Stochastic Modeling of Fluidized Bed Granulation: Influence of Droplet Pre-Drying

A stochastic Monte Carlo method was used to solve the population dynamics of fluidized-bed granulation. Special emphasis was put on the addition of liquid to the process and on the microprocess of droplet pre-drying. Pre-drying can occur during the flight of droplets from the tip of the nozzle to the fluidized bed, especially in top-spray configuration. A single-droplet drying model that considers the change of droplet diameter and of the radial concentration profile of binder in the droplet was developed and validated by experiments in an acoustic levitator. Combined with spray flow field considerations, this model can be used to retrieve an initial droplet diameter from spray measurements. Integrated in the Monte Carlo simulation, it shows that pre-drying can significantly decrease the agglomeration rate due to overspray and premature solidification instead of successful droplet deposition.