Improving Energy Efficiency Via Optimized Charge Motion and Slurry Flow in Plant Scale Sag Mills Page: 4 of 109
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A research team from the University of Utah is working to make inroads into saving energy
in these SAG mills. In 2003, Industries of the Future Program of the Department of Energy
tasked the University of Utah team to build a partnership between the University and the mining
industry for the specific purpose of reducing energy consumption in SAG mills. A partnership
was formed with Cortez Gold Mines, Outokumpu Technology, Kennecott Utah Copper
Corporation, and Process Engineering Resources Inc. At Cortez Gold Operations the shell and
pulp lifters of the semiautogenous grinding mill was redesigned. The redesigned shell lifter has
been in operation for over three years and the redesigned pulp lifter has been in operation for
over nine months now. This report summarizes the dramatic reductions in energy consumption.
Even though the energy reductions are very large, it is safe to say that a 20% minimum reduction
would be achieved in any future installations of this technology.
In the current project, Cortez Gold Mines played a key role in facilitating the 26-ft SAG mill
at Cortez as a test mill for this study. According to plant personnel, there were a number of
unscheduled shut downs to repair broken liners and the mill throughput fluctuated depending on
ore type. The University team had two software codes, MillsoftTM and FlowModTM to tackle the
problem. MillsoftTM is capable of simulating the motion of charge in the mill. FlowModTM
calculates the slurry flow through the grate and pulp lifters. Based on this data the two models
were fine-tuned to fit the Cortez SAG will.
In the summer of 2004 a new design of shell lifters was presented to Cortez and in September
2004 these lifters were installed in the SAG mill. By December 2004 Cortez Mines realized that
the SAG mill is drawing approximately 236-kW less power than before while maintaining the
same level of production.
In the first month there was extreme cycling and operators had to learn more. However, the
power consumption is 0.3-1.3 kWh / ton lower than before. The actual SAG mill power draw is
230-370 kW lower. Mill runs 1 rpm lesser in speed on the average. The re-circulation to the cone
crusher is reduced by 1-10%, which means more efficient grinding of critical size material is
taking place in the mill. On average the plant operating work index decreased by 1.2 kWh/ton
milled over 2 sets of the new shell liner design. The SAG power draw has been reduced 94-262
kW (126-351 HP) with the new shell liner design. This was due to the SAG mill grinding more
efficiently with optimized ball strikes and feeding a better product to the ball mill circuit, while
yielding essentially the same average throughput before and after the design change. All of the
savings have resulted in reduction of operating cost of $0.023-$0.048/ ton.
After completing the shell lifter design, the pulp lifter design was taken up. Through a series
of mill surveys and model calculations it was figured that the radial pulp lifter installed on the
mill had less than optimum discharge capacity. A number of alternative designs were evaluated.
The final choice was the Turbo Pulp Lifter for which Outukumpu Technology, Centennial,
Colorado had filed a patent. After installation of the pulp lifter a 22% increase in throughput rate
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Rajamani, Raj K. Improving Energy Efficiency Via Optimized Charge Motion and Slurry Flow in Plant Scale Sag Mills, report, July 21, 2006; Utah. (digital.library.unt.edu/ark:/67531/metadc895912/m1/4/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.