Effect of Process Conditions on Thermodynamics of Gasification

Abstract

Coal gasification involves the conversion of coal with steam (allothermic gasification), or with steam and oxygen (autothermic gasification). In this paper, the effect of temperature and pressure on the thermodynamics of gasification are discussed. The most important products of gasification are carbon monoxide, hydrogen, carbon dioxide, and methane. With increasing temperature, the concentrations of hydrogen and carbon monoxide in the product gas increase, while both carbon dioxide and methane go through a maximum. A higher pressure negatively influences the hydrogen and carbon monoxide production. Lowering of the feed temperature very much increases the heat required in allothermic gasification, and the oxygen to steam ratio in autothermic gasification. A comparison is made between gasification of pure carbon and CH, which gives a more accurate representation of coal. Naturally, CH yields a product gas with higher hydrogen content. Finally, the thermodynamic equilibrium composition is related to typical operating ranges of industrial gasifiers. This gives an indication of optimal operating conditions for specific applications, although an absolute measure of performance cannot be based on these data.