Experimental investigation of coal particle size on the kinetic properties of coal oxidation and spontaneous combustion limit parameters

Investigating the behavior of coal spontaneous combustion (CSC) is of great significance to the prevention of coal mine fires. and the dangerous area. In this paper, we firstly analyzed the CO concentration variation at different coal sample particle sizes based on the programmed heating experiments, and initially determined the critical temperature (TC) and xerochasy temperature (TX), the two key characteristic temperatures in the CSC process. Afterwards, the three oxidation stages of the coal spontaneous combustion process were divided as per TC and TX, and the apparent activation energy of the corresponding stages was obtained. Conclusively, the variation patterns of the coal spontaneous combustion limit parameters (minimum float coal thickness hmin, upper limit air leakage intensity Qmax and lower limit oxygen concentration cmin) were analyzed. It was found that the smaller the particle size, the greater the CO concentration, oxygen consumption rate and exothermic intensity of the coal samples. An exponential function was fitted between the exothermic intensity and the coal temperature. The apparent activation energy of the oxidation kinetic parameter increases as the coal spontaneously combusts, and is positively correlated with the particle size. This is mainly due to the fact that the larger the particle size, the smaller the contact area between the coal and oxygen and the corresponding reduction in the active material in the coal, resulting in a greater apparent activation energy required for the coal oxygen reaction. Grain size plays a non-negligible role in the spontaneous combustion limit parameters of coal. The smaller the particle size, the smaller the minimum floating coal thickness and the lower oxygen concentration limit, and the greater the upper air leakage intensity. The relationship between coal spontaneous combustion limit parameters and grain size is not only a quadratic function, but also an exponential function. The smaller the grain size of the relict coal in the mining area, the greater the risk of coal spontaneous combustion. The content of this study can provide some support for predicting and preventing the risk of coal spontaneous combustion.