US1863397A - Combustion chamber and draft system therefor - Google Patents

Description

June 14, 1932. R. D. DE WOLF COMBUSTION CHAMBER AND DRAFT SYSTEM THEREFOR Original Filed May 1, 1926 6 Sheets-Sheet l -SEPA/FATOR INVENTOR ATTORNE III lIII llllrrllll'll ll! I'IIIL June 14, 1932. D fDE WOLF 1,863,397

COMBUSTION CHAMBER AND DRAFT SYSTEM THEREFOR Original Filed May 1, 1926 6 Sheets-Sheet 2 NVENTOB I V %zs A EY June 14, 1932. 5 WOLF 1,863,397

COMBUSTION CHAMBER AND DRAFT SYSTEM THEREFOR Original Filed May 1, 1926 6 Sheets-Sheet 5 June 14, 1932. R. D. DE WOLF 1,863,397

COMBUSTION CHAMBER AND DRAFT SYSTEM THEREFOR Original Filed May 1, 926 6 sheets-Sheet 4 @Ai%3:"2f f ZSATTOR s June 14, 1932. R. D. DE WOLF COMBUSTION CHAMBER AND DRAFT SYSTEM THEREFOR OriginaIF'ile ay 1. 1926 6 Sheets-Sheet 5 INVENTOR 3323 7%Z9ATTOR EY June 14, 1932. DE WOLF 1,863,397

d Ma 1, 1926 I 6 Sheets Sheet 6 l 5 Z Z5 in i and @ifiQient-comhnstion of the fuel may be 1 inggthe, air; ivhich is forced ordrawn :into the 'pointedout in theclainis at the endv ofthe a lustratinq oneembodi-nient of theinvention.

oneavall ofthe combustion chamber, taken.

Patented June 14, 1932 .etsmmes m oe me rcomausnon CHAMBER ANnnRAF'r SYSTEM THEREFOR or-igi nal applioation flled liay 1,--1926,- -Ser1a1 No. 106 123. -;Div ided -and-th-is aPmicationfiled/April :19,

1928.--Seria1' 'bns'tion chambers, so lhatqlnore; satisfactory bt'ained; at;v alldtimes va ary'ingiileads A; further object of theinvention is the -provision ofinapro-ved; meansl for; preheateven A 1 under wvidely :;It isan additionaL-objeet ofthe invention to provide, a combustion .ehaniber having an improved shape which allows room for ex- -2aupansiono the'fiflmetand of the; products of Y combustion at the; points .Where the; need for such expansion is greatest, and Which-isso I designed that {the tendency of. fusecl -ash or re egate; adhere-$ ithesual s O ::'l h '=QQm tion a hamberfis reduced to a inininiuni.

Still; another-object is theprov-ision of a rsystem of eombustion and of m-clombustion chamber which are especially; adapted-for the -,efiieient and-satisfactorv combustion of fuel -3 in n pu-lverized .orfinelyydi-videdstate.

:To these and other ends the invention re- IISid6SiI1T eert'ain;irnprove1nents and combina- ;..be} understood that many-of the features are I applicable equally Well to ,othe naces=or-hurning other kinds :tions of ipart-s, all as-ywillbaherei-nafter; more llfiilly r ideseribed,i;;tl1e,a novel vsfeatures :=,.hen1g specification.

-ln the drawings:

Fig. I is a side elevation-bfafurnace'ilf F 'igsQ is afrontelevationthereon-With parts broken"au ay-inorder to show, the

structure; better.

is averticalsectlonal View through approximately "on the line 3-3 of -Rig. 2.

ff 4 a similar verticali-seetional view,

an F ig.= 5};is, a :vertiealrsee ional; view taken 1 combustion cha n1ber, with parts ish ssmately on the 1 line 7--7 of.-

,part oofone of the walls: of; the chamber,- gillustrating certain 1$ *ua ils of, con- =struetion and especially adapted for burning Pate-ntNo. 1,810,203, ion in like. 7

orally by :iak nrapproximately on the lines of a,

f; the upper; ipart {oi the oavn; in

seot-ignr the isec tion being taken appro n nately. on the line 6 -6 lofgEigr 8.

Fig; '1'; is a verticalseetionalview through part oft-the; upper,pont oniofith cmllbu io chamber, the section being;taken apprgxt 8 is 21-;VQItlCtl sectional view through part. of the upper portion ,of the gGQIXlbLlSfiiQD Ql111l1b8I,-, 5th n atelynon the line 8+8'of Fig.5 and at right; angles to the plan e section being t-aleen approgcii a i j-Fig; 9-is an elevation of part offthe front Wall of the furnace, with the outer; covering removed and w th parts broken:

aw y- 0t th sam 9. etionalview t ee bus i -'F ig, 10 is a horizontal section port on of 'Wall' ;sho vn in Fig;

:1 F 1g. 1131s a vert-1c ,perspective vie-Wei; a part-of l of the combustion chamber,

Fig. 12 is'a the; front-val i lust tingcerta eta l The same reference charaotersarefierito the ;san1e parts throughoutthe several-views.

The furnace shown in this appli eationgis rfuel in pnL butii shoul verized or finely: divided form,

yp s far of fu This applicationis a division of-my -application Serial? N 0.,- 106,123,; filed May;;1,- 1926, IIIZlCQSpflHdgllhG In the embodiment illustrated in' draw-e90 -;ings, there is shown a furnace having a gcom- .bust-ion chamber numeral 21 this combustion clmmbeii being -substantia1l -1et atthe upper portion of its ream-side.

;indieated generally :by the yreetangulan-and having an outpass out of the combustion chamber. able water tubes or other boiler elements, indicated diagrammatically by dotted lines in Fig. 1, are placed within the boiler enclosing casing 22 so that they absorb the heat resulting from combustion. A suitable duct 23 is connected to the structure 22 toremove the products of combustion therefrom, and this duct preferably is connected to a stack or other appliance for creating a draft in the furnace.

The walls of the combustion chamber and of the boiler enclosing structure may be, constructed in any suitable manner. In the embodiment here shown, the combustion chamber is of considerable height, and the form of wall construction used is especially adapted to combustion chambers of such form.

The wall construction is shown in detail in the parent a division, and itwill, therefore, be described only briefly in this application, reference be ing had to the parent case for more complete description of the details.

In a furnace structure of considerable height, the weight ofthe upper portion of the structure often bears excessively on the lower part thereof. Furthermore, if the lowerportions of the walls have to be renewed for any reason, it is usually necessary to tear down the whole wall, as there is nothing to support the upper portion of the wall when the lower part is removed. To eliminate these undesirable features, there has been provided in the present instance a skeleton or framework upon which the walls are supported at intervals. This skeleton not only bears the weight of the upper part of the walls, so as to reduce the weight on'the lower. portion, but also acts as supporting means for the upper portion even when the lower part is entirely removed for repairs or replacement. v

This framework or skeleton comprises up- "rightbeams 25 spaced at intervals along the outline of the walls of the furnace, and pro vided with suitable braces and anchoring meansx Angle bars 26, best shown in Fig.

i 12, are fixedhorizontally to the upright beams 25 so that they provide a series of vertically spaced flanges extending inwardly from the beams 25 toward the center of the furnace. The horizontal flanges formed by these angle bars 26 constitute supporting ledges on which the walls'of the furnace aresupported at vertical intervals. Each section of wall supported on one flange is independent' of the sections above and belowit, so that it neither bears against the section below nor carries the Weight of the section above. On each of the flanges26 and opposite each of the beams 25 there is mounted a hanger block 27 which is clamped securely to the adjacent beam25 by clamping members 28 best shown in Figs. 10 and 11. These hanger blocks 27 Suitcase of which this application is 1 are formed with cut-out portions 29 and wing portions 30, as illustrated clearly in Fig. 12. i On top of each hanger block 27 there is built up a column of similar hanger blocks 31, these latter blockshaving similar cut-out portions 29 and wings 30, but being slightly shorter, than the blocks 27 so that the lowerinostblock 27 which rests on the shelf 26 projects slightly "further inward than the column blocks 31 which are superimposed on it. This is shown clearly in Figs. 10, 11 and 12. Each ofthe blocks 31 in thepolumn is secured; to the adjacent beam 25 by clamps 28, and the column of hanger blocks extends upwardly from one flange 2G to a point just' the cut-out portion 29 behind the wing of the hanger block. Thus each'brick is kept in place and prevented from falling out of the wall. Each brick also has a portion extending across the face of the hanger block to approximately the center line thereof, as shown in Figs. 10 and 12 so that it meets a similar extension on the corresponding brick on the otherside of the same'hanger block and thus completely protects the hanger bloik from heat by covering the entire face thereof.

The lining bricks 35 which cooperate with the long hanger blocks 27 are made narrower than the other bricks which cooperate with the shorter blocks 31, so that the inner surface of the finished wall 1S smooth, as shown in Fig. 11. The brick next above'each of the long hanger blocks '27 rests upon the'ledge formed by'the inwardly projecting end of thehanger block, and thus the lining bricks are divided into independently supported vertical columns resting upon the long hang er blocks 27 which, in turn, are supported by the ledges 26. The narrow lining bricks which are placed opposite the long hanger blocks rest upon and form part of the column of bricks immediately below those'long-hanger blocks, as shown clearly in Fig..11. In order to allow for expansion'. cracks'37 are left between eachcolumn of hanger blocks and lining bricks and the next column above t. These cracks are preferably filled-with some heat resisting compressible packing, for example flaked asbestos.

It will now be seen that the walls are divided into independently supported vertical units carried by the anglebars 26 attached to the upright beams 25. If repairs tof the wall are needed at any point, a limited sec- Leeann? tion of the wall may be torn down without affecting-the sections above it. Thus an efficient form of construction is provided, in which the cost of repairs and the time con sumed thereby .are reduced greatly. Also, a wall construction in this form may be car'- ried to any desired height, since the weight is supported by the beams and does not cause undue crushing strain in the lower parts of'the wall.

Prefera bly the side walls of the combustion chamber, at least in the lower portionthereof, are flared outwardly so that the combustion chamber has a downwardly increasing cross section, as shown in Figs. 2 and 5. .Vhen the walls are formed in this manner, there is less tendency for clinker to adhere to the walls, since the liquid drops of fused ash or other products of combustion will have a tendency to drop off of the walls into the ash pan 40 rather than to run down the sides of the walls and solidify thereon. This flared formation of the walls of the combusti on chamber is also useful for another purpose. As will be explained in greater detail below, the fuel is preferablyadmitted to the top of the combustion chamber, and the flame travels downwardly to a point near the bottom of the chamber, then turns and ascends again. The greatest cross sectional area is needed at or near the point where the flame turns, and it is just at this point that the increased area is provided in the present construction. Also. by increasing the cross section of the combustion chamber in the downward direction of flame travel, additional space is provided where it is most needed for the expansion of the products of combustion. i

The top wall of the combustion chamber maybe formed in any suitable manner. For

instance, as shown in Figs. 3, 4 and 5, beams mav extend across the top of the combustion chamber and hanger blocks 46 may be secured thereto, by clamps 47, fire bricks 48 being supported from and held in place by the hanger blocks 46.

As has been mentioned before. this combustion chamber is especially adapted for burning pulverized or finely divided fuel, a though it may be used with fuelof other kinds or forms. There is shown in the present instance a pulverizer 50 adapted to receive coal by gravity through a chute .51. A separator 52 may be provided at the outlet of the pulverizer for separating the coarser particles from the finer ones and for returning the former to the pulverizer. blower 53 draws the pulverized fuel up from the pulverizer 50 through the separator 52 and delirers it through a conduit 54 to the fuel inlet 55. As shown in Fig. 6, a plurality of fuelinlets may be formed in the combustion chamber, and a separate pulverizerandblower may he -used for each fuel inlet if desired, or a single pulverizer and blower maybe used for two or more of the inlets. The fuel inlets in the present instance are shown as extending through the top of the combustion chamber, but other suitable positions might be used if deemed preferable. I

The fuel, after entering the combustion chamber through one or more of the inlets 55, will pass downwardly through the combustion chamber, burning as it travels. At a point near the bottom of the chambenthe flame will turn and pass upwardly again and into the boiler enclosing structure 22 and thence to the stack. If desired, suitable air or water preheaters may be provided in the connections to the stack or elsewhere, and suitable forced draft mechanism may be employed. e i

'In order to promote complete and efficient combustion of the fuel, it is desirable to ad m'it air into the combustion chamber in ad dition to such air as may be admitted along with the fuel, and it is also desirable to be able to control the air varying conditions. The means for doing these things will now be described.

Covering members 60, best shown in Figs; 10, 11 and 12, may be fixed to the outer edges of the upright wall beams '25. Thus, the walls of the combustion chamber are, in effect, made hollow, and are provided with a series of substantially vertically extending conduits or ducts. The covering member forms one of the sides of each of these ducts,

the lining members 35 formanot-her side, while the beams 25 31 serve as partitions to separate eachcondulit from the adjacent conduits at either SIC e.

The conduits in'the front wall of the com bustion chamber may be divided into upper and lower portions by baflle walls 161, as

supply to adapt it to and hanger blocks 27 and shown in Figs. 3 and 4,, while the conduits in the sidewalls may extend throughout the full height of the combustion chamber. It should be understood that the terms front andv side are used simplyfor ease of .description, and are not ing sense. The upper conduits inthe front wall, above the baffle walls 61,, may be designated by the numeral 62, while the lower conduits in the front wall are marked 63.. The conduits in the side walls are denoted 64.

Openings wall of the combustion chamber leading from each of the conduits 62 into the chain ber, each of the conduits having a series of these openings vertically spaced from one as shown especially in Figs. 3, 4

another, and 5. In order to prevent direct radiation of'heat through the openings 65, baflie plates 72 may to be taken in a ,limit- 65 may be formed in the front beplaced opposite each of the openings, with 1n the channels 62 and'slightly spaced'from' if outer surfaces of the lining bricks 35, as shown in Figs; 3, 4 and 12. -These battle members 72 may. rest against flanges 73 formed on the hanger blocks 27 and 31, and may be held in place against these flanges by vertical bars74 (Fig.9) which extend over several of the bafiie plates 7 2 and hold them inplace, these bars 74: being held inwardly against the baflie plates by cross bars-75 which have their ends set against the "clamping devices 28, as shown in Figs. 9 and 10. Posts 76 hold the baflle plates 72 vertically spaced from each'other, so that each plate will be properly placed in alinement with one of the openings 65, as shown in Figs. 3, 4 and 9. These baflie plates 72 therefore prevent heat from radiating directly out through the openings against the cover member 60 to such an extent as to injure this covering, butthey do not interfere with the passage of air from the conduits 62through the openings 65, for the air may flow around the edges of these baffle plates as indicated by the arrows in Figs. 3 and 4, j r

A part of the conduits-64 in the side walls of the combustion chamber are connectedat their upper ends through openings 66a to aconduit 66 which extends around the sides and the front of the combustion chamber, and is connected through an opening 666 to the upper ends of the conduits 62 in the front wall. The openings 666 from the conduit 66 into the conduits 62 is preferably controlled by a plurality ofdampers 67 (Figs. 3 and 4E) having operatingmembers 68 so that the dampers may be opened or closed, as desired, either individually or in gangs. The conduits 64 in the side walls have inlet openings 69 at their lower ends, these openings being controlled by dampers 70 which may be provided with suitable operating means.

If the dampers 67 and 70 be opened, it will be seen that air may enter the conduits 6% at their lower ends and pass upwardly therein, in the direction of the arrows in Fig. 5. As the air passes upwardly through these conduits, it becomes heated by contact with the hot lining walls of the combustion chamber and serves at the same time to absorb heat from the walls and to cool them considerably. Thus the effective life of the furnace lining is lengthened, because the bricks, when keptcool by means such as this. do not burn out as rapidly as when no coolingmeans is. pro.-

: vided.

' The heated air rising through the conduits 64 passes through the openings 66a is collected by the conduit 66 and carried around the sides of the combustion chamber to the front, as shown especially in Figs. 6 and 7, where it passes through the openings 66?) into the up perends of the conduits 62. The air then flows down these conduits andthrough the openings 65 into the combustion chamber in proximity to the burning fuel therein. This provides some of the additional air necessary to obtain proper combustion of the fuel.

When the furnace is being operated at a low rate, some of the dampers 67 and 7 0 may be fully or partially closed, so that the supply of air flowing into the upper ends of the conduits 62 is limited. It should be noted that the air in these conduits flows in substantially the same direction as the travel'of the flame within the combustion chamber, and comes first to those openings 65 which are nearer to the fuel inlet. In order to reach the lower openings 65 which are farther from the fuel inlet, the air must flow through av greater length of the conduits 62, which will, of course, produce greater frictional resistance to the flow. Thus the air tends to flow into the combustion chamber through the upper openings 65, since this is the path of least resistance, rather than to continue along the conduits and enter the combustion chamber through openings nearer to the bottom thereof. In this way, practically all of the air flowing in the conduits 62 when the furnace is operating at a low rate will enter the combustion chamber through openings 65 comparatively near the fuel inlet, where it is most needed for efiicient combustion, and very little air will find its way through the-lower openings 65. i

When the furnace is being operated at a high rate, however, a greater quantity of air is admitted to the conduits 62, and an in creased amount of fuel is introduced into the combustion chamber. ,Under these conditions, it would be undesirable to have the air distributed in the. same proportions mentioned above, for if most of the air in the conduits 62 passed through the upper openings 65, it would have; too great a cooling 7 effect upon the burning fuel. At high load,

therefore, a greater proportion of the air should pass by the upper openings 65 and should continue along theconduits 62 so as to enter the combustion chamber'through some of the openings 65 farther down. i

This desirable result is accomplished largely automatically by the present construction. hen large quantities of air are flowing through the conduits 62, it is obvious that the greater part of the air is no longer able to pass through the openings 65 near the upper ends of the conduits, for the resistance to the flow of such a large amount of air through these openings is too'great. Consequently a large part of the air flows on down the conduits 62 and passes through other openings 65 farther away from the-fuel inlet. Furthermore, when the furnace is being operated at a higher rate, the so-called chimney effect 7 is more pronounced, and will produce a greater draft in the lower part'of the combustion chamber than in the upper part thereof. This will tend to draw a greater quantityof air through the openings 65 in the lower chamber.

portions of the conduits 62 than through the openings in the upper portions. In this way the air is distributed differently-when the furnace is operating at difierent rates or under different loads. The distribution, as above p inted out, is'largely automatic, and the present construction is very effective promoting efficient combustion at all times in furnaces which must be operated at different rates from time to time.

The conduits 63 in the lower portion of the front wall of the combustion chamber may be provided with inlet openings at their lower ends, these openings. having dampers 81 controlled by operating members 82. A part of these conduits (for example, each alternate conduit) may have vertically spaced openings 83 extending through the wall of the furnace into the combustion chamber, as shown in Fig. 4, these openings 83 having battle plates 72 similar to those associated with the openings 65.

These conduits 63 which open into the combustion chamber at 83 thus form additional means for admitting air into the combustion chamber in proximity to the path of flame travel. The air entering the conduits 63 through the inlets 80 and rising through the conduits becomes preheated by contact with the lining walls of the combustion chamber and serves to keep these walls cool, as is the case also with the air in conduits 62 and 64. Thus the conduits 63 having the openings 83 form a means for admitting preheated air to the lower part of the combustion chamber in proximity to the path of flame travel, and

also a means for cooling the walls of this part of the combustion chamber. When the furnace is operating at a low rate, the dampers 80 may be placed so that little or no air enters the lower part of the combustion chamher through the openings 83. When the rate is increased, the greater volume of air required may be admitted partly by allowing air to enter the openings 83 and partly by allowing an increased quantity of air to enter the combustion chamber by way of the conduits 62 and openings 65.

The remaining conduits 63 which do not have openings 83 former. therein, are provided at their upper ends with openings 84 leading into a duct or conduit 85 which extends across the front of the combustion chamber, as shown in Figs. 1 to 4. These conduits 63 which open into the duct 85 are provided with inlets 80 and dampers 81, similar to those provided for the conduits having the openings 83 leading into the combustion- The duct 85 is connected by a conduit 86 to the pulverizer 50, as shown in F 1. Thus the air passing through part of the conduits 63, and becoming preheated therein, is collected in the duct 85 and conducted to the pulverizer, where it is mixed conduits tion chamber were connected by means of the with the 'fueliprior to the injection thereof into the combustion chamber.

It was mentioned aboveithat part of the 64 in the side walls of the combusconduit 66 to the upper ends of'the conduits 62 in the front wall of the furnace, The remaining conduits 64 in the side Walls Which are not'so connected to the conduits 62 may open into a duct 90, best shown in Figs. 6 and '1', this duct 90having branches 91' leading to air inlet openings 92 adjacent and preferably surrounding the fuel inlet openings 55. Those conduit-s 64 which are thus connected to the inlets 92 have air inlet openings 69 and dampers 70 to the inlets and dampers provided for the rest of the conduits 64.

The inlet openings 92 provide means for injecting air closely adjacent to the fuel inlet, this being point at which air is needed and in which it will be of considerable benefit in promoting efiicient combustion.

It willnow be seen that an improved combustion chamber has'been provided,- which is equippedwith means for cooling the walls thereof, this. cooling means serving also as air preheating means. Part of the vair' thus-preheated is mixed with the fuel" before its in j ection into the combustion chamber; another partis injected-into the combustion chamber adjacent the fuel inlet; and other parts of the preheated air are arranged to enter the combustion chamber through openingsspaced in the direction of fuel and flame'tra-vel and inproximity to the line of travel thereof. A portion of this last mentioned quantity of an is conducted through passageways so. arranged that it chamber at points comparatively close-to the fuel inlet, and encountersincreasing resist ance as it passes these points to enter the combustion chamber farther along the path of travel of the flame. Various dampersare arranged for controlling the quantity of air admitted to each part of the". combustion chamber. Thus a highly satisfactory and efiicient draft system. is disclosed, which has many advantageous and desirable features.

Although the term fuinace has been used throughout this specification, it should be understood that this combustion chamber has been described in connection with a furnace only by wayof example, andis not limited in its applicationto boilers or furnaces of any particular type, but may be used whereever any, sort 0 combustion chamber isdesired. 1 i V 1 While one embodiment of theinventionhas been, disclosed, it is to be understoodtthat the inventive idea may be carried out in a number. of ways. This application is therefore-not. to be limited to the precise details shown, but'is intended to cover all variations andmodi-ficm at their lower ends, similar into the combustion chamber.

tends to enter the combustion" tions thereof falling within the spirit of the invention or the'scope of the appended claims I claim as my invention: V

1. In a furnace construction, the combination with a combustion chamber, of means for admitting fuel thereto, a plurality of separate conduits extending substantially vertically in a wall of said combustion chamber, said wall having a plurality of spaced openings leading from the lower portion of one conduit into said combustion chamber, and a plurality of spaced openings leading from the upper portion of another conduit into said combustion chamber, means for admitting air to the upper end of the conduit having openings in its lower portion, and means for admitting air to the lowerend of the conduit having openings in its upper portion.

2. In a furnace construct-ion, the combination with a combustion chamber, of means for injecting pulverized fuel into the top of said chamber, a plurality of substantially vertical conduits in the front wall and side walls of said combustion chamber, said conduits having inlet openings leading from the conduits in the front wall into said combustion chamber, means for admitting air to the lower ends of the conduits in the side walls, means forconnecting the upper ends of a part of the conduits in the side walls to the upper ends of the conduits in the front wall, and means for collecting air from other conduits in the side walls and introducing it into the top of the combustion chamber adjacent the inlet for said pulverized fuel.

3. In a furnace construction, the combination with a combustion chamber, of means for injecting pulverized fuel into the top of said chamber, a plurality of substantially vertical conduits in the front wall and sidewalls of said combustion chamber, said conduits having inlet openings leading from part of the conduits in the front wall into said combustion chamber, means for admitting air tothe lower ends of the conduits in the side walls, means for connecting the upper ends of a partof'the conduits in the side walls to the upper ends of a part of the conduits in the front wall, means for admitting air to the lower ends'of the rest of the conduits in the front wall, means for collecting air from the upper ends of a part of said last named conduits, and means for mixing said collected air with .the pulverized fuel prior to its injection into the combustion chamber.

4. In a furnace construction, the combination with a substantially vertically arranged combustion chamber, of a plurality of conduits in the front and side walls of said combustion chamber, mechanism for pulverizing fuel, means for leading pulverized fuel from said mechanism and injecting it into said chamber, means for admitting air to the lower ends of said conduits in a side wall of the chamber, means for collecting air from the upperends of certain of said conduits having admitting means intheir lower ends and for admitting such collected air into said combustion chamber in proximity to the fuel inlet, means for collecting air from the upper ends of certain other of said conduits having admitting means in their lower ends and for supplying such collected air to the upper ends of certain of the conduits in the front wall, such front wall conduits having inlets leading into said chamber, means for admitting air to certain other conduits in the front wall, and means for collecting air from said last named conduits and for mixing such air with the pulverized fuel prior to its in jection into said chamber.

' ROGER D. DE WOLF.

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