Evaporators

Evaporators are thermal concentrators. Evaporators are for concentrating dilute liquids, for increasing solids content & for reducing volume by evaporating water.

Evaporators are based on steam economy i.e. Kg of solvent evaporated per Kg of steam used. Reusing evaporated solvent as heating medium, higher steam economies are achieved. This method of increasing utilization of steam is used in multi-effect evaporator. In multi-effect evaporator vapour from the first effect is passed over to the next effect in which boiling takes place at lower temperature & pressure.

Thermo-compression evaporator is another alternative to increase steam economy. Vapor of solvent evaporated is compressed & is used as heating medium in the same evaporator.

Selection of evaporator depends on the various properties of feed & product such as crystallization, foaming, corrosion, salting & scaling.



Types of Evaporators:

Falling Film Evaporators Rising Film Evaporators Forced Circulation Evaporators Short Tube Evaporators

Falling Film Evaporators The feed gets distributed and thin film is formed Hold up and residence time is short hence liquid does not get overheated In Falling film evaporators, feed solution forms a film in the evaporator tubes & gets evaporated. These are best suited for heat sensitive materials such as fruit juices. The hold up time is short & liquid doesn't get overheated. Falling film evaporators are not suitable for crystallizing liquids. They are not suitable for salting & severely scaling liquids or solutions.