Improved performances of vacuum membrane distillation for desalination applications: Materials vs process engineering potentialities

Abstract

Membrane distillation (MD) is considered an attractive technology for water desalination processes, but the low transmembrane water fluxes, compared to other desalination processes, is however often pointed out as an important disadvantage. This limitation can be tackled through an effective process engineering analysis. Membrane materials performances and process design (including operating conditions) can both generate increased water flux. These two possibilities are explored in this study, in order to better evaluate the interplay between materials and process role. In a first step, the impact of highly permeable and thin dense selfstanding membranes as an alternative to avoid pore wetting is studied. The use of passive process engineering strategies such as Dean vortices to enhance mass and heat transfer is further analyzed. It is shown that a highly permeable dense membrane material offers a potential twofold increase in water flux, when a permeability of 10−5 kg·m−2·s−1·Pa−1 is achieved. Alternatively, Dean vortices (helical hollow fibers) are of interest only when this level of permeance is obtained; a 20% increase in water flux could be achieved, thanks to a decrease of the temperature polarization effect.