However, falling film evaporators
must be designed very carefully for each operating
condition; sufficient wetting (product film thickness)
of the heating surface by liquid is extremely
important for trouble-free operation of the plant.
If the heating surfaces are not wetted sufficiently,
dry patches and incrustations will occur; at worst,
the heating tubes will be completely clogged.
In critical cases the wetting rate can be increased
by extending or dividing the evaporator effects,
keeping the advantages of single pass (no recirculation
of product) operation.
The proper design of the product
distribution system in the head of the evaporator
is critical to achieve full and even product wetting
of the tubes.
Because of the low liquid holding
volume in this type of unit, the falling film
evaporator can be started up quickly and changed
to cleaning mode or another product easily.
Falling film evaporators are
highly responsive to alterations of parameters
such as energy supply, vacuum, feed rate, concentrations,
etc. When equipped with a well designed automatic
control system they can produce a very consistent
The fact that falling film evaporators can be
operated with small temperature differences makes
it possible to use them in multiple effect configurations
or with mechanical vapor compression systems in
modern plants with very low energy consumption.
Features of RAJ F. F. E.