Forced Circulation Evaporator
Also here the mixture is circulated in each stage over one or more heating elements which are mostly located outside the evaporator. These are usually designed as a tube heat exchanger or plate heat exchanger. The circulation is driven by an outside source, i.e. circulation pump or air circulation (forced circulation). To reduce steam costs, especially with large evaporation rates, also evaporators with several stages can be designed.
Overheating at the heating surface
The liquid level above the heating surface prevents evaporation at the heating surface. Expansion takes place only in the separator which prevents fouling at the heating surface. The liquid is circulated by means of a pump with high flow rate. Forced recirculation evaporators are suitable for liquids which deposit in the evaporation solids or salts.
Oustanding features of Forced Circulation Evaporators:
- Sometimes long residence time of the product in the evaporator
- Large circulation pump and energy input by pumping
- High flow rates
- No boiling