THERMALLY-DRIVEN EJECTOR FOR VACUUM FREEZING DESALINATION AT THE TRIPLE POINT
Recently an energy-efficient desalination process based on spray vacuum freezing of seawater at the triple point was developed. During this process, the freezing and evaporation of the water happen simultaneously at the triple point with net-zero thermal energy consumption. One of the most critical challenges in this technology is to continuously remove the vapor generated during triple-point freezing-evaporation process, since the pressure in the vacuum freezing chamber needs to be maintained at or below a level corresponding to the triple point of water. The removed vapor is transferred to a water regenerator and condensed on ice to produce liquid freshwater. The electrical energy consumption for this vapor compression and transport process can be substantial if a compressor is used. In this work, we designed and manufactured an innovative ejector system which can be driven by low-grade waste heat, therefore significantly reduce the energy cost. Another very important feature of this ejector system is that it can create ultralow pressure at the exit of the primary nozzle. Therefore, the low-pressure vapor generated in the vacuum freezing chamber can be continuously sucked into the ejector as entrained flow, which is extremely difficult to achieve in traditional commercial ejector systems. Applications that can directly benefit from the use of this technology include seawater desalination, brackish water treatment, as well as fresh water supply for remote communities or dry regions where solar thermal energy or low-grade waste heat is abundant.