Partic. vol. 21 pp. 187-195 (August 2015)
doi: 10.1016/j.partic.2014.10.011

Onset velocity of circulating fluidization and particle residence time distribution: A CFD–DEM study

Qiqi Han^{a, b}, Ning Yang^{b, *}, Jiahua Zhu^{c, *}, Mingyan Liu^a

nyang@home.ipe.ac.cnjhzhu@scu.edu.cn

Abstract

Until now, the onset velocity of circulating fluidization in liquid–solid fluidized beds has been defined by the turning point of the time required to empty a bed of particles as a function of the superficial liquid velocity, and is reported to be only dependent on the liquid and particle properties. This study presents a new approach to calculate the onset velocity using CFD–DEM simulation of the particle residence time distribution (RTD). The onset velocity is identified from the intersection of the fitted lines of the particle mean residence time as a function of superficial liquid velocity. Our results are in reasonable agreement with experimental data. The simulation indicates that the onset velocity is influenced by the density and size of particles and weakly affected by riser height and diameter. A power-law function is proposed to correlate the mean particle residence time with the superficial liquid velocity. The collisional parameters have a minor effect on the mean residence time of particles and the onset velocity, but influence the particle RTD, showing some humps and trailing. The particle RTD is found to be related to the particle trajectories, which may indicate the complex flow structure and underlying mechanisms of the particle RTD.

Graphical abstract

Keywords

Discrete element method (DEM); Computational fluid dynamics (CFD); Liquid–solid circulating fluidized bed; Particle residence time distribution; Onset velocity