Effect of Oxygen on Radical Reaction During Oxidation of Different-rank Coals

The spontaneous combustion disaster caused by low-temperature oxidation of coal often leads to mine fire which poses a serious threat to the safe mining of underground coal resources. Due to the complexity of coal and the variability of gas atmosphere, it is difficult to prevent the spontaneous combustion of residual coal in goaf. In this paper, the radical characteristics during oxidation of lignite, bitumite, and anthracite in anaerobic, anoxic, and normal oxygen atmospheres were measured by preparing mixed gases with different oxygen concentrations. On this basis, the spontaneous combustion characteristics of different-rank coals under different oxygen concentrations were explored. The experimental results show that the primary radical concentrations of different-rank coals are quite different in the initial stage of oxidation. Among the three types of coals, anthracite has the highest primary radical concentration while lignite has the lowest primary radical concentration. As the oxidation proceeds, the radical concentration of lignite grows at a significantly higher rate than those of bitumite and anthracite. In addition, the g factor values of the three types of coal all increase slightly with the rise of temperature, and the g factor value of lignite is always greater than those of bitumite and anthracite. During coal oxidation, the Delta H values of lignite, bitumite and anthracite vary in the range of 0.78-0.70, 0.6-0.48, and 0.70-0.50, respectively. The Delta H value of lignite is larger than those of bitumite and anthracite, but it experiences a smaller decrease than bitumite and anthracite. With the increase of oxygen concentration, the radical concentration and g factor of coal increase while the line width decreases. Through the analysis, the growth rate of radical concentration and g factor, instead of radical concentration, were used to evaluate the oxidation capacity of coal. The results reveal that the radical reaction in lignite is more sensitive to oxygen than those in bituminous and anthracite.