A fresh water generator evaporator is a marine desalination device that produces potable water from seawater using low-temperature vacuum evaporation. It is widely installed on commercial vessels, offshore platforms, and cruise ships.

The system uses waste heat—typically from the main engine jacket water—to evaporate seawater under reduced pressure.

Basic Working Principle

The process is based on two key principles:

1. Lower pressure → Lower boiling point

2. Phase change → Separation of salt from water

Under vacuum, seawater can boil at around 45–60°C, instead of 100°C at atmospheric pressure.

Step-by-Step Operation

1. Vacuum Creation

A vacuum is generated inside the evaporator shell using:

• An air ejector (driven by seawater)

• Or a vacuum pump

This reduces internal pressure and lowers the boiling temperature.

2. Heating the Seawater

Hot jacket cooling water (typically 70–85°C) from the engine flows through the heating side of the evaporator plates or tubes.

Seawater is sprayed or distributed as a thin film over the heat transfer surface.

Because of the vacuum:

• The seawater boils at low temperature

• Pure water vapor separates from salt

Salt and concentrated brine remain behind and are discharged.

3. Vapor Separation

The generated vapor rises through:

• A demister pad

• Or a separator mesh

This prevents salt droplets from being carried over.

Only clean water vapor proceeds to the condenser.

4. Condensation

Cold seawater flows through the condenser section.

The vapor condenses on the cooling surfaces and becomes distilled fresh water.

5. Fresh Water Collection

The condensed water:

• Passes through a salinity sensor

• Is discharged to the fresh water tank if purity is acceptable

If salinity is too high, it is automatically diverted overboard.

Main Components

• Evaporator heat exchanger (plate or tube type)

• Condenser section

• Demister

• Brine discharge line

• Air ejector or vacuum pump

• Salinity monitoring system

Why Vacuum Evaporation Is Used

• Uses engine waste heat (energy efficient)

• No high-pressure membranes required

• Robust and reliable for marine environments

• Simple operation and maintenance

Typical Performance

• Capacity range: 5–50 tons/day (depending on vessel size)

• Operating temperature: ~45–60°C boiling under vacuum

• Salinity of output: typically <10 ppm

Summary

A fresh water generator evaporator works by:

1. Creating a vacuum

2. Heating seawater with engine waste heat

3. Evaporating water at low temperature

4. Separating vapor from salt

5. Condensing vapor into fresh water

It is an energy-efficient and reliable desalination solution for ships and offshore applications.