Second-law analysis of a reverse osmosis plant in Jordan

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.