US2374808A - Gravity-fed coal furnace - Google Patents

Description

y 1945- H. c. EDWARDS Q 2,374,808

GRAVITY FED COAL FURNACE- Filed Nov. 19, 1941 5 Sheets-Sheet l HOWARD C .EDWARDS v ilbtomwg y ,1945. H. c. EDw/ARDs 2,374,808-

GRAVITY FED .COAL FURNACE Filed Nov. 19, 1941 s Sheets-Sheet 2 HOWARD QEDWAI DS 1945- H. c. EDWARDS 2,374,808

' GRAVITY FED COAL FURNACE,

Filed Nov. 19, 1941 I 3 Sheets-Sheet 5 FIG.5.

[L v I I HoWA n CEDWA DS Patented May 1945 GRAVITY-FED COAL FURNACE Howard G. Edwards, Zanesville, Ohio, assignor of per cent to Louise E. Marks, Cin

cinnati,

Ohio, and 10 per cent to Emanuel S. .Marks, Cincinnati, Ohio, trustee Application November 19, 1941, Serial No. 419,753

7 Claims. (01.. 110-29) This invention relates to'heatingapparatus, having particular reference to stoves or furnaces of the type adapted for burning solid fuels.

In its more specific aspects, the present invention is concerned with coal-burning stoves or furnaces of the type in which the fuel is fed gravitationally to the combustion zone or grates from an enlarged magazine. A stove or furnace of this category is formed to embody an internal vertically disposed fuel magazine. At the bottom of the latter, a grate structure is provided on which the fuel is supported'for combustion. Air for combustion purposes enters the furnace casing below the grate structure, passing upwardly to combine with the fuel to produce active fuel combustion.

, Surrounding the fuel magazine of such a furnace is an intermediate heat-exchanging casing, the walls of which are spaced from the magazine walls to provide flame-confining chambers at the opposite sides of the magazine, which chambers merge over the top pf the magazine and communicate with the chimney, stack or other'waste gas outlet of thefurnace. The walls of the fuel magazine at the bottom thereof, adjacent to the grate structure, are formed with restricted openings, or are spaced from the grate structure, so that, the fuel gases or volatiles, under draft action of the furnace, are drawn into the flame chambers and, while burning, are passed upwardly therethrough to the waste gas outlet, thereby heating the metal walls of the intermediate casing. Around the latter, such furnaces are provided with an outer casing having its walls spaced from those of the intermediate casing to form passages for the transmission of air to be heated.

Such air, flowing through the passages, becomes heated through heat exchange with the walls of the intermediate casing, the heated air being delivered to a plenum chamber provided in the top of the outer casing.

From the plenum chamber, customary ducts are employed for leading the heated air to the various rooms of a house; or other structure, adapted to be heated by the furnace, and cold air return duct or ducts leads back from the rooms so heated to the bottoms of the air-heating passages disposed between the intermediate and outer casings.

Down-fed, coal-burning furnaces of this classiflcation possess certain advantages .over furnace apparatus of more conventional design, particularly from a standpoint of improved combustion of the fuels utilized and in the storage capacity of the coal-receiving magazines thereof. When its magazine is filled with coal, such a furnace will operate for prolonged periods of time, in an automatic manner, without requiring the frequent fuel replenishments necessary in obtaining proper firing of a conventional furnace. In fact, their operation, without requiring manual attention, is quite analogous to that obtained by the employment of Stoker-fired furnaces, where motor-driven mechanical means are utilized for transferring coal from the hopper or magazine and conducting the coal to the combustion chamber of the furnace. By feeding the coal through the action of gravity to the combustion zone, the expense and complications of mechanical stokers are eliminated,

However, as heretofore constructed, the gravity fed furnace is open to certain criticisms which have militated against its more general adoption.

Such criticisms are largely attributable tothe difiiculty'which such furnaces have encountered in maintaining proper and sustained fuel combustion particularly during periods of low heat demand. Most of these furnaces utilize natural or chimney induced drafts for drawing air through the fuel bed. During periods of low heat demand, with the draft-admitting openings beneath the grate structure closed or restricted, the throttled or subnormal air supply to the fuel is often insufficient tosupport active fuel combustion, Under such conditions, the draft through the restricted openings formed in the furnace between the bottom of the fuel magazine and the 4 magazine, eliminating the presence of smoke in communicating flame chambers, is often inadequate tomaintain proper fuel combustion and to draw the fuel volatiles into the flame chambers from the magazine. This condition often results in causing smoke or gases to travel upwardly, in a manner reverseto their desired or normal travel, through the fuel contained in the magazine, passing to the top of the latter and venting into the furnace room through the fuel-introducing passages, or, in certain instances, causing back-firing explosions.

It is, therefore, an object of the present inven: tion to provide a gravity-fed furnace of the type under consideration with improved means operating under natural draft conditions for produc- \ing a positive, uniform and sustained flow of-air through the grate structure of such a furnace at all stages of operation of the latter, to the end of providing efflcient combustion of thesolid fuels positioned on the grate in the bottom of the fuel the furnace room, preventing back flashes when the feed door is opened, and producing improved combustion of the fuel volatiles in the flame chambers of the furnace.

Another object of the invention resides in providing the flame chambers of such a gravity-fed furnace, at the bottoms thereof, and immediately over the grate structure, with a plurality of restricted Venturi members, which members serve to render positive, uniform and effective air and gas travel through the fuel bed and into the flame chambers, insuring complete mixing of the gases for their efllcient combustion and effecting an adequate flow of air through all parts 'f the combustion zones of the furnace to continuously sustain eflicient fuel combustion'at all stages of furnace peration.

Another object resides in so forming the furnace that all the generated gases will be drawn into the combustion chambers, thus eliminating the accumulation thereof in the reserve fuel chamber.

Another object resides in providing a gravity fed furnace having in the bottom of its fuel magazine a fuel support composed of movable grate. members, said members being disposed to occupy reversely and downwardly inclined positions on each side of the center of the furnace, said grates extending under the flame chambers and providing for increased grate area and also positive lateral spreading movement of the burning fuel on the grates to positions beneath the flame chambers.

Further objects rest in the provision of a furnace of the type set forth which is economical to manufacture and operate; one enabling low-cost fuels to be advantageously utilized; a furnace requiring but a minimum of manual attention to maintain the same in efficient operation; the provision of means for venting the top of the'fuel magazine when its coal-introducing passage is opened; and in other features of construction which will be in part obvious and in part pointed" out hereinafter.

For a further understanding of the invention, reference is to be had to the following description and the accompanying drawings, wherein: Fig.1 is a vertical transverse sectional view taken through a gravity fed furnace formed in accordance with the present invention;

Fig. 2 is a vertical longitudinal sectional view taken through the furnace on the plane indicated by the line IIII of Fig. 1;

Fig. 3 is a detail horizontal sectional view on the plane indicated by the line III-III of Fig. 2;

Fig. 4 is a detail sectional view disclosing the fulcrum supports for the grate members;

Fig. 5 is a horizontal sectional view on the plane indicated by the line V--V of Fig. 1;

' slightly modified form of the invention and showing the auxiliary air-admitting tubes for the flame-chamber Venturi members; x Fig. 7 is a horizontal sectional view through a further modified form of' furnace embodying'the present invention, wherein the furnace is of cir cular formation in horizontal cross section.

Referring more particularly to the drawings, the furnace disclosed therein comprises a base plate I upon which is supported a vertically disposed fuel -receiving magazine 2. This magazine comprises a vertical back wall 3, a top wall 4, side walls 55 and a'front wall 6, the'l'atter also serving as the front wall of the furnace. Near the top of the magazine, thefront wall Sis provided with anopening or passage 1 for the introduction of a solid fuel into the magazine, said opening or passage I being normally opened or closed by means of a hinged door 8, carried in connection with the wall 6.

The open bottom of the magazine, at approximately its center, i provided with a stationary, horizontally disposed grate bar 9 extending longitudinally through the furnace. This bar is formed with journaling trunnions H for cooperation with sockets l0 formed in the upper ends of a plurality of rockable grates [2. These grates are arranged on opposite sides of the bar 9 and slope downwardly in reverse order from the horizontal. The lower or outer ends of the grates G2 are formed with sockets l3, which receive journaling studs l4 formed with and projecting from cast metal side plates l5-I5, constituting the lower part of an intermediate or eat exchanging casing Hi. The lower edges of the side plates I5 rest on the base plate l forming in connection with complemental portions of the back wall 3 an ash pit ll.

Above their vertical lower portions, the plates l5 diverge outwardly and upwardly to form laterally expanded combustion spaces l8. The latter communicate with flame-confining chambers l9-| 9 which are formed between the spaced walls of the magazine 2 and the intermediate casing l6. Above the top wall 4 of the fuel magazine, the flame chambers merge into a common chamber 19a, and a waste gas outlet 20 leads from this chamber to an associated stack or chimney.

The front of the ash pit I1 is closed by means of a hinged door 2| carried by the front wall 6. The door 2| is provided with the usual adjustable draft-controlling opening 22, by mean of which r, drawn from the furnace room, is admitted into the furnace'for passage upwardly through the grate structure and into combustion promoting contact with the fuel reposing thereon. The grates l2 may be provided with depending arms 23, pivotally joined as at 24 with reciprocatory shaker bars 25. The latter extend through the front wall 6 and are connected at their outer ends with grate rocking levers 26. The opening 22 may be covered by a hinged closure member 21. This member may be thermostatically operated, or, if desired, merely manu'ally controlled for governing the volumes of air entering the ash pit for combustion-sustaining purposes.

The lower portions of the walls of the fuel magazine 2 are usually provided with refractory facings 28, and the lower edges of the side walls 5 of said magazine are terminated in spaced relation from the upper surfaces of the grates l2 in order to produce openings, slots or passages 29 through which the fuel passes for combustion. By sloping the grates l2, in the manner indicated in Fig. l, I am enabled, without interfering with the fuel holding capacity of the magazine 2, or'

To further insure this action and the development of flame propagation in the chambers IS,

'the lower ends of the latter have positioned therein a plurality of Venturi members 30. The lower ends of these members are seated on shoulders 3| formed in connection with the side walls 5 of the magazine 2 and the upper portions of i l9. ,these flames sweep over the walls of the heat exchanging casing l8, passing upwardly through the side plates IS. The members 30 serve to produce positively and uniformly an efiective flow of air through the fuel undergoing combustion in the region of the spaces I8, drawingoff the volatiles of such combustion and mixing the same with air in said spaces, so that elongated flame propagation takes place in the chambers When the furnace is in active operation,

the chambers I9 and thence into the upper communicating chamber l9a. The action of these Venturi members is that of controlling an flow through the coal or coke bed, and drawing off gases released from the coal as thelatter progresses through various stages of distillation and the noticeable defects in prior furnaces of this type.

The passages of the Venturi members are, of course, proportioned to create the necessary suction forces for drawing the proper amount of air through the coal or coke bed. .This prevents a higher rate of combustion than that normally desired in the furnace, even though an excess amount of air were to be supplied through the draft door. Further, the Venturi members establish uniform draft conditions over the entire actively burning portions of the fuel bed, avoiding channeling of the draft in localized portions of the fuel bed. As the coal descends in the magazine, it becomes gradually heated, aprogressive distillation operation taking place .in which the volatiles of the coal are drawn off into the Venturi members. The coal thus changes to coke by the time the same is delivered to the combustion grades, the coke burning to produce a non-clinkering ash. This ash may be readily sifted through the slots of the grate members into the ash pit.

The top wall 4 of the magazine 2 is provided with a smoke outlet opening 32, which establishes communication between the upper portion of the magazine 2 and the chamber l9a. This opening is employed to release smoke when the fuel admitting passage l is opened to the furnace room by the opening of the door 8. Normally the opening 32 is closed by a hinged cover plate 33. This plate is provided with a depending finger 34, which rides on the upper surface of a substantially arcuate cam 35. the latter being connected with the door 8. When. the door is opened,

7 the cam 35 is moved to a'position automatically walls of which being spaced from those of the inner casing 16 to provide air heating chambers or passages 31. The lower ends of these passages are connected'by means of suitablecold air return ducts 38 to the rooms of an associated buildm nace is provided with ail outer" casing 36, theing heated by the furnace. As the air is heated, the same passes upwardly through the passages 31, contacting with the walls of the inner casing or has its temperature elevated by radiation from such walls. The heated air passes into a plenum chamber 39 at the top of the furnace and, from this chamber the heated air may be drawn off by means of conventional ducts 40 and delivered to the rooms of anassociated building. A watercontaining reservoir M may be suitably positioned in the chambers 39 to add moisture to the air passing therethrough in a usual manner.

It is, of course, within the scope of the invention to utilize the various auxiliary controls commonly employed in connection with coal burning furnaces, such for instance as thermostatically controlled dampers and doors, motor driven fans or blowers and the like. A thermostatic control for governing the volume of air entering the ash pit through the opening 22, however, is desirable. The furnace operates effectively with low cost coals of small particle sizes,

such as those customarily employed in the operation of furnaces fed by mechanical stokers. The combustion characteristics of the fuel are such that the same burns to a fine ash which is readily passed through the grates when the latter are rocked. Usually the ash pit is provided with a removable tray for convenience in the removal of the ash from the furnace.

As coal descends in the magazine, its temperature, as it approaches the grates, is gradually raised to that when active combustion takes place, such combustion being in the region of the spaces l8. As its temperature increases, volatiles are released from the coal and drawn into the spaces 58 and the associated Venturi members 30. In these members, the volatiles are thoroughly mixed with air and their velocity increased so that elongated visible flames issue from the outlets of the Venturi members. The furnace requires but a minimum of manual attention, and functions to sustain combustion through all stages of heat demand.-

As shown in Fig. 6, the Venturi members it may be provided with auxiliary air admitting tubes 15. These tubes are positioned to by-pass the grate structure and fuel bed. The air inlet.

ends 46 of these tubes may be positioned in communication with the ash pit at points below the grate structure, and the air discharge ,ends M of said pipes enterthe Venturi members at the more restricted portions of their fiuid passageways. By this means, an additional quantity of uncombined oxygen may be introduced into the Venturi passages to aid in the combustion of the fuel volatiles and eliminate or reduce smoke production. In Fig. '7, a further modified form of the invention has been disclosed wherein the fuel magazine 48, instead of being substantially rectangular in horizontal cross section is substantially circular, the same being surrounded by a circular flame chamber 49, in which the Venturi members 30 are positioned.

In view of the foregoing, it will be seen that the present invention provides a gravity fed or self-stoking furnace for burning efiiciently various types of furnace coal. By extending the grates laterally so that the same are positioned beneath the flame chambers and with the use of the Venturi members, greatly improved draft and combustion conditions are obtained in the furnace over prior art -designs wherein the grate structure isconfined to the bottom of the fuelmagazine and highly restricted slots or openings As the Venturi members cause an increase in the rate of gas flow into the flame passages, low pressure zones are created between the Venturi inlets and the fuel bed which cause the gases to be more readily liberated from the fuel in the magazine, drawn into the Venturi and burned. The reduced pressure zones provide for a continuous flow of gases downwardly through the fuel body and efiectively prevent the accumulation of explosive gases in the upper portion of the magazine. To further insure the downward flow of gases through the magazine, the door 8 may be provided with air inlet means which, if desired, may be adjustable. slight amounts to replace that drawn from the space above the fuel to the end that no resistan cc to the gas flow will be oifered.

When unadulterated air is introduced into the flame spaces adjacent to the venturi, this air may be taken from a source exterior of the furnace and may be controlled in amount in any desirable manner. This introduced of air will materially assist in eliminating smoke by efiecting complete combustion of the gases.

While the members 30 have been denominated as Venturi means, it is obvious that the particular shape thereof is not important as long as the elements'employed function to increase the rate of gas flow from the magazine to the flame passages.

While the accompanying drawings disclose certain preferred embodiments of the furnace forming the present invention, nevertheless, it will be understood that the structure illustrated in the drawings, and specifically described above, is subject to change and modification without departing from the scope of the following claims.

What is claimed is:

1. Heating apparatus comprising a casing defining a combustion chamber, a, grate forming the bottom of said combustion'.chamber, an air-admitting ashpit formed in the bottom of said casing below said grate, an open-bottomed fuel magazine having fuel storage capacity mounted withinsaid casing, the lower part of said magazine terminating above said grate, the side walls of said casing being spaced from those of the magazine to provide a vertical flame chamber, the bottom of the latter being in open communication with said combustion chamber and the upper Portion of said flame chamber being in communication with a smoke outlet, and a plurality oi" vertically disposed Venturi members of substantially circular contour in cross section, mounted in the'lower part of said flame chamber, and through which Venturi members all gases and products of combustion released from the burning fuel within the combustion chamber are passed.

Air is introduced in duit means communicating with the ash pit and the side walls of the magazine being terminated,

above said grate structure to provide laterally disposed combustion spaces defined by the walls of said inner casing, grate structure and magazine, the vertical walls of said inner casing and said magazine being spaced to form flame-confining chambers, a smoke outlet communicating with the upper portions of said flame-confining chambers, a plurality of Venturi members which in cross section form substantially regular geometric figures, provided in the lower portions of said flame chambers immediately above said grate structure and through which all the products of combustion released from the burning fuel on said grate structure are passed prior to entering said flame chambers, an ashpit formed by said inner casing below said grate structure, and conbustion chamber above the grate and betweenthe magazine wall and casing wall, said smoke outlet communicating with said combustion chamber and a plurality of conduits in the form of Venturi members, which in cross section form substantially regular figures, interposed between the casing and magazine walls above the grate, and between said grate and said smoke outlet, the said conduits forming substantially the entire passageway between the magazine and combustion chamber and being disposed with their inlets in communication with the magazine and their outlets in communication with the combustion chamber.

4. A furnace for burning solid fuel, comprising a casing having a smoke outlet, a. grate extending substantially across the casing, a magazine having an open bottom spaced above the grate and having at least one wall spaced laterally from a wall of the casing to provide a combustion chamber above the grate and between the magazine wall and casing wall, said smoke outlet communicombustion chamberand being disposed with their inlets in communication with the magazine and their outlets in communication with the combustion chamber.

5. A furnace for burning solid fuel, comprising a casing having a smoke outlet, a grate extending substantially across the casing, a magazine hav-' ing an open bottom spaced above the grate and having at least one wall spaced laterally from a wall of the casing to provide a. combustion chamber above the grate and between the magazine wall and casing wall, said smoke outlet communicating with said combustion chamber, a plurality of conduits in the form of Venturi membars which in cross section form substantially regular figures interposed between the casing and magazine walls above the grate, and between said grate and said smoke outlet, the said conduits forming substantially the entire passageway between the magazine and combustion chamber and being dispoud with their inlets in communication with the magazine and their outlets in communication with the combustion chamber. and conduit means for introducing secondary air into said Venturi members at substantially thethroatsthereoi. n s

6. A furnace for burning solid fuel, comprising I a casing having a smoke outlet, a grate extending substantially across the casing, a magazine havinganopenbottomspacedabovethegrate anddisposed substantially centrally within the casing,

the walls of the magazine-being spaced laterally inwardly from the walls of the casing to provide a combustion chamber above the grate and be- 4 tween the magazine andcasing, said make out-' let communicating with said combustion chamber,

and a plurality of Venturi members which in cross section form substantially regular figures interposedbetween the casing and magazine walls above the grate, and between said grate and'said smoke outlet, the said Venturi members forming substantially the entire passageway between the 2,s14,sos

the magazine and their outlets in communication and combustion chamber and'being' dis- 5 posed with'their inlets in communication with theandtheiroutletsincommimication with the combustion chamber.

"I. A furnace for burning solid fuel, comprising a casing having a smoke outlet, a-grate extending substantially across the casing, a magazine having anopen bottom spaced above the grate and disposedsubstantially centrally within the cas-r' smoke outlet, the "said Venturi members form-- ing substantiallythe entire passageway between the magazine and combustion chamber and being disposed with thelr'inlets in communication with with the combustion chamber, and conduit means for introducing secondary air-to said Venturi HOWARD C. EDWARDS,

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