Analysis of a Three-Zone Model for Melt Granulation in a Continuous Fluidized Bed

BERTIN, DIEGO ESTEBAN; BUCALÁ, VERÓNICA; PIÑA, JULIANA

Nuremberg, Alemania

Congreso; World Congress on Particle Technology; 2010

In the industrial fluidized bed melt granulation processes, molten material is atomized onto the bed of fluidized particles by means of several nozzles. The particles grow by solidification of the tiny melt droplets deposited on the solids surface area. Although the particles are usually fully mixed on the entire volume of the bed, the droplets are concentrated in a zone close to the atomization nozzles. Due to the non-homogeneous distribution of the coating material, uniform growth along the granulator height is not always a good assumption. As an alternative to model these processes, the bed can be divided into three zones: a lower zone whose height is fixed and equal to the  height  of  the  atomizing  nozzles,  a  spray  (or  middle)  zone  whose  height depends of  the penetration depth of  the spray  jet and an upper  zone where only particles mixing  takes place. The proposed model is particularly applied to the production of granular urea in an industrial multichamber fluidized bed. The relative importance of the three- and one- (perfectly-mixed) zone models is thoroughly studied by simulation of mass, energy, momentum and population balances.