Thermodynamic Analysis of a Combined Power and Water Production System

Most of the potable water and electricity are produced by dual purpose plants. Dual-purpose plants are the one that supplies heat for a thermal desalination unit and produces electricity for distribution to the electrical grid. In this paper a power plant is combined with a multi-effect evaporation thermal vapor compression (METVC) system. Compared with the most widely used (Multi Stage Flash) MSF desalination, METVC has more advantages. Then, energy and exergy analysis equations for desalination plant, power generation cycle, heat recovery steam generator and combined power and water cycle are developed and the results are presented. Results show by rising number of effect from 2 to 14, performance ratio, exergy efficiency and specific heat transfer area rise steadily. For combined system, the maximum and minimum values of exergy destruction rate are related to combustion chamber and desalination effects, respectively. Also, with increasing TIT, exergy destruction rate of power generation cycle decreases while the exergy destruction rate of METVC, especially thermo compressor, goes up and fresh water production reduces dramatically.