Operation of a melt film crystallizer

Abstract

arated is supplied in melted form to the top of the apparatus (the film former) where a temperature is maintained which keeps the substance melted. Flowing over a comb-like ridge the melt flows as a thin film down the inner surface of the apparatus. This surface is cooled in such a way that at the upper and lower ends the temperature is above the melting point of the desired component and in the middle section above the melting point of the components to be removed and of the eutectic. The initial melt is supplied batchwise in such quantities that a film 0.2-1.5 mm thick is formed on the inner surface of the apparatus. In the lower temperature region the melt begins to crystallize. The highmelting substances crystallize first while the lowmelting components flow downwards and are lead away in liquid form over the expanded lower end of the apparatus to the impurities collector, where they crystallize and are scraped off by the knife in the form of scales. A crystal layer is formed on the inner surface of the apparatus, the composition of which corresponds to the temperature gradient. When the layer has equilibrated, the scrapers are brought to the walls of the apparatus by switching on the drive, the shaft of wMch carries, besides the scrapers, the funnel for the removal of the purified product and the impurities collector. �9 The shaft performs 1-2 revolutions and stops again. The scrapers remove the purified crystal layer; the crystallized impurities are cut off with the blade and at the start of the separation are mixed completely and at later stages partially with the starting product. The surfaces are purified of crystals and the cycle is repeated,