Pilot Scale Studies For Vacijum Membrane Distillation Of Seawarrer Desalination Brine

Membrane distillation(MD) was one of the membrane separation techniques which received much concerns in recent years. Compared with other membrane separation technologies, MD has the obvious advantage. The combination of membrane distillation and desalination technology, using other low grade heat source for seawater desalination, would reduce the cost of desalination, which will become one of the effective ways to solve fresh water shortage.The effect of module performance parameter (ratio of height to diameter, the packing fraction) for polyvinylidene fluoride (PVDF) hollow fiber membranes on vacuum membrane distillation(VMD)flux was studied in this work. VMD performances were developed using the ratio of height to diameter of25:2,15:1,35:2,20:1,45:2and the packing fraction of1%,5%,10%membrane modules. The results showed that VMD flux increased with increasing the ratio of height to diameter or decreasing the packing fraction. VMD performances of seawater desalination brine were studied using the PVDF membrane modules with length50cm, the ratio of height to diameter of25:2and the packing fraction of1%, the VMD permeate flux reached to18.98kg/(m2-h) when the pressure of vacuum side was-0.095MPa; the temperature of feed was85℃and flow rate of feed was0.4m/s. The performance parameters of membrane module in this condition were regarded as the preparation basis in pilot scale studies for vacuum membrane distillation of seawater desalination Brine.The influence of operating conditions on membrane distillation flux and rejection rate was investigated in vacuum membrane distillation pilot test. It was shown that VMD permeation flux increased significantly with the increasing of feed temperature and vacuum. With the increasing of flow rate of feed, the permeation flux increased slowly. When the pressure of vacuum side was-0.09MPa; the temperature of feed was80℃, flow rate of feed was30L/min, the VMD permeate flux of seawater desalination brine reached to18.98kg/(m2-h). The VMD flux of seawater desalination increased with decreasing of the ratio of height to diameter or the packing fraction of the membrane modules..The rejection of vacuum membrane distillation production was higher than99.9%during this process.