Thermodynamic and Exergy Analysis of a Combined Power and Desalination Plant

Making potable water through desalination plants is a very important process in Iran where clean water is highly required. On the other hand, large amount of fossil fuel sources leads to the development of gas turbine power plants all over the country. Furthermore, Persian Gulf in the south and Caspian Sea in the north could be the main sources for supplying potable water in water scarcity areas, especially in the south. Dual-purpose plants are the ones that supply heat for a thermal desalination unit and produce electricity for distribution to the electrical grid. In this paper a gas turbine power plant was combined with a multi stage flash desalination system. Then, energy and exergy analysis for desalination plant, power generation cycle, heat recovery steam generator (HRSG), and combined power and water cycle were developed. Results showed that by increasing the number of desalination effect, performance ratio, exergetic efficiency, and specific heat transfer area steadily increase. Additionally, the sensitivity analysis showed the relationship between the parameters that are not known precisely or difficult to foresee such as steam pressure of HRSG and compression ratio on the performance parameters of dual purpose plant.