(430f) Experimental Study and Cfd Modelling of An Inorganic Membrane Module for H2 Purification

This work is aimed at investigating the capability of a fully predictive Computational Fluid Dynamics approach to reliable calculate the fluid dynamic and the separation performances of a lab-scale module based on inorganic membranes, for hydrogen purification. The simulations are based on the numerical solution of the Navier-Stokes equations for a gas phase mixture on the three dimensional domain representing quite closely the module geometry. The tubular membrane is modeled as a selective layer, which allows the permeation of different components as a function of the transport mechanism and the driving force. The simulations were performed running the general purpose finite volume CFD code Fluent 6.2. To account for the mass flow of the different species across the membrane, a user defined function provided by Fluent Inc., modified for modeling the specific physical phenomena occurring in the separation module, was used. The computational strategy is strictly evaluated by comparing the results with experimental data obtained through permeation experiments on a porous membrane with hydrogen-nitrogen mixtures. The experiments reveal that diffusion across the membrane shows the typical feature of Knudsen mechanism, with selectivity related to the different components molecular weight. The presence of concentration polarization phenomena was expected to be limited, however experiments at different operating conditions (i.e. with/without a purge gas feed on the permeate side) suggest the presence of a non-negligible resistance to transport in the gas phase. The mass flux across the membrane was modeled assuming a single value of the permeability constant for each component, that was obtained from the data collected in pure gas permeation experiments. Therefore, no adjustable parameters were introduced in the model equations. The simulation results show fairly good agreement with the experimental data, both for pure and gas mixture conditions, at different operating pressures, gas flow rates and compositions; more than that the simulation results allowed to recognize different critical local fluid dynamic features of the system, as the presence of important inlet effects related to the feed geometrical characteristics and a non-uniform mass flux along the separation module.