Prevention of crystallization fouling during eutectic freeze crystallization in fluidized bed heat exchangers

• Published in: Chemical engineering and processing Vol. 47; no. 12; pp. 2140 - 2149
• Main Authors: Pronk, P., Infante Ferreira, C.A., Witkamp, G.J.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.11.2008; Elsevier
• Subjects: Applied sciences; Chemical engineering; Crystallization, leaching, miscellaneous separations; Eutectic freeze crystallization; Exact sciences and technology; Fluidization; Fouling; Heat and mass transfer. Packings, plates; Heat exchangers and evaporators; Heat transfer; Liquid–solid fluidized beds; Eutectic freeze crystallization; Liquid–solid fluidized beds; Fouling; Heat transfer; Cooling; Crystallization; Crystallizer; Fluidization; Mass transfer; Fluidized bed heat exchanger; Heat exchanger; Eutectic; Liquid-solid fluidized beds; High purity; Fluidized bed
• ISSN: 0255-2701; 1873-3204
• DOI: 10.1016/j.cep.2007.11.006

Eutectic freeze crystallization is a promising separation technique to produce salt and ice crystals with very high purities and requires less energy than competitive evaporative crystallization techniques. A drawback of this technique is crystallization fouling, which seriously reduces heat transfer rates. Solid–liquid fluidized bed heat exchangers may be attractive crystallizers for this purpose, since they have demonstrated to prevent severe crystallization fouling, for example of ice crystals. This paper presents crystallization experiments with a single-tube fluidized bed heat exchanger. A first experimental series showed that fluidized beds are also able to prevent salt fouling during cooling crystallization from KNO 3 or MgSO 4 solutions. A second series revealed that fouling during eutectic freeze crystallization is more severe than during separate salt or ice crystallization and is therefore difficult to prevent by the fluidized bed. The explanation for this phenomenon is that the salt crystallization process strongly reduces the solute mass transfer limitation for ice crystals growing on the wall resulting in an increased growth rate and more severe crystallization fouling. The addition of a non-crystallizing component strongly reduces fouling and enables to perform eutectic freeze crystallization in fluidized bed heat exchangers for industrial applications.