Understanding the impact of process parameters on the crystallization process within an integrated suspension melt crystallization pilot plant

• Validation of vibration analysis for crystal layer detection. • Determination of the operating window for water crystallization in a scraped cooling crystallizer. • Fast identification of influencing factors by Design of experiments. Developing environmentally-friendly and efficient purification technologies is an inevitable trend in the chemical industry. Freeze concentration is gaining attention due to its high separation efficiency and low energy demands, relying only on electricity, which allows for integration with renewable energy sources and could be an alternative for dewatering processes like desalination and wastewater treatment. To utilize the full potential of freeze concentration, the solid–liquid separation and purification of ice crystals are essential, and they are efficiently combined in continuously operated wash columns. However, the complex operation of these columns and their connection to the suspension crystallization unit requires a fundamental understanding of the effects of different process parameters on the operating window and the quality attributes of the suspension, especially the particle size distribution. Using a simple binary aqueous substance system with sodium chloride, the operating window of the scraped cooling crystallizer with a forced circulation loop is determined regarding the three main process parameters: the scraper rotational rate, the volume flow rate in the circulation loop, and the cooling rate. A vibration measurement is implemented and validated as a suitable tool to detect unstable process conditions, such as a crystal layer formation on equipment walls. The effects of the process parameters on the particle size distribution are quantified and optimized to achieve a desired large median particle diameter and a narrow size distribution. Here, the volume flow rate highly significantly affects the particle size distribution and the interaction with the scraper rotational and cooling rate shows a significant effect. Prioritizing the median particle diameter results in a diameter of 553 µm with a low volume flow, high scraper rotational, and low cooling rate. However, the stirred tank behavior results in a relatively broad distribution of 510 µm.