Renewable Energy, Vol.104, 259-270, 2017
Numerical studies of the influences of bypass on hydrogen separation in a multichannel Pd membrane system
A multichannel palladium (Pd) membrane system in association with flow bypass is designed for hydrogen separation with high recovery, and the mass transfer phenomena in the system are simulated by developing a computational fluid dynamics (CFD) model. Two Pd membranes are installed in the system. The predictions suggest that the H-2 recovery (HR) can be substantially improved by the bypass. The higher the feed gas Reynolds number, the more pronounced the improvement of H-2 recovery by the bypass. The HR by the first membrane is independent of the bypass ratio (BR), revealing that the enhancement of HR is completely contributed by the second membrane. An increase in H-2/CO2 molar ratio in the feed gas reduces HR, but raises the H-2 permeation rate. The maximum HR by the second membrane always develops at the feed gas Reynolds number (Re-r,Re-M1) of 500, regardless of bypass ratio. This reveals that the aforementioned Reynolds number is an appropriate condition for H-2 separation in the designed membrane system. Based on the HR in the absence of flow bypass (i.e., BR = 0), the higher the Re-r,Re-M1, the larger the intensification of H-2 permeation. A contour map and a correlation from regression analysis in terms of Re-r,Re-M1 and BR are established. Under a desired H-2 recovery, the combination of Re-r,Re-M1 and BR can be suggested to provide flexible operation for H-2 separation in the membrane system. (C) 2016 Elsevier Ltd. All rights reserved.