Heat Release Evolution Characteristics of Coal Low-Temperature Oxidation in Low-Oxygen Environments

During the mining process of shallow buried coal seams, the oxygen concentration in the goaf is unevenly distributed, and most residual coal is in a low-oxygen oxidation state, posing a significant challenge to the accurate prevention and control of coal spontaneous combustion (CSC). In order to study the characteristics and mechanisms of low-temperature oxidation heat release evolution in a low-oxygen environment, the long flame coal from the Daheng coal mine was selected as the research object. Through C600 microcalorimetry experiments, the effects of oxygen concentration on the heat flow, heat release acceleration, heat release amount, and kinetic characteristics during the low-temperature oxidation of coal were analyzed. The results show that as the oxygen concentration decreases, the temperature at which heat release initially starts shows a significant delay. The total heat release of coal has a positive linear relationship with the oxygen concentration: when the oxygen volume fraction decreases from 21% to 7%, the total heat release decreases from 521.43 J/g to 222.13 J/g, a reduction of 57.40%. As the oxygen concentration decreases, the apparent activation energy of the coal oxidation reaction increases, leading to a decrease in reaction activity. When the oxygen volume fraction is 7%, the activation energy of coal reaches 117.50 kJ/mol, an increase of 61.18% compared to the 21% oxygen concentration. The decrease in oxygen concentration also inhibits the formation of carboxyl groups (-COOH), leading to the accumulation of peroxides (-O-O-), which further reduces the heat release. The findings of this study are of significant importance for revealing the spontaneous combustion mechanism of coal in low-oxygen environments and provide a theoretical basis for fire prevention and extinguishment strategies in shallow coal seam mining.