Effect of off-bottom clearance of a turbine type impeller on crystal size distribution of aluminum potassium sulfate in a batch crystallizer

Abstract

The effect of the off-bottom clearance of the impeller upon the product crystal size distribution, and upon the flow pattern and complete suspension speed have been investigated to find operation conditions of a batch crystallizer. The optimum off-bottom clearance to obtain larger, more uniform sized crystals and less agglomerated crystals was found to be about C D ≈ 0.2−0.25 in this experiment, where C is the off-bottom clearance, and D is the diameter of the crystallizer. The main flow pattern of the solution changed from one recirculation loop to two recirculation loops at about C D ≈ 0.2−0.25 , corresponding to the optimum off-bottom clearance. The relation between the measured complete suspension speed, N js and the off-bottom clearance could be expressed as N js = 11.2( C D ) 0.11 for 0.03 < C D < 0.16 , and N js = 32.8( C D ) 0.71 for 0.32 < C D < 0.54 .