Impact of gas recharging on wetting control in membrane distillation for the concentration of highly saline brines
Sprache des Vortragstitels:
3rd International Conference on Desalination using Membrane Technology
Sprache des Tagungstitel:
Membrane pore wetting (MPW) is still a potential obstacle in membrane distillation processes which considerably deteriorates the separation efficiency. This makes the hydrophobic membranes vulnerable to lose the liquid repelling property when treating low surface tension feed solutions. Based on the newly developed gas recharging method for wetting prevention in a full direct contact membrane distillation (DCMD) setup, this study evaluates the influences of gas/liquid two-phase flow on MPW for water separation of highly concentrated saline brine containing a representative surfactant. The impacts of gas bubble diameter, gas flow rate, gas recharging frequency, gas sparger type and gas bubble motion on the membrane wetting were examined. Due to higher area fraction of air/liquid interface to volume on the membrane surface, a higher wetting resistance can be obtained in a gas recharging system with either a smaller bubble size, lower gas/liquid flow rates, continual gas recharging mode and porous sparger. It was also found that gas recharging not only controlled the wetting occurrence when concentrating the 3.0 M brine to saturation but also enhanced the permeate flux by average 52% and reduced the wetting rate up to 99% due to enhanced local agitation and reduced salt/surfactant deposition/adhesion on the membrane surface/pores.