Assessment of coal spontaneous combustion prediction index gases for coal with different moisture contents

Much of the residual coal in a goaf was immersed in water for extended periods of time, which leads to complicated coal spontaneous combustion (CSC) characteristics that are difficult to predict. In this work, five kinds of coal samples with different moisture content (MC) of 4%, 11%, 18%, 25% and 32% were prepared by soaking, and a temperature programmed test was carried out. The gas produced by the oxidation of coal samples with different moisture contents and its concentration variation law were analyzed during temperature rise, and the index gas suitable for predicting CSC was selected. The concentration of gas generated by coal sample heating increased with increasing temperature. We also found that CO, C2H6, C2H4 and C3H8 can be used as the single auxiliary index gas for CSC prediction, and the composite gases CO/CO2 (ω) and C2H4/C2H6 (ξ) can be used to predict the CSC oxidation stage comprehensively and reliably under different degrees of water immersion. The process of coal oxidation was divided into three stages: oxygen absorption and thermal storage (ω ≤ 0.133), slow oxidation stage (0.758 ≤ ξ ≤ 0.919) and accelerated oxidation stage (ω ≥ 0.401 or ξ ≥ 0.919). Combined with the actual conditions at different coal mines, timely parameter index correction can improve the CSC prediction index and provide guidance for preventing and controlling coal spontaneous combustion and safety management of coal mines.