Eutectic freeze crystallization in a new apparatus: the cooled disk column crystallizer

Abstract

Eutectic freeze crystallization (EFC) is a technique for simultaneous crystallization of ice and salt that is energetically more efficient than conventional evaporative crystallization. In this paper, a new type of crystallizer is introduced for simultaneously conducting EFC and separating the ice from the salt crystals, the cooled disk column crystallizer (CDCC). Crystallization is achieved by indirect cooling with wiped disks and separation by means of gravity. The liquid feed stream enters the column at the center, ice leaves the column at the top and salt is discharged at the bottom. The heat flux from bulk fluid to disk in a 14 l CDCC using CuSO 4–water as a model system (eutectic temperature −1.6 °C) was 1.9 kW m −2 for a temperature difference between disk and bulk of 4.5 K. The CuSO 4 · 5H 2O crystals formed were well faceted with an average size of 200 μm. Ice crystals were disk shaped with an average size 150 μm. Both ice and salt crystals were easily filtered. The impurity level in the ice crystals was below 100 ppm Cu.