PSA and VSA Processes

Traditionally, PSA (Pressure Swing Adsorption) systems have been developed for gas purification processes, mainly hydrogen purification of off-gas streams in crude oil refinery plants.

In the past 15 years considerable effort has been given (mainly by UOP, Inc. - former Linde Division of Union Carbide, Inc.) to bulk gas separation processes via PSA or VSA (Vacuum Swing Adsorption), with air separation to nitrogen and oxygen being the most notable class of such processes.

PSA and VSA processes are based on the selective gaseous component adsorption on specialized solid sorbents as zeolites and carbon molecular sieves. Sorbent loading and selectivity are two major factors influencing the overall process efficiency and thereby economics. However, mass transfer limitations and (sometimes) heat transfer limitations play also a crucial role on the overall process efficiency. Given the fact of the intermittent nature of a PSA or VSA process, which involves, pressurization, equalization, feed, blowdown, purge steps in a mutliple bed system, it is obvious that process scheme and its parameters play an equal role with sorbent loading and selectivity.

Thus, the research in this area is twofold: Make of "better" sorbents, and improved process operation. Process insight is gained via process simulation. A detailed mathematical model involving the process unit operation was developed. In the upcoming reports much details are given on model development, model coding (Fortran 90) and solving (on a pentium III type PC) and involved results analysis.

Two case studies are performed adopting the well known processes in the area, namely the BAYER cycle (a two bed system) and the YOKKAICHI cycle (a three bed system).

In addition, the same model technique is also applied to a SBS (single bed simulator) for sorbent "quick and dirty" screening results and evaluation.

© Solon Zarkanitis, Ph.D.
GR-190 04 Spata