Experimental investigation on microstructure fractal characteristics of low-temperature oxidation of gas-bearing coal

Abstract In order to study the multi-field coupling mechanism of gas and coal spontaneous combustion, low-temperature nitrogen adsorption and SEM were applied to carry out microstructure testing experiments on oxidation of gas-bearing coal in this paper. And a pore fractal calculation model incorporating pore size distribution was established. The effects of low-temperature oxidation and gas ad/de-sorption on the change of coal pore structure were investigated. The results showed that the pore volume of coal oxidized and gas-bearing coal oxidized were decreased by 1.805 and 2.232×10− 3 cm3·g− 1 in all pore size distributions, where the micropores and macropores were converted to mesopores after oxidation of coal and macropores were formed by destruction of micropores and mesopores after oxidization of gas-bearing coal; coal oxidation and gas-bearing coal oxidation specific surface area decreased by 2.264 and 2.320 m2·g− 1, respectively, and the modifying effect of coal pore surface was stronger in the latter than in the former; the irregularity of the surface morphology increased after oxidation of the coal, and a large number of micropores were connected to form microcracks, while the surface morphology of the pores of the oxidized gas-bearing coal tended to be more regular compared with the oxidation of the non-gas-bearing coal; a pore fractal model based on the characteristics of the pore diameter distribution was established, and Dfb is 2.14–2.23, and the coupled action of gas desorption and oxidation on pore modification is stronger than the oxidation. The gas storage state of gas-bearing coal and the distribution of desorbead gas in goaf were affected by change of pore structure, so that the oxidation of gas-bearing coal can be weakened and the risk of spontaneous combustion of gas-bearing coal can be declined, which can provide a theoretical basis for the judgment of the risk of spontaneous combustion of gas-bearing coal in goaf.