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.