How Freshwater Generator Transforms Seawater into Freshwater for Consumption?

How Freshwater Generator Transforms Seawater into Freshwater for Consumption - Merchant Navy Info - Blog

Water production equipment is one of the important machines that are indispensable to ships. The freshwater produced by freshwater generator is used for drinking, cooking, washing, and also even running other important machines that use fresh water as a cooling medium.

Onboard ships produce fresh water through evaporation. On board, he has two things in abundance: seawater and also heat to make fresh water. Therefore, fresh water is produced by evaporating seawater using heat from any source. The evaporated seawater is cooled by seawater again, and also the cycle repeats.

The Impact of Generating the Available Heat Source from the Main

Generally, the available heat source is obtained from the main engine jacket water and is used to cool the main engine components such as cylinder heads, liners, etc. The temperature obtained from this mantle water is approximately 70°C. Celsius. But we all know that water evaporation occurs at 100 degrees Celsius under atmospheric pressure, so water evaporation is not possible at this temperature.

What is a Freshwater Generator?

The Freshwater Generator (FWG) converts seawater (salt water) into freshwater. FWGs are commonly found on many ships because they can produce the fresh water needed at sea. The process of obtaining fresh water is done by distillation. Water There are three main ways to produce fresh water from seawater: boiling, evaporation, and reverse osmosis (RO). Most ships and industrial facilities use either evaporators or RO systems to produce fresh water. Large desalination plants can be connected to the steam cycle of thermal power plants, and also the steam is used to evaporate seawater. The 3D model in the saVRee database is based on a low-pressure flash evaporator (flash distiller) with a plate heat exchanger. However, his FWG with tube bundle heat exchanger is also available.

What are the Main Components of a Freshwater Generator?

The FWG consists of the following main components: Hot and cold water connections.

  1. Shell Condenser 
  2. Evaporator 
  3. Demister 
  4. Fresh Water Pump 
  5. Ejector/Eductor 
  6. Temperature Monitor 
  7. Vent Valve Safety 
  8. Valve (SRV) Salinity Meter

How Does a Freshwater Generator Transform Seawater into Freshwater

Produce Fresh Water

Therefore, to produce fresh water at a temperature of 70 degrees, the atmospheric pressure must be lowered by creating a vacuum in the chamber where evaporation occurs. Because of the vacuum, the evaporated seawater also cools at a lower temperature. This cooled water is collected and supplied to the tank.

Reverse osmosis is one of the methods currently used to produce fresh water onboard ships. Generally, this is used on passenger ships where the need for fresh water production is high. However, reverse osmosis is expensive and membrane maintenance is expensive, so evaporation methods are used in commercial ships.

Arrangement of the Freshwater Generator 

The body of the freshwater generator on the ship consists of a large cylindrical body with two compartments. One of the compartments is the condenser, and also the other is the evaporator. The freshwater generator also features an educator to help create the necessary vacuum. Freshwater pumps and ejector pumps help transfer water to and from freshwater generators.

Starting the Freshwater Generator 

1. Before starting the freshwater generator, you must ensure that the vessel is not stuck in water or canals and is 20 nautical miles from shore. This occurs because effluents from factories are discharged into the sea near the coast and can reach water production equipment.

2. Make sure the engine is not spinning more than 50 rpm. The reason is that at low speeds, the temperature of the water in the jacket is about 60 degrees, which is not enough for the water to evaporate.

3. Make sure the drain valve at the bottom of the generator is closed.

4. Now open the seawater pump suction and outlet valves. A seawater pump supplies water to the educator for evaporation, cooling, and vacuum generation.

5. Open the seawater drain valve to allow seawater to be returned to the sea after circulating through the freshwater generator.

6. Close the vacuum valve on top of the generator.

7. Next, start the seawater pump and check the pump pressure. The pressure is typically 3-4 bar.

8. Wait until vacuum is established. Vacuum should be at least 90%, which can be checked with a gauge on the generator. It usually takes about 10 minutes to generate a vacuum.

Initial Steps

1. Once the vacuum is achieved, open the water treatment valve to prevent limescale buildup within the plates.

2. Next, slowly open the hot water inlet and outlet valves (jacket water) about halfway. Always open the exhaust valve first, then the intake valve. Open the valve slowly until it is fully open.

3. You can now see that the boiling temperature begins to increase, and also the vacuum begins to decrease.

4. The vacuum level has dropped to approximately 85%, indicating that evaporation has begun.

5. Open the valve from the freshwater pump to the drain.

6. If a manual start is required, switch on the salinity meter. Autostart is usually enabled.

7. Next, start the freshwater pump and try to see water coming out of the drain.

8. Once freshwater production begins, the boiling temperature drops slightly again and also the vacuum returns to normal.

9. Check that the water coming out of the salinity meter does not contain salt, and also check the reading on the salinity meter. This is done to determine if the salinometer is working properly and to prevent all fresh water from being contaminated with salt water. Salinometer readings are kept below ten ppm.

10. After checking the taste of the water coming out of the salinity meter, open the pump tank valve and close the drain valve.

Stopping the Freshwater Generator 

1. Close the jacket water inlet valve. Generally, the intake valve is closed first, followed by the exhaust valve.

2. Close the valve for water treatment.

3. Stop the fresh water pump.

4. Switch off the salt meter.

5. Stop the seawater pump (also known as the ejector pump).

6. Open the vacuum valve.

7. Close the seawater intake valve and also the outboard valve. These are check valves, so they are usually not needed. However, if a leak or valve damage occurs, these valves must be closed.

Scroll to Top