Self-heating of a coal bed under conditions of complicated access for air

Abstract

The kinetics of the temperature conditions of a coal bed depending on the concentration of oxygen in coal was analyzed. The spatiotemporal dependence of the temperature and oxygen concentration in a coal bed was determined. It was found that oxygen penetrates into the bed to a limited depth; the presence of residual methane prevents the penetration of oxygen into the bed. It was demonstrated that, at limited access of oxygen to the bed, the temperature of the bed always achieves a specific stationary value unlike the case of a constant oxygen concentration, when conditions for an unlimited increase in the temperature can occur; a criterion for the appearance of these conditions was found. The stationary bed temperature was determined depending on the rate constant of sorption, bed voidage, residual methane pressure, bed thickness, coefficient of heat transfer to host rock, and flow rate of air from the headway to the bed.