Theoretical Derivation of a Prediction Model for CO₂ Adsorption by Coal

Abstract

Adsorption characteristics of CO 2 by coal are an important reservoir parameter to determine the CO 2 storage capacity of the coal seam. The Langmuir isotherm adsorption model is commonly used to describe the isothermal adsorption line of coal. However, we cannot predict the CO 2 adsorption capacity at other temperatures by using the Langmuir model based on the experimental data at a fixed temperature. This paper analyzes the ε−V ad adsorption characteristic curves of three coal samples over a range of temperatures and pressures. The study demonstrates that the adsorption characteristic curves of CO 2 gas are independent of temperature and depend mainly on the dispersion force between coal and the CO 2 molecules. In addition, the adsorption potential of CO 2 gas has a negative correlation with the volume of the adsorbed phase. Hence, the CO 2 adsorption characteristic curve of coal conforms to the logarithmic function. Based on the adsorption potential theory, the prediction model of CO 2 adsorption by coal is derived. The deviation analysis from measured data shows that the average relative deviation of the three coal samples is ∼5%, and the prediction results are accurate and reliable. Under different temperature and pressure conditions of the three coal samples, the results from the prediction model of CO 2 adsorption by coal and the Langmuir model have a strong correlation with the experimental results. In comparison with the Langmuir model, the prediction model of CO 2 adsorption by coal can predict the adsorption capacity under different temperature and pressure conditions. Hence, it has a wide range of applications when compared to that of the Langmuir model. In practical applications, better results are achieved with a significant reduction in experimental time and labor.

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

“…In the same coal-CO 2 system, the CO 2 adsorption characteristic curves of coal at different temperatures are almost on the same curve, indicating that the CO 2 gas adsorption characteristic curve is not affected by temperature, the intermolecular force is the dispersion force, and the adsorption process is physical adsorption. The literature 28,29 found that there is a negative correlation between the adsorption potential and the adsorption space through the analysis of experimental data, which was not affected by the temperature of the sample. Therefore, in the same adsorption system, the adsorption characteristic curve of coal for CO 2 is generally not affected by temperature.…”

Experimental Study on Replacing Coal Seam CH4 with CO2 Gas

“…Many researchers have studied the mechanism of CH 4 stimulation by gas injection. − Huo et al observed that the increase in CO 2 injection pressure increases the CH 4 recovery and CO 2 storage rates. Sun et al divided the enhanced production process into three stages: initial depressurization, medium-term CO 2 adsorption and replacement, and, finally, the CH 4 and CO 2 coproduction stage.…”

Experimental Research on the Law of Energy Conversion during CO2 Sequestration in Coal

“…The temperature significantly impacts coal permeability and further affects the adsorption capacity of the different rank coal samples [19]. In addition, Hao et al indicated that the equilibrium adsorption capacity of CO 2 in coal is logarithmic to pressure and proposed a prediction model of CO 2 adsorption capacity, whose predictions are slightly different from the measured data [20].…”