Thermal Desalination – MSF – Multi-Stage Flash
WABAG multi-stage flash (MSF) thermal desalination plants are used for the production of potable and process water from sea- and brackish water.
The process employs proven once-through and recirculation technologies, saline water being heated by steam and then
led into a series of effects (stages) where reduced pressure results in immediate boiling (flash) without the need for
MSF desalination process is mainly employed for large-scale, thermal desalination plants where thermal energy is available in the form of low-pressure steam (>2 bar a), e.g. in combination with thermal power plants or industrial complexes.
Corrosion is the greatest problem in plants of this type and as a result of its long-term experience, WABAG uses special steels for condenser apparatus manufacture. For example, titanium pipes are employed for the heat exchanger surfaces in evaporators in order to ensure maximum plant availability.
In an MSF plant, the raw water is heated to the highest brine temperature in a vessel (brine heater) by condensing steam
on the tube bundles carrying the water. The heated saline water then flows into the following effect (stage) where the
ambient pressure is lower. This causes the water to boil immediately, flashing into steam until the brine has reached its saturation temperature. This procedure takes place in all the following effects at decreasing temperature and pressure.
The steam released in the effects by flashing passes through demisters and condenses into fresh water on the outside surface of heat exchanger tube bundles, which run through the effects and carry the cooler raw water. This allows a gradual preheating of the raw water, reducing the necessary thermal energy in the brine heater. The condensate produced in the effects is the source of the desalinated product water (distillate).
The MSF process operates with maximum efficiency at temperatures of up to 115° C, which results large plant sizes and low energy consumption.
- Zliten (Libya), Comprehensive Refurbishment
Capacity: 3 x 10,000 m3/d, potable water