Study of thermal characteristics and functional group changes of Yanghuopan Coal during spontaneous combustion

Abstract

The generation and accumulation of heat is the major direct cause of the spontaneous combustion of coal. In the initial stage of coal spontaneous combustion, the heat is mainly released by low temperature oxidation reaction of coal. To investigate the thermal characteristics and the change of key functional groups in the process of coal oxidation, Yanghuopan coal sample was used for research. First, the heat flow curves of the Yanghuopan coal sample were measured by a microcalorimeter at different heating rates of 0.2, 0.4, and 0.6 °C min−1. Then, the infrared spectrogram of coal oxidation process was measured by Fourier transform infrared spectroscopy. The results indicated that the oxidation process of coal occurred in stages that had distinct characteristics. When the temperature increased, the heat flow curve of coal first decreased, then increased. And the heat flow curve was divided into three stages: endothermic, slow exothermic, and fast exothermic. By the study of the key functional groups and structural parameters of the characteristic temperature point, the endothermic and exothermic processes of coal oxidation at low temperature are mainly caused by the reactions of methyl, methylene, hydroxyl and carboxyl groups. The methyl and methylene first increased and then decreased. A increase was observed in the Carboxyl group with the increase in the temperature. And the hydroxyl group decreased greatly with the increase of temperature. This information can guide firefighting operations in the field and help develop firefighting materials.