Working Principle of Fresh Water Generator on Board Ship

Fresh water generator(FWG) is one of the essential machineries on board ship, After-all a large amount of fresh water is utilized on ship every day. On board ship Fresh water is used for the most part by huge boilers having steam turbines as main propulsion or cargo pumps driven by turbines. They all in all record for 30+ Tons of fresh water every day separated from the day by day necessities of 10+ ton for crew consumption as drinking, cooking, washing,Tank cleaning and different utilities. Adequate consumable water might be taken up against the cargo load capacity in the port for satisfying crew and machinery necessity yet isn't prescribed to utilize shore water for boilers because of their low quality, so Fresh water generator is unavoidable on board ship.

But why do we need the FWG on board in first place?

In the middle of good old days people used to bring across lots of water in their ship. It was good however it expands the load on the ship and furthermore water lack issues were always there. Be that as it may, the nature of shore water will be extremely (too much) bad to be used in water tube boiler and filling (expansion) tanks. The storage space that could have been used for fresh water can as a result be used for fuel or added/more space for payload and products (that are bought and sold) when fresh water generator is installed on a ship. As you may know the first (or most important) concern for running a ship or any transportation business is to make money. Further more Boiler needs demineralized water to reduce overall scale development and corrosion issues. It is also normally used to build the general efficiency of the running machinery, mostly it uses the engine warmth/heat by Cooling The Hot Jacket Cooling Water At Around 85 Deg Celsius To 65 Deg Celsius.

Working Principal Of FWG?

Extremely important rule of all low weight freshwater generator is that, boiling point of water can be decreased by lessening the pressure of the air surrounding it. By keeping up a low pressure, water can be bubbled at low temperatures say 55 degree Celsius. The source of warmth for the fresh water generator could be waste heat rejected by generators and main engine jacket cooling water. This decrease In Saturation Temp lead to early vaporisation of water due to vacuum created within the chamber. It Is Created By The Help Of An Air Ejector, Which Extracts The Air From That compartment/chamber. An Air Ejector Works On Bernoulli's Rule and being used side by side with a brine ejector used to suck salt water from the chamber. The vacuum help disappear the water leaving behind the salt or salt water to be sucked by salt water ejector. It is then passed through the dimmister (A sort of punctured plate with very minute gaps) which traps any water or salt particle traveling through it. The evaporated water is then condensed together with the help of ocean water and after that tested for sality with the help of salino-meter.

Regulations Regarding Production of sea water on board ship:

1. Ship must be 12 nautical miles away from the nearest coastline to start the FWG.
2. Engine must be running at full ahead sea speed during start of FWG.
3. Ensure main engine parameters are normal.
4. Ship is not in congested water.
5. Ship is not maneuvering.
6. There is no oil/chemical spill reported in the visinity of the ship.

Safety Equipments on A Typical FWG:

1. Vacuum Breaker For Releasing Vacuum when we shut down the FWG.

2. Relief Valve For Releasing The Excess Pressure.

3. High Salinity Alarm: It Is Fitted To The Salinometer As It Measures Higher Salt Content In The Water Produced.

4. Temperature Gauge.

Starting Procedures for Fresh water generator:

• First we need to ensure that suction, discharge and overboard valves for ejector pumps are under open condition. Now once been checked, start the ejector pump.
• Close the vacuum breaker valve.
• Make Sure the S.W pressure at ejector (air) is not less than 3 bar. Now wait for 10-15 minutes to build vacuum in the generation chamber of fresh water generator. Wait until it shows more than 90% vacuum.
• Now open the sea water feed to the evaporator. Check for the sea water level in the shell through the sight glass and ensure it is at optimum level controlling feed through feed valve. Once the heating coils are fully submerged by the sea water open the J.C.W valves to the evaporator slowly.
• Purge out any air in the system by opening air vent at the top of the evaporator.
• Check for evaporation from the sight glass and then start the salinometer.
• Divert the outlet back to the feed water until the salinity is under the limit.
• When the salinity level is as per the desired or set value, open the discharge valve of distillate pump which sends the water to the fresh water holding tank through flow meter.
• Increase the evaporation rate and start the discharge pump. Check for the sytem to be stable.

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Author Amit                                                          Article requested by: NIÑO GONZALES

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