Detailed modelling and optimal design of membrane separation systems
The search for alternatives to traditional energy intensive separation methods such as distillation has led to the introduction of processes based on membranes. In this research, the use of detailed mathematical models for the optimal design of membrane systems is investigated. Mathematical models of hollow-fibre and spiral-wound membrane modules are presented in this thesis. The models are developed from rigorous mass, momentum and energy balances and can be used to describe a generic membrane separation. This is in contrast to most existing models which are typically process specific and are only valid within a limited operating range. The generality of the new approach is demonstrated by application to gas separation, pervaporation, and reverse osmosis case studies. Simulation results for these systems show excellent agreement with published experimental data. The thesis also introduces an optimal design strategy for membrane separation systems. This strategy is characterised by two main features: firstly, detailed models are used. This is essential if sub-optimal and inaccurate solutions are to be avoided. Secondly, an optimisation technique based on genetic algorithms is implemented. This provides multiple solutions, allowing the user to interpret the results and make a more informed decision. The feasibility of the optimal design strategy is investigated using two realistic case studies. In the first study, the optimal design of reverse osmosis desalination plants is considered and the use of both hollow-fibre and spiral-wound modules is examined. The results of this study compare favourably with work published in the open literature and highlight the importance of using detailed models to describe membrane separation systems. In the second study, the use of pervaporation for ethanol dehydration is investigated. An existing pervaporation plant is evaluated and a significantly improved design is found.