Effect of gas atmosphere change on radical reaction and indicator gas release during coal oxidation

Coal spontaneous combustion (CSC) caused by coal oxidation is the leading cause of mine fires. The essence of most CSC preventive measures is to change an oxygen-containing atmosphere into a nitrogen-rich atmosphere for suppressing continuous coal oxidation. This study investigates the effect of gas atmosphere change on the micro group reaction and gas product release during coal oxidation. To achieve this aim, the radical parameters and CO were measured with the aid of an electron spin resonance (ESR) spectrometer and a gas chromatograph. The following conclusions show that, after converting the gas atmosphere from dry air to nitrogen, the linewidth of the ESR spectrum drops suddenly and ultimately stabilizes at around 0.46. Besides, a lower conversion temperature corresponds to a higher turning point temperature and a smaller maximum value of the g factor, especially when the temperature is below 90 degrees C. After the gas atmosphere is converted, the radical concentration drops suddenly and rises again. The second increase of radical concentration is significant when the conversion temperature exceeds 130 degrees C. While the atmosphere changes, CO release falls abruptly, and then it continuously increases. Finally, the mechanism of the effect of gas atmosphere conversion on the radical reaction of coal was analyzed. The results could enrich the coal oxidation research and be applied in CSC management and control.