Optimum arrangement of two-stage plug and concentrate recycling RO systems using thermodynamic and exergy analysis

Abstract

Purpose

This paper aims to determine the optimum arrangement of a reverse osmosis system in two methods of plug and concentrate recycling.

Design/methodology/approach

To compare the optimum conditions of these two methods, a seawater reverse osmosis system was considered to produce fresh water at a rate of 4,000 m3/d for Mahyarkala city, located in north of Iran, for a period of 20 years. Using genetic algorithms and two-objective optimization method, the reverse osmosis system was designed.

Findings

The results showed that exergy efficiency in optimum condition for concentrate recycling and plug methods was 82.6 and 92.4 per cent, respectively. The optimizations results showed that concentrate recycling method, despite a 36 per cent reduction in the initial cost and a 2 per cent increase in maintenance expenses, provides 6 per cent higher recovery and 19.7 per cent less permeate concentration than two-stage plug method.

Originality/value

Optimization parameters include feed water pressure, the rate of water return from the brine for concentrate recycling system, type of SW membrane, feedwater flow rate and numbers of elements in each pressure vessel (PV). These parameters were also compared to each other in terms of recovery (R) and freshwater unit production cost. In addition, the exergy of all elements was analyzed by selecting the optimal mode of each system.

Citation

Naeimi, A., Ahmadi, M.H., Sadeghzadeh, M. and Kasaeian, A. (2020), "Optimum arrangement of two-stage plug and concentrate recycling RO systems using thermodynamic and exergy analysis", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 30 No. 6, pp. 3323-3348. https://doi.org/10.1108/HFF-12-2018-0766