US2468415A - Method of and apparatus for burning coal - Google Patents

Description

April 26, 1949. D. E. sTAlR 2.468.415

METHOD OF AND APPARATUS FOR BURNING COAL Filed Aug. 17, 1945 5 Sheets-Sheet 1 INVENTOR.

April 26, 1949. D E sTAlR 2,468,415

METHOD OF AND APPARATUS FOR BURNING COAL Filed Aug. 17, 1945 5 Sheets-Sheet 2 IN V EN TOR.

BMM/MMV April 26, 1949. D. E. sTAlR 2,468,415

METHOD oF AND APPARATUS FOR BURNING coAL Filed Aug. 17, 1945 5 Sheets-Sheet 3 1N V EN TOR.

April 26, 1949. D. E. sTAlR METHOD OF AND APPARATUS FOR BURNING COAL 5 Sheets-Sheet 4 Filed Aug. 17, 1945 INVENTOR. BYQM f f/wy 1n.

5 Sheets-Sheet 5 D. E. STAIR METHOD OF AND APPARATUS FOR BURNING COAL April 26, 1949.

Filed Aug. 17, 1945 V IN V EN TOR. @WMM 6 M' A ffy;

atentec pr. 26, 1949 UNITED STATES PATENT oFPIcE METHOD oF AND APPARATUS Fou BURNING CoAL Daniel E. Stair, Chicago, Ill.

Application August 17, 1945, Serial No. 610.991

- Claims. l

This invention relates to an improved method of burning coal and to certain new and useful improvements in apparatus for carrying out the several steps of the improved method.

A principal object of the invention is to provide an improved and practical method of burning coal, whereby coal of various qualities may be converted and 'burned either individually or as mixed'fuel in the same apparatus.

Another principal object is to provide a method for burning coal which involves complete 'conversion of the volatiles and the fixed carbons into heat energy before delivering the hot combustion products into the heat transfer chamber of the heating apparatus, whereby the maximum heat units are utilized in connection with the heating operation.

The various methods of burning coal in fuel beds, as heretofore practiced, have included introducing the coal directly into the heat transfer chamber, to-wit, the usual re box of a furnace, which is in close association with the boiler.' Consequently, the temperature of the fire bed is so reduced by the transfer of heat to the boiler or to the water coils thereof, that insuiiicient heat is retained in the fire bed to break down the cellular structure of bone coal surrounding particles of fixed carbon and thereby liberate this carbon in the form of heat units.

It is a specific object of the present invention to provide an improved method for burning coal in a fire bed in which the coal is advanced in an angular course through zones of progressively increasing temperatures, which temperatures insure complete' liberation of all combustible substances contained in the coal, and whereby the angular coniiguration of the iire bed will permit diierent amounts of air to pass through different zones of the re bed and thereby insure complete and efficient combustion of the free and the fixed carbons of the coal. For example, the configuration of the coal bed is such that there is less resistance to the air currents passing through the cooler upper portion of the bed in which a major portion of the more volatile combustibles are liberated or to which they migrate from other zones. In this way, the volatile gases are supplied with the proper amounts of combustion air and the air iiow through the lower and higher temperature zones of the bed may be restricted so as to avoid cooling the incandescent fuel.

A further object of the invention is to provide a combustion chamber in which the zone of highest temperature will be near the bottom of the chamber and thereby expedite the removal of the ash and other noncombustlble portions of the fuel from the fuel bed in the form of liquid slag.` In this way, the invention avoids the collection of fly ash in the :dues of the boiler and also avoids the matting together of the incandescent fuel particles in the combustion chamber or the formation of clinkers therein in a manner to obstruct the passage of air'.

Another object is to provide an improved method4 of burning coal in which the temperature changes in the heat transfer chamber of the heating apparatus will be gradual and consequently avoid the recurrent abrupt expansion and contraction of the boiler and other metal parts of the furnace.

Another object is to provide an improved apparatus having a preferred form of combustionl chamber adapted for use in connection with the various furnace constructions now in general use and which is particularly adapted for use in connection with the simplified means herein shown for automatically advancing the coal through the combustion chamber.

A further object of the invention is to provide a fuel advancing mechanism in the form of a revolvable retort which will move the coal through the combustion chamber and at the same time agitate the coal within the retort, by moving it from the lower portion to the upper portion thereof and thereby keep it relatively loose so that the combustion supporting air may pass freely through the upper portions of the coal bed to combine with the free carbons liberated from the coal.

Another object of the invention is to provide improved structure for forming adequate `air passages leading into the lower portion ofthe coal bed within the combustion chamber and to provide controllable means for varying the amount of air entering the combustion chamber in proportion to the heating requirements of the furnace. In this connection, the invention includes the provision of a suction fan and dampers interposed between the fan and the combustion chamber, the dampers being controlled to vary their positions relative to the temperature or pressure of the boiler so that the air drawn into the combustion chamber will be proportional to the furnace temperatures or the boiler pressure.

Another object of the invention is to provide a convenient means for removing the revolvable retort when it is necessary to repair any part of the combustion chamber, `whereby these repairs can be taken care of with minimum delay and inconvenience.

, 3 Another object is to provide a simplied means i'or removing and disposing of the slag discharged from the combustion chamber. In this connection, the invention includes the provision of a pit and a container removably positioned therein to receive waste water; the molten slag being discharged from the combustion chamber directly into the water filled container.

The improved method of the present invention and a preferred form of apparatus for carrying out the steps of the method are illustrated in the accompanying drawings wherein:

Fig. l is a front view of a revolvable retort, and the mechanisms associated therewith.

Fig. 2 is a side view of the structure shown ln Fig. 1 showing parts of the furnace broken away to illustrate the path of travel of the combustion gases.

Fig. 3 is a vertical section taken substantially online 3-3 of Fig. 1 but illustrating only a portion of the boiler and heat transfer chamber of the furnace.

Fig. 4 is a fragmentary sectional view taken substantially on li'ne 4 4 of Fig. 3, looking in the direction indicated by the arrows.

Fig. 5 is a similar fragmentary sectional view which is taken substantially on line v5---5 of Fig. 3.

Fig. 6 is an enlarged fragmentary sectional view illustrating an I-beam grate construction which provides a series of tuyre passages leading into the lower portion of the combustion chamber.

Fig. 7 is a faceview of a base ring which encloses a gear for rotating the revolvable retort.

Fig. 8 is a fragmentary plan view of certain of the operating elements which are shown removed from their operative positions on the base ring for the purpose of clearness.

Fig. 9 is a fragmentary sectional view taken through the base structure substantially on line 9-9 of Fig. 1.

Fig. 10 is a detail view of side frame members for slidably supporting the retort structure in its operative position. l

Fig. 11 is a partial sectional View to further illustrate the supporting frame structure of Fig. 10, the said sectional view being taken on line lI-H OfFig. 2.

According to the improved method which forms a. part of the present invention, the coal bed is so maintained as to provide a general triangular configuration in vertical section so as to progressively decrease the mass of material toward the upper limit of the bed and thereby permit combustion air to pass more freely through the upper portions of the bed than through the lower portions thereof. In order to maintain a coal bed of the desired configuration, a combustion chamber I Il is provided which includes a relatively large bowl portion I l for receiving the fuel and an outlet passage I2 connected therewith. The said A bowl portion I I and the outlet passage extend at angles to each other so that the longitudinal axis of the bowl portion extends upwardly and out'- wardly from the furnace and the longitudinal axis of the discharge passage extends upwardly and inwardly. This passage communicates with lthe heat transfer chamber I3 of the furnace.

The coal is passed through a retort so as to subject it to heat and thereby release large amountsl outwardly inclined axis so as to keep the coal in agitation by continuously moving it from the lower portion of the retort into the upper portion thereof. This agitation of the coal keeps it loose so as to permit the air to flow through the upper strata of the fuel bed with less obstructionthan through the lower portion, but higher temperature zones of the bed. According to the improved method, the fuel bed is maintained at a sumcient depth and the air is passed lengthwise through the bed, with increasing resistance toward the lower portions thereof so that the temperature of the fuel bed progressively increases from the top to the bottom thereof, the zone of highest temperature being at the lower portion of the combustion chamber. In this way, the several stages of combustion will be carried out simultaneously. For example, the high volatile free carbons contained in the coal are distilled off in the cooler upper Strata of the fuel bed, particularly that p0rtion of the bed which is contained in the retort and in the cooler portion of the combustion chamber adjacent to the retort. Certain other of the free carbons are liberated from the coal in the lowery zone of higher temperature and migrate upwardly through the fuel bed toward the upper strata thereof wherein they are mixed with the combustion air passing through this strata of the coal bed. The fixed carbons of the coal which require higher temperatures to convert them into combustible gases are liberated from the fuel in the lower and consequently. higher temperature zones of the fuel bed. 'I'he final stage of combustion takes place in the lowest strata of the fuel bed which is maintained at a sufficiently high temperature to break down the bone coal cellular structure so as to free the combustible carbons entrapped therein and to liquefy the ash and other noncombustible substances contained in the coal so that these materials are removed from the re bed in the form of a molten slag.

The.air is preferably drawn through the fuel bed by a controlled suction device as distinguished from an ordinary stack and the operation of this device together with dampers associated therewith are controlled by temperature responsive means associated with the furnace. In this way, the volume of air drawn through the re bed will be controlled in relation to the temperature desired to be maintained. The combustible gases distilled from the coal and migrating toward the upper portion of the fuel bed are carried by the air currents into the higher temperature zones where they are burned.V For example, a portion of the gasied fuel may be carried downwardly and directed into the heat transfer chamber through the discharge passage I2 as shown by the path of arrows in Fig. 3. Another portion of the said gases may be directed into the heat transfer chamber through a plurality of ducts I4 which pass through the wall of the furnace immediately above the arch I5 of the discharge passage l2. Inasmuch as the lower portion of the fuel bed provides greater resistance to the passage of air, my improved method includes the introduction of air through tuyre passages which extend into the fuel bed at a location intermediate the top and bottom thereof and through passages at other locations near the bottom of the fuel bed; These passages are provided with damper doors which function in connection with flue dampers to control the volume of air passing into the combustion chamber. Preferably, the same device which is utilized to control the position of the ue dampers controls the position of the said damper doors.

In addition to agitating the coal contained in the retort, the coal is advanced through the combustion chamber in a downwardly and then upwardly directed path so that each particle of coal will pass through the several temperature zones of the combustion chamber and thereby be completely converted into combustible gases and the hot products of this combustion are directed into the heat transfer chamber of the heating apparatus. Inasmuch as the complete conversion of the coal takes place outside of the heat transfer chamber, the absorption of heat by the boiler or by water coils arranged in the furnace does not materially affect the temperature of the fuel bed and therefore makes'it practlcable to maintain the high temperatures re- 'quired to liberate all combustible products of Fig. 3, unite with a curved bottom portion as shown in Fig. of the drawings. The side wall A of the bowl Il terminates at the entrance end of the discharge passage I2 and diverges from the plane of the mouth of the bowl I I so that the combustion chamber will have a general triangular configuration in vertical section as shown in Fig. 3 of the drawings, and the wall A will dene the general slope of the inner inclined face of the fuel bed.

The combustion chamber is separated from the heat transfer chamber I3 of the furnace by means of a wall of refractory material which defines the discharge passage I2. This manner of construction removes the fuel bed from the cooling influence of the boilers I6 and other heat absorbing elements located in the transfer chamber and also makes it practicable to make the walls defining the said chamber II and passage I2 as thick as maybe necessary to provide the desired heat insulation to maintain relatively high temperatures within the combustion chamber. In connection with the combustion chamber as herein illustrated, the present disclosure includes a tubular boiler I6 arranged horizontally above the heat transfer chamber I3 so that the hot combustion products will flow through the boiler ilues. It will be understood however that the speciiic form of boiler and heat transfer chamber is not important, but is shown herein merely for convenience of illustration. The combustion chamber and other parts associated therewith for advancing the fuel through the combustion chamber may be used in connection with furnace structures and boilers of various types.

The lower portion of the combustion chamber I0 is provided with air inlet openings I1, I1 for the admission of air; the amount of air being controlled by means of dampers I8, I8 in connection with other damper means hereinafter described. A series of I-beams I9 are arranged in close relation to each other to provide a grate structure extending around a portion of the combustion chamber. The top webs of the I-beams are, preferably, of less width than the bottom webs 2l so as to permit the said I-beams to be arranged in a radial pattern as shown in Figs. 4

and 6 of the drawings. The spaces between the said I-beams provide tuyre passages 22 through which air is directed into the lower portion of the 'combustion chamber II) so that an adequate supply of air will pass through the body ofv material lying in the lower and higher temperature zones of the combustion chamber I0. The coal -is constantly fed into the retort so as to keep a desired level of coal therein. By reason of the configuration of the combustion chamber and the inclined arrangement of the revolvable retort, the normal upper and lower capacity lines of the fuel bed are inclined relative to each other as indicated by the reference numerals 23 and 24 respectively in Fig. 3 of the drawings. The side of the fuel bed represented by the numeral 24 extends across the discharge passage I2 while the other inclined side of the fuel bed extends diagonally across the retort chamber.

The retort is of circular structure and is com-A posed preferably of a plurality of segments 25. The segments are made of cast metal and have inwardly extending flanges 26 at their opposite edges which are secured to corresponding flanges of an adjacent segment to provide inwardly extending vanes 21. The outer ends of the retort segments 25 are secured together by means of a flanged ring 28, one flange of which overlaps the outer ends of the segments and another flange 29 thereof extends inwardly for a short distance along the inner edges of the vanes 21. Preferably, the seams between adjacent segments 25 of the retort and between the outer ends of the segments and the flange ring 28 are sealed to provide air tight constructions. The upper portions of the retort, therefore, serve as a trap for retaining any of the distilled free carbons which may rise upwardly through the coal bed and enter the upper portion of the retort. The combustible gases thus entrapped will be entrained with the air currents passing into and through 'the retort and carried into the high temperature zone for combustion. The lower portion of the retort is tapered to provide a cone configuration and the outer surface of this portion is provided with a ring gear 30. The gear 30 may be secured to the retort by any suitable means, for example, by bolts 3| which extend through the ring gear and into a shoulder portion 32 formed on the retort segments. The teeth 3| of the ring gear are formed on the outer periphery thereof and are of awidth less than the thickness of the ring.

The lower face 32 of the ring gear and the smooth peripheral portion 33 thereof, adjacent the teeth 3I provide bearing spaces which engage corresponding surfaces of a base ring 34 which seats upon the upper face of a base casting 35.

The base casting 35 is of rectangular construction, but is provided with a circular opening which receives an inwardly extending rib 36 formed on the bottom surface of the base ring adjacent its inner perimeter. 'Ihe central opening through said base casting 35 together with the inclined outer wall of the retort define an air space 31 which extends entirely around the retort and communicates with the bowl portion I I ofv the combustion chamber. At the lower portion of the said bowl Il, the said air is delivered into the combustion chamber through the space intervening between the grates and the outer surface of the retort and through the tuyre passages 22 between the grate members. 'Ihe lower portion of the base casting 35 is provided closing of this inlet opening is controlled by a damper door 39 which is automatically opened and closed simultaneously with the openingand closing -of damper doors I8, I8.

The retort is rotated preferably at a low'rate of speed by means of an electric motor 40 which may be supported on a shelf 4I secured to the base ring 34. 'I'he motor shaft is provided with a. worm (not shown) which meshes with a worm gear 42 enclosed within a housing 43 (Figs. 1 and 8) The worm gear 42 is connected by means of a shaft 44 with a pinion 45 which meshes with the teeth 3| of the ring gear 30.

It will be seen from the above description .that

Y the operation of motor 40 will rotate the retort about its axis which inclines at a suitable angle to maintain the capacity line 23 of the fuefwithin the retort substantially at the inclination shown in Fig. 3 of the drawings. The lower ends of the retort segments are provided with impeller elements 46 which are -in the form of Z-bars curved to conform to the circular structure of the retort segments and having their lower outturned flanges 41 inclined in the direction of their length and in the direction of rotation of the retort so as to exert wedging pressure on the body of fuel within the bowl portion II of the combustion chamber. During this rotation` of the hopper, the inwardly projecting vanes 21 bustion air into the combustion chamber, for example' when increasing the re after'a prolonged inactive period. a damper 61 positioned in a branch draft passage 68 leading to the chimney 52 may be adjusted to any desired position. However, during normal operation of the l furnace, the damper 61 is closed. After the temperature of the furnace approaches its maximum, the operation of the pressure motor 54 will function to'proportionately adjust the positionsand other metal parts of the furnace.

thereof keep the coal in constant agitation by moving the coal from the lower portion of the retort and discharging it onto the upper portion of the coal bed. The supply of coal to the retort may be maintained by any. suitable means, for example, a spout 48 which may lead from a source of coal supply (not shown) Draft Control The amount of combustion air drawn into the combustion chamber is controlled, preferably, by induction means, for example a suction fan 49, which is preferably operated at a continuous speed by means of a suitable motor 50.

from the discharge end of the boiler I 6 to the chimney 52. The degree of suction for drawing air into the combustion chamber and for inducing the flow of the products of combustion through the boiler tubes is controlled by the position of a damper 53 positioned in the draft passage 5I.

-The position of the damper 53 and likewise the positions of the damper doors I8, I8 and 39 are controlled by means of a pressure motor 54 which responds to temperature changes within the furnace.v The pressure actuated motor 54 is of conventional construction and includes an arm 55, the inner end of which is pivoted at 56 to the motor. casing 54 and is operated by a pressure actuated rod 51. The outer end of the lever is connected to the damper 53 by means of a cable 58 which extends'over pulleys 59 and 60, the latter of which is connected to the damper 53. The free end of the cable 58 is provided with counter weights 6I so as to maintain the cable taut at' all times. The damper doors I8, I8 and 39 are connected to the arm 55 of the pressure motor 54 by means of cooperating conecting rods 62, 63 and 64, the latter of which connects with i thebell crank 65. Similar connecting rods for operating the damper doors are arranged at opposite sides of the furnace and may be operatively connected together by any suitable means, for example, shaft 86 which connects the pulleys 59 located on opposite sides of the furnace. When it is desired to manually increase the flow of com- The fan is interposed in the draft passage 5I leading When it is desired to bank the re, the cable 58 and rods- 62 may be disconnected from the motor arm 39 so that the damper 53 and the damper doors I8 and 39 maybe closed. The manually controlled damper 51 may then be opened slightly so as to permit a small amount of combustion air to be drawn through-the fuel bed by the natural or chimney draft.

Slag disposal As previously indicated in connection with the disclosure of the improved method, the ash and other noncombustible substances contained inthe fuel are removed in the form of liquid slag. This slag-is discharged from the bottom of the combustion chamber through a duct 58 into a cinder disposal pit 10 located below the floor level of the furnace room. A removable container 1I in the `form of a bucket is positioned in the pit 19 below the slag discharge duct 69, preferably a pipe 12 discharges Waste water into the container 'II so that the slag, when discharged from the combustion chamber, will fall directly into a body of water and thereby instantaneously be cooled. This cooling action on the slag, as it is discharged from the combustion chamber, forms it into small particles. When the container 1I is filled with waste water, it will overow into the pit 10 until the water reaches the level to be discharged through an overflow passage 13. When it is desired to empty the container 1I, a drain plug 14 is removed so as to drain the water from the pit 10. The bail 141iL of the container is then connected to a suitable hoist 15 to lift the container out of the pit as indicated in dot and dash-lines in Fig. 3. Thev hoist 15 is movably supported on the over-head frame structure by means of a carriage 16. The carriage operates on the outer flanges of I-beams 11, 18 of which the over-head frame is formed, Y

Removal of fuel hopper In order to facilitate repairing the grates or the masonry of the combustion chamber, the retort is slidably supported on a carriage 19 which is movably supported on the inner anges of said I-beams 11, 18. The carriage 19 is provided with depending frame members 89 and BI, the latter of which is inclined at an angle corresponding to the inclination of the axis of the hopper and slidably supports channels 82, 83 which are secured to diametrically opposite sides of the base ring A$4. Cables 8l and 85 connect the channels `B2,

with a windlass 86 mounted in the framework of the carriage 19. By rotating the windlass 88; the fuel hopper together with the base ring 34 maybe drawn upwardly and outwardly until the impellers 46 at the lower end of the hopper clear the base casting 35. The carriage 19 may then be moved lengthwise of the I-beams 11, 18 to any suitable position which will provide free access to the combustion chamber for purpose of repair.

I claim:

l. The method of burning coal which consists in forming a fire bed of substantially triangular` configuration in vertical longitudinal section'so that the volume of coal therein progressively increases toward the bottom of the bed, drawing' a stream of air through the upper portion of the opening of the combustion chamber to receive heat therefrom and deliver the coal into said bed from one inclined face to the other, igniting and burning the fuel in the lower portion of the bed and along said opposite inclined face, feeding coal to the inclined face of the bed at the air receiving side thereof and forcing it toward the burning inclined face of the bed, drawing air into the lower portion of the bed intermediate the inclined faces thereof, and agitating the coal adjacent said feeding side of the bed by moving the coal from a lower to an upper portion of the bed. V

2. A coal burning apparatus comprising means dening a heat distributing chamber, means dening a combustion chamber of angular configuration in vertical longitudinal section separate from the heat distributing chamber butv communicating therewith, means including a revolvable retort for delivering coal into'the combustion chamber to maintain it filled so as to form a fuel bed therein conforming to the shape of the combustion chamber and for agitating the coal adjacent the receiving end of the combustion chamber, impeller means carried on the retort for forcing the fuel through the combustion chamber, and means for passing' air lengthwise through the fuel bed to mix with the combustion gases liberated from the burning coal.

3. A coal burning apparatus including means dening a combustion chamber having a receiving opening for coal, a retort revolvably supported in the said coalreceiving opening of the combustion chamber and revolvable about an axis which inclines upwardly and outwardly from the combustion chamber and adapted to receive coal and deliver it into the combustion chamber, and impeller means carried by the retort for advancing the coal throughthe combustion chamber.

4. A coal burning apparatus including means defining a combustion chamber having a receiving opening for coal, a retort supported to extend into the said coal receiving opening of the combustion chamber and revolvable about an axis which inclines upwardly and outwardly from the combustion chamber and adapted to receive coal and deliver it into the combustion chamber, and impeller means comprising a series of wedge shaped members carried by the retort for advancing the coal through the combustion chamber.

5. A coal burning -apparatus including means dening a combustion chamber having a receiv ing opening for coal, a retort supported to extend into the coal receiving opening of the combustion chamber and revolvable about an axis which inclines upwardly and outwardly from the combus tion chamber and adapted to receive coal and deliver it into the combustion chamber,`impeller means comprising a series of wedge shaped mem-y lso combustion chamber, means for rotating the retort, and inwardly extending vanes fixed to the retort and movable therewith for agitating the coal contained therein during the rotation of Vthe retort, and a flange projecting inwardly from the side wall of the retort to partially close the open end thereof and form a gas retaining trap.

A'1. In a coal burning apparatus including means defining a combustion chamber having a receiving opening for coal, a retort for receiving coal and for delivering it into the combustion chamber and comprising a plurality of segments secured together and supported to extend into the coal receiving opening of the combustion chamber and revolvable about an inclined axis, means for rotating the retort, means at the junction of said segments deiining inwardly extending vanes movable with the retort for agitating the coal during the rotation of the retort, and a circular flange projecting inwardly from the side wall of the retort to partially close the open end thereof and form a gas retaining trap.

8. A coal burning apparatus including means providing a heat transfer chamber, means denning a separate combustion chamber formed with a coal receiving bowl having an upwardly and outwardly inclined axis and an upwardly and inwardly inclined passage leading from said bowl into said heat transfer chamber, there being a plurality of ducts connecting the upper portion of said combustion chamber with said heat transfer chamber, a retort for heating the coal before it enters the combustion chamber, a base ring for supporting said retort with the lower end of the retort extending into the coal receiving opening of the combustion chamber, the said base ring also defining an air passage for supplying air to the combustion chamber throughout the entire circumference of the coal receiving opening of the combustion chamber.

9. A coal burning apparatus including means providing a heat transfer chamber, a separate combustion chamber in the form of a bowl having an upwardly and outwardly inclined axis and an upwardly and inwardly inclined passage leading from the bowl into said heat transfer chamber, there being a plurality of ducts connecting the upper portion of said combustion chamber with said heat transfer chamber, a retort supported tc extend into said bowl of the combustion chamber and adapted to receive coal and deliver it into the combustion chamber, means defining an air passage communicating with the entire circumference of the coal inlet opening of the combustion chamber for supplying air to the combustion chamber at the lower end portion o! the retort, suction means for drawing air from said air passage through the coal, and means including a damper positioned in the ow path of said air and adapted to be moved toward and away from its closed position to vary the flow of air through the coal.

10. A coal burning apparatus including means defining a heat transfer chamber, means deiining a separate combustion chamber in the form of a bowl having an upwardly and outwardly inclined axis and defining also an upwardly and inwardly inclined passage leading from said bowl into said heat transfer chamber, a retort supported to extend, at its lower end, into said combustion chamber and adapted to receive coal and deliver it into the combustion chamber, means defining an air passage extending entirely around the lower end of said retort for supplying air to the combustion space throughout the entire circumference of the coal receiving opening of the combustion chamber, and grate elements arranged in close relation toeach other along a lower surface of said bowl to provide tuyre passages leading from said air passage into the lower portion of the combustion chamber.

DANIEL E. STAIR.

REFERENCES UNITED STA'TEB PATENTS '.Number Number Name Date Maxwell Nov. l, 1921 Sargent Jan. 9, 1923 Burg Feb. 22, 1927' lSchutz Jan. 31, 1928 Gainey et al. June 12, 1934 Hoffman Aug. 14, 1934 Kraeft July 2, 1935 Kraeft Apr. 20, 1937 Fulton Aug. 9, 1938 Lockwood 4 May 3 0, 1939 Raddatz June 20, 1939 Peitz Feb. 20, 1940 Casey Jan. 14, 1941 Fellows 'et al Sept. 15, 1942 Fulton -..1..-- Feb. 26, 1946 Sanford et al. July 9, 1946 FOREIGN PATENTS Countryv Date Germany May 2, 1923 Great Britain 1890 Great Britain Sept. 14, 1925 Netherlands sept. 7, 1933

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