9 Ben Steyn - Minerality Pty Limited
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Transcript of 9 Ben Steyn - Minerality Pty Limited
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Continuous Optimisation Strategy for Grinding Circuits
Achieving the Maximum Performance from your Grinding Circuit & Liners
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Opt
imis
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Presentation
The condition of the mill liner is an excellent indicator of chargebehaviour and can indicate specific operational problems.
Optimising the grinding circuit will save you money and will ensurethat your liners will perform as expected.
The grinding circuit needs a more modern optimisation approach. Acontinuous optimisation approach is essential for the moderngrinding plant.
The grinding circuit can not be optimised without considering themill liner quality and design.
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Grinding Circuit Performance is dependent on:
Throughput Required final product size Total power draw Equipment & product quality
LINERS, cyclones, screens
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The design flow sheet can be improved by changing:
Feed size or conditions
Operating variablesExamples: ball load, ball size, cyclone spigot
ProductsDifferent mill liners, cyclones, screens
Making calculated changes to operating variables is essential for optimum operation
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Common problems: Low throughput Incorrect final product size Specific operational problems (roping cyclone)
Product Problems:High wear on mill linersCyclone wearSpillage and vibration
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Cause of problems
Change in ore type or properties -harder or softer part of ore body
Change in crushing procedure, different F80
Change in equipment performance (Wear)
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This slow down in performance costs money
In most cases liner damage can be alleviated by adjusting the process
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60 mins
Traditionally, the changes made to improve circuit performance are based on only an hours snapshot
of the circuits performance
Is the snapshot survey still representative for year 10?
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Plant Survey
Typical Optimisation Procedure
Data Analysis
Identify Variables/ Constraints
Fine-tune Variables to Achieve
Optimised State
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Take samples of all streams over periods of one hour. Structural dimensions of equipment and operational parameters from the control room are collected.
Attempt to remove trouble spots by making adjustments and testing response.
Check the liner profile to check for clues about circuit performance.
Monitor the performance of equipment during the survey.
All samples must be sized and assays can be done to measure
content for valuables.
Plant Survey
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Calibrate the collected data against mathematical equations that represent the behaviour of each equipment piece.
Data Analysis
The operational variables that can be easily changed must be identified. There is no use in suggesting unrealistic changes to circuit. Example: The cyclone spigot can be changed, but the only possible sizes are 60 mm, 70 mm and 80 mm.
The constraints are identified to ensure that the circuit is operating within its limitations. Example: Every cyclone cluster has a maximum pressure limit.
Identify Variables / Constraints
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Fine-tune the available variables until the required conditions are satisfied. Making these changes will result in meeting the
required conditions.
Fine-tune Variables to Achieve
Optimised State
= USD 35,000 PER DAY NET GOLD INCREASE
Clients Problems:
Lower than expected throughput at 1700 tph vs Mineralitys estimated throughput of 1760 tph from initial assessment.
Final product was too coarse.
Harder ore expected in future; unsure how to operate with this ore.
After Optimisation
Throughput increased from 1700 tph to 1740 tph.
Required grind also achieved, with P80 = 106 m
Recommendations:
Increase SAG Ball load
Increase SAG Mill speed
Open pebble ports
Change Crusher Gap
Change Cyclone Spigot & Vortex Finder
Change water additions
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60 mins
After making recommended changes the circuit may perform better temporarily.
However, the recommendations are only valid as long as the snapshot survey is representative and the inputs are unchanged.
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Unexpected Changes
The optimisation strategy may be invalid shortly after study completed. The optimisation report is rarely referenced in years to come.
The ore may become harder through the years which will drop throughput/damage liners
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60 mins
2 main problems with traditional approach to optimisation:
1. Operating Strategies, Choice of Variables based on 60 minute snapshot survey
2. Most optimisation studies solve problems for only a single scenario
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An ongoing optimisation advice strategy will:
Ensure operation of circuit close to maximum potential
Alleviate wear and problems with mill liners
Continuous Optimisation
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Continuous Optimisation Strategy -Demonstration
Grinding circuit was built in 2002.Year 1-2: Good performance
Year 3: Throughput dropped 20 %(Snapshot survey and optimisationdiscussed)
The approach to solving the following scenarios will now be shownYear 4: Major drop in throughputYear 5: Severe cyclone ropingYear 6: Very soft feed material
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1 2 3 4 5 - nFeed (tph) 153Primary Crusher Gap (inch) 6.5
Primary Mill 1 2 3 4 5 - nPower (kW) 2500Speed (rpm) 13Mill Water Addition (m3/h) 25
Secondary Mill 1 2 3 4 5 - nPower (kW) 2000Speed (rpm) 15Mill Water Addition (m3/h) 17
Cyclone Cluster 1 2 3 4 5 - nPressure (kPa) 93Number Operating 7Stream 7 Volumetric Flow (m3/h) 2150
1 2 3 4 5 - nStream 5 SAG Undersize P80 (um) 723Stream 8 Cyclone Underflow P80 (um) 213Stream 8 Cyclone Overflow P80 (um) 75
Continuous Inputs to Calibrate Model
Control Samples to Take to Calibrate Model
Calibration Models Continuously Refined
Primary Mill ScreenConst 1 Const 1Const 2 Const 2Const 3
Primary Mill Cyclone ClusterConst 1 Const 1Const 2 Const 2Const 3
Continuous Calibration
This unique approach allows for continuous upgrading of simulation base, instead of
using outdated, non-representative snapshot data
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Enter VariableFeedOre Hardness (kWh/t) 14Ore Density 2.8
Primary MillBall Load (% Vol) 20Ball Size (mm) 150Speed (rpm) 15
ScreenOpenings (mm) 10
Secondary MillBall Load (% Vol) 30Ball Size (mm) 65Speed (rpm) 15
CyclonesNumber Operating 6Spigot Size (mm) 80Vortex Finder (m) 150
Effect of Variable ChangeThe following information about every stream
Dry Rate (tph)% SolidsSize Distribution
Primary MillPower (kW)Total Load (% Vol)
Secondary MillPower (kW)Recirculating Load (%)
CyclonesOperating Pressure (kPa)
Case Studies
Year 4: Major drop in throughputYear 5: Severe cyclone ropingYear 6: Very soft feed material
Continuous Optimisation Strategy
Day to day issues easily solved by referencing the Minerality optimisation
approach
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PROCESS PRODUCTS
RIGHT PROCESS+
RIGHT PRODUCTS
What variables can you change to achieve maximum throughput?
Continuous optimisation strategy
Mill Liners Mill Lifters Discharge Grates Screens Column Flotation Conveyor Audits Wear and Spillage Control
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Opt
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Minerality and Tega Industries provide a very unique consulting service.It is essential for us to provide the grinding circuit operator and plantmanager with:
Solution to achieve the best performance (throughput, final productsize, power draw) with high quality liners which are performing well.
Ability to continuously update the initial mathematical presentationof the grinding circuit.
High quality continuous strategy to solve challenges which may befaced long after our consulting job is finished.