Rate of sodium chloride attrition fragment generation in a mixed-suspension crystallizer

Attrition of crystals in industrial crystallization is the major source of secondary nucleation and has strong effects on product quality. This work describes attrition in industrial crystallizers using an empirical engineering model based on dimensionless groups describing crystal properties, suspension properties, and crystallizer geometry and operating conditions. Here the attrition rate of sodium chloride crystals in a small scale mixed-suspension crystallizer is studied, varying the following parameters: impeller speed, parent crystal size, suspension density, draft-tube impeller clearance, off-bottom impeller clearance, impeller type, and impeller material. It was found that the attrition rate depends on most of the variables investigated. The direction of the dependence is predictable based on intuitive modeling. An empirical power law model based on dimensionless groups predicted by Buckingham-Pi theory (using variables mentioned above) gives a good fit to the data.