Physical Simulation of Temperature Influence on Methane Sorption and Kinetics in Coal (II): Temperature Evolvement during Methane Adsorption in Coal Measurement and Modeling

The dynamic thermal process for methane sorption in coal has not been quantitatively studied, and the temperature change induced by the heat of adsorption on the sorption equilibrium state has not been confirmed by tests. In order to probe the temperature evolvement and its effect on methane adsorption in coal, the temperature of the coal sample is measured using a digital temperature gauge during methane isothermal adsorption in coal. Isothermal adsorption tests for methane in coal under six different temperatures (50, 40, 30, −10, −20, and −30 °C) are conducted. Blind experiments show that the temperature increase of the tested coal sample induced by external energy brought via the filled methane and the possible Joule–Thomson effect is within 0.5 °C in this test and thus will not be considered during methane adsorption in coal. Both real test and modeling results show that the temperature of the coal sample induced by the heat of adsorption can go up to 13.79 °C during the methane adsorption process in coal, and the methane adsorption in coal is not an isothermal process in the initial sorption stage. During the methane adsorption process in coal, the temperature induced by the heat of adsorption first increases to the peak sharply, then decreases gradually with time, and finally drops down to the environmental temperature prior to reaching sorption equilibrium. The closer the distance of the monitoring point is from the wall of the steel sample canister, the smaller the peak temperature value is and the shorter the time needed. This can be attributed to the different heat transfer efficiency in the different places inside the sample canister. The total specific power decreases exponentially with time, which can work as one index to model the heat transfer behavior of the coal sample in different places inside the canister. Temperature influence on the sorption equilibrium state induced by the heat of adsorption can be neglected because the temperature variation stage only lasts a short time in the initial sorption stage.