Feed water cooler to increase evaporation range in MSF plants

Multistage flash (MSF) desalination is the most widely used process to provide potable water. In MSF plants, water starts to evaporate in the top stage at a temperature set by the scale prevention techniques and stops at the bottom stage whose temperature is controlled by the feed water conditions. Increasing the difference between these two temperatures elongates the span along which evaporation occurs (evaporation range) and therefore increases the mass of the fresh water produced. This paper suggests installing a cooling system at the seawater intake in order to reduce the feed water temperature, and hence the temperature of the last stage. This technique leads to increasing the evaporation range without exceeding the conventional limits of top brine temperature and eliminates the effects of seasonal climatic changes. Moreover, the proposed scheme is a suitable arrangement to improve the water production from dual-purpose plants since the power needed to operate the cooling system is available on the same site. An improvement in the yield by 1.4–1.84% for every 1 °C reduction in the feed temperature can be achieved at the expense of a less than 0.2% of the power produced by the expansion of the heating steam.