Effects of inert gas CO2/N2 injection on coal low-temperature oxidation characteristic: Experiments and simulations

To deeply understand the mechanism of inert gases in inhibiting coal spontaneous combustion, the effects of dry air, CO2, and N2 on coal spontaneous combustion were analyzed experimentally. To this end, bituminous coal prepared from Dongrong No. 2 Coal Mine was considered the research object. Based on the adsorption configuration of the oxygen-containing coal, the displacement behavior of O2 by CO2 /N2 was studied using the grand canonical Monte-Carlo (GCMC) and molecular dynamics (MD) methods. The obtained results show that the injection of CO2 and N2 reduces the ability of spontaneous combustion of coal. It is found that among the studied gases, CO2 has a stronger inhibition effect on coal spontaneous combustion, which increases the temperature of CO occurrence by 5℃, decreases the concentration of CO by 29.91%, and inhibits low-temperature oxidation of coal. From the microscopic point of view, CO2 /N2 gases can effectively displace O2 by diffusion and occupying adsorption sites. It is found that after the injection of CO2, the concentration of O2 molecules increases significantly in the vacuum layer. Compared with N2, injection of CO2 increases the diffusion activation of O2 by 5.89%. This indicates that the injection of an inert gas significantly reduces the oxygen absorption capacity of coal, thereby decreasing the coal-oxygen combination reaction and preventing the spontaneous combustion of coal. The performed analyses demonstrate that CO2 outperforms N2 in restraining the spontaneous combustion of coal.