Effect of injecting inert gas at different spontaneous combustion stages on active groups in coal

Abstract

Inert gas injection into the mine gob where coal spontaneous combustion occurs can effectively avoid the loss of coal resources, reduce greenhouse gas emissions and realize the green and sustainable mining of coal resources. In this paper, a continuous process of abruptly changing coal from an oxygenated atmosphere to an inert atmosphere in one experiment was realized by a gas atmosphere conversion device, and the effect of inert gas injection on reactive groups in coal at different stages of oxidation was studied based on electron spin resonance technique and spectral peak splitting fitting technique. The experimental results show that the g factor of lignite decreases slowly and then increases with the rising temperature under dry air, and the g factor turning point temperature is 80 °C. The concentration of radicals in lignite increases continuously with rising temperature. The injection of N2 and CO2 at 130 °C has the most significant inhibitory effect on the g factor of coal, with 41.61 % and 65.11 %, respectively. After injecting N2 and CO2 at different stages, the radical concentration of coal suddenly decreases and then continues to increase with the extension of constant temperature time, and the injection of N2 and CO2 at 130 °C has the most significant inhibitory effect on the radical concentration of coal, 28.35 % and 35.44 %, respectively. The radicals in coal can be classified into oxygen-containing radicals, aliphatic radicals, simple aromatic radicals, and π- or σ-type oxygen-containing radicals by the spectroscopic peak splitting technique. The injection of inert gas produces a significant inhibition effect on oxygen-containing radicals in coal. And finally, the inhibition pathway of inert gas on oxygen-containing radicals in coal was revealed from the perspective of radical reaction.