Hydrogen purification from refinery fuel gas by pressure swing adsorption

Abstract

Hydrogen purification and recovery from various process streams constitutes the largest commercial use of pressure swing adsorption (PSA) technology. This study investigates the performance of a six-bed, dual-sorbent PSA operation for hydrogen purification from the refinery fuel gas. Major impurities are methane, ethane, propane and butane, and comprise 30-40% of the feed. The dual-sorbent PSA bed consists of an initial layer of silica gel adsorbent for trapping heavier hydrocarbons and a subsequent layer of activated carbon for removing lighter hydrocarbons. A numerical simulation model of the H2-PSA process developed with all the essential features of the actual operation shows that butane is more strongly adsorbed on activated carbon than silica gel, and, hence, is less easily desorbed from the former using simple pressure reduction in the PSA cycle. Therefore, the initial layer serves to prevent butane from degrading the adsorptive capacity provided by activated carbon for other lighter hydrocarbons. The simulation model agrees well with the experimental results from a laboratory unit as well as with available H2-PSA plant data from a refinery. The results also indicate the importance of heat effects in this process. Extensive parametric studies, which show effects of feed velocity and cycle time on the variation of product recovery and purity obtainable from the industrial unit, provide a valuable guide for its proper operation.