Experimental study on oxygen adsorption capacity and oxidation characteristics of coal samples with different particle sizes

This study is aimed at investigating the effect of particle size on the oxygen adsorption capacity and spontaneous combustion and oxidation of coal, so as to provide guidance for the prevention of spontaneous combustion of residual coal in goafs. First, gas adsorption experiments, low-temperature oxidation (LTO) experiments and electron spin resonance (ESR) experiments were carried out to obtain the oxygen adsorption capacities of coal samples with different particle sizes (less than0.075 mm, 0.075–0.096 mm, 0.096–0.125 mm, 0.125–0.180 mm and 0.180–0.425 mm) and the variations of macroscopic and microscopic characteristic parameters (CO concentration, crossing-point temperature, g-factor, linewidth △H, free radical concentration Ng) during LTO. The results show that the cumulative amount of oxygen adsorption on coal surface presents grows linearly with the rise of adsorption equilibrium pressure. A smaller particle size corresponds to a higher growth rate and larger cumulative amount of oxygen adsorption. At the same temperature, coal samples with smaller particle size generate higher concentrations of CO at higher rates, and the crossing-point temperature decreases with the decrease in particle size. Such a result indicates that coal samples with smaller particle sizes are more capable of oxidizing and self-heating. During LTO, the free radical concentrations of different-sized coal samples increase continuously with the rise of temperature, and the increase differs in different stages. Specifically, after the temperature reaches 150 °C, the rate of coal-oxygen reaction accelerates, and the free radical concentration surges. For the coal sample with the particles size of less than 0.075 mm, the growth of free radical concentration in the temperature range of 150-250 °C accounts for 90.23 % of the total growth. In summary, a smaller particle size and a higher temperature conduce to accelerating the spontaneous combustion and oxidation of coal.