If the liquor is exhausted faster in the product than in impurities, then batch crystallization is required.
Cascade of serial crystallizers
The value of a cascade is twofold compared with a single large device:
The concurrent circulation of liquor and slurry has the consequence that, with more devices, we approach more operation of the double envelope tube (in the case of cooling); in other words, we approach batch crystallization. This explains why the median size increases with the number of serial devices.
However, this system includes many pumps, and attrition can be severe.
Particles in the slurry
In the liquid of an industrial crystallizer, we can encounter a certain particle diversity:
- real seeds consecutive to primary nucleation;
or agitator impeller.
Possible crystal dimensions
Of course, the size obtained for the crystals depends not only on the system in question, but also on the type of crystallizer used:
Crystallizer type Median size (mm)
Forced circulation 0.2-0.5
Draft tube 0.5-2
Fluidized bed (and batch crystallization) 1-10