Study of non-uniform potential well distribution of coal and its effect on methane adsorption/desorption

In order to study the non-uniform potential well distribution of coal and its effect on the methane adsorption/desorption process, a non-uniform potential well model based on adsorption science and molecular dynamics theory was developed in this study. The model characterizes the adsorption/desorption properties of coal, and accurately calculates the number of potential wells corresponding to different potential wells in the coal. To verify the accuracy of the characterization ability of the non-uniform potential well model in terms of coal adsorption/desorption performance, it was fitted separately to the Langmuir model for the methane adsorption/desorption process, and then the correlation coefficients of the fitted data and isothermal adsorption lines were compared separately. The results show that the non-uniform potential well model is superior in characterizing the adsorption/desorption performance of the coal body. In the study of the potential well distribution within the coal, it was found that the potential well distribution within the coal shows some significant differences during the adsorption/desorption of methane by the coal at different temperatures and pressures. In the analysis of the potential well pattern of coal, it was found that the number of potential wells in the coal is more in the adsorption phase than in the desorption phase, but the average potential well depth in the coal is larger in the desorption process than in the adsorption process. And the average potential well depth decreases as the coal rank decreases. In the adsorption phase, the number of potential wells is concentrated within a certain range of potential depth, but in the desorption phase, the distribution of the number of potential wells is more dispersed in comparison. At the same temperature, the number of potential wells decreases with decreasing coal rank. In terms of the potential well distribution, the variance of the potential well distribution is significantly larger for high rank coals than for low rank coals at the same temperature. An increase in temperature causes the average potential well depth to decrease as the temperature increases. For the same coal rank, the change in temperature has a greater effect on the potential well depth in the range of 5−15 kJ/mol, and this phenomenon is more pronounced in lower rank coals. In the study, it was found that the potential wells with larger potential well depths are more resistant to the effects of temperature variations on them. The nonlinear variation of methane adsorption/desorption rates during the heating or pressurization of the coal body is caused by the inhomogeneity of the potential wells.