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A CFD–DEM study of the behaviour of single-solid and binary mixtures in a pyramidal spouted bed

Particuology 2019年第1期17卷 79-91页

作者： Filippo Marchelli cristina moliner Barbara Bosio Elisabetta Arato Faculty of Science and Technology Free University of Bozen-BolzanoPiazza Universita 539100 BolzanoItaly Department of Civil Chemical and Environmental EngineeringUniversity of GenovaVia all'Opera Pia 1516145 GenovaItaly

We simulated a lab-scale cold-flow spouted bed through computational fluid dynamics (CFD), coupled with the discrete element method (DEM) for the solid phase, using a commercial CFD program, ANSYS FLUENT 18.0. To limit the computational expense, we tested both a simplified pseudo-2D geometry and a complete 3D geometry. We found that the Haider and Levenspiel drag model is suitable for the pseudo-2D geometry;however, this model does not correctly predict fluidisation in the 3D geometry. Conversely, the Gidaspow drag model behaves accurately in the 3D geometry but overestimates the motion of particles in the pseudo-2D geometry. We studied several single-solid and binary mixtures to assess the reproducibility of segregation phenomena. The pseudo-2D model was able to predict the onset and minimum spouting flow rates of all mixtures with good accuracy. An analysis of the volume fraction contours of the binary mixtures permitted us to confirm that segregation phenomena were correctly predicted at low gas velocities. We showed that segregation decreased as the inlet gas flow rate was increased. Calculations performed in the complete 3D geometry were preliminarily assessed as more reliable but required almost four times as much computational time as those for the pseudo 2D geometry.

关键词： Spouted beds Computational fluid dynamics Discrete element method Binary mixtures Segregation phenomena

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Spouting behaviour of binary mixtures in square-based spouted beds

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Particuology 2019年第2期17卷 193-201页

作者： cristina moliner Filippo Marchelli Massimo Curti Barbara Bosio Giorgio Rovero Elisabetta Arato Department of Civil Chemical and Environmental Engineering (DICCA) University of Genova (UNIGE) Genova Italy Faculty of Science and Technology Free University of Bolzano (UNIBZ) Bolzano Italy Department of Applied Science and Technology (DISAT) Polytechnic University of Turin (POLITO) Turin Italy

From experime nts, the influe nee of the physical characteristics of different bin ary mixtures of solids on the spouting regime of a pyramidal square-based spouted bed reactor is assessed. The applied methodology permits a more precise evaluation of the effects of the tested variables (diameter, density, sphericity) on the response variables (minimum air flows at which spouting begins and at which to maintain spouting con ditions). The associated pressure drops along the bed of particles a nd the height of the formed fountai n are analysed in each case. During the initial stages of fluidisation, binary mixtures containing different density ratios show dead zones. Segregation becomes more evident at large-size and high-density ratios. The lack of sphericity was found to be the main reason leading to blocking, channelling, and start-up problems when system failures occur. Nevertheless, the extent of segregation in all cases decreases with increasing the spouting velocity. In addition, a computational fluid dynamic model based on the discrete element method, previously validated for a single solid bed, is proposed as a tool to predict and evaluate potential segregation phenomena in binary mixtures. This model reproduced with high accuracy the encountered segregation phenomena. Its use may help define the technical limts inherent in the pyramidal spouted bed reactor.

关键词： Spouted bed reactor Segregation Computational fluid dynamics

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