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 (CUR) 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 CUR 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 CUR. For the higher feed and permeate velocities, there were increases in water flux, water production and the CUR. 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 degrees C. the WPC can be reduced considerably by cutting down the heat exchanger cost. (C) 2011 Elsevier B.V. All rights reserved.