Molecular simulation and experimental studies on CO₂ and N₂ adsorption to bituminous coal

A coal fire is one of the most serious disasters in coal mining. To improve the efficiency of an inert gas for extinguishing the fire, the adsorption behavior of coal in CO₂/N₂ mixed gas was investigated in this study. Proximate analysis, ultimate analysis, solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR), X-ray photoelectron spectroscopy (XPS), and molecular dynamics (MD) were applied to analyze and establish the bituminous coal molecular model. The adsorption behavior of bituminous coal in mixed gas mixtures with different proportions was studied using the bituminous coal model and Materials Studio (MS) software. A self-built coal adsorption experimental system was used for experiments. The adsorption of bituminous coal to CO₂ is stronger than that to N₂, and there is a competitive adsorption relationship between them. The amount of CO₂ adsorbed by the coal gradually increases as the CO₂ partial pressure rises, consistent with the Langmuir model. With an increase in CO₂ pressure, the total adsorption capacity, which is divided into the rapid increase stage, slow growth stage, and stable stage, also increases. The coal adsorbs 0.5050 cm³/g, 0.7455 cm³/g, 0.9450 cm³/g, 1.0715 cm³/g, and 1.2000 cm³/g for pure N₂, 2%, 5%, 7%, and 10% CO₂, respectively, in the experiment. The results of the simulation and experiment show the same trend, which means that the injection of a small amount of CO₂ into pure N₂ will greatly improve the gas adsorption volume of the coal, demonstrating that it is feasible to improve the ability of the coal to absorb mixed gases by changing the gas concentration and consequently to increase the efficiency of inert gas for fire extinguishing and suppression.