Seeding Condition Strategy for Mitigating the Scale Formation and Enhancing the Yield in Suspension-Type Cooling Crystallization

Cooling surface crystallization, termed scale formation, is a serious problem in suspension-type cooling crystallization. The heat transfer efficiency of the cooling surface decreases when scale formation occurs during suspension crystallization. Consequently, the productivity of the suspension crystallization process worsens. Suspension crystallization operations eventually fail to continue. Previous studies on scale formation discussed its mechanisms, focusing on supersaturation near-heat transfer surfaces, flow dynamics, surface materials, and geometrical structure of the surface. These studies showed that suspended crystals affect the scale formation dynamics. Our group has studied scale formation phenomena considering the effect of suspended particles on these phenomena. This work focuses on the effect of suspended crystal characteristics, namely, size and shape, and suspension amount (like the number of suspended crystal particles) to clarify how they affect scale formation. Cooling crystallization experiments of melt crystallization for ethylene carbonate containing 5 mass % of water show that the scale layer characteristics (e.g., thickness or density) vary depending on conditions. Small size (length in the maximum axis direction), small aspect ratio, and small number of crystals are important in suppressing scale formation and enhancing suspension cooling crystallization to improve the suspended crystal yield. A guideline example is proposed for seeding conditions in terms of suspended crystal characteristics and suspension amount.