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Implementing Strategies to Improve Mill Capacity, with Case Studies. Presented by Nic Barkhuysen From Recent Advances in Mineral Processing Plant Design ; 2009; Malhotra, Taylor, Spiller, and LeVier, Editors; p. 433-443. Overview. - PowerPoint PPT Presentation
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Implementing Strategies to Improve Mill Capacity, with Case Studies.Presented byNic Barkhuysen
From Recent Advances in Mineral Processing Plant Design; 2009; Malhotra, Taylor, Spiller, and LeVier, Editors; p. 433-443.
OverviewFine wet screening definition, mechanism, and rules of thumbDevelopment of high capacity multiple feed point screening machines and screen surfacesThree case studies describing the application of fine screens in closed circuit grinding
DefinitionsScreening: the process of separating particles according to size
Fine screening: separation of particles ranging from 10 mm (3/8 inch) to 38 microns (400 mesh)
Mechanism and rules of thumbDifferent for wet and dry screeningIn fine wet screening, the undersize particles are transported through the screen openings by the fluid; vibration promotes fluid throughput and oversize conveyanceReasonable efficiency is obtained at about 20% solids by volume (80% water)Wet screening process is essentially complete when most of the fluid has passed through the openings, and this usually occurs within a relatively short screen length
Multiple feed point machines1977 - Multifeed screening machineTypically 1.5 to 2 times more capacity than an equivalent single feed point machine
Multiple feed point machines1977 - Multifeed screening machineTypically 1.5 to 2 times more capacity than an equivalent single feed point machine2001 - Stack Sizer screening machineCapacity generally equivalent to 3 to 4 Multifeed machines
Stack Sizer ScreenUp to 5 vibrating screen decks operating in parallelTypically fed from a single or multiple stage flow distribution system, depending upon the number of machines
Stack Sizer ScreenUp to 5 vibrating screen decks operating in parallelTypically fed from a single or multiple stage flow distribution system, depending upon the number of machinesDriven by two 1.9 kW (2.5 HP) vibrating motors rotating in opposite directionsCapacity typically ranges from 100 to 350 t/h per machine depending upon screen panel opening, mass recovery to oversize, amount of nearsize particles, particle shape, and slurry viscosity
Urethane screen surfacesOpenings as fine as 75 microns (200 mesh)High open area (35 to 45% actual)Capacity similar to fine woven wireLong life (6 to 12 months is common)Rarely blinds due to slotted openings and tapered relief anglesUnique technology developed by Derrick
The application of fine screens in closed circuit grindingResearch work over many decades has demonstrated the benefits of improved classification in grinding circuits, butUp until recently, screens have rarely been considered as the primary classifier in mill circuitsWith the availability of high capacity screens and long life, non-blinding screen surfaces, it is now practical to consider screens to close grinding circuits, as illustrated by the following case studies
Three case studies demonstrating the use of screens in closed circuit grindingPhosAgro OJSC Apatit (phosphate mine in Russia)OJSC KMAruda (iron ore mine in Russia)Sociedad Minera El Brocal S.A.A. (lead-zinc mine in Peru)(Fourth case study in paper: Minera Cerro Lindo (copper, lead, and zinc mine in Peru)
PhosAgro OJSC ApatitPhosphate mine located north of the Artic Circle in northwestern Russia
PhosAgro OJSC ApatitPhosphate mine located north of the Artic Circle in northwestern RussiaCrushed ore is fed to multiple parallel lines of single stage ball mills in closed circuit with single or double stage hydrocyclones
PhosAgro OJSC ApatitPhosphate mine located north of the Artic Circle in northwestern RussiaCrushed ore is fed to multiple parallel lines of single stage ball mills in closed circuit with single or double stage hydrocyclonesCircuit product from all lines is combined and pumped to the flotation plants
PhosAgro OJSC ApatitDesired to improve classification efficiency, grinding efficiency, and mill production ratesScreening tests were conducted in 96-97 with a Multifeed screen but screens were eliminated as an option due to the high number of screens required and limited space availableWith the development of the Stack Sizer, Apatit wanted to take another look at the use screensContinuous pilot-scale closed circuit grinding tests were conducted in 2005 with single-deck Stack Sizer screen
Single deck Stack Sizer (screen width restricted to simulate proper loading for full-scale operation)
PhosAgro OJSC ApatitEncouraging pilot test results justified the next phase of the investigation, the conversion of one mill line to screensTo minimize the cost, Mill 24 chosen as it was the smallest line
Mill 24 grinding circuit - cyclone classification
New Feed(crushed ore)95 t/h
Overflow44% solids95 t/h
Underflow 80% solids409 t/h
Water72 m3/h
Flotation
Cyclone feed 504 t/h
77%solids
Water 48 m3/h
Ball Mill
3.6 m x 4.0 m
(430% Circulating Load)
Hydrocyclones
PhosAgro OJSC ApatitEncouraging pilot test results justified the next phase of the investigation, the conversion of one mill line to screensTo minimize the cost, Mill 24 chosen as it was the smallestCyclones were replaced with 4 Stack Sizer screens with 390 m urethane panels
Mill 24 grinding circuit - screen classification
New Feed(crushed ore)124 t/h
Four (4) Stack Sizer Screens
Undersize34% solids124 t/h
Oversize 82% solids167 t/h
(135% Circulating Load)
Flotation
Screen feed291 t/h
Ball Mill
3.6 m x 4.0 m
Benefits of improved classification
Comparison of circuit products
Chart3
100100
93.290
82.373.6
73.162.4
55.747.3
46.538.2
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Comparisons
Sociedade Minera El Brocal S.A
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
50072.471.698.9
30062.359.996.2
21249.245.091.7
15036.328.485.4
7520.511.467.7
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
50069.522.298.4
30057.111.585.2
21252.810.578.0
15042.18.768.9
7538.18.256.3
Milpo - Compania Minera Cerro Lindo
=
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
500100.0100.0100.0
300100.0100.0100.0
21263.952.194.4
15046.131.085.4
7522.58.458.9
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
50091.088.0100.0
30075.354.999.3
21259.431.190.6
15047.820.575.0
7530.49.947.0
Compania Minera Condestable
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
50078.064.096.0
30055.239.394.4
21242.727.081.9
15035.621.477.0
7525.915.153.3
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
50077.063.098.0
30059.131.895.1
21248.419.685.2
15039.613.472.8
7527.98.752.0
OJSC Apatit
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
40072.665.6100
32061.152.993.2
20043.83482.3
16034.524.673.1
10022.213.655.7
7117.710.346.5
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
40064.036.8100.0
32051.422.390.0
20038.912.873.6
16032.09.062.4
10023.65.847.3
7119.04.538.2
0.427.434.40
0.3238.947.16.8
0.256.26617.7
0.1665.575.426.9
0.177.886.444.3
0.07182.389.753.5
36.0342688363.20
48.677.710
61.0658788887.226.4
68.046676519137.6
76.3617429894.252.7
81.0144756395.561.8
Comparisons
10099.26
94.410456713490.63
85.391053832375.04
72.026094709759.46
58.898824916447.01
48.301601210937.92
42.948445747333.59
38.605117642729.23
Overground Materialin Cyclone Circuit
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percentage Passing
Grinding Circuit Product Size Distribution CurveMilpo Unit - Minera Cerro Lindo S.A.A.
Cerro Lindo Comparisons
99.9399.67
99.4895.09
97.8385.2
93.8272.75
87.1761.64
76.9152
66.2
54.12
Underground Materialin Cyclone Circuit
Overground Materialin Cyclone Circuit
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Grinding Circuit Product Size Distribution CurveCompania Minera Condestable
Silica Sand
100100
98.999.9
96.2498.04
91.6692.16
85.3885.16
77.378
67.768.9
59.8662.38
55.8656.26
51.64
49.28
46.98
Overground Material in Cyclone Circuit
Hydrocyclone Overrflow
Stack Sizer Undersize
Particle Size, microns
Weigth Percent Passing
Grinding Circuit Product Size Distribution Curve Sociedad Minera El Brocal
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Compania Minera Milpo S.A.A. - Cerro LindoCompania Minera Condestable
Control ParametersHydrocyclone D-26Stack SizerClassificationHydrocyclone DS-26Stack Sizer
Tonnange t/hr242275Ciculating Load243124
Ball charge %3737Classification Efficiency49.880.3
RPM15.515.5Mill DischargeHydrocyclone DS-26Stack Sizer
Critical Speed76.876.8% - 200 mesh25.927.9
Mill MotorHydrocyclone D-26Stack Sizer% solids7370
HP 3000Flotation FeedHydrocyclone DS-26Stack Sizer
Voltage39614139% - 200 mesh53.352
Amperage319316P80 microns196185
Kw21832200
Energy Comsumption (Kw-h/Ton)77
grams of steel/Kw-h778696
ClassificationHydrocyclone D-26Stack Sizer
Circulating Load244108
Classification Eficiency5879
Mill DischargeHydrocyclone D-26Stack Sizer
% - 200 mesh23.5847.01
% solids82.578.7
Flotation FeedHydrocyclone D-26Stack Sizer
% - 200 mesh5547
P80 microns140.5160
Satck Sizer ScreenHydraulic Classifier
Dimensions1.2 m wide x 1.5 m long2.6 m dia. upstream classifier
Feed Rate (t/h)120120
40300
PhosAgro OJSC ApatitFinal product grade from flotation circuit is similar, even though the flotation feed is coarserApatit is now moving forward with plans to upgrade two large mill lines in the newer grinding plant, each requiring 10 Stack Sizers, confident that the mill production rates will increase by a minimum of 30 percent
OJSC KMArudaIron ore mine in RussiaRun of mine ore is about 34% Fe2 stages of grinding each consisting of 2 ball mills operating in parallelPrimary mills closed with spiral classifiersSecondary mills closed with cyclonesEach grinding stage followed by magnetic separation
Secondary grinding with cyclone classification
Second Stage Wet Magnetic Separation
Tailings
Concentrate
Hydrocyclones
Third Stage Wet Magnetic Separation
Concentrate
Ball Mill
Ball Mill
Tailings
Magnetic concentrate from primary grinding circuit
OJSC KMArudaTwo Stack Sizer screens with 100 micron urethane panels installed in the secondary grinding circuit in place of the cyclonesGoal was to maintain the same final product gradeSubsequent testing and optimization resulted in the shut down of one of the two secondary ball mills
Secondary grinding with screen classification
Ball Mill
Magnetic concentrate from primary grinding circuit
Second Stage Wet Magnetic Separation
Undersize
Oversize
Tailings
Concentrate
Two (2) Stack Sizer Screens
Third Stage Wet Magnetic Separation
Concentrate
Tailings
Benefits of improved classification
Mineral Processing Journal, 2009, No. 2.
Sociedad Minera El Brocal S.A.A.Lead / zinc concentrator located in Peru at 4,300 meters above sea levelRun of mine ore is 2.4% leadThree rod mills in open circuit feed three ball mills in closed circuit with hydrocyclones; cyclone overflow goes to flotationCyclone underflow is 10 to 15% lead due to high difference in specific gravityCirculating load typically ranges from 350 to 400%Considerable slime losses before flotation
Rod Mill
Rod Mill
Rod Mill
Ball Mill
Overflow138 t/h
483 t/h
Ball Mill
621 t/h
Ball Mill
7 x 12
7 x12
7x12
8 x 10
8 x 10
8 x 10
New Feed 138 t/h
Flotation
(350% Circulating Load)
Hydrocyclones
Sociedad Minera El Brocal S.A.A.Required additional capacity, so considered adding a fourth ball millFollowing full-scale tests, two Stack Sizer screens with 500 micron urethane panels were installed in place of the cyclones
Initial ImprovementsTwo of the three ball mills were shut downCapacity increased 10%Lead recovery increased about 9 percent due to reduction in slime losses before flotationScreen oversize is less than 2% lead (recall, cyclone underflow was 10-15% lead)
To take advantage of increased grinding capacityCrushing circuit was modified to increase capacity and reduce production of fines Rod mill speed was increased to achieve better throughputThree additional Stack Sizer screens were installedA second ball mill was put back into operationInstalled additional flotation and filtration capacityConcentrator throughput increased over 75%
Five (5) Stack Sizer Screens
Ball Mill
Flotation
Rod Mill
Rod Mill
Rod Mill
Ball Mill
147 t/h (60% Circulating Load)
392 t/h
7 x 12
7 x 12
7 x 12
8 x 10
8 x 10
New Feed 245 t/h
245 t/h
Benefits of improved classification
Comparison of circuit products
Chart2
100100
98.999.9
96.2498.04
91.6692.16
85.3885.16
77.378
67.768.9
59.8662.38
55.8656.26
51.64
49.28
46.98
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Comparisons
Sociedade Minera El Brocal S.A
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
50072.471.698.9
30062.359.996.2
21249.245.091.7
15036.328.485.4
7520.511.467.7
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
50069.522.298.4
30057.111.585.2
21252.810.578.0
15042.18.768.9
7538.18.256.3
Milpo - Compania Minera Cerro Lindo
=
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
500100.0100.0100.0
300100.0100.0100.0
21263.952.194.4
15046.131.085.4
7522.58.458.9
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
50091.088.0100.0
30075.354.999.3
21259.431.190.6
15047.820.575.0
7530.49.947.0
Compania Minera Condestable
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
50078.064.096.0
30055.239.394.4
21242.727.081.9
15035.621.477.0
7525.915.153.3
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
50077.063.098.0
30059.131.895.1
21248.419.685.2
15039.613.472.8
7527.98.752.0
OJSC Apatit
MicronsCyclone FeedCyclone UnderflowCyclone Overflow
% Pass% Pass% Pass
40072.665.6100
32061.152.993.2
20043.83482.3
16034.524.673.1
10022.213.655.7
7117.710.346.5
MicronsStack Sizer FeedStack Sizer OversizeStack Sizer Undersize
% Pass% Pass% Pass
40064.036.8100.0
32051.422.390.0
20038.912.873.6
16032.09.062.4
10023.65.847.3
7119.04.538.2
0.427.434.40
0.3238.947.16.8
0.256.26617.7
0.1665.575.426.9
0.177.886.444.3
0.07182.389.753.5
36.0342688363.20
48.677.710
61.0658788887.226.4
68.046676519137.6
76.3617429894.252.7
81.0144756395.561.8
Comparisons
10099.26
94.410456713490.63
85.391053832375.04
72.026094709759.46
58.898824916447.01
48.301601210937.92
42.948445747333.59
38.605117642729.23
Overground Materialin Cyclone Circuit
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percentage Passing
Grinding Circuit Product Size Distribution CurveMilpo Unit - Minera Cerro Lindo S.A.A.
Cerro Lindo Comparisons
99.9399.67
99.4895.09
97.8385.2
93.8272.75
87.1761.64
76.9152
66.2
54.12
Underground Materialin Cyclone Circuit
Overground Materialin Cyclone Circuit
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Grinding Circuit Product Size Distribution CurveCompania Minera Condestable
Silica Sand
100100
98.999.9
96.2498.04
91.6692.16
85.3885.16
77.378
67.768.9
59.8662.38
55.8656.26
51.64
49.28
46.98
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Overground Materialin Cyclone Circuit
Hydrocyclone Overflow
Stack Sizer Undersize
Particle Size, microns
Weight Percent Passing
Grinding Circuit Product Size Distribution CurveOJSC Apatit
Compania Minera Milpo S.A.A. - Cerro LindoCompania Minera Condestable
Control ParametersHydrocyclone D-26Stack SizerClassificationHydrocyclone DS-26Stack Sizer
Tonnange t/hr242275Ciculating Load243124
Ball charge %3737Classification Efficiency49.880.3
RPM15.515.5Mill DischargeHydrocyclone DS-26Stack Sizer
Critical Speed76.876.8% - 200 mesh25.927.9
Mill MotorHydrocyclone D-26Stack Sizer% solids7370
HP 3000Flotation FeedHydrocyclone DS-26Stack Sizer
Voltage39614139% - 200 mesh53.352
Amperage319316P80 microns196185
Kw21832200
Energy Comsumption (Kw-h/Ton)77
grams of steel/Kw-h778696
ClassificationHydrocyclone D-26Stack Sizer
Circulating Load244108
Classification Eficiency5879
Mill DischargeHydrocyclone D-26Stack Sizer
% - 200 mesh23.5847.01
% solids82.578.7
Flotation FeedHydrocyclone D-26Stack Sizer
% - 200 mesh5547
P80 microns140.5160
Satck Sizer ScreenHydraulic Classifier
Dimensions1.2 m wide x 1.5 m long2.6 m dia. upstream classifier
Feed Rate (t/h)120120
40300
CIA Condestable S.A.Copper and Gold PeruRequired additional capacity, from 4100 tpd to 5500 tpd.
Replace Cyclones with Stack SizersTM.
ImprovementsCirculating load reduced, 204% to 96%
Classification efficiency increased 62% to 85%
Capacity increased 4100 tpd to 5500 tpd (34%)
Lower energy consumption
Economic BenefitsInstalled cost of one 5 deck Stack Sizer US$300k
Economic Margin US$2,630k (17% production increase)
Investment Recovery 1.4 months.
Thank you for your time
Over 900 Stack SizersTM in production world wide
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