Improved CO2 recovery from flue gas by layered bed Vacuum Swing Adsorption (VSA)

Performance of a two column five-step vacuum swing adsorption cycle is tested for CO2 enrichment and recovery from a simulated ternary flue gas mixture containing 13% CO2, 82% N-2, and balance O-2. The results are compared when a layered bed of commercial activated carbon (AC) (F-400, Calgon) and 13X zeolite (Z10-04, Zeochem) is employed with reference to an only single layer of AC and 13X adsorbent. With the layered bed, in which the first layer at the feed entry end is AC followed by 13X, the CO2 recovery obtained is 84% which is 42% more than that of pure 13X bed and the purity of CO2 is almost at the same level as that with 13X bed (similar to 90 mol %). The VSA is compared at same adsorption time, set as a 70% of CO2 breakthrough time. The CO2 purity obtained with the activated carbon bed was 76 mol% which is considerably lower compared to the bed with only zeolite 13X layer (90 mol%). The result can be explained due to higher CO2/N-2 selectivity of the zeolite than activated carbon. The recovery of CO2 with activated carbon is, however, higher (97%) than zeolite (59%) due to its lower heat of CO2 adsorption compared to that with 13X. The lower heat of CO2 adsorption on the activated carbon surface implies weaker interaction and thus better desorption characteristics than 13X. VSA performance of the layered bed are also compared under different adsorption/evacuation time, bed temperature and evacuation level.