Alternative PSA process cycle with combined vacuum regeneration and nitrogen purging for CH4/CO2 separation

A pressure swing adsorption (PSA) process cycle with nitrogen purge and vacuum regeneration has been studied for the purification of methane from a methane/carbon dioxide gas mixture (CH4/CO2 60:40% by volume). The separation process used zeolite 13X pellets and was carried out at an adsorption pressure of 400 kPa (abs) and a vacuum pressure of 8 kPa (abs). A four-column PSA process with nine operating steps including nitrogen purge and vacuum regeneration of adsorbent yielded a CH4 product flowrate of 0.06 m3 STP/min with 99% CH4 purity and a methane recovery of 93%. The methane recovery obtained in this study was higher than that of PSA processes which employ the product gas to purge the adsorption columns. It was found that a PSA process which used only vacuum regeneration of adsorption columns gave 90% CH4. However, as a result of using pure nitrogen generated from air by another PSA process, the electrical energy consumption with both nitrogen purging and vacuum regeneration was approximately 0.10 kW h per m3 of CH4 higher than for the process with only vacuum regeneration.