Performance simulation of a multi-VMD desalination process including the recycle flow

In this paper, a performance evaluation of a multi-vacuum membrane distillation (VMD) module was conducted using a one-dimensional model. The mathematical model consisted of momentum, mass and energy balance equation using the water permeate flux model and heat flux model. The simulation results were in good agreement with the experimental results from previous literature. The validated VMD model was implemented into Aspen Plus. Then, a multi-VMD module with one-through flow was simulated. As a result, in the high velocity region, the hydraulic pressure was used as the constraint to determine the number of membrane modules. In the low velocity region, the number of membrane module was determined based on the feed temperature. To improve water recovery and thermal efficiency of the multi-VMD module, the recycle flow was considered and the waste heat included in the discharge brine was recovered. As a result, it was possible to achieve water recovery over 40%. In addition, as the recycle flow ratio increased, thermal efficiency also improved since heat duty and thermal consumption per unit water production decreased.