Chemistry and physics of entrained coal gasification

Pulverized coal, when entrained in a stream of hot, hydrogen-containing gas, can be converted in good yields to methane and other combustible gases. Quantitative expressions have been developed, relating the methane yields obtained from this rapid hydrogenation of coal to process variables such as temperature, hydrogen partial pressure, and coal rank. Equally important to the methane yield obtained in entrained coal gasifiers are the mixing patterns established between the coal and hot gas streams. In experiments carried out at BCR using a 100 lb/hr internally fired gasifier, the momentum of the coal feed stream injected into a hot synthesis gas created recirculating flows that reintroduced a portion of the methane, formed in the direct methanation reactions, back into a higher temperature region of the gasifier. There, steam reforming of the methane occurred, with resultant decrease in overall methane production. Although it is difficult to express this loss quantitatively, design objectives for entrained gasifiers are proposed, which should minimize the methane losses due to reforming in secondary flows.