6
Solution—Process Control Strategies
Now that the optimal mill filling has been determined and
a SAG mill load model has been developed to know what
the mill load should be for the life of the liners, the process
control strategy needs to be developed and tuned to main-
tain that mill filling.
A well-tuned comminution circuit process control aims
to maintain circuit stability and comminution efficiency
with highly variable conditions such as ore competency,
feed size, feed rates and ore specific gravity [1].
The following steps to setup an effective comminution
circuit controller was described by Chandramohan et al [1]:
• Step 1: Understanding the ore source
Geometallurgy is a valuable tool that can define
the changing ore properties over the LOM and the
impact on the comminution circuit performance.
• Step 2: Understand the feed size distribution
impact on the performance of each comminution
device
Once the ore source has been defined in the mine
plan schedule, each comminution device’s feed size
distribution range should be assessed providing
insight into potential mechanical changes required
to maintain a stable mill load i.e., grate aperture and
grate open area.
• Step 3: Start with a basic controller—review the
complexity
The base layer of control uses experienced operators
to set operating setpoints and limits. Several focusing
questions should be asked to determine the require-
ment for fuzzy, MPC or Adaptive controllers such
as, is the ore highly variable hourly? Can the opera-
tor achieve stability? Are the operators adequately
trained?
• Step 4: Develop an implementation road map for
the Life of Mine
For brownfield operations, a roadmap should be
developed to assess the level of operator training
required, reviewing the circuit performance, and then
consider process optimization and operator training
to achieve the required targets. Once optimized, then
consider advanced controllers to increase circuit per-
formance and minimize operator input.
For an effective process control for a SAG mill treat-
ing highly variable feed, requires working instrumentation,
correct tuning of the process control and knowledge of the
process and operation of the equipment. In summary:
• Instrumentation
The instrumentation installed on a SAG mill is inte-
gral to control [1]. Instrumentation should be rou-
tinely calibrated and replaced if faulty.
Maintaining a stable mill load depends on
accurately measuring mill dilution via flow meters
and belt scales. An example of poorly regulated mill
dilution due to faulty instrumentation is shown in
Figure 8. Figure 8 shows a significant decrease in
SAG mill power draw, at constant mill speed and
mill load, due to slurry pooling when an unmetered
source of water was added to the mill feed to com-
pensate for scaling of the main water addition line.
The addition of this unmetered water hampered the
operator’s ability to know and control the density
inside the mill.
SAG mill microphones and vibration sensors
are essential in providing information for optimizing
SAG mill control. A fundamental application of this
instrumentation is to prevent grinding media from
impacting the shell liners, either due to running the
mill at an excessively high speed relative to the lifter
profile or maintaining a mill filling that is too low.
Phu Kham is an excellent example of employ-
ing instrumentation to manage variable feed, in this
case, specific gravity. Mill dilution is controlled by
an inferred specific gravity determined by measuring
the volume of material on the feed belt [1].
• Defining the correct tuning
There is not a generic control strategy that can imple-
mented across all SAG mills but there is a consid-
erable amount of reusable engineering [15]. SAG
mill control manages the mill load to a set point by
Figure 8. Impact of unmetered density control on SAG mill
power draw
Solution—Process Control Strategies
Now that the optimal mill filling has been determined and
a SAG mill load model has been developed to know what
the mill load should be for the life of the liners, the process
control strategy needs to be developed and tuned to main-
tain that mill filling.
A well-tuned comminution circuit process control aims
to maintain circuit stability and comminution efficiency
with highly variable conditions such as ore competency,
feed size, feed rates and ore specific gravity [1].
The following steps to setup an effective comminution
circuit controller was described by Chandramohan et al [1]:
• Step 1: Understanding the ore source
Geometallurgy is a valuable tool that can define
the changing ore properties over the LOM and the
impact on the comminution circuit performance.
• Step 2: Understand the feed size distribution
impact on the performance of each comminution
device
Once the ore source has been defined in the mine
plan schedule, each comminution device’s feed size
distribution range should be assessed providing
insight into potential mechanical changes required
to maintain a stable mill load i.e., grate aperture and
grate open area.
• Step 3: Start with a basic controller—review the
complexity
The base layer of control uses experienced operators
to set operating setpoints and limits. Several focusing
questions should be asked to determine the require-
ment for fuzzy, MPC or Adaptive controllers such
as, is the ore highly variable hourly? Can the opera-
tor achieve stability? Are the operators adequately
trained?
• Step 4: Develop an implementation road map for
the Life of Mine
For brownfield operations, a roadmap should be
developed to assess the level of operator training
required, reviewing the circuit performance, and then
consider process optimization and operator training
to achieve the required targets. Once optimized, then
consider advanced controllers to increase circuit per-
formance and minimize operator input.
For an effective process control for a SAG mill treat-
ing highly variable feed, requires working instrumentation,
correct tuning of the process control and knowledge of the
process and operation of the equipment. In summary:
• Instrumentation
The instrumentation installed on a SAG mill is inte-
gral to control [1]. Instrumentation should be rou-
tinely calibrated and replaced if faulty.
Maintaining a stable mill load depends on
accurately measuring mill dilution via flow meters
and belt scales. An example of poorly regulated mill
dilution due to faulty instrumentation is shown in
Figure 8. Figure 8 shows a significant decrease in
SAG mill power draw, at constant mill speed and
mill load, due to slurry pooling when an unmetered
source of water was added to the mill feed to com-
pensate for scaling of the main water addition line.
The addition of this unmetered water hampered the
operator’s ability to know and control the density
inside the mill.
SAG mill microphones and vibration sensors
are essential in providing information for optimizing
SAG mill control. A fundamental application of this
instrumentation is to prevent grinding media from
impacting the shell liners, either due to running the
mill at an excessively high speed relative to the lifter
profile or maintaining a mill filling that is too low.
Phu Kham is an excellent example of employ-
ing instrumentation to manage variable feed, in this
case, specific gravity. Mill dilution is controlled by
an inferred specific gravity determined by measuring
the volume of material on the feed belt [1].
• Defining the correct tuning
There is not a generic control strategy that can imple-
mented across all SAG mills but there is a consid-
erable amount of reusable engineering [15]. SAG
mill control manages the mill load to a set point by
Figure 8. Impact of unmetered density control on SAG mill
power draw