The Impact of Using Tanks for the Equalization Step on the Performance of a PSA Process

The pressure equalization step between two adsorption beds is a key cycle step in many pressure swing adsorption (PSA) processes. It involves connecting two beds together, or two beds and a tank as a medium. The utilization of tanks for equalization in a bed-to-tank-to-bed (BTB) configuration could be advantageous to reduce the number of beds in PSA cycle. In this study, a binary gas mixture A and B, with A more strongly adsorbed than B, was used for the investigation of Stafstrom-type PSA cycles with bed-to-bed (BB) and bed-to-tank-to-bed (BTB) equalization steps using linear isotherm and isothermal equilibrium theory. For tractability, it was assumed that the gas produced from the light end of a bed contained only B, and that all of the A would be recovered in the heavy product. Performances of the PSA cycle were expressed analytically in terms of the recovery of B in the light product ,, the purity of A in the heavy product ̅, and the final pressures of the BB and BTB equalization steps. The effects of the number of equalization steps n (varying from 1 to 10) and the relative size of the equalization tanks (varying from 0.1 to 500) were investigated. It was discovered that increasing the size of the tanks and the number of equalization steps improved the separation performance. In addition, the air separation process using Zeolite 13X adsorbent was used as a case study to examine the effect of equalization tanks on the performance of a practical PSA process. In this research study, only O2 and N2 were considered as feed mixture, and weakly adsorbed species like argon were clubbed with O2. The purity and recovery of O2 in LP were compared between PSA cycle schedules containing bed-to-bed (BB) and bed-to-tank-to-bed (BTB) equalization steps. This comparison revealed that the utilization of tanks for equalization step not only reduces the required number of beds, but also improves the recovery of the O2 in LP. Besides, our in-house Dynamic Adsorption Process Simulator (DAPS) was used to simulate the PSA cycles and identify the mass transfer coefficients based on the LDF model that shows excellent predictions of the experimental performance data