Low reaction threshold of ambient temperature oxidation of coal: Perspective from oxygen concentration and airflow rate

Coal spontaneous combustion remains a significant hazard in mining operations. In this study, the temperature rise characteristics of sub-bituminous coal were investigated using an air stream of varying concentration and airflow rate. The chemical structure changes under various oxygen contents were analyzed using the FTIR technique. The findings demonstrate that ambient temperature oxidation can occur even under low oxygen and airflow rate conditions, emphasizing the need for vigilance. Although oxygen enrichment in the atmosphere promotes the coal-oxygen complex and increases the total temperature rise (TTR), TTR can still reach 0.31 degrees C with 6 vol% oxygen. There exists an optimum ventilation rate to maximize the TTR. TTR at the flow rate of 25 mL/min is 47 %, 36 %, 165 % and 308 % higher than at the 10, 50, 75 and 100 mL/min. Moreover, FTIR experiments indicated the difference of active groups under different oxygen concentrations is slight. The low reaction threshold for ambient temperature oxidation complicates the prevention of coal spontaneous combustion during latency periods.