing 5. The lower end of the duct 45 is open to the atmosphere, and is provided with a/weighted gate valve 46 normally open in response to natural draft, and adapted to close in the event of back pressure.

The burner assembly comprises a powdered fuel Vnozzle 41 positioned to discharge a mixture of fuel and primary air under pressure downwardly through a flanged opening 43 in the wall II oentrally into the upper end of the combustion chainber'2. AThe opening 48 is substantially larger than the nozzle 41 to define an annular space for the admission of secondary air from the hood 44. Secured on the wall Il and partially overlying the opening 48 is a mounting bracket i9 for the nozzle 41. A fuel mixture supply line is connected to the nozzle 41, and consists of an elbow 5I with an enlarged end secured to the nozzle 41, a series of connected pipe sections 52, 53 and 54 Within the hood 44, and a iiexible tube 55 leading to the feeding apparatus 4.

The duct55 is supplied with a mixture of cornminuted fuel and air under pressure from the feeding mechanism 4. The mechanism gener ally comprises a centrifugal fan or blower 81,k a fuel hopper 68, a fuel feeding member 89 for conveying fuel from the hopper into the inlet passage of the blower for entrainrnent with the air passing therethrough, an agitator 10 in the hopper, and a common drive means for the blower, the feeding member and the agitator.

In its preferred form, the blower F51 (see Figs. 3 and 4) comprises two opposite side walls 1I and 12 defining a casing with a peripheral outlet 13 to which the duct 55 is connected, and a rotary propeller V11| mounted on a shaft 15 and consist ing of a closed circular disk with peripherally spaced vanes 16 on opposite sides.. r'he'side wall 1I has a plurality of centrally located air inlet openings 11 under the control of a manually ad-V justable damper 18. The otherside wall 12 is formed on the exterior with a radial horizontal duct 19 defining an inlet passage opening axially to the blower casing. To support the blower 61, the wall 12 is bolted to an upstanding flange 89 Von one end of a bracket 8| adjustably mounted on a horizontal base plate 82. The propeller shaft 15 constitutes one shaft of an electric drive motor 83 also mounted on the bracket 9|. A bolt 84 extending through the base plate 82 and an elongated'slot 85 in the bracket 9| affords means for-clamping these parts togethenand when loosened permits adjustment of the bracket, the blower 61 and the motor 83, as a unit, longitudinally of the duct 19.

The hopper 68, in its preferred form (see Figs. 2 -to 5), comprises an upright base section 86 circular at its upper end and tapered downwardly,

and a relatively large superstructure 81 mounted` thereon. Preferably, the base section 86 is generally V-shaped in one vertical cross-section, and rounded at its closed lower end in the perpendicular cross-section, and comprises two flanged side walls 88 and 89 securely bolted together. The side wall 88 is formed integral with a mounting bracket 98 securely bolted to a bracket 9| on the base platev 82. The upper end portion of the superstructure 81 is cylindrical in form, and is closed at the top by an end wall 92 having a central' man hole cover 93 accessible from above the housing 5. The lower portion of the superstructure 81 is tapered conically, and merges into a circular neck portion 94 on the base section 86.

To support the hopper 68 and the other units of the feeding mechanism 4, vertical posts or standards 95 are connected at their upper ends to the superstructure 81, and horizontal tie bars 96 serve to connect the superstructure to the shell I2 of theheater I.

Comminuted fuel may be introduced into the top of the hopper 68 through a pipe 91 adapted to be connected to a suitable source (not shown). Fuel is adapted to be delivered from the base section 86 of the hopper 68 through an elongated vertical opening or slot 98 between the marginal edges of the walls 88 and 89. The base section 86 is formed with a fuel entraining chamber or passage 99 in alinement with the duct 19, and in com munication intermediate its ends with the delivery opening 98. One end of the entrainingpassage 99 may be connected to a. suitable source o f air, and preferably is connected to a, line Illu-Ilma. Secured in the other end of the entraining passage 99 is a connecting duct I0| which extends telescopically with a close sliding fit into the free outer end of the blower inlet passage 19. It will be seen that the telescoping relation of the passage 19 and the duct IUI permits adjustment of the blower 61 with the bracket 8|.

Fuel is delivered throughY the opening 98 by the feeding member 69 which preferably consists of a thin thoothedsprocket or feed wheel or disc mounted on a horizontal shaft |02 in the bottom of the base section 86, and conforming closely to the curvature thereof. A portion of the periphery of the wheel 59 extends through the opening 98 into the passage 99. The passage 99 is generally elliptical in cross section with the major axis generally vertical toV receive a relatively large portion of the periphery of the feed disc 69 for a relatively small cross sectionalow area of the passage. Preferably, the wheel or disc 59 is rotatable on an axis parallel toV and in substantially the same horizontal planeas the passage 99. The shaft |82 may be driven from any suitable source of power, such as the motor 83. Preferably, one end of the shaft |92 extends through a bearing |83 into a gear housing |04 integral with the exterior of the side wall 89. A worm wheel |65 fixed on the shaft |02 meshes with a worm |06 on a transverse shaft |91 journaled in and extending from the housing |84. A pulley |08 is secured to one end of the shaft |81, and is connected throughV a V-belt |09 to a pulley III) on a second shaft III of the motor 83. Pulleys I| 0 of different sizes may be substituted to drive the feed wheel 69 at different speeds, and thereby vary the rate of from-entering .and remaining betweenthe sprocke et 1teeth 4of .the feed wheel-69. 'In the :presentinstancathe `guard I I2 :consists of two vertcalcontacting-flanges projecting inwardly from the edge margins of the walls 88 and 89 about the `delivery opening 98. Formed inthe inner` vertical edge of the guard I l|2 is a deep 4groove II3 receiving the adjacent portion of .the feed wheel r69, and communicating intermediate its ends with thedelivery opening 98. The grooved edge-ofthe guard ||2 extends substantially from the top of the feed when ts and directly over, the shaft |02 downwardly at an angle toward vthe edge of the base section 86. Of the groove ||3, the `root surface conforms to and hasaclose fitwith the periphery of `the feed'wheel 69, Vthe sides closely embrace opposite sides of the wheel, and the upper end defines a horizontal slot II4 `through which the wheel 69 is adaptedto carry fuel lodged in the interdental spaces between the teeth. The side edges of the slot IIlI extend tangentially across and are in shearing relation to the upper teeth of thewheel 69, and, upon rotation of the wheel in a clockwise direction as viewed in Fig. 5, act to lift and remove any foreign bodies therefrom unless the latter are small enough to completely enter the interdental' spaces and pass out with the fuel. In operation, fuel enters between the upper teeth of the wheel 69, and, as the teeth enter the groove I I3, is trapped therein until delivered through the opening 98 to the entraining passage 99.

The agitator I0 is mounted within the base section 86 of the hopper 68 to insure the movement of fuel to the feed wheel 69. In its preferred form, the agitator 10 comprisesa plurality of ro tary members, such for example ras two end members ||5 and two intermediate members I I6, mounted in axially spaced relation on a shaft II'I over the feed wheel 69 andA parallel to the shaft |02. If the agitator 'I0 were not provided, the feed wheel 69 would tend to cut a groove through the body of the fuel, and the fuel would tend to pack and bridge without entering the interdental tooth spaces.

The agitator is formed and located to prevent packing and bridging of the fuel adjacent the upfper portion of the feed wheel 69, and to cause the fuel to move inwardly from the sides of the base section 86 toward the wheel and between the teeth. Thus, the intermediate members H6` closely overlap with and are positioned respectively at opposi'tesides of the upper portion of the feed wheel 69, and are in the form of disks having closely spaced peripheral vanes IIS. Ihe vanes of each member |56 are alternately bent longitudinally to extend angularly in opposite directions out of the plane of the disk, and are all twisted laterally in the same direction so that upon rotation in a counter-clockwise direction as viewed in Fig. 5 they will impart an axial thrust on the fuel toward the feed wheel 69. The end members II5 also have closely spaced periperal vanes |I9.` In each instance, the vanes' I|9' are bent longitudinally at an angle toward the feed wheel 66, and are twisted laterally in the same direction to urge the fuel inwardly toward the wheel. By reason of the inward axial thrust exerted by the agitator and opposed rotation of the wheel 69 and the agitator '10, Vthe spaces between the teeth are filled with fuel even though the wheel is comparatively thin.

' The agitator shaft III is journaled in and extends through bearingsA |20 and I2| `respectively onthe side walls 188 and 89. One fouter end of the shaft TIITI .is connected 'rth-roughf'redirction gears |22 `and 123.1-to the shaft |62 Iwhichyextencls out of the housing |04 through a bearing |24. v

A'flanged lspacer ring |25is interposed between the base section 86 and the'neck portion 94 ofthe hopper 68 to fspace `the superstructure 81 .above the agitator 10. If it should be desired to empty theibasesection 86 withoutemptyingthe superstructure '87, a plate (not shown)V may be inserted between` the neck portion 941:and the ring |25,y without interferencewith the agitator I0, to close the bottom of the-superstructure.

The'motor 83 serves to drive the blower 61, `the feed wheel 69 and the ragitator 10. -The belt vHNI may be suitably tensioned by adjusting the bracket B2, thismovement being permittedby the telescoping,relationship of the duct 'I9 landwthe duct IDI. The agitator -'I|I loosens the fuel in =the hopperl 68, and causesit lto move 'towardgthe feed wheel 69 and` into the tooth spaces. Packing and bridging `ofthe lcomminuted fuel is thus effectively prevented. In the rotation r of- 4the ,feed wheel 69, the interdental spaces betweenthe Vteeth become filled with fuel, and carry the Atrapped fuel through the groove II 3 and the delivery opening 98` into the passage 99. Here,v the fuel is entrained in atmospheric air drawn in by the` suction of lthe blower 61 from the hopper 68. f It will `be seen that the blower 6I .takes in two separate streamsof air, one through the passage 'I9rladen withentrained fuel,` and the other. di-.

rectly fronde-the atmosphere through lthe open-A ings, I'I. Hence; thezblower 61- may be considered functionally as two separate blowers. The total volume of airentering the blowerl constitutes` the primary air of combustion. The velocityof the air for Ventraining the fuel may be adjusted by means of a damper |26 transverselylslidable in -thepassage 99 towardand from; the periphery of the feed wheelsSS. The volume of-airenter ing the inlet openings` I'I may .also be adjusted by the damper 18, this adjustmentf'ser-ving mainly Eo vary the richness of the primary `fuel-airmixure. I I l I`-claim las my` invention:

. 1. In a powdered fuel combustionlapparatusfa feeding. mechanism comprising, in combination; `a vertical hopper having a base sectiongformed with` a horizontal air-flow entraining4 passage and a Vvertical delivery slot `communicating therewith, a peripherally toothed `feed disc rotatable in said section `on an axisin thesame horizontal planeas said passage and projecting over a` portion of its periphery through saidslot into said passage, means yfor causingydiow of `air through said 4passage to entrain the fuel delivered thereto lby said feed disc, and meansfor drivingisaidlfeeddisc, said passage being generally elliptical in cross section with the major axis generally vertical atsaid slot toreceive a relatively` large portion of the periphery of saiddisc for a relatively small cross, sectional area offsaid passage.

2. In a powdered fuel combustion apparatus, a feeding `mechanism comprising; .in combination, a `blower having .afsuction"inletypassaga a hop` per having a. base section `generally V-shaped in form and with a generallyvertical elongated ide,- livery slot in one edge opening to said passage, a periphery toothed thin feed disc rotatable in said section in freely spaced relation to. thewalls thereof i and projecting over a= portion of its periphery through said slotrinto said passageyand a-guard projecting. from.` about said s1ot, into said sectionandl closelyoverlapping the sides-of said disc'to close the ends-'and sides of theitoothlspaces.

of saidldisc as theteeth approach and leave said slot, and means for driving said blower and said disc.

- 3. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, means defining an air-flow passage, a fuel hopper having a delivery outlet opening to said passage, a peripherally toothed rotary feeding member in said hopper for discharging fuel through said outlet into said passage, a guard within said hopper about said outlet and coacting with said member to eject large foreign obstructions substantially radially from between the teeth on said member as said teeth approach said outlet, and means for driving said member.

1 4. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, means defining an air-flow passage, a fuel hopper having a delivery outlet opening to said passage, a rotary toothed feed wheel in said hopper and projecting through said outlet into said passage, a guard about said outlet and formed with a closely -fitting notch receiving the adjacent portion of said feed wheel,one end of said. notch defining shearing edges extending tangentially across the approaching teeth of said wheel to lift foreign obstructions therefrom, and means for rotating said wheel. p 5'. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, pressure discharge means having anV air-flow passage, a hopper having a delivery outlet opening to saidY passage,` 'a rotary peripherally toothed feeding disc mounted for rotation on an axis generally parallel to said passage for delivering fuel! through said outlet into saidV passage for entrainment by the air flowing through and past the 'tooth spaces of said disc in a direction generally parallel to said axis, an agitatorcomprising a plurality of rotary vane members axially offset from said disc and overlapping with and disposed respectively at opposite sides of a portion of the toothed periphery of said feeding disc, saidV vane members having inclined faces to advance fuel axially and Vperipherally into the spaces between therteeth on said disc, and means for driving said discand members. v

6. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, pressure discharge means having an air-flow passage, a hopper having apdelivery outlet opening to said passage, a vertical rotary peripherally toothed feeding disc in said hopper for delivering fuel through said outlet into said passage for entrainment by the air owing therethrough, the axis'of said disc being generally parallel to the directinvof flow of air in said passage across said outlet, two rotary agitator disks axially offset from said feeding disc and closely overlapping opposite sides-of the upper toothed portion of said feeding disc, each disk having a plurality of peripheral vanes twisted laterally tol advance fuel axially toward said feeding disc and into the tooth spaces thereof and alternately inclined longitudinally in opposite directions, and means for driving said feeding disc and said disks.

7. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, pressure discharge means having an air-'flow passage, a hopper having a delivery outlet opening to said passage, a vertical rotary peripherallyY toothed feeding disc disposed in freely spaced relation in said hopper for delivering fuel through said outlet into said passage for entrainment by rotary agitator disks axially offset from said feeding disc and closely overlapping opposite sides fr" of the upper toothed portion of said feeding disc, each agitator disk having a plurality of peripheral vanes twisted laterally to advance fuel axially toward said feeding disc and into the tooth spaces and alternately inclined longitudinally in opposite directions, two additional rotary agitator members respectively at opposite sides of said agitator disks and having peripheral vanes twisted laterally to Yadvance fuel toward said feeding disc and inclined longitudinally toward said agitator disks, a shaft for supporting said agitator disks and members in coaxial relation,land means for driving said feeding disc and said shaft. Y

8. In a powdered fuel combustion apparatus, a fuel feeding mechanism comprising, in combination, a vertical hopper base having two connected opposite side casing members with contacting externally flanged marginal edges to define a space substantially closed excepting at the top and generally V-shaped in a transverse vertical crosssection and rounded at the lower end in aperpendicular vertical cross-section, means on said base defining a horizontal transverse flattened air-flow passage, said edges along a portion of one vertical margin of said base being spaced to define a narrow vertical slot establishing communication between said space and said passage, and being formed with internal contacting marginal flanges extending substantially to the center of said space, said flanges having free vertically inclined margins and free upperrhorizontal margins and being recessed in their adjacent sides to define a narrow vertical groove with an arcuate roo-t, a thin peripherally toothed feed wheel mounted in said base for rotation on an axis in the same horizontal plane as saidy passage and projecting over a substantial portion of its periphery with a close running lit into said groove closely to said root and through said slot into said passage, said upper margins of said flanges extending at an angle Y V-shaped in a transverse vertical section, meansY on said base sectiondefining a horizontal transverse air-flow passage, said edges along a portion of one vertical margin of said base being spaced to define a narrow vertical Vslot establishing communication between said space and said passage, and

being formed with internalv contacting marginal flanges extending substantially to the center of said space, said` flanges having free upper margins and being recessed in their adjacent sides to define a narrow vertical groove with an arcuate root, a thin peripherally toothed feed wheel mounted for rotation in said base .section and projecting over a substantial portion of its periphery with a close running fit into said groove closely to said root and through said slot into said passage, said upper Vmargins of said flanges extending at an angle acrossthe sides of the uppermost teeth of said Wheel at the point Where said teeth enter said groove, and drive means for rotating said wheel in a direction to move said teeth across said upper margins into said groove.

10. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, a ftuel hopper having an outlet opening, air supply means having an air-now passage extending transversely of said hopper and communicating laterally with said opening, a feed wheel mounted for rotation in said hopper and projecting over a portion of its periphery through said opening to one side of said passage, a slide valve extending into the other side of said passage in the plane of said wheel and having an arcuate inner edge conforming to the curvature of said wheel and adjustable toward and from the periphery of said Wheel to control the effective flow area of said passage, and means for driving said wheel.

, 11. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, a fuel hopper having an outlet opening, air supply means having an air-flow passage communicating laterally with said opening, a feed wheel mounted for rotation in said hopper and projecting over a portion of its periphery through said opening into one side of said passage, a slide valve extending into the other side of said passage and being adjustable in the plane of said wheel toward and from the periphery of said wheel to control the yeffective flow area of said passage, and means for driving said wheel.

12. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, a centrifugal blower having an axial atmospheric air inlet at one side and having an air induction passage opening axially into the other side, an adjustable valve for said inlet, a fuel hopper having an outlet communicating laterally with said passage, a peripherally toothed feed wheel mounted for rotation in said hopper and projecting over a portion of its periphery through said outlet to permit the entrainrnent of fuel from between the teeth in the air fiowing through said passage, and adjustable valve means coacting with said wheel for controlling the flow of air through said passage.

13. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, means defining an air-flow passage, a fuel hopper having an elongated narrow delivery outlet to said passage, a guard projecting into said hopper and formed in its free edge with a groove opening intermediate its ends to said outlet, a peripherally toothed feed wheel mounted for rotation in said hopper and projecting over a portion of its periphery with a close side fit through said groove into said outlet, the root of said groove at opposite ends of said outlet being arcuate and conforming closely to the periphery of said wheel.

14. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, means dening an air-flow passage, a fuel hopper having an elongated narrow delivery outlet to said passage, a guard projecting into said hopper and formed in its free edge with a groove opening intermediate its ends to said outlet, a peripherally toothed feed wheel mounted for rotation in'said hopper and projecting over a portion of its periphery with a close side fit through said groove into said outlet, the root of said groove being arcuate and conforming closely to the periphery of said wheel, the inlet end of said groove defining edges in shearing relation with the sides of the teeth of said wheel, and adapted to lift obstructions therefrom.

15. In a powdered fuel combustion apparatus, a feeding mechanism comprising, in combination, a hopper base having an outlet and open at the top, a spacer ring removably secured to the top of said base, a hopper super-structure mounted on and removably secured to the top of said ring, a peripherally toothed feed wheel mounted for rotation on a horizontal axis in said base for discharging fuel through said outlet, and a rotary agitator mounted in said base over said feed Wheel and in overlapping relation with the sides of said feed wheel, said agitator projecting upwardly `into said spacer ring and terminating below said super-structure.

16. In a powdered fuel combustion apparatus, a fuel feeding mechanism comprising, in combination, means defining an air-flow passage, a fuel hopper having a delivery outlet to said passage, a peripherally toothed feed wheel mounted for rotation on a horizontal axis in said hopper for delivering fuel to said outiet for entrainment by the air flowing through said passage, said axis being generally parallel to said passage at said outlet, a shaft for supporting said feed Wheel extending into said hopper, a parallel shaft ex- Itending into said hopper directly above said first mentioned shaft, spaced rotary agitators mounted on said last mentioned shaft respectively at opposite sides of said feed wheel, said agitators havinginclined faces adapted to direct fuel axialg

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