Effects of particle size and concentration on bubble coalescence and froth formation in a slurry bubble column--颗粒学报PARTICUOLOGY

Sarhan, A. R., Naser, J., & Brooks, G. (2018). Effects of particle size and concentration on bubble coalescence and froth formation in a slurry bubble column. Particuology, 36, 82-95. https://doi.org/10.1016/j.partic.2017.04.011

Effects of particle size and concentration on bubble coalescence and froth formation in a slurry bubble column

A.R. Sarhan ^{a b}, J. Naser ^a^*, G. Brooks ^a

a Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
b Department of Mechanical Engineering, University of Anbar, Ramadi, Anbar 31001, Iraq

10.1016/j.partic.2017.04.011

Volume 36, February 2018, Pages 82-95

Received 30 July 2016, Revised 6 April 2017, Accepted 18 April 2017, Available online 1 September 2017, Version of Record 22 December 2017.

E-mail: jnaser@swin.edu.au

Highlights

• A new approach for simulating the formation of a froth layer in slurry bubble column was proposed.

• The effects of hydrophilic particles on bubble dynamics in a multiphase system were proposed.

• Effects of particle size and concentration on gas holdup and coalescence efficiency were studied.

• Froth density for froth with different particles size was predicted.

Abstract

A new approach for simulating the formation of a froth layer in a slurry bubble column is proposed. Froth is considered a separate phase, comprised of a mixture of gas, liquid, and solid. The simulation was carried out using commercial flow simulation software (FIRE v2014) for particle sizes of 60–150 μm at solid concentrations of 0–40 vol%, and superficial gas velocities of 0.02–0.034 m/s in a slurry bubble column with a hydraulic diameter of 0.2 m and height of 1.2 m. Modelling calculations were conducted using a Eulerian–Eulerian multiphase approach with k–ε turbulence. The population balance equations for bubble breakup, bubble coalescence rate, and the interfacial exchange of mass and momentum were included in the computational fluid dynamics code by writing subroutines in Fortran to track the number density of different bubble sizes. Flow structure, radial gas holdup, and Sauter mean bubble diameter distributions at different column heights were predicted in the pulp zone, while froth volume fraction and density were predicted in the froth zone. The model was validated using available experimental data, and the predicted and experimental results showed reasonable agreement. To demonstrate the effect of increasing solid concentration on the coalescence rate, a solid-effect multiplier in the coalescence efficiency equation was used. The solid-effect multiplier decreased with increasing slurry concentration, causing an increase in bubble coalescence efficiency. A slight decrease in the coalescence efficiency was also observed owing to increasing particle size, which led to a decrease in Sauter mean bubble diameter. The froth volume fraction increased with solid concentration. These results provide an improved understanding of the dynamics of slurry bubble reactors in the presence of hydrophilic particles.

Graphical abstract

Keywords

Computational fluid dynamics; Slurry concentration; Gas holdup; Particle size; Froth; Coalescence efficiency

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