Cadia Expansion The Impact of Installing High Pressure Grinding Rolls Prior to a Semi-Autogenous Grinding Mill Andy Apfel Maintenance Foreman Tom Waters Plant Metallurgist
Outline About Cadia Valley Operations Cadia East Upgrade Construction and commissioning Operational lessons
CVO Operational Overview Deposits Cadia Hill Open Cut Care and Maintenance Cadia East Underground Ridgeway Underground Concentrator 1 Concentrator 2 Concentrators Gold Doré Copper Concentrate
Old Concentrator 1 Circuit x2 Throughput and stability of circuit primarily dictated by SAG mill and availability of recycle crushing circuit. Typical circuit throughput 17-18 Mt/y.
Drivers for Circuit Expansion Parameter Units May 2008 Plant Trial May 2008 Plant Trial Cadia East Model Ore Source Cadia Open Pit Cadia East Underground (Blasted) Cadia East Underground (Caved) DWI kwh/m 3 8.1 9.9 10.0 RWI kwh/t 20 26.5 31.1 BWI kwh/t 17.5 21.4 21.5 Throughput Mt/y 18.8 12.1 12.4 Cadia East ore harder and fines deficient compared to Cadia Hill. Significant reduction in throughput expected if treating in existing concentrator.
Final Flow Sheet Design x2 Modeled throughput of 2450 t/h:1770 t/h through the HPGR and 680 t/h of screen undersize or primary crushed ore. Target primary grind of 150µm.
Role of the Owners Team An Owners Team was established for the Cadia East Project. Their role was: To ensure that the project design met operational needs. Develop and manage an operational readiness plan
Purpose of the Owners Team The Owners Team was established for the following reasons: Gain site acceptance. To ensure people had adequate time for reviews. So the Operation was prepared to take on the project. The Cadia East Project had to be delivered as a high quality project.
HPGR Circuit Design The Project consulted with many parties in regards to the operation of a HPGR, these included: HPGR suppliers Polysius, KHD and Köppern. HPGR user forum: Freeport, Boddington and Cerro Verde. The following initiatives were included in the design: Feed gate design changes. Magnets, metal detectors and bypass chutes. Process control system that allowed 2500 t/h to be fed to a 30t HPGR feed bin.
HPGR Circuit Design
Commissioning Schedule Benefits of the staged implementation was to: Level labor resource Minimise process disruption Match the Cadia East underground mine ramp up Stage 1 Ball Mill Q3 FY11 Stage 2 Crushing and Screening Q2 FY12 Stage 3 Flotation and Regrind Q4 FY12 Stage 4 HPGR Q4 FY12 Concentrate pumping and Filter plant upgrade Q4 FY12
Stage 2 Commissioning Initial performance of circuit was poor - frequent trips and instability. Stage 2 ramp up team formed which consisted of a multidisciplinary group that focused on key issues in addition to their normal roles. Team had insufficient resources to focus on longer term problems and complete training and handover documentation.
Review of Stage 2 Commissioning Post Stage 2 reviews found the commissioning strategy had underestimated the complexities and intensive workload of commissioning a plant upgrade of this size. Newcrest formed an Operational Commissioning Team who were separate from day-to-day operations. Professional operators, process control, technical writers, fitters, electricians and process engineers.
Commissioning and Ramp-Up Team Process Engineer x 2 Process Control Maintenance Planner Technical Writer Superintendent Business Improvement Operational Commissioning Lead Mechanical Commissioning Lead Electrical Commissioning Lead Administration Operational Technician x 2 Mechanical Technician x 2 Electrical Technician x 4 Operational Labour
Stage 3 and 4 Commissioning HPGR was commissioned successfully. Team created operator training packages, operating strategies and maintenance packages prior to handover. Stage 4 handed over mid August 2012 to the operational team. Daily throughput consistently above 2400 t/h by December 2012.
Project and Commissioning Advice Operations need to be involved in Projects at a pre-feasibility stage. Operational readiness is a holistic process and not confined to one discipline. Commissioning activities are labor intensive and should not be underestimated.
HPGR Operation Gradual increase in HPGR F 80 over first 10 months of operation to approach design feed conditions. Operates at fixed speed to a pressure setpoint of 130 Bar. Circuit throughput now dependent on HPGR availability.
Circuit Operation Steady state conditions in secondary circuit with bin levels controlled by feed forward loops. Screen and crusher efficiency improvements targeted to reduce recirculating load in secondary circuit. SAG mill speed, water and feedrate process control systems simplified. SAG mill F 80 can range from 16mm to 100mm. Ball charge and liner design encompass these extremes.
Circuit Performance Relative to Design Cadia East survey conducted in November 2013 with AMIRA P9P. Parameter Survey Design ROM Ore F 80 (µm) 100,320 170,000 Cyc OF P 80 (µm) 141 150 Circuit specific energy (kwh/t) 21.2 22.0 A*b 35.1 27.5 BWI 19.5 21.5 Lower energy requirement and lower Cyc OF p80 than design. ROM F 80, A*b and BWI: Survey ore was finer and softer than design. HPGR reduction ratio approximately 2, % -1mm increased by 2. Negligible change in BWI through HPGR at various pressures.
Design and Implementation Negatives Partial charge up of 16MW ball mill prior to increased site power availability. Horizontal transfer points create segregated feed to main distribution bin and secondary crusher feed bin. Operating speed dead band in vibrating screen feeder motors.
Design and Implementation Positives HPGR feed stockpile decouples front end and SAG. Three feed options to SAG: HPGR product, screen undersize and coarse feed which provide flexibility and redundancy. SAG: Full wraparound electric motor, fully curved pulp lifters, large shell lifter spacing.
Acknowledgements Authors: Dieter Engelhardt: Manager Ore Processing, Cadia Valley Operations Greg Lane: Chief Technical Officer Ausenco Malcolm Powell: Professional Research Fellow, The University of Queensland, SMI/JKMRC Newcrest Mining Limited for providing the opportunity to publish and present the paper. All the professionals, tradesmen, operators and contractors who helped commission the plant upgrades at CVO. HPGR suppliers: Polysius, KHD and Köppern Polysius User s Forum: Freeport, Boddington and Cerro Verde