Steady-state analysis of multi-stage flash desalination process

The multi-stage flash (MSF) water desalination process plays a vital role in the provision of fresh water in many areas of the world, particularly in the Arab Gulf countries. This paper describes a steady-state mathematical model developed to analyze the MSF water desalination process. Relationships between parameters controlling the product water cost (e.g., thermal performance ratio, specific heat transfer surface area, and specific flow rate of cooling water and recirculated brine) to other operating and design variables are established. These relationships can be used to design new plants or to analyze already existing units. The model assumes the practical case of constant heat transfer surface area per stage in each section. It considered the variation of the physical properties of water with temperature and salt concentration, the effect of fouling factors and presence of non-condensable gases on the overall heat transfer coefficients, and variations in stage flash down and thermodynamic loss from stage to stage. The model also takes into consideration the heat transfer losses from the stages to the surroundings and through rejection of the noncondensable gases. The results obtained from the model developed are compared with data from six different MSF plants. Good agreement is obtained between data of these plants and model predictions.