US2365679A - Underfed stoker - Google Patents

Description

J. A. CASEY 2,365,679

- UNDERFED STOKER v Filei Nov. 25, 1941 3 Sheets-Sheet 1 J. A, CASEY UNDERFED STOKER Dec, 26, 1944,

3 Sheets -Sheet 2 I Filed Nov. 25, 1941 Dec. 26, 1944. J. A. CASEY UNDERFED STOKER Filed Nov. 25, 1941 3 Sheets-Sheet 3 Patented Dec. 26, 1944 UNITED STATES PATENT OFFICE UNDERFED STOKER James A. Casey, Wilkes-Barre, Pa.

Application November 25, 1941, Serial No. 420,413

Claims.

This invention relates to automatic coal stokers of the type havin an underfed burner comprising' an inverted frusto-conical casing defining a fuel chamber and surrounded by a jacket in communication with the conduit of a blower, the easing having circumferential narrow louvers at different levels for admitting air from said jacket into the fuel mass in said fuel chamber. Said burner is, of course, in a combustion chamber which communicates with a chimney.

Coal is fed from a, bin, hopper or other form of coal supply, to the lower part of the burner by a conveyor in a coal tube; the coal particles being generall of small size and accompanied by considerable dust. A layer of ashes of varying. thickness may overlie the combustion bed in the fuel chamber and constitutes more or less of an obstruction through which the air entering through the louvers must be forced.

As heretofore constructed, such stokers have certain drawbacks in operation. The layer of ash may sometimes create back pressure, causing the forced draft to blow the products of combustionback through the coal tube into the bin.

hopper or coal box as the case may be, letting the gas and coal dust escape into the building.

The coal dust carried into the burner with the coal may not only clog the interstices in the fuel mass, but may stop up more or less of the c the burner and coal box, to prevent the back travel of gas from the burner to the anterior part of the coal feeding system.

A further object of the invention is to provide a coal box intermediate the bin and coal tube,

the atmosphere of which is evacuated into the combustion chamber adjacent the burner, and to provide for a cascade of the coal column mov-- ing from bin to burner, within said coal box, whereby the dust is separated from the larger coal particles, drawn on with the atmosphere of the coal box into the combustion chamber and ignited by the name from the burner.

Still another object of the invention is the.

formation of a coal seal at the point where the feed conveyor from the bins enters the coal box,

for the purpose of holding the vacuum in the coal box which is essential'to the withdrawal of the dust.

Another object of the invention is to provide a pulverizer in the line of the feed conveyor from bin to coal box for reducing the coal to uniform small size. and producing a quantity of dust auxiliary to that which incidentally accompanies the coal, so asto have sufficient dust to maintain lively incandescent combustion in the combustion chamber adjacent the burner.

A further object of the invention is to provide conveyors of varying pitch and diameter in their different zones of travel in both the feed tube from bin to coal box and the coal tube from coal box toburnenfor producing optimum conditions of flow, density and fullness in different parts of the coal tubes, as will appear.

A still further object of the invention is to provide a 'novel construction of conveyor end portion and the adjacent casing portion within the bin, enabling the conveyor to pick up coal from an extensive area of the coal pile within the bin. I

Another object of the invention is the novel combination of stoker air feed and the boiler served by said stoker wherein the air is preheated by products of combustion on their way to the stack through the gas passages of the boiler.

Another object of the invention relates to the j provision of various means for evacuating thev coal box.

Other objects of the inventionwill appear as the following description of a preferred and practical embodiment thereof proceeds:

In the drawings which accompany and form a part of the following specification and throughout the several figures of which the same char: acters of reference have been employed to designate identical partsz Y Figure 1 is a side view, partly in section, of a stoker mechanism embodying the principles of the present invention;

. Figure 2 is a longitudinal section, on an -enlarged scale, of the coal tube and conveyor extending from bin to coal box;

Figure 3 is a cross-section taken along the line 3-3 of Figure 2;

Figure 4 is a cross-section taken along the line 4-4 of Figure 2;

Figure 5 is a plan view, partly in section, showing an air system for evacuating the coal box, in which an auxiliary fan is employed;

,Figure 6 is a similar view of a modified form in which the natural stack draft is used;

Figure '7 is a side elevation, partly in section, showing a form of the invention in which the main blower produces a draft on the coal boxj 1 Figure 8 is a side view, partly in vertical section, showing means for preheating the air to the stoker through heat interchange with the products of combustion passing through a boiler and to the stack;

Figure 9 is a similar view illustrating a modified form of the invention.

' Referring now in detail to the several figures,

and first adverting to Figures 1 to 4, inclusive, the numeral l represents in general a coal stoker having th chassis 2 which supports, on the one hand a burner 3, and onthe other the coal box I and blower 5. The burner 3 is located in a combustion chamber 6, a wall of which is shown at 1. To the left of the coal box as shown, is a bin 8.

A coal tub 9 with an enclosed coal conveyor l0 extends from within the bin 8 to the. coal box 4. A coal tube H with enclosed coal conveyor l2, extends'from the coal box 4 to the burner. The

' which is underfed from the coal tube II, the

ashes developing toward the top of the burner and being dislodged by means such as the rotary arm l9 which travels around the lip 20, forming the upper periphery of the burner.

The coal tube I I is surrounded by an air conduit 2| in communication with the pressure end of the blower 5, the induction end of which blower is open to atmosphere. The end of the air conduit 2| adjacent the burner is an upturned elbow 22, upon which rests an air Jacket 23, the chamber of which communicates with the fuel chamber of the burner through the louvers l8.

So much of the structure as has thus. far been described is present in known stokers.

The operation of such a stoker is attended by certain drawbacks. For instance, after long periods of slow combustion an ash mass may collect on top of the burner, which constitutes a material obstruction to the passage of air through the fuel bed. The result may be a development of back pressure in which products of combustion are forced back through the coal tube l I, escaping from the coal box or traveling through the coal tube to the bin, in either case, escaping into the building.

Inasmuch as the small sized coal generally employed in domestic stokers is accompanied by a considerable proportion of coal dust, the latter may clog the interstices between the coal particles in the fuel bed and may also more or less stop the burner.

.efliciency of the stoker plate by maintaining a lively incandescent combustion in the combustion chamber in the region of the top. of the burner. The reference character 24 designates a vent communicating at one end with the coal tube H adjacent the burner and opening into the combustion chamber 6. This vent short-circuits any gas back pressure from the burner into the coal tube and. delivers the gases into the combustion chamber where they are burned at the mouth of In order to assure that all of the back flowing combustible gases shall be so shortcircuited, I provide a coal seal in the coal tube two conveyors are driven from a sprocket l3 or other suitable drive, located outside of the coal intermediate the coal box and vent, and this leads to a consideration of the conveyor l2 within the coal tube II. It will be observed in Figure 2 that this conveyor has a wide pitch in that portion which lies adjacent the coal box and in that portion which extends from a point anterior to the vent, to the burner, but that between these region's of wide pitch there is a zone a in which the helices of the conveyor have a narrow pitch. The result of this is that while the coal leaving the coal box under the propulsion of that part of the conveyor of wide pitch has a loose and open formation and does not fill the coal tub to the top, it is congested, densified and banked 4 up in the zone a so that it fills the coal tube and acts as a plug or trap to block the passage of gas through the coal tube toward the coal box. After the coal has passed through the zone a its forward movement is accelerated by the wide pitch helices In order to localize this region of congestion, the

last helix or so 25 of the conveyor is made of somewhat greater diameter than the helices that precede it and also of wider pitch. The extreme end 26 of the conveyor is preferably made of noncorroding and wear-resisting steel.

Exclusion of coal dust from the burner is accomplished by the following instrumentalities. The coal box 4 which in existing stokers serves merely as the base for hopper employed as alternative to the bin as a coal supply, in the present invention is closed by a plate 2! converting the coal box into a substantially air-tight chamber. The floor of the coal box has the form of a ramp 28 having a gradual upward incline from the adjacent mouth of the coal tube 9 and an abrupt downwardly inclined side 29 toward the adjacent mouth of the coal tube 1 I. The coal with its accompaniment of dust is delivered from the bin by the conveyor ID to the gradually inclined side of the ramp which it ascends under pressure of the conveyor and then cascades loosely down the abrupt side 29. The coal dust released from the larger coal particles goes into suspension in the atmosphere of the coal box I. The reference character 30 indicates the mouth of a suction vent which leads into the combustion chamber 6 near the mouth of the burner 3. Suction may be produced in several ways, as will by means of which the atmosphere of the coal box, including the suspended dust, is continuously evacuated through the vent 30 and into the combustion chamber 6. The coal freed from the dust is picked up by the conveyor l2 and delivered to the burner.

It is well known that about two-thirds of the heating efllciency of any burner is in the form of radiant heat which accompanies incandescence, and the coal dust being in the form of small particles, burns incandescently in the ignition zone of hot air immediately over the mouth of the burner. Inasmuch as the quantity of coal dust may vary in different samples of coal, it is desirable to produce an auxiliary quantity of coal dust so as to ensure continuous lively incandescent combustion of dust at the mouth of the burner. This I provide by means of a pulverizer 3| on the shaft 32 of the conveyor 9, Figures 1 and 4 show that this pulverizer comprises a deeply ridged drum 33, the ridges 34 of which engage the coal particles as the shaft 32 rotates and crushes them against one another, reducing them all to a substantially uniform size, pulverizing some and producing coal dust which is separated from the coal column with the inherlocalized region where the coal column is densified and fills the coal tube. To prevent this region of densiflcation from working forward,

the diameter of the helix immediately preceding the pulverizer is made the full diameter of the interior of the coal tube, as shown at 38 in Figures, 1 and 2. Another region of densification occurs where the coal is elevated in the coal box 4 up the ramp 28. In order to relieve the pulverizer of the back pressure effects of this region of densification, the terminal helices 39 of the ,fconveyor II] are made with a wide pitch and a diameter substantially equal to that of the interior of the coal tube. The end of the conveyor I0 adjacent the coal box is preferably made of wear-resistant steel.

The shape of the ramp 2B affords a housing beneath the coal box, into which the aligned ends ent dust as the coal cascades over the ramp 28. l

vided with elongated openings 35 and 36, substantially throughout that portion which reaches into the bin, the sides of said portion being preferably closed as shown in Figure 3. The extreme end portion of said coal tube remains in the form of an unbroken circle, as shown at 31 in Figure 2. The shaft 32 and the conveyor l0 extend substantially to the end of the coal tube, but the shaft I0 preferably has no bearing in the end of the coal tube. This permits the conveyor to normally lie freely against the lower wall of the coal tube in that portion which extends into the bin. The helices of the conveyor, 'at least in this portion of the coal tube. are of smaller diameter than the interior of the coal tube, which permits the end portion of the conveyor to flex in various directions through the inherent resiliency of the shaft yielding to local excess pressure of the coal entrained by the conveyor through the openings 35 and 36 and 'avoiding jamming of the conveyor and breaking or stalling of the apparatus. This is a very important feature of the invention, for it will be lunderstood that while the coal .in the bin has been sized at the mine, there will be many lumps not of the proper size which might cause jamming of the conveyor if it were rigidly mounted so as to rotate inflexibly in a prescribed path.

That portion of the conveyor helix which extends into the bin is made with a relatively close pitch so as to pick up the maximum quantity of coal. The pitch widens in the zone b of the conveyor which lies between the bin and the pulverizer -3l, so that the coal mass is loosened and does not'iill the conveyor to the top. This promotes easy flow of the coal toward the pulverizer, reduces the power required to operate the stoker, and minimizes the hazard of the conveyoriamming. The pulverizer 3| creates a of the conveyors l0 and I2 extend, said conveyors being coupled to the sprocket l3 which is positioned in said housing and protected from becoming clogged with coal or other debris;

Referring now to the groupof Figures 5, 6, and Y 7, Figure 5-shows that the vent 30 which evacuates the coal dust from the coal box 4 into the combustion chamber 6 is, served by an auxiliary fan 40 blowing into the combustion chamber 6 and entraining the dust-laden air from the coal box. I

Figure 6 shows a slightly modified form of the invention in which the chimney draft induces vacuum in the vent 30. I

Figure 7 shows a still further modification of the invention, in which the vent 30 opens-into a branch air conduit, debouching from the main air conduit 2|- and entering into the combustion chamber 6, suction upon the coal box being produced through the forced draft through the branch conduit 4|.v

Referringnow to Figures 8 and 9, a development of the invention is disclosed which ine eludes the preheating of the air admitted to the burner 3. Figure 1 shows the stoker I associated with a boiler 42, said boiler having a com bustion chamber 43 beneath an anterior group of water sections 44. The combustion chamber is walled off as at 45 at an intermediate point, leaving certain of the water sections 46 outside of the direct heating influence of the burner 3. These water sections are heated by products of combustion which pass upwardly between the water sections of group 44, across the top of the boiler, and down between the water sections 46, then out through the smoke pipe 41 to a stack 48.

In this form of the invention, the air for supplying the blower 5 comes in through a number of tubes 49 which extend through a portion of the smoke pipe, as shown, then upwardly through the spaces between thewater sections 46, then across the top of the boiler, then downwardly through the space in front of the first water section of the group 44, opening into a headeril] which forms the end wall of the air conduit leading to the center of the blower. It will be observed that the air travels contra-flow to the combustion gases, an arrangement which produces the maximum rate of heat exchange all along the line. The boiler has a cover plate 52 which when removed exposes an opening giving access of a garden hose by means of which the combustion spaces within the boiler and including the outer surfaces of the tubes 49 may be cleaned-*1 An ash pit 53 underlies the boiler in communication with the lower part of the combustion chamber 43. The rear portion of the ash pit- 53 which underlies that portion ofthe boiler which is not in the direct influence of the burner 31s separated Y from theash pit by a removable plate 54, which plate normally prevents escape of the combustion products into the ash pit, and when removed permits the accumulation of fly ash to dump'into the ash pit.

Figure 9 shows a slightly modified form of the invention in which the air enters a conduit 55 and passes to the center of the blower outside of the boiler. A drum 56 is intercalated both in the smoke pipe 41 and in the air conduit 56. This drum has a, core of tubes 51, the opposite ends of which open in headers 58 and 59 and communicate with the smoke pipe. The fresh air passes through the drum on the outside of these tubes and is w armedthrough heat transfer from the combustion gases passing through said tubes. It is within the purview of the invention to reverse the direction of the tubes and headers, if desired, so as to take the fresh air in through the tubes and have the products of combustion pass by the tubes. f"

It will be understood to those skilled in the art that I have in the above description disclosed what I consider to be a preferred and practical embodiment of the invention and one which tests have proven to be more emcient and reliable in operation than stokers as heretofore manufactured. It will be also understood that the specific details of construction and arrangement of parts as shown and described are by way of illustration and not to be construed as limiting the scope of the invention as defined in the appended claims.

What I claim as my invention is:

1. Coal stoker of the underfeed type having a burner comprising a casing defining a fuel chamber, a blower, a jacket surrounding said casing and in communication with said blower, said casing having air louvers communicating with the jacket chamber and the fuel chamber, a coal tube connected to the lower end of said casing, a helical conveyor in said coal tube for feeding coal to said burner having the intermediate portion of its helix of narrower pitch than the extreme portions whereby condensation-of coal is produced in said portion of narrow pitch forming a gas stop, and a vent from said coal tube into said combustion chamber between said burner and gas stop.

2. Coal stoker of the underfeed type having "a burner comprising a casing defining a fuel chamher, a blower, a jacket surrounding said casing and in communication with said blower, said casing having air louvers communicating with the jacket chamber and the fuel chamber, means forming a combustion subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal,

. coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply source to said separating chamber,

coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, means in said separating chamber interposed between the-adjacent ends of said conveyors comprising a ramp sloping upwardly from said first named conveyor up which coal is pushed by the first conveyor, terminating in an abruptlydownwardly extending shoulder causing gravitational fall of coal from said ramp into the second conveyor, for causing the column of moving coal to loosen whereby 16 the dust is'i'reed from the coal so that it goes into suspension in the atmosphere of said separating chamber, and means for evacuating the dust-laden atmosphere of said separating chamber into the combustion zone in said combus-- tion chamber.

3. Coal stoker of the underfeed type having a burner comprising a casing defining a fuel chamber, a blower, a jacket surrounding said casing andin communication with said blower, said casing having air louvers communicating with the jacket chamber and the fuel chamber, means forming a combustion chamber subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal, coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, a ramp insaid separating chamber providing an incline facing the first named conveyor up which the coal is elevated by said first named conveyor, said ramp providing an abrupt drop on the side facing the second named conveyor permitting the coal to cascade gravitationally toward the second named conveyor whereby the coal mass is lodsened freeing the dust from the coal so that it goes into suspension in the atmosphere of said separating chamber, and means for evacuating the dust-laden atmosphere of said separating chamber into the combustion zone in said combustion chamber.

'4. Coal stoker of the underfeed type having a burner comprising a casing defining a fuel chamber, a blower, a Jacket surrounding said casing and in communication; with said blower, said casing having air louvers communicating with the jacket chamber and the fuel chamber, means forminga combustion chamber subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal, coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end or said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, a ramp in said separating chamber providing an incline facing the first named conveyor up which the coal is elevated by said first named conveyor, said ramp roviding an abrupt drop on the side facing the second named conveyor permitting the coal to cascade gravitationally toward the second named conveyor whereby the coal mass is loosened freeing the dust from the cool so that it goes into suspension in the atmosphere of said separating chamber, the elevation of coal up said ramp providing gravitational densiflcation of the coal mass at the discharge end of said first named conveyor, restricting air induction into said separating chamber by way of said first named coal tube, ancl'means for evacuating the dust-laden atmosphere of said separating chamber into the'combustlon zone in said combustion chamber.

5. Coal stoker of the-underfoot! type having a burned comprising a casing defining a fuel chamher, a blower, a jacket surrounding said casinl ing having air louvers communicating with the jacket chamber and -the fuel chamber, means forming a combustion chamber subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal, coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, a ramp in said separating chamber providing an incline facing the first named conveyor up which the coal is elevated by said first namedconveyor, said ramp providing an abrupt drop on the side facing the second named conveyor permitting the coal to cascade gravitationally toward the second named conveyor whereby the coal mass is loosened freeing the dust from the coal so that it goes into suspension in the atmosphere of said separating chamber, the elevation of coal up said ramp providing gravitational densification of the coal mass at the discharge end of said first named conveyor, restricting air induction into said separating chamber by way of said first named coal tube, means for evacuating the dust-laden atmosphere -of said separating chamber into the combustion zone in said combustion chamber, the second named helical conveyor having an intermediate portion of its helix of narrower pitch than the extreme portions, whereby densification of coal is produced in said portion of narrow pitch forming a gas stop, and a vent from said coal tube to said combustion chamber between said burner and gas stop.

6. Coal stoker of the underfeed type having a bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, means in said separating chamber interposed between the adjacent ends of said conveyors for causing the column of moving coal to loosen whereby the dust is freed from the coal so that it goes into in communication with said blower,said casinghaving air louvers communicating with the jacket chamber and the fuel chamber, means forming a combustion chamber subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal,

coal feeding means including a coal tube and enclosed conveyor comprising a shaft and helical vane adapted to bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, a ramp in said separating chamber interposed between adjacent ends of said conveyors presenting an incline to the end of the first named conveyor for causing the column .of moving coal to be elevated up said ramp and having an abrupt drop facing the end of the second named conveyor causing the coal to cascade gravitationally whereby its mass is loosened and dust freed from the coal which goes into suspension in the atmosphere of said separating chamber, a pulverizer interposed on the shaft of said first named conveyor for sizing the coal and producing coal dust, and means for evacuating the dust-laden atmosphere of said separating chamber into the combustion zone in said combustion chamber.

8. Coal stoker of the underfeed type having a burner comprising a casing defining a fuel chamber, a blower, a jacket surrounding said casing and in communication with said blower, said casing having air louvers communicating with the jacket chamber and the fuel chamber, means forming a combustion chamber subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal, coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply sourc to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, means in said separating chamber interposed between the adjacent ends of said conveyor for causing the column of moving coal to loosen whereby the dust is freed from the coal so that it goes into suspension in the atmosphere of said separating chamber, and means for evacuating the dustladen atmosphere of said separating chamber into the combustion zone in said combustion chamber, said means including an eduction conduit from said separating chamber opening into said combustion chamberin th active combustiorr zone thereof and subject to stack draft.

9. Coal stoker of the underfeed type having a burner comprising a casing defining a fuel chamber, a blower, a jacket surrounding said casing and in communication with said blower, said casing having air louvers communicating with the jacket chamber and the fuel chamber, means forming a combustion chamber subject to stack draft, surrounding said burner, means forming a chamber in which coal dust is separated'from the coal, coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, means in said separating chamber interposed between the adjacent ends of said conveyor for causing the column of moving coal to loosen whereby the dust is freed from the coal so that it'goes into suspension in the atmosphere of said separating chamber, and means for evacuating the dustlation to said auxiliary blower conduit;

10. Coal stoker of the underfeed type having a burner comprising a casing defining a fuel chamber, a blower, a jacket surrounding said casing and in communication with said blower, .said casing having air louvers communicatingwith the jacket chamber and the fuel chamber, means forming a combustion chamber subject to stack' draft, surrounding said burner, means forming a chamber in which coal dust is separated from the coal, coal feeding means including a coal tube and enclosed helical conveyor adapted to bring coal from a supply source to said separating chamber, coal feeding means comprising a coal tube from said separating chamber connected to the lower end of said casing and an enclosed helical conveyor for moving coal from said separating chamber to said burner, means in said separating'chamber interposed between the adjacent ends of said conveyor for causing the column ofmoving coal to. loosen whereby the dust is freed from the coal so that it goes into 'suspension in the atmosphere of said separating chamber, and means for evacuating the dustladen atmosphere of said separating chamber into the comlmstlon zone in said combustion chamber, said means including a branch conduit from said blower opening into said combustion chamber in the active combustion zone thereof and subject to stack draft, and an eduction conduit from said separating chamber in air-entraining relation to said branch conduit.

'JAMES A. CASEY.

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