Study on the Effect of Oxygen on Free Radical Generation in Coal

According to the theory of coal–oxygen combination, oxygen has an important effect on the spontaneous combustion of coal. In this study, Hailar lignite is taken as the research object to prepare and analyze the coal sample. The variation trends of the free radical concentration, g factor value, line width and line shape are measured by electron spin resonance (ESR) technology, and the influence of different oxidation times and oxygen concentrations on the free radical parameters in coal are studied. The results show that the relationship between the free radical reaction and the oxidation time is not linear. The critical point of the free radical reaction is the oxidation time of 5 h. With an increase in the oxygen concentration, the free radical concentration, g factor value and line width also increase. In a nitrogen environment, the free radical reaction still exists, but the new free radicals are hydrocarbon free radicals or alkyne free radicals, which will not lead to spontaneous combustion of coal. Oxygen molecules, meanwhile, make the free radical reaction more active. Oxygen atoms combine with carbon chains to form oxygen-containing free radicals and peroxide free radicals, which further decompose and oxidize to produce CO and CO2, eventually triggering the spontaneous combustion of coal.