Exergy analysis of major recirculating multi-stage flash desalting plants in Saudi Arabia

A simple and auspicious scheme to estimate exergy losses in multi-stage flash (MSF) plants is discribed. This method is used to evaluate major MSF plants in Saudi Arabia, namely, Al-Khobar II, Al-Jubail II, and Shuaibah. This study presents a quantitative assessment of the exergy losses, exergetic efficiency, and exergy-destruction term for each plant. The effect of these terms on the performance of the three MSF plants when operating at various top brine temperature (load conditions) is also investigated. The results obtained for the three plants show that the three MSF desalting plants are highly irreversible with exergetic efficiencies ranging from 1.12-10.38%. The associated total exergy destruction is found to range from 6.75-26.16% MW, with the exergy-destruction term ε ranging from 40.52-77.96 kJ/kg. The exergetic efficiency of brine heaters, when calculated separately, ranges from 72.20-87.98%, with exergy losses of 1.20-5.42 MW. The study concludes that the top brine temperature (TBT) is directly proportional to the exergy losses in the MSF plants.