Falling Film Evaporator
A = Product
B = Concentrate
C = Condensate
D = Heating steam
E = vapor
1 = Head
2 = Calandria
3 = Separator
4 = Separator duct
5 = Calandria base
Operation
FFE mostly running under vacuum condition. In most case steam (D) is used for heating the evaporator.
The liquid to be concentrated (A) is supplied to the top of heating tubes (1) and distributed in such a way as to flow down the inside of the tube walls as a thin film.
A thin film enters the heating tube as it flow downwards at boiling temperature. The liquid film starts to boil due to the external heating of the heating tubes and is partially evaporated as a result.
The downward flow, caused initially by gravity, is enhanced by the parallel, downward flow of the vapor formed.
The separation of the concentrated product (B) form its vapor (E) is undergoing in the lower part of the calandria 排管 (5) and separator (3). It is essential that the entire film heating surface, especially in the lower regions, be evenly and sufficiently wetted with liquid. Where this is not the case, dry spots will result that will lead to incrustation and the build-up of deposits.
For complete wetting, it is important that a suitable distribution system is selected for the head of the FFE. Wetting rate are increased by using longer heating tubes, dividing the FFE into several compartments or by recirculating the product.
FFE are highly responsive to alterations of parameters such as energy supply, vacuum, feed rate, concentration, etc.
Advantages of FFE:
- FFE can be operated with very low temperature differences between the heating media and the boiling liquid,
- extremely short residence times in the FFE, have very short product contact times, typically just a few second per pass.
- FFE can be started up quickly
References:
http://www.niroinc.com/evaporators_crystallizers/falling_film_evaporators
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