Numerical Investigation of Particles Breakage and Growth in Gas-Solid Processes: Spiral Jet Milling and Polyolefin Polymerization in Fluidized Bed Reactors

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A detailed CFD analysis of flow patterns and single-phase velocity variations in spiral jet mills affected by caking phenomena

8siIn this work we present a method to investigate the fluid-dynamics of a 3D, real-scale spiral jet mill when caking is occurring. CFD simulations are employed to deeply study the pressure and the velocity fields of the gas phase when the nozzles inlet pressure and the chamber diameter are varied to mimic the condition generated by the aggregates formation during the micronizaton process. The computational model is built replicating the experimental observation consisting in the fact that most of the crusts form on the outer wall of the chamber. Simulations underline that caking causes the deterioration of the classification capabilities of the system if the gas mass flow rate is kept constant at nozzles, allowing larger particles for escaping the system. It is shown that it is possible to mitigate this phenomenon by gradually reducing the gas mass-flow rate to keep constant the nozzles absolute pressure. This keeps unchanged the fluid spin ratio and the classification characteristics when caking is advancing.openopenSabia, Carmine; Frigerio, Giovanni; Casalini, Tommaso; Cornolti, Luca; Martinoli, Luca; Buffo, Antonio; Marchisio, Daniele L.; Barbato, Maurizio C.Sabia, Carmine; Frigerio, Giovanni; Casalini, Tommaso; Cornolti, Luca; Martinoli, Luca; Buffo, Antonio; Marchisio, Daniele L.; Barbato, Maurizio C

FBR for Polyolefin Production in Gas Phase: Validation of a Two-phase Compartmentalized Model by Comparison with CFD

Two different modeling approaches are applied in this work to the simulation of fluidized bed reactors containing solid particles of Geldart A-B type and operated at conditions typically used for polyolefins production. On one side, a fully detailed computational fluid dynamics (CFD) model is developed, considering a 2D planar geometry and a multi-fluid description with kinetic theory of granular flows. On the other, a conventional three-phase, 1D compartmentalized model (SCM) is also developed, implementing the fluid dynamic description based on popular, semi-empirical relationships available in the literature. Given the huge difference of computational effort associated with the corresponding numerical solutions, our aim is to confirm the reliability of the simplified model by comparison with the results of the detailed CFD model. The comparison is carried out considering the fluidization of a bed of solid particles without reaction and solid injection or withdrawal, thus focusing on the steady-state fluid dynamic behavior of the expanded bed. Three different gas velocities and different monodisperse and polydisperse particle populations are analyzed. The results show that the oversimplified compartmentalized approach is capable to predict the solid mixing features established inside the reactor operated in bubbling fluidization regime with good reliability for non-reactive polyethylene particles. Average solid volume fractions are particularly close to the values predicted by the CFD model when monodisperse particles are considered inside the examined range of gas velocity values. A generally good agreement is also found when solids with broad size distribution are analyzed. Overall, these comparisons provide a meaningful validation of the simplified compartmentalized models: given their negligible computational demand and general versatility (complex kinetic schemes and single particle models are easily accounted for), they still represent an effective tool of industrial process design

Comparison between detailed (CFD) and simplified models for the prediction of solid particle size distribution in fluidized bed reactors

This work is aimed at developing a simplified model suitable to effectively describe the fluidization behavior within fluidized beds with minimal computational efforts. The simplified model was validated through detailed CFD Euler-Euler simulations showing a good agreement in the case of large particles (about 450 micron) at all the gas velocities considered (20, 40, 61 cm/s). Slightly less accurate outcomes were observed for smaller particles (about 220 micron). This was due to the underestimation of the particle size effect on the fluidization behavior by the simplified approach

A novel uncoupled quasi-3D Euler-Euler model to study the spiral jet mill micronization of pharmaceutical substances at process scale: model development and validation

In this work we present a novel approach to model the micronization of pharmaceutical ingredients at process scales and times. 3D single-phase fluid-dynamics simulations are used to compute the gas velocity field within a spiral jet mill which are provided as input in a 1D compartmentalized model to calculate solid velocities along the radial direction. The particles size reduction is taken into account through a breakage kernel that is function of gas energy and local solid holdup. Simulation results are validated against micronization experiments for lactose and paracetamol, comparing the model predictions with D10, D50 and D90 diameters values coming from Design of Experiments isosurfaces. The developed model allows for a fair estimation of the outlet particle size distribution in a short computational time, with very good predictions especially for D90 values

Asthma in patients admitted to emergency department for COVID-19: prevalence and risk of hospitalization

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