A study on the combustion characteristics and kinetic parameters of coal during the inertization process at different metamorphic degrees

To examine the impact of different heating rates and oxygen concentrations on the combustion characteristics and kinetic parameters of coals at various metamorphic degrees, this study selected four different metamorphic degrees as experimental subjects. Thermogravimetric experiments were conducted under various heating rates and oxygen concentrations to obtain characteristic temperature points, mass loss rates, and heat absorption and excretion characteristics of coal samples under different conditions. Furthermore, reaction mechanism functions were determined, and the reaction kinetics "three factors" of coal samples under different conditions were calculated to ascertain activation energy. Based on characteristic temperature points, different phases of coal spontaneous combustion were delineated, and the oxidative characteristics of coal samples at each phase were analyzed. The study explored the impact mechanisms of different temperatures and oxygen concentrations on coal spontaneous combustion from the perspectives of characteristic temperature points and activation energy. The results indicate that inertization, meaning the introduction of inert gases, has an inhibitory effect on the coal–oxygen complex process for coals at different metamorphic degrees. As the degree of inertization increases, the two phases most affected are the oxygen uptake and mass gain phase and the combustion phase. Compared to the oxygen uptake and mass gain phase, the TG curve of the combustion phase shows a delayed phenomenon with increased inertization degree. With rising temperature, the overall trend of the DTG curve initially decreases, followed by an increase, and then reaches a steady plateau, with the minimum value occurring at the trough. The maximum mass loss rate of coals at different metamorphic degrees decreases with an increase in inertization degree, indicating that inertization inhibits the coal oxidation process. Additionally, the temperature points corresponding to the maximum exothermic rate all shift backward. The DSC curves of coal samples exhibit an overall trend of initial decrease followed by an increase with temperature variation. With enhanced inertization degree, the maximum exothermic rate of coals at different metamorphic degrees decreases, and the corresponding temperature points shift backward. As the inertization intensity decreases, the activation energy (E_a) of the low-temperature oxidation phase generally decreases for coals at four different metamorphic degrees. Under the same inertization intensity, coals with higher metamorphic degrees have higher activation energy. This study can provide theoretical support for the prevention and control of coal spontaneous combustion.