Energy efficiency evaluation and economic analyses of direct contact membrane distillation system using Aspen Plus

A direct contact membrane distillation system (DCMD) was simulated by using Aspen Plus for the purpose of energy efficiency and economic analyses. A cross-flow membrane module was firstly modeled and then incorporated into the flowsheet for system simulation. Detailed investigations have been conducted to understand the relationships of the water flux/production, the gain output ratio (GOR) and the water production cost (WPC) with respect to various design and operation parameters of the DCMD system.Simulation results revealed that in the DCMD studied here, a critical membrane area existed, below which, significant increases of water production and the GOR were observed with increasing membrane area, leading to a significant drop in the WPC. Increasing feed temperature imposes positive impacts on water flux and the GOR. For the higher feed and permeate velocities, there were increases in water flux, water production and the GOR. However for the WPC there were optimum fluid velocities beyond which the penalty of more energy input in the form of electricity consumption for pumping was significant. It was also found that when the temperature difference in the heat exchanger was increased to 6 °C, the WPC can be reduced considerably by cutting down the heat exchanger cost.

Research highlights
► A direct contact membrane distillation system was simulated by using Aspen Plus to analyze energy efficiency and cost.
► A significant increase of water production and GOR were observed with increasing membrane area in a certain range.
► There were optimum fluid velocities beyond which the penalty of the electricity consumption for pumping was significant.
► When the temperature difference in the heat exchanger was 6 ºC, the water production cost can be reduced considerably.