Generation of fresh water from seawater
- Shipbuilding industry
Operating principles and constructional features
The SWD (Westfalia Separator®SeaWaterDistiller) is working on the well known vacuum distillation principle. Waste heat from the main engine on board is utilized as heating medium for evaporation. The evaporation takes place in the evaporation plate bundle located in the lower part of the housing.
A part of the incoming seawater evaporates due to the high vacuum inside the housing. The generated vapour is cleaned from seawater droplets while flowing through a wire mesh demister. The condensation takes place in the condenser plate bundle located in the upper part of the housing. The condenser is cooled by seawater. The latent heat from condensation is transferred to the seawater. The condensation / evaporation temperature varies with the seawater temperature.
A small portion of the heated seawater is utilized as feedwater for the evaporator bundle. The biggest part is used as driving medium for the combined air- / brine ejector. This ejector has a double function: Extraction of the surplus seawater (socalled brine) out of the housing and vacuum creation by exhaust of the noncondensable gases.
The distillate quality (salinity) is monitored at the control panel. If the salinity exceeds the adjusted set point (2 - 10 ppm) the distillate is rejected back to the evaporator via a solenoid valve.