XXXI International Mineral Processing Congress 2024 Proceedings Page 1897 (1921 of 3836)

1986
A Computational Study on the Hydrodynamics and Particle
Transport in a Laboratory-Scale Reflux Classifier
Mst Farhana Diba, Dion Weatherley, Kym Runge
Julius Kruttschnitt Mineral Research Centre, Sustainable Minerals Institute, The University of Queensland
Joshua Starrett, Kevin Galvin
ARC Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals, Newcastle Institute for Energy and
Resources, The University of Newcastle.
ABSTRACT: The performance of a Reflux Classifier (RC) depends on the hydrodynamics of a fluidised bed
and its transport mechanisms. The detailed hydrodynamics inside an RC cell are very difficult to measure
experimentally. However, they can be simulated computationally. In this work, a 3D model is developed to study
how the hydrodynamics of the laboratory-scale RC affect the particle size partition curve using a Computational
Fluid Dynamics (CFD) technique. The results are compared with experimental measurements. This comparison
shows that the simulations reproduce the important features of the experimental measurements, validating the
model developed and allowing the hydrodynamic behaviour influencing these measurable phenomena to be
explored computationally.
INTRODUCTION
Gravity separation, a physics-based process that offers
cost-effective separation of solid particles, has been widely
applied in the coal and mineral processing industry (He
et al., 2020). The Reflux Classifier, devised by Prof. Kevin
Galvin (Galvin, 2003), operates on the principles of the
Boycott effect (Boycott, 1920), serving as a density-based
gravity separation unit. Comprising a fluidised bed located
below a set of parallel inclined channels, the classifier facili-
tates the dispersion and segregation of solid particles (refer
to Figure 1) (Galvin &Nguyentranlam, 2002). The lower
fluidised bed functions as an autogenous dense medium
dominated by the hindered settling mechanism, with par-
ticle terminal velocity playing a crucial role (Amariei et
al., 2014 Galvin et al., 2020a). The inclined plates intro-
duce a sedimentation area, promoting gravity separation
governed by the Boycott effect. Particle settling behaviour
on the inclined plates relies on available surface area and
vertical settling velocity (Nakamura, 1937 Tarpagkou &
Pantokratoras, 2014). Previous studies investigated the
impact of inclined channels on particle size classification,
supporting the notion of an optimal inclination angle of
70 degrees relative to the horizontal (Doroodchi, Galvin,
&Fletcher, 2005 Galvin et al., 2020a, 2020b Galvin &
Nguyentranlam, 2002 Galvin, Walton, &Zhou, 2009
Laskovski et al., 2006 Peng, Galvin, &Doroodchi, 2019
Starrett &Galvin, 2023). It was also noted that closely
spaced inclined channels, under specific conditions, gen-
erate high shear rates capable of overcoming particle ter-
minal settling velocity, enhancing particle transport along
the inclined surface. Additionally, laminar flow in narrow,
inclined channels facilitates a linear velocity distribution,
enabling particle elutriation at the same hydraulic velocity
and thus segregating particles based on density while elimi-
nating size-based separation. These observations indicate

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Extracted Text (may have errors)

1986
A Computational Study on the Hydrodynamics and Particle
Transport in a Laboratory-Scale Reflux Classifier
Mst Farhana Diba, Dion Weatherley, Kym Runge
Julius Kruttschnitt Mineral Research Centre, Sustainable Minerals Institute, The University of Queensland
Joshua Starrett, Kevin Galvin
ARC Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals, Newcastle Institute for Energy and
Resources, The University of Newcastle.
ABSTRACT: The performance of a Reflux Classifier (RC) depends on the hydrodynamics of a fluidised bed
and its transport mechanisms. The detailed hydrodynamics inside an RC cell are very difficult to measure
experimentally. However, they can be simulated computationally. In this work, a 3D model is developed to study
how the hydrodynamics of the laboratory-scale RC affect the particle size partition curve using a Computational
Fluid Dynamics (CFD) technique. The results are compared with experimental measurements. This comparison
shows that the simulations reproduce the important features of the experimental measurements, validating the
model developed and allowing the hydrodynamic behaviour influencing these measurable phenomena to be
explored computationally.
INTRODUCTION
Gravity separation, a physics-based process that offers
cost-effective separation of solid particles, has been widely
applied in the coal and mineral processing industry (He
et al., 2020). The Reflux Classifier, devised by Prof. Kevin
Galvin (Galvin, 2003), operates on the principles of the
Boycott effect (Boycott, 1920), serving as a density-based
gravity separation unit. Comprising a fluidised bed located
below a set of parallel inclined channels, the classifier facili-
tates the dispersion and segregation of solid particles (refer
to Figure 1) (Galvin &Nguyentranlam, 2002). The lower
fluidised bed functions as an autogenous dense medium
dominated by the hindered settling mechanism, with par-
ticle terminal velocity playing a crucial role (Amariei et
al., 2014 Galvin et al., 2020a). The inclined plates intro-
duce a sedimentation area, promoting gravity separation
governed by the Boycott effect. Particle settling behaviour
on the inclined plates relies on available surface area and
vertical settling velocity (Nakamura, 1937 Tarpagkou &
Pantokratoras, 2014). Previous studies investigated the
impact of inclined channels on particle size classification,
supporting the notion of an optimal inclination angle of
70 degrees relative to the horizontal (Doroodchi, Galvin,
&Fletcher, 2005 Galvin et al., 2020a, 2020b Galvin &
Nguyentranlam, 2002 Galvin, Walton, &Zhou, 2009
Laskovski et al., 2006 Peng, Galvin, &Doroodchi, 2019
Starrett &Galvin, 2023). It was also noted that closely
spaced inclined channels, under specific conditions, gen-
erate high shear rates capable of overcoming particle ter-
minal settling velocity, enhancing particle transport along
the inclined surface. Additionally, laminar flow in narrow,
inclined channels facilitates a linear velocity distribution,
enabling particle elutriation at the same hydraulic velocity
and thus segregating particles based on density while elimi-
nating size-based separation. These observations indicate

Help

1985
Physical Separations
Combination of Physical Separation Techniques

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XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1987
that closely spaced inclined channels will promote density-
based separation of particles of smaller size but would be
detrimental for size-based separation of particles of similar
density.
Many studies have been conducted to understand
the hydrodynamics and transport mechanisms of the RC
and how they influence its performance (Doroodchi et
al., 2006 Galvin et al., 2005 Galvin &Nguyentranlam,
2002 Nguyentranlam &Galvin, 2001). Recently Starrett
and Galvin (2023) carried out an experimental study to
classify a feed suspension as a function of particle size in a
Reflux Classifier. A secondary inflow of water (spilt fluidi-
sation) was applied in the experiment for achieving control
on the separation size and to provide sharp separation at
high throughputs. This investigation demonstrated that the
hydrodynamics of the fluidised bed delivers control over
separation size whilst the precise velocity field within the
inclined channels yields sharp separation. Studying the
hydrodynamics experimentally of a device like the Reflux
Classifier is a complicated task because of difficulties in
measuring shear rates, observing velocity fields and/or par-
ticle trajectories in 3D. In addition, challenges associated
with sample preparation with precisely controlled physical
properties, as well as the scale-up process, can limit a solely
empirical approach, rendering experiments expensive and
time consuming. Computational fluid dynamics (CFD)
provides an alternative avenue to study and analyse Reflux
Classifier hydrodynamics, at significantly reduced cost and
time. CFD has been proven to be effective in predicting
the local and global hydraulic characteristics inside devices
without affecting the working conditions (Diba, Karim, &
Naser, 2022 Zhou et al., 2017). CFD has been applied for
studying the hydrodynamics and flow behaviour of various
equipment, including fluidised beds, conventional flota-
tion cells, sedimentation tanks, and inclined plate settlers
(Diba, Karim, &Naser, 2020a, 2020b Islam &Nguyen,
2021 Peng, Galvin, &Doroodchi, 2019 Salem, Okoth,
&Thöming, 2011 Tarpagkou &Pantokratoras, 2014).
These investigations have shown that CFD is an effective
tool in understanding the flow dynamics and the influ-
ence of operating conditions on the overall performance
of the equipment. Doroodchi, Galvin and Fletcher (2005)
investigated the influence of inclined plates on expansion
behaviour of solid suspensions in a two-dimensional flui-
dised bed and found reasonable agreement with experimen-
tal results. Peng, Galvin and Doroodchi (2019) conducted
computational studies on the liquid-solid flow behaviour
in a fluidised bed, as well as the influence of inclined plates
on the flow characteristics of the bed. Some investigations
have also been conducted using a segregation-dispersion
model to study the Reflux Classifier (Syed et al., 2018
Syed, Galvin, &Moreno-Atanasio, 2019). The present
work builds upon the most recent experimental work and
understanding, especially the basis for controlling the sepa-
ration size.
In this study, we examine the hydrodynamics of a lab-
oratory-scale Reflux Classifier using CFD simulations. A
three-dimensional Eulerian-Eulerian model is formulated
to explore the impact of particle size on hydrodynamics
and transport mechanisms. The numerical investigations
were performed in two stages. Firstly, a batch mode flui-
dised bed is simulated and validated against experimental
results. Subsequently, a continuous flow model is applied to
generate a simulated partition curve for specific operating
conditions drawn from published literature. This simulated
curve is then compared with experimental data, revealing
that the CFD simulations accurately capture key features
of the experiments. This validation affirms the reliability
of the developed computational model, enabling computa-
tional exploration of the hydrodynamic behaviour underly-
ing these observable phenomena.
METHODS AND MATERIALS
Numerical Method
The simulation of multiphase flow was performed using the
Eulerian-Eulerian two-fluid model (TFM) approach. This
widely-used method is common in modelling fluidised bed
hydrodynamics, treating the fluid (gas/liquid) as the con-
tinuous phase and the solid as the dispersed phase (Diba,
Karim, &Naser, 2020a Islam &Nguyen, 2021 Peng et
al., 2021). In this approach, phases are considered as inter-
penetrating continua, with conservation equations solved
independently for each phase and source terms used for
phase coupling (Anderson &Jackson, 1967). Governing
equations for mass and momentum conservation account
for spatial pressure gradients, stress tensors for both solid
and fluid phases, gravitational forces, and interphase
momentum transfer through a drag force. The kinetic
theory of granular flow (KTGF) model captures solid
phase behaviour (Gidaspow, 1994), with the Gidaspow
drag model estimating the crucial drag force facilitating
momentum exchange between fluid and solid phases. Bed
pressure drop within dense solid regions is determined
using the Ergun equation (Ergun &Orning, 1949), while a
modified Stokes law (Bouillard, Lyczkowski, &Gidaspow,
1989) is employed for low concentration regions. The drag
coefficient is calculated based on the solid Reynolds num-
ber (Gidaspow, Seo, &Ettehadieh, 1983). Turbulence is
another important aspect in CFD multiphase modelling.
For modelling turbulent flow, the k-epsilon turbulence

Previous Page Next Page

Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1987
that closely spaced inclined channels will promote density-
based separation of particles of smaller size but would be
detrimental for size-based separation of particles of similar
density.
Many studies have been conducted to understand
the hydrodynamics and transport mechanisms of the RC
and how they influence its performance (Doroodchi et
al., 2006 Galvin et al., 2005 Galvin &Nguyentranlam,
2002 Nguyentranlam &Galvin, 2001). Recently Starrett
and Galvin (2023) carried out an experimental study to
classify a feed suspension as a function of particle size in a
Reflux Classifier. A secondary inflow of water (spilt fluidi-
sation) was applied in the experiment for achieving control
on the separation size and to provide sharp separation at
high throughputs. This investigation demonstrated that the
hydrodynamics of the fluidised bed delivers control over
separation size whilst the precise velocity field within the
inclined channels yields sharp separation. Studying the
hydrodynamics experimentally of a device like the Reflux
Classifier is a complicated task because of difficulties in
measuring shear rates, observing velocity fields and/or par-
ticle trajectories in 3D. In addition, challenges associated
with sample preparation with precisely controlled physical
properties, as well as the scale-up process, can limit a solely
empirical approach, rendering experiments expensive and
time consuming. Computational fluid dynamics (CFD)
provides an alternative avenue to study and analyse Reflux
Classifier hydrodynamics, at significantly reduced cost and
time. CFD has been proven to be effective in predicting
the local and global hydraulic characteristics inside devices
without affecting the working conditions (Diba, Karim, &
Naser, 2022 Zhou et al., 2017). CFD has been applied for
studying the hydrodynamics and flow behaviour of various
equipment, including fluidised beds, conventional flota-
tion cells, sedimentation tanks, and inclined plate settlers
(Diba, Karim, &Naser, 2020a, 2020b Islam &Nguyen,
2021 Peng, Galvin, &Doroodchi, 2019 Salem, Okoth,
&Thöming, 2011 Tarpagkou &Pantokratoras, 2014).
These investigations have shown that CFD is an effective
tool in understanding the flow dynamics and the influ-
ence of operating conditions on the overall performance
of the equipment. Doroodchi, Galvin and Fletcher (2005)
investigated the influence of inclined plates on expansion
behaviour of solid suspensions in a two-dimensional flui-
dised bed and found reasonable agreement with experimen-
tal results. Peng, Galvin and Doroodchi (2019) conducted
computational studies on the liquid-solid flow behaviour
in a fluidised bed, as well as the influence of inclined plates
on the flow characteristics of the bed. Some investigations
have also been conducted using a segregation-dispersion
model to study the Reflux Classifier (Syed et al., 2018
Syed, Galvin, &Moreno-Atanasio, 2019). The present
work builds upon the most recent experimental work and
understanding, especially the basis for controlling the sepa-
ration size.
In this study, we examine the hydrodynamics of a lab-
oratory-scale Reflux Classifier using CFD simulations. A
three-dimensional Eulerian-Eulerian model is formulated
to explore the impact of particle size on hydrodynamics
and transport mechanisms. The numerical investigations
were performed in two stages. Firstly, a batch mode flui-
dised bed is simulated and validated against experimental
results. Subsequently, a continuous flow model is applied to
generate a simulated partition curve for specific operating
conditions drawn from published literature. This simulated
curve is then compared with experimental data, revealing
that the CFD simulations accurately capture key features
of the experiments. This validation affirms the reliability
of the developed computational model, enabling computa-
tional exploration of the hydrodynamic behaviour underly-
ing these observable phenomena.
METHODS AND MATERIALS
Numerical Method
The simulation of multiphase flow was performed using the
Eulerian-Eulerian two-fluid model (TFM) approach. This
widely-used method is common in modelling fluidised bed
hydrodynamics, treating the fluid (gas/liquid) as the con-
tinuous phase and the solid as the dispersed phase (Diba,
Karim, &Naser, 2020a Islam &Nguyen, 2021 Peng et
al., 2021). In this approach, phases are considered as inter-
penetrating continua, with conservation equations solved
independently for each phase and source terms used for
phase coupling (Anderson &Jackson, 1967). Governing
equations for mass and momentum conservation account
for spatial pressure gradients, stress tensors for both solid
and fluid phases, gravitational forces, and interphase
momentum transfer through a drag force. The kinetic
theory of granular flow (KTGF) model captures solid
phase behaviour (Gidaspow, 1994), with the Gidaspow
drag model estimating the crucial drag force facilitating
momentum exchange between fluid and solid phases. Bed
pressure drop within dense solid regions is determined
using the Ergun equation (Ergun &Orning, 1949), while a
modified Stokes law (Bouillard, Lyczkowski, &Gidaspow,
1989) is employed for low concentration regions. The drag
coefficient is calculated based on the solid Reynolds num-
ber (Gidaspow, Seo, &Ettehadieh, 1983). Turbulence is
another important aspect in CFD multiphase modelling.
For modelling turbulent flow, the k-epsilon turbulence

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