2014 Volume 47 Issue 1 Pages 78-84
To develop a new industrial crystallization operation or crystallizer capable of realizing a higher crystal growth rate, a method of enhancing apparent crystal growth through the use of fine-crystal adhesion was examined using a classified bed-type crystallizer. We were able to clarify the effects of incorporating a pump for applying shear stress to a supersaturated mother solution along the path between the supersaturating section and the crystal growth section of the apparatus. A fine-generator pump was found to be effective at creating a discharge flow from the path, stimulating nucleation by impeller-based agitation, and recycling the solution back into the path. We found that the number of fine crystals could not be increased significantly with crystallization in a normal classified bed-type crystallizer that excludes the use of a fine-generator pump, whereas these parameters were controllable using the fine-generator pump. As an indicator of the output of the fine-generator pump, we defined the agitation rate m3/m3, which is expressed as the ratio of the flow rates between the fine-generator pump and the circulation pump. The fine-generator pump is effective at enhancing crystal growth rates at agitation rates of less than 1 m3/m3 and at an operational degree of saturation of less than 1.4 g/L. The most effective agitation rate was found to be 0.5 m3/m3, and it was independent of the degree of saturation. The maximum crystal growth rate was found to be 160 µm/h at a degree of saturation of 1.4 g/L, which was about three times greater than the maximum crystal growth rate without the use of the fine generator. These results are effective for the actual method of enhancing apparent crystal growth, although elucidation of the mechanism based on the phenomenological model is necessary.
