Thin-film distillation coupled with membrane condenser for brine solutions concentration

Abstract

A novel concept of film distillation equipped with the membrane condenser (FD-MC) was proposed and implemented for the concentration of brine salt solutions. In this thermo-gradient method, the water was evaporated from the thin liquid film flowing alongside the hot surface, and then directly condensed on the cold surface of the porous membrane placed at the distance of few millimeters from the feed. The change of the membrane positioning from the hot feed solution to the cold water stream (coolant circuit) enables to overcome the common challenges of the membrane distillation process like long-term stability towards pores wetting, membrane scaling, and latent heat loss. Comparing with the air gap membrane distillation with membrane condenser (AGMD-MC), FD-MC demonstrated higher water flux (14.7 kg/m2·h) and stable performance during the concentration of NaCl solution from 50 up to 230 g/kg (microcrystal formation was noticed) even in the presence of organic pollutants (kerosene or surfactants). A mathematical model of heat and mass transfer in FD-MC process was proposed and successfully verified. With the respect to the temperature of hot (40–100 °C) and cold (10–60 °C) circuits, the energy consumption and thermal efficiency of FD-MC process were in the range of 2.7–3.2 MJ/kg and up to 97%, respectively.