关键词: DA模型, 等温吸附线, 高低温环境, 理论预测

Abstract: Methane adsorption characteristics in coal play an important role in the gas content estimation and gas productivity prediction in coal-bed, one group of methane adsorption data in coal under a certain temperature is only applicable to the adsorption isotherm in this temperature which can't predict methane adsorption capacity under other temperature and pressure conditions. In the practical work, both the coalbed methane resources exploration and the prevention and control of gas disaster in coal mine need to know methane adsorption characteristics in coal seam at certain temperatures and depth. Because there are differences of methane adsorption isotherms at different temperatures, so many adsorption isotherms need to test at each temperature, which will cause high cost and long time. So according to the metamorphic grade of coal, gas-fat coal, cooking coal, meager coal and anthracite coal were chosen as test coal samples, methane isothermal adsorption tests at 243.15, 263.15, 283.15, 303.15 and 323.15 K were carried out with high and low temperature environment test system for gas adsorption and desorption. Based on Dubinbin?Astakhov (DA) equation and polanyi adsorption potential theory, the relationships of saturated adsorption quantity and characteristic adsorption energy with temperature can be gotten by fitting the measured data, and then the gas adsorption isotherm of coal at other temperature were predicted. The results showed that the gas adsorption capacity of coal with different metamorphic degree increased with the temperature decreasing, and there had good linear relationships between the gas saturated adsorption capacity and the characteristic adsorption energy of different metamorphic coals, which correlation coefficients reached above 0.98. At the same temperature, as the coal metamorphism degree increases, the methane adsorption amount increases under the same adsorption equilibrium pressure. Under different temperatures the predicted adsorption isotherms of coal based on the DA model with different metamorphic degrees agreed well with the experimental results. The relative error was no more than 5%. With little measured data of isothermal adsorption tests, DA model can accurately predict the adsorption abilities of coal at different temperatures and pressures, which will greatly reduce the workload and provide an important basis to study the coal reservoir adsorption properties.

Key words: DA model, isothermal adsorption curve, high/low temperature environment, theoretical prediction