Graphical approach for formulating pressure swing adsorption cycle schedules with unlimited equalization steps

Abstract

A graphical unit block was used to formulate new PSA cycle schedules that include an unlimited number of equalization steps, no idle steps, no dead time and a minimum number of just three PSA beds assisted with two or more equalization tanks. The approach to designing these PSA cycle schedules is based on three simple rules: (1) restrict the placement of all the equalization steps within the boxes of the PSA cycle schedule to be in sequence with no other cycle steps in between them; (2) place all the equalization steps in the left most boxes of the PSA cycle schedule underneath the Bed 1 feed step with no other cycle steps below them except other equalization steps; and (3) add equalization tanks as needed. These new 3-bed PSA cycle schedules may include any of the common PSA cycle steps in such a way that the equalization steps do not interfere with any of the non-equalization steps affording the non-equalization steps additional degrees of freedom. Since a bed-to-tank-to-bed equalization step may not be as effective as a bed-to-bed equalization step, a forced cocurrent depressurization (CoD) step coupled with an intermediary light end pressurization (LEP) step can be added to this 3-bed PSA cycle schedule. These coupled steps take place after the last of the equalization down and up steps with the aid of a compressor or vacuum pump. Since the utilization of several equalization steps and the utilization of forced CoD/LEP steps may limit the duration of the countercurrent depressurization (CnD) and/or light reflux (LR) steps, one or more additional beds can also be added to this 3-bed PSA cycle schedule. These additional beds increase the durations of the CnD and LR steps without affecting the duration of the feed step. Any combination of these PSA cycle schedule improvements can be used to improve the PSA process performance in terms of capital and operating costs, productivity or throughput, and recovery and purity of the species of interest whether it is the heavier, lighter or both species.