Abstract
Gas adsorption and desorption is a thermodynamic process that takes place within coal as temperature changes and that is related to methane (CH4) storage. As infrared thermographic technology has been applied in this context to measure surface temperature changes, the aim of this research was to further elucidate the distribution law underlying this process as well as the thermal effects induced by heat adsorption and desorption in coal. Specimens of two different coal ranks were used in this study, and the surface temperature changes seen in the latter were detected. A contour line map was then drawn on the basis of initial results enabling a distribution law of temperature changes for samples. The results show that different regions of coal sample surfaces exhibit different heating rates during the adsorption process, but they all depends on gas storage capacity to a certain extent. It proposes a correlation coefficient that expresses the relationship between temperature change and gas adsorption capacity that could also be used to evaluate the feasibility of coalbed CH4 extraction in the field. And finally, this study is deduced a method to reveal the actual adsorption capacity of coal or CH4 reservoirs in in situ coal seams.
Highlights
Adsorption and desorption are physical processes that occur between coal and gases because of Van der Waals molecular forces in gases and the interactions between solid and gas molecules (Toth, 2002)
The thermodynamic process of gas adsorption and desorption in coal includes changes in temperature; some previous experimental studies have shown that methane (CH4) adsorption releases heat and that the corresponding temperature rise in a parent coal can reach a maximum of 8◦C and varies with adsorption capacity (Guo et al, 2000a)
Mean values from the array of coal surface temperatures at different adsorption and desorption times obtained via infrared scanning in this experiment were subtracted from one another to determine an average difference before adsorption
Summary
Adsorption and desorption are physical processes that occur between coal and gases because of Van der Waals molecular forces in gases and the interactions between solid and gas molecules (Toth, 2002). Data show that adsorption heat is released during the production of CH4 and carbon dioxide (CO2), as well as the adsorption of other gases in coal, resulting in overall temperature increases (Liu et al, 2015) This means that temperature variation during CH4 adsorption presents a new approach that could be used to evaluate coal adsorption and desorption capacity as well as the basis for predicting the dynamic of geological disasters such as coal and gas outbursts (Guo et al, 2000b; Zhao et al, 2018). The thermal effects of the dynamic adsorption process have not yet been considered seriously in coalbed CH4 development,
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