3755
The Effect of Grates Radial Position on an AG Mill Discharge
System Using Coupled DEM SPH Simulations
Vasile Murariu
Metso USA
Håkan Ståhlbröst, Jenny Åkerström
Metso Sweden
Alex Heath
Metso Australia
ABSTRACT: The performance of the discharge system of a large Autogenous Mill is investigated using Metso’s
Discrete Element Method (DEM) coupled with Smoothed Particle Hydrodynamics (SPH) code. The simulations
were carried out on an existing discharge system in terms of pulp lifter design and with sufficient pan depth to
focus mainly on the effect of the grate design. The main goal of the numerical investigation is to quantify the
effect of the grates’ radial position and grates’ open area on the performance of the discharge system. Several
simulations were run with incremental increases of the grates’ open area by adding more openings radially. The
mill speed and filling level of the mill are kept unchanged for all cases at 74% critical speed and 34% filling
level, respectively. Several key performance parameters were computed and compared including: outflow, inflow
and net flow of both the solids and slurry through the grates, and also the hold-up of both the solids and slurry
in the pans. The simulations showed that the radial positioning of the grate openings has a clear effect on the
discharge system performance.
INTRODUCTION
Grinding Mills constitute, still, the main equipment in
mineral processing for size reduction of the ores. Their
performance depends on many factors that includes both
design and operational parameters. In grate discharge
(SAG/AG) mills, the broken ore inside the mills is removed
by a system of discharge grates that allows the smaller rocks
to leave the mill. At the same time, very fine particles are
carried with the water and discharged easily through the
grates. The entire process of breaking of the ore, its move-
ment along the mill from the feed end to the discharge end
and the transport of the fine ore through the grates is a very
complex and a very difficult process to model or simulate
in its entirety. A model of a full-scale mill should include
the breakage of the rocks, the coupling between solids
and water and a very large number of particles. Due to its
complexity, simplified models have been developed using
population balance models (Lynch, Whiten and Draper,
1967, Lynch, 1977, Herbst, Lo and Rajamani, 1985, 1986
Morrell, 2004) that relies on plant data and experimental
tests to estimate breakage characteristics of the ore.
Over the last 20 years new techniques were developed
to model the granular flow of solids rocks and their interac-
tions. Such a technique is the Discrete Element Method
(DEM) (Campbell, 1997) that is a numerical algorithm
that solves the equation of motions of every particle at
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3755
The Effect of Grates Radial Position on an AG Mill Discharge
System Using Coupled DEM SPH Simulations
Vasile Murariu
Metso USA
Håkan Ståhlbröst, Jenny Åkerström
Metso Sweden
Alex Heath
Metso Australia
ABSTRACT: The performance of the discharge system of a large Autogenous Mill is investigated using Metso’s
Discrete Element Method (DEM) coupled with Smoothed Particle Hydrodynamics (SPH) code. The simulations
were carried out on an existing discharge system in terms of pulp lifter design and with sufficient pan depth to
focus mainly on the effect of the grate design. The main goal of the numerical investigation is to quantify the
effect of the grates’ radial position and grates’ open area on the performance of the discharge system. Several
simulations were run with incremental increases of the grates’ open area by adding more openings radially. The
mill speed and filling level of the mill are kept unchanged for all cases at 74% critical speed and 34% filling
level, respectively. Several key performance parameters were computed and compared including: outflow, inflow
and net flow of both the solids and slurry through the grates, and also the hold-up of both the solids and slurry
in the pans. The simulations showed that the radial positioning of the grate openings has a clear effect on the
discharge system performance.
INTRODUCTION
Grinding Mills constitute, still, the main equipment in
mineral processing for size reduction of the ores. Their
performance depends on many factors that includes both
design and operational parameters. In grate discharge
(SAG/AG) mills, the broken ore inside the mills is removed
by a system of discharge grates that allows the smaller rocks
to leave the mill. At the same time, very fine particles are
carried with the water and discharged easily through the
grates. The entire process of breaking of the ore, its move-
ment along the mill from the feed end to the discharge end
and the transport of the fine ore through the grates is a very
complex and a very difficult process to model or simulate
in its entirety. A model of a full-scale mill should include
the breakage of the rocks, the coupling between solids
and water and a very large number of particles. Due to its
complexity, simplified models have been developed using
population balance models (Lynch, Whiten and Draper,
1967, Lynch, 1977, Herbst, Lo and Rajamani, 1985, 1986
Morrell, 2004) that relies on plant data and experimental
tests to estimate breakage characteristics of the ore.
Over the last 20 years new techniques were developed
to model the granular flow of solids rocks and their interac-
tions. Such a technique is the Discrete Element Method
(DEM) (Campbell, 1997) that is a numerical algorithm
that solves the equation of motions of every particle at

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