Desalination by distillation
Distillation means evaporation and condensation of a fluid. The resulting condensed product is free from salt. This basic principle, as natural as rain, is widely used in sea-water desalination.
The two main sea water distillation processes are called multi-stage flashing (MSF) or multi-effect desalination (MED). Depending on the availability of energy on-site, and its quality, MED plants may be fitted with a compressor (thermal or mechanical) in order to enhance their performance and to optimise energy requirements. The processes are then called MED-TVC (thermal vapour compression) and MED-MVC (mechanical vapour compression).
Most of the time, and in particular for large plants, the lowest cost is obtained by coupling power and water production, the exhaust conditions of the turbines being optimised to feed the desalination units. The large desalination plants of the Arabian Sea are usually developed on such concept, called cogeneration. Sometimes reverse osmosis is associated to the thermal desalination process to optimise the Power Plant turbines: the hybrid plant.