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Fresh water makers from Wärtsilä
Remembered by many as 'Serck Como'

Multi Stage Flash Evaporators

Wärtsilä’s Multi Stage Flash (MSF) principle is the most reliable thermal seawater desalination process in the world. More over: it is the only evaporation principle where heat transfer and evaporation are strictly separated. This approach minimises the risk of scaling and greatly reduces maintenance costs.  

The Wärtsilä's multi-stage flash evaporators are used for producing fresh water from seawater, well or industrial water. A specific advantage of the multi-stage flash technology is that the heat consumption - or thermal efficiency - can continuously be  adjusted to the set requirements of each application.

The distillate produced by a MSF has a very low salt content, which makes it very suitable to be used as technical water (e.g. boiler feed water). The distillate quality and quantity are are not impacted by the seawater temperature. This makes the MSF technology a reliable source for freshwater on board of ships. 



    • Technology with the lowest lifecycle costs. 
    • Heat transfer and evaporation takes place in different areas, minimising risk of scaling (flash).  
    • Sturdy construction with low maintenance demands resulting in high availability. 
    • Lowest sensitivity to malfunction or maloperation. 
    • Components in contact with seawater or distillate are  manufactured with corrosion resistant materials (e.g. copper-nickel). 
    • Flexible dimensions allow for optimal use of available space. 
    • Operating frequency converter for pumps saves energy. 
    • Salt content of the distillate ≤ 4 ppm NaCI. 


    • Capacity up to 1500 t/d. 
    • Steady production of freshwater at seawater temperatures 0 - 32°C. 
    • Either steam, engine jacket water or combination can be used for heating 
    • Full-automatic or semi-automatic operation
    • Can be operated in part load

    Materials used:

    • Condenser tube material: CuNi, CuZn  
    • Pipes in contact with seawater: CuNi 
    • Pipes in contact with steam, motor-water, condensate: Steel 
    • Distillate: CuNi  
    • Shell: CuNi 


    After leaving the first stage condenser, the seawater flows through the brine heater, where the heat input to the plant (steam or engine jacket water) causes a further temperature increase.

    The seawater leaves the brine heater and enters the first flash chamber, reaching a brine top temperature of approx. 80°C. At this point the pressure of the incoming seawater is suddenly reduced, by means of an orifice, below its equilibrium vapour pressure resulting in explosive boiling or evaporation (flashing).

    The pure vapour produced is then condensed giving up its latent heat to preheat the incoming seawater. If this process is repeated over a large number of effects, at successively lower pressures and temperatures, large distillate production rates at reasonable performance ratios can be achieved. 
    process depiction multi stage flash evaporation; Serck Como; MSF flow chart


    System Capacity (m3/day) Thermal power (kW/t) Dry weight (kg) Wet weight (kg) Footprint
    (L x W x H, m)
    Water quality (ppm)
    MSF 115-5 115 915 18000 21000 5,7 x 2,9 x 3,0 3 ppm
    MSF 300-6 300 2388 27000 32000 7,3 x 2,9 x 3,3 3 ppm
    MSF 650-6 650 5146 37000 45000 9,2 x 3,5 x 3,9 3 ppm
    MSF 775-8 775 4812 42000 52000 10,5 x 3,6 x 3,9 3 ppm
    MSF 850-8 850 4780 43000 53000 11,7 x 4,2 x 3,9 3 ppm
    MSF 950-8 950 6395 45000 55000 12,0 x 3,7 x 3,9 3 ppm


    Delivered as standard:

    • Flash vessel with condenser and condenser tubes 
    • Base frame 
    • Pumps, including e-motors 
    • Air ejectors 
    • Feed water heater 
    • Distillate cooler 
    • Complete internal pipework 
    • Control equipment and instrumentation 
    • Optional steam booster 


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