EnginSoft - CAE Conference Abstracts

EnginSoft International Conference 2011
CAE Technologies for Industry

Improving the Design and the Separation Performances of Membrane Modules for H2 Purification by CFD Simulations

Montante Giuseppina - Università di Bologna (Italy)
Coroneo Mirella - Institute for Computational Mechanics, Technische Universität München (Germany)
Paglianti Alessandro - Università di Bologna (Italy)

Abstract

In this work the impact of the non-ideal fluid flow features on the performances of gas separation membrane modules is investigated and the benefits of adopting the CFD simulation to the design and optimization of the pilot membrane module are shown. Specifically, the case of a pilot scale module equipped with three Pd-Ag membranes, that are well-suited for the separation of H2 from methane steam reforming gas mixtures, is considered. Palladium-based membranes are characterised by an high capability to separate hydrogen from gaseous mixtures and are particularly significant for industrial application aimed at the production of ultra pure hydrogen. Among the critical issues of membrane modules for gas mixture separations, apart from the membrane properties, concentration polarization and non-ideal flow effects have been identified in previous works. As a result, in order to reduce the design uncertainties and to take into account all the fundamental parameters affecting the process, comprehensive modelling methods, which may ensure appropriate scale-up from laboratory to pilot or industrial scale module, are required. To this purpose, we have adopted a CFD method devised by our group, which was developed in the realm of Fluent 6. With our method, the velocity and the pressure fields of the gas mixture are obtained from the numerical solution of the mass and momentum conservation equations, while the species concentration distribution and the relevant permeate and retentate fluxes are obtained from a scalar convection-diffusion equation including a source term to tackle the mass flow of the species across the membrane.
For the pilot membrane module, a simple shell and tube geometry was selected. It consists of three Pd-Ag tubular membranes, placed inside a cylindrical elliptical-bottomed shell. Modified geometries including purposely-designed baffles were also considered in order to investigate the effect of fluid flow on the module separation performances.
The simulation results show that the improvement of the separation performances of the module increases with the baffles number, although it is expected that an optimum geometrical configuration can be identified above which a further baffles addition does not lead to any separation advantage. The number of baffles in the final module design has to be selected depending on the required separation efficiency: as a guideline, starting from a single baffle configuration look at the flow and concentration fields and add a new baffle at the location where the washing effect of the first baffle vanishes.