A new multi-bed vacuum swing adsorption Cycle for CO₂ capture from flue gas streams

Adsorption Processes for CO₂ capture have been extensively researched within the last decade and have been piloted at many field installations and in research laboratories. Many reported VSA cycle designs for CO₂ capture are based on single- and dual- adsorbent beds. The performance of such cycles is typically poor due to the lack of room to incorporate more relevant auxiliary intermediate process steps such as pressure equalization, co-current purge, etc. Very low vacuum pressures (< 3kPa) are therefore necessary to achieve higher CO2 purity. This is difficult and expensive to provide at large scale. To address this concern, a new 4-bed PVSA cycle has been developed in our laboratory and tested experimentally and through simulation. The cycle configuration provides a means to internally recycle parts of the product and CO₂-lean gases to enhance the separation efficiency and also to minimize energy consumption. A dry gas mixture of 15%CO2 in N₂ was used as the feed gas and zeolite 13x as the adsorbent. A product purity of 92.4% was obtained at 64% recovery at 8 kPa desorption, while 5 kPa desorption produced >75% recovery with a purity of > 95%CO₂. The calculated specific power consumption is approximately 0.33 MJ/kgCO₂. Including two pressure equalization steps after a product rinse step contributed to the relatively lower specific power consumption achieved.