A dual-temperature zone strategy for enhanced crystallization control in helical coiled tube crystallizers: flow behavior and population balance modeling

Helical coiled tubes (HCTs) have significant potential for crystallization due to their high heat transfer efficiency and narrow residence time distribution. However, their application is limited by fouling issues. To address this, the mechanisms of fouling and clogging in HCTs were investigated through cold-model and crystallization experiments, revealing wall deposition of fine crystals and heterogeneous nucleation under high supersaturation. Based on these findings, a novel dual-temperature zone strategy was proposed, employing two sequential crystallizers: the low-supersaturation first zone promotes crystal growth, while the second zone uses the grown crystal surfaces to consume high supersaturation and suppresses nucleation. Compared to the single-temperature zone configuration, the dual-temperature zone strategy reduced fouling by 29.5%, 67.1%, and 88.1% across three different flow regimes. Moreover, it enabled operation at lower temperatures, with fouling levels at a cooling temperature of 10 °C in the dual-zone configuration being comparable to those at 20 °C in the single-zone setup. However, it achieved an 89.8% reduction in fouling compared to the single-zone setup with a cooling temperature of 15.1 °C. Furthermore, a population balance equation (PBE) model was developed to predict crystal size distributions (CSDs) under various temperature configurations and to explore the relationship between variations in crystallization kinetic parameters and fouling. This dual-temperature strategy demonstrates significant advantages in preventing fouling and clogging in HCT crystallizers, offering a promising solution for antifouling processes in continuous crystallization.<p></p>