Bi-flow rotary kiln coal gasification process

A dry process for continuously gasifying unsized particles of coal which upon being progressively heated to a final temperature of approximately 2,000.degree. F. through heat treatment stages in which the coal gives off a combustible mixture of gases containing water vapor, hydrogen, carbon monoxide, carbon dioxide, hydrocarbon vapors (tar-laden) and smoke (aerosols) and hydrocarbon-free gases (tar-free) at 1,600.degree.-2,000.degree. F. in a final and highest temperature stage of said series of stages, with said treatment stages each being achieved in zone within a rotary kiln inclined downwardly from a material inlet toward a material outlet, the process comprising the steps of:

• (a) feeding a continuous supply of said coal to the inlet to form a bed of the coal in the kiln, and rotating the kiln to advance the bed from the inlet to the outlet of the kiln;
• (b) increasing the temperature of the bed progressively as the coal is advanced through said heat treatment stages to increase the temperature of the coal in the final stage to approximately 2,000.degree. F. and the temperature of the hydrocarbon-free gases liberated in the final stage to approximately 1,900.degree. F.;
• (c) admitting air and steam through the kiln shell and bed of coal where the coal is heated to at least a tar-free gasification temperature and at locations in a plurality of radial planes spaced apart along the central axis of the kiln;
• (d) selectively controlling the discharge of a proportion of the process gas from each end of the kiln to split into two streams the tar-free gas produced by air and steam passing through the coal and draw the split tar-free gas streams apart to flow in axially opposite directions within the kiln with one of the tar-free gas streams flowing axially away from the zone in which tar-laden gases emerge from coal heated to devolatilization temperature and toward the material outlet of the kiln for discharge from the kiln as tar-free gas, and with the tar-free gas stream flowing toward the material inlet of the kiln mixing with said emerging tar-laden gases to flush tar-laden gases out the material inlet end of the kiln and away from the stream of tar-free gases flowing toward and out the material outlet end of the kiln;
• and
• (e) adjusting the proportion of process gases discharged out each end of the kiln to move the location of the tar-free gas flow split along the central axis of the kiln to a position between the beginning of said tar-free gasification stage and the material outlet end of the kiln with said position of the split selected to maintain a maximum attainable flow of tar-free gas out the material discharge end of the kiln while maintaining the temperature of the mixed gases flowing out the material feed end of the kiln at above tar condensing temperature.