Raheja Ecotech Engineers

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Falling Film Evaporators

In falling film evaporators the liquid product or the feed (A)is pumped at the head (1) of the Calandria (vertically mounted shell and tube heat exchanger).The product spreads on a distribution plate which evenly distributes it into the heating tubes. A thin film enters the heating tube flowing downwards at boiling temperature (in vacuum conditions) and is partially evaporated. The heating medium (D) which is steam in most cases is used for heating the product. The product and the vapor both flow downwards in a parallel flow. This gravity-induced downward movement is increasingly augmented by the co-current vapor flow. The concentrated product (B) is separated from its vapor (E) in the lower part of the Calandria (5) and the separator (3).
Advantages of Falling Film Evaporator:
Very short product contact times, typically just a few seconds per pass
Very low ?T (temperature difference) between the heating media and the boiling liquid
Suitable for heat-sensitive products
Due to 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.
When equipped with a well designed automatic control system they can produce a very consistent concentrated product.
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 Thermo/mechanical vapor compression systems in modern plants with very low energy consumption.

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