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R. K. Connelly1, K. M. DHANASEKHARAN2, and R. W. Hartel1. (1) Dept. of Food Science, Univ. of Wisconsin, Madison, 1605 Linden Dr., A-13 Babcock Hall, Madison, WI 53706-1565, (2) Fluent Inc., 10 Cavendish Ct., Lebanon, NH 03766 Lactose is the main constituent of whey. It is used primarily as a filler or sweetener, and in small amounts in infant and dietetic foods and coffee whiteners. It is also widely used as an excipient in pharmaceuticals. Lactose crystals are formed in crystallization tanks by holding the slurry over a carefully controlled time / temperature profile. After crystallization, the lactose crystals are recovered from the mother liquor and washed in decanter type centrifuges. Control of crystallization is needed to optimize product quality and separation efficiency. The objective of this work was to understand the coupling between non-ideal mixing characteristics and crystallization phenomena in industrial scale crystallizers. The modeling approach was to combine numerical simulation of fluid flow and heat transfer to understand non-ideal mixing phenomena with the crystallization kinetics through population balance modeling. The model was built systematically by first analyzing lab-scale crystallizers to validate the numerical simulations. The results predicted spatial and temporal distributions of the crystal sizes, area and mass. Experimental data on lactose crystallization from previous publications were used to verify the model. At each point within the crystallizer volume, the model predicted the temperature and concentration. Assuming secondary nucleation and growth kinetics, the size distribution was predicted through the population balance equation. Good agreement between experimental and predicted results was obtained. Coupling of mixing patterns in a crystallizer with crystallization kinetics allows for better understanding and control of crystallization. In the case of lactose refining, the model has the potential to determine optimal conditions for producing a crystalline product with higher purity, larger crystal size and higher value.
Session 93, Carbohydrate: General
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