For any mariner ‘fresh water generator’ is the most simple but most important machine on board. It uses the sea water and by evaporation it gives us the fresh water. It is not a very huge machine, but a simple one and whose sole purpose is to produce clean and pure water. Fresh water generator is also considered to be the efficiency increasing device and thus what it makes this device so important also. The ship is itself a complete city which has own fresh water sources, power sources etc. During the early days people used to carry lots of water in their ship. It was all right but it increases the load on the ship and also water shortage problems were always there. So let’s scroll down
what are the uses of the fresh water generator.
Why we need the fresh water generator
A very good question about any machinery present in any industry. See in shipping the main thing is the time and money and its pure business out there. The owner wants to get as much profit as he or she can. So, why we need fresh water generator? One use is the simple one that we need fresh water for drinking. But why we install machinery which is bigger in size to generate water for drinking only. So what are the major uses of this? The major use of this water comes for the Boiler which operates in the ship. The boiler needs de mineralized water as it will help in reducing the corrosion and scale formation in the boiler surfaces. We can’t carry water in advance for the boiler as the consumption will be more. The boiler steam is used for heating oil’s, laundry, cleaning etc. In the tanker ships which carry oil, the steam turbine which is used to pump oil also needs steam.
The fresh water generator is an efficiency increasing device also. The jacket cooling water which comes out of the engine after taking heat from the various combustion spaces like near ‘liner’ etc is used to heat the water. So we are using the heat of engine to generate fresh water. So here we are saving money by not installing any separate burning mechanism for it. Now it’s time to check how this machine works.
How fresh water generator works
The thing which I said in above Para that it uses engine heat to generate water was looking good but here is a flaw. The flaw is that the temperature of the water coming out of the engine is hardly 60 or 70 degree Celsius. So how come we can evaporate water to generate fresh water generator because water boils only at the 100 degree Celsius. So here come the minds of the marine engineers. It uses both sea water and fresh water to. We use vacuum to evaporate water at lower temperatures like 50 or 55 degree Celsius.
Principal of fresh water generator
The main principal behind this is that at vacuum water boils at a much lower temperature. At vacuum the boiling temperature of the water decreases a lot and hence we are able to generate the water using sea water.
The mechanism: The mechanism of the fresh water
generator is very simple. Mainly fresh water generator consists of
1) Condenser unit
2) Evaporation unit,
3) Ejector unit
4) Saline meter unit
5) Whole casing
The working mechanism is as follows:
1) The fresh water generator is started when a ship has traveled enough distance that the temperature of jackets of main engine are stable. This distance can be 12 nautical miles.
2) Then the outlet supply of jacket water is opened and the evaporative unit of FWG is on.
3) The sea water feeder pump is turned on and the ejector is start working and the vacuum is built up.
4) The vacuum builds up helps the water to evaporate leaving behind any salt content which is present in the sea water.
Note: The evaporated water coming from the main engine is in the coils. So, no direct contact with sea water.
5) The evaporated water has to be passed through demister plate which acts like the barrier for any particle moving into the condenser unit.
6) The evaporated water is
condensed by the sea water which is in the coils and then fresh water is
7) After that it passes through a saline meter to check whether water generated is having standard PPM of salt content.