US2567058A - Apparatus for sequentially degassing and combusting solid fuel having a low sintering temperature - Google Patents

Description

p 1951 D. DALIN ET AL 2,567,058

APPARATUS FOR SEQUENTIALLY DEGASSING AND COMBUSTING SOLID FUEL HAVING A LOW SINTERING TEMPERATURE Filed March 8, 1945 2 Sheets-Sheet 1 6 m m m 6E 6 1' I Z 3* INVENTORS DAVID DALIN, m:%% m h l0 CLAES JOEL GEJROT BY Smw Sept. 4,

' APPARATUS FOR UENT FUEL H NG Filed March 8, 1945 D. DALIN ET AL LLY SSING D DEGA OW SINTERING T P 2 Sheets-Sheet 2 2 f 7 '2, r 23 I -INVENTORS DAVID o CLAES J GEJROT ATM Patented Sept. 4, 1951 APPARATUS FOR SEQUENTIALLY DEGAS- SING AND COMBUSTING SOLID FUEL HAV- 'ING A LOW SINTERING TEMPERATURE David Dalin, Ronninge, and Claes Joel Gejrot, Qrebro, Sweden; sa irot assig r to said Dal a Application March 8, 1945, Serial No. 581,700 In Sweden March 31, 1944 4 C aims.-

as in the combustion of such slates in undistilledcondition. Many different methods have been used for the control of the temperature in the fuel charge, such as water .cooled walls and tubes arranged in different ways. However, the nature of the fuel and its qualities from the point of view of combustion have not been duly considered. Thus, the size of the fuel is of very great importance from the point of View of combos..- tion. The individual fuel pieces must not be too large .or too small. In the combustion .de-- vices of the types now used the piece size, which is the best with regard to the combustion, might vary from 5 to 3.0 mm. in cross section. Yet this fine size involves rather great crushing .cost. Therefore, it is desirable to considerably increase the maximal piece size. In combustion furnaces constructed according to the present invention it has been possible to advantageously .combust fuel pieces having a diameter of up to 120 mm. Of course, the crushing cost for such .a material will only be a sli ht fraction of the sam cost o finer pieces. a considerable cnonomic gain in itself.

Wi h the methods now in use the combustion of the fuels in question takes place rather slowly because the combustion temperature must be held very low and because for this reason the temperature required in the center of the fuel pieces is only slowly reached. -I'Iowever, it has appeared that in those cases in which the com-- bustion temperature can be held as near the sintering temperature as possible without reaching the same, the combustion speed can be increased so that on the same grate surface more than to times as much fuel has been combusted without disadvantage than What is possible with the methods now in use. Accordingly, as the combustion proceeds the caloric value of the fuel naturally sinks. Therefore, in order that the combustion shall become as complete as possible and proceed at a tolerably uniform and quick rate, it is necessary that the oxygen content of the air should bcthe highest Where the caloric value of the fuel is the lowest, and decrease as the caloric value of the fuel becomes greater. Finally the rest .of it leaves the fuel shaft with the gases containing the greatest possible The use of larger pieces thus means carbon dioxide con-tent obtained by the combustion, without any great quantities of uncombusted particles or COegases accompanying the flue gases.

The present invention has for its object to control the temperature in the fuel charge by leading off and utilizing the heat obtained by the combustion so that in all parts of the fuel charge he temperature is the most suitable for the purpose and heatin 0 ,Sintering temperature is prevented.

According to the invention we use a vertical fuel charge of considerable depth to which the fuel is fed at the top, and the ashes are discharged from the bottom of the charge by means of Suit-rable dlscharge rolls and gather in an airtight chamber preferably provided with a water seal so that the ashes are extinguished and can be conveyed off in cold state. As the ashes are discharged, the fuel charge sinks due to its own weight, and a corresponding Quantity .of new fuel is supplied from the top. The combustion air is supplied below the grate preferably by means of a fan so that a pressure higher than atmospheric pressure prevails under the fuel bed. Of course, good results might also be obtained even if the combustion air is sucked through the fuel charge.

In any event the air most rich in oxygen is admitted through that portion of the fuel charge Which has the least caloric value or, in other words, is most burnt out. The most intense com-- bus'tion takes place in a zone lying somewhere midway between the grate and the uppermost portion of the fuel charge where the uncombusted or raw fuel is fed in. In order to control the temperature in the fuel charge so that the quickest and best possible combustion per grate area and volume unit of the fuel bed takes place without any drawbacks ensui throu h the si er n of the u l o the shes, tub coi s are arran ed to be mb dded with n the fuel char e.

and a heat absorbing medium is circulated through said coils. This medium consists either of water, a mixture of water and steam, or steam alone, in which latter case heat is absorbed by superheating of steam. In the first mentioned two cases heat is absorbed by heating the water or by steam generation. Thus, the coils may form part of a hot water boiler, a steam boiler or a superheater, or a suitable combination of the same.

In order that the control of the temperature in the fuel bed shall be most suitable for the character of the fuel throughout the height of the column, the tube coils are preferably disposed vertically to project into the fuel charge like fingers, and are of difierent lengths so that the total heat absorbing (cooling) surface of the coils is substantially proportional to the intensity of the combustion in the different portions of the fuel charge. Consequently, that portion of the fuel charge where the most intense combustion takes place and where the highest temperature would be reached if measures had not been taken to prevent a detrimental temperature increase, will have the largest heat absorbing surface. With the coils arranged like fingers the wear thereon is reduced; and moreover this arrangement facilitates replacement when necessary.

The distance between the different coil portions and the coils mutually must be adjusted in such a way that the cooling of the fuel bed which takes place by the heat absorption effected by the coolant circulating through the coils, is sufficient to prevent the temperature rising to the sintering point of the fuel quantity lying between the respective coil portions. Heat transmission from the fuel charge to the coils takes place substantially by radiation and only to a small degree by direct contact.

The combustion air which is admitted from below, first passes through the ash bed where it is preheated and at the same time cools the ashes, then passes through the most combusted fuel charge where, due to the high oxy en content of the air, a comparativelv good combustion still can be maintained. F nallv, after having pa sed the fuel charge most rich in calories, the combustion air preferably leaves as fiue gas most rich in. carbon dioxide to a waste gas boiler where the heat still present in the waste gases is further utilized.

In practise it has been found that the intensity of the combust on fluctuates considerably, partly because of varyi g caloric va es of the fuel and partly because of the great difference in the size of the fuel pieces. For this reason the coils often must absorb more than their proportional share of the heat. This differs materially from the conditions in ordinarv furnaces, steam boilers for example, in which the tem erature variations which might arise in the fuel bed itself. have time to be e ualized in the combustion chamber, and in which the heat absorption per surface unit of the heating surface can be determined with great exactness. For this reason, the ouantitv, and the speed respectively of the heat absorbing medium flowing in the coils must be considerably greater than in ordinary steam boilers. In order to insure a satisfactory and continuous circulation of the heat absorbing medium, forced circulation by mechanical means, a pumn or the like, for example has been found desirable. Natural circulation is, however, possible if the heat absorbing members are constructed. in such a way that the water circulating therethrough is quick and positive, and sufficient in quantity to carry away the abstracted heat.

The apparatus illustrated in the accom anying drawings is especially adapted to the combustion of slate coke and oil slate which can be admitted in a hot or cold state to the combustion chamber.

In these drawings:

Figure 1 is a vertical sectional view through an apparatus embodying this invention, said view being taken through Figure 2 on the plane of the line l-l.

Figure 2 is a vertical sectional view taken through Figure 1 on the plane of the line 2+2.

Figure 3 is a cross sectional view taken through Figure 1 on the plane of the line 3-3.

Figure 4 is a vertical sectional view through a modified form of the invention wherein the combustion gas and the distillant gases are drawn oil" through separate ducts; and

Figure 5 is a vertical sectonal view through Figure 4 on the plane of the line 5--5.

In both embodiments of the invention shown, the furnace comprises a vertical shaft with fireproof, for example brick walls I. In the bottom of the furnace shaft is a grate consisting of rotatable roller-like grate bars 2 journalled at both ends in bearings 3 and 4. These bars are rotated in the direction of the arrows by a chain driven from a main shaft, not shown, and trained over sprocket wheels 5 and 6. As shown in Figures l and 4, the roller-like grate bars are arranged in pairs with adjacent pairs spaced from one another, and to preclude direct passage through the grate, deflectors 1 are disposed over the spaces between the pairs of grate bars.

The combustion air is supplied to the chamber below the grate through an opening 8 under super atmospheric pressure by a fan or the like.

The reference numeral I0 indicates the pipes or tubes through which the heat absorbing medium circulates in indirect heat exchange relation with the fuel in the shaft. These pipes or tubes form coils bent double in such a way that each coil has a straight-piece a, b. Fig. 1 shows such a pipe in elevation with five straight'pieces a, b which project like fingers into the shaft. Each straight piece consists of a feed line a and a return line b. The ends of each pipe or tube are connected to an inlet header I2 and an outlet header l3. Certain of these coils project farther down into the shaft than others so that the heat absorption and consequently, cooling of the bed diminishes towards thebottom of the shaft where the temperatures are less intense. The number of pipe fingers can be varied as well as the number of pipes according to the size of the spaces, but it is important that they be distributed and arranged to have their cooling effect reach all portions of the fuel bed. As already pointed out, these tubes may constitute part of a steam boiler, a hot water boiler, or a superheater depending upon whether they contain water and/or steam.

Above the shaft there is mounted a cap 15 with a hopper It provided with a valve, through which the furnace is charged with fuel, such as slate coke. The flue gases leave the top of the shaft through a deflector hood l8 and an exhaust duct I9.

The object of the invention being to control the combustion in such a way that the temperature is held below the sintering temperature in all places of the shaft, the temperature must be controlled for different charges. For this reason instrument openings 29 are disposed at different levels in the furnace wall, the said openings being covered by shutters 20'. Further, the furnace wall is provided with inspection openings 2| covered by shutters 2 I as well as with a larger access opening 23.

The discharge opening 25 of the ash pit has a water seal arranged in such a way that it shuts off the ash pit in an airtight manner from the outside and at the same time extinguishes the ashes.

The above described furnace is to be fired with slate coke for heating purposes only, and during operation the temperature the fuel charge-can.

be controlled according to need in different ways, for example by varying the circulation speed of the medium circulated through the pipes it! by the pump P.

The embodiment illustrated in Figures 4 and 5 does not deviate very much from the one already described, as will be seen from the drawing. The same details in both embodiments have the same reference numerals. However, in this case the furnace can be used for the distillation of the fuel, and to this end the furnace is fired with unburnt slate which is first distilled off in the upper portion of the shaft and then burned in the lower portion thereof. However, the flue gases must not get mixed with the distillation products. This can be avoided by sucking the flue gases through pipes 26, the inlets of which are located below the level above which the slate is distilled. The said pipes are united in an we haust drum l9. Above the shaft there is provided a cap of similar shape as the cap it with an outlet l5 for recovering the distillation products. The pipes may be arranged in such a way (telescopically, for example) that their inlets can be raised and lowered, in order to be located at the most suitable level.

From the foregoing description taken in connection with the accompanying drawings it will be apparent to those skilled in this art that the present invention provides a simple solution to the problem of maintaining the temperature of low temperature sintering fuel in all portions of a vertical fuel bed at a temperature value as near the sintering temperature as possible without reaching the same, so that the highest combustion speed possible is obtained.

Having now described our invention, what we claim as new and. desire to secure by Letters Patent is:

1. Apparatus for sequentially degassing and combustlng solid fuel, comprising: means delining an upright shalt having a Iuel inlet at the top; a grate at the bottom upon which the fuel in the lower portion of the shaft may be burned whereby said lower portion of the shaft comprises a combustion zone and the upper portion of the shaft provides a degassing zone; and means 101 controlling the temperature of the fuel in said degassing and combustion zones comprising a plurality of boiler fluid conducting tubes, and means mounting said tubes within the shaft with portions thereof in the degassing zone and portions thereof in the combustion zone to be direct- 1y embedded in the fuel filling said zones, and

said tubes being spaced at close intervals transversely across the shaft so that the cooling influence of boiler fluid of a temperature less than that generally prevailing in the combustion and degassing zones circulating therethrough effectively reaches all portions of the fuel in said two zones to thereby control the temperature of the same, and inlet and outlet headers connected with said tubes for supplying and receiving boiler fluid circulated through the tubes.

2. In an apparatus of the character described: an upright shaft adapted to hold a column of fuel to be combusted; means for feeding fuel into the top of the upright shaft; means for introducing combustion air into the shaft; means for removing ash from the lower portion of the shaft; and means for simultaneously abstracting heat from fuel burning in said column for utilization elsewhere and to maintain the temperature of the fuel in the column below its sintering point comprising a plurality of ducts disposed within the shaft so as to be imbedded in the fuel therein, said ducts being relatively closely spaced with respect to each other and the sides of the shaft so that the cooling influence of boiler fluid of a temperature below that generally prevailing in the shaft circulated through said ducts emanates from a large number of sources at relatively closely spaced intervals across the horizontal area of the shaft so as to effectively reach all portions of the fuel in the shaft; and inlet and outlet headers connected with the ducts for supplying and receiving boiler fluid for circulation through the ducts.

3. Apparatus for combusting and degassing solid fuel comprising: means defining an upright shaft having a fuel inlet at the top; a grate in the lower portion of the shaft to support the shaft contents and upon which the lower portion of the shaft contents may be burnt so that the lower portion of the shaft constitutes a combustion zone and the upper portion thereof 'a degassing zone; and rows of finger-like water conducting tubes within the shaft projecting downwardly from the top thereof through the degassing zone and into the combustion zone, all of said tubes terminating short of the grate, the endmost tubes in said rows of tubes being spaced from the sides of the shaft so that all of the tubes are embedded in the fuel within the shaft, and said tubes being so spaced with respect to one another as to be located at relatively closely spaced intervals transversely across the shaft so that the cooling influence of water or other fluid cooling medium circulating through the tubes emanates from a plurality of sources relatively closely spaced transversely across the shaft to thereby effectively reach all portions of the fuel within the degassing and combustion zones and thereby protect the liberated gas from excessive temperatures and preclude sintering of the fuel within the shaft.

4. The apparatus set forth in claim 3 further characterized by the fact that the upper ends of the tubes are at substantially the same level and further characterized by the fact that the tubes are of different lengths so that the total cooling influence emanating from the tubes is greater in the upper portion of the shaft than in the lower portion thereof.

DAVID DALIN. CLAES JOEL GEJROT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 307,599 Steele Nov. 4, 1884 387,393 Button Aug. 7, 1888 479,405 Delanoy July 26, 1892 742,359 Scholl Oct. 27, 1903 1,050,632 Erk Jan. 14, 1913 1,482,665 Strong Feb. 5, 1924 1,618,566 Bergh Feb. 22, 1927 1,700,560 Coe Jan. 29, 1929 1,780,653 McDevitt Nov. 4, 1930 1,846,647 Leitch et a1 Feb. 23, 1932

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