The basic design criteria are twofold:
The classifying crystallization chamber is the lower part of the unit. The upper part is the liquor-vapor separation area where supersaturation is developed by the removal of the solvent (water for most applications). The slightly supersaturated liquor flows down through a central pipe and the supersaturation is relieved by contact with the fluidized bed of crystals. The desupersaturation occurs progressively as the circulating mother liquor moves upwards through the classifying bed before being collected in the top part of the chamber. Then it leaves via the circulating pipe and after addition of the fresh feed, it passes through the heat exchanger where heat make-up is provided. It is then recycled to the upper part.
Additional devices, such as described for the forced circulation crystallizer, are of course available.
It is worth bearing in mind that the operating costs of the Oslo type crystallizer unit are much lower than with any other type when both large and coarse crystals are required. Since crystals are not in contact with any agitation device, the amount of fines to be destroyed is lower and so is the corresponding energy requirement.
This Oslo type crystallizer (classified – suspension crystallizer) allows long cycles of production between washing periods.
Typical products are:
- (NH4)2SO4
- Na2SO4
- AgNO3
- Mono ammonium phosphate (MAP)