The characterization of flow patterns in downflow reactors has progressed significantly in recent years (1,2). Major advances have been made in the development of fiber optic sensors and in the characterization of particle clusters (3,4). It is felt however, that Computational Particle Fluid Dynamics (CPFD) simulation may assist considerably towards a complete flow pattern characterization. The present study contributes with a fluid dynamic simulation based on the numerical solution of continuity and momentum balance equations in a 3D framework using CPFD's Barracuda software. The proposed model includes both a configuration and specific CD drag coefficients recommended for down flow reactors. The CPFD simulation conditions selected in this study correspond to actual flow conditions used in a gas-solid down flow reactor unit with FCC particles. Model results are established in the context of stabilized solid and fluid flow patterns which involve numerical calculations in excess of 1.5 second. The CPFD model predicts local densification of solids. In addition, the model forecasts higher particle velocities than gas velocities once the flow reaches an axial position from the gas injector larger than 1 meter (z> 1m).These expected findings are accompanied with valuable original observations about the intrinsic rotational character of the flow in downer reactors. Numerical 3D calculations show that both gas and particle velocities involve the following: a) axial velocity component, b) later velocity component (about 5% of axial velocity component), c) angular velocity component. The relevance of the observed velocity components for determining the rotational flow pattern are established for a significant range of operational conditions and solid flux/gas flux ratios.
(1) Cheng, Y.; Wu, C.; Zhu, J.; Wei, F.; Jin, Y. Downer reactor: From fundamental study to industrial application. Powder Technol. 2008, 183, 364-384; (2)Zhao, Y.; Ding, Y.; Wu, C.; Cheng, Y. Numerical simulation of hydrodynamics in downers using a CPFD–DEM coupled approach. Powder Technol. 2010. 199, 2-12; (3) Nova, S. R.; Krol, S.; de Lasa, H. Particle velocity and particle clustering in down-flow reactors. Powder Technol. 2004, 148, 172–185; (4) Islam, M. A.; Krol, S.; de Lasa, H. I. Slip velocity in downer reactors: Drag coefficient and the influence of operational variables. Ind. Engng. Chem. Res. 2010. 49, 6735-6744; (5) Snider, D. M. Three fundamental granular flow experiments and CPFD predictions. Powder Technology. 2007, 176, 36–46.
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