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

Abstract

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 400kPa (abs) and a vacuum pressure of 8kPa (abs). A four-column PSA process with nine operating steps including nitrogen purge and vacuum regeneration of adsorbent yielded a CH4 product flowrate of 0.06m3 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 0.10kWh per m3 of CH4 higher than for the process with only vacuum regeneration.