Increasing Grinding Circuit Robustness with Advanced ... · Increasing Grinding Circuit Robustness with ... • Stability and dry flotation feed primary ... Increasing Grinding Circuit

Increasing Grinding Circuit Robustness with Advanced Process Control

A.Rantala, P.Blanz, K.Aberkrom, O.Haavisto

MetPlant 2015, 7-8 September, Perth

© Outotec – All rights reserved

Outline

• Introduction • Basic control of grinding • Key measurements • Advanced process control • Objectives of grinding optimisation • Case study examples • On-line mill charge measurement • Conclusions


Introduction

• Grinding is often a bottleneck for plant capacity

• High running and energy costs

• Grinding affects the performance of downstream processing

• How to process more compex and lower head grade ores more efficiently?

• Optimization • Maximize profit €

• Control maintenance and production processes • Schedule resources • Reporting and transparency

MES

• Manipulate base level targets • Process models, Soft sensors • Multivariable control • Model based control

Advanced Process Control

• PID control • Ratio control • Sequences

Process Control

• Actuators (valves, pumps) • Measurements • Analyzers (XRF-analysis, Image

analysis, Particle size measurement) Instrumentation

• Crushing • Grinding • Flotation • Dewatering

Process and Process Equipment


Basic control of a grinding circuit


Key measurements


Advanced Process Control (APC)

• Higher level control based on multiple inputs, process knowledge and multiple outputs (set-points)

• Expert control • Rule based control, easy to understand

• Model predictive control (MPC) • Uses process models to find optimal

control actions to reach targets

• Usabilitity is a key element (often forgotten) to gain operator trust and high utilization rates

• Potential for significant continuous improvement


Objectives

• Maximize grinding capacity while keeping the particle size between optimal range

• Minimize disturbances and stabilize feed to downstream processing • Optimize circulating loads, manage variable interaction and delays • Minimize energy and consumable usage • Increase the availability of the grinding circuit and equipment

F80 14 mm

100

150

200

250

300

8 10 12 14 16 18 20 22 24

Work index kWh/t

Throu

ghpu

t t/h

F80 14 mm


Modular APC template for grinding optimisation

• Basic framework for an APC application for a grinding circuit

• Process estimation module ensures the measurement validity and soft sensor and sensor fusion data

• Cyclone and particle size control modules typically stabilising and limiting

• Mill control often the master controller pushing the circuit within limits

• Operators to provide hard limits and targets*

*or plant optimiser


Outline

• Introduction • Basic control of grinding • Key measurements • Advanced process control • Objectives of grinding optimisation • Case study examples • On-line mill charge measurement • Conclusions


Case study 1: A SABC circuit

• Highly alternating ore hardness • Unexpected ore feed shutdowns and spillages • Particle size variance

• Proper particle size distribution important for the downstream processing

• Good level of instrumentation and basic control • Load cells in the mill • Particle size analyser

• APC control strategy was implemented based on the template


Case study 1: Results of the on/off trial campaign

Result Standard deviation t-test (p)

SAG Feed (t/h) + 1.2 % - 44.5 % < 0.005

Particle Size (% -200 mesh) Process value deviation to target (P80: 80%)

- 83.7 % - 62.3% < 0.005

SAG Power (kW) - 8.3 % - 42.6 % < 0.005

Cyclone Feed Density (%) + 3.8 % - 61.2 % < 0.005

Cyclone Feed Flow (m3/h) - 2.5 % - 11.6 % < 0.005

Pump Box Level (%) + 33.2 % - 85.6 % < 0.005


The effect of APC during softer ore feed


The effect of APC during harder ore feed


Case Study 2: an AG/Pebble mill circuit

• Low grade feed with alternating hardness

• Stability and dry flotation feed primary objectives • Proper combined particle size to flotation • Balancing AG/Pebble mill circulations • Allow operators focus on overall efficiency of

the plant

• High level of instrumentation and basic control ensure good basic process stability

• APC control strategy was implemented based on the template


Case Study 2: Results of mill control module Result Standard deviation t-test (p)

Flotation dry feed (t/h) + 2.0 % + 19.0 % 0.04

Grinding circuit feed (t/h) + 0.3 % - 24.3 % 0.86*

AG Energy/ton milled (kW/t) + 1.3 % - 26.3 % 0.58*

Particle size (% -75 µm), Mill 1 Process value deviation from target (75 %)

+ 5 % - 7.6 % 0.68*

Particle size (% -75 µm), Mill 2 Process value deviation from target (75 %)

- 55.0 % + 34.0 % < 0.005

*not significant


Case Study 3: On-line mill charge analysis

• Valuable control input for indicating the state and condition changes of a mill

• Charge volume has a great impact on

the grinding efficiency

• Estimation methods: • Mass indicators, e.g. bearing pressure,

load cells • Noise, aqoustic sensors • Power signal • Embedded probes, e.g. strain gauge • Model-based (soft sensors)

Charge volume (%)

Spe

ed(%

of c

ritic

al)

Inefficientimpacts

Optimum

Reduced impact area

Reduced impact area

Liner damage

Liner damage


On-line mill charge measurement development

• Direct measurement of toe position with a strain gauge on the mill shell

• Wireless data transfer and inductive powering*

• Prototype testing on-going at three AG/SAG mills with rubber liners, a steel lined mill test to commence soon

*patents pending


Correlation between mill variables and mill charge

6% mill charge variation

Mill feed and mill charge (AG mill)


Conclusions

• Lower grade, more complex and changing ore feed increases the challenge of efficient grinding circuit operation

• APC can provide significant annual benefits through improved stability and more continuous operation at the circuit’s limits • Adequate level of instrumentation and tuned basic process control is a requirement for APC

performance

• The potential APC benefits demonstrated by two case studies indicate better control of particle size, improved throughput and energy efficiency

• On-line mill charge measurement development adds an essential variable to grinding circuit control


Acknowledgements

Companies of the case studies are greatly acknowledged for their co-operation and permitting the data in this paper to be presented

Documents

Increasing Grinding Circuit Robustness with Advanced ... · Increasing Grinding Circuit Robustness with ... • Stability and dry flotation feed primary ... Increasing Grinding Circuit