(562a) Designing a Lactose Crystallization Process Based On Dynamic Metastable Zone Width

In the dairy industry, lactose crystallization typically produces crystals with huge number of fines (< 50 µm). This greatly reduces the efficiency of the downstream processes, and requires the final product be further processed. Theoretically, operating a seeded industrial cooling crystallization process in the dynamic metastable zone width (MSZW) will ensure the production of large lactose crystals (> 150 µm) with minimum fines. However, the result might vary depending on the design of the crystallizer. In this study, three designs (including draft-tube baffled, scraper and scraper-propeller crystallizers) at three regions of operation (in the MSZW) were investigated. First, the temperature-time profile for operations in different MSZW regions was estimated by solving four mass balance differential equations. Then, the batch crystallization process was conducted with these cooling profiles. The laser diffraction technique was used to measure the Crystal Size Distribution (CSD) of the product. In addition, Computational Fluid Dynamics (CFD) was also used to simulate the flow profile of all the crystallizers. The yield of the crystallization process was affected by the amount of lactose lost by encrustation (on the crystallizer assembly). Draft-tube baffled crystallizer had excessive encrustation (> 50%), resulting in very low yield (< 10%). Scraper and scraper-propeller system had reasonably high yield (> 70%), with minimum number of small crystals, and aggregates (depending on the regions of operations). This difference might be attributed to different flow characteristics, as shown in the CFD analysis. Therefore, depending on the crystallizer design, large lactose crystals with minimal fines can be produced when operating in the optimal region in the dynamic MSZW.