Simulation of adsorption process of low-concentration coal bed methane

Abstract：The adsorption process, supported by Aspen Adsorption software, was simulated for low concentration coal- bed methane (CBM) composed of 30% CH4 and 70% N2,and the effects of operating pressure,temperature and the mass transfer coefficient on the outlet methane concentration were studied. Moreover, the variations of the concentra- tions of methane/nitrogen with adsorption time, and the axial distributions of methane/nitrogen adsorption quantity along the adsorption column were obtained. The results show that the simulation values of methane concentration are basically consistent with the results of experiment. The methane is saturated when adsorption time is 3 000 s, with the adsorption quantity of 6. 75 x 10-4 kmol/kg, which is about 2 times larger than that of nitrogen. In addition, the break- through curves of methane shifts to the longer time from 392 s to 2 187 s,with the pressure increasing from 100 kPa to 500 kPa, and the effect of temperature on the breakthrough curve is negligible within the range of 273-323 K. Further- more, the methane adsorption quantity changes evidently when the value of mass transfer coefficient is smaller than 1. 000 s-1 , and the breakthrough time at the value of mass transfer coefficient 0. 001 s-1 is about two times when the mass transfer coefficient is 0. 010 s-1 ,but there is almost no effect on the breakthrough curve when the mass transfer coefficient is greater than 1. 000 s-1.