(533d) Image-Based Experimental Investigation of Crystal Aggregation in Pipe-Flow

The aggregation behavior of crystals in a crystallizer depends on numerous parameters among which the flow field and crystal concentration are play an important role. Process models accounting for aggregation require a population balance. Thus, the knowledge of kinetic expressions for aggregation is necessary, however, can be determined only if appropriate data is available.

This contribution presents the experimental investigation of the aggregation behavior of three selected crystallization systems along a pipe. The experimental setup is designed to be applicable to a broad range of crystalline materials and works as follows. Saturated solution is withdrawn from a vessel and pumped continuously through the aggregation pipe. Sieved crystals are then suspended in saturated solution and directly injected to the pipe stream. By traveling along the pipe the crystals can interact which leads, depending on residence time, velocity and particle load to varying amounts of aggregated material. This is observed with the help of a microscope which takes photographs of crystals passing through a flow cell. The so recorded images are processed with a Matlab routine and can be analyzed with respect to size distribution but also other measures which allow a reliable aggregate detection and characterization.

The experimental results show the expected tendency, e.g. that with a higher residence time and particle concentration the fraction of aggregated material increases. The strength of the proposed procedure is twofold: the acquisition of property distribution data is based on a high number of particles (typically 50,000 ? 100,000) and thus the statistical significance is ensured. Secondly, the conditions within the pipe can be well controlled such that the influence of different parameters can be studied independent of each other, e.g. particle concentration and velocity.