Operating Principle

: Fig. 1: Thin Film Principle

Thin Film Dryers are characterised by a mechanically agitated thin product layer inside the dryer (Fig. 1).

The Vertical Thin Film Dryer (Fig. 2) consists of a cylindrical,vertical body with heating jacket and a rotor inside of the shell which 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 film over the heated wall. The thickness of the layer is defined by the clearance between the blade and the wall. A highly agitated bow wave is formed in front of the rotor blades. The turbulence increases as the product passes through the clearance before entering a calming zone situated behind the blades. The volatile component evaporates continuously. The product layer is typically less than a millimetre in thickness. The hinged pendulum blades are designed to give a minimum clearance with the dryer wall to prevent fouling of the heating surface by product, but do not themselves contact the heated wall.

: Fig. 2: Vertical Thin Film Dryer

Normally, the drying process in a Vertical Thin Film Dryer consists of a preheating, a slurry and a powder zone.

In the preheating zone the product reaches boiling point. Evaporation starts and solids are formed.

In the slurry zone, the concentration of solids increases. Many products during this phase tend to form agglomerates which are crushed by the pendulum blades.

In the final powder zone surface moisture is further removed and the drying process is completed.

The length of the various zones depends for a given product largely on the feed rates and feed moisture content. With increasing feed rate the preheating and the slurry zone increase due to the increased heat demand. As a result the powder zone decreases in size and the final moisture content may increase.

The vapour moves through the dryer counter-current to the product flow and is condensed in an external condenser.

The free flowing powder leaves the dryer via a suitable air lock system.

Our manufacturing program includes Vertical Thin Film Dryers with heating surfaces up to 60 m². The dryers are heated with steam, warm water, thermal oil or electrically.




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