EXPERIMENTAL AND CFD MODELLING OF MEMBRANES FOR HYDROGEN SEPARATION

This work is aimed at investigating the capability of a Computational Fluid Dynamics (CFD) approach to reliably predict the fluid dynamics and the separation performances of inorganic membranes modules for gas mixtures separation. The simulations are based on the numerical solution of the Navier-Stokes equations on the three dimensional domain representing quite closely the module geometry. The membrane is modelled as a selective layer, which allows the permeation of different components as a function of the chosen transport mechanisms and of the driving force. The behaviour of two commercial Pd-Ag membranes and of a simple inorganic ceramic membrane has been examined. Since the selected membranes are totally or partially constituted from a ceramic structure that is extremely complicated to predict theoretically, the diffusion coefficients of all the membranes have been experimentally evaluated. The experimental data available at different working conditions (pressure and feed flow rate) and different hydrogen concentrations in the feed stream have allowed to strictly test the CFD results. The different membranes have been modelled with a simple approach considering four different transport mechanisms: molecular diffusion (self and mutual), Knudsen diffusion, Poiseuille flow and Sieverts’ law. The excellent agreement between the experimental and the predicted data suggests that CFD can be considered an useful and reliable tool for designing new modules or optimizing existing ones.