Crystal Size Too Small

Low suspension density. This decreases average retention time, hence, the amount of time for crystal growth is insufficient. To correct, increase crystals in suspension to maintain design density. 

High circulation rate. This causes the fluidized crystal bed to become overextended resulting in too many void areas. This will result in improper release of supersaturation. To correct, maintain the circulation rate at the design rate. 

Solids in feed. This introduces nuclei into the crystallizer in excess of the number required for size control. To correct, make sure the feed solution is free of solids, especially crystals. 

Designfeed rate exceeded. At design suspension density, this results in a reduced average retention time. Within limits, this can be corrected by increasing the suspension density. An increase in production rate usually requires an increase in circulation rate to handle the additional supersaturation and the heavier fluidized bed of crystal 

Excessive nucleation. In addition to points 1 to 3 above, this is caused by excessive turbulence, local cold spots and subsurface boiling. To correct, maintain level at design point and maintain pump or agitator speed at design point. 

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Crystal size too small low suspension density/high circulation rate/solids in feed causing nucleation sites/feed flowrate > design/excessive turbulence/local cold spots/subsurface boiling/supersaturation too high or too dose to the metastable limit. 

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