Numerical analysis of a dual refluxed PSA process during simultaneous removal and concentration of carbon dioxide dilute gas from air

The simultaneous removal and concentration of carbon dioxide present in ambient air were carried out by a dual refluxed Pressure Swing Adsorption (PSA) process with intermediate feed inlet position. The feed inlet position divides each column into rectifying and stripping sections from which enriched and lean gases can be simultaneously produced. A simple isothermal model with negligible axial dispersion and pressure drops through the PSA beds was developed to investigate the effects of various combinations of the operating variables and to analyze semi-quantitatively the effects of the main characteristic parameters such as the dimensionless feed inlet position (Z_R/L_T) and the stripping-reflux ratio (R_r). A good agreement between the model prediction and the experimental results was obtained. Moreover, an optimum feed inlet position was found and it corresponded to a position where the carbon dioxide mole ratio in the feed flux and that in the upstream flux leaving the stripping section were equal. The carbon dioxide mole ratio in the enriched product (Y_E) as well as that in the lean product (Y_L) were strongly dependent on the ratio of feed/enriched product flow rates (Q_F/Q_E) and the ratio of feed/lean product flow rates (Q_F/Q_L). Although the pressure ratio (P_a/P_d) was crucially important for the separation performance, a smaller value of R_r was sufficient to reach a performance which is unattainable in conventional PSA processes.