Effects of membrane properties on water production cost in small scale membrane distillation systems

Abstract

Membrane distillation (MD) has shown potential as a desalination process. As a thermally driven membrane technology which runs at relatively low pressure and can tolerate high salinity feed, MD may be useful for desalination under condition for which reverse osmosis is not a good option. However, improved energy utilization and reduced water production cost in MD systems remains an important technical challenge. In this paper, we examine how optimization of the heat and mass transfer properties of the MD membrane can raise water flux and reduce unit energy consumption. Numerical modeling tools and factorial analysis are used to examine the effect of five MD membrane characteristics: porosity, tortuosity, thermal conductivity, pore diameter, and thickness. The water production cost (in USD/m3 of purified water) is calculated as a function of these parameters for a small-scale, single-stage MD process driven by waste heat. Two MD configurations were considered: Direct Contact MD (DCMD) and Air Gap MD (AGMD). All five membrane properties examined were found to have a significant effect on water production cost, although the magnitude of this effect was greatly dependent on the MD configuration.