EXPERIMENTAL AND THEORETICAL STUDY OF A NOVEL FREEZE DESALINATION METHOD USING AN INTERMEDIATE COOLING LIQUID

Abstract

Freeze desalination (FD) emerges as a promising method for treatment of high-salinity brines. In this work, experimental and theoretical studies are conducted on the design, fabrication, and testing of a novel FD system for desalinating brines with salinities up to 100,000 ppm. The system integrates a refrigeration unit with a desalination unit via an intermediate cooling liquid (ICL). The desalination unit is comprised of a freezing chamber, a slurry transport section, and separation modules. Operating at atmospheric pressure, the FD system leverages the efficient heat transfer achieved through direct contact between the brine and the ICL, thus avoiding complications like ice adhesion to cooling surfaces and the mixing of refrigerant with the treated water. A key factor in increasing the energy efficiency of the developed method is recovering the cold energy of the generated ice to cool the condenser of the refrigeration unit. This can be achieved by running an ice-water slurry through a heat exchanger to absorb heat from the condensing refrigerant. To better understand the fundamentals of ice-water slurry heat transfer, a computational model is developed to simulate the melting of a suspended solid particle in its own melt. The fabricated prototype is used to study the impacts of various operational parameters such as feed brine salinity, cooling temperatures, and centrifugation times on the recovery ratio and the purity of the treated water. It is found that lower cooling temperatures and feed brine salinities enhance the recovery ratio, while increasing the salinity of the treated water. Specifically, a feed brine with a TDS of 70,000 ppm and a cooling temperature of -17°C resulted in a recovery ratio of approximately 50% and a treated water TDS of about 2,600 ppm. This study demonstrates a novel method for desalinating high-salinity brines, which potentially offers greater energy efficiency compared to conventional evaporative methods. This method could have significant applications in industrial brine management and brine mining.