Numerical Simulation of Gas-Solid Flow in Downer with a New Drag Model Based on the Fluidized Spatial Superposition

Nowadays,
substantial progress has been made in simulating downers by using two-fluid
model (TFM). Li et al. pointed out that the accuracy of the TFM model mainly
depended on the drag model. After that, the drag model continued to be
developed. Currently, three drag models that based on the homogeneous structure
or heterogeneous structure are often used by many researchers. However, these
models either simulation results
deviated from the experimental data greatly or considered most comprehensive
and sufficient so that need solve many structure parameters and equations. Therefore,
it is needed to construct a novel drag model that simultaneously considering
the two existing forms of particles in the downer and reducing the complexity
of the model for easy solution.

Fig.1. Decomposition of the control volume

In this work, the
heterogeneous multiphase flow structure is divided into dilute phase and
agglomerate phase, as shown in figure.1. Moreover, the dilute and agglomerate
particles are uniformly dispersed in the control volume and are fluidized by
all gas. Therefore, the real flow structure is formed by spatial superposing
the flow behavior of the dilute and agglomerate phase. According to this new
approach, five structure parameters were obtained and then used to calculate
the drag coefficient for a control volume, which is further incorporated into
the TFM. Finally, comparisons of the simulation results between this new drag modification
and the Wen & Yu/Ergun Equations are carried out to demonstrate that
present work have the capacity to capture major hydrodynamic features of downer
reactor.