US3434931A

US3434931A - Coke,tar,and clean coal gas producing method and apparatus

Info

Publication number: US3434931A
Application number: US612445A
Authority: US
Inventors: Vaughn Mansfield
Original assignee: Peabody Coal Co
Current assignee: Peabody Coal Co
Priority date: 1967-01-30
Filing date: 1967-01-30
Publication date: 1969-03-25
Anticipated expiration: 1986-03-25

Description

March 25, 1969 SPENT COMBUSTION 3O GASES GREEN COAL IN BOILER HOPPER AIR IN PREHEATER Filed Jan. 50, 1967 V. MANSFIELD COKE, TAR, AND CLEAN COAL GAS PRODUCING METHOD AND COAL PRE HEATED 40 IIIIIIIIIIIII 'IMI CERAMIC WALLS SOLID GRATE IN SEGMENTS MRS COAL GAS, INCLUDING ms 600 T0 900 F TAR RECOVERY SYSTEM VAUGHN IMO.

APPARATUS COKE OUT 48 CLEAN COOL GAS SUCTION FA N INVENT OR MANSFIELD ATTORNEY United States Patent US. Cl. 201-27 8 Claims ABSTRACT OF THE DISCLOSURE Preheated coal is gravity-fed via an upright input shaft onto an imperforate endless grate moving horizontally through a hot carbonizing furnace, the coal in the shaft forming a stack on the grate. Overfire air is fed into the furnace above the coal on the grate so as to react above the coal with volatiles driven from the coal, thereby heating by radiation and conduction and extensively but not completely carbonizing the coal on the grate. At the end of the grate the nearly coke coal drops into a shaft furnace wherein carbonization to acceptably low volatile content is completed. At least some of the hot gaseous byproducts of combustion in the furnace are back-drafted through the coal at the bottom of the input shaft so as to gasify low temperature volatile content of the coal, including tars, the thusly enriched back-drafted gas then passing to a tar recovery system wherein the tars are extracted, leaving clean coal gas for utilization.

Summary of invention Forming a stack of coal on an endless imperforate grate running horizontally through a hot carbonizing furnace, bottom-unstacking the coal to form a bed on the grate, feeding overfire air over the bed so as to react with volatiles driven from the coal so as to heat the coal by radiation and conduction and substantially coke the same, further coking the coal in a vertical shaft furnace, sweeping from above the bed at least part of the hot gaseous products of combustion back through the coal at the bottom of the stack so as to extract therefrom low-temperature volatile matter including tar, and recovering the tar from the back-swept gases.

Brief description of drawing The sole figure is a diagrammatic longitudinal cross section taken vertically through the apparatus.

Referring now to the drawing, in which like reference numerals denote similar elements, the carbonizer furnace 2, constructed with conventional refractory walls, encloses an endless, air infusion, flexible grate 4 running over sprockets 6 and 8. At least one sprocket shaft 10 is driven by a suitable source of power so that the upper run of grate 4 moves from the input end of the furnace to the output end thereof, respectively designated generally 12 and 13.

Coal 14 is fed to a furnace input shaft 15 from a preheater 16 supplied from a suitable hopper 18. The coal entering input shaft 15, having been preheated to about from 225 F. to 300 F., from a stack 19 on the upper run of grate 4, and downstream of stack 19 a spreader gate 20 forms a coal bed 22 on the grate of about ten inches in a typical example. Beneath the output end 13 of carbonizing furnace is a shaft furnace 24. A suitable shaft furnace is shown in my Patent No. 2,997,426, it being sufiicient for present purposes to note that the coke in the shaft furnace moves slowly down therein, it is cooled by inert gas circulating through the lower part of the furnace, the coke is discharged from the bottom of the shaft furnace, and some of the heat extracted from the coke is used to preheat the coal in preheater 16. Above the output end 13 of furnace 2 is a flue 26 which may, if desired, supply hot gases to a boiler 28, the spent combustion gases emerging therefrom via a suitable stack 30.

Suitably spaced in a carbonizing furnace 2 above the level of coal bed 22 are overfire air ports 32, these being conventionally supplied with air through lines 34 controlled by valves 36. Adjacent the input end 12 of furnace 2, upstream of input shaft 15 is a hot gas outlet 38, from which leads a gas line 40 to a tar recovery system 42. A fan 46 pulls the gases out through outlet 38 and tar recovery system 42, the output 48 of fan 46 being connected to a suitable gas utilization means, not shown.

The operation of apparatus described above, which apparatus is suitable for producing tar, gas and char from various hydrocarbon materials such as coking and noncoking coal or lignite, will be described in connection with the production of coke, tar and gas. Let it be assumed that the starting material is West Kentucky No. 11 coal, sized 2" x 0", and normally consisting of about:

Percent Volatiles 38 Fixed carbon 45 Moisture 10 Ash 7 In preheater 16, the moisture is driven off so that the makeup of the coal fed to infeed chute 1:5 is about:

It will further be assumed that, at startup, a fire has been built on grate 4 so as to heat up the interior of hirnace 2 sufficiently so that an exothermic reaction of volatile matter in the coal with air will occur when the air is admitted through overfire air ports 32, and that grate 4 is moving so as to remove coal slowly from the bottom of stack 19'.

Fan 46 is started, and overfire air ports 32 are opened so as to create a draft running counter "to the movement of the coal or bed 4. Sufficient air is admitted via ports 32 to burn with volatiles issuing upwardly from bed 22 to create a temperature of about 1500 F. above the bed. As some of these hot gaseous combustion byproducts are drawn back through the incoming coal at the bottom of the stack, they create a temperature gradient across the coal in the lower portion of the stack, ranging from about 1500" F. at the downstream side of the stack bottom to somewhere between 600 F. and 900 F., depending upon the speed of grate 4 thereby driving off hydrocarbon gases from the coal at the infeed stack bottom. The resulting gases are then induced via line 40 to the tar recovery equipment from which a scrubbed gas is issued that is made up essentially as follows:

Percent N 18.4 C0 7.2 CO 12.1 H 23.2 CH, 34.5 Illuminants 4.6

It is noteworthy that the gas issuing via line 40 contains a considerable amount of tars which come off from the coal in the range of from 600 F. to 900 F.

The amount of gas withdrawn via gas outlet line 40 depends in part upon the amount of heat needed to be emitted from flue 26. If the system is to be operated without a boiler 28, as could be the case, then most or all of the available hot gas from above bed 22 would be drawn back through the incoming coal at the lower part of stack 19. If a boiler 28 or other heat utilizing device is used, then a lesser amount of hot gas would be drawn back through the coal in the lower part of the stack.

As the coal in bed 22 starts through furnace 2, it is quickly heated by the almost 1500 F. gases which are drawn through it, the heat driving off a considerable amount of the volatiles before the coal has progressed much beyond the spreader gate. As the coal progresses through the furnace, it is heated by radiation and conduction from the heat produced by volatiles burning with the overfire air so that by the time it drops off the end of grate 4, it is carbonized, with only about 8% volatile matter therein. Most of these remaining volatiles are driven off the coke as the latter progresses downwardly through shaft furnace 2-4.

In the foregoing specification and following claims, the term coal is intended to include all solid or semisolid substances which comprise fixed carbon, low-temperature volatiles, i.e., those which include tars and which become gaseous at about 600 F. to about 900 F., and high-temperature volatiles, i.e., those which become gaseous at about 900 F. The term coke is also intended to include char.

I claim:

1. In combination, a furnace having input and output ends laterally spaced from one another, a substantially air-impervious endless grate running horizontally in said furnace including an upper grate run running from the input end of the enclosure to adjacent the output end thereof, means for driving said endless grate so that said upper grate run moves from the input end of the furnace towards the output end thereof, a material input shaft extending upwardly adjacent the input end of the enclosure and having a lower end disposed over the upper grate run, overfire air ports in said enclosure above the upper grate run on one side of the shaft, a gas outlet conduit communicating with the lower end of said input shaft on the other side of the shaft, a tar recovery system connected to the gas outlet conduit, and means for creating a draft serially running from said overfire air ports, through material at the bottom of said input shaft, and through said gas outlet conduit and tar recovery device.

2. The combination claimed in claim 1, and a clean gas outlet line running from the tar recovery system.

3. The combination claimed in claim 1, and a shaft furnace depending from the output end of the first-named furnace, said shaft furnace being positioned to receive material off the endless grate.

4. The combination claimed in claim 1, the lower end of said material input shaft terminating above the upper grate run and having forward and rear wall portions laterally spaced from one another and defining gaps between lower ends thereof and said upper grate run, said gas outlet conduit running from the gap between the forward wall portion of the input shaft and the upper grate run to the tar recovery device.

5. The method of producing coke, tar and clean gas which comprises forming a stack of coal at one end of the top run of a substantially air-impervious endless grate running through a hot carbonizing furnace, bottomunstacking the coal by moving said top run horizontally through the furnace while forming a horizontal bed of coal on said top run, feeding overfire air into the furnace above the horizontal coal bed so as to combust with gaseous hydrocarbon driven from the coal in the bed and heat the latter by radiation and conduction sufficiently to partly carbonize the same, withdrawing hot gaseous combustion byproducts from above the horizontal coal bed through the coal at the bottom of the stack so as to drive off and entrain volatile matter including lowtemperature volatiles from the coal at the bottom of the stack, and recovering tars and clean coal gas from the withdrawn gaseous byproducts and entrained low-temperature volatiles.

6. In the method recited in claim 5, the step of preheating the coal prior to reaching the bottom of the stack sufliciently to drive off substantially all the surface moisture thereof.

7. The method defined in claim 5, the amount of overfire air fed into the furnace above the bed being sufficient to raise the temperature in the furnace above the bed to about 1500 F.

8. In the method recited in claim 5, the further step of substantially completing carbonization of the coal by dropping the same off the endless grate into a shaft furnace, and maintaining said coal in said shaft furnace until heat from the coal drives off most volatile matter remaining therein after passage through the carbonizing furnace.

References Cited UNITED STATES PATENTS 5/1933 Karrick 201-24 12/1961 Mansfield 20l27