Aspen Plus and CFD coupled simulation for the optimisation of the membrane distillation process

Optimising the performance of Vacuum Membrane Distillation (VMD) requires a good understanding of how fluid conditions influence both heat and mass transfer. Computational Fluid Dynamics (CFD) programmes can be used to model flow through individual modules over a range of operating conditions and module configurations, however, separate simulation tools are required to model the overall process efficiency in terms of mass, energy balance and recovery. In this paper a CFD module has been combined with Aspen Plus to simulate submerged VMD performance in a submerged configuration operating on a hypothetical concentrated salt stream. The approach can improve both the simulation accuracy of Aspen Plus while providing key insights to refine the CFD modelling of alternative module designs. VMD systems have been investigated using this method to compare their energy efficiency and productivity. ANSYS Fluent was used to predict the performance of membrane modules with various geometries. A User Define Function (UDF) for Fluent was developed to utilise simulation results of the membrane module and create an Aspen Plus flowsheet. A FOURTUNE code was applied to manipulate the flowsheet into a User Model in Aspen Plus to complete the plant process. Simulations indicate that operating temperature and membrane module design have limited effects on energy consumption of VMD system. Significant decrease of energy consumption can be found by including heat recovery in the submerged VMD system.