Flow structure formation and evolution in circulating gas-fluidized beds--颗粒学报PARTICUOLOGY

Li, J., & Kuipers, J. A. M. (2004). Flow structure formation and evolution in circulating gas-fluidized beds. China Particuology, 2(1), 1-12. https://doi.org/10.1016/S1672-2515(07)60013-X

Flow structure formation and evolution in circulating gas-fluidized beds

Jie Li ^{a b *}, J.A.M. Kuipers ^a

a Department of Chemical Engineering, Twente University, Enschede, 7500 AE, The Netherlands
b Materials Science Division, Argonne National Laboratory, Argonne, IL. 60439, USA

10.1016/S1672-2515(07)60013-X

Volume 2, Issue 1, February 2004, Pages 1-12

Received 2 September 2003, Accepted 12 December 2003, Available online 27 November 2007.

E-mail: jieli@anl.gov

Highlights

Abstract

The occurrence of heterogeneous flow structures in gas-particle flows seriously affects the gas-solid contacting and transport processes in high-velocity gas-fluidized beds. Particles do not disperse uniformly in the flow but pass through the bed in a swarm of clusters. The so-called “core-annulus” structure in the radial direction and “S” shaped axial distribution of solids concentration characterize the typical flow structure in the system.

A computational study, using the discrete particle approach based on molecular dynamics techniques, has been carried out to explore the mechanisms underlying formation of the clusters and the core-annulus structure. Based on energy budget analysis including work done by the drag force, kinetic energy, rotational energy, potential energy, and energy dissipation due to particle-particle and particle-wall collisions, the role of gas-solid interaction and inelastic collisions between the particles are elucidated.

It is concluded that the competition between gas-solid interaction and particle-particle interaction determines the pattern formation in high-velocity gas-solid flows: if the gas-solid interaction (under elevated pressure) dominates, most of particle energy obtained by drag from the gas phase is partitioned such that particle potential energy is raised, leading to a uniform flow structure. Otherwise, a heterogeneous pattern exists, which could be induced by both particle-particle collisions and gas-solid interaction. Although both factors could cause the flow instability, the non-linear drag force is demonstrated to be the necessary condition to trigger heterogeneous flow structure formation. As gas velocity increases and goes beyond a critical value, the fluid-particle interaction suppresses particle collisional dissipation, and as a consequence a more homogeneous flow regime is formed.

Graphical abstract

Keywords

flow structures; particle collision; gas-solid interaction; nonlinear drag; circulating gas-fluidized beds

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