Mathematical modeling of alternating injection of oxygen and steam in underground coal gasification

The results show that product composition and temperature oscillation can be predicted with a reasonable accuracy. The stored heat can deliver additional energy that can maintain the gasification during the steam injection period for a limited time. During the steam injection cycle, at low pressure the volumetric flow and the hydrogen content of the product gas are both high, but at higher pressures while the hydrogen composition is still high the coal conversion decreases considerably. The results confirm that the alternating injection of air/steam describes a practical process for UCG at low pressure. However, at high pressure, injecting a mixture of steam and oxygen instead of alternating injection of oxygen/steam results in a higher coal conversion rate, with a final product that contains higher carbon content.