Dispersion of lateral and axial solids in a cocurrent downflow circulating fluidized bed

Axial and lateral mixing of fine particles in a binary-solid riser have been investigated using a phosphor tracer method. The measured bimodal residence time distribution (RTD) demonstrated two types of axial dispersions of the fines: the dispersion of discrete particles and that of clusters. A proposed one-dimensional, bimodal dispersion model describes the bimodal RTDs very well. The axial Peclet number of the fines is not sensitive to the fraction of coarse particles, gas velocity and solids circulation rate. Lateral solids dispersion was determined by measuring the solids RTD at different radii using a point source tracer injection. A two-dimensional dispersion model describes the measured RTDs satisfactorily. Lateral solids mixing decreased as coarse particles were added into the riser. Correlations of the axial and lateral Peclet numbers obtained fit the experimental data well.On a etudie le melange axial et lateral de particules fines dans une colonne montante binaires-solides a l'aide d'une methode de traqage au phospore. La distribution du temps de sejour (DTS) bimodale mesuree illustre deux types de dispersions axiales des particules fines: la dispersion de particules discretes et la dispersion de grappes. On propose un modele de dispersion unidimensionnel bimodal qui decrit tres bien la DTS bimodale. Le nombre de Peclet axial des fins n'est pas sensible a la fraction des particules grossieres, a la vitesse du gaz et a la vitesse de circulation des solides. On a determine la dispersion laterale des solides en mesurant la DTS des solides a differents rayons a I'aide d'une injection de traceur ponctuelle. Un modele de dispersion bidimensionnel decrit les DTS de maniere satisfaisante. Le melange lateral des solides diminue avec I'ajout de particules grossieres dans la colonne. Des correlations obtenues pour les nombres de Peclet axial et lateral montrent un bon accord avec les donnees experimentales.

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“…Details of the apparatus and the phosphor tracer method have been reported elsewhere (Wei et al, 1994). …”

Section: Experimental Apparatus and Tracer Methodsmentioning

confidence: 99%

Axial and lateral dispersion of fine particles in a binary‐solid riser

Wei

Cheng

et al. 1998

Can J Chem Eng

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“…A series of hydrodynamic experiments Ž were carried out by Jin's group Wang et al, 1992;Cao et al, . 1994;Wei et al, 1994 in a 14-cm modified riser-downer combination unit. Work on the formation of homogeneous downflow gasrsolid suspensions at high velocities was re-Ž .…”

Section: Introductionmentioning

confidence: 99%

Characterization of downflowing high velocity fluidized beds

Cao

Weinstein

2000

AIChE Journal

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“…The axial dispersion coefficient for the solids can be determined from the Bodenstein number by the following correlation as a function of the Reynolds number and the voidage according to Wei et al [12]. …”

Section: Materials Balances For the Downer Reactormentioning

confidence: 99%

Computer Simulation of the Performance of a Downer-Regenerator CFB for the Partial Oxidation of n-Butane to Maleic Anhydride

Emig

May

Scheidel

2002

Chem. Eng. Technol.

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A reactor model for a downer‐regenerator circulating fluidized‐bed (CFB) during the partial oxidation of n‐butane to maleic anhydride is presented. Upflow reactors (risers) suffer from severe solids back mixing and gas‐solids‐separation, in comparison down flow reactors exhibit a more uniform gas‐solids flow and reduced backmixing, resulting in narrower residence time distributions. Due to the sensitivity of the VPO catalyst to over‐reduction, downer reactors present an interesting alternative to riser reactors. The reactor models for the downer and the regenerator fluidized‐bed are coupled with reduction and oxidation kinetics for the catalyst, respectively. The influence of the solids residence time distributions for the combined system of both reactors on the oxidation state of the catalyst is explored by a novel newly developed oxygen loading distribution. Simulation results suggest the limited solids‐flux in downers restrict the maximum butane concentrations, while the scale‐up is predicted to be uncritical.

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Dispersion of lateral and axial solids in a cocurrent downflow circulating fluidized bed

Cited by 69 publications

References 4 publications

Axial and lateral dispersion of fine particles in a binary‐solid riser

Axial and lateral dispersion of fine particles in a binary‐solid riser

Characterization of downflowing high velocity fluidized beds

Computer Simulation of the Performance of a Downer-Regenerator CFB for the Partial Oxidation of n-Butane to Maleic Anhydride

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