Comparative design of plug and recirculation RO systems; thermoeconomic: Case study

The main objective of this article is to determine which arrangement between the plug and recirculation reverse osmosis (RRO) is the optimal reverse osmosis (RO) system for a specific test case. Another objective is to compare the optimal operating conditions of these two arrangements. The RO system is designed to supply a water mass flow rate of 4000 m3/day for a 20-years period from Caspian Sea's brackish water to the city of Miarkelar, Iran. A multi-objective genetic algorithm is used to determine the best design of both arrangements of RO systems. Hence, feed water pressure, recirculated water flow rate, sea water membrane types, feed water flow rate and the number of elements in each pressure vessel were optimized. The objective function were the recovery rate and the unit production cost. Considering the optimal state of each arrangement, an exergy analysis has been performed. An exergy efficiency of recirculating and plug systems of 82.6% and 92.4% were obtained respectively. The thermo-economic analysis demonstrates that RRO results in a 36% decline in investment cost, 2% increase in operation cost, 6% recovery rate increment, and 19.7% permeate salt content decrease compared to the plug RO arrangement.