Optimal design of dual-reflux pressure swing adsorption units via equilibrium theory: Process configurations employing heavy gas for pressure swing

Dual-reflux pressure swing adsorption process is theoretically capable of completely separating binary feed gas mixtures into two pure species. The pressure of bed to which the binary gas mixture is fed and the type of gas utilized for pressure swing, results in different process cycle configurations, even if the majority of the previous studies of DR-PSA are restricted to two cycle configurations: that employ heavy gas for pressure swing and deliver feed to the bed operated at either high or low pressure. However, the comparative assessment and the optimal operating pressure ratio of these two process cycle configurations are not well-established. We previously reported an optimal design strategy (that identified a triangular operating zone, inside which, complete separation of binary gas mixtures can be achieved) for one such DR-PSA process cycle configuration. In this work, we report an optimal design strategy for another DR-PSA process cycle configuration: feed to low pressure bed and pressure swing using heavy gas. With respect to previous literature, the equilibrium theory based comprehensive tracking of the characteristic curves and shock transitions during constant and non-constant pressure steps of this specific cyclic process revealed distinct constraints, design parameter values and boundary conditions of the triangular operating zone. Additionally, an in-depth comparative assessment of the impact of process variables (adsorbent selectivity, feed gas composition and, operating pressure ratio) on the design parameters (optimal feed injection position and ratio of pure light reflux to feed rate) and a novel selection criterion is discussed for both of these cycle configurations in order to (i) facilitate the choice of appropriate cycle configuration and (ii) identify the optimal high to low operating pressure ratio range