A New Empirical Model to Predict Methane Adsorption Amount of Anthracite Considering Temperature Effect

Geo-temperature is a key geological parameter for coalbed methane (CBM) recovery. Especially for deep CBM, the impact of temperature on methane adsorption of coal should receive more emphasis. In this study, the methane adsorption performances of three anthracite coal samples from Shanxi Province, China, under different temperature and gas pressure conditions (20-60 ?, 1-10 MPa) are simulated based on the grand canonical Monte Carlo (GCMC) method. The results show that the Dubinin-Astakhov (DA) model has a higher applicability for characterizing CH4 adsorption than the Langmuir model and Dubinin-Radushkevich (DR) model, which can be attributed to the heterogeneous micropore surface of coal with great specific surface area, and the unfixed value of the structural heterogeneity parameter s. Further analysis indicates that the CH4 adsorption capacities of the studied coals are reduced by approximately 3.3 cm(3)/g for each 10 & DEG;C increase in temperature. This finding is mainly related to the great kinetic energy of gas molecules and the easier transformation of the adsorbed gas into free gas under high temperature conditions. Moreover, the net heat of CH4 adsorption in coal increases with temperature, because of the enhanced thermal movement of gas molecules. Furthermore, a new equation for the adsorbed gas amount of coal that considers temperature effect is established, where both the DA adsorption model and a negative power-type equation n = 0.011P-0.39 are introduced. Compared to the classical equation, the newly established model provides a better predication of the adsorbed gas amount of anthracite. This indirect calculation method is a good supplement to the field tests of the CBM content.

Automated summary

This study simulated the methane adsorption performances of three coal samples from Shanxi Province, China, under different temperature and gas pressure conditions. The results show that temperature has a significant impact on the methane adsorption capacity of coal.