Investigation of the kinetics of fluidized bed spray agglomeration based on stochastic methods

Abstract

in Wiley Online Library (wileyonlinelibrary.com).Particle formation during fluidized bed spray agglomeration is modeled by a Monte Carlo method. The methodology is based on the micromechanisms occurring within the bed. The most important model parameters are identified as interparticle collision time, deposited droplet drying time and droplet addition time. It is found that a high number of collisions leads to a negligible role of the drying mechanism. In the real bed, however, the process is dependent on the gas inlet temperature. This indicates that the number of collisions relevant to agglomeration is relatively low. The accordance of the model with experimental results for variations of several process parameters demonstrates that the approach is a promising way to simulate the formation of agglomerates. In addition, the model is able to reproduce slower agglomeration at increased temperatures. This result is, for the first time, based on physical mechanisms rather than on the use of fitted agglomeration kernels.

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

“…An attempt of measurement by Buffiére and Moletta [20] refers to a three-phase fluidized bed and is therefore not applicable to gas fluidized beds. According to Terrazas-Velarde [12], too high values of collision frequency completely suppress the influence of thermal processes such as droplet drying, which is contradictory to experimental results.…”

“…Implemented microprocesses include droplet deposition on particles, drying and penetration, collision and rebound of particles, breakage and fragmentation. A comprehensive analysis of the upgraded model in comparison to Terrazas-Velarde et al [11,12] and to experimental results will be presented separately. Here, the discussion shall be concentrated on droplet addition and time step selection, as well as on the pre-drying of droplets prior to droplet-particle collision.…”

“…The focus is on the further development of the model of Terrazas-Velarde et al [11,12] in terms of simulated particle structure and the extension of internal coordinates describing the particle phase. The influence of thermal parameters, such as the gas inlet temperature, and material properties on the granulation result is taken into account by means of physical approaches for relevant microprocesses.…”

“…Microprocesses such as the spreading, penetration and drying of dispersed binder droplets on the particle surface can be modeled directly without fitting any kind of macroscopic kinetics. Terrazas-Velarde et al [11,12] used the MC method to model the agglomerate formation in fluid-bed processes. Their model overcomes the problems of discretization, does not require the application of the inverse method and can be compared directly to experimental data.…”

Particle Residence Times in Fluidized Bed Granulation Equipments

“…In that zone, particle coatings grow actively or rather liquid bridges between colliding particles are formed after the impact of particles with atomized droplets of binder or liquid. Meanwhile, further microprocesses do occur, comprising, e.g., droplet absorption or drying, which are described in detail by Terrazas-Velarde et al [10,11]. The second zone is the drying zone which can be characterized by the solidification and hardening of coatings and liquid bridges due to drying processes based on heat and mass transfer.…”