Thermal desalination – MED – Multi-Effect Distillation
WABAG multi-effect distillation (MED) desalination plants are used for the production of potable and process water from sea- and brackish water. MED represents the most economic distillation process with respect to energy efficiency, whenever a low-pressure steam source (>0.3 bar a), or waste heat is available from a power station, or an appropriate industrial process. MED is generally employed for medium-sized to large plants.
In the port of Rotterdam, Netherlands, WABAG has installed one of Europe’s largest thermal desalination plants. The two MED units have a capacity of 24,000 m3/d and supply process water to a number of plants in the industrial complex. Waste heat from incinerators represents the main energy source for the thermal desalination process.
MED distillation takes place in a series of effects (stages), which are all equipped with heat exchanger pipe bundles. The raw water is sprayed onto these bundles, which are heated on the inside by condensed steam.
Due to the transportation of heat via the pipe walls, part of the liquid film on the outside of the pipe bundle evaporates. The steam thus generated is then employed in the next effect, where it again condenses on the inner surfaces of the pipe bundle. The first effect is the only one to be heated from an external source of steam.
The MED process operates at low temperatures, which results in:
- small to medium-sized plant sizes
- reduced scaling risk
- low thermal energy consumption
- reduced operating costs
- AVR, Rotterdam (Netherlands)
Capacity: 24,000 m3/d, process water