New Approach for Modeling Hybrid Pressure Swing Adsorption–Distillation Processes

Abstract

A new methodology for modeling hybrid pressure swing adsorption (PSA)–distillation processes has been developed. This new approach involves two parts. Part I determines if energy savings are possible. It can be done easily with sufficient knowledge of distillation process design, but with only minimal knowledge of PSA process design. Part I is carried out using a distillation process simulator such as Chemsep to model a distillation column connected to a PSA unit that is treated as a “black box” with an assumed process performance. In this way, a hybrid PSA–distillation process can be analyzed simply by performing mass balances around these units and running Chemsep to determine if energy savings are possible compared to a reference (commercial) process. Once an energy savings hybrid “black box” PSA–distillation process is found in part I, part II determines if an “actual” PSA process exists that mimics its performance. Part II is carried out using a rigorous PSA process simulator such as Adsim from AspenTech; thus, it requires significant knowledge of PSA process design. The outcome of part II is a hybrid PSA–distillation process that has the potential to be more energy efficient than the reference process. This new approach was successfully demonstrated using the commercial hybrid PSA–distillation process developed for fuel grade ethanol production as the reference case. This two-part analysis found several, more energy efficient designs than the reference case. All of them had proportionately reduced internal vapor and liquid flows in the distillation column, a direct effect of reducing condenser or reboiler duty. These results illustrated that the new methodology should be very useful for quickly accessing the utility of hybrid PSA–distillation processes for a variety of other applications, with many possibilities for achieving significant energy savings and/or throughput debottlenecking.