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Freshwater Generators from Wärtsilä
Also known as 'Serck Como'

Multi Stage Flash Evaporators


Wärtsilä’s Multi Stage Flash (MSF) is one of the most reliable thermal seawater desalination plants in the world. More over: it is the only evaporator that strictly separates heat transfer and evaporation, minimizing the risk of scaling and greatly reducing maintenance costs.  

The Wärtsilä's Multi-Stage Flash evaporator is 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. 
    • Water conductivity of distillate < 4 μSv.


    • 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 (3), the seawater flows through the brine heater (1), where the heat input to the plant (steam or engine jacket water) causes a further temperature increase.

    The seawater leaves the brine heater (1) and enters the first flash chamber (2), 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 (3).

    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 flow within a W&#228;rtsil&#228; Water &amp; Waste (Serck Como) Multi Stage Evaporator; MSF process illustration


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

    Water conductivity of distillate for all models: < 4 μSv


    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 


    • Steam booster  
    • Distillate cooler 
    • Frequency converters for pumps 
    • Cleaning stations 

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