Optimization of coal spontaneous combustion characteristics and reaction kinetic model under lean-oxygen conditions

To obtain the variation of coal spontaneous combustion (CSC) characteristics and the best reaction kinetic model under different oxygen concentrations (LOCs), the characteristic parameters such as mass loss and exothermic of CSC under LOCs were investigated by using TG-DSC experiments. The results show that: as the oxygen concentration increases, the TG curve as a whole shifts to the low-temperature region, especially the oxygen adsorption and mass gain (OAWG) and the pyrolysis combustion (PC) stage changes are more obvious. The total heat release of the coal samples first increases slowly (O₂ < 3%) and then increases in leaps and bounds. In the fitting process using the model-free method, the best fit was found for the OAWG and the PC stage in the KAS and Friedman methods, respectively, while in the single-step reaction model fitting process, the reaction kinetic model of the NMG and TN coal samples was essentially a simple cascade reaction in the oxygen adsorption stage, where the oxygen concentration was reduced from 20 to 3%, and the apparent activation energy (E_a) increases with the increase in equal conversion rate (a). In the PC stage, the E_a first increases and then decreases with a, and the reaction kinetic model is phase boundary reaction and three-dimensional diffusion mode when the oxygen content is more abundant, on the contray, the reaction kinetic model is simple cascade reaction. The fitting effect of the multi-step reaction model is better than that of the single-step. The research results provide reference for the development of CSC mechanism.