7
manipulating mill speed and feed rate and is con-
strained by mill power and noise. The correct tun-
ing is a function of the circuit design and the ore
characteristics to define the step size and frequency
of manipulated variable changes.
• Operator training
The degree of operator experience, training and indi-
vidual philosophies of plant operation play a role in
plant performance [2]. A finely tuned control system
is ineffective if the operator does not trust the control
system and opts to operate manually.
Training and experience for the operators is
invaluable, while the control system should clearly
display relevant data and operating trends, and dis-
play a manageable volume of prioritized alarms, to
simplify operator interactions.
SAG Mill Liners and Internal Design
Challenge—Suitable Liner Design for the Duty
SAG mill liners are the primary barriers to protect the mill
shell from excessive wear and transfer the mill power to
the charge by cascading and cateracting [3] and the SAG
mill liner design has a large impact on the SAG mill per-
formance in terms of stability and throughput over the life
of the liners.
The following challenges need to be addresses to main-
tain optimum SAG mill load:
• Not selecting a suitable liner design for the duty
Design challenges with the SAG mill liner are often
a result of not designing to the required duty, for
example, is the liner being designed for extended
life or to maximize throughput. This was a challenge
faced at Newmont’s Penasquito operation, a bi-
directional liner with a steep lifter face angle limited
the safe operating speed and resulted in below target
throughput. The fixed reline schedule and steep lifter
design meant at the time of change out the lifters
had plenty of lift remaining resulting in excessive
steel waste [11].
• Poor slurry flow through the discharge system
Insufficient grate discharge capacity and mill pump-
ing capacity, coupled with low SAG mill slurry den-
sities, can result in slurry pooling. Slurry pooling, the
build-up of slurry within the mill that exceeds the
height of the charge, results from a slurry inflow rate
greater than the discharge capacity of the pulp cham-
ber and grates [3]. An example of slurry pooling is
shown in Figure 9.
– No slurry pooling =inflow flow rate grate flow
capacity mill pumping capacity
– Slurry pool =inflow flow rate grate flow capacity
mill pumping capacity
• Failure to measure the wear of liners
The wear of liners that are not routinely measured
and tracked can result in the failure of liners before
the reline date or intact liners being thrown away. As
previously discussed, not measuring liner wear typi-
cally means that the SAG mill load is not compen-
sated in the control system to target the optimal mill
filling.
Solution—Designing Mill Internals for the Duty (liners
and discharge system)
The following solutions are required for maintaining an
optimum SAG mill load:
• Selecting a suitable liner design for the duty
There are two design philosophies when design-
ing the SAG mill liners: designing for liner life and
designing for SAG mill throughput [3]. The design
philosophy should be married to the requirements
for each operation based on performance targets and
ore characterization.
Chandramohan et al. [8] explain that the lifter
face angle changes the surface friction component
between the charge and lifter, affecting the wear rate,
and a steeper lifter prolongs the wear life. If the oper-
ation’s objective is to maximize throughput, a steeper
face is counterproductive as it limits the safe operat-
ing mill speed range decreasing the ability to maxi-
mize power draw. Figure 10 shows a new lifter design
Figure 9. SAG mill slurry pooling
manipulating mill speed and feed rate and is con-
strained by mill power and noise. The correct tun-
ing is a function of the circuit design and the ore
characteristics to define the step size and frequency
of manipulated variable changes.
• Operator training
The degree of operator experience, training and indi-
vidual philosophies of plant operation play a role in
plant performance [2]. A finely tuned control system
is ineffective if the operator does not trust the control
system and opts to operate manually.
Training and experience for the operators is
invaluable, while the control system should clearly
display relevant data and operating trends, and dis-
play a manageable volume of prioritized alarms, to
simplify operator interactions.
SAG Mill Liners and Internal Design
Challenge—Suitable Liner Design for the Duty
SAG mill liners are the primary barriers to protect the mill
shell from excessive wear and transfer the mill power to
the charge by cascading and cateracting [3] and the SAG
mill liner design has a large impact on the SAG mill per-
formance in terms of stability and throughput over the life
of the liners.
The following challenges need to be addresses to main-
tain optimum SAG mill load:
• Not selecting a suitable liner design for the duty
Design challenges with the SAG mill liner are often
a result of not designing to the required duty, for
example, is the liner being designed for extended
life or to maximize throughput. This was a challenge
faced at Newmont’s Penasquito operation, a bi-
directional liner with a steep lifter face angle limited
the safe operating speed and resulted in below target
throughput. The fixed reline schedule and steep lifter
design meant at the time of change out the lifters
had plenty of lift remaining resulting in excessive
steel waste [11].
• Poor slurry flow through the discharge system
Insufficient grate discharge capacity and mill pump-
ing capacity, coupled with low SAG mill slurry den-
sities, can result in slurry pooling. Slurry pooling, the
build-up of slurry within the mill that exceeds the
height of the charge, results from a slurry inflow rate
greater than the discharge capacity of the pulp cham-
ber and grates [3]. An example of slurry pooling is
shown in Figure 9.
– No slurry pooling =inflow flow rate grate flow
capacity mill pumping capacity
– Slurry pool =inflow flow rate grate flow capacity
mill pumping capacity
• Failure to measure the wear of liners
The wear of liners that are not routinely measured
and tracked can result in the failure of liners before
the reline date or intact liners being thrown away. As
previously discussed, not measuring liner wear typi-
cally means that the SAG mill load is not compen-
sated in the control system to target the optimal mill
filling.
Solution—Designing Mill Internals for the Duty (liners
and discharge system)
The following solutions are required for maintaining an
optimum SAG mill load:
• Selecting a suitable liner design for the duty
There are two design philosophies when design-
ing the SAG mill liners: designing for liner life and
designing for SAG mill throughput [3]. The design
philosophy should be married to the requirements
for each operation based on performance targets and
ore characterization.
Chandramohan et al. [8] explain that the lifter
face angle changes the surface friction component
between the charge and lifter, affecting the wear rate,
and a steeper lifter prolongs the wear life. If the oper-
ation’s objective is to maximize throughput, a steeper
face is counterproductive as it limits the safe operat-
ing mill speed range decreasing the ability to maxi-
mize power draw. Figure 10 shows a new lifter design
Figure 9. SAG mill slurry pooling