Power consumption in mechanically stirred crystallizers

The power consumption in a stirred crystallizer for different combinations of impellers, system geometry and solids content was experimentally investigated. The results show that the power dispersed in a crystallizer, operating with the usual solid content of 50-200 kg/m(3) and producing medium-large crystals cannot be safely predicted from the knowledge of the power number determined for the impeller of interest from measurements in liquid, since the power dissipation can be higher than expected. The geometry of vessel influenced the power number, also in the absence of the solid phase: in this case, the use of an elliptical bottom reduced the power dissipation, while that of a draft-tube caused this variable to decrease or increase depending on the impeller under exam.