Membrane development and energy analysis of freeze desalination-vacuum membrane distillation hybrid systems powered by LNG regasification and solar energy

The feasibility of an energy-efficient hybrid system consisting of freeze desalination and vacuum membrane distillation (FD-VMD) powered by waste energy and solar energy for seawater desalination was investigated in this study. FD, being the first step, was used to harvest clean ice by freezing the simulated seawater. To ensure the purity of the product ice, the raw ice was washed by about one-half of the VMD distillate. To treat 1 kg seawater by FD, the cold energy could be provided by the regasification process of 1.26 kg LNG. The concentrated FD brine was further treated by VMD to increase the total water recovery. The membranes used in VMD were tri-bore PVDF hollow fiber membranes. The green solvent, triethyl phosphate, was for the first time used to fabricate membranes with such a geometry. The resultant membrane had an optimum permeation flux of 51.7 kg/m(2).h for a feed temperature of 70 degrees C. For each 1 kg of seawater fed to the system per hour, the total water recovery is 0.74 kg per hour. The heating duty could be covered by either solar panels of 13.8 m(2) or the regasification of 3.10 kg LNG if the system is fully integrated.