Falling film crystallization

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Falling film crystallization is also known as falling film crystallization and is a process of fractional crystallization from melts. This process was patented by the Swiss company Sulzer AG based in Winterthur .

Crystallization process

Schematic representation of the falling film crystallization (here: 1st stage)

With trickle film crystallization, the crystallization of a raw material into the desired end product is achieved in three stages.

The base material to be crystallized is first fed in the molten state into a storage tank, which is located below the actual crystallizer . Using a pump , this melt is fed from the top into the crystallizer, where it collects as a precipitate at the lower outlet and is fed back into the storage tank. This creates a cycle, in the course of which a crystal layer forms on the inside of the crystallizer, as the melt wets these (cooler) surfaces. To accelerate the crystallization, the outside of the crystallizer is also cooled by cooling hoses and a heat exchanger .

If a previously defined crystal layer has grown, the entire process is interrupted and the remaining raw material is removed from the collection tank. The resulting and cooled crystal layer is then slightly heated ("melting"), with which impurities drip off as melt (called partial melt) into the collecting tank. This process is also interrupted after a predetermined amount of impurities has dripped off and the melt collected is removed from the collection tank.

In the third step, the now cleaned crystal layer is completely melted and fed into the collection tank. The liquid obtained is available as the end product.

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