A fresh water generator produces distilled water from seawater by using a process called vacuum distillation.
The Principle: Vacuum Distillation
Fresh water generators are designed to create fresh, usable water from the abundant supply of seawater. The core principle they utilize is vacuum distillation. This means the process occurs in a low-pressure environment, significantly lower than atmospheric pressure.
Operating under a vacuum is crucial because it lowers the boiling point of water. Instead of needing to reach 100°C (212°F) at sea level, seawater can boil and evaporate at much lower temperatures, often around 40-60°C (104-140°F). This allows the system to efficiently use low-grade heat sources, such as the waste heat from a ship's engines, making the process very energy-efficient.
According to the reference, the fresh water generator produces distilled water from seawater. It operates on the principle of vacuum distillation.
The Process
The process inside a fresh water generator typically follows these steps:
- Seawater Inlet: Seawater is pumped into the evaporator section of the generator.
- Heating: A heat source (commonly jacket cooling water from diesel engines) is used to warm the seawater. Because the system is under a vacuum, this relatively low heat is sufficient to cause the water to boil.
- Evaporation: As stated in the reference, water evaporates in the lower part of the FWG and raises to the top. This separates the pure water (as vapor) from the dissolved salts and other impurities in the seawater.
- Brine Separation: The dissolved solids and remaining concentrated seawater, now called brine, remain in the lower part. As per the reference, solid particles remain in the brine which is returned overboard. This brine is continuously pumped out and discharged back into the sea.
- Vapor Condensation: The pure water vapor rises to a condenser section. Here, it comes into contact with colder seawater (often the cooling water for the condenser, which then might pre-heat the incoming seawater for the evaporator). This causes the vapor to condense back into liquid form – distilled water.
- Fresh Water Collection: The condensed, fresh water is collected and typically pumped to storage tanks. A sensor often monitors the salinity of the produced water to ensure it meets purity standards before it's stored.
Input and Output Summary
The process can be summarized simply:
| Input | Process | Output 1 | Output 2 |
|---|---|---|---|
| Seawater | Vacuum Distillation | Distilled Water | Brine |
| Waste Heat |
Practical Applications
Fresh water generators are essential equipment on many vessels, such as:
- Merchant ships
- Cruise liners
- Naval ships
- Offshore platforms
They provide a reliable source of fresh water for crew use, cooking, and various onboard systems, significantly reducing the need to carry large volumes of fresh water, which frees up space and reduces weight.
