Flow structures in the downer circulating fluidized bed

Lu, Xuesong; Li, Songgeng; Du, Lin; Yao, Junqiang; Wei, Lin; Li, Hongzhong

doi:10.1016/j.cej.2005.06.002

Cited by 46 publications

(19 citation statements)

References 19 publications

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“…Wang et al 7 specified the flow patterns of clusters and the dispersed particles in a riser by positive and negative peaks of the detail signals from wavelet multiresolution analysis of the simulated particle concentration fluctuations. Lu et al 21 also determined the cluster frequency and size by the cross-correlation and wavelet analysis of local voidage signals in a downer CFB. Guenther and Breault 14 analyzed the fiber optic signals by using discrete wavelet analysis to characterize the dynamic behavior of clusters of cork particles at different axial and radial positions in a large scale CFB operated at three different flow regimes.…”

Section: Introductionmentioning

confidence: 99%

Multiresolution analysis on identification and dynamics of clusters in a circulating fluidized bed

Yang

Leu

2009

AIChE Journal

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). An appropriate level of approximation subsignal was systematically specified as a threshold for cluster identification, based on multiresolution analysis (MRA) of wavelet transformation. By the established threshold, the dynamic properties of clusters including the appearance time fraction of clusters F cl , average cluster duration time s cl , cluster frequency f cl , and local average solids holdup in clusters e sc , at different radial and axial positions were determined under the turbulent, transition and fast fluidization flow regimes. The results also describe the dynamic properties of clusters and flow patterns in the splash zone along with the dense bottom region of the circulating fluidized beds.

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Section: Introductionmentioning

confidence: 99%

Multiresolution analysis on identification and dynamics of clusters in a circulating fluidized bed

Yang

Leu

2009

AIChE Journal

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“…Compared with the up-flow fast fluidized bed riser, downer reactors of fluidized bed have many advantages such as good gas-solids contact, less gas and solids back-mixing, a short contact time and more uniform residence time distribution. (Srivastava et al 1998;Lehner and Wirth 1999;Cheng et al 1999;Liu et al 2001;Li et al 2004;Lu and Gidaspow 2003;Lu et al 2005;Luo et al 2007;Wu et al 2008;He et al 2009a, b). Computational fluid dynamics (CFD) with an Euler-Euler two-fluid modeling approaches has been widely used to predict hydrodynamics in circulated fluidized bed.…”

Section: Introductionmentioning

confidence: 94%

Hydrodynamic Modeling of Dense Gas-Particle Turbulence Flows Under Microgravity Space Environments

Liu

Kallio

2010

Microgravity Sci. Technol.

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An Euler-Euler two-fluid model based on the second-order-moment closure approach and the granular kinetic theory of dense gas-particle flows was presented. Anisotropy of gas-solid two-phase stress and the interaction between two-phase stresses are fully considered by two-phase Reynolds stress model and the transport equation of two-phase stress correlation. Under the microgravity space environments, hydrodynamic characters and particle dispersion behaviors of dense gas-particle turbulence flows are numerically simulated. Simulation results of particle concentration and particle velocity are in good agreement with measurement data under earth gravity environment. Decreased gravity can decrease the particle dispersion and can weaken the particle-particle collision as well as it is in favor of producing isotropic flow structures. Moreover, axial-axial fluctuation velocity correlation of gas and particle in earth gravity is approximately 3.0 times greater than those of microgravity and it is smaller than axial particle velocity fluctuation due to larger particle inertia and the larger particle turbulence diffusions.Y. Liu (B) Marine Engineering College,

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“…Wavelets have been used successfully to investigate pressure fluctuations in a bubbling bed (Lu and Li, 1999) and clusters in the downer of a circulating fluidized bed (Lu et al, 2005). In these investigations, flow conditions produced very clear spikes in time series representing the passing of a bubble (using high frequency components in the pressure fluctuation signals) or a cluster (using micro-video data).…”

Section: Data Processingmentioning

confidence: 99%

Clusters identification and characterization in a gas–solid fluidized bed by the wavelet analysis

2009

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The local solid flow structure of the bubbling fluidized bed of sand particles was investigated in order to identify and characterize the clusters. Extensive experiments were carried out using an optical fibre probe, measuring the velocity and the diameter of clusters. Under all operating conditions, ascending and descending clusters co-existed at all measurement locations. The locus of the inversion point at which the directions of cluster motion changed was determined. The velocity of the ascending clusters was a function of both superficial gas velocity and the radial and axial position. With increasing superficial gas velocity, both the velocity and the diameter of ascending clusters decreased near the wall. However, the velocity of descending clusters depended mainly on superficial gas velocity and the largest clusters existed closer to the wall. The results of this study help to explain cluster hydrodynamics in fluidized beds.On aétudié la structure locale de l'écoulement des solides dans un lit fluidisé bullant de particules de sable dans le but de déterminer et caractériser le phénomène d'agrégation. Des expériences approfondies ontété menéesà l'aide d'une sondeà fibres optiques, qui mesure la vitesse et le diamètre des agrégats. Les résultats montrent dans toutes les conditions opératoires la coexistence d'agrégats qui montent et qui descendent aux endroits où ontété prises les mesures. L'emplacement du point d'inversion où se produisent les changements de direction des agrégats aété déterminé. La vitesse des agrégats ascendants est fonctionà la fois de la vitesse de gaz superficielle et de la position tant radiale qu'axiale. Avec l'augmentation de la vitesse de gaz superficielle, la vitesse des agrégats ascendants diminue près des parois. La même tendance est observée pour le diamètre des agrégats ascendants. Toutefois, la vitesse des agrégats descendants dépend principalement de la vitesse de gaz superficielle et les plus gros agrégats se trouvent plutôt près des parois. Les résultats de cetteétude contribuentà la compréhension des agrégats dans les lits fluidisés.

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Flow structures in the downer circulating fluidized bed

Cited by 46 publications

References 19 publications

Multiresolution analysis on identification and dynamics of clusters in a circulating fluidized bed

Multiresolution analysis on identification and dynamics of clusters in a circulating fluidized bed

Hydrodynamic Modeling of Dense Gas-Particle Turbulence Flows Under Microgravity Space Environments

Clusters identification and characterization in a gas–solid fluidized bed by the wavelet analysis

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