Falling-film evaporators
Paul Kestner soon noticed that, in order to reach a steady working rate,
the climbing-film evaporator needed a temperature difference of 10°C minimum
(i.e. temperature differential between heating steam and evaporation liquid).
So in 1905 he designed and patented a falling-film evaporator, in which
the separator was located in the bottom part, with a tube bundle above where
the liquid fell in the form of a film.
With this type of apparatus,
which has continuously been improved from the very beginning, no minimum figure
is required for the temperature difference, as it can be as low as 1 or 2°C.
Two designs can be used:
- Constant wetting of the tubes regardless of the feed rate is ensured by the
associated recirculation pump. The unit can then be operated between 30% and
100% of the design while maintaining good stability of the plant.
- Non-constant wetting of the tubes.
A: Product
B: Vapor
C: Concentrate
D: Heating
Steam
E: Condensate
1: Head
2: Calandria
3: Calandria,
Lower part
4: Mixing Channel
5: Vapor Separator