Numerical study of cluster and particle rebound effects in a circulating fluidised bed

Abstract Gas–particle flows in a vertical two-dimensional configuration appropriate for circulating fluidised bed applications were investigated numerically. In the computational study presented herein the motion of particles was calculated based on a Lagrangian approach and particles were assumed to interact through binary, instantaneous, non-frontal, inelastic collisions including friction. The model for the interstitial gas phase is based on the Navier–Stokes equations for two-phase flows. The numerical study of cluster structures has been validated with experimental results from literature in a previous investigation. Numerical experiments were performed in order to study the effects of different cluster and particle rebound characteristics on the gas–particle flow behaviour. Firstly, we investigated the hard sphere collision model and its effect on gas–particle flow behaviour. The coefficient of restitution in an impact depends not only on the material properties of the colliding objects, but also on their relative impact velocity. We compared the effect of a variable restitution coefficient, dependent on the relative impact velocity, with the classical approach, which supposes the coefficient of restitution to be constant and independent of the relative impact velocity. Secondly, we studied the effects of different cluster properties on the gas–particle flow behaviour. Opposing clustering effects have been observed for different particle concentrations: within a range of low concentrations, groups of particles fall faster than individual particles due to cluster formation, and within a well-defined higher concentration range, return flow predominates and hindered settling characterises the suspension. We propose herein a drag law, which takes into account both opposing effects and have compared the resulting flow behaviour with that predicted by a classical drag law, which takes into account only the hindered settling effect.

[1]  D. Joseph,et al.  Nonlinear mechanics of fluidization of beds of spherical particles , 1987, Journal of Fluid Mechanics.

[2]  R. Whitmore,et al.  A generalized theory of sedimentation , 1958 .

[3]  C. Crowe,et al.  The Particle-Source-In Cell (PSI-CELL) Model for Gas-Droplet Flows , 1977 .

[4]  Jinghai Li,et al.  Discrete simulations of heterogeneous structure and dynamic behavior in gas-solid fluidization , 1999 .

[5]  Hans J. Herrmann,et al.  Collective drag and sedimentation: comparison of simulation and experiment in two and three dimensions , 1998 .

[6]  Kemal Tuzla,et al.  Parametric effects of particle size and gas velocity on cluster characteristics in fast fluidized beds , 2000 .

[7]  R. Clift,et al.  A NOTE ON TERMINOLOGY - CLUSTERS AND AGGLOMERATES , 1992 .

[8]  Said Elghobashi,et al.  On predicting particle-laden turbulent flows , 1994 .

[9]  S. Patankar.  Numerical Heat Transfer and Fluid Flow , 2018, Lecture Notes in Mechanical Engineering.

[10]  Y. Tsuji,et al.  Cluster patterns in circulating fluidized beds predicted by numerical simulation (discrete particle model versus two-fluid model) , 1998 .

[11]  B. J. Mason,et al.  The behaviour of clusters of spheres falling in a viscous fluid Part 1. Experiment , 1964, Journal of Fluid Mechanics.

[12]  R. Glowinski,et al.  Fluidization of 1204 spheres: simulation and experiment , 2002, Journal of Fluid Mechanics.

[13]  Claus Hübbe Ibsen,et al.  An Experimental and Computational Study of Gas-Particle Flow in Circulating Fluidised Reactors , 2002 .

[14]  Kakichi Hirai,et al.  Fluidization of Solid Particles , 1953 .

[15]  Masayuki Horio,et al.  THREE-DIMENSIONAL FLOW VISUALIZATION OF DILUTELY DISPERSED SOLIDS IN BUBBLING AND CIRCULATING FLUIDIZED BEDS , 1994 .

[16]  M. T. Mason,et al.  Two-Dimensional Rigid-Body Collisions With Friction , 1992 .

[17]  L. Fan,et al.  On the formation and disintegration of particle clusters in a liquid—solid transport bed , 1991 .

[18]  J. Kuipers,et al.  Granular dynamics simulation of cluster formation in dense riser flow , 1998 .

[19]  C. Wen.  Mechanics of Fluidization , 1966 .

[20]  E. Peirano.  Modelling and Simulation of Turbulent Gas-Solid Flows applied to Fluidization , 1998 .

[21]  Ahmad H. Kharaz,et al.  The measurement of particle rebound characteristics , 2000 .

[22]  J. Li,et al.  Flow structure formation in high-velocity gas-fluidized beds , 2002 .

[23]  Daniel D. Joseph.  Interrogation of Direct Numerical Simulation of Solid-Liquid Flow , 1999 .

[24]  A Note on Terminology , 1968 .

[25]  Lounes Tadrist,et al.  Numerical study of cluster formation in a gas–particle circulating fluidized bed , 2000 .

[26]  Arthur M. Squires,et al.  The Fast Fluidized Bed , 1976 .

[27]  Dimitri Gidaspow,et al.  Computation of flow patterns in circulating fluidized beds , 1990 .

[28]  Lounes Tadrist,et al.  Computational study of fluctuating motions and cluster structures in gas–particle flows , 2002 .

[29]  John M. Matsen,et al.  Mechanisms of choking and entrainment , 1982 .

[30]  Michel Y. Louge,et al.  Measurements of the collision properties of small spheres , 1994 .

[31]  D. Tabor.  A simple theory of static and dynamic hardness , 1948, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.