3^rd generation cooled disk column crystallizer and a skid mounted unit for eutectic freeze crystallization

Soluble inorganic salts from industrial processes and aqueous waste streams can be recovered by Eutectic Freeze Crystallization (EFC). Around the eutectic temperature both highly pure salt and ice crystals can be simultaneously recovered as valuable products. In this work, the third generation Cooled Disc Column Crystallizer (CDCC-3) is presented. It has a capacity of 250-liters, 7 compartments and 6.72 m²/m³ cooling surface area. Compared to previous designs [Ham99, Vae02, Ham03, Vae03, Gen05], the CDCC-3 has more effective heat flux, a further optimized crystallizer geometry for gravitational separation, and an optimum residence time for nucleation and growth of both ice and salt crystals in continuous operation has been determined. A complete mobile (skid mounted) pilot unit for industrial applications was designed and constructed, allowing the system to be easily installed and integrated into an industrial plant. The unit consists of the CDCC-3, belt filtration, wash column, separation and storage tanks and special measurement devices (image analysis, data acquisition and a field bus based control system). As a practical application, the skid mounted unit was designed for producing 40 ton/year MgSO₄·7H₂O salt. The CDCC-3 is designed to obtain a production rate (in kg per second per cubic meter of the main crystallizer body) of 0.016 kg.s^-1.m^-3 for ice and for MgSO ₄·12H₂O salt. Besides process flow diagrams, the practical performances of the CDCC-3 in terms of heat transfer properties, optimal gravity separation, efficiency of ice scale removal from the cooled surfaces, nucleation and growth kinetics and particle sizes of salt and ice crystals are presented.