US2533330A - Stoker system, including fuel and air feed controls - Google Patents

Description

1950 w. M. SCHWEICKART E'I'AL 2,533,330

STOKER SYSTEM, INCLUDING FUEL AND AIR FEED CONTROLS 5 Sheets-Sheet 1 Original Filed Aug. 28, 1937 Dec. 12, 1950 w. M. SCHWEICKART ETAL 2,533,330

STOKER SYSTEM, INCLUDING FUEL AND AIR FEED CONTROLS 5 Sheets-Sheet 2 Original Filed Aug. 28, 1937 TML ATTORNEY wlNvENTorliiS XWM w. M. SCHWEICKART ET AL 33,330

EM, INCLUDING FUEL AND AIR FEED CONTROLS Dec. I2, I950 STOKER SYST 5 Sheets-Sheet 3 Original Filed Aug. 28, 1937 Ill- I v42 foray Deco 112, 1950 w. M. SCHWEICKART ETAL 2,533,330

STOKER SYSTEM, INCLUDING FUEL AND AIR FEED CONTROLS Original Filed Aug. 28, 1937 5 Sheets-Sheet 4 1 ill 5 Sheets-Sheet 5 STOKER SYSTEM, INCLUDING FUEL AND AIR FEED CONTROLS "J. 2 214 MW Dec. 12, 1950 Original Filed Aug. 28, 1937 Patented Dec. H2, 1950 STOKER SYSTEM, INCLUDING FUEL AND AIR FEED CONTROLS William M. Schweickart, Mentor, and Fred G.

Julyan, Euclid, Ohio, assignors, by mesne assignments, to iron Fireman Manufacturing Company, Portland, reg., a corporation of Oregon Application August 8, 1941, SerialNo. 405,894, now Patent No. 2,405,982, dated August 20, 1946, which is a division of application Serial No. 161,494, August 28, 1937, now Patent No.

2,306,189, dated December 22, 1942.

Divided and this application August 15, 1946, Serial No.

2 Claims.

This invention relates to improvements in automatic coal burners.

A primary feature of this invention is the pro-- vision of a burner that will burn different types of coking coal efficiently and economically, in small domestic installations as well as in larger furnaces, and which is adapted to utilize various sizes of coal down to slack.

The burner is arranged to provide a novel combustion zone properly related to the feed so as to assure efficient coking, ignition and combustion of the solid and gaseous components without danger of back coking or clinker formation at points that would interfere with the coal feed and efficient combustion, arranged moreover to avoid the back flow of gas under appropriate operating conditions.

Another object is to provide a burner that will have high combustion efficiency, particularly when burning bituminous coal. The burner is arranged to produce a relatively thin bed of burning fuel, and to eliminate difficulties with clinker formation and ash accumulation which would tend to interfere with proper combustion. The ash removal mechanism removes the ashes and small clinkers rapidly and uniformly Without interference with the fire bed, conveying them continuously to an ash discharge.

Another purpose is to improve the efficiency and control of the air supply to the fire. The forced draught is introduced in a zone at the top of the retort and outward over the grate,v

and is provided with an adjustment to meet the conditions of each installation as well as the varying fusion points and other characteristics of combustion of different types of coal. Under banking conditions provision is made for independent regulation of the air drawn by natural draught, permitting the eflicient and certain maintenance of a suitable fuel bed.

An eflicient electrical control system has been provided, which may be incorporated in combination with standard proven electrical devices. In general, the drive unit is controlled from the room thermostat and is protected by safety devices. An important feature of the invention is the provision of an efilclent, sensitive and reliable banking control cooperating with the burner construction and the banking air control to assure the maintenance of a. minimum fire by automatically providing fuel and forced draught accurately as needed.

An important object is to provide apparatus embodying features set forth herein which is simple, compact, strong, suitable for installation under widely varying conditions and economical in operation.

Other objects and advantages of the invention will appear from the following description considered in connection with the accompanying drawings in which Fig. 1 is a perspective view of the assembly;

Fig. 2 is a longitudinal vertical section through the burner;

Fig. 2a is a plan view of the burner with parts broken away;

Fig. 3 is a detailed side elevation of the grate drive;

Fig. 4 is a fragmentary view of the coal and air feed tubes and air control;

Fig. 5 is a fragmentary side elevation of the blower and air control viewed from the side of the assembly which is to the rear as shown in Figs. 1 and 4;

Fig. 6 is a diagram of an electrical control arrangement schematically applied to the burner assembly installed in a domestic furnace; and

Fig. 7 is a diagram illustrating the operation of the banking control switch shown in Fig. 6.

In the specific embodiment shown (Fig. 1) the apparatus comprises a drive unit B, a burner unit C, and an ash discharge unit D.

A coal collecter unit, not shown, is positioned in the coal bin and supplies coal to the coal feed tube 22 in which is positioned the coal screw 2|, with the collector unit driven from the coal feed screw 2 I. A suitable collector unit is shown and described in our Patent No. 2,233,085 granted February 25, 1941.

Where the conveyor tube 22 requires a bend, this is preferably made as an angle, for instance, a right angle, through a feed knuckle (not shown) provided for conveying the coal around the angle.

The drive unit B includes the motor with its 3 controls, the blower and air supply. the drive fortheooalfeedandashdischargescrews,the grate rotor drive and gas withdrawal construction.

The drive assembly is mounted on a base 12 provided with a. longitudinal cylindrical passage for the coal to which sections of the coal feed tube 22 are connected and through which the last section of the coal feed screw iI passes. Supported upon the base I2 is the motor I! having the rotor ll of the blower ll secured to one end of its shaft. A housing It surrounds the blower air inlet, and air is admitted to the housing by the air inlet tube 82. The other end of the shaft of motor 15 is connected to the ash removal shaft 8! through reduction gearing contained within the casing 86 and through a sprocket and chain drive including the chain OI which engages a sprocket mounted upon the ash removal shaft 89. These connections may include a clutch operable from the handle Ill extending outside of-the drive unit cover.

The burner unit C hereinafter described includes a rotating grate structure which is intermittently operated by reciprocating shaker rod III. A suitable mechanism is provided for imparting such reciprocating movement at the proper rate. In the form shown best in P18. 1, the sprocket engaged by chain SI and mounted on ash removal shaft as is provided with a suitable cylindrical face cam IIII enga i cam roller III rotatably mounted on the upper end of rocker arm II2 pivoted at its lower end to base 12. Pawl Ill is pivoted at one end on rocker arm II2 with its other end engaging ratchet Ill which is rotatably mounted on base 12 and is prevented from backlash by a silent detent cam III having an offset pivotal mounting Ilt on vertical web Ill of the base 12 arranged so that the unbalanced weight of cam II! will maintain its cam surface in looking engagement with the teeth of ratchet II4 to prevent backlash, lug Ill on cam II! being positioned to engage the upper face of web Ill when cam H5 is rotated out of engagement with ratchet II, preventing cam II! from being accidentally jarred or otherwise shifted into inoperative position.

Means for regulating the throw of pawl H3 and thereby varying the actuation of the rotary grate structure includes an upward extension I It on pawl Ill positioned to engage stop lug I adJustably mounted as by a slot and a locking screw on web III to control the length of the return throw of pawl III. The lu '20 acts to swing the pawl I I3 downward into engaging position with the ratchet I I4. Cam roller II I is suitably maintained in engagement with cam II, as by leaf spring I23 bearing against base 12 and rocker arm H2.

The intermittent movement of ratchet Ill, which in the form shown is actuated twice during each revolution of the sprocket engaged by chain I. is suitably transmitted to the ash grate, as by eccentric I24 mounted on ratchet Ill and carrying eccentric strap I28 on connecting rod I28 which may be connected to shaker rod III! by a suitable shock absorbing arrangement. For this purpose rod I26 may terminate in frame I21 in which the spring cage I-2l is mounted, including end flanges I29 in which shaker rod III is slidably mounted, between which flanges shock absorber spring I" is set under initial compression and maintained in compressed condition by compression collar III held in suitable position on rod I by stop pins I33 projecting fromshakerrod Illinpositiontoengagethe adjacent flange I20 and collar III under pressureofspring I. Collar Ill isheldagainst rotation by engagement with cage I28, and operates through clamp screw I82 to hold rod Ill in adlusted position. Cage II. is preferably mounted removably on frame I21. This shaker rod spring construction will allow the stoker to run even though the grates are jammed, the rest of the mechanism continuing to function normally and the placing of the absorber spring Ill under initial compression is important to quiet operation.

This rotary grate structure surrounds an inner retort of the burner unit C of the type in which the coal is forced upwardly through the bottom of the burner retort or pot structure. burning in the upper portion thereof and traveling over the edge onto the grate structure through which the ashes pass. In the arrangement disclosed the section of the coal feed tube 22 extending from the drive unit base 12 is clamped in the burner body I" and supplies coal to the throat ISI at the bottom of the fire pot I52, which preferably is tapered outwardly from throat ISI.

The lower portion of pot I52 may consist of a pot wall I53 integral with burner body I", and a frusto-conical pot liner I64 having a smooth, preferably enameled inner surface, fitting within wall I53 and resting on a suitable led e I" to provide a smooth continuation of the surface of throat IiI.

A pocket I56 extending beyond throat Iii concentric with the axis of coal feed screw 2| has mounted therein a reverse screw I51. One end of this reverse screw is connected to the adjacent section of feed screw II by a connecting shaft Ill and the other end is connected to a terminal shaft I which extends through the bearing I59 at the end of pocket Iii, the projecting end of shaft I" having a sprocket 23! mounted thereon by means of which the terminal shaft I60, reverse screw I51, connecting shaft I58, coal feed screw 2| and the mechanisms of the coal collector unit (not shown) are driven.

To provide for supply of air to the burning fuel, inlet air chamber IBI surrounds the pot wall I52, formed by bottom wall I62 and outer wall I63 and generally open at the top.

A suitable upper margin for the pot IE2 is provided preferably in separable form and is generally referred to as a retort. While the retort may be formed and mounted in various ways, it is advantageous to provide a retort base ring I which may perform a number of functions. In the form illustrated ring its is held in position by bolts Ii'l threaded into lugs I on outer wall I83 of air chamber ISI, and may have a sealed engagement therewith by employing an asbestos gasketdil. Base ring I66 may likewise form a closure for the junction between pot wall I" and pot liner I, the form shown having an annular ridge I'll engaging a seal ring I" of asbestos or the like located on the suitably beveled edges of wall III in liner I. The ring I I. is provided with openings Ill (Fig. 2a) to permit the air from air chamber III to pass upwardly to the retort.

The retort I12 is mmovably mounted on the base ring I and forms a continuation of the pot I52, being provided with air outlets or tuyeres for furnishing air in the most advantageous zone for efllcient operation. In the form shown the retort m is provided with an inner wall in form.

of base ring I66, and resting on an asbestos gasket I14 in a suitable depression in base ring I66.

The outer wall I16 slopes outwardly and downwardly to the grate structure, and rests on an asbestos gasket I16 in a suitable depression in base ring I86. The retort crown I11 provides an integral smooth curve between walls I13 and I16, and is preferably relatively narrow to prevent retention of material theron.

Suitable tuyere openings I18 extend through the retort I12 at appropriate points. It has been determined that the most advantageous construction comprises provision of a series of tuyre openings I18 in the upper part of the inner retort wall I13, preferably sloping slightly downward. and a smaller number of tuyre openings I18 extending through the upper part of the outer retort wall I15 at about the same level. The retort I12 is held in place by means which preferably permits its ready removal and replacement, such as hooks I19 which may be cast integral with the retort walls I13 and I15, and which engage the lower face of the retort base ring I86 through suitable retort lock openings.

The rotary grate structure located around the retort I12 is adapted to receive the burning coal and ashes which flow outwardly over the retort, sifting the ashes into a suitable annular receiver in which they are carried around the burner to a point of discharge. The various parts are carried by a rotor ring I8I which is rotatably mounted on the pot I52. The mounting of rotor ring -I6I on ball bearings is such that the parts may be readily assembled, the bearing will be easily accessible and the structure will function smoothly under the substantial variations in temperature and consequent expansion and contraction of the parts encountered under these conditions, the ball race being formed by cast surfaces. The arrangement comprises a ball race groove I82 in the inner face of the upper part of rotor ring III. An upwardly beveled flange I83 on wall I63 and a downwardly beveled flange I84 on base ring I68 are arranged to provide a ball race groove I85 cooperating with groove I82 to retain the balls I86. By the removal of retort base ring I66, the balls I86 will be readily accessible; and as the faces of grooves I82 and I85 are substantially at 90 to each other, their spacing permits smooth unobstructed travel of the balls under various conditions of expansion clue to changes in temperature.

The outer margin of the retort base ring I66 is provided with an apron I81 extending outwardly and downwardly over the upper edge of the rotor ring I8I, apron I81 providing a smooth path of flow for ashes around the ball bearing structure and beyond the outer face of rotor ring "I, the adjacent faces of apron I81 and rotor ring I8I being suitably shaped to provide a relatively slight clearance and prevent substantial amounts of ashes from reaching the balls I86, the opening I49 below said balls permitting any ashes or the like to fall out of the raceway. The annular pocket 233 below apron I81 accumulates ashes and an inner seal of ashes 234 is formed at the lower edges of the apron, restrictin the passage of air to the space above the grate.

In the embodiment shown a grate ring I88 is utilized, removably mounted on rotor ring I8I and adapted to receive removable grate segments I89. These segments are preferably fiat integral castings provided with an inner flange I90 extending into close relationship to retort base ring apron I81. Suitable slots permitting ashes to pass the segments I83 include the radial slots I8I, restricted marginal slots I92 in flange I88,

preferably angled inwardly in the direction of rotation, and the spaces left between the periphery of each segment I 83 and the adjacent parts.

Segments I89 are mounted on the grate ring I88 in suitable manner securel held in operation but permitting ready removal and preferably adapted to construction by casting. In the form shown each grate segment I89 is provided with two downwardly extending slightly elongated annular sockets I93 adapted to receive supporting studs I94 on the upper margin of grate ring I88. An integral locking tongue on the advance end of each segment I88 extends beneath a locking lug formed on the upper edge of grate ring I 88. Grate ring I88 may extend to a point higher than the lower edge of apron I81, the intervening space normally filling with ashes which form the air seal across the narrow slot between the apron margin and ring I8I.

The grate ring I88 is suitably mounted on rotor ring I8I to permit ready removal without atfecting the rigidity and reliability of the mounting under service conditions. A suitable arrangement is indicated best in Fig. 2a, and includes beveled wedge lugs I81 on rotor ring I8I engaging beveled wedgelugs I98 on grate ring I88 to force the grate ring downwardly into proper position by rotating it relative to rotor ring I8I; stop lugs I99 on rotor ring IN and removable locking slugs 200 fitting between stop lugs I99 and wedges I98 when the grate ring I88 has been turned into proper position.

The grate rotor structure is preferably provided with an ash table 204, receiving ashes which pass the grate segments I89 and conveying such ashes to a point of discharge. A plurality of ash table segments 205 forms a continuous annular platform around rotor ring I8I adapted to receive the ashes. Each table segment 205 is provided with an inner flange 206 extending inwardly and upwardly, resting on an annular shoulder 231 on rotor ring I8I, the abutting edges of the table segments 205 being preferably in overlapping relationship to provide continuity and accurate registration. The lower rim 208 of grate ring I88 bears against flanges 206 and securely locks the table segments 205 in firm fixed position when the rotor ring and grate ring wedge lugs are interlocked as above described. Table segments 285 may be accurately located by positioning lugs on rotor ring I8I engaging corresponding positioning recesses in segments 205.

An ash trough extends around and below the ash table segments 206, for the direct discharge of ashes from the ash table. The ash trough 208 has an outer wall 2I0, a bottom 2 extending beneath and slightly spaced from the table segments 205, and an inner flange 2I2 extending upwardly substantially beyond the lower face of table segments 205. Segments 205 are preferably provided with diagonally tangential ribs 2 I 3 which serve to plow outwardly toward wall 2I0 ashes which fall between ash table 204 and wall 2I0, preventing the ashes from escaping over flange 2I2 while avoiding any engagement between the rotating and fixed parts. The ashes brushed outward by the ribs 2 I3 accumulate at the outer edge of the bottom plate 2 and form an outer ash seal 26I at the periphery of the table 204 so as to restrict the flow of air to the space above.

The ashes carried around by ash table 204 are continuously discharged by a scraper 2I4 includassasao 2 ing an ash plow or vertical plate on the outer wall 2|. of the ash trough extending into juxtaposition to the ash table 224 and grate ring I" and deflecting ashes outwardly through a discharge opening 2" in wall 2" into the ash discharge pocket 2|! formed in said wall (Figs. 1 and 6). An ash discharge chamber 211 forms a downward continuation of pocket 2|. and houses the receiving end of the ash removal screw 2!! mounted on ash removal shaft 22 '(Fi 6).

A suitable arrangement is provided for supporting ash trough 222 and for connecting it to the furnace body. For convenience, trough 222 may be constructed in three segments, supported at the right of the burner (Figs. 1 and 2) by two bracket legs 220 overlying the two junctions of the segments and removably mounted on the burner body ISO to permit convenient mounting and disassembly of the ash trough 222. The remaining junction between segments 2|! overlying the coal feed tube 22 is supported by a bracket 22! on the burner body Ill, provided with a detachable clamp 222 overlying the junction and which may be detachably fastened to the bracket 2.

The upper margin of the ash trough 222 is connected to the furnace body to close the space between the body and the burner unit. This may be accomplished by providing a closure plate 224 resting on shoulder 22! formed at the upper margin of outer wall 212 of the ash trough, and extending outwardly to the furnace walls. A suitable filling or lagging 226, such as furnace cement or the like, may be employed to fill the spaces between plate 224 and the furnace walls, which are shown as comprising the usual water leg 221 of a domestic furnace. Plate 224 may be locked on shoulder 225 by segmental locking plates 222 fitting into an annular recess 222 in the upper margin of the outer wall 212 of the ash trough and provided with a longitudinal rib 222.

The mechanism for rotating the grate unit employs an intermittent drive, imparting a periodic impact to the rotating structure, as such an arrangement serves to break up the fuel mass and to facilitate the sifting of the ashes and small clinkers through the grate. In the construction shown the shaker rod ll! extends beneath the ash trough 202 and is pivotally connected at its end to the lower end of a feed dog arm 2 extending upwardly between the air chamber iil and the grate rotor ring 181 and having at its upper end a feed dog 242 projecting laterally between the support flange 242 on the inner face of rotor ring I2 I, and rack 244 on said ring overlying flange 242. The feed dog 242 is provided with a rocking face 245 riding on flange 242, and suitable teeth 242 at its forward end adapted to engage rack 244. The arrangement is such that when the shaker rod I09 is shifted to the left of Fig. 3 the dog 242 will be rocked on face 245 until teeth 244 engage rack 244, further movement of the shaker rod is serving to rotate ring l8l and the grate parts mounted thereon, while ring I21 will be free from dog 242 at the end of such stroke and during the return stroke of shaker rod I29 owing to the disengagement of teeth 246 when the dog 242 is rocked in the reverse direction by continued travel of the grate rotor ring I21 under its own momentum or by the return travel of shaker rod I02.

To prevent reverse rotation of the grate ring Ill and associated parts a detent dog 241 is provided on detent arm 242 pivotally mounted on stud 242 on the burner body III at any convenient circumferential point and held yieldably in operative position as by counterweight 2".

Figs. 4, 5 and 6 show the air suppl and control system between the blower 12 and the burner unit C. The volume of air from blower 12 is suitably regulated, as by butterfly damper 224 mounted in air control housing 2" on spindle 222 preferably provided with suitably locking means, the form illustrated having a locking disc 241 mounted on the end of spindle 224 at the rear of housing 2" (Fig. 5) and held in adjusted position by locking knob 264 threaded on screw stud 2" extending through concentric slot 212 and mounted on housing 2".

Means are provided for indicating the now of air from blower 12, for preventing backflow into the blower system from the burner unit C, and for permitting a regulable flow of air to the burner unit when the blower is not in operation. These functions may all be performed by a single mechanism comprising a valve flap 211 fixed to pivot spindle 212 located in the upper part of a. section of the air control housing 224 in advance of damper 284 and engaging valve seat 212, which is preferably inclined in the direction of air flow from the blower. The end of spindle 212 may be bent downwardly outside of housing"! to form a pointer 214 serving in conjunction with suitable marks 215 or the like on the outer face of housing 265 to indicate the position of flap 2".

To arrest valve flap 2" at a predetermined preferably variable distance from seat 212 we provide a natural draft regulator spindle 212 threaded in housing 265, provided with laterally extending stop arm 211 within housing 244 positioned for engagement with the face of flap 2" and serving as a variable stop for arresting the downward movement of flap 2" at any point between the valve seat 212 and the maximum desired opening of flap 21! by rotation of spindle 212 by means of knob 212. spindle 218 being frictionally held in adjusted position as by spring washer 212.

The air control housing 2" is connected to a suitable air duct 2" running to air inlet chamill) her 2 (Fig. 5) in the burner body Ill, and merging, around the casing for the coal feed passage, with the air inlet chamber ICI to provide a generally tangential air feed adapted to distribute the air evenly throughout the air chamber iii and thence to tuyere openings I12.

A suitable arrangement is provided for automatically removing the ashes from the burner unit C and discharging them at an appropriate point, the construction shown including an ash removal conveyor .nd an elevator for transferring the ashes from the conveyor to a suitable discharge point. In the form illustrated the ashes are removed from the ash discharge chamber 2 I 1 by ash removal tube 22! mounted in the burner body I50 and forming a continuation of chamber 211. Tube 225 extends to an appropriate point and is shown as terminating adjacent drive unit B (Fig. 1). At this point a suitable elevator unit D is positioned to receive the ashes. A convenient construction is disclosed, employing an arrangement in which the ash removal tube 225 terminates in an elevator pocket formed in elevator base 2". Ash removal screw Ill terminates at the pocket while the shaft 22 on which the screw is mounted extends through the pocket and a suitable bearing at the opposite side of the elevator base 222, and thence to the drive mechanism as already set forth.

An elevator tube 222 is mounted in elevator wardly in any desired direction to permit discharge at any appropriate point dictated by local conditions, the angle of tube 290 being readily adusted by clamping base 288 in any desired rotated position about ash removal tube 285 through a suitable clamping screw. An elevator screw is positioned in tube 290 to pick up ashes discharged into the elevator pocket and raise them in tub'e 290 to a discharge at the upper end of the tube.

A suitable discharge arrangement is provided at the upper end of elevator tube 290. This may comprise a discharge head 305 mounted on the upper end of elevator tube 290 and carrying an upper bearing for the elevator shaft. Head 306 is provided with suitable spout discharge means, the illustrated construction employing two dis charge spouts at an angle to each other, each of which may be provided with a flexible tube 3H) clamped thereto for directing the ashes to any suitable receptacle, such as ash can 3 (Fig. 1). A suitable arrangement is provided for driving the coal feed screw 2| from shaft 89. In the arrangement indicated shaft 89 extends through a bearing in chamber 2|! and a bearing on a bracket on burner body I50, and drives coal feed screw 2| through a sprocket on shaft 89, sprocket chain 240 and sprocket 239 mounted on shaft ISO to which the coal feed screw 2| is connected.

While various proportions and designs may be employed in the different parts of the apparatus disclosed herein, the proportions are of importance in various parts, and particularly in the burner structure, the size and proportions of the- I pot, retort, grate segments, ash slots in the spacing thereof, having been determined after substantial experiment as adapted to most efficient operation with coking bituminous coal; and the drawings herein are drawn to scale to show the proper dimensional relationships between the various parts.

A suitable electrical control arrangement is illustrated in Fig. 6, and may be of the type in which the motor 15 is operated at full speed at 1 suitable intervals, though the invention is not necessarily restricted to a control of this type.

Motor 15 is connected to the line 320 by motor circuit 32l in which suitable motor protective devices are located, such as the overload cutout 322 and the thermal type cutout 323 which may include a heating coil 324 and a bimetal strip 325 adjacent thereto. The thermal cutout 323 may be mounted directly on the motor so that it may be affected rapidly by all conditions which cause overheating of the motor.

The motor circuit 32l includes the upper contacts 326 of duplex relay 321 whose coil 328 is in line 329 passing through the secondary of the low voltage transformer 330 whose primary is connected across the main line 320. The main secondary lead 329 carries the protective and control devices in the heat generating apparatus, which in the present instance is illustrated by a domestic hot water furnace 33!. In the form illustrated the line 329 carries a high point cutout switch 332 operative to break the circuit when the heating medium has reached a predetermined temperature or pressure, and this line 329 also carries the banking control switch unit 333 hereinafter described. Line 329 continues to the lower contact 334 of a room thermostat 335 of the type which includes a bimetal strip 336 operative'when the room drops below the desired temperature to close contacts 334 initially and T5 t e c pe of such gases.

10 after a further temperature drop to close the connected upper contacts 331, thermostats of this type being well known. a

The contacts 334 and 331 are connected through strip 338 and holding circuit line 333 with the lower contacts 339 of relay 321 which connect with the main circuit 329. The upper room thermostat contacts 331 are connected through shunt circuit line 340 with the line 323 at relay 321.

The banking control switch unit 333 is provided with two switches, a bank switch arranged to start motor 15 when additional fuel and air are required during banking periods, stopping motor 15 automatically after a suitable period; and an out switch arranged to stop motor 15 automatically if its operation under control of the bang switch does not result in a suitable pickup of the fire. These switches are operated by a thermal element located suitably for prompt andsensitive reaction to changes in the temperature of the fire. There are extreme diflerences in such temperature between periods of maximum operation and the low fire bed which it is desirable to maintain under banking conditions when the effort is simply to maintain a minimum heating as in domestic installations in spring and fall.

Electrical control apparatus regulating the operation of motor 15 in connection with the house thermostat system may have appropriate parts thereof mounted as shown in control housing 143 (Fig. 1) carried by a bracket on drive casing 86. It has been found advantageous to locate the thermally responsive element of the banking control apparatus in the combustion chamber 34! at a distance from the fire sufficient to permit the employment of a sensitive thermal device which will operate accurately with slight changes in temperature. For instance, such device may be located upon or at the furnace door mounted in suitable position to be directly affected by both radiation and convection from the fire, without being influenced by various factors affecting temperature at other points in the furnace. Specifically, it has been found that the absorption and radiation of heat by portions of the furnace such as the water legs 221 and 342, the variations in draught due to dampers and stack openings such as those shown at 343, and other variations in draught and temperature conditions seriously affect a sensitive thermal control unit located in the furnace at points other than the combustion chamber 3.

In the form shown the thermal element comprises a bimetal coil 345 arranged to extend through a suitable opening in the furnace door or other part of the furnace into position in the combustion chamber 34| where there will be no obstructions between thermal coil 345 and the fire in retort H2.

The thermal cell 345 is connected at its rear end to rotary switch rod 351. Switch arm 358 is centrally mounted on the end 01' rod 351 and is provided at its lower end with a clip carrying the mercury type bank switch 360. The mercury type out switch 36I is carried by a clip which is referably mounted on arm 358 by means permitting the angular adjustment of switch 36l relative to switch 360.

Under certain circumstances, and particularly when burning certain types of coal, gases may be forced back through the coal feed tube 22, and an arrangement is provided for preventing Such an arrangement or flowing qualities of coahlifia1 this point.

a,sss,sao

lect. and means for conducting the gases from the trap to a suitable discharge. In the preferred arrangement the gases are conveyed to the burner. Owing to the relatively low velocity of such gases it has been found that under certain conditions there is a tendency for fine solid particles to accumulate in the return pipe and eventually to clog the pipe. The preferred form therefore includes means for preventing such accumulation of dust and the like, and for returning the gases to the burner or elsewhere by positive means, such as a suitable supply of air, which may be taken from the blower system.

An arrangement of this type is embodied in the preferred form illustrated herein, and is,

shown best in Fig. 4. It includes a fresh air connection I35 with the outlet of blower 18 connected by air pipe I36 and return bend I31 with Jet nozzle Ill extending through a wall of the gas pocket I formed in the upper face of the coal feed passage I! in base 12. The fresh air connection I thus utilizes a higher pressure from the blower than can be found anywhere beyond the damper control. A gas return pipe I extends through the other side of pocket I39 in alinement with nozzle Ill and spaced therefrom by a distance suitable for obtaining an injector eflect under the conditions of air pressure and dimensions employed in the arrangement. The gas return pipe I40 is connected to the burner unit 0 at the ash discharge pocket 2|. Gas pocket I" is sealed by\ a removable cover Ill.

While the apparatus is adapted for use with various types of coal it has been particularly designed to solve certain special problems encountered in the burning of bituminous coal, which has special characteristics affecting its collection, transportation and combustion.

The burner unit C is particularly designed to provide thoroughly emcient combustion both under active operating conditions during coal feed and operation of the blower, and under banking conditions. There is also secured a careful balancing between the rate of coal feed, the rate of. air supply and the combustion characteristics of the coal, both as to the time required to burn to ash and the volatilization of combustible gases. The latter problem is especially important in the burning of bituminous coal, and involves likewise the formation of coke, which heretofore has been a source of serious difliculty and obstruction due to the tendency of the coal to coke back into the feed zone, interfering with the operation of the feed mechanism and frequently causing complete stoppage of the machine. The design also contemplates the effect of oil which is frequently used for dust prevention.

The rotating element I51 provided at the side of the throat opposite to the discharge end of the coal feed tube serves to prevent the coal from forming a packed mass at this point, and thereby increasing notably the facility with which it may be forced upwardly by the horizontal pressure of the feed screw. In one sense it may be said that this auxiliary screw increases the relative fluidity In the preferred form the rota g element is in the form of a reverse screw exerting a counterbalancing horizontal pressure the coal discharged by the feed screw while 1 kewise preventing the formation of a solidly packed mass of coal, the result being that the coal will travel upward as gradually as may be desired without exert g any pressure whatever on the surfaces opposite the coal feed tube discharge. The reverse screw may be arranged to impel coal continuously away from the feed screw bearing. which may therefore be of any desired type. The elimination of the tendency to pack the fuel in throat III furthermore permits the maintenance of fuel feed in tube 22 at substantially less than the full capacity of the tube as already indicated since substantial back pressure on the fuel at the burner owing to the resistance caused by forcing the fuel upward under previous conditions causes the coal to back up along the feed screw; and even if feeding at less than coal tube capacity is attempted, substantial back pressure at the burner and the resultant accumulation of coal in the tube will make it impossible to operate the feed tube 22 partially filled at any point within a substantial distance of the burner. With the construction illustrated however the feed tube is filled for only a short distance from the burner. an arrangement which not only reduces to a minimum the power necessary for feeding at this most exacting point, but which also is desirable since a full feed tube 22 for a short distance from the burner is serviceable in forcing the gases to travel upwardly through the burner and not back through tube 22. V

In burner retorts of the prior art difficulties have been encountered because of the tendency of the coal under certain conditions to burn down in the pot toward the feed screw, resulting in the formation of coke and clinkers which obstruct the feed and burning of the coal and may result in breakage or stoppage of the mechanism. The travel of the coal upwardly in the pot may likewise be obstructed by the formation of clinkers and the like which adhere to the pot walls, and by mechanical obstructions provided by the wall surfaces. In the present construction a retort is provided in which the zone of active combustion is restricted to the upper portion, and which extends downwardly for a sufilcient distance below the lowest point of air supply so that the fire will not reach the region where the formation of clinkers, coke and the like will-interfere with the feed mechanism. Any clinker formation developing will be prevented from adhering to the not by the smooth liner I but will be forced upward and broken up by the incoming coal.

Under full draught conditions the relation between the coal feed and the rate of combustion is such that the burning fuel overflows gradually across the retort I I2 and over grate segments Ill, and may reach the walls of the furnace. The relatively slight projection of the retort I12 above segments Ill facilitates the lateral flow, and is particularly advantageous in bituminous coal combustion in which the incandescent coke is more or less fluent, the arrangement permitting the formation of a relatively wide thin fire which produces maximum eificiency, rather than a high fire above the retort. The rate of combustion will naturally increase with the spreading of the fire until it will equal the rate of coal feed when the fire has reached its maximum area at the walls of the furnace. The inner tuyere openings I'll assure full combustion of gases which pass upwardly from the coking zone and provide an adequate supply of air for full combustion, the outer tuyere openings in wall I'll assisting if necessary in the combustion of the portion of the fire outside of the retort I12. The spreading of the fire is facilitated by the unusual power of the upward thrust of the coal, which likewise assaaao 13 serves to scour away any clinkers which may tend to form on and adhere to the surface of the pot structure or retort I12.

When the drive unit is cut off and the fire op crates under banking conditions, the portion of the burning coal beyond retort I12 will grad-- ually burn up. and if banking conditions are maintained for a sufficient period, the fire area will gradually contract toward retort I12. Eventually the fire may contract to a zone in the upper part of retort I12 limited in depth by the distance that air will penetrate from tuyere openings I18. This arrangement, limiting the bank tuyere to a zone at the top of the pot substantially spaced from the feed worm 2i, eliminates the possibility of coking back under banked conditions, a serious difiiculty with prior arrangements. At the same time a small zone of definitely burning fuel is maintained so that when the drive unit is again started and the coal feed is resumed, there will be no difiiculty about kindling promptly the green coal that is more or less abruptly forced upwardly in the pot I52.

When operating under banking conditions air is drawn through the tuyere openings I18 by the ordinary stack draught in a manner similar to The arrangement likewise is adapted to minimize the tendency to form coke in the lower portion of the pot where it might interfere with screw 2| through the depth of the pot, the aircooled walls and the double-wall construction. If however coke should form in throat I51, it would not wedge between the screw and the end of the feed passage, as in prior arrangements, but would tend to be broken up by the rotary action of the feed screw 2| and reverse screw I51.

The rotary ash collecting unit is arranged to remove accumulations of ashes with a minimum disturbance of the fire bed. This operation is facilitated by the smooth-surfaced grate segments I89 and the intermittent shaking action imparted thereto. The formation of the described type of fire bed likewise facilitates the scouring of fine clinkers from the retort I12 and their discharge on to segments I89, which may be provided with slots sufiiciently large to receive the small clink ers as formed and to maintain a clean fire even under conditions which operate the burner at infrequent intervals. The ashes are effectively sealed in the ash receptacle and readily discharged from the burner in a manner already indicated.

Any gas which is formed will normally be generated so high in the pot I52 that it will tend to fiow upwardly and to be burned; but in case gas is forced back through coal feed tube 22 it will be positively returned to the ash pocket 2H5 by the action of jet nozzle I38, and will pass upwardly to combustion past the grate segments I39. This arrangement will also provide a slight air feed outside of the retort I12 which will be operative to some extent when the blower 18 is not running, since the natural flue draught of the furnace will exert a certain suction effect on the gas return pipe I40. This arrangement also prevents any tendency for dust to collect in the gas return line. It may be noted that when the valve flap 2" is allowed to fall upon its seat it provides positive means for preventing gases from the combustion zone from'returning through the blower structure, if conditions should arise that demand such an arrangement.

The operation of the arrangement for conveying the ashes to a suitable point of discharge will be apparent from the detailed description. The construction is such that the ashes may be discharged at any desired point, and are kept completely housed in conveniently located conveying tubes.

The drive, operated by a single motor and compactly arranged, is constructed so that the blower may be operated without the coal feed, which may at times permit operation by hand firing in cold weather pending repairs to the coal feed mechanism. The clutch is likewise arranged to permit throwing in the coal feed and ash removal mechanism abruptly after motor 15 is up to speed, exerting a sudden impulse that may be valuable in dislodging a slight obstruction. The apparatus is l kewise arranged so that the motor 15 will be stalled before breakage of any'of the drive parts, allowing the electrical system to throw out the motor circuit and take care of emergency conditions without damage to any part of the machine.

The blower structure has been carefully arranged to give rapid and accurate control of an adequate supply of air at all times without the usual excessive intake noise.

The general operation of the electrical control system will be understood from the specific description. Assuming that the building is at or above the desired temperature for which the room thermostat 335 is set, the motor 15 will be out of operation, since contacts 334 and 331 of thermostat 335 will'be open and relay 321 will consequently be de-energized. opening the motor circuit. at the upper contacts 326. When the thermal element 336 contracts due to reduction in room temperature thermostat contacts 334 will first be closed; and continued reduction in temperature will thereafter close contacts 331, completing the circuit between the line 329 and the shunt line 340, closing relay 321 and starting motor 15. At the same time the contact 339 of relay 321 will be closed; and as thermostat contacts 331 open when the room becomes warmer, motor 15 will continue to operate since the secondary circuit through line 329 will be completed by the holding circuit line 338 until the room is warm enough to open thermostat contacts 334, whereupon relay 321 is de-energized and motor 15 will stop. A sudden excessive load on motor 15 will open cutout'322, while heating of motor 15 for any reason will operate thermal cutout 323, affording full protection to the motor. If the temperature of the heating medium should reach a point beyond which it is dangerous to continue, the high point cutout 332 will operate to break the main secondary circuit line 329, open relay 321 and stop motor 15. It is noted that as soon as the heating medium returns below the danger point said circuit will be closed and the motor again started, assuming of course that the room thermostat 335 is in appropriate position with the contacts 334 and 331 closed.

The banking control unit 333 is arranged for operation at times when the room thermostat 335 is open; and such operation may be readily understood from Fig. 6. The thermal coil 345 will naturally expand and contract in accordance with the heat given off by the fire, thereby rotating switch rod 351 and the switch structure mounted thereon. The coil I is constructed and arranged so that the bank switch I" will be appropriately positioned with the mercury out of contact with the terminals when the temperature in the chamber I is above a predetermined minimum banking temperature. As the temperature in said chamber approaches such banking temperature rod 351 is rotated by thermostat I to turn the arm-carrying switches I and Ill and swing switch "I downwardly until the mercury flows to the contacts of both switches when such banking minimum temperature is reached thereby closing an auxiliary circuit including conductor I26, switch I32, switch contacts I", III, conductors 312, l, coil 32' of relay 321 and conductor 329. The resultant closing of switch I" completes a circuit through the banking shunt line 312 with the shunt circuit 3 and through the out switch Iii with the main secondary line I29, energizing relay 321 and starting motor IS. The resulting increase in heat from the fire will rotate the switch rod 351 in the opposite direction until bank switch I" is turned off by the flow of mercury from its terminals at the maximum banking temperature, thereby opening relay I21 and stopping motor 315. It is noted that this operation is independent of the thermostat 3", and is effective only when said thermostat is not closed.

The arrangement consequently serves to maintain a minimum banking fire independently of the house temperature control without interfering with the operation of such control'and effective when such control is not active. It permits highly accurate and eilicient regulation of banking conditions, since it may be constructed for any desired range of banking temperatures, and the temperatures at which it operatesmay be readily adjusted by shifting arm 358. Furthermore, it is located at a point where it is affected promptly and directly by very small changes in the banked fire, and is sensitive to slight variations in temperature.

Out switch "I is arranged and connected to stop motor if the fire temperature should not rise after the motor has been turned on by switch 380. If the temperature in combustion chamber 3 drops to a predetermined extent below the minimum banking temperature, switch rod 351 will continue to rotate and tilt banking switch "i until at a predetermined temperature the mercury will flow away from the contacts of switch I, breaking the circuit between bank switch 360 and line 329 and opening relay 321.

This arrangement is utilized to provide manual regulation of the coal feed and forced draught during starting of the fire. This is accomplished by pressing the button Ill, closing contacts I" and 3N, short-circuiting the out switch I and starting motor 15, which runs as long as button 3H is pressed. If the fire ignites properly the heat will promptly affect thermal element 345, which may be so sensitive that even very slight heat from the fire will be sufficient to close out switch I and permit release of button 3'". In igniting bituminous coal fires this period is extremely short, and may be two minutes or less, since the unit 333 preferably operates at very low temperatures and thereby reduces to an absolute minimum the amount of coal burnt during non-heating bank periods.

The operation of control unit "I cooperates with the setting of the main air damper 204, which controls the forced draught, and the setting of valve flap 2', which controls the natural 16 draught: l0 there is thus provided a novel and highly efficient banking arrangement by employing a sensitive control directly responsive to changes in a very low fire, with an air regulating means especially suited for the maintenance of the tire steadily at such low point, combined with a forced draught regulation which appropriately :ilixlnilds up such small 'i'ire properly in a brief The air supply for the fire is intended to come mainly from the tuyere openings of the retort ring I", and this supply serves in addition to maintain a proper cooling of the retort. Under running conditions substantially all of the air from the fan passes through the air spaces around the retort tending to cool it and prevent overheating and improper coking and clogging of the rising column of coal. Under banking conditions the natural draft draws air through the partly open valve flap ill and damper 2 into the spaces around the retort and through tuycre openings H8 together with some slight leakage from the coal tube through pipe I" and opening 2" into the space below the grate. There may also be some seepage of air through the ash seals for the rotor ring Ill and ash table 2. In this way the air supplied below the grates is negligible in amount, substantially the entire supply being through thetuyere openings of the retort both under running and banking conditions.

This is a division of our application Serial No. 405,894 filed August 8, 1941, now Patent No. 2,405,982 granted August 20, 1946, which is in turn a division of our application Serial No. 161,494 filed August 28, 1937, now Patent No. 2,306,189 of December 22, 1942. 7

We claim:

1. In a stoker combustion system including a flue for combustion gases and a retort expanding and opening upward and having a surrounding rotary grate ring structure adapted to underlie a layer of burning fuel from said retort, means forming a combustion chamber above said retort and grate ring adapted to be subjected to subatmospheric pressure by virtue of the fiue draft, acoal supplying means for said retort and air supplying means comprising inwardly directed tuyres in the upper portion of the retort and passages connected thereto, air seal means around said retort including stationary parts cooperating with said rotary grate ring structure to retain ashes in sealing ring formation acting to restrict the air flow to that which passes through said tuyeres to the combustion chamber, control means for said air supply automatically regulating the air seepage through said tuyeres under the action of said flue draft, means for raising the pressure of said air supply through said tuyeres comprising a blower in said air passages and means for regulating the air fiow therefrom, and room and combustion chamber thermostats actuating said coaland air pressure supplying means to increase or decrease the coal and air supplies at predetermined respective minimum and maximum temperature settings.

2. A stoker combustion system as set forth in claim 1 in which the control means for the air supply comprises a fixed member set to regulate the air flow under pressure and a movable member floating to different positions under the pressure of said air flow.

WILLIAM M. SCHWEICKART. FRED G. JULYAN.

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