Catastrophic temperature of oxidation-spontaneous-combustion for bituminous coal under uniaxial stress

To explore the influence of the oxidation and spontaneous combustion process of fractured coal at different burial depths under uniaxial stress, the spontaneous combustion characteristics of coal under loading was studied within the testing device of coal spontaneous combustion and loading. Bituminous coal from the Liuhuanggou mining area in Xinjiang was selected and oxidized in the oxygen-lean environment loaded at the range of 0–8 MPa. Based on the relationship between the gas generated in the experiment and the temperature, we calculated the apparent activation energy and oxygen consumption rate of coal samples under uniaxial stress. We combined the oxidation kinetics and pyrolysis parameters of spontaneous coal combustion to describe the nonlinear development of coal from slow to rapid oxidation under uniaxial stress. Based on catastrophe theory, the catastrophic temperature and critical temperature of bituminous coal oxidation-combustion process under test conditions were calculated, and four characteristic parameters were determined: catastrophic temperature T_\mathrmC\mathrmO (characterization of CO) and T_\mathrmH\mathrmY (characterization of oxygen consumption rate), and critical temperature T_\mathrmC\mathrmO^' (characterization of CO) and T_\mathrmH\mathrmY^' (characterization of oxygen consumption rate), and analyzed the variation of different characteristic parameters with uniaxial stress. The analysis results show that the pyrolysis gas concentration, apparent activation energy, and oxygen consumption rate follow a cubic function law that first increases, then decreases, and then increases with increases in the uniaxial stress (the critical axial pressures at 1.8 and 5.5 MPa). At 1.8 MPa, the apparent activation energy and various parameter values are lowest, the oxygen reaction rate of coal is fastest, and the oxygen consumption rate is the highest. When the uniaxial stress is 5.5 MPa, the oxygen consumption rate is the highest, the greatest number of new cracks is created, and the characteristic T_\mathrmC\mathrmO parameters have the greatest impact. The temperature index of spontaneous coal combustion slowly transitions to rapid oxidation, and the catastrophic temperature T_\mathrmC\mathrmO characterized by the CO concentration is the most accurate. The research results have important theoretical guiding significance for the early warning and prevention and control of spontaneous combustion of coal at different buried depths.