Advances in life cycle costs of Flotation machines Kari Föhr Symphos Symph os 11 Confer Conference ence Marrakech Marra kech,, May 11th, 2011 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
Cell Volume, m3 Energy consumption in Mechanism, kW Energy consumption in Blower, kW Energy consumption in Total, kW Specific energy, kW/m3 Hours / year Total energy consumption / cell / year, kW Energy cost, US$/kWh Energy cost US$/year x cell Number of Cells Total Volume Cost of Total Energy , US$/year Comparison per Year
a) Energy cost $0,05 / kWh Outotec "Self Aspirated" 300 257 160 280 40 0 200 280 0,67 1,09 8 300 8 300 1 328 000 2 324 000 $0,05 $0,05 $66 400 $116 200 12 3600 $796 800
14 3598 $1 626 800 $830 000
b) Energy cost $0,10 / kWh Outotec "Self Aspirated" 300 257 160 280 40 0 200 280 0,67 1,09 8 300 8 300 1 328 000 2 324 000 $0,10 $0,10 $132 800 $232 400 12 3600 $1 593 600
14 3598 $3 253 600 $1 660 000
Size matters! 1800 m3 flotation volume – the options Consider a plant requiring 1800 m 3 of rougher/scavenger volume. Three possible scenarios for this volume can be: a) 18 x 100 m3 cells in 2 rows of 9. b) 12 x 150 m3 cells in 2 rows of 6. c) 9 x 200 m3 cells in 1 row of 9. d) 6 x 300 m3 cells in 1 row of 6
Size matters 1800 m3 flotation volume
From the table we can see that the use of 300 m 3 cells leads to a 1. Reduction in capital equipment cost of 50 % when compared to using 100 m 3. 2. A decrease in plant footprint area of 54 % 3. Savings of 28% and 50 % for power and air requirements 4. Savings in maintenance: 6 shafts instead of 18 – equal time per shaft means 67% reduction in maintenance time!!
Factors Affecting Energy Usage
P
3
* k * n * D
5
P = drawn Power rho = density k = power factor (efficiency of the mechanism) n = shaft / rotor speed D = rotor diameter
Factors Affecting Energy Usage
P
3
* k * n * D
10% reduction in the Speed equals 30 % reduction in Energy ~ 20% reduction in Wear Rate
5
Can you reduce the speed? YES, if • There is enough mixing to avoid sanding • The air dispersion is good enough • There is enough torque to start after blackout • The drive type allows adjustment • V-belts • If the transmission ratio allows. Practical limit is 1:8 • Variable Frequency Drive (Converter) • Only if you have low voltage motors (max 690 V)
In a Real Case
Cell Volume, m3 Speed Energy consumption in Mechanism, kW Energy consumption in Blower, kW Energy consumption in Total, kW Specific energy, kW/m3 Hours / year Energy cost, US$/kWh Energy cost US$/year x cell Number of Cells Cost of Total Energy , US$/year Comparison per Year
Outotec 300 Nominal 160 40 200 0,67 8 300 1 328 000 $0,10 $132 800 12 $1 593 600
Case 2 - TankCell 300 with Optimized Speed Outotec Outotec 300 300 -5 % -10 % 137 117 40 40 177 157 0,59 0,52 8 300 8 300 1 138 594 968 112 $0,10 $0,10 $113 859 $96 811 12 $1 366 313 -$227 287
12 $1 161 734 -$431 866
Outotec 300 -15 % 98 40 138 0,46 8 300 815 558 $0,10 $81 556 12 $978 670 -$614 930
• Note: – TankCell® 300 at Chuquicamata at specific power of 0,49 kW/m3 produced over 5% better recovery than TankCell® 160 at higher sp. Power.
Metallurgy?
Can rotor speed be reduced without sacrificing the metallurgy? -> plant tests with Outotec FloatForce® Flotation mechanism
Site test results – case Harjavalta TankCell ® 50, slag copper, heavy material, slurry SG 1,8 • Two day test campaign, samples from 3-5 composites Copper Recovery and Grade vs. Power Draw 90
. ] 80 % [ 70 e d 60 a r 50 G / 40 y r e 30 v o c 20 e R 10 0 0,60
0,75
0,85
1,00
Power Draw [kW/m 3] Cu Re cove ry [%]
Cu Gra de [%]
1,10
Site test results – case Pyhäsalmi TankCell ® 60 • Left over zinc flotation from pyrite concentrate • P80 80-90 μm, average slurry SG 1,7 • Several month test campaign • Initial tests with several mechanism set-ups • FloatForce-1050 with Jg 1,0 cm/s was selected to further tests • Several thousand samples taken to increase statistical reliability
Site test results – case Pyhäsalmi Zinc recoveries and grades of TankCell ® 60 Zinc Recovery and Grade vs. Power Draw 70,0 % [ e d a r G / y r e v o c e R
60,0 50,0 40,0 30,0 20,0 10,0 0,0 0,6
1,1
1,6 3
Power Draw [kW/m ] Zn Recovery [%]
Zn Grade [%]
On Electric Systems
Frequency Converters have become significantly cheaper HOWEVER, they are only cheap for LOW VOLTAGE systems, < 690 V.
In a Real Case
Cell Volume, m3 Speed Energy consumption in Mechanism, kW Energy consumption in Blower, kW Energy consumption in Total, kW Specific energy, kW/m3 Hours / year Energy cost, US$/kWh Energy cost US$/year x cell Number of Cells Cost of Total Energy , US$/year Comparison per Year
Outotec 300 Nominal 160 40 200 0,67 8 300 1 328 000 $0,10 $132 800 12 $1 593 600
Case 2 - TankCell 300 with Optimized Speed Outotec Outotec 300 300 -5 % -10 % 137 117 40 40 177 157 0,59 0,52 8 300 8 300 1 138 594 968 112 $0,10 $0,10 $113 859 $96 811 12 $1 366 313 -$227 287
• NOTE: – If VSD costs ~ USD 18 000 / unit – With –5% speed decrease – Pay-off in ONE YEAR!!
12 $1 161 734 -$431 866
Outotec 300 -15 % 98 40 138 0,46 8 300 815 558 $0,10 $81 556 12 $978 670 -$614 930
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% Energy cost comparison of industrial size flotation machine, agitator power consumption 100 kW 120 000
100 000
] D S U [ t s o c y g r e n E
80 000 vDrive 60 000
vDrive (0,54 deg angle fault) vDrive (1,08 deg angle fault)
40 000
eDrive Gearbox+v-belt drive
20 000
0 1
3
5
7
9
11 Years [a]
13
15
17
19
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
