Solar Thermal Assisted Vacuum Freezing Desalination of Seawater at the Triple Point

A spray vacuum freezing desalination process is proposed to meet the required seawater desalination cost, with water subcooling suppression at freezing. Both the energy consumption of the proposed desalination method and the cost of water are lower than that of state-of-the- art technology, and the system can be driven by either electricity or low grade thermal energy. The major energy-consuming process, i.e. the vapor pumping, can be satisfied with low-quality thermal energy such as solar thermal energy. To decrease the energy need in vapor compression, nucleating agents is used to suppress subcooling of freezing the sprayed seawater droplets, so that the pressure of vapor generated in the triple point desalination process can be elevated and less pumping power is needed for transferring the vapor to condenser. The Phase II work will focus on building and testing sub-scale prototype of the spray vacuum freezing desalination system, since the Phase I work has successfully demonstrated the feasibility of the proposed concept. Nucleating agents will be optimized and tested for seawater application, and a sub-scale vacuum freezing chamber will be designed, fabricated, and tested based on the Phase I benchtop chamber. Other essential modules in the sub-scale system including the water regenerator, nucleating agent separator, and thermal ejector will also be designed and fabricated. The modules will be integrated as an effective desalination system and the performance of the system will be evaluated experimentally. In addition, ACT will collaborate with industrial partners to commercialize the technology. The proposed technology could be applied to seawater desalination and brackish water treatment. The low energy requirement and low operation cost are the competitive edges of this technology. Subcooling suppression techniques developed in Phase I work could also be applied in the application of phase change materials.