Cluster identification and characterization in the riser of a circulating fluidized bed from numerical simulation results

Abstract

A methodology of identification and characterization of coherent structures mostly known as clusters is applied to hydrodynamic results of numerical simulation generated for the riser of a circulating fluidized bed. The numerical simulation is performed using the MICEFLOW code, which includes the two-fluids IIT's hydrodynamic model B. The methodology for cluster characterization that is used is based in the determination of four characteristics, related to average life time, average volumetric fraction of solid, existing time fraction and frequency of occurrence. The identification of clusters is performed by applying a criterion related to the time average value of the volumetric solid fraction. A qualitative rather than quantitative analysis is performed mainly owing to the unavailability of operational data used in the considered experiments. Concerning qualitative analysis, the simulation results are in good agreement with literature. Some quantitative comparisons between predictions and experiment were also presented to emphasize the capability of the modeling procedure regarding the analysis of macroscopic scale coherent structures.

Numerical Simulation of Gas-Solid Flow in CFB Riser Using Different Approaches of Kinetic Theory of Granular Flows

“…In this work is used a Cartesian coordinate system considering uniform computational mesh in radial direction with 22 cells (δ x = 0.381 cm) and uniform in axial direction with 148 cells (δ y = 3.81 cm) totalizing a number of 2920 cells in the whole domain. An appropriateness of using this computational mesh for gas-solid flows simulation is discussed in Cabezas-Gómez et al (2008). The simulations with all models are performed for t = 100 seconds of fluidization.…”

Non-intrusive measurement and hydrodynamics characterization of gas–solid fluidized beds: a review

“…In a fluidized bed, particle clusters and agglomerate are defined as regions with higher solids concentration relative to the mean solids concentration, which are formed by a large number of particles assembling [76]. Such particle groups move as a whole without obvious internal slip motion.…”

Direct Numerical Simulation of Fluid Flow and Mass Transfer in Particle Clusters

“…Although there is no firmly established definition for a cluster, ,,,− one feature is universally accepted that a cluster is composed of particles and possesses an internal solid volume fraction significantly larger than its surroundings (which is normally below 0.1 in CFB). Clusters can be characterized by duration of their existence, occurrence frequency and internal solids concentration, as studied by Sharma et al and other researchers. − In the past decades, numerous empirical correlations for fluid-particle mass transfer have been proposed for multisphere systems. − Although these correlations are helpful for a quick and rough estimation of overall mass transfer behavior for design purposes, it does not consider the influence of particle heterogeneities. Significant deviations of the Sherwood number in risers have been reported, and Breault and Chalermsinsuwan et al pointed out these values even differ by several orders of magnitude.…”