Intrinsic Characteristics Combined with Gaseous Products and Active Groups of Coal under Low-Temperature Oxidation

Coal spontaneous combustion (CSC) characteristics were identified by their different types of coal. In this study, the samples of lignite, non-caking coal, lean coal, and anthracite were chosen to investigate the variations of gaseous products and main active groups during the low-temperature oxidation. The law of indicator gases was obtained by temperature-programmed experiment, and active groups of four coal samples had specific and different probabilities of spontaneous combustion via Fourier transform infrared spectrometer (FTIR). The relationship between the indicator gases at different stages and the main functional groups of coal were explored by Grey correlation analysis. The results indicated that the characteristic temperatures of water evaporation and gases desorption period of four types of coal showed the similar variation with those in thermal storage stage (Stage 1). Moreover, temperature ranges (TRs) in Stage 1 of lignite, non-caking coal, lean coal, and anthracite were 20-60, 20-60, 20-60, and 20-80 degrees C, respectively; TRs in Stage 2 were 60-100, 60-140, 60-120, and 80-200 degrees C, respectively; TRs in Stage 3 were 100-180, 140-180, 120-180, and 200-240 degrees C, respectively. Based on the correlation analysis, the hydroxyl, carboxyl, and methylene had a sound temperature correlation with indicator gases emission. Eventually, the prediction system for CSC during the low-temperature oxidation was revealed.