Eutectic freeze crystallization: Application to process streams and waste water purification

Two case studies are presented using eutectic freeze crystallization (EFC) as an alternative for evaporative crystallization: a 7.8 ton day−1 35 w% aqueous sodium nitrate and a 24 ton day−1 12 w% copper sulfate stream. The proposed crystallizer is a cooled disk column crystallizer (CDCC), using indirect cooling for heat transfer. In single stage operation, the formed ice crystals are used to pre-cool the feed stream. A two stage refrigeration unit utilizes the formed ice crystals in the condensation of refrigerant. Expressed as a thermal equivalent energy requirement, EFC requires 1282 kJ kg−1 NaNO3 and 1037 kJ kg−1 CuSO4•5H2O. Compared to conventional multi-step evaporation, the energy reductions are 30% for sodium nitrate and 65% for copper sulfate.