US2341252A - Automatic stoker - Google Patents

Description

Feb. 8, 1944. A. wlN-l-ER 2,341,252

AUTOMATIC STOKER Filed March 31, 1941 3 Sheets-Sheet l.

Feb. 8, 1944. l. A. WINTER AUuToMATIc sToKER Filed March 51, 1941 5 Sheets-Sheet 2 ATTORNEYS.

Feb. 8, 1944. 1 A wlmTER 2,341,252

AUTOMATIC STOKER Filed Marchl, 1941 3 Sheets-Sheet 5 II'IIIE l l l l l 77 S s. 1N VENTOR:

MAQ

BY y v y ATTORNEYS.

Patented Feb. 8, 1944 UNITED STATES PATENT OFFICE 2,341,252 y v aurolmrricl sToKER Ireal A. Winter, Birmingham, Ala. Application March31, 1941, Serial No. 386,153

9 Claims.

This invention relates to automatic stokers for the burning of solid fuel, and particularly to fully automatic stokers and ash removal systems for use in home and apartment house heating plants,

and in industrial installations.

Objects of the invention are to provide automatic stokers of novel design, and of novel combustion characteristics, in which various types ofl anthracite and bituminous coals may be burned with equal ease and facility. An object is to provide an automatic'stoker in which the fuel and air passages are sol related, and the ash is continuously removed in such manner, that the fuel burns with a torchlike flame. An object is to provide an automatic stoker including a rotary hearth, mechanism for feeding crushed coal upwardly through the hearth, passages for supplying combustion air at regions that result in'a fuel bed of substantially constant depth and surrounded by an ash bed that protects the hearth from damage, and devices for agitating the ashes and preventing the formation of a clinker ring. A further object is to provide an automatic stoker of the stated rotary hearth type in which the hearth is retained upon its support by the weight of the hearth and the coal and ash upon the hearth, the hearth being rotated by a rotary screw conveyor that removes the ashes to a remote point.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawings in which:

Fig. l is a plan view of a Stoker and automatic mechanical ash remover embodying the invention;

Fig. 2 is a side elevation of the same;

l Fig. 3 is a fragmentary end elevation, with parts in section, as viewed from the plane indicated by line 3-3 of Fig. 2;

Fig. 4 is a fragmentary transverse section, on

an enlarged scale, taken on the plane of lineA 4 4 of Fig. 3;

Fig. 5 is a fragmentary section taken on the plane of line 5-5 of Fig. 4;

Fig. 6' is a fragmentary section, on an enlarged scale, taken on the plane of line 6-6 of Fig. l1;

Fig. 7 is a fragmentary horizontal section taken on the plane of line 'I--T of Fig. 6, with parts broken away to show the rotating elementsin plan;

Fig. 8 is a fragmentary vertical section through the burner, and shows the combustion phases, air flow and other elements of the burning process;

Figs. 9 and 10 are fragmentary transverse sec tions on the planes of lines 9 9 and lil-I0, respectively, of Fig. 6;

Fig. 11 is an enlarged and fragmentary plan view of the rotating hearth andtuyre;

Fig. 12 is a-sectional view taken on the plane of line I2-I2 of Fig. 11;

Fig. 13 is a fragmentary plan View of another embodiment of the invention that includes an automatic pneumatic ash remover; i

Fig. 14 is a fragmentary section, on an enlarged scale, taken on the plane of line I4-I4 of Fig. 13; y p

, Fig. 15 is a vertical section taken on the plane of line I5 -I5 of Fig. 14;

Fig. 16 isa fragmentary enlarged section taken on the plane of line IG--IB of Fig. 15; and

Fig. 17 is a'fragmentary section taken on the plane of line I'I-II vof Fig. 16. In the drawings, the reference numeral I identitles a motor that drives the blower 2 and the associated fuel feed mechanism by which the combustion components, i. e., air from the blower 2 and crushed fuel from the hopper 3, are supplied to thel burner 4through the dual passages of the tubular member 5. The burner is located in the usual position within the furnace 6, and ashes are removed from the interior of thefurl nace through an ash tube 1 and deposited in an ash hopper 8. The volume of air delivered to the burner through the air passage 9 at the bottom of the tubular member 5, see Figs. 3,` 6 and 9, is regulated by the thumbscrew II) that controls the air inlet opening II between the blower manifold and the intake orifice plate I2.

The blowershaft is directly driven by the mol tor shaftbut thefffuel and ash conveyors are driven at low speed, and intermittently, through a transmission including sheaves I3, I4 on the motor shaft and a countershaft I5, respectively, and a V-belt I6. The shaft I5 carries an eccentrically mounted roller bearing I'I that imparts rotation to the fuel feed drive shaft I8 through the ratchet wheel I9, spring-returned pawl 20 and rocker arm 2|. Y The eccentricity of the ball bearing II is adjustable by known mechanism, not shown, to provide a regulation of the rate of fuel supply. u v

A shear pin 22 couples the hub ofthe ratchet wheel I9 to the stub shaft I8 to prevent damage upon a fouling of the fuel feed screw 23 that has a squared end seated in a correspondingly shaped socket in the enlarged inner end of the shaft I8. A lubricated roller bearing. is mounted on the sheave guard 25V to support the stub shaft I8, the

alinement ofthe aShscrew shaft. 3| whilefthe felt packingsr 34 protect the bearings' from the in# trusion of coal dust from the hopper. The enlarged end of the drive shaft |8 extends into the;

fuel hopper through the housing plate 21, and a felt packing 36 seals the shaft to prevent the escape of fuel at this point.

The upper passage of the tubular member comprises the fuel feed tube 38 that is turned upwardly, at its inner end, to open into and toY support the stationaryv conical retort 39, that flares outwardly to terminate in a slightly concaved annular flange 4|). The burner ring or rotating hearth 4| is locatedimmediately -above the flange 4U and a large number of tuyre oriilces 42 are provided betweenthese vmembers to admit combustion air to the Aretort and hearth from the annular air chamber 43 at the upper end of the air supply passage 9. The tuyre orifices are preferably formed in the base of the rotating hearth by deep notches between the lugs 44 that have lower faces conforming to the curvature of the flange 4| and rspaced from the flange by a small clearance of, for example, about '12 inch. The cross-sectional area of each tuyre is substantially constant,` and the air velocity through the tuyre is therefore practically constant, but the circumferential lengthV and the axial height of the tuyre vary progressively along the radial length of the tuyre to provide a longand shallow inlet opening at the outer edge of the hearth 4| Aand a short and deep outle opening at the inner edge of the hearth.

As shown in Figs.`6, 7, 11 v'and l2, the side walls ofv each tuyre orice are plane surfaces, and the top and upper walls are conical surfaces of different slope comprising, respectively, the flange 40 and the upper surfaces of the hearth 4| between the lugs 44. The inner ends of the tuyre orifices are approximately Square With an aggregate circumferential length of about 180, and a relatively large number of orifices are used to distribute the airv efnciently around the burner and to direct the jets into the` fuel bed. Any ash or small Aclinkers that may collect in the tuyre orifices 42 and on the retort flange 40, during periods of quiescence when the burn-` ing is vof Aa slow smoldering character, are loosened and scraped back into the retort by a plowing action of the lugs 44 or are blown back by the air blast. l

The hearth 4| is rigidly secured by screws 45 to the ash scraper ring 46- that is 'intermittently rotated by the attached tooth ring -41 and drive pins -48 on`a collar 49 on the end of the ash conveyor screwv 5|, Figs. 6, 7 and 9. 'The collar 49 is lubricated by a spring loaded graphite stick 5U carried by the casing. The pitch ofthe pins 48 is somewhat greater than that of the teeth Aof thering 41 andthe centerline of the ash screw 5| and collar 49 is offset from the axis of thetoothed ring 41, thus limiting the engagement of the drive pins 48 with the teeth 41 to a horizontal approach to and a downward movement along thevertical flanks of the teeth. This :operating characteristic is important since the hearth 4| and the ash scraper ring 46 are retained in place on the burner solely by their weight. Supporting wheels 52 are secured to the ring 46 between certain of the radially project 5 ing fins 53, the wheels being mounted on inclined shafts 54 for supporting the hearth and ash scraper ring upon the housing member 55. The double-coned Wheels 52 roll along the inner edge of the annular flange 55' that projects radially from the housingmember.v 55 at--a point slightly lbelowits: upper `edge.y Theupper part of the member 55 thus forms a cylindrical guide for centering the rotatable assembly to maintain a small clearance 56 between the ash scraper ILS-ringl 46 vand the housing member 55. This clear- Y ance is essential as the resulting flow of air from Vthe annular` chamber 43 sweeps across the supl porting flange 55 to remove ashes from the wheel track and to provide preheated secondary air for rapid and efficient combustion of gases above the fuel bed. Additional preheated-secondary air is supplied through the annular orifice 59 be# tween the upper edge of the ash scraper ring 46 and the hearth 4|.

A rake 63 is hinged upon the open topped ash hopper 64 that is secured to the housing `55 of the burner and supports the inner end'of the ash removal tube 1, Figs. 1,' 2 and 6. 'I'herake 63 is a tapered metal plate with its smaller end or point resting upon the edge of the rotating hearth 4| to agitate the ash bed and prevent the formation of the large annular clinker ring that is characteristic ofrsome prior rotating hearth burners. The hingedmountingof the rake pe r mits Yeasy removal of the hearth and ash scraper ring, and also permits the rake to ride over any unburned embers that may be present in the ash, thus serving to expose thel embers to the surrounding air .to facilitate complete combustion. The tapered rconstruction of the rake protects itfrom destruction as'the large radiating surface outside of the yfuel bed dissipatesheat more rapidly v'than it is absorbed by the small innerendthat -is exposed tothe ash and fuel bed. Theash conveyorscrew 5| is connected to the ash screwshaft 3| bv a coupling 65 and shear pin EB. An agitating arm 61. is secured to the ash screw within the discharge T 68 from which the outlet branch 69 slopes upwardly to deliver the ashes to the ash can 8. The-agitating arm 61 prevents the ash from packing tightly in the end of the discharge T, and stirs and aerates the ash to maintain the condition of vsemi-fluidity that is essential to a free flow of the ash.` The blade of the ash screw 5| does not extend to the agitating arm 61 but terminates at about the center line of the outlet branch 69, thus leaving a small space in which the ash is relatively at rest. The agitating arm and the exposed end of the screw move the ash up the outlet branch by a pumping action at each rotation of the ash screw and, since the displacement of the ash screw is about three times the volume of ash being removed, the zone of non-agitation forms a storage pocket that prevents a-constant grinding of the ash between the rotating parts and the. wall of the discharge T. The crosssectional area of the discharge branch '69 increases towards the discharge end to prevent the ash from packing, the increase being equivalent to that of a conical tube of from 2 to'5 total included angle. The cross-section of the outlet branch preferably varies progressively from a square inner end, Fig. 6, to the cylindrical'outer endk upon which the thin conical shield 1|lis semblingplastic flow, andthe upward inclination of the discharge branch. 69 provides a. body of ashes that forms a seal to. prevent the escape of pressure air, and? entrained fine ash, from` the interior of the furnace. f

The phases and. elements of combustion. for the burner are illustrated. Fig. 8'. The body of fuel Ay is. forced' upward. into thef conical retort. 39` byA the feed screw 2.3, and' is ignited in the regionf B by air. blastsfa that are directed inwardly through the tuyrev orifices 42; The fuel bed: is agitated bythe intermittent rotation off the hearth di, through the toothed wheel 4"| and pins 48; and. theair readily penetrates tothe interstices of the burn'ingfuel and effects rapid and' eicient combustion.. A lportionV of the air and gas'.l which has' been preheated in the-annular combustion region B isv forced infwardiy to supplement' radiant heat from'` region B in preheating the fuel in the interiorI vzone C, thereby driving off the gas and volatile mat,-

ter to form a cone D above the fuel bed'. The

remainder ofy the primary air: fromthe tuyre serves to complete the' combustion of the outwardly mushrooming degasifiedi fuel from the region C, while preheated secondary air issues from the annular orifice 59 and. the clearance 5S; as indicatedv by arrows b, c, respectively, to effect the complete combustion ofthe gases of cone Dr in the torchlike flame E.` These secondary air'streams flow alongthe rotating hearth and ash scraper ring to protect-them against overheating and warping.

The bed E of ashes and embers whicheverlies the outer flange of the rotating hearth 4| acts as an insulation for the hearth and also serves to maintain a fuel bed` of sufficient depth to' force the air blasts a into the incoming body of fuel: A to preheat it, and to prevent they upwardly moving air streams from blowing` the fuel from the. burner at the. combustion region B. The depth of the burning region Bis thus govcrned by thev slope ofA the outer ange' of the hearth 4|, and this slope may be selected in accordance with the weight and burning characteristics of the fuel. TheV illustrated slopev of about 35 degrees is appropriate for various grades of lignite, bituminous and anthracite coal bu-t a 'greater slopev may affordA more efficient operation when burningcoke or sawdust.

The described process ofr burning the fuel results in a high burner eiiiciency, both with respect to the quantity of fuel-which may' be burned; in a. given time and with respect to; the heat value received per. unit of fuel. Further, since; com.- bustion withinthe burner is confined tothefsmall annular region B and producing a name which, both in appearance and the rapidity with which it builds up from quiescence, resembles that produced by an oil burner, overheating of the parts is prevented as is attested by the fact that after a short period of quiescence during which burning recedes into the retort, the ashes can be scraped away and the burner lifted out using only a gloved hand. The protection of the burner parts from destructively high temperatures results from the described paths of ow of the combustion air through and around the burner. The combustion zone B is spaced from the metal parts. by the incoming fuel A. or by the ash bed F; and the secondary air streams ow along: and

.cool theouter'portion ofthe burner, being thereby-l preheated to effect a quick and eiiicient com'- bustion ofthe gases that rise above the fuel bed.

The supply of fresh fuel forces ashes outwardly from the rim of the ash bed F, and this .flow is.v facilitated by the slight shaking action resulting from the-step-by-step movement of the rotary hearth. 42| and by the' scraping action of rake 63` that prevents the formation of a elinker ring; The ash falls upon the radial ange 55" .of the housing 55, and is swept along the ange and into the ash hopper 64 by the ns 53 of the ash scraper ring 4B. The removal of ash is essential to stable burner operation and the illustrated construction has a number of struc'- tural features or operating characteristics. that are of major importance. It is essential that the clearance between the radial flange 55 and the lower edges of the ash scraping fins 53 be small. Ashes and clinkers are forced along the flange by the ns 53, and the clearance must be limited to prevent clinkers from lodging under the ns and thus lifting the hearth 4| that is retained in` position by gravity, Another-feature that prevents an inadvertent lifting of the hearth is the cutting back of the ash screw 5| so that no part, or only a small part, of the screw extends beheathV the ns 53. InsuiicientV clearance at this point might allow clinkers to jamb between the screwV 5i and the fins 53, thereby lifting the hearth 3| to disengage the toothed wheel 41 from the drive pins 118 andv thus preventing further rotation,

A relatively large quantity of ash will accumulate within the burner Aduring quiescent operation and, when thev burner isagain operatedA at full capacity', the rate ,of ash discharge from the burner mayv exceed the capacity of the ash screw 5| for ashort interval; The excess quantity of ashes is temporarily stored upon the flange 5'5' of the housing 55, between. the iins 53, and is eventually removed through the ash hopper 64 when the ash screw catches up? with the rate of ash discharge.

In an alternative embodiment of the invention, as shown in Figs. 13 to 17, inclusive, the ashes are removed by a pneumatic system. In general, the burner and` associated mechanisms may be substantially as previously described and like parts are therefore designated by correspendingV reference numerals but will not be described in detail.

They drive pins 48 for the rotary hearth are carried byr a shaft 5| that is. alined with and coupled: to the shaft 3|-, The shaft 5| extends through the ash hopper l2 and carries Crusher Wheels i3 for breaking up clinkers before they enter'tl'ie` outlet sectionV I4 of the ash hopper. The ashes and. finely ground clinkers that col.- lect in the section 14 are sucked away and blown into the ash can 15- by the ejector 'I5 which receives an air blast. through the connecting pipe 'Hf that extends into the pressure air passage 9. The air and ash stream is delivered to the ash can 'l5 through the tube I8 which has the diffusing section 'i9 for decreasing the velocity of the stream as it approaches the ash can. 'Ihe air and ash stream enters the ash can tangentially and the imparted swirl will effect a separation of the solids from the air by centrifugal force. The air vent is placed at the center of the can where the suspended ash is at a minimum; but as a further precaution against the escape ofV nelydivided ash and gas, the vent pipe 8l) is carried to the intake orifice on the blower 2, thus providing a closed circulation system which aidsV in removing ashes to the ash can 'l5 by reducing vthe back pressure on the ejector 1G.

The ash can 15, which for convenience of i1- lustration has been shown adjacent to the stoker,

canv be located anywhere that may be desired, such as in the alley, in which case the vent'80 a' vention.

I claim:

1. An underfeed stoker comprising a stationary upwardly flaring conical retort member, a rotatable annular hearth member supported above and concentric with said retort, means for forcing fuel upwardly through said retort and hearth member, a pressure air chamber surrounding said retort, said annular hearth member having tuyre passages in the underside thereof for discharging air from said pressure air chamber radially into the fuel bed and having a conical upper surface sloping outwardly and upwardly from the upper end of said stationary retort for supportingan annular fuel and ash bed of suflcient depth to coni-lne the iiow of airentering through said tuyres to the central portion of the fuel bed within the hearth and retort, and means for rotating the hearth member.

` 2. An underfeed stoker as claimed in claim 1, in combination -urith a horizontally hinged rake mounted laterally of the hearth and having the tip thereof resting upon the upper edge of the rotatable hearth, thereby to'prevent the formation of a clinker ring about the combustion zone.

3. An underfeed stoker comprising an upwardly aring conical retort member terminating at its upper end in an outwardly flaring annular flange, a rotatable hearth member disposed above said annular flange, means for forcing fuel upwardly through said members, a pressure air chamber surrounding said retort, and tuyre orices comprising recesses in the under surface of said hearth member facing the annular iiange of said retort, wherein each tuyre orifice is of substantially co-nstant cross-sectional area through the length thereof, and is of less height at its air entrance end than at its air discharge end.

4. An underfeed stoker comprising an upwardly flaring conical retort member terminating at its upper'end in an outwardly fiaring `annular `marcate flange, a rotatable hearth member disposed above said annular flange, means for forcing fuel upwar-'Lilyv through said members, a pressure air chamber surrounding said retort and multiplicity 'of Vtuyre orifices comprising recesses in the un- Ader surface vof said hearth member facing the annular flange of said retort, said multiplicity of tuyre orfices having an aggregate circumferential length of approximately at the interior wall of the member in which said orince-defining recesses are formed, each adjacent pair of recesses being spaced apart at said wall byan extension of the member of substantially the same circumferential length as said recesses.

5. In an underfeed stoker, a stationary conical retort, a rotatable hearth above said retort and having an outwardly and upwardly flaring ashsupporting flange, and a horizontally hinged rake supported laterally of said hearth and having an active end thereof resting with a line contact upon the edge of said rotatable hearth and adapted to extend into a bed of ash adjacent the edge thereof, said rake being tapered to pro'- vide a large heat-radiating surface spaced from the hearth to cool the small active end of the rake that 'contacts the hearth and the ash bed upon the same.

6. In an underfeed Stoker, a stationary conical retort, a housing member surrounding said retort having a radial flange adjacent the upper end thereof, a rotatable assembly comprising an annular hearth member of less circumference than said flange disposed above and concentric with said retort and an ash scraper ring secured to said hearth member and having radial fins extending over said flange on said housing member, wheels mounted on said rotatable assembly and bearing on said flange to support said assembly thereon, an ash hopper adjacent said housing member positioned to receive ash falling on said flange over the edge of said hearth and swept from said flange vby said i-lns, means for removing ash from said hopper, means for forcing fuel upwardly through said retort and hearth,

meansfor forcing air into said housing and re- Etort and means for rotating said assembly comprising said hearth and ash scraper ring.

'7. In an underfeed Stoker, the invention as claimed in claim 6, wherein said wheels support said assembly above said flange to provide an opening through which air flows to blow ashes from said fiange, thereby cleaning the track upon which said wheels rotate.

8. In an underfeed stoker, the invention as claimed in claim 6, wherein an annular air orifice is provided between said hearth and said ash scraper ring to direct 'a cooling stream of air along the lower surface of said hearth.

`9.. In an underfeed Stoker, the invention as claimed in claim 6, wherein said housing member extends above said flange to provide a cylindrical surface engaged by` said wheels to center said rotatable assembly above said retort.

IREAL A. WINTER.

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