ارائه يك روش تركيبي حرارتي _ شيميايي براي بازيافت آب و استفاده از نمك شورابه واحدهاي نمك‌زدايي

Proposing a Combined Thermo-Chemical Process for Water Recovery an‎d Utilization of Reject Brine from Desalination Units

مهندسي شيمي

With the increasing deman‎d for water in human societies, the scarcity of available freshwater, an‎d the uneven distribution of rainfall, communities have turned to reliable an‎d permanent sources of water to ensure sustainable supply. This has led to a faster pace of seawater desalination. Desalination of water is primarily carried out using two methods: thermal an‎d membrane processes. In both approaches, the main challenge is the production of brine that has a salinity twice that of seawater, which not only presents environmental issues but also incurs costs for its disposal into the sea. This study focuses on one of the methods for converting brine from desalination units into value-added products using a modified Solvay process. The result of this research is the use of a combined thermal-chemical process in which the brine effluent from the desalination unit is concentrated in an evaporator, an‎d 83% of the water is separated in a fully desalinated form through thermal methods. The remaining concentrated brine has a salinity of approximately 36% an‎d is used in both the Solvay an‎d modified Solvay processes, where sodium bicarbonate is produced as the product of the reaction. The yield of this process was calculated to be 34.8%. To increase the yield of the reaction, effective factors were investigated, an‎d it was found that a temperature of 15°C, the pH of the reaction environment, the residence time at low temperature, the re-injection of carbon dioxide into the decanted wastewater, an‎d a sodium chloride concentration of 36% were recognized as key factors. To further increase the yield an‎d reduce the drawbacks of using ammonia in the Solvay process, the modified Solvay process was examined. Among three materials—monoethanolamine, diethanolamine, an‎d calcium oxide—diethanolamine, with a yield of 43.59%, was selec‎ted as a substitute for ammonia. To achieve better product purity, control side reactions, an‎d reduce reaction time, it is recommended to use pure carbon dioxide gas, which will increase the reaction rate an‎d improve product purity.

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