Performance optimization of a double-effect desalination unit integrated in a steam power plant of a chemical factory

• Published in: Desalination and water treatment 2019-04, Vol.147, p.284-295
• Main Authors: Hafdhi, Fathia, Khir, Tahar, Yahyia, Ali Ben, Brahim, Ammar Ben
• Format: Article
• Language: English
• Subjects: Double-effect desalination; Energy; Exergy; Optimization; Power plant
• ISSN: 1944-3986
• DOI: 10.5004/dwt.2019.23804

An energetic and exergetic optimization of a double-effect thermal vapor compression desalination system is performed. This unit is integrated in the thermal power plant of phosphoric acid factory owned by The Tunisian Chemical Group. The daily production of this unit is about 528 m3 of fresh water. A mathematical model based on energy and exergy balances is established using EES software. The effects of the main operating parameters on the desalination unit performances are analyzed. Obtained results show that the maximum exergy efficiency is obtained for the evaporator 2 followed by the distillate and brine pumps. The condenser has the lowest exergy efficiency. The thermocompressor is the major contributor in exergy destruction. The mass flow rate and the pressure of the motive steam affect positively the gain output ratio, while the last one decreases slightly with the motive steam temperature. In order to preserve suitable overall exergy efficiency, the motive steam temperature should be taken between 152°C and 154°C, which corresponds to motive steam pressure between 4.4 and 4.7 bar. These ranges constitute optimum operating conditions.