(31c) Simulation of Pressure Swing Adsorbers Using the Moving Bed Model

Simulation of pressure swing adsorption (PSA) units remains a challenge for practicing engineers, which hinders the process intensification potential of the technology. The Moving Bed model, a steady-state model which represents any adsorption process as a series of interconnected continuous adsorption units, has the potential to alleviate some of the difficulties in modeling PSA. [1, 2, 3] In the Moving Bed model, the cycle is divided into multiple constant-pressure operating states bearing similarity to the individual steps of the cycle which allows the properties of the state to be evaluated from equilibrium considerations alone. The operating steps are arranged from highest-to-lowest pressure to represent the driving force gradient exploited during the cycle and then connected by a virtual moving bed. The virtual moving bed does not physically exist in the system but represents the adsorbate and void space hold-up retained in the adsorption column at the end of the operating state. However, modeling a cyclic batch process as a continuous, equilibrium process neglects the rate-based transport phenomena involved. Using the idea of adsorption efficiencies [4] to account for non-idealities like mass transfer resistance and dispersion, similar to the tray efficiencies used in rate-based distillation modeling, the retentate flow rates can be adjusted to match the actual performance of the unit. [2, 3] To showcase the capabilities and current limitations of the model, a case study will be presented which investigates a lab-scale air separation unit. Guidelines for ensuring convergence and robustness will be given and the effect of important parameters will be discussed.

1. Sees, M.D. (2018, October). Novel Steady-State Process Modeling Methodology for Pressure Swing Adsorption. Paper presented at the 2018 Annual Meeting of the American Institute of Chemical Engineers, Pittsburgh, PA.
2. Kirkes, T. (2018, October). Steady-State Modeling of Air Separation by Pressure Swing Adsorption Using a Bed-State Efficiency Model. Poster presented at the 2018 Annual Meeting of the American Institute of Chemical Engineers, Pittsburgh, PA.
3. Sees, M.D. (2019, April). Modeling of Gas Separations by Pressure Swing Adsorption Using a Novel Steady-State Methodology. Paper presented at the 2019 Spring Meeting of the American Institute of Chemical Engineers, New Orleans, LA.
4. Smith, O.J. and A.W. Westerberg. Eng. Sci., 1991, 48(12), 2967 – 2976.