Advances in life cycle costs of Flotation machines Kari Föhr Symphos 11 Conference Marrakech, May 11th, 2011
Advances in life cycle costs of Flotation machines
Kari Föhr
Symphos 11 Conference
Marrakech, May 11th, 2011
Starting point
Flotation machine life-cycle energy cost is
significant compared to initial investment
There are both economical and environmental
reasons to concentrate on energy efficiency
Factors Affecting Energy Usage
Choice of Technology
• Size matters!
• Mechanism rpm
Electric system
Power transmission
Factors Affecting Energy Usage
Choice of Technology
• Forced Air Outotec TankCell® 300
including Mixer AND Blower
• 0.49 kW/m3 - water only,
• 0.67 kW/m3 - operating at pulp density of 1,35 kg/dm3
• Source: Press release published by Outotec and Codelco
• Self Aspirating 257 m3:
• 0.88 kW/m3 - water only,
• 1.09 kW/m3 – estimated with pulp of 1,35 kg/dm3.
• Source: A Weber, L MacNamara, H Scheiber, 2008
In a Real Case
Outotec "Self Aspirated" Outotec "Self Aspirated"
Cell Volume, m3 300 257 300 257
Energy consumption in Mechanism, kW 160 280 160 280
Energy consumption in Blower, kW 40 0 40 0
Energy consumption in Total, kW 200 280 200 280
Specific energy, kW/m3 0,67 1,09 0,67 1,09
Hours / year 8 300 8 300 8 300 8 300
Total energy consumption / cell / year, kW 1 328 000 2 324 000 1 328 000 2 324 000
Energy cost, US$/kWh $0,05 $0,05 $0,10 $0,10
Energy cost US$/year x cell $66 400 $116 200 $132 800 $232 400
Number of Cells 12 14 12 14
Total Volume 3600 3598 3600 3598
Cost of Total Energy , US$/year $796 800 $1 626 800 $1 593 600 $3 253 600
Comparison per Year $830 000 $1 660 000
a) Energy cost $0,05 / kWh b) Energy cost $0,10 / kWh
6
Size matters!
1800 m3 flotation volume – the options
Consider a plant requiring 1800 m3 of
rougher/scavenger volume.
Three possible scenarios for this volume
can be:
a) 18 x 100 m3 cells in 2 rows of 9.
b) 12 x 150 m3 cells in 2 rows of 6.
c) 9 x 200 m3 cells in 1 row of 9.
d) 6 x 300 m3 cells in 1 row of 6
7
Size matters 1800 m3 flotation volume
From the table we can see that the use of 300 m3 cells leads to a
1. Reduction in capital equipment cost of 50 %
when compared to using 100 m3.
2. A decrease in plant footprint area of 54 %
3. Savings of 28% and 50 % for power and air requirements
4. Savings in maintenance: 6 shafts instead of 18 – equal time per shaft
means 67% reduction in maintenance time!!
Factors Affecting Energy Usage
P = drawn Power
rho = density
k = power factor (efficiency of the mechanism)
n = shaft / rotor speed
D = rotor diameter
53 *** DnkP
Factors Affecting Energy Usage
10% reduction in the Speed equals
30 % reduction in Energy
~ 20% reduction in Wear Rate
53 *** DnkP
Can you reduce the speed?
YES, if
• There is enough mixing to avoid sanding
• The air dispersion is good enough
• There is enough torque to start after
blackout
• The drive type allows adjustment
• V-belts
• If the transmission ratio allows. Practical limit is 1:8
• Variable Frequency Drive (Converter)
• Only if you have low voltage motors (max 690 V)
In a Real Case
Outotec Outotec Outotec Outotec
Cell Volume, m3 300 300 300 300
Speed Nominal -5 % -10 % -15 %
Energy consumption in Mechanism, kW 160 137 117 98
Energy consumption in Blower, kW 40 40 40 40
Energy consumption in Total, kW 200 177 157 138
Specific energy, kW/m3 0,67 0,59 0,52 0,46
Hours / year 8 300 8 300 8 300 8 300
1 328 000 1 138 594 968 112 815 558
Energy cost, US$/kWh $0,10 $0,10 $0,10 $0,10
Energy cost US$/year x cell $132 800 $113 859 $96 811 $81 556
Number of Cells 12 12 12 12
Cost of Total Energy , US$/year $1 593 600 $1 366 313 $1 161 734 $978 670
Comparison per Year -$227 287 -$431 866 -$614 930
Case 2 - TankCell 300 with Optimized Speed
• Note:
– TankCell® 300 at Chuquicamata at specific power of
0,49 kW/m3 produced over 5% better recovery than
TankCell® 160 at higher sp. Power.
Metallurgy?
Can rotor speed be reduced without sacrificing the metallurgy?
-> plant tests with Outotec FloatForce® Flotation mechanism
Site test results – case Harjavalta
TankCell® 50, slag copper, heavy material, slurry SG 1,8
• Two day test campaign, samples from 3-5 composites
Copper Recovery and Grade vs. Power Draw
0
10
20
30
40
50
60
70
80
90
0,60 0,75 0,85 1,00 1,10
Power Draw [kW/m3]
Reco
very
/Gra
de
[%]
.
Cu Recovery [%] Cu Grade [%]
Site test results – case Pyhäsalmi
TankCell® 60
• Left over zinc flotation from pyrite concentrate
• P80 80-90 μm, average slurry SG 1,7
• Several month test campaign
• Initial tests with several mechanism set-ups
• FloatForce-1050 with Jg 1,0 cm/s was selected to
further tests
• Several thousand samples taken to increase
statistical reliability
Site test results – case Pyhäsalmi
Zinc recoveries and grades of TankCell® 60
Zinc Recovery and Grade vs. Power Draw
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
0,6 1,1 1,6
Power Draw [kW/m3]
Re
co
ve
ry/G
rad
e [
%]
.
Zn Recovery [%] Zn Grade [%]
On Electric Systems
Frequency Converters have becomesignificantly cheaper
HOWEVER, they are only cheap for LOW VOLTAGE systems, < 690 V.
In a Real Case
Outotec Outotec Outotec Outotec
Cell Volume, m3 300 300 300 300
Speed Nominal -5 % -10 % -15 %
Energy consumption in Mechanism, kW 160 137 117 98
Energy consumption in Blower, kW 40 40 40 40
Energy consumption in Total, kW 200 177 157 138
Specific energy, kW/m3 0,67 0,59 0,52 0,46
Hours / year 8 300 8 300 8 300 8 300
1 328 000 1 138 594 968 112 815 558
Energy cost, US$/kWh $0,10 $0,10 $0,10 $0,10
Energy cost US$/year x cell $132 800 $113 859 $96 811 $81 556
Number of Cells 12 12 12 12
Cost of Total Energy , US$/year $1 593 600 $1 366 313 $1 161 734 $978 670
Comparison per Year -$227 287 -$431 866 -$614 930
Case 2 - TankCell 300 with Optimized Speed
• NOTE:– If VSD costs ~ USD 18 000 / unit
– With –5% speed decrease
– Pay-off in ONE YEAR!!
Power Transmission
Drive mechanism efficiency
Every drive component has its own efficiency
• Typical electric motors 95% (when selected correctly)
• Bearing unit 99%
• V-belts 90-98% (when aligned and tightened correctly)
• Two-stage gearbox 98% (when size is correct)
• Frequency converter 96-98%
Everything has to be installed properly
• E.g. incorrect belt alignment can cause significant losses
Case example!
Drive mechanism selection – case example
Energy cost comparison of different drive arrangements
• Cost of energy is considered to be 0,1 $/kWh
• Cost of capital is 6%
0
20 000
40 000
60 000
80 000
100 000
120 000
1 3 5 7 9 11 13 15 17 19
Ene
rgy
cost
[U
SD]
Years [a]
Energy cost comparison of industrial size flotation machine, agitator power consumption 100 kW
vDrive
vDrive (0,54 deg angle fault)
vDrive (1,08 deg angle fault)
eDrive
Gearbox+v-belt drive
V-belt drives
Feasible for the small cell sizes <70m3
Expensive Motors
• Low speed
• High bearing load
Low start-up torque
Tightening of belts
Changing of belts
Poor efficiency when (usually) misaligned
Noisy
The new TankCell® eDrive
Motor
• Standard Four Pole
(1500/1800 rpm)
• Flange mounted
No V-belts
Custom made Gearbox
Air feed through
Gearbox
The new TankCell® eDrive
High Efficiency
• No belts
Low Maintenance
• Standard mineral oil
One oil change /
year
• Synthetic oils
One oil change / 3
years
The new TankCell® eDrive
Compact
• Clean platforms
• Easy access
Conclusions
Flotation life cycle energy cost is significant
compared to initial investment
Energy consumption can be significantly
reduced via:
• Correct choice of technology enabling slower rotor
speed
• Using as big Flotation Cells as possible
• Correct selection of the Electric system
• Correct selection and maintenance of Power
transmission
Acknowledgements
Mr Antti Rinne, Mr Aleksi Peltola and Mr
Sami Grönstrand, Outotec
People at Boliden Harjavalta
People at Inmet Pyhäsalmi