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

Han, Q., Yang, N., Zhu, J., & Liu, M. (2015). Onset velocity of circulating fluidization and particle residence time distribution: A CFD–DEM study. Particuology, 21, 187-195. https://doi.org/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

a School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
b State Key Laboratory of Multi-Phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
c College of Chemical Engineering, Sichuan University, Chengdu 610065, China

10.1016/j.partic.2014.10.011

Volume 21, August 2015, Pages 187-195

Received 19 February 2014, Revised 28 September 2014, Accepted 9 October 2014, Available online 28 February 2015, Version of Record 6 June 2015.

E-mail: nyang@home.ipe.ac.cn; jhzhu@scu.edu.cn

Highlights

• A method to calculate the onset velocity of liquid–solid fluidized bed was proposed by simulation.

• Onset velocity was determined by the fitted particle mean residence time vs. liquid velocity lines.

• Collisional parameters did not affect mean residence time and onset velocity.

• Humps and trailing on residence time distribution curves originated in particle-scale behavior.

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

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