Fluidized-bed Melt Granulation: Coating and Agglomeration Kinetics and Growth Regime Prediction

VILLA, MARTA P.; BERTIN, DIEGO E.; COTABARREN, IVANA; PIÑA, JULIANA; BUCALÁ, VERÓNICA

POWDER TECHNOLOGY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2016 vol. 300 p. 61 - 72

0032-5910

Mass and population balance equations are used to describe the spray-on melt granulationprocess in a batch fluidized bed where coating and agglomeration can occursimultaneously. Two different models are considered to describe the agglomerationkinetics: the Equipartition Kinetic Energy (EKE) and Size Independent (SI) kernels, whilethe coating kinetics is represented by a power law. Based on experimental data obtainedunder different operating conditions (melt and air atomization flowrates, air fluidizationvelocity, seed diameter and bed temperature), the coating and agglomeration kineticparameters are fitted to correctly predict the final particle size distributions. It is concludedthat the SI kernel and the zero-order coating kinetics best describe the agglomeration andcoating mechanisms, respectively. A correlation to predict the SI kernel from macroscopicvariables and properties of the system is proposed. This tool can be used to provide startingkernel factors for solving the PBEs governing spray-on melt granulation in fluidized-bedgranulators. Finally, a criterion to predict the limit of agglomeration occurrence isformulated. The criterion, which is developed in terms of dimensionless numbers thatdepend on process conditions and take into account mass, heat and momentum transferphenomena, is found to be appropriate to predict the growth regime for fluidized-bed sprayonmelt granulation of urea (i.e., the specific studied system).