Adsorption and diffusion behavior of CO2/N2 in coking coal matrix based on molecular simulation: Considering the effects of moisture and temperature

The moisture content and temperature of coal has a significant impact on the efficacy of inert gases (CO2/N2) in inhibiting coal spontaneous combustion (CSC). Therefore, this study explores the changes in microporous structure, adsorption capacity, heat of adsorption as well as energy distribution and diffusion of CO2/N2 at varying moisture contents (1%–5%) and temperatures (303–343 K). The results demonstrate that water molecules gradually transform large pores in the microporous structure into multiple smaller pores, thus reducing the volume proportion of free pores. The adsorption of CO2/N2 is constrained by the pre-adsorbed water molecules occupying the adsorption sites. Both temperature and moisture exert similar effects on gas adsorption capacity, with higher levels of both reducing the adsorption capacity. Notably, temperature rise is associated with an increased heat of adsorption for the gas molecules. Under moisture effects, there is an observable positive relationship between the gas diffusion coefficient and the adsorption capacity. Conversely, there is a negative correlation with temperature. At low moisture content, CO2/N2 injection is enhanced. High temperatures reduce the effectiveness of CO2/N2 in preventing CSC, while heat can only be exchanged by diluting the oxygen concentration. These results provide crucial insights into the adsorption behavior of CO2/N2 at different temperatures and moisture contents.