Exergo-economic analysis of a seawater reverse osmosis desalination plant with various retrofit options

The current study is focused on carrying out exergo-economic analysis of a seawater reverse osmosis (SWRO) desalination plant. The main objective is to compare the performance as well as the product cost of an existing SWRO plant, including post-treatment and distribution sections, for four different retrofit options made by coupling high-efficiency pressure exchangers (PXs) in place of conventional energy recovery turbines. For this purpose, first- and second-law analysis is carried out to estimate the energy requirements and second-law efficiency for each retrofit option. Finally, the product cost is compared by performing an exergo-economic analysis using appropriate seawater properties for the calculations. The analysis revealed that, by introducing a PX, the specific energy consumption (SEC) can be reduced by about 24%; thus, increasing the second-law efficiency. Besides this, it is also demonstrated that the addition of post-treatment and distribution sections enhances the product cost by almost 20%. Furthermore, the study suggested that using a booster pump with a PX (as used in retrofit # 3) is best suited for enhancing the plant capacity compared to retrofit # 4 in which a PX is used in place of the pump. It has the least product water cost among all the options discussed.