US2295781A - Downdraft furnace - Google Patents

Description

Sept; l5, 1942.

J. R. FELLOWS ET'AL DOWN DRAFT FURNAGE Filed March 6, 1940 2 Sheets-Sheet 1 A 4.. d.. ai!

J. R. FELLows Erm. 2,295,781

DOWN DRAFT FURNACE Filed March 6, 1940 2 Sheets-Sheet 2 Fie-z5 WML Sept. l5, 1942:

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Patented Sept. i 5, 1942 nowmmm rUaNAcE :anni nobel-t reno, Urbana, and John clem Miles, Chamvllm Ill.. signments, to University of ors, by meine aslllinois Foundation,

Urbana, lll., a corporation of Illinois Application March 6, 1940, Serial! No. 322,562

z claims. (ci. 11o-24) This invention relates to down-draft furnaces,

or green coal is converted into coke by low temperature carbonization, the volatile matter distilling off and passing under a baille wall and burned without substantial smoke, the temperature necessary for smokeless combustion being maintained from burning coke, and the oxygen and mixing essential to smokeless combustion being provided by an air stream entering adjacent or through said wall, and so arranged thatl when the furnace is recharged with fresh or green coal the coke may be forced down the inclined grate into a coke-burning chamber, the coke burning as a smokeless fuel while the new charge of coal is being coked.

It is highly desirable and it is also an object of this invention to provide in such a furnace for the supply of a proper amount of air for each of the three stages of combustion, preferably from an independent source or opening, with stackdamper control or other suitable draft regulation.

Another object of the invention is to provide 4 a coking chamber with a double roof comprising an air passage for the introduction of secondary air.

A further object of the invention is to provide a novel type of baffle wall separating the upper part of the coking chamber from the upper part of the combustion chamber and so constructed as to form a conduit uniting with that in the roof of the coking chamber forconducting secondary air to that portion of the furnace below the baiile wall.

It is also an object of the invention to provide a grate or grates of Vsuch form and arrangement as to permit proper combustion of the fuel but less than enough for complete consumption of the fuel thereon during Athe period required to coke an entire charge of fresh fuel in the coking chamber.

Other objects and advantages of the invention will readily appear from the following description.

Referring to the drawings:

Figure 1 is a longitudinal sectional view of a portionv of a furnace embodying our invention, diagrammatically shown;

Fig. 2 is a Vvertical sectional view, taken as indicated at line 2 of Fig. 1;

Fig. 3 is a vertical sectional view, taken as indicated-at line 3 of Fig. 1;

Fig. 4 is .a horizontal sectional view, taken as indicated at line 4 of Fig. 1;

Fig. 5 is a front view;

Fig. 6 is a perspective view of grate I8;

`Flg. 7 is a view of the lower end of bale wall I6;

Fig. 8 is a view of another form of grate.

Fig. 9 is a partial sectional view of a modified form of baille wall.

In the preferred form illustrated in Figs. 1-7, inclusive, the down-draft furnace Il comprises a roof I2 having an opening I3 in the upper, front central portion thereof and an air conduit I4' extending horizontally and rearwardly to approximately the mid-portion of said roof and there connecting with a downwardly extending air conduit or conduits I5 in depending, transversely extending baille wall I6 having an opening or openings I1 in its lower end, and refractory portion IIa, the lower end ISb thereof serving as an ignition surface. Suitably supported in said furnace `is a grate I8 having an inclined front portion I 8a, a second inclined portion I9 rearwardly of said first inclined portion, shaker- 'grate portions 20 and flat, rear portion 2l, said rear portion supporting a transversely extending, refractory stop 26 having a face 26a, preferably inclined and positioned adjacent and to the rear f the shaker-grate portions 20; said grate, said baiiie wall and said stop being so proportioned and disposed as substantially to divide said furnace into four compartments or chambers, namely, a coking -charnberr22, a coke-burning chamber 23, a gas-combustion chamber 24, and an ash receiver 25, so proportioned with respect to each other and to the grate area as to conduce to substantially uniform and smokeless consump- V tion of the fuel when air is admitted in suitable proportions.

The inclination of the portion I8a of said grate may be of any suitable angle but is preferably of such angle that the coking coal may be conveniently forced downwardly when the coking has vsuiciently progressed and green fuel is added.

We have obtained good results with an angle of approximately 20 from the horizontal. The inclination of the portion I9 of th' grate is preferably sharper, of the order of 45 to 60 from the horizontal, so as to provide a chamber or pit 23 beneath the baffle wall I6 for the burning of the coke formed in the coking chamber 22, and the provision of a substantially continuous source of heat suitable for igniting the green fuel in chamber 22 and the heating of the ignition surface lsb.

Baiie wall I6 consists of channel plates 33 supported by an intermediate plate 33a. Plates 33 have rearwardly extending iianged portions 3ft and a suitablydisposed anchoring portion 35 extendingthrough an opening 33o provided in said intermediate plate 33a and secured thereto by welding a head 36 on the end of said anchoring portion in position as indicated in Figs. land 4, the rear of said intermediate plate 33a having' suitably disposed indented portions 33h to seat the heads 36.. The plates 33 are preferably of special heat resisting material capable of withstanding a temperature of at least 1800" F. We have obtained satisfactory results with plates of 28% chromium and 8% nickel cast iron. A. heat resisting alloy also is used in welding the head 36. AThe plates 33 may be of any suitable dimensions. We have obtained good results using plates of the material mentioned approximately 3" wide and 1A" thick, spaced a suitable distance, approximately 1x6" in they example referred to, to allow for expansion.

Supporting plate 33a may be of any suitable material such as 5/8" locomotive iirebox steel. The plate 33a 1s of the same width as the furnace but is preferably of substantially less depth than the baille wall to avoid exposing its lower portion to intense heat. Plate 33a may be secured in any suitable manner, by screws, welding, or otherwise, to the sides or roof of the furnace.

The baiile wall may be supplemented by a refractory block or blocks Ilia, which has a cut away portion adapted to t against the rear of plate 33a and beneath its lower portion as shown in Fig. 1. `The block ida may be of any suitable a refractory block they are preferably of they form shown in Fig. 9, the part 33d being disposed beneath the bottom of the supporting plate 33a.

The refractory stop 26 serves to block the coke pushed down from. the coking chamber and to form one sideof the coke-burning chamber; its forward surface 26a, especially the upper portion thereof, also serves as a supplemental ignition surface. for mixing and igniting the gas and air passing over it in a manner similar to the lower portion `Ilb of the refractory surface of the baille Wall i6. While it is preferable to use it,

l y stop 2S may be omitted.

The roof I2 may be so formed as to provide a hood I2a over the door 2, said hood having a laterally extending opening B2b in its underside communicating with air passage It and adapted to admit smoke that maybe emitted upon opening the door 2,1; said door 21 having an outwardly extending horizontal flange 21a across its upper edge adapted to close the .opening |2-b `when the door is closed.

Air is admitted to the furnace through opening 23 in door 2l and opening 30 in door 2@ provided in the front thereof and opening I3 previously referred to in such quantities as may be needed. These openings may be adjustable for various fuels but the adjustment having been determined for a given fuel it should remain unchanged to provide for the admission of relatively xed quantities of air; whatever regulation is required being provided by damper 32 in stack 3l or other suitable draft regulating means.

The opening 28 is of such size and shape and so placed as to admit suiiicient air to the coking chamber for coking the coal at a suitable rate butsmall enough to prevent excessive combustion ofv coke in the coking chamber and thus 'avoid overheating of the materials in the baille wall. The opening 30 and the openings or perforations in the grates are of such configuration as to admit a quantity of air suicient for l maintaining an ignition temperature in the coke thereon at all times but insufcient for complete burning out of the coke on the grate during the period required fully to coke a charge of coal in the coking chamber. The opening I3, the conduit Id-Iiu and openings I l thereof are of such form and proportions as to provide a stream of air suitable for substantially complete combustion of the gases passing beneath the baiie wall and into the gas combustion chamber. As shown the opening i3 is a round hole similar to l openings 28 and 30, while the configuration of openings Il is indicated in Fig. 7. The advantages of such an arrangement is readily apparent. Especially advantageous is the correct proportioningof the quantities of air admitted to the three stages or phases of combustion, namely, primary air to the coking chamber, primary air beneath the grate to facilitate the burning of the coke, and secondary air to mix with the combustible gases beneath the baiile wall and facilitate their further combustion; all being more or less directly related to the configuration of the several chambers and the grate and contributing to the substantially uniform and smokeless consumption of the fuel.

The rate of combustion is controlled by regulation of the draft (usually by means of a check door in the smoke pipe or stack). With such an arrangement it is possible, by proper apportionment of air, to time the several phases of combustion so that, for example, the coke-burning period will be approximately the same as lmodate 40 pounds `of green coal, taking into account the slope of the coal when piled into the coking chamber and` the waste space resulting, or approximately 2 cubic feet; the volume of the coke-burning chamber 23 would be approximately 1 cubic foot; the volume of the combustion chamber 24, depending on the design and arrangement of the heating surface, would be not less than approximately 2 cubic feet. For combustion of such a charge of fuel, using Illinois bituminous coal, to the best advantage and without substantial smoke loss the openings for the admission of air to the furnace should be approximately as follows: opening I3, one and threequarters inches in diameter; 28 and 30, each one inch in diameter. Draft available should be approximately 0.12" of water. Openings I8b and Isa in inclined portions I8a and I9 of grate I8 may be of the order of 1/3" diameter on 1" cenizontal shaker grate portion 2li.

Instead of the arrangement of grates shown in Q v Fig. 6, an arrangement such as that shown in Fig.

8, in which the forward grate has a single inclined portion may be employed. The openings |817 and lila of grate portions l8r, and i9 may be omitted, in which case the free area in the grate 2li should be enlarged accordingly.

While not shown in the dras, the side walls of the furnace would ordinarily be suitably lined with refractory material from the level of the grate to a height approximately even with the lower end of the baille wall i6.

We have used the words coke and coking in describing our invention, not in the limited sense of the terms as applied to the commodity7 known as coke or making or forming that commodity strictly but in the sense of the product resulting when heat is applied to solid fuel and the volatile matter driven oil therefrom, and the process of making or forming such product Our invention is to be understood as residing in the method of controlling the combustion` of fuel as herein set forth as well as in the combi nation, construction and arrangement of par coking chamber, a coke-burning chamber, a com- 4s bustion chamber, a baille wall between said cokingY chamber and said combustion chamber, the lower portion of said baille wall forming an ignition sur-1 face above the forward portion of said cokeburning chamber, a vertically extending conduit through said baille wall having an outlet in the lower portion thereof for introducing secondary air into said furnace downwardly near the forward portion of said coke-burning chamber to mix with and facilitate the combustion of gases emanating primarily from said co chamber and secondarily from said coke-burning chamber., said coke-burning chamber being disposed adjacentl to the lower portion of said cclrins chamber so that coke burning in said coke-burning chamber will provided an ignition surface for gases emanating from the coking chamber, and means for admitting air'into said furnace beneath the coke-buming chamber so as to pass upwardly into the bed of coke bg therein, the parts having' such relative dimensions and being so arranged as to enable the flow of air to the coking chamber and to and beneath the coke-burning chamber in predetermined proportions and 'to provide reguable; progressive. substantially smokeless combustion of successive charges of fuel, proceeding sequentially' through the coking of one charge con- ,curreutly with the burning ci coke derived from a preceding charge.

2. A down-draft furnace as set forth in claim l, in which the outlet of the secondary air conduit is disposed above the rearward portion of the inclined forward grate, the conformation of the structure being such as to provide a stricture between the lower portion of the coking; chamber and the adjacent portion of the coke-burning chamber whereby the fu l charge is retained in the coking chamber untl coke burning in the coke-burning chamber is substantially consumed, and the coking oi the fuel in the coking chamber progresses regulably, forwardly and upwardly from said stricture. u

JULIAN ROBERT rsmows. JQHN CIEM

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