Development of a vacuum crystallizer for the freeze concentration of industrial waste water

Freeze concentration has proven to be a viable technology for the concentration of hazardous industrial waste waters before incineration. Owing to the relatively high investment cost of the technology, its applicability has been limited until now. This paper investigates the feasibility of a vacuum crystallizer as potential replacement of the scraped surface heat exchanger, which is one of the most cost- and maintenance-intensive items in conventional freeze concentration technology. Different crystallizer configurations and vapour treatment methods were evaluated for the system design. A thermodynamic analysis was performed to predict the phase transition behaviour in the condenser. A hydrodynamic analysis was performed to establish design rules and to determine the operating window. Finally, the principle of vacuum freeze crystallization was proven experimentally.