Particle size and shape are two important properties affecting the force structure in particle pa... more Particle size and shape are two important properties affecting the force structure in particle packings. By means of discrete element method, we investigate the force ratios, force network and force probability distribution in the three-dimensional packing of fine ellipsoids. The simulation results demonstrate that with particle size decreasing, the linear relationship between contact force ratio and bed depth fluctuates more significantly for ellipsoids. The force network for coarse particles demonstrates that the forces can propagate in long chains in the vertical direction for spheres; while they become more complex and zigzag for ellipsoids. Similar to spheres, exponential relationship also exists between porosity and inter-particle force ratio for ellipsoids, but it is also a function of particle shape. The probability distribution of contact force and total (normal) force are examined in details to quantify the force variation in the disordered packings of fine ellipsoidal particles.
Industrial Engineering Chemistry Research, Oct 19, 2011
A CFD simulation was performed to evaluate the performance of a novel multiregime gasÀsolid fluid... more A CFD simulation was performed to evaluate the performance of a novel multiregime gasÀsolid fluidized riser reactor that was designed to maximize the propylene yield from the catalytic cracking process. Simulation results of the industrial-scale riser reactor show the coexistence of different regimes in the reactor. Also, both the outlet product compositions and the reaction rate vectors indicate that the cracking reactions mainly take place in the feed injection section. The product quality and distribution demonstrate the superiority of this novel process technology. The results of the CFD simulations are in good agreement with the test run results of a real industrial FCC reactor.
Discrete element modeling of gas fluidization of fine ellipsoidal particles
ABSTRACT Particle properties are important factors affecting gas fluidization. In the present wor... more ABSTRACT Particle properties are important factors affecting gas fluidization. In the present work, the effects of particle size and shape on the fluidization characteristics are studied using the combined approach of computational fluid dynamics for gas phase and discrete element method for particles. It shows that a bed becomes loosely packed when particle size becomes small. The minimum fluidization velocity increases exponentially with the increase of particle size. Higher minimum bubbling velocities are predicted for ellipsoidal particles compared with spherical ones. ``Chain phenomenon'' exists in the expanded and fluidized beds for fine prolate particles.
Particle-fluid interaction Particle-particle interaction Gas-solid fluidized bed Monodisperse Bin... more Particle-fluid interaction Particle-particle interaction Gas-solid fluidized bed Monodisperse Binarydisperse Both particle-fluid and particle-particle interactions have profound effects on particle segregation and aggregation phenomena. Numerically, these effects are taken into account through an appropriate drag law formulation that should be accurate enough to predict the overall particulate flow behavior. In this work, several drag law models are used to study their effects on particle segregation in a gas-solid fluidized bed. Compared to Syamlal and Bell model, the non-particle-particle drag model yields a significant particle separation in the axial direction, with the tendency of large particles to settle down in the bottom of the bed while small particles gather in the upper part of the bed. The predicted numerical results agree well with Mathiesen's experimental results. The segregation profiles generated by the ad hoc modified drag model and the binarydisperse Van der Hoef drag model are contradictory. Inverse segregation results from the use of the Van der Hoef drag model, which is similar to the Brazil Nut Effect, and the results show significant discrepancies from Mathiesen's experimental results.
A CFD simulation was performed to evaluate the performance of a novel multiregime gasÀsolid fluid... more A CFD simulation was performed to evaluate the performance of a novel multiregime gasÀsolid fluidized riser reactor that was designed to maximize the propylene yield from the catalytic cracking process. Simulation results of the industrial-scale riser reactor show the coexistence of different regimes in the reactor. Also, both the outlet product compositions and the reaction rate vectors indicate that the cracking reactions mainly take place in the feed injection section. The product quality and distribution demonstrate the superiority of this novel process technology. The results of the CFD simulations are in good agreement with the test run results of a real industrial FCC reactor.
A novel circulating fluidized bed riser which features an enlarged bottom and a draft tube has be... more A novel circulating fluidized bed riser which features an enlarged bottom and a draft tube has been introduced and investigated in terms of its applicability for FCC. Multi-flow regimes were observed in this novel riser, which had a dense bottom and a dilute upper region. The flow pattern in the bottom part almost had no effect on the flow behavior in the upper part. The dense bed height could be adjusted easily. A funnelform draft tube enabled the solids to follow two flow patterns: an upward flow to the riser top and a downward flow from the annulus to the riser bottom. A solids distribution ratio was proposed to qualify this distribution relationship. Furthermore, the flow structure in the bottom region was depicted, and an obvious core-annulus countercurrent structure was observed.
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