Optimization Strategy for Enhancing the Product Recovery of a Pressure Swing Adsorption through Pressure Equalization or Co-current Depressurization: A Case Study of Recovering Hydrogen from Methane

The step sequence of a pressure swing adsorption (PSA) cycle for gas separation can be as simple as the four steps of Skarstrom cycle, but it can also be made to be very complex by adding new steps with a view to enhancing the product recovery. In particular, pressure equalization (PE) or co-current depressurization (CoD) steps are often introduced to the step sequence of a H2 purification PSA, as the strategies have been proven successful. However, the PE and CoD steps have been incorporated into the PSA cycle without due consideration on what is the best way of including and operating the steps. In this study, an equilibrium theory method was taken to optimize the PE and CoD steps for improving the product recovery to the maximum. The theoretical PSA model turned out reliable and insightful when applied to an exemplary H2 purification PSA system, as the results obtained by simply solving the algebraic equations were so consistent with those of the sophisticated numerical simulation and optimization. In this study, the equilibrium theory analysis of a PSA elucidated clearly that there exists an optimal number of the PE steps, and an optimal column pressure at the end of CoD step and the results would be affected greatly by the operating conditions, such as feed composition, operating pressure, and so forth.