Why is vacuum used in FWG evaporators?

Vacuum is used in Fresh Water Generator (FWG) evaporators to lower the boiling point of seawater. Under vacuum conditions, seawater can evaporate at much lower temperatures, typically 40–60°C, instead of the normal 100°C at atmospheric pressure.

Main Reasons for Using Vacuum

1. Use of Low-Temperature Waste Heat
Marine FWG systems usually use engine jacket cooling water as the heat source, which is typically around 70–90°C. By creating a vacuum, this relatively low-temperature heat becomes sufficient to evaporate seawater.

2. Improved Energy Efficiency
Because the system uses waste heat from the engine, the ship can produce fresh water without additional fuel consumption, making the process energy-efficient.

3. Reduced Scaling and Salt Deposits
Lower evaporation temperatures help reduce the formation of scale and salt deposits on heat exchanger surfaces, improving reliability and reducing maintenance.

4. Faster Evaporation Process
The reduced pressure accelerates evaporation, allowing the FWG system to produce fresh water continuously during engine operation.

Summary

Vacuum operation in FWG evaporators allows seawater to boil at lower temperatures, enabling the system to use engine waste heat efficiently, reduce scaling problems, and improve freshwater production efficiency on ships.