GB953878A - Improvements in or relating to a method and apparatus for treating carbonaceous material such as coal - Google Patents

Abstract

A method of treating coal containing relatively low-temperature volatiles driven off by heating the coal to a predetermined temperature and other or higher-temperature volatiles driven off only at a temperature above the predetermined temperature, comprises transporting a substantially uniform thick bed of coal progressively through discrete contiguous regions of a closed chamber, raising the temperature of the coal to the predetermined temperature in one region and blowing the low-temperature volatiles therefrom by upward-flowing gases followed by the exhaustion thereof, then raising the temperature of the coal as the bed is moved through a succeeding discrete region until a substantial portion of the other volatiles is driven therefrom for separate exhaustion from the low-temperature volatiles. Apparatus for treating coal comprises an oven 20 (Fig. 1) having a roof 22 and horizontally-spaced input and output ends, a conveyer grate 18 extending substantially from end-to-end of the oven 20 and movable therebetween, a hopper 14, and spreader 17 to feed and spread coal over the grate 18 to form a uniformly thick bed 19 thereon, a curtain wall 110 extending from the roof 22 having edges to seal against the top of the bed 19, and an air-box 56 to feed air and gases upwardly through the grate 18, having zones 1 to 8 as shown to pass varying quantities of fuel gas, preheated air and stack gas therethrough, and the wall 110 dividing the oven 20 above the grate 18 into zones 21, 23 each <PICT:0953878/C3/1> registering with a number of air-box zones, so that gas and preheated air may be progressively and selectively applied beneath the coal on the grate 18 and low-temperature and high-temperature volatiles may be progressively driven from the coal and selectively removed from the oven 20. From the grate 18 coke is discharged into a retort 26, and cooled gas is added to the coke by means of a pump 94 from a line 92 and manifold 96 in the retort 26 to quench the coke. To provide this gas heated gas is withdrawn through a line 106 and manifold 104 at an upper lead of the coke in the retort 26 and cooled in an exchanger 50. To the air-box zones 1 to 4 is connected a fuel-gas manifold 54 and to the air-box zones 5 to 8 is connected a stack-gas manifold 84, a preheated-air manifold 68 being connected to all the air-box zones, so that the quantity and quality of mixed gas passing through the grate 18 and the bed 19 may be adjusted. The fuel gas and air applied are heated in exchangers 50 and 64 (heated by gas withdrawn along the line 106a ), overfire air being fed from exchanger 64, through lines 66, 67 and valve 70A to the zone 23 through ports 71 to combust with the volatile matter therein to increase the temperature. Some of the stack gas from an outlet 24 above the zone 23 is taken off and circulated through a coal preheater 12 and returned therefrom via lines 72, 74 before introduction through a shoot 13 or suitable conveyer to an input hopper 14. Part of the remainder is passed through line 78 and pump 72 to stack-gas manifold 84. The low-temperature volatiles have an outlet 34 to a product-recovery unit 38, fuel gas discharged through a line 42 being fed partly by a line 44 to e.g. an igniter 16, and partly by a line 46, pump 48, exchanger 50 and line 52 to fuel-gas manifold 54. In a modified form spent gas is moved downward through most of the coal in the initial or preheating part of the first zone, through air-box zones therebeneath and then exhausted from the apparatus. Fuel gas is then stripped from the low temperature volatiles and part of it is heated after removal from the latter part of the first zone and recirculated through the coal passing through the said latter part and through the initial part, at the end thereof, in the absence of sufficient oxygen to permit full combustion of the fixed carbon in the coal therein. The said two parts of the first zone are separated by a curtain wall. The roof of the latter part is much lower than the roofs of the initial part and the second zone, two air-boxes take the spent gas moving downward, one box introduces gas at the end of the initial part, and five admit gas to the second zone. Another part of the fuel gas in burnt to create heat as well as the spent gas that is moved downward, the heat being utilized to heat the previously-mentioned part of the fuel gas. In a second modified form char is produced, the temperature in the zones is not so high, hot spent gas is taken from the top of the retort, which is separated from the oven by a partition forming a throat for the descent of coke, and moves upward and over the oven to descend after passing through an exchanger, through the first zone into two gas-boxes. Fuel gas is introduced at the end of the initial part of the first zone through a gas-box and through nine gas-boxes for the second zone and is taken from a manifold receiving it from the top of the second zone after stripping off volatiles and heating in the said exchanger. The char is cleared of volatiles by the action of a gas burner receiving the cooled fuel gas. The only manifold is for fuel gas. Whereas the first form includes an external preheater 12, the second and third forms having preheated zones instead, in a modification of the third form the oven has a construction embodying an exchanger above it, enabling the coal to be preheated by spent gas passed through it from the retort. U.S.A. Specifications 2,209,255 and 3,013,951 are referred to.