Melt crystallization is a highly selective and energy-efficient method for separation and purification of chemical mixtures. Suspension melt crystallization especially, offers a possibility to produce a highly pure crystalline product in a single separation step. The easiest way of producing the necessary supersaturation in a chemical mixture is by cooling. However, during indirect cooling deposits of the crystallizing material tend to form on the heat exchange surfaces. This often necessitate complex constructions and techniques, which from their part increase the costs of suspension melt crystallization. The aim of this work has been to investigate the possibility of simplifying the crystallizer construction by making use of standard heat exchanger structures. The crystalline deposits on the heat exchange surface have been dealt with by precise selection of the process variables, with special attention given to the flow conditions. The possibility of continuously circulating the crystal suspension through a heat exchanger in order to avoid the use of agitated vessels, has been investigated. The crystal characteristics produced by suspension melt crystallization using various equipment constructions and the formation of crystalline layers on cooled surfaces have been observed. The final aim of the experiments undertaken was to simplify the equipment construction and to obtain better control over the product characteristics for suspension melt crystallization processes. The results presented in this work will serve for improved understanding of the process of crystal formation and the phenomena at the cooled surfaces during crystallization processes. The improved understanding of these processes gives a basis for the further development of the suspension melt crystallization processes. The results obtained for the deposit removal in the tubular heat exchanger are applicable to removal phenomena in ordinary heat exchangers where problems of deposition by freezing are encountered. |