Development of an axisymmetric population balance model for spray drying and validation against experimental data and CFD simulations

An incremental model for spray drying, including a full droplet size distribution, has been implemented in a flowsheeting package incorporating tracking of distributed particle properties. Results were compared with expected trends based on standard theory and with results from a laboratory-scale spray dryer with a two-fluid nozzle for atomization. Predicted trends were as expected, with larger droplets giving substantially longer drying times and higher final moisture content. Predicted final moisture content was lower than measured values, as the very short residence times for fine particles were inadequately represented by first-order falling-rate drying kinetics. Dryer gas flow patterns were simulated by computational fluid dynamics. Calculated droplet residence times were much lower than for a plug-flow or fully mixed gas flow, because a high-velocity gas flow zone from the two-fluid atomizer persists down a substantial part of the dryer.