Fresh water generator, one of the important machinery on board a ship, is something that
cannot be done without.
Fresh water produced from fresh water generator is used
for drinking, cooking, washing and even running other important machinery which
use fresh water as a cooling medium.

Fresh water is generally produced on board using
the evaporation method. There are two things that are available in plenty on
ship to produce fresh water –Seawater and heat.

Thus fresh water is produced by
evaporating sea water using heat from any of the heat source.

The evaporated sea water is then again cooled by the sea water and the cycle repeats.

Generaly the heat source available is taken from the main engine jacket water, which is
used for cooling the main engine components such as cylinder head, liner etc.
The temperature available from this jacket water is about 70 deg. centigrade.

But at this temperature the evaporation of water is not possible as we all know
that the evaporation of water takes place at 100 deg centigrade under
atmospheric pressure.

Thus in order to produce fresh water at 70 degrees
we need to reduce the atmospheric pressure, which is done by creating a vacuum
inside the chamber where the evaporation is taking place. Also, as a result of
the vacuum the cooling of the evaporated sea water will also take place at
lower temperature. This cooled water is collected and transferred to the tank.

Nowadays,reverse osmosis is one of the methods which are used on board for generating

fresh water. Generally this is used on passenger vessels wherein there is a
large requirement of fresh water production. However, in merchant ships the
evaporation method is used as reverse osmosis is costly and includes large maintenance cost for membrane.

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