Energy variation in coal samples with different particle sizes in the process of adsorption and desorption

Abstract The study of energy variation rules in the process of gas adsorption and desorption in coal is important to predict mine outburst disasters. In this study, an adsorption-desorption experimental device was developed and used to evaluate six coal samples of various particle sizes under different pressure conditions. Temperature was measured in real-time throughout the process. The rate of temperature change, maximum temperature variation, and adsorption quantity increased with particle size and an increase in equilibrium pressure. There is a positive linear relationship between adsorption quantity and temperature variation. This study focused on energy variation during adsorption and desorption. The results showed that the smaller the coal particle size, the larger the reduction in surface free energy and the change in heat. With an increase in equilibrium pressure, the rate of reduction in the surface free energy slows gradually, indicating that there is a non-uniform adsorption potential field on the surface of coal. By comparing the difference of temperature and heat data between a columnar coal sample and a granular coal sample in the process of adsorption and desorption, it can be concluded that the surface free energy is converted into heat and deformation energy in the adsorption process, and the deformation energy is converted into heat energy in the desorption process.