Microstructure of coal spontaneous combustion in low-oxygen atmospheres at characteristic temperatures

Coal spontaneous combustion (CSC) has a devastating effect on the environment and human health. CSC primarily involves oxygen-lean oxidation and combustion states. In this study, to investigate the evolution of the coal microstructure during CSC in an oxygen-lean atmosphere, coal for oxygen-lean combustion was obtained and combusted at characteristic temperatures by using an independently developed electric tube furnace. Through Fourier-transform infrared spectroscopy, the relative contents of the active functional group of the initial-state oxidation coal were explored, and the main active functional groups, namely aromatic hydrocarbon, the oxygen functional group, aliphatic hydrocarbon, and the hydroxyl group, with the characteristic temperature, were determined. The sensitivities of different active functional groups to oxygen concentrations were analysed. In practice, a 10 vol% oxygen concentration was the key factor, inhibiting and promoting various active functional groups and exhibiting distinct dominance at various stages. Finally, the oxygen concentrations affected the gas concentration release characteristics, thereby determining the correlation degree of the key group and the oxygen concentration, as well as verifying the oxygen concentration sensitivity of the microstructure. The groups highly correlated with CSC characteristic parameters were mainly –CH2 and –CH3. The research results suggested remarkable explanatory potential to further elucidate the evolution of microstructures in oxygen-lean CSC.