The tubular falling film evaporator is specifically suited for processing temperature sensitive products with a low viscosity and tendency for fouling. It consists of a tube bundle crowned by a proprietary liquid distribution device, which ensures an efficient and uniform distribution of the liquid to all the tubes, as well as a continuous film along the tube length. Usually the liquid and resulting vapours flow co-currently from the top to the bottom and a gas-liquid separator is applied to separate the exhaust streams. This separator is not required in counter-current applications (stripping) or when the falling film evaporator is used as a reboiler of a distillation column.
The thin or wiped film evaporator is the ideal apparatus for continuous processing of heat sensitive, viscous and/or fouling products. It consists of a single evaporation tube fitted with a mechanical rotating device that ensures a uniform distribution of the liquid on the heated surface, a constant mixing of the film and minimal fouling of the evaporation surface. The vapours produced rise upwards, counter-currently to the liquid and, when required, pass through a mist eliminator mounted in the top section. Thanks to the large cross-sectional area, the pressure drop across the evaporator is low (typically less than 0.05 mbar) and operation in the vacuum range as low as 0.5 mbar is possible.
In the short path evaporator, a vertical condenser is placed inside the wiped evaporation chamber. This results in a very short distance between the heating and condensing surface. The pressure drop across the system is thus minimized and evaporation in the pressure range below 1 mbar is feasible. Due to the short residence time, highly temperature sensitive substances and compounds with high molecular weight can be purified at high purities and yields.