Methane simultaneous recovery from CH4/N2 stream and CH4/CO2 stream by the displacement VPSA process

Both CO2 and N2 are the common impurities in unconventional natural gas, their existence reduces the utilization efficiency of methane. Therefore, research and development of decarbonization and nitrogen removal technologies from the unconventional natural gas is more significant. In this article, the displacement VPSA process is developed to recover simultaneously methane from CH4/N2 and CH4/CO2 mixtures (two important unconventional natural gas sources). This proposed VPSA process is the integration of CH4/N2 and CH4/CO2 adsorption separation, including seven steps of pressurization, adsorption, displacement, depressurization, blowdown under vacuum pressure, two purges under vacuum pressure. After the adsorption separation by the developed process, three product and by-product gases can be obtained at the same time, namely as CH4-rich product gas acquired at the displacement step, N2-rich by-product gas got at the adsorption step, CO2-rich by-product gas obtained at the blowdown step. Experimental demonstration is carried out for methane simultaneous recovery from CH4/N2 and CH4/CO2 mixtures by the proposed process with coconut shell activated carbon adsorbents. Furthermore, the mathematical model is developed to predict the composition of three product and by-product gases, and to explore the effect of CO2 existence in CH4/N2 stream on the separation performance of the displacement VPSA process. Both the experimental results and numerical predictions testify the high-purity methane product gas (∼95.0% CH4 purity) can be acquired by the proposed process from CH4/N2 and CH4/CO2 mixtures.