In-Flux Crystallization of Lactose

Lactose can be crystallized in condensed whey during cooling in a continuous plate-and-scraper crystallizer. In this study, the mathematical model of whey cooling relied on the heat transfer equations and the hydrodynamics of incompressible nonlinear viscous fluid in a cylindrical coordinate system. It took into account the pseudoplastic properties and the radial velocity of the feed. Based on the precalculated temperature distribution in the interplate area, the authors developed a new engineering methodology for determining the product temperature at the outlet of each heat exchange plate, as well as the total area of the heat-transfer surface. The research made it possible to identify the optimal temperature mode for the mass crystallization of lactose in condensed whey at a given solids mass fraction during countercurrent feed of the product and the coolant. The share of crystalized lactose and the average crystal size depended on the temperature during cooling and heating. Higher temperatures dissolved crystals and reduced their average size by 35–40%. The seeding stage had no effect on the crystallization degree and could be eliminated from industrial settings. The theoretical and experimental studies resulted in rational whey cooling modes and a new engineering methodology for a continuous plate-and-scraper crystallizer with in-flux lactose crystallization. It provided uniform crystals at lower energy costs and equipment deterioration. Expanding the industrial range of milk sugar and its derivatives, the new approach may update whey processing lines and improve the drying modes for lactose-containing products.