US1389982A - Automatic stoker of the underfeed type - Google Patents

Description

M. RATEL. AUTOMATIC STOKER OF' THE UNDERFE-ED TYPE.

APPLICATION FILED OCT. 5,1920

Patented Sept. 6, 1921.

2 SHEETSSHEET 1.

M. RATEL- AUTOMATIC STOKER OF THE UNDERFEED TYPE.

APPLICATION FILED OCT. 5, I920. 1,389,982. e e fi p 6,1921.

2 SHEETSSHEET 2.

UNITED STATES PATENT OFFICEQ AUTOMATIC STOKER OF THE UNDERFEED TYPE.

Specification of Letters Patent.

Patented Sept. 6, 1921.

Original application filed March 30, 1914, Serial No. 828,423. Divided and this application filed October 5, 1920. Serial No. 414,836.

To all whom it may concern Be it known that I, MAURICE! RATEL, a citizen of the Republic of France, and a resident of New York, N. ,Y., U. S. A., have invented new and useful Improvements in Automatic Stokers of the Underfeed Type, (for which I have filed applications in France,

March 28, 1912, and July 5, 1912; in Great Britain, March 28, 1913, and in Germany, March, 1913,) which invention is fully set forth in the following specificationf This invention relates toautomatic stokers and, more particularly, to' automatic stokers of the undcrfeed type, and it has for its object to provide an improved device of this character which overcomes the serious defects and disadvantages inherent in automatic underfeed stokers heretofore employed. f;

It has heretofore been proposed to provide an automatic underfeed Stoker comprising a series of alternatingfuel retorts or troughs and downwardly-inclined twyers, together with means in each of said retorts for feeding fuel therethrough to the ,fuel bed. The stokers of this type heretofore suggested, however, have been more or less defective because their fuel Supporting surfaces have been steeply inclined, generally at anangle of about 30, so that the feeding of the fuel and solid products of combustion would be effected to a large extent, if not entirely, by the force of gravity.

p In the first place, a stoker of this type requires a relatively large space in a vertical direction and, therefore, is inapplicable to many furnace installations where it is impossible to raise the boilers or lower the boiler-room floor.

In the second place, a stoker of this type provides a bad distribution of fuel and, consequently, an imperfect combustion thereof owing to the unequal supply of air to different partsof the fuel bed :As gravity has been-relied upon to effect feeding of the fuel and solid products of combustion, the fuel bedhas taken a shape conforming at one side to. the fuel-supporting surfaces and at its opposite side to the angle of repose of the fuel and solid products of combustion, which is an angle of or more with ordinary fuels. This difference in the inclination between the fuel supporting surfaces of the stoker and the natural angle ofrepose of the fuel has therefore resulted in a fuel bed which varies greatly 'in thickness from top to bottom, being relatively thin opposite the uppermost portion of the twyers, relatively thick opposite the intermediate portion of the twyers and relatively thin opposite the lowermost portion of the twyers. This uneven distribution of the fuel has been accompanied by an equally uneven distribution of the air :-The air, tending to follow the lines of least resistance, has passed in excess through the thinneriportions of the fuel bed and in insufficient quantities through the thicker portions of the fuel bed. Consequently, this insufficient supply of air at the thicker portions of the fuel bed has resulted in incomplete combustion and the formation of carbon monoxid which escapes without combustion, owing to the inadequate air supply, and with a consequent loss of heat.

In the third place, the ashes and fuel tend to fuse, forming large lumps, which in turn tend to take a steeper angle than the normal angle of repose of the fuel, until, becoming detached, they produce a sudden movement of the fuel and solid products of combustion in the nature of an avalanche, which carries with it both fuel and solid products of combustion onto the dumping sections of the stoker. Here the unburned fuel is smothered in the ashes and slag and is carried into the ash pit and lost.

It has also been proposed to provide an automatic underfeed stoker of the above type with fuel-feeding members at both the top and the bottom of each fuel retort or trough. Devices of this type, however, have not overcome the difiiculties arising from the fuel tending to take its natural angle of repose while, on the other hand, the lower fuel-feeding member has pushed much unburned fuel from the retorts, where no provision has been made for supplying the same with sufficient air to insure proper combustion, directly onto the dumping sections of the stoker, where it is smothered in the ashes and slag and becomes extinguished and lost.

In fact, considerable fuel that has become well ignited while opposite the twyers is pushed onto the dumping sections of the stoker and, becoming smothered in the ashes and slag, also is extlnguished and lost. On

the other hand, this repeated feeding of inmovement of the fuel and solid products of combustion in the fuel bed and feeding progressively decreasing quantities of fuel to the successive portions from top to bottom of said bed, so as to provide proper distribution of the fuel and air in said bed and maintain thelatter of substantially uniform thickness.

Another object of this invention is to provide, in combination with fuelfeeding means of the character referred to, means at the rear of the fuel retorts or troughs, at the rear of the twyers, or both, whereby the fuel fed from the bottom of the retorts and distributed to the rear of the twyers will be supplied with sufficient air to insure its combustion.

A further object of this invention is to provide, in combination with fuel-feeding means of the character referred to, a receiving grate at the rear of the series of twyers and fuel retorts or troughs which is provided with an air supply decreasing progressively in the direction of the feed of the fuel, whereby unburned fuel reaching said grate may be properly supplied with air to support combustion, and which is also provided, if desired, with means-for the injection of moisture at the rear of said grate whereby the solid products of combustion may be e fectively cooled before reaching the dumping sections of the'stoker and the heat conserved in forming combustible gases.

A further object of' this invention is to provide, in combination with fuel-feeding means of the character refererd to, a receiving grate at the rear of the series of twyers and fuel retorts or troughs which comprises a plurality of movable grate bars that act in the nature of a sifter and facilitate a gegular advancing movement of the fuel Another object of this invention is to obviate the difficulties heretofore experienced from the rapid burning of the twyers by so constructing them that they may be effectively cooled.

A further object of the invention is to provide, in combination with an automatic underfeed stoker of the type referred to, means for simultaneously varying the rate at which the fuel and air are supplied thereto.

Other objects relate to the provision of an automatic underfeed stoker which is simple in construction, eflicient in operation, inexpensive to maintain, and economical in its use of fuel.

Broadly stated, the invention comprises an automatic underfeed stoker having a series of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, and a plurality of fuel feeding members having progressively decreasing capacity and disposed throughout the major portion of the length of each retort, said fuel feeding inembers being operatively con nected with the main, power shaft of the stoker, so as to feed progressively smaller or decreasing quantities of fuel to the fuel bed in substantially parallel directions. This progressive decrease in the capacity of the successive fuel-feeding members may be effected by rendering said fuel-feeding member of progressively decreasing stroke, or progressively decreasing size, or both. Said fuel-feeding members preferably afford supports for the fresh fuel, and thereby insure its continuous and'progressive distribution to the fuel bed throughout the major portion of the length of each retort and also, by their movement, produce an undulatory or wave-like motion in said fuel bed.

The invention is capable of receiving a variety of mechanical expressions, some of which are shown on the accompanying drawings, but it is to be expressly understood that the drawings are for purposes of illustration only and are not to be construed as a definition of the limits of the invention, reference being had to the appended claims for that purpose.

In said drawings:

Figure 1 is a longitudinal section through an automatic underfeed stoker embodying the present invention;

Fig. 2 is a' longitudinal section through another automatic underfeed stoker embodying the present invention; I

Fig. 3 is a partial plan to illustrate the disposition of apertures at the rear of the twyers and in the bottom of the fuel retorts or troughs, the twyers and retorts being shown diagrammatically, with the main and secondary fuel feeding members, grate bars and dumping plate omitted;

Fig. 4 is an enlarged horizontal section of one construction of twyer which embodies the present invention;

Fig. 5 is an enlarged horizontal section of another construction of twyer which als embodies the present invention; Fig. 6 1s a side new of another construction of twyer which also embodies the present invention; I

Fig. 7 is a face view of the twyer of Fig. 6';

- Fig. 8 is a horizontal section on the line 8-8 of Fig. 6;

Fig. 9 is ,a side view of a twyer built up of a plurality of separate bars;

Fig. 10 is a face view of the twyer of Fig. 9; and

Fig. 11 is a schematic view of means for automatically and simultaneously controlling the speed of the stoker and the admission of air. Y

, The present invention is applicable to a wide variety of boilers 'and forms of furnaces and, therefore: as it is not limited to any particular type of boiler or furnace construction, the details of the latter have not been illustrated.

In the form shown in Fig. 1, the automatic stoker consists of a series of alternating fuel retorts or troughs 1 and downwardly-inclined twyers 2 of any suitable construction. Said twyers accordingly provide downwardly-inclined fuelsupporting surfaces whereby the advancing movement of the fuel bed is effected with-theaid of gravity. The fuel is fed through each retort or trough 1 from a hopper 3 by a plurality of fuel-feeding members which, in conformity with the present invention, are of progressively decreasing capacity and disposed throughout the major portion of the length of' said retort. In the form shown in Fig. 1, thev fuel-feeding members comprise a main fuel-feeding ram or piston 4 and a plurality of secondary fuel-pushing members 5. The main fuel-feeding member 4 maybe reciprocated in any suitable way, as by a crank 6 rotated by a shaft 7. The connecting rod 8 from said crank to the member 1 is shown as a bell crank lever to 'the'depending end 9 of which is pivotally connected a rod 10 having its opposite end pivotally mounted at 11. A plurality of connecting rods 12 are operatively connected to said rod 10 and said connecting rods are in turn operativelyconnected to the secondary fuel-feeding members 5. As the rod 10 is stationarily pivoted at one end and has a range of movement at its opposite end equal to that of the main fuel-feeding memberl. each of the succeeding secondary fuelfeeding members 5 has a proportionately decreasing range of movement. whereby said members are of successively decreasing capacity and adapted to'feed progressively smaller quantities of fuel to the fuel bed. It is to be expressly understood, however, that any other suitable means for effecting a proportionate decrease in the stroke 'or capacity of the successive fuel-feeding members may be employed, if desired. Any suitable anti-friction means may also be employedto facilitate the movement of said fuel-feeding members.

As the plurality of fuel-feeding members are disposed substantially throughout the length of each fuel retort or trough and have substantially parallel movement in a horizontal direction, they operate to agitate the entire fuel bed, giving the same a waving motion as the reciprocating fuel pushers ness of the bed effected by said settlingmovement. Therefore the resultant of the progressively decreasing feed of the fuel from top .to bottom of each retort and the agitation of the entire fuel bed is to obtain a fuel' bed of substantially uniform thickness, whence arises a proper distribution of fuel and air and a substantially uniform combustion. This continuous agitationhas the further advantage of breaking up the fuel bed and preventing the formation-of large lumps of coke or clinker. Also, as the fuel bed is maintained at an inclination less than the normal angle of repose of the fuel, any sudden rush of fuel and solid )roducts of combustion down the slope is e ectively prevented.

Air is supplied the twyers in any suitable way, as through an air box 16 communicating with a pipe 17 which may lead from any suitable blower or other air supplying devices.

At the rear of the series of twyers and fuel retorts or troughs is a receiving grate, shown as composed of a plurality of movable bars 18 of any suitable construction. the same preferably having movement in the same plane and transversely to said twyers and retorts, and desirably alternate bars move in opposite directions. Said grate bars' ls may be actuated in any suitable way. as'by cams 19 rotated by a shaft- 2O driven through beveled gears 21 and belt or chain drive 22 from the main shaft 23. Said grate bars 18 preferably have an air supply which is decreased progressively from front to rear in any suitable way. as

diagrammatically illustrated by the size .of a

bar or bars this air supply may be replaced by a steam or other wet fluid injection, so that the moisture when coming in contactwith the heated clinkers will form combustible gases while. at the same time, cooling the solid products of combustion.

In the rear of the grate afforded by said bars 18 is a fixed or tiltable dumping plate for discharging the solid products ofv combustion into the ash pit 26.

The shaft T may be rotated from shaft 23 in any suitable way, as through the belt or chain drive 27 and"speed-reducing mechanism of any suitable construction in the housing :28.

In the form shown in Fig. 2, the fuelfeeding mechanism takes the form of a main fuel-feeding member or ram 28' and a plurality of secondary, wedge-shaped fuel-feeding members '29 of progressively decreasing size and mounted on a connecting rod 30 operatively connected to the main fuel-feeding member 28. Said fuel-feeding members 28 and 29 havea reciprocating movement parallel to the bottom 31 of the re tort 1. but each ofthe fuel-feeding members has a substantially vertical fuelpushing face and each of the secondary fuelfeeding members has a substantially hori- Zontal fuel-supporting face, as do the fuelfeeding members in the embodiment of Fig. 1. It will therefore be perceived that said fuel-feeding members in the embodiment of Fig. 2 are of progressively decreasing capacity and disposed substantially throughout the length of each retort, whereby, as

' in the embodiment of Fig. 1. they feed the air to insure its ignition. To this end the bottom plate 3t at the rear of each retort'is preferably provided with one or more apertures 35 for the passage of air to the fuel, and each of the twyers may also be provided with an extension plate 36 at its rearin which are provided one or more apertures 37 for the passage of air. Instead of using.

apertures in the plates 3-1 and 36, however,

suitable grate bars may be employed at the rear portions of the fuel retorts and the extensions of. the twyers. l his auxiliary supply of air at the rear of the fuel retorts and twyers insures that the fuel fed along twyers are preferably so constructed that.

their "surfaces are maintained relatively cool.

To this end they may be provided interiorly with partitions 38 for directing the incoming air into cooling contact with their upper or fuel-supporting surfaces 39 before it escapes through the lateral apertures 40,

as shown in Fig. 4, or in-addition they may have corrugated walls 41 to increase their cooling surface, as shown in Fig. 5. The provision of corrugations also has the additional advantage that the twycrs are formed with external recesses 42 in which the ashes may collect and form a protective layer.

The twyers may also be provided with apertures l3 in their upper or fuel-supporting faces, as well as with the lateral aper tures 40. as shownin Figs. 8 to 10, so that the entire surface of the. twyers may be cooled by the passage of air therethrough. This construction has the further advantage that the fuel-supporting surface of each twyer also functions as agrate so as to considerably increase the combustion rate without increasing the air pressure, or to maintain the same combustion rate with a. smaller air pressure or even enabling the stoker to work with natural draft. Said twyers may be either of unitary construction\ as shown in Figs. 6, 7 and 8. or they may be built up ofa plurality of separate bars 44 as shown in Figs. 9 and 10, in which eventv the separate bars may be held together inany suitable way.

It. is to be expressly understood that the grate bars may be-of any suitable cross section, as round, triangular, etc., and the apertures therein may be of any suitable shapeand of the same or varying section. Furthermore, any and all of these provisions for COOllIlg the twyers may be combined with means for cooling the same through the use of a steam jet, humid air, water spray, circulation of water, etc.

Any suitable means may be provided for supplying air, driving the stoker and vary ing the speed of said mechanism. When a steam engine or direct current motor is employed the speed may be varied automatically or otherwise in any suitable way, as by automatica-lly-controlled valves or an automatically-controlled rheostat. When an alternating current is used and especially when a three-phase current is employed, so that only slight variations of speed may be obtained by variation of the current, changespeed devices of any suitable construction may be applied to the air-supplying mecha nism and the stokers and also individually to each stoker-to secure a proper regulation of the speed. A change-speed box for ap-' 'tion for connecting the gear 46 with the driving shaft of the change-speed mechanism in the box 45, said clutch being normally pressed into operative position by the spring 54. The change-speed mechanism is shown as controlled by a lever 49 having a handle 50 which controls a' catch for engagement with the teeth 51 of the sector plate 52. Said lever 49 may have an ex te-nsion53 for engagement with the arm 53 of the bell crank 55, which in turn controls the movement of the clutch 47 .into and out of operative position.

- It is also desirable that the mechanism for changing the speed of the Stoker be connectedto the means for controlling the supply of air to the furnace, so as to maintain a constant relation between the quantity of fuel and the quantity of air admitted thereto. This isaccomplished in the structure diagrammatically illustrated in Fig. '11 by the connection of. the damper 56 in the air-- supplying conduit with the lever 49 of the speed-regulating device by a cable 57, a counter weight 58 being shown as connected to the arm 59 of the damper 56 to facilitate adjustment of the latter.

It is to be expressly understoodthat the term capacity as employed in the claims with reference to the fuel feeding members is to be construed as generic to fuel feeding 'members of successively decreasing feeding capacity whether effected by pro ressive decrease in size, stroke, or otherwise. While the constructions shown on the drawings have been described with considerable particularity it is to be expressly understood that the invention is not limited thereto, as the same is capable of being embodied in, a variety of forms. In lace of the crank mechanism shown for riving the fuel-feeding members an other suitable devices may be employed. he number, size, form, and inclination of the twyers and fuel retorts or troughs may also be varied in conformity with the fuel to be employed. Certain features of the invention may be employed without other featuresthereof, and changes may be made in details of construction, proportion and arrangement of parts without departing from the spirit of this invention. Reference is therefore to be had to the claims hereto appended for a definition of said invention.

- This application is a division of my application Serial No. 828,423 filed March 30, 1914, which has matured into Patent No. 1,366,098, dated Jan. 18, 1921, and which in turn is a division of my application Sr. No. 757,353, filed Mar. 28, 1913.

What is claimed is:

1. In an automatic underfeed stoker, a series of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, and means for feeding fuel through said retorts to said fuel bed comprisin a main fuel-feeding member and a plurality of secondary fuel-feeding members disposed substantially throughout the length of each retort, the successive members in each retort having progressively decreasing capacity in the direction of inclination of the fuel bed and substantially parallel movement to feed progressively smaller quantities of fuel to the fuel bed in substantially parallel directions.

2.' In an automatic underfeed stoker, a series of alternating twyers and fuel retorts or troughs providin an inclined fuel' bed whereby the fuel an solid products of combustion are fed downwardly with the aid of gravity, and means for feeding fuel through said retorts to said fuel bed comprising a main fuel-feeding member and a plurality of secondary fuel-feeding members disposed substantially throughout the length of reach retort, the successive members in each parallel movement in the same direction to feed progressively smaller quantities of fuel to the fuel bed.

3. In an automatic underfeed stoker, a series of alternating twyers and fuel retorts or troughs providing an inclined fuelbed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, and means for feeding quantities of fuel through said retorts to said fuel bed in substantially parallel directions and comprising a main fuel-feedin member and a plurality of secondary fuel-feeding and fuel supporting members disposed substantially throughout the length of each retort, the members in each retort having substantially parallel reciprocating motion and being of progressively decreasing capacity from the top to the bottom of the retort.

4. In an automatic underfeed stoker, a

series of alternating fuel retorts or troughs v creasing capacity, said fuel feeding memof each retort and having progressively decreasing capacity, said fuel-feeding members in each retort constituting supports for the fuel and having substantially parallel movement in the same direction to\ feed progressively smaller quantities to the fuel 6. In an automatic underfeed stoker, a series of alternating fuel retorts or troughs and downwardly-inclined twyers providing a downwardly inclined fuel bed, and means for feeding quantities of fuel in substantially parallel directions through said retorts to said fuel bed and comprising a main fuel-feeding member at the upper end of each retort and a plurality of secondary fuel-feeding members disposed throughout the major portion of the length of each retort, the members in each retort having substantially parallel motion of progressivelydecreasing stroke.

7. In an automatic underfeed stoker, a series of alternating fuel retorts or troughs and downwardly-inclined twyers providing .a downwardly inclined fuel bed, and means for feeding quantities of fuel in substantially parallel directions through said retorts to said fuel bed andcomprising a main fuel-feeding member at the upper end of each retort and a plurality of secondary fuel-feeding members disposed throughout the major'portion of the length of each res tort, the members in each retort being of progressively-decreasing capacity and having substantially parallel motion.

8. In an automatic underfeed stoker, a series of alternating fuel retorts or troughs and downwardly-inclined twyers, and means for feeding fuel through each of said re- .torts comprising a main fuel-feeding memher, a rod operatively connected to said main fuel-feeding member and pivotally mounted at its opposite end, and 'a plurality of'secondary' fuel-feeding members operatively connected to said rod and moved progressively-decreasing amounts. 1

9. In an automatic underfeed stoker, a series of alternating fuel retorts or troughs and downwardly-inclined twyers providing a downwardly inclinedfuel bed, and means for feeding quantities of fuel in substantially parallel directions through each of said retorts to said fuel bed and comprising a main fuel-feeding member and a plurality of secondary fuel-feeding members opera tively connected to said main fuel-feeding member and having substantially horizontal upper faces and substantially vertical fuel" gravity, and means for feeding fuel through said retorts-to said fuel bed comprising a main fuel-feeding member and a plurality of secondary fuel-feeding members disposed throughout a major portion of the length of each retort, said fuel feeding members in each retort having progressively decreasing capacity and substantially parallel and si-- multaneous feeding motion in the same 'direction.

11. In an automatic underfeed stoker, a

series of'alternating fuel retorts or troughs 'and'twyers providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, and means for feeding fuel through said retorts to-said fuel bed comprising a main fuel-feeding member and a plurality of secondary fuel-feeding members disposed substantially throughout the length of each retort, said members having pro ressively decreasing capacity and successive y adapted to feed progressively smaller quantities of fuel to the fuel bed in substantially paral lel directions. v

12. In an automatic underfeed stoker, a' series of alternating fuel retorts or troughsand downwardly-inclined twyers providing an inclined fue bed whereby the fuel and solid products of combustionare fed downwardlv'with the aid -of gravity, and a plurality of fuel-feeding members in each of said retorts adapted to feed the fuel in substantially parallel directions toward successive portions of said fuel bed and agitate the same to aid gravity in the movement of the fuel and solid products of combustion down the incline of said bed, said fdel-feed- 18; In an automatic underfeed stoker, a

ing members having progressively decreasing capacity to feed fuel to said bed in inverse proportion to the thickness of the bed arising from gravitational movement of the fuel and solid products of combustion.

14. In an automatic underfeed stoker, a series of alternating fuel retorts or troughs and downwardly-inclined twyers providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, and a plurality of fuel-feeding members in each of said retorts disposed throughout the major portion of the length of each retort and adapted to agitate substantially the entire fuel bed to aid gravity in the downward movement of the fuel and solid products of combustion, said fuel-feeding members having progressively decreasing capacity to supply fuel in substantially parallel directions to said bed in inverse'proportion to the thickness of said bed arising from gravitational movement of the fuel and solid products of combustion.

15. In-an automatic underfeed stoker, a series of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, and means for feeding quantities of fuel in substantially parallel directions through said retorts to said fuel bed and comprising a plurality of fuel-feeding members having progressively decreasing capacity in each of said retorts and successively adaptedto feed progressively smaller quantities of fuel to the fuel bed, the rear end of each of saidretorts being provided in its bottom with apertures for the passage of air.

16. In an automatic underfeed stoker, a series of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, each of said'twyers having an extension at its rear end provided with an aperture for the passage of air, and means for feeding fuel through said retorts comprising a plurality of fuel-feeding members in each of said retorts, said members having progressively decreasing capacity and successively adapted to feed progressively smaller quantities of fuel to the fuel bed in substantially parallel directions.

17. In an automatic underfeed stroker, a plurality of alternating twyers and fuel retorts or troughs, means for feeding fuel through said retorts comprising a plurality of fuel-feeding members successively adapted to feed progressively smaller quantities of fuel to the fuel bed, and a grate at the rear of said retorts and twyers provided with an air supply decreasing progressively in the direction of the travel of the fuel,

plurality of alternating twyers and fuel re-.

through said retorts comprising a plurality of fuel-feeding members successively adapted to feed progressively smaller uantities of fuel to the fuel bed, and a plura ity of reciprocating grate bars at the rear of said retorts and twyers and movable transversely of the same.

20. In an automatic underfeed stoker, a plurality of alternating twyers and fuel retorts or troughs, means for feeding fuel through said retorts comprising a plurality of fuel-feeding members successively adapted to feed progressively smaller quantities of fuel'to the fuel bed, and a plurality of're ciprocating grate bars at the rear of said retorts and twyers, alternate grate bars having movement in reverse directions.

21. In an automatic underfeed stoker, a plurality of alternating twyers and fuel retorts or troughs, means for feeding fuel through said retorts comprising a plurality of fuel-feeding members successively adapted to feed progressively smaller quantities of fuel to the fuel bed, and a plurality of reciprocating grate bars at the rear of said re: torts and twyers provided with an air supply decreasing progressively in the direction of the feed of the fuel, alternate grat bars having movement in reverse directions.

22. In an automatic underfeed stoker, a plurality of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel'and solid products of combustion are fed downwardly with the aid of gravity, said twyers having internal airdirecting walls for directing air into cooling contact with the heated surface of the twyers, and means for feeding fuel through said retorts comprising a plurality of fuelfeeding members in each of said retorts, said members having progressively decreasing capacity and successively adapted to feed progressively smaller quantities of fuel to the fuel bed in' substantially parallel direc tions.

23. In an automatic underfeed stoker, a

plurality of alternatingrtwyers and fuel re- 1 torts or troughs provi ng an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, said twyers having corrugated walls and providing external ash-collecting recesses, and means for feeding fuel through said retorts comprising a plurality of fuelfeeding member in each of said retorts successively adapted to feed progressively smaller quantities of fuel to' the fuel bed in substantially parallel directions.

24. In an automatic underfeed stoker, a plurality of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid '0f gravity, said twyers being provided with purality of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, said twyers being constructed to be cooled by fluid circulation, and means 'for feeding fuel through said retorts comprising a plurality of fuel-feeding members in each of said retorts, said members having progressively decreasing capacity and successively adapted to feed progressively 26. In an automatic underfeed stoker, a

plurality of alternating twyers and fuel retorts or troughs providing an inclined fuel bed whereby the fuel and solid products of combustion are fed downwardly with the aid of gravity, said twyers being each composed of aplurality of bars operatively re lated and constructed to be cooled by the flow of air therethrough, and means for feeding fuel through said retorts comprising a plurality of fuel-feeding members in each of said retorts, said. members having progressively decreasing capacity and successively adapted to feed progressively smaller quantities. of fuel to the fuel bed in substantially parallel directions.

27. In an automatic underfeed stoker, a

series of alternating twyers and fuel retorts or troughs, means for feeding fuel through said retorts comprising a plurality of fuelfeeding members in each of said retorts, said members having progressively decreasing.

capacity and successively adapted to feed progressively smaller quantities of fuel to the fuel bed, means for regulating the supply of air, means for regulating the speed of said stoker, and operative connections between said last-namedmeans whereby the supply of fuel and air may b varied simultaneously.

In testimony whereof I have signed this specification. 1

MAURI OE RATEL.

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