Water is a crucial question everywhere even on a ship !!
aboard the water tanks hold 150 Tons ( 150000 L): that is to say 3 day supply !
So the ship has to produce fresh water very soon after the departure.
The production is about 50 tons of fresh water a day; about 575 L /pers/day ( average consumption in USA : 400-500L /pers/day).
How to produce fresh water?
By desalination: using sea water, removing salt.
2 processes are used after the sea water has been pumped into a tank through a steel mesh and a 30 micron filter.
- The water is poured out in an other tank under low pressure where the water can boil at 165°F ( instead of 212°F at standard atm. pressure. 165°F = +/_ 73,9°C).
- Water vapor is collected
- stored in a tank.Second process: longer with a lot of steps:
- the incoming sea water passes through heat exchanger
- then through a sprayer and
- the vapor passes through a demister and a condenser
- the liquid water under high pressure and temperature passes in coils
- the vapor is cooling through a heat exchanger ( exchange with the incoming sea water )
- the water is finally collected in a holding tank.
At different levels of these processes the water is treated by chemicals as bromine and chlorine .
When needed, water from holding tank passes through a pressurized tank and just before passing into the pipes for consumption water is sterilized by UV light