Evaluation of the effect of wall boundary conditions on numerical simulations of circulating fluidized beds

Abstract A computational fluid dynamics (CFD) modeling of the gas–solids two-phase flow in a circulating fluidized bed (CFB) riser is carried out. The Eularian–Eularian method with the kinetic theory of granular flow is used to solve the gas–solids two-phase flow in the CFB riser. The wall boundary condition of the riser is defined based on the Johnson and Jackson wall boundary theory ( Johnson & Jackson, 1987 ) with specularity coefficient and particle–wall restitution coefficient. The numerical results show that these two coefficients in the wall boundary condition play a major role in the predicted solids lateral velocity, which affects the solid particle distribution in the CFB riser. And the effect of each of the two coefficients on the solids distribution also depends on the other one. The generality of the CFD model is further validated under different operating conditions of the CFB riser.

[1]  Lounes Tadrist,et al.  Drag reduction and cluster formation in a circulating fluidised bed , 2007 .

[2]  Weixing Huang,et al.  Hydrodynamics and Flow Development in a 15.1 m Circulating Fluidized Bed Riser , 2007 .

[3]  Muthanna H. Al-Dahhan,et al.  Influence of solid-phase wall boundary condition on CFD simulation of spouted beds , 2012 .

[4]  R. Jackson,et al.  Frictional–collisional constitutive relations for granular materials, with application to plane shearing , 1987, Journal of Fluid Mechanics.

[5]  Madhava Syamlal,et al.  Evaluation of boundary conditions used to model dilute, turbulent gas/solids flows in a pipe , 2005 .

[6]  D. Gidaspow,et al.  A bubbling fluidization model using kinetic theory of granular flow , 1990 .

[7]  Sankaran Sundaresan,et al.  Coarse-Grid Simulation of Gas-Particle Flows in Vertical Risers , 2005 .

[8]  F. R. Steward,et al.  New closure models for CFD modeling of high-density circulating fluidized beds , 2006 .

[9]  S. Sundaresan,et al.  The role of meso-scale structures in rapid gas–solid flows , 2001, Journal of Fluid Mechanics.

[10]  Lothar Reh,et al.  Challenges of circulating fluid-bed reactors in energy and raw materials industries , 1999 .

[11]  X. Qi,et al.  Friction between gas–solid flow and circulating fluidized bed downer wall , 2008 .

[12]  Fariborz Taghipour,et al.  Computational fluid dynamics of high density circulating fluidized bed riser : Study of modeling parameters , 2008 .

[13]  S. Savage,et al.  Stresses developed by dry cohesionless granular materials sheared in an annular shear cell , 1984, Journal of Fluid Mechanics.

[14]  Jesse Zhu,et al.  Scale-Up Effect of Riser Reactors (1): Axial and Radial Solids Concentration Distribution and Flow Development , 2004 .

[15]  Rui Xiao,et al.  Modeling on the Hydrodynamics of a High-Flux Circulating Fluidized Bed with Geldart Group A Particles by Kinetic Theory of Granular Flow , 2010 .