Improving Energy Efficiency Via Optimized Charge Motion and Slurry Flow in Plant Scale Sag Mills Page: 3 of 14
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ABSTRACT
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,
Kennecott Utah Copper Corporation, Process Engineering Resources Inc. and
Outokumpu Technology.
EXECUTIVE SUMMARY
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 softwares, Millsoft and
FlowMod to tackle the problem. Millsoft is capable of simulating the motion of charge in
the mill. FlowMod 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 were 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. Now
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. All of the savings have resulted in
reduction of operating cost be about $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, Colarado had filed a patent. After installation of the pulp lifter a
22% increase in throughput rate from 344 stph to 421 stph was realized. A 35% decrease
in the SAG mill power draw from 3,908 HP to 2,526 HP (2,915 kW to 1,884 kW) was
recorded. This equates to a 47% decrease in SAG unit energy consumption from 8.98
kWh/ton to 4.74 kWh/ton. A 11% decrease in SAG mill speed was observed indicating
optimized ball strikes. Also, the ball chip generation from the SAG mill was reduced
considerably. Further more, a 7% decrease in ball mill power draw from 4,843 HP to
4,491 HP (3,613 kW to 3,350 kW) was observed. This equates to a 24% decrease in ball
mill unit energy consumption from 11.13 kWh/ton to 8.43 kWh/ton.3
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Rajamani, Raj K. & Delgadillo, Jose Angel. Improving Energy Efficiency Via Optimized Charge Motion and Slurry Flow in Plant Scale Sag Mills, report, July 21, 2006; Utah. (https://digital.library.unt.edu/ark:/67531/metadc887347/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.