Enriching Reflux and Parallel Equalization PSA Process for Concentrating Trace Components in Air

Abstract

The enrichment of useful trace components in air was carried out using a new two-bed pressure swing adsorption (PSA) process that utilized an enriching reflux (ER) cycle designed specifically for enriching the heavy component. Another new feature of this PSA process was the use of parallel equalization (PEQ), which not only saved recompression energy, but also favorably exchanged the axial concentration distribution between the two columns. These new PSA concepts were demonstrated by experimentally enriching Xe and CO2 in air using 13X MS zeolite. ER PSA substantially enriched both gases to values as high as 80 times the feed concentration with 90% recovery using a pressure ratio of only 12.5. This enrichment was far superior to that achieved with a conventional stripping reflux (SR) PSA cycle, which was limited thermodynamically to the pressure ratio and was typically less than half of it. A parametric study revealed the effects of the pressure ratio, half-cycle time, feed flow rate, flow rate ratio (enriched gas/feed), and several different PEQ schemes on the enrichment of each gas. Increases in the flow rate and pressure ratios resulted in increases in the enrichments of both gases, whereas increases in the feed flow rate and half-cycle time revealed maxima in the enrichments. Partial PEQ through the upper half of the column nearer to the feed (lean) end was also determined to be superior to other PEQ schemes.