US1646111A - Air-draft system for furnaces - Google Patents

Description

Oct. 18, 1927,

J. REID AIR DRAFT SYSTEM FOR FURNACES Filed Jilly 16, 1926 Patented Oct. 18, 1927.

UNITED STATES JOHN REID, OF NEW YORK, N. Y.

AIR-DRAFT SYSTEM FOR FURNACES.

Application filed July 16, 1926.

This invention relates to boiler-furnaces and en'ibodies desirable improvements over my U. S. Patent No. 1,1'tTO,8T6 dated c tober 16, 1923. It aims to improve the con struction and operation of such furnaces, more particularly with reference to draft control.

One of the principal ditliculties presented to the efficient operation of boiler-furnaces is in the proper supply, distribution and circulation of drafting air in adequate pro portions to and through the 'l'urnai es. Ilnless the air supplied to the furnaces is prop crly distributed and circulated through and ox er the fires in proportions causing the fuel to be burned evenly and steadily over the full area of the grates. inefficient operation and waste of fuel will inevitably result. In the operation of marine engine boilers a especially, for which drafting air must first l;e supplied to the hold of a vessel by means of air ventilators. efficient distribution or supply and etl'ectual circulation of the air to and through the furnaces is problematb cal. lt is therefore essential that the limited supply of air forced below for the induced drafting of ship furnaces should be utilized to the best (Ill *antage. drafting air to the furnaces. forced draft systems are very generally employed, but while such sy tems may :csist in supplying available air to the furnaces, they do not climinat'c the difficulties encountered. nor enable the furnaces to be operated at maximum efficiency. especially in ships where there are a number of turn-aces to be kept in operation siniultaneously. One of the reasons for the incomplete success of such systems is that in addition to the problem of supplying requisite amounts of air to the furnaces, there is also the problem of etl'ecting a proper distribution and circulation of the delivered air thercthrough. This lattcr problem seems to have been largely overlooked by marine engineers. as there has been very little done to overcome it in practice during the past several years.

In boilcr-furnaces of the different types in general use. particularly in marine work, the air supply has not heretofore been utilized to the best advantage within the furnaces. and the cost of operation is therefore t XtfcA-sltt through loss of heat and waste of fuel in furnace constructions lacking in pro vision of proper means for controlling the To aid in supplying Serial No. 122,948.

air circulation therethrough. In furnag es of \arious types and constructions, I have observed that the fuel generally burns effectually onl at. the back of the grates. This obvious y results from the fact that the air supplied to the furnaces, either by natural or forced draft, is allowed to, pass largely uncontrolled through the ash-pitopenings and is almost invariably drawn under the stack-draft directly toward the back of the grates Where a very hot fire naturally results. Since the air is thus free- 1y drawn to the back of the grates instead of being properly distributed over the entire tire-bed. the fuel at the front of the grates receives little if any drafting air and therefore burns very slowly and inefliciently. Furthermore, this slowly'ignited and inetl'ectually-burned fuel at the front ends of the grates not uncommonly becomes smothered with green fuel resulting from the frequent stolting which is necessar in order to sustain the tires at the back 0 the grates. Large volumes of smoke and incompletely consumed gases from the fuel at the front of the grates are therefore c0n tinuously carried off through the funnels, with consequent loss of heat and undue waste of fuel.

In order to remedy this condition, which seems generally to be considered the result of insnliicient air circulation through the furnaces, it is common practice to increase the speed of the draft fans so as to deliver the drafting air with greater force through the air trunks. This may inetfectually relieve the condition in one or more furnaces in a group, but inevitably disturbs or injuriously affects the operation of other furnaces. The practice also frequently imposes an overload upon the draft-tans and cannot possibly correct the condition in furnaces as heretofore constructed.

I have discovered that the most efficient and economic operations, with substantially complete combustion and great saving of fuel, depends upon the maintenance of a comparatively gentle but steady and properly controlled circulation of air to the furnace and through and over the fire-bed from the forward end of the grate. rather than by increasing the force of air circulation through the grate as is now done. I have also found that controllable means for properly distributing and directing ade- Ill) quate proportions of air to circulate through and over the tire-beds under varying working requirements, induces the complete combustion of fuel over the entire grate-area and will materially increase the efficiency of boiler operation with great savings in fuel, regardless of the frequency or carelessness of stoking, since no part of the fire-bed is left unaffected by drafting air, so that rapid ignition and etiicient burning of the fuel is assured. My discovery conclusively shows that the principle of operation and constructive designs of difierenc types of boiler-furnaces in general use are defective and subject to material improvement.

The method embodying this invention and means for carrying the same into effect are based upon a somewhat different prin ciple from that upon which different types of boiler-furnaces heretofore known and used have been designed to operate. This method and suitable means for effecting its practice in the operation of furnaces are readily adaptable to boiler-furnaces of various types of manufacture and require mere corrective changes in standard constructions, which changes are negligible in cost as compared with the great savings in fuel made possible within brief operating periods. The invention necessarily embodies changes of somewhat differing character and varying extent in the different types of boiler-furnaces now in use, but the necessary changes in each type are based upon the same operative principle of air draft and seek to accomplish the same effectual resultv For this reason. the means for carrying my improved method into practice obviously may not be standardized beyond the fundamental principle and a general form of means embodying the invention for etfecting the desired results in different types of furnaces.

The invention will best be understood by reference to the accompanying drawings in which a furnace of practicable form is shown adapted to be operated ac ording to my improved method with means for assuring a proper distribution and adequate circulation of air through and over the firebed from the for aid end of the grate so that the fires may be evenly maintained at maximum heat-producing efficiency with resulting economic consumption of fuel and prevention of waste.

In said drawings:

Fig. 1 is a sectional side elevation of an illustrative water-tube boiler of known type in which appropriate changes in the other wise standard furnace construction have been incorporated to adapt the same to op eration according to my improved method of air distribution and circulation through and over the fire-bed; and

Fig. 2 is a fragmentary sectional view of the lower part of the furnace. illustrating a practicable modification of the structure shown in Fig. 1.

Referring to the drawings, the illustrative furnace is shown constructed with the usual front and back walls or shells b and 4 respectively, a bridge with fire-back wall 5, water-tubes 6. a bottom ash-pit space 7 and grate-bar sections 8 spanning the ashpit space from front structure to fire-back wall or bridge,

The ash-pit space of the furnace is advantageously divided into sections by means of diaphragm plates 9 disposed longitudinally under the gratebars on partitioning lines between the ash-pit openings in the front structure of the furnace. only one of said plates being visible in the sectional views of the illustrative furnace-structure. Closing the ash-pit openings in the front structure of the furnace. ash-pit doors 10 are provided. Said doors are shown adapted to be swung inwardly on intermediate pivots rather than outwardly as is more. common, and means are represented for holding said doors in the desired angular positionv Air in adequate volumes may be supplied to the ash-pit openings either by natural or forced draft and in Fig. 1. the terminus of an air-feeding trunk 11 of a forced draft system has been indicated in dotted lines overextending the ash-pit door opening.

Between said ash-pit door and the fire door 3 in the front-structure of the furnace, controlled louver-openings 12 are shown provided through which auxiliary supplies of air may be admitted for circula tiou around the hollow tire-door fram s 3* and through the inner perforate walls thereof over the fire-bed.

A hollow dead-plate 13 is shown dis posed transversely along the front end of the grate through which a substantial or variable proportion of the air supplied through the ash-pit opening may normally be directed through and over the top of the fire-bed as indicated by the arrows.

l\leans for dire ting air through said hollow dead-plate is shown provided subiacent said plate and the fire-door frame. In Fig. 1. said means is represented in the form of an elongated flue-member or box-like structure open at opposite ends or sides. which may be divided into a series of funnel-l ke spaces by means of transverse partition plates. Said means or member. hereinafter referred to as the air director. is shown pivotally mounted to swing in angular adjustable relation to the dead-plate and ashpit door.

An opening 16 is shown provided in the sill or base-extension-plate 3 of the tiredoor frame structure, through which a sub fit) lltl

stantial proportion of the air from the ashpit opening will be directed upwardly into the fire door opening and thence over the fuel forwardly of the hollow dead-plate at the front of the grate, as indicated by the arrows. The air passing through said opening 16 and circulated with drafting effect over the fire-bed may be referred to as the top air supply.

Abutting the vertical edge of the perforate inner wall of the hollow tire-door frame on a line of partition or division between fire-door openings of the furnace, a perforate cast iron baffle-plate 15 is shown. into and through which air is supplied to the hollow shell of the furnace or the frame of the fire-door opening may be directed to jet or nozzle over the top of the tires above the aforesaid top air supply.

An opening 17 is shown provided in the outer wall of the hollow fire-door frame 3 through which the auxiliary supply of air entering at the louverqueuing 12 will pass to circulate around said frame and through the perforate walls thereof over the top of the fire-bed. A portion of this air passing around the tire-door frame may, as above suggested. he directed into and through the perforate baffle-plate 15 which is preferably triangular in cross-section so as to jet or nozzle in fan shape over the fire-bed with advantageous ctlert in sup plementing the top air and auxiliary air supplies through the tiredoor opening.

A plate 18 is shown secured to the bottom of the fire-door frame to provide a partition between the top air and auxiliary air- supply openings 16 and 17 respectively. An inclined air -deflecting plate 19 is also shown bolted to the bridge-plate at the back of the ash-pit space for a well known purpose.

From the foregoing description with reference more particularly to Fig 1. it will be appreciated that air supplied to the ashpit space, either by natural or forced draft. may be directed in proper proportions under, through and over the top of the fuelbed so as to cause an even burning and complete combustion of fuel throughout its entire area, with increased efficiency and matcrial saving of fuel in boiler operation.

In practice. the tire door 3 is kept normally closed while the ash-pit door it) should be set in angular position causing the most effectual distribution under \\'()I'l iug conditions of the air entering the furnace through the opening of said door: The airdirector 14 should also be set in a position most effectually causing air to be directed through the hollow dead-plate 13 over the tire-bed. hen these two elements have been fixed in effectual position, a substantial proportion of air entering the ash-pit opening over the top of the ash-pit door will obviously pass through said air-director and hollow dead-plate members under the suctional force of the funnel draft, with effectual draughting or combustive action upon the fire-bed at the forward end of the grate. A portion of th air supply entering the ash-pit opening will also pass or circulate below the air director and be drawn through the grate section along the front thereof. A. hot tire and complete combustion of fuel at the forward end of the grate is thus assured. because the air passing through and under said air-director is adequately distributed over the width of the fire-bed. its force of flow being sufficient to 'ienetrate the fuel-bed so as to produce ctfectual and rapid combustion.

Air entering or forced into the ash-pit space under the ash-pit door may be left free to circulate below the grates in the man ner indicated by the arrow as is common in present furnace constructions. thus supplying adequate proportions of drafting air for the fuel from below the grates. This air flowing under the grate tends to move more gradually toward the back of the grate section and will maintain a hot tire at that point as heretofore. while part of such air will be drawn through the fuel-lied at intermediate HftlfIth' 11s it moves along the length of the grates by the su tional force of the top-air cir ulation. rihould it he desired more effectually to break up or retard the flow of the bottom drafting air toward the back of the grates. deflector plates 20 similar to those shown in Fig. 2. may be provided at inter mediate points along the length of the grate section to pocket the air so that it inav be drawn through the grates at intern'iediate points from front to rear.

A proportion of the air entering the ash pit space over the top of the ash-pit door will obviously pass oyer the top of the air-director and through the opening 16 in the extension-plate of the tire-door framestructurc. forwardly of the hollow dead-plate. This air. termed the top air supply which becomes quickly heated. passes over the top of the lire-bed. aiding the draft through said deadplate so as to maintain an even and .steady circulation of air over the fuelbed at all times. thus assuring the effective and complete cmnbust'ion of gases arising therefrom.

The auxiliary air supply entering through the louver-opening 12. passes through the opening 17 into the hollow tire-door frame to circulate therearound where it becomes heated and emerges through the perforate walls thereof so as to project or flow over the fuel-bed, thus augmenting the top air circulation over said tire-be\'l. A portion of this auxiliary air supply circulating through the hollow lire-door frame may be directed into and through the perforate baffle-plate 15 so as to jet or nozzle in spreaded flow over the fire-bed with advantageous effect in supplementing the top-air draft as herein before stated.

By the means described for effecting the operation of a furnace according to my improved method of air distribution and circulation within the furnace. a maximum efficiency in performance with greater saving in fuel may be attained in spite of careless stoking. Should the hollow dead-plate member 13 become entirely covered with a bed of green fuel which interrupts the normal circulation of drafting air therethrough or completely smothers the air draft through the front of the grate section, the increased force of suction under the funnel draft, resulting at the forward end of the fuelbed, will cause air supplied to the ash-pit space to be drawn proportionally in much greater volume and with increased force through the top air feed-opening 16 and through the perforate walls of the fire-door frame and baffle plate members over the fuel-bed. thus producing a stronger draft or circulation of air over the fire-bed in compensation for the air normally drawn through the dead-plate. whereby the smoke gases which would otherwise accumulate densely at this point. will immediately be cut and carried off through the funnel. while the normal air draft through said hollow dead-plate member will be gratlually reestablished, so that the fuel will continue to burn effectually rather than smother the fire and the temperature at the forward end of the grate will be maintained at high degree permitting the desired chemical reactions of combustion to take place with resulting maximum efficiency in operation. The gradual restoration of the air draft through the hollow dead-plate member 13 under the above described conditions. is augmented by the correspondi ng force of suction created in the ash-pit space into which the air is drawn for distribution, whereby a portion of the air supply becomes trapped below the grates and above the air director from whence it is drawn strongly by the force of suction above the fuelbed and pressed by the incoming volume of air below the fuel-bed so that it quickly finds its way through the dead-platc member and openings between the door frames. and provides an adequate volume or supply of air for the suction over the fire to feed upon. This is a highly advantageous feature resulting in a furnace constructed or modified in accordance with my invention.

It is of course important in the efficient operation of boiler-furnaces according to this invention. that air in adequate \olume should be supplied to the furnaces through their ash-pit openings, as the hereinbefore described method and means for effecting a proper distribution and circulation of air within and through the furnaces in requisite proportions would not assure maximum efficiency in operation unless a sufficient volume is supplied thereto. The proper distribution and circulation of air through the furnaces is not alone sufficient to assure efficient operafimi and pl'OYttlitltiOll of waste. The distributive \olume of air supplied to the furnaces either by natural or induced draft must be sufficient to promote complete combustion of fuel without restricting the funnel draft or stifling the fires. However, suitable means for supplying adequate volumes or proportions of drafting air to the furnaces embodies subject-matter separate and distinct from the present invention and need not therefore be shown or described herein.

The advantages of my in'iproved structure with provision for automatic correction by alternatiy'e flow of air in effective circulation under. through and over the top of the fuel-bed from the forward end of the furnace. will be obvious to those familiar with the difficulties presented to the effectual op eration of boiler-furnaces as at present constructed and operated.

In the boiler-furnace construction of modified form shown in Fig. 2, an air-director clement li f is shown in the form of an elongated plate-member mounted to swing on a pivot and adapted to be held in adjusted position. In such form, the air-director is more in the nature of a guide-vane than a ffucancmber as in the form shown in Fig. 1, but will function similarly to accomplish substantially the same result. \Vhen an air director of this latter form is employed, the air entering the ash-pit opening over the top of the ash-pit door is permitted a somewhat less restricted distribution and circulation through the dead-plate and top air feedopening 16, so that a larger proportion of the air may pass through the latter opei'iing than would be the case in the first defined form. In the modified furnace structure. inclined deflectorplates 20 are shown provided at spaced intervals beneath the grate for the purpose of breaking up or retarding the circulation of air toward the back of the grate. entering the ash-pit opening below its door, as hereinbefore indicated in describing the operation with reftu'ence to the structure shown in Fig. f.

In this figure also. an arcuate plate .21 is shown secured below the tiresdoor frame in substitution for the partition plate 18 in Fig. f. This arcuate plate separates the air entering the ash pit opening from the air entering the louvci opening 12. causing the latter supply to pass directly into the hollow fire-door frame 3" and into the baffle-- plate 15 through the perforate walls thereof over the fire-bed, as hereinbefore described with reference to the preceding figure. This what different form from that represented in Fig. 1. The air defiector 19 in this figure is also of slightly different form and cxtent from that shown in the preceding figure, the lower part thereof in the latter figure being shown hinged and adapted to swing for convenience in cleaning out the ash-pit space.

The operation of the furnace illustrated in the modified structure is substantially the same as that hereinbefore described with reference to Fig. 1, the movable parts mentioned being similarly related and adjustable to position assuring a proper and adequate distribution and circulation of drafting air through and over the fuel-bed so as to cause the effectual burning and consumption of fuel.

From the foregoing description, it will be appreciated that the illustrated structures provide material improvements adaptable to boiler-furnace constructions of different types, which will eliminate faults in design and structure heretofore preventing the efficient and adequate distribution and circulation of drafting air therethrough. The highly beneficial results obtained according to my invention. enabling the efficient and economic consumption of fuel in boiler operation. will be obvious'to those skilled in the art.

Since various changes in form and construction may be made and different coinbinations and sub-combinations may be embodied in a furnace in structural modification thereof. or in the development of new designs adapted to operate according to the method embodying this invention without departing from the spirit and scope there of, I do not wish to be limited by the appended claims to the specific constructions and arrangements hereinbefore illustratet and described.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. The improved method of drafting a furnace, which consists in supplying air to the front of the furnace below the level of the grate in a continuous comparatively gentle flow; causing a portion of the air supply to pass under the grate with a retarded rearward movement; causing another portion of the air supply normally to pass through a section of the grate and rearwardly over the fuel-bed at the forward end of the grate; causing still another portion of the air sup ply to pass rearwardly over the fuel-bed from a point forwardly of the grate and forwardly of that portion of air supply passing through a section of the grate at the forward end thereof so as to provide a top air circulation effecting combustion of fuel at the forward end of the grate, thus aiding the induction through the grate and fuelbed of the air circulating under the grate by the force of off-draft suction above the tire-bed; causing an additional portion of air supply to circulate around and into the furnace fueling opening and thence over the fuel-bed from points forwardly of that portion of air supply passing over the fuel-bed from a point forwardly of the grate so as to supplement the top air circulation and volatilize gas es passing with the off-draft; said drafting air circulations being maintained with the fire door normally closed. whereby the air supplied to the furnace will be evenly and uniformly distributed under, through and over the bed of fuel to effect perfect combustion thereof throughout its entire area.

2. The improved method of drafting a furnace, which consists in supplying air to the front of the furnace below the level of the grate in a continuous comparatively gentle flow; causing a portion of the air supply to pass under the grate with a retarded rearward movement promoting its induction through the grate and fuel-bed at intermediate stages therealong; causing another portion of the air supply to pass normally through a section of the grate and rearwardly therefrom over the fuel-bed at the forward end of the grate; causing still another portion of the air supply to pass rearwardly over the fuel-bed from a point forwardly of the grate and forwardly of that portion of air supply passing through a section of the grate at the forward end thereof so as to provide a top air circulation effecting combustion of fuel at the forward end of the grate and aiding the induction through the fuelbed of the air circulating under the grate; causing an additional portion of air supply to circulate around and into the furnace fueling opening and thence over the fuelbed from points forwardly of said portion of air passing rearwardly over the fuel-bed from a point forwardly of that portion of air passing through a section of the grate at its forward end, so as to supplement the top air circulation and volatilize over the fuel-bedz said drafting air circulations being influenced by the force of off-draft suction above the fuel-bed and maintained with the furnace fire door normally closed. whereby the air supplied to the furnace will be evenly and tlllifOI'IIllfV di tributed under. through and over the bed of fuel to effect perfect combustion thereof throughout its entire area.

v. The improved method of drafting a bed of fuel on the grate section of a fur nace. which consists in supplying air to the furnace in a continuous comparatively gentle flow under the suctional influence of the off draft flue at a point below the level of the grate; causing a portion of the air supply to circulate under the grate with a retarded rearward movement promoting the induction of such air through the grate and f1 telbed at intermediate stages of its movement thereunder; causing substantial proportion of the air supply to be directed normally upwardly through a section of the grate and over the fuel-bed from a point at the for ward end of the grate; causing another por tion of the air supply to be directed upwardly through the bottom of the furnace fueling o ening and rearwardly over the fuel-bed rom a point forwardly of that portion of the air supply normally passing through a part of the grate section so as to effect a top air circulation over the fuelbed tending to aid the induction therethrough of the air circulating under the grate; and causing an additional portion of the air supply to circulate around and into the fueling opening and over the fuel-bed from points forwardly of that portion of the air supply passing through the bottom of the fueling opening, said additional portion of the air supply providing an auxiliary circulation of air over the aforesaid top air circulations for effecting the complete combustion of gases arising from the fuel-bed at the forward end of the grate whereby the air supply is evenly and uniformly distributed under, through and over the bed of fuel to effect perfect combustion thereof.

4. The improved method of drafting a furnace, characterized by supplying air in comparatively gentle flow to the orward end of the furnace at a point below the level of the grate; effecting a division and circular tion of relative proportions of the air supply in diverging directions from the point of admission to the furnace; directing a portion of the air supply to move below the furnace grate with a retarded rearward movement promoting the induction of such air through a bed of fuel overlying the, grate, at intermediate stages of its movement thereunder by the force of euction from the off-draft flue; directing a substantial portion of the air supply to pass normally through a section of the grate at the for ward end thereof and over the bed of fuel in a comparatively gentle draughtiug action upon the fuel-bed so as to effect the combustion of fuel overlying the grate section at such points directing another portion of the air supply to pass upwardly through the bottom of the normally closed furnace fueling opening and rearwardly over the fuelbed from a point forwardly of that portion of the air supply normally passing through a section of the grate so as to effect a top air circulation; and causing an additional portion of air supply to circulate around and into the furnace fueling opening and over the, fuel-bed from points forwardly of that portion of the air supply passing through the bottom of said opening for supplementing the aforementioned circulations of air over the fuel-bed and effecting the combustion of any gases accumulating at the for ward end of the fuel-bed, whereby air is evenly and uniformly distributed and caused to circulate under, through and over the bed of fuel to effect perfect combustion thereof over the entire area of the grate by the force of a gentle flow of air through the furnace.

5. The improved method of drafting a bed of fuel on the grate section of a furnacc. which consists in continuously supplying air to the front of the furnace below the level of the grate at a rate of flow and in volume substantially directly proportional to the rate and volume of discharge through the off-draft flue; effecting a distribution and circulation of the air supply in relative proportions under, through and over the fuelbed from the point of air admission to the furnace so that a portion of the air supply will pass normally through a section of the grate and rearwardly over the fuel-bed at the forward end of the grate and another portion of the air supply will pass continuously through the bottom of the furnace fueling opening and rearwardly over the fuel-bed from a point remote from and forwardly of that portion of the air supply normally passing through a section of the grate at the forward end thereof, while still another portion of the air suppl 7 is caused to circulate under the grate with a retarded rearward movement promoting the induction of such air through the fuclbed at intermediate stages of its movement thercunder by the force of off-draft suction over the fuel-bed; an additional portion of air supply being simultaneously caused to circulate around and into the fueling opening and rearwardly along lines extei'uling above the aforesaid top air circulations from points forwardly of that portion of the air supply passing through the bottom of the fueling opening to effect a slq'iplemental top air circulation assuring complete combustion of fuel and gases over the entire area of the furnace grate.

6. The herein described method of supply ing and distributing air in a furnace so as to effect complete combustion of fuel, which consists in introducing air at the front of the furnace below the fuel-supporting grate and effecting a retarded movement of a portion thereof beneath the grate toward the rear of the furnace; dividing and causing a portion of the air so introduced to pass upwardly at the front of the fuel-bed and rearlit) lot)

Ill)

lllf) wardly along the upper surface thereof while another portion is directed upwardly at a point nearer the furnace front and caused to move real-wardly therefrom so as to provide a top circulation of air overlying the first mentioned rearwardly moving portion, thereby inducing a flow of air supplementing and increasing th quantity of air flowing normally from below upwardt through the fuel-bed. and pre-heating and introducing pro-heated air at the front of the furnace to be con'uningled with the aforesaid portions passing upwardly and rearwardly along the top of the fuel-bed.

7. The herein described method of drafting a bed of fuel on a furnace grate. which consists in effecting a division and circulation of relative proportions of the air supply in diverging oirections from the point of delivery to the furnace: causing a portion of the air supply to circulate under the grate with a retarded rearward tl.0\'0- ment promoting the induct on of such air through the grate and fuchbed at intermediate stages thercalong by the force of suction from the off-draft: causing another l)()ltion of the air supply normally to pass upwardly through a section of the grate at the forward end thereof and rearwardly therefrom over the fuel-bcdz causing still another portion of the air supply to pass continuously u] vardly through the bottom of the furnace fueling opening at a point forwardly of the grate and forwardly of that portion of air normally passing through a section of the grate, and rearwardly therefrom over the fuel-bed so as to provide a top air circulation for effecting the combustion of fuel at the forward end of the grate and aiding the induction through the fuelbed of the air circulating under the grate. while causing an additional portion of air supply to circulate around and into the fueling opening and over the fuel-bed along lines extending above the aforesaid portions of top air circulation from points forwardly of the portion passing through the bottom of the fueling opening; that portion of the air supply normally passing through a section of the grate at the forward end thereof being caused to pass upwardly through the bottom of the fueling opening and rearwardly over the fuel-bed in supplei'nenting volum. and increasive force with the portion of air supply continuously passing there through. when a blanket of fuel is thrown upon that section of the grate through which said portion of air supply normally passes. thereby temporarily preventing the passage of said air therethroun'h: such increased volume and force of air circulation over the fuel-bed from a point forwardly of said fuel-blanketed section of the grate producing a rapid combustion of the blanketing fuel upon said section of the grate so that air ma again find its way therethrough,

thus quickly restoring the normal circulation of said portion of the air supply through said section of the grate. whereby an even and uniform distribution of the air supply is automatically maintained under. through and over the bed of fuel to effect the continuous and perfect combustion thereof.

8. In combination with a furnace having a fuel grate with hollow dead plate. an ash compartment a normally closed fueling opening, and an off-draft flue; means for c ntrolling the admission and effecting a division of an air supply to the furnace, whereby a portion of the a r supply is directed under the grate with a retarded rearward movement; means causing another portion of the air supply to pass through the hollow dead plate and rearwardly of the furnace above the fuel overlying the grate: means located between the dead plate and the closure for said fueling opening whereby still another portion of the air supply is caused to pa s through the bottom of the fueling opening and reary'ardly therefrom over the fuel-bed: and means causing an additional portion of air supply to pass around and into said fueling opening and over the fuchbed from points forwardly of said portion passing through the bottom of said opening.

1). In combination with a furnace having a. fuel grate with hollow dead plat-e. an ash compartment, a normally closed fueling opening. and an oft-draft flue: means below the level of the grate for controlling the admission and effecting a division of an air supply to the furnace. whereby a portion of the air supply is directed to circulate under the g ate with a ctarded rearward movement: means causing another portion of the air supply to upwardly through the hollow dead plate and rearwardly of the furnace in blasting action upon fuel overlying the grate: means causing still another portion of the air supply to pass upwardly through the bottom of the fueling opening and rearwardly therefrom over the fuelbed from a point forwardly of the dead plate: and means causing an additional portion of air supply to pass around and into said fueling opening and over the fuel-bed from points forwardly of said portion passing through the bottom of said opening.

10. In combination with a furnace having a fuel grate with hollow dead plate. an ash compartment. a normally closed fueling opening. and an off-draft flue: means below the level of the grate for controlling the admission and effecting a division of an air supply to the furnace. whereby a portion of the air supply is directed to circulate under the grate with a retarded rearward movement; means causing another portion of the air supply to pass upwardly through the holill) low dead plate and rearwardly of the furnace over the grate: means causing still another portion of the air supply to pass upwardly through the bottom of the fueling opening and rearwardly therefrom over the fuel-bed at a level above and from a point forwardly of the dead plate; means causing an additional portion of air supply to pass around and into said fueling opening and over the fuel-bed at a level above and from points forwardly of said portion passing through the bottom of said opening; and means tending to retard the circulation of that portion of air moving below the grate toward the rear thereof.

11. In combination with a furnace having a fueling opening and closure therefor. a back off-draft flue. an ash compartment and a fuel supporting grate with hollow dead plate member; means below the level of the grate for controlling the admission and effecting a division of an air supply to the furnace, whereby a portion of the air supply directed to circulate under the grate with a retarted rearward movement: means for 'lirecting a portion of the air supply norn'i'illy through the hollow dead-plate member and i'e'tuwardly over the fuel-bed at, the forward end f the grate: means for directing :ino! through the bottom of the normally closed fueling opening and rearwardly over the fuel-bed from a point forwardly of the deadplate member to aid combustion of fuel at the forward end of the grate; and means for effecting the circulation of an auxiliary sup- P f f air around and into the fueling opening and rearwardly over the fuel bed along ines extending over the aforesaid top air circulations from points forwardly of that portion of the air supply normally passing through the bottom of said opening for volatiliziug gases arising from the fuel at the forward end of the grate.

In testimony whereof I affix my signature.

J OHN REID.

ner portion of the air supply upwardly

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