Membrane Module Design & Analysis for Gas Separation

Abstract

The expected worldwide market for membrane separation technologies is estimated to be $16 billion by the year 2017 because of extensive acceptance of the membrane technology in several end-user markets. With the increase in demand for high-quality products, environmental concerns, stringent regulations and exhausting natural resources, membrane separation technologies are predicted to see substantial development in the future. The scope of membrane technology likely is expected to be interesting as new membrane materials, innovations and processes make their way to the marketplace. The recent development in industrial applications of membrane gas separation is: to develop robust membranes, which show higher separation capacity, and are consistent and durable for specific applications. Process simulation is a method to optimize the design and operating conditions in the process. A process configuration and optimum operating conditions result in enhanced separation performance and are less expensive. In addition, with the growth of new process models, new membrane applications are arising. This study focuses on emerging models that can be used to bring improvement in the operation and design of membrane gas separation processes. Numerical models for the better performance of gas separation with high permeation were developed and verified. The pressure gradient on both sides of the membrane in different flow patterns has been considered i.e. co-current, cross and counter current. The numerical models are useful as they need least computational effort and deliver better solution stability. The robustness and the predictions of the numerical models were verified with experimental data for different membrane systems with different flow patterns. The numerical models were applied to several case studies to investigate the performance of different membrane module configurations. The research shows that the new numerical models can effectively handle the high permeate membrane problems with various flow configurations. It is a common perception that working at higher pressures permeates more gasses, and hence, occasionally the membrane module is analyzed or characterized at lower pressures to save gas utilization. It is also believed that membrane ability of gas separation declines at higher feed pressures. The obvious and key permeances of different grasses for different membranes were assessed from numerical analysis based pure gas permeation experiments reported in the ii literature. It was found that the membrane performs near to its real separation capability if it is worked at high feed pressures. The effect of pressure on the membrane performance is minimized under some special conditions. One of the most powerful features of the ASPEN HYSYS program enables users to add additional unit operations to the program through Extensibility. Using this capability, the ASPEN HYSYS could be customized for the simulations to match specific operating conditions. The built in unit operation of membrane is not available in ASPEN HYSYS. In this research, a membrane extension has been developed in ASPEN HYSYS. Developing and implementing the successful Extensions for ASPEN HYSYS requires a good understanding of the ASPEN HYSYS program, an object-oriented programming language (Visual Basic), and the purpose of the Extension. This research will help combine the knowledge of all three areas and allow us to create useful and powerful extensions for the ASPEN HYSYS program. This extension allows ASPEN HYSYS to simulate the industry specific membrane based separation processes. Computational fluid dynamics (CFD) simulations were carried out for the separation of gasses using membranes. This CFD code was used to examine the flow profile for gas separation in a membrane. To the best of our knowledge, the availability of CFD simulation on membrane gas separation is found to be limited, hence, it was attempted in the present study. The aim of this research is to use commercial CFD simulation package ANSYS FLUENT to predict flow conditions and gas permeation. For CFD calculations, the commercial solver based on finite volume method (FVM) has been used and the mass transfer through the membrane has been modeled by user-defined functions (UDFs). Two key aspects are significant for the design of membrane modules used for gas permeation. These aspects include flow distribution and concentration polarization. The later causes a reduced driving force, considerably affecting membrane performance. A uniform flow distribution will ensure that the complete membrane area is utilized. In order to reduce the influence of concentration polarization and to ensure an even flow distribution, baffles located between two membrane surfaces or plates containing flow channels are employed. Turbulence model has been integrated into the solution of incompressible flow equations.