Effect of N₂/CO₂ Injection on O₂ Desorption in Coal Rocks Containing CH₄

To investigate the desorption behavior of O₂ through CO₂/N₂ injection in the gob of a gassing mine, we focused on the adsorption configuration of coal containing O₂–CH₄. The mechanism underlying the enhancement of O₂ desorption in coal due to CO₂/N₂ injection was elucidated using the Grand Canonical Ensemble Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. Furthermore, the impact of CH₄ on O₂ desorption was unveiled by detailed calculations and studies of energy variation, concentration distribution, and diffusion coefficients of oxygen.Our findings indicate the following: (1) CO₂ and N₂ facilitate the displacement of oxygen primarily by occupying adsorption sites. The CO₂–O₂ model exhibits a significantly higher concentration of free O₂ molecules compared to the N₂–O₂ model, and the CO₂–O₂–CH₄ model surpasses the N₂–O₂–CH₄ model in free O₂ molecules. (2) The total energy of the CO₂–O₂ model is lower than that of the N₂–O₂ model, indicating greater stability in the former. Similarly, the total energy of the CO₂–O₂–CH₄ model is lower than that of the N₂–O₂–CH₄ model, highlighting its superior stability. It is concluded that CO₂ injection is more effective in promoting oxygen desorption than N₂, regardless of the presence of methane. (3) Under equivalent injection pressure, the root mean square displacement of O₂ in the CO₂–O₂ system surpasses that in the N₂–O₂ system. Furthermore, compared to the N₂–O₂–CH₄ system, the CO₂–O₂–CH₄ system exhibits a larger root mean square displacement of O₂, signifying higher O₂ molecule activity. The diffusion coefficient of O₂ in the CO₂–O₂ system is higher, underscoring the superior effectiveness of CO₂ in promoting O₂ desorption.In summary, our research outcomes offer valuable theoretical insights for fire prevention technology in goaf.