Optimization for design of large RO seawater desalination plants

Abstract

The increasing interest for large seawater desalination plants with reverse osmosis (RO) is primarily due to the favourable economy and good operating experience. As an example energy recovery is a well established method in order to lower the water cost. However, the importance of design optimization has not been investigated in detail. The aim of this paper is to evaluate design parameters, which have a great impact on the optimization. The main parameter discussed is the water recovery, which is exemplified for 56,500 m 3/d (15 MGD) RO seawater desalination plant in the Middle East. The computer program developed for this evaluation is based on actual tenders from the Middle East area. In addition membrane design programs and information from RO-manufacturers have been used. The water recovery determines the capacity of the pretreatment plant and the configuration of the desalination plant. It has accordingly an influence on a great number of cost items such as pumps, filters, membranes, chemicals and civil works (buildings etc.). Design optimization with respect to different water recoveries is reported for several commercial membranes. The results show that the optimum for water recovery is rather broad and somewhat depending on the type of membranes used. The possibility to change from one membrane to another in a RO plant, designed for a specific membrane, is also discussed. Finally, the hybrid RO-MSF concept is compared with respect to the optimized design of such a RO plant compared to the double-pass system in the case studies mentioned above.