Agglomeration of Ni-Rich Hydroxide in Reaction Crystallization: Effect of Taylor Vortex Dimension and Intensity

Abstract

The effect of a Taylor vortex flow on the agglomeration of Ni-rich hydroxide (Ni0.90Co0.05Mn0.05)(OH)2 was investigated in a Couette–Taylor (CT) crystallizer. The agglomeration process was found to be significantly affected by the rotation speed of the inner cylinder (hydrodynamic intensity) and gap size between the inner and outer cylinders of the CT crystallizer (vortex dimension), as these parameters affected the fluid shear and stability of the Taylor vortex flow. Thus, the agglomerate size was reduced when increasing the rotation speed and decreasing the gap size due to the increased fluid shear. A high rotation speed also improved the agglomerate size distribution and tap density. However, the agglomerate size distribution became broader and the tap density lower when decreasing the gap size, despite the increased fluid shear. This was due to an increase in the axial dispersion effect in the CT crystallizer when decreasing the gap size. As a result, the effective fluid motion of the Taylor vortex produced narrowly distributed and spherical agglomerates with a coefficient of variation of 0.22 and tap density of 2.15 g/cm3 when using a high rotation speed (1500 rpm), wide gap size (0.89 of radius ratio), and only 1-h mean residence time in the continuous CT crystallizer. This confirmed that a Taylor vortex would be highly applicable for the practical production process of agglomerates of Ni-rich hydroxide.