Study on carbon monoxide, carbon dioxide and oxygen competitive adsorption properties of bituminous coals

In order to clarify the adsorption pattern between coal and CO, CO₂ and O₂, the competition between CO and CO₂ and O₂ in coal is studied. Qianjiaying bituminous coal is used as the research object, and the molecular unit parameters are calculated by quantitative analysis method based on the experimental results of Fourier transform infrared spectroscopy (FTIR). The molecular cell structure of Qianjiaying bituminous coal is constructed (C₁₁₆₀H₈₆₀O₈₀N₂₀). To verify the accuracy of the model, the infrared spectrum of molecules is simulated by quantum chemical calculation, and the calculated results are basically consistent with the experimental results. On this basis, the effects of pressure(0−16 MPa) and temperature(20−60 ℃) on the adsorption of CO, CO₂ and O₂ by coal are investigated by using the Grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods. From the experimental results, it can be concluded that the fitted isothermal adsorption curves conformed to the Langmuir equation. Under the same pressure, the adsorption capacity of CO, CO₂ and O₂ is weaker as the temperature increases. At the same temperature, there is a positive correlation trend between the burial pressure of coal seam and the adsorption amount. The magnitude of adsorption of single gases CO, CO₂ and O₂ is CO₂ > O₂ > CO, and CO₂ can reach saturation adsorption state in the first. The competitive adsorption results of binary gases show that the adsorption selectivity of CO₂/CO has obvious advantages in low-pressure or shallow buried coal seams. However, the adsorption selectivity of O₂/CO did not change significantly with the change of pressure. The competitive adsorption capacity of CO₂ is greater than that of CO, and the adsorption capacity of CO₂ decreases with the increase of CO concentration; The competitive adsorption of O₂ is greater than CO when the ratio of CO to O₂ molar concentration is ≤ 1, but the adsorption of CO is greater than O₂ when the molar concentration of CO is much greater than O₂. Therefore, the molar concentration of CO is high, which inhibits the adsorption capacity of CO₂ and O₂. In other words, in bituminous coal seams with high abnormal CO concentration, the effect of using CO₂ injection to control fire extinguishing is not significant, so the amount of air leakage from the working face should also be controlled to prevent CO from desorption to the coal body and to ensure that the CO concentration in the well is within the permissible range.