Identification of regions in a spray dryer susceptible to forced agglomeration by CFD simulations

Agglomeration during spray drying improves the rehydration and flow properties of produced powders. However, tools for predicting agglomeration are rare. In this work a rigorous mapping approach incorporating number density and stickiness state of particles was developed for CFD simulations, which identifies different zones prone to coalescence and agglomeration inside a spray dryer. This approach was found to be quick, informative, reasonably accurate and resource efficient, as it bypasses the modelling of collision phenomena. The predictions were validated with experimental data of particle size distribution and SEM analyses of the powder morphology performed on samples produced in a lab-scale counter current spray dryer with varying two-nozzle- configurations. For the investigated dryer, the optimum nozzle configuration to achieve effective agglomeration was successfully identified and configurations yielding size enlargement dominated by coalescence could be distinguished. The developed method is generic and hence can be applied to find suitable location and angle for multiple atomization as well as fine returns in industrial practice to achieve controlled agglomeration. This study forms the fundament of a rigorous CFD model for agglomeration, which along with the findings from this study will allow the agglomeration phenomenon to be better understood and thus attain more efficient design, scale-up and operation of spray dryers.