posted on 2024-02-02, 14:05authored byShoji Kudo, Yukina Morota, Michiya Ota
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.