Multiple Effect Distillation

Introduction to Multiple Effect Distillation

Multiple Effect Distillation (MED) is a thermal desalination process.  It distills water by boiling it under vacuum, then condensing the pure water vapour.  It uses multiple shell and tube heat exchangers, called cells or effects.

By maintaining low pressure throughout the system, the boiling point of water can be reduced to below 65 °C.  This both reduces energy costs, and critically decreases fouling, when compared with Multi-Stage Flash (MSF).

Multiple Effect Distillation with Thermal Vapour Compression (MED-TVC)

The addition of a thermocompressor to the evaporator allows the system to use the pressure of the available steam to extract low pressure vapour from an evaporator cell.  This allows the latent heat of the vapour to be reintroduced to the evaporator.

MED-TVC with high pressure steam can result in the highest possible gain output ratio (GOR).

Multiple Effect Distillation with Mechanical Vapour Compression (MED-MVC)

Where no steam is available, a mechanical compressor can be employed.  This allows the evaporator to operate with only electrical energy. MVC systems tend to be limited by the size and cost of the compressor.