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

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 and specific surface area of JJK and YJL with different pretreatment conditions were similar in trend, adsorption–desorption process further attenuates the ability of the coal pore to resist the thermal damage, V₁ and V₂ of JJK-3 and YJL-3 decreased by 0.199, 0.212 and 1.88, 4.214 × 10^–3 cm³·g⁻¹, respectively. The pore fractal model based on pore size distribution characteristics was found, and the D_fb of JJK-3 and YJL-3 was 2.23 and 2.33, respectively, which were higher than that of JJK-2 (2.20) and YJL-2 (2.05). The coupling effect of desorption of gas and oxidation was stronger than the effect of oxidation on pore modification. The gas storage state of gas-bearing coal and the distribution of desorbed 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.