Automatic management of sucrose cooling crystallisation based on near infra-red spectroscopy

The control and correct management of an industrial crystallization process requires the knowledge in real time of some chemico-physical and technological parameters. These often are difficult to evaluate because the process is in continuous evolution. To optimize an industrial crystallization process in order to obtain the best characteristics of both the crystals and the magma, we need to know not only the solubility curve and its variation with the concentration of the impurities, but also: the real-time supersaturation of the growing solution; the growth kinetics and their variations with the temperature, concentration of impurities and the hydrodynamic conditions of the magma;the surface area of the crystals and their variations during the crystallization process; and, the morphology of the crystals and their variations with the temperature, supersaturation and the presence of impurities. The correct management of an industrial process is possible if we could know, in real-time, the amount of crystals present in the magma, the ratio between the crystals and the mother liquor, the composition of the mother liquor and, as a consequence, the correct value of the supersaturation and the optimal conditions of the growth kinetics. To obtain all these data and their variations during the crystallization process, we tried to utilize the NIR (near infra-red) technique via a special probe submerged in the growing magma. The first results obtained using this technique applied to a cooling crystallization of pure sucrose are presented and discussed.