Hydrodynamic modelling of circulating fluidised beds

Abstract

Abstract-A one-dimensional model for the riser section of a circulating fluidised bed has been developed which describes the steady-state hydrodynamic key variables in the radial direction for fully developed axisymmetric flow. Both the gas and the solid phase are considered as two continuous media, fully penetrating each other. As a first approximation gas phase turbulence has been incorporated in our hydrodynamic model by applying a slightly modified version of the well-known Prandtl mixing length model. To solve the resulting set of transport equations, the solids distribution along the tube radius is required. Several strategies are given to obtain this information. In addition the effect of clusters on the momentum transfer between both phases has been modelled using an empirical correlation. Theoretically calculated results agree welt with reported experimental data of different authors.

A review of multiscale CFD for gas–solid CFB modeling

“…Clearly big discrepancies exist on their estimation of the drag coefficient. In general, besides EMMS/matrix, we may distinguish two trends of drag correction within these correlations: the first is represented by the work of Yang et al (2004), which undergoes a steep drop due to initial clustering and then gradual increase with solid concentration; the second is represented by the correlation of Nieuwland et al (1994), which decays monotonically with the increase of solids volume fraction. There are also some other contributions need to mention, such as O'Brien and Syamlal (1993), Andrews et al (2005), which were proposed for specific set of operating conditions and hence hard to compare within this work.…”

Searching for a mesh-independent sub-grid model for CFD simulation of gas–solid riser flows

“…Sub-grid models can be obtained through empirical correlations (Nieuwland et al, 1994;O'Brien and Syamlal, 1993) or through analyzing details achieved from fine-grid simulations, as is the situation that DNS of Navier-Stokes equations are used to obtain large eddy information for single phase turbulent flows. Agrawal et al (2001) pioneered the latter approach to explore the effect of unresolved structures on the drag force.…”

The role of meso-scale structures in rapid gas–solid flows

“…At the same time, various research groups Enwald, Peirano & Almstedt 1997;Nieuwland et al 1995Nieuwland et al , 1996Samuelsberg & Hjertager 1996;Tsuo & Gidaspow 1990;Gidaspow 1993Gidaspow , 1994 have pursued research on simulation of riser flows through direct numerical integration of the locally averaged equations. These simulations do reveal the presence of persistent fluctuations and particle clusters.…”