Low-temperature oxidation characteristics of coals at the methane-containing atmosphere

The coupling disaster of coal spontaneous combustion and methane seriously threatens the safe production of coal mines. In order to study the low-temperature oxidation characteristics of coals oxidized at the methane-containing atmosphere, characteristics of free radicals and thermal effects of two coals oxidized at atmosphere containing different concentrations of CH4 were studied by employing calorimetric and electron spin resonance (ESR) spectrometer experiments. Furthermore, the oxidation characteristics of coals were related to its thermal effect based on the enthalpy changes of active groups’ reactions calculated by Gaussian 16. It was found that CH4 in the oxidation atmosphere could reduce the amount of heat both absorbed and released during the process of low-temperature oxidation. And, the higher the concentration of CH4 in the atmosphere was, the smaller amount of heat absorbed and released. Experimental results of ESR suggested that the concentration, the g-factor, and the linewidth of free radicals were decreased as the concentration of CH4 in the oxidizing atmosphere increased. Analysis of elementary reactions and its corresponding enthalpy change indicated that the reduction of absorbed and released heat resulted by CH4 attributed to the fact that CH4 could block the generation of peroxides and depress the decomposition of the oxygen-containing free radicals. The changes of released carbon monoxide as the function of the concentration of CH4 were in agreement with this indication as well. This study will provide a scientific guidance for the prevention and control of the coupling disasters of coal spontaneous combustion and CH4 and benefit the development of the high-efficiency coal spontaneous combustion inhibitor.