Experimental Study on Influencing Factors and Thermal Effects of CO₂ Adsorption by Coal

The utilization of CO₂ is extremely important to solve the environmental problems and coal spontaneous combustion in goaf. There are three kinds of CO₂ utilization in goaf: adsorption, diffusion, and seepage. Since adsorption will consume CO₂ in goaf, the optimization of CO₂ injection amount is very critical. A self-developed adsorption experimental device was used to determine the CO₂ adsorption capacity of three different particle sizes of lignite coal samples at 30-60 °C and 0.1-0.7 MPa. The factors affecting CO₂ adsorption by coal and its thermal effect were studied. In the coal and CO₂ system, the CO₂ adsorption characteristic curve is not affected by temperature, but there are differences in that with different particle sizes. The adsorption capacity increases with the increase of pressure, while it decreases with the increase of temperature and particle size. Under atmospheric pressure, the adsorption capacity of coal is a logistic function relationship with temperature. Furthermore, the average adsorption heat of CO₂ on lignite shows that the interaction force between CO₂ molecules has a stronger effect on CO₂ adsorption than the effect of heterogeneity and anisotropy on the coal surface. Finally, the existing gas injection equation is improved theoretically with CO₂ dissipation, which provides a new idea for the work of CO₂ prevention and fire suppression in goaf.