3780 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
consisting of two gearless mills will meet the throughput
objective: one 35 MW SAG mill, one 932 kW (2500 HP)
pebble crusher, and one 30 MW ball mill.
Figure 2 demonstrates the throughput of large gear
driven grinding mills processing the same median “2008”
sample. Two lines of these large, geared mills almost meet
the throughput target – two 16 MW SAG mills, two
716 kW (800 HP) pebble crushers, and two 16 MW ball
mills.
Note that the total energy values shown in Figures 1
and 2 are based upon the actual power draw at the mill shell.
But for a correct comparison the values of the two line alter-
native with RMDs should be based upon the power draw
at the pinions instead, resulting into around 1.5% higher
total energy requirements for the SAG and ball mills due to
the additional losses of the ring gear and pinions the total
circuit energy requirement would be 11.05 kWh/t for the
two line option with RMDs compared to 10.92 kWh/t for
the one line option with larger mills and GMDs. One line
with two large gearless mills has an estimated 20% smaller
footprint compared to two lines with four geared mills.
One line will also require half the number of upstream and
downstream mechanical equipment such as conveyors, sep-
arators. The savings in footprint and equipment lower the
construction costs when fewer larger mills are used.
Looking at the OPEX, the main drivers are the cost
of electricity and the availability. The cost of electricity is
impacted by the drive efficiency. Due to the absence of
mechanical losses, the efficiency of the complete drive train
is 1.0 to 1.5% lower for a geared mill and up to 4% lower
if a gearbox is used. The efficiency range reflects the condi-
tion of the mechanical components – misalignment of the
gears, wear or improper lubricants will quickly lead to the
higher loss figure. Considering a total power of 65 MW, a
cost of electricity of 0.15 USD/kWh and 96% availability,
this leads to yearly electricity savings of 1 million USD for
Figure 2. Two lines with RMDs
consisting of two gearless mills will meet the throughput
objective: one 35 MW SAG mill, one 932 kW (2500 HP)
pebble crusher, and one 30 MW ball mill.
Figure 2 demonstrates the throughput of large gear
driven grinding mills processing the same median “2008”
sample. Two lines of these large, geared mills almost meet
the throughput target – two 16 MW SAG mills, two
716 kW (800 HP) pebble crushers, and two 16 MW ball
mills.
Note that the total energy values shown in Figures 1
and 2 are based upon the actual power draw at the mill shell.
But for a correct comparison the values of the two line alter-
native with RMDs should be based upon the power draw
at the pinions instead, resulting into around 1.5% higher
total energy requirements for the SAG and ball mills due to
the additional losses of the ring gear and pinions the total
circuit energy requirement would be 11.05 kWh/t for the
two line option with RMDs compared to 10.92 kWh/t for
the one line option with larger mills and GMDs. One line
with two large gearless mills has an estimated 20% smaller
footprint compared to two lines with four geared mills.
One line will also require half the number of upstream and
downstream mechanical equipment such as conveyors, sep-
arators. The savings in footprint and equipment lower the
construction costs when fewer larger mills are used.
Looking at the OPEX, the main drivers are the cost
of electricity and the availability. The cost of electricity is
impacted by the drive efficiency. Due to the absence of
mechanical losses, the efficiency of the complete drive train
is 1.0 to 1.5% lower for a geared mill and up to 4% lower
if a gearbox is used. The efficiency range reflects the condi-
tion of the mechanical components – misalignment of the
gears, wear or improper lubricants will quickly lead to the
higher loss figure. Considering a total power of 65 MW, a
cost of electricity of 0.15 USD/kWh and 96% availability,
this leads to yearly electricity savings of 1 million USD for
Figure 2. Two lines with RMDs