A Strategy for Optimal Process Design and Operation of a Pressure Swing Adsorption (PSA) System through Pressure Equalisation and Co-Current Depressurisation

A Pressure Swing Adsorption (PSA) system is known for its unrivalled capability in various industrial applications for gas separation and purification, e.g. H2 purification and air drying. Accordingly a PSA has been actively researched to enhance its performance and adaptability, expanding its horizons for emerging gas separations, e.g. CO2 capture.
Design of a PSA process involves its associated cycle scheduling table that is directive of how the cyclic batch system is to be operated. It is very common to see the step sequence include Pressure Equalisation (PE) step or Co-current Depressurisation (CoD) step aiming to improve the light product recovery. But it is also very hard to find a reliable guideline on how many PE steps to include and what is the optimal column pressure at the end of CoD step.
In this study, the Equilibrium Theory model for analysing a PSA system [1,2] was developed further so that it could be applied to a system with complex step configurations and non-linear isotherms, enabling a systematic analysis of the effects of PE or CoD steps on PSA performance.
It was found that in case of a feed gas containing a high fraction of the light component adding PE or CoD steps could get the product recovery improved notably, and there exists an optimum number of PE steps or CoD pressure for maximizing the product recovery. On the other hand, adding even one PE cycle to the step configuration may ruin the product recovery if the light component fraction is low in the feed. Alternatively, having CoD step instead could improve the product recovery on the ground that the CoD step pressure can be controlled more flexibly than the PE step pressure. This work did not study only the effect of feed gas composition, but it also looked into the effects of other parameters such as adsorption pressure, the extent of purging, etc.

1. Chiang, A. S. T. An Analytical Solution to Equilibrium PSA Cycles. Chemical Engineering Science 51, 207-216 (1996).
2. Ahn and Lee, Equilibrium Theory Analysis of Vacuum Swing Adsorption for Separation of Ethanol from CO2 in a Beverage Dealcoholization Process, Industrial & Engineering Chemistry Research 59(50), 21948 - 21956 (2020).