Influence of temperature on coal sorption characteristics and the theory of coal surface free energy

An experimental study was undertaken to examine the sorption and desorption characteristics of coal at temperatures of 35 °C, 45 °C and 55 °C. The study focused on the effect of changes in temperature and coal particle sizes on gas sorption and desorption characteristics. The coal size used ranged from fragmented coals, 16 mm, 8 mm, 2.4 mm, powdered coal of 150 μm and 54 mm core samples. The samples were tested in pressure vessels, known as “bombs”, charged with CO2 gas at different pressure levels up to a maximum of 4000 kPa. It was found that temperature has a significant influence on the sorption and desorption behaviour of gas in coal. The degree of hysteresis phenomenon was found to be influenced by the coal surface area as well as temperature. Based on the principle of surface chemistry, the method of calculating coal surface energy with sorption parameters was used and the main parameter of surface tension was analysed. The calculation result showed that reduced value of surface tension parameter decreased with increasing temperature. Also the reduced value of surface tension parameter of adsorption is smaller than the desorption. The theory of coal surface free energy can be used to explain the coal sorption characteristics with CO2 at higher temperatures. Results from this study have useful implication for enhanced CBM and gas drainage in coal mines.