Development of simultaneous membrane distillation-crystallization (SMDC) technology for treatment of saturated brine

We have developed the simultaneous membrane distillation crystallization (SMDC) hybrid desalination technology for the concurrent productions of pure water and salt crystal from the saturated brine solutions. The effects of feed temperature variation from 40 degrees C to 70 degrees C on the SMDC performance in terms of membrane flux and kinetics of NaCl crystallization have been investigated. Increasing feed temperature increases membrane flux but the flux declines rapidly with time at higher feed temperatures (60 degrees C and 70 degrees C) due to the occurrences of membrane scaling and wetting facilitated by salt oversaturation at the boundary layer. In order to prevent salt oversaturation, we have calculated the critical fluxes at different Reynolds numbers and crystallizer temperatures. For instance, the critical fluxes when the feed temperature is 70 degrees C increase from 5 kg m(-2) h(-1) to 20 kg m(-2) h(-1) for the laminar and turbulent flows, respectively. By keeping the membrane flux lower than the critical flux, a stable membrane performance during a continuous SMDC operation over the period of 5000 min has been achieved. Increasing feed temperature also increases the yield of NaCl crystals from 7.5 kg per m(3) solution to 34 kg per m3 for feed temperatures of 40 degrees C and 70 degrees C after 200 min operation, respectively. However, the average crystal sizes decrease from 87.40 mu m to 48.82 mu m with increasing feed temperatures from 40 degrees C to 70 degrees C due to a higher nucleation rate at a higher degree of supersaturation. Regardless of the feed temperature, the NaCl crystals are in a uniform cubical shape with the coefficient of variations which are in the range of 30-38% that implies a narrow dispersion. (c) 2013 Elsevier Ltd. All rights reserved.