Wall heating - Import export

The vertical thin film dryer consists of a cylindrical, vertically arranged body with heating jacket and a rotor inside. The rotor is equipped with rows of pendulum blades all over the length of the dryer. The hinged blades spread the wet feed product in a thin product layer over the heated wall and mix the product layer material intensively. Therefore the volatile components evaporate continuously from the product layer with high evaporation rates. The hinged blades are designed with a minimum gap to prevent fouling of the heating surface by product, but are never in contact with the heated wall. The product enters the dryer at its top. The evaporation starts after heating to the boiling point. In the slurry zone first solids are formed and with advancing evaporation of the volatiles and continued shearing by the hinged blades the paste breaks up to powder. The final solid product is discharged by gravity at the bottom of the dryer via a suitable air lock.

For the thermal separation of a mixture a thin film is produced at the heated wall of a cylindrical or conical evaporator. A distribution ring on the rotor distributes the liquid evenly across the periphery. Then, the blades fitted at the rotor spread the liquid as a thin film of min. 0.5 mm over the heat transfer surface. The model concept for the flow in the thin film evaporator assumes that prior to each rotor blade a bow wave is formed. In the gap between the rotor blade and the heating surface, fluid is supplied from the bow wave of a highly turbulent area with intense heat and mass transport. This results in a good heat transfer performance even with viscous products. In addition, the formation of deposits is avoided and the intensive mixing also protects temperature-sensitive products from overheating.