Spontaneous combustion properties and quantitative characterization of catastrophic temperature for pre-oxidized broken coal under stress

Coal Spontaneous Combustion (CSC) is one of the most important natural disasters in coal mining safety production. To deeply restore the real state of CSC left in goaf during the face mining of coal mines, the experiments are carried out to simulate the oxidation characteristics of coal left in goaf under the coupling of the stresses (0 MPa, 4 MPa, 8 MPa) and the pre-oxidation temperatures (25 °C, 70 °C, 120 °C, 180 °C) employing the load-pressure-based device equipped with temperature-programmed. The oxidation characteristic parameter of CO gas generation, the O2 consumption rate, the apparent activation energy (Ea), and the critical temperature(T1) are calculated. It is found that both the pre-oxidation temperature and the stress have a promotion range for coal spontaneous combustion, and although they inhibited each other beyond the promotion range, they still show a promotion result. The pre-oxidation temperature and stress mainly affect the content of oxygen-containing functional groups and the permeability, thus influencing the process of coal spontaneous combustion. Based on the engineering application, a cusp catastrophe model is established to predict the catastrophic temperature of coal spontaneous combustion, and it is verified that the catastrophic temperature could correctly characterize the transition of coal spontaneous combustion, and it is found that the catastrophic temperature lagged behind the critical temperature, which provides sufficient time and space for the prevention and control of coal spontaneous combustion.