CFD modeling of two-stage H2 recovery process from ammonia purge stream by industrial hollow fiber membrane modules

Abstract

This research introduces an unabridged two-dimensional mathematical model for H2 recovery from an ammonia plant's purge stream through two-stage industrial polyimide hollow fiber (PIHF) membrane modules. According to validated results, the effect of operational and geometrical parameters beside flow patterns was investigated on H2 recovery potential at first and second stages of PIHF membrane modules. H2 recovery at first and second separation stages decreased from 5.887% to 4.82% and from 99.57% to 99.05%, respectively when the feed mass flow rate increased from 0.3847 to 0.5014 kg/s at constant pressure of 97.5 barg. However, a reverse trend between H2 cumulation and feed pressure was observed at constant feed mass flow rate for each separation steps. As fiber length increased from 2 m to 3.06 m, the H2 recovery percentage grew up at each of those separation stages at fixed operational conditions. Counter-current flow pattern showed higher H2 recovery in comparison with co-current flow arrangement at the same operation conditions due to the higher partial pressure difference. Moreover, a concentration polarization index (CPI) was also described to demonstrate the scope of polarization. Evaluations depicted that CPI enhanced with increasing the feed pressure and serious concentration polarization arose at higher feed pressures.