Study on gas adsorption and desorption characteristics on water injection coal

Abstract

To study the desorption mechanism of methane in coal by H2O injection and establish the Wiser molecular structure model of bituminous coal, the Grand Canonical Monte Carlo method was used to study the desorption behavior of CH4 in coal with different amounts of H2O injection at molecular scale. The results showed that at 293 K, the maximum adsorption capacity of H2O was about 16 mmol/g, and that of CH4 was about 8 mmol/g, which was about twice that of CH4. This indicates that H2O has a stronger adsorption capacity than CH4. For methane-bearing coal, when the amount of water injected is 100, the average relative concentration of CH4 is 0.5446, and the average relative concentration of CH4 decreases by 33.77% compared to the water content of 20. Under the same time conditions, the root mean square displacement and diffusion coefficient of CH4 decrease with the increase of H2O injection quantity. With the increase of H2O injection, the motion velocity of CH4 in vacuum layer decreased. When water was injected, methane was trapped in the coal by water. The more H2O injected, the more methane trapped in the coal, and the less methane desorption. This research lays a theoretical foundation for further research involving coal-water interaction.

Keywords

• H2O injection promotes CH4 desorption
• Analytical dynamics
• Molecular simulation
• Diffusion