Exergy analysis of a MSF desalination plant in Yanbu, Saudi Arabia

This study focuses on determining exergy destruction in a MSF Desalination plant located in Yanbu Saudi Arabia. A non-iterative code in MATLAB is developed to perform mass, energy, and exergy balances around the plant at normal load of distillate production (~ 159 kg/s) at 22.9 °C in the winter and at peak load (~ 200 kg/s) at 35.2 °C in the summer. Exergy flowrates are calculated and exergy destruction around each of the equipment is estimated. An exergy diagram is prepared to indicate equipment with highest exergy destruction. As expected the major exergy destruction occurs at the Heat Recovery Section (74.9%). The simulation results indicate that as the number of stages increase from 25 to 31 the percent exergy destruction drops from 74.9% to 69.2%. The second law efficiency of the plant is 3.22% and 2.84% at normal and peak load respectively. This efficiency is quite low and several measures can be done to improve it by decreasing inlet exergy to the plant and controlling exergy losses during process operation. Two variations in MSF designs i.e., Once Through (MSF-OT) and Brine Mixing (MSF-M) are considered. It is found that the design of MSF-M is a viable option to minimize exergy losses.