Fresh Water Generator or Evaporator (Alfa Laval Type)
A considerable amount of fresh water is consumed in a ship. The crew consumes an
average 100 liter/head/day. In a steam ship (a ship whose main propulsion unit
is steam turbine or a ship which is a large tanker having steam turbine driven
cargo oil pumps) the consumption for the boiler can be as high as 30 tonnes/day.
Working principle of the low pressure evaporator is that, boiling point of water
can be reduced by reducing the pressure of the atmosphere surrounding it. By
maintaining a low pressure, water can be boiled at low temperatures say 50
degree Celsius. The source of heat could be waste heat rejected by main engine
jacket cooling water.
Such plants are widely used because of:
Operation of the Plant
Heat from the diesel engine cooling water is used to evaporate a small fraction of the seawater feed in the plate type evaporator. Unevaporated water is discharged as brine (by brine ejector) and that which is evaporated passes through the demister to the plate type vapour condenser, where, after condensation it is discharged to fresh water storage tank by fresh water distillate pump. During entire operation the feed rate to the evaporator is fixed by the orifice plate.
Freshwater Generator (Alfa-Laval Type)
In the event of salinity of freshwater
density exceeding a predetermined value (maximum usually 10 ppm) the solenoid
controlled dump valve diverts the flow to the bilge, preventing contamination of
the made water. Excess salinity could be used by many factors include leakage of
seawater at condenser or priming of evaporator or malfunctioning of demister, or
many other reasons.
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