Modern Gasworks Practice

THE COMPLETE GASIFICATION OF COAL 781 column. During the gas-making operation, the air biast is shut off. the stack valves are closed, and the heat transf erring gas, consisting of steam or a mixture of gas with ■water vapour, is circulated up through the fuel column. During the first part of the blasting operation, the heat-transferring gas is circulated up through the fuel column with sufficient velocity to hold the oils or tars Condensed in the coal-distilling zone from limning back into the coal-carbonizing zone. When the air biast is biült-up to füll pressure, the heat-transferring gas circuit is cut off, and sufficient back-pressure is placed on the final regenerator to force a portion of the biasting gas upwardly through the fuel column and so prevent the tar or oil in the column from riinning clown into the coal-carbonizing zone. When the temperature of the hot mid-zone has been built-up sufficiently for making gas, the heat-transferring gas is circulated up through the fuel column before the air biast is entirely cut off. In this way, gas is always Ibeing circulated up through the fuel column above the hot mid-zone to prevent tar or oil from limning down into the coal-carbonizing zone. When carbonizing coal and producing gas, the temperature of the mid-zone is maintained sufficiently high to decompose the steam, and the temperature of the coal-carbonizing zone is maintained sufficiently high to decompose the pitch distilled from the coal, so that practically all the heavy tars and pitch, which condense in the coal-distilling zone and run back into the coal-carbonizing zone, are broken up into fixed gases and free carbon. The heat-transferring gas used when carbonizing coal preferably consists of a mixture of water vapour and water gas, or any'other combustible gas which will not be decomposed in passing through the hot mid-zone. In this way, the water gas acts as a carrying medium to introduce the vapour into the fuel-bed for making water gas, and a very large amount of coal can be cai'bonized for producing coke. If the water gas produced in the operation, however, contains coal-distillation products which will be decomposed by passing them through the hot mid-zone, it may be desirable to introduce steam only. The temperatures of the fuel column, are so regulated that the gases leaving the generator will be of a temperature just sufficient to carry off steam and the low-boiling products. It is pointed out by the inventar that the sensible heat of the issuing gases is not lost, since it is employed to heat up the water of the condenser, which water is utilized in the absorber. Carbon-Hydrogen Gas T. O’Connell has introduced a process1 for making what he calls carbon-hydrogen gas. Coal charged into a gas producer is subjected to a somewhat complicated series of runs and blows. The operations commonly employed are as follows:— (2) Coal subjected to an air-blast, then a steam rim, both periode being of equal duration. (3) A second cycle similar to above. (4) Air-blast, followed by a down run lasting five-eigliths of the time of the blow. (5) Up run, lasting three-eighths of the time of the blow. 2 U.S.P. 1 340,495/May, 1920.