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.
The present study describes the theoretical modeling of particle formation by agglomeration in fluidized beds. The model is mathematically solved by applying a stochastic Monte Carlo method. It takes into account the complete droplet history (predrying during flight, spreading, solidification and penetration after deposition on a particle) so that thermal effects such as the increase in fluidization gas mass flow or gas temperature have a physically based impact on process kinetics. Contradictions between measured and simulated particle moisture contents were found. Thus, we present a modified drying model and compare results with experimental data.
Stochastic Modeling of Particle Formation in Fluidized BedsThis paper presents a stochastic method to solve the population balance describing fluidized bed spray agglomeration. It dynamically develops a discrete sample of particles, presenting the entire solid holdup, under the influence of micro processes such as droplet addition, pre-drying and deposition on the particles. Special emphasis is put on the addition of liquid to the process, as well as on the micro process 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.
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