Vapour Compression Distillation

In the process of vapor compression distillation, the outgoing fresh and salt water streams is used to preheat the sea water in a tubular heat exchanger. Boiling of the sea water takes place in the tubes of the still. After this, compression of the vapors take place which are forced back to the still to condense on the outside of the tubes. Heat required for the boiling process is provided here by the vapors.

The steam-condensation space is emptied by removing the non condensing gas by a vent pump or ejector. This is necessary for the condensation of the vapors on the tubes carrying boiling seawater. The pressure of the vapors is increased to help them to condense.

The operation of vapor compression distillation is simple and is quite similar to MED. The main difference is that it is based on compression of the vapor generated by evaporating water to a higher pressure. This enables the reuse of the vapor for supplying heat for the evaporation.

Vapor may be compressed using mechanical compressor or they can be compressed by mixing with small amounts of high pressure steam. Heat is normally transferred in the form of a double falling film, which is an effective heat transfer mechanism.

The latent heat of the condensing vapor is utilized for generating more vapor on the other side of the heat transfer surface.

Whole process operates in two or three stages hence for the best optimization of the process operating temperature must be chosen carefully. The technique relies on the electric power supply and no external source of heat is required for the mechanical compressor.

The vapor compression distillation (VCD) process can be operated singularly or can be integrated with other processes such as the MED. The heat required for evaporation is generated from the compression of vapor. The system don't take the heat from the direct exchange of heat from steam produced in a boiler. These vapor compression (VC) units come in different types of configurations and designs. The heat for evaporation is generated by a mechanical compressor.