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

BERTIN, DIEGO; COTABARREN, IVANA; BUCALÁ, VERÓNICA; PIÑA, JULIANA

Nuremberg

Congreso; World Congress on Particle Technology 6; 2010

partec

A steady-state model of the continuous industrial fluidized bed granulator for urea production is presented, based in mass, energy, momentum and population balances. Because the non-uniformity of mass of coating on fluidized beds observed in different studies suggests that the assumption of perfect mixing for particles is not always correct, the total volume of each growth chamber is divided in three perfectly mixed zones: a lower zone whose length is fix and equal to the height of the atomizing nozzles, a spray (or middle) zone whose length depends of the penetration depth of the spray jet and an upper zone where only occurs mixing of the particles. The interface between the lower and spray zones determines the output of the urea solution and the atomization air through the nozzles. The mathematical model is formulated considering that the particles within each zone are perfectly mixed. The only growth process taken into account is accretion and takes place within the spray zone in the growth chambers. The two-phase theory is considered for the air, assuming plug flow for the emulsion and bubbles. The water evaporation occurs at the droplet-emulsion gas interphase; once the water vapor reaches the emulsion phase may be transported to the bubbles. energy balance for air is implemented assuming that the air in the emulsion and bubble phases are at the same temperature at each value of the axial coordinate. The particles flowrates between zones and the spray length for each growth chamber are estimated by means of correlations obtained from literature.