MODELING OF AGGLOMERATION IN INDUSTRIAL CRYSTALLIZATION FROM SOLUTION

A phenomenological approach to evaluating the agglomeration rate of growing crystals is presented. Crystals larger than the Kolmogoroff microscale collide because of the fluctuating velocity field. Bridges between the crystals form as a result of competition between crystalline growth and the turbulent velocity fluctuations on the opposite sides of the agglomerate. Crystals smaller than the Kolmogoroff microscale collide because of viscous laminar microshear stresses within the same turbulent eddy, are kept close together by Van der Waals forces and are joined together by crystalline bridges that grow between them. The strength of these bridges depends on the supersaturation level during the moments following the collision. These two sets of phenomena lead to two different preferential generation mechanisms for agglomerates. One example involving important agglomeration effects is developed for each case: the crystallization of adipic acid belongs to the first group (large crystals), whereas the precipitation of calcium oxalate monohydrate is typical of the second case (small crystals).