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direct energy usages, but indirect energy usage must also
be considered. In direct energy would be the energy cost
associated with grinding media. Many countries have
already instituted cap and trade systems and carbon taxes
with more to come. As political pressure increases to
control carbon emissions, the cost of energy will continue
to outpace inflation. Also, mining practices are generally
viewed by the public as a hazard to the environment.
Using energy efficient technology will not only decrease
operating costs, but could also generate a more positive
public opinion since the most energy efficient technology is
being used. In August of 2009, the Mining Journal reported
that the Australian government responded to the EIA
(environmental impact assessment) with concerns over
the potential green house gas emissions. Using Vertimill®
technology may help project get the require environmental
permits as people are more concerned about carbon
emmissions.
Economics of Secondary Grinding with
Vertimills®
If the entire grinding energy of a concentrator is
considered, there is significantly more energy in grinding
the whole stream than concentrate, so it would follow that
there should be more Vertimills® in secondary than in
regrind applications. But, as previously stated, the majority
of Vertimills® are in regrinding applications. One of the
reasons for this is that Vertimills® are most efficient in
finer grinds, so naturally they will be applied first where
they can achieve the greatest savings. Vertimills® are still
a new concept to many operators that are used to ball mills
and there remains resistance by some to adopt the new
technology to Secondary applications. In the past, for many
operations, power and media costs were relatively low but
since they have increased, and are predicted to increase,
faster than inflation, now is the time that Vertimills® will
move into the larger grinding roles.
Another reason for slow acceptance in whole stream
grinding may have been the previous limitation in
Vertimill® sizes. As the Vertimill® has developed, larger
and larger sizes have been created. The first Vertimills®
were installed in the mining industry, were only 450 HP
(335 kW) and it took many years to increase the size up to
3000 HP (2240 kW), not because of mechanical limitations,
but the quest for the site which would try the first to install
the new size. However, for a large concentrator, multiple
Vertimills would still be required. The Vertimill® has many
other advantages beyond energy and media. It is a vastly
simpler machine compared with a large ball mill which
Issue 04 | 2010
TRANSFER OF TECHNOLOGY
means that multiple Vertimills® are still less maintenance
than a single ball mill - also the Vertimill® has superior
wear characteristics and a greater operational safety.
Many times, a multiple mill arrangement offers superior
circuit operability and flexibility.
Table 2 shows the assumptions for a sample calculation
to determine the energy, media, and carbon savings of
using Vertimills® in place of ball mills.
Table 2: Assumptions
Required Ball Mill Power 3333 kW
VTM Efficiency 70 %
Required Vertimill® Power 2333 kW
Power Cost 0,5 /kWh
Circuit Availability 93 %
Ball Mill Media Consumption 0,065 kg/kWh
Vertimill® Media Consumption 0,05 kg/kWh
Delivered Media Cost 1150 $/mt
Annual Power Cost Increase 4 %
Annual Media Cost Increase 4 %
Carbon Dioxide Emissions 0,609 kg/kWh
Energy in Media 6 kWh/kg
Internal Rate of Return 8 %
Table 3: Vertimill® savings
Year Energy Savings Media Savings
Carbon Savings
(mt of CO2)
1 $ 407,340 $ 936,882 7,938
2 $ 423,634 $ 974,357 7,938
3 $ 440,579 $ 1,013,332 7,938
4 $ 458,202 $ 1,053,865 7,938
5 $ 476,530 $ 1,096,019 7,938
6 $ 495,591 $ 1,139,860 7,938
7 $ 515,415 $ 1,185,455 7,938
8 $ 536,032 $ 1,232,873 7,938
9 $ 557,473 $ 1,282,188 7,938
10 $ 579,772 $ 1,333,475 7,938
NPV $ 3,201,290 $ 7,362,967 79,382
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