Numerical simulation of flow behavior of particles and clusters in riser using two granular temperatures

Cluster in CFB riser significantly affects performance of circulating fluidized beds. To model hydrodynamic behavior in CFB risers, three phase flows were assumed in the riser, the gas phase, the dispersed particle phase, and the clusters phase. The gas–solid multi-fluid model is extended to give the macroscopic averaged equations with constitutive equations for both particle phases from kinetic theory of granular flow. The clusters and the dispersed particles have their own fluctuating energy or two individual granular temperatures. Interactions between the cluster and its surrounding dispersed particles were obtained from kinetic theory of granular flow. Drag force for gas to dispersed particles and the clusters are empirically determined. The momentum exchange between dispersed particles and clusters is modeled using the concept of molecular dynamics. Cluster properties are predicted with the cluster-based approach. The distributions of volume fractions and velocities of gas, dispersed particles and clusters are predicted. Computed solid mass fluxes and volume fractions agree with Manyele et al. [S.V. Manyele, J.H. Parssinen, J.X. Zhu, Characterizing particle aggregates in a high-density and high-flux CFB riser, Chemical Engineering Journal, 88 (2002) 151–161.] and Knowlton [T.M. Knowlton, Modelling benchmark exercise. Workshop at the Eighth Engineering Foundation Conference on Fluidization, Tours, France, 1995.] experimental data.

To model hydrodynamic behavior of clusters in risers, three phase flows were assumed in the riser, the gas phase, the dispersed particle phase, and the clusters phase. A gas-solid multi-fluid model was proposed with specifically considering particle and cluster flows. Interactions between the cluster and its surrounding dispersed particles were obtained from kinetic theory of granular flow. The fluctuating energy or granular temperatures of clusters and dispersed particles were predicted. The clusters and dispersed particles have different granular temperature in riser. The granular temperatures of dispersed particles and clusters decrease with the increase of volume fraction of particles phases. The cluster diameters increase with the increase of volume fraction of clusters. Computed solid mass fluxes and volume fractions agree with the measured data.Figure optionsDownload as PowerPoint slide