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