0011-9164/09/$– See front matter © 2008 Elsevier B.V. All rights reserved Desalination 239 (2009) 207–215 Second-law analysis of a reverse osmosis plant in Jordan Isam H. Aljundi Chemical Engineering Department, Mutah University, Al-Karak, 61710, Jordan Tel. +962 (3) 237-2380; Fax: +962 (3) 237-5540; email: aljundi@mutah.edu.jo Received 31 October 2007; Accepted 14 March 2008 Abstract Exergy analysis is a powerful tool to determine inefficiencies of a process and to evaluate the performance. The reverse osmosis (RO) plant of Al-Hussein thermal power station was analyzed thermodynamically using actual plant data. Exergy flow rates are evaluated throughout the plant. The rates of exergy destruction and their percentages are calculated so that the locations of highest exergy destruction can easily be identified. The highest exergy destruction (56.8%) occurs within the throttling valves followed by the exergy destruction in the two-stages RO units (about 21%). The exergy destruction in the pumps and motors account for 19.6% of the total. The second law efficiency of the plant is very low, 4.1%. This indicates that opportunities of improvement exist to reduce exergy destruction and make the plant operation more cost effective. This may include the use of high-efficiency pump/motor set-up with a variable frequency drive and the replacement of the traditional throttling valves with energy recovery devices such as pressure exchangers. Keywords: Exergy analysis; Reverse osmosis; Desalination; Plant performance 1. Introduction Many areas of the world have limited fresh water resources. Exploitation of water resources along with higher water demand led to an increased exigency for improvements on existing water processes as well as alternative fresh water resources to make potable water sources more efficient and economical. Desalination provides such an alternative source to overcome regional water scarcity, offering water otherwise not accessible for irrigational, industrial and municipal use. Desalination technologies can be classified by their separation mechanism into thermal and membrane based desalination. Thermal desali- nation separates salt from water by evaporation and condensation, whereas in membrane desali- nation water diffuses through a membrane, while salts are almost completely retained [1]. Most of the world’s desalinated water is produced by the doi:10.1016/j.desal.2008.03.019