Technoeconomic analysis of tri hybrid reverse osmosis-forward osmosis-multi stage flash desalination process
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2017 Desalination Publications. All rights reserved. A new tri-hybrid reverse osmosis-forward osmosis-multi stage flash (RO-FO-MSF) desalination process is developed to increase the overall plant recovery ratio and reduce energy consumption. The FO membrane is employed as pretreatment to the MSF section to allow the increase of the top brine temperature and to obtain maximum allowable recovery from the RO brine reject. The product blend of the MSF distillate and the single pass RO permeate enables controlling the boron concentration below the acceptable limit. The current recovery ratio limitation of the existing MSF and RO plant is analysed. A process simulator is developed to carry out mass balance, heat balance, and electrical and thermal energy consumption. The total energy consumption of the tri hybrid process is compared with that of commercial MSF and RO desalination plants. The simulation results show that the RO-FO-MSF process recovery ratio is 30% higher than that of the standalone RO and MSF processes. The specific total energy consumption, (electrical plus equivalent thermal) of the tri hybrid process is 65% lower than that of MSF, but 20% higher than RO. The lifecycle cost analysis showed that the unit water cost of the tri hybrid process is 20% lower than that of the RO and 40% lower than that of the MSF standalone processes. This water cost saving is attributed to the use of the MSF cooling rejected as feed to the RO section and using the RO brine as feed solution to FO, which decreases the capital cost of the civil work and construction of the intake/outfall facilities. Moreover, the product blend of the MSF distillate and the RO permeate enables employing a single pass RO and eliminate the need for a second pass and thus reducing the capital investment.
