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Throughput Optimisation in Milling Circuits

Overview

MillStar

Advanced Process Control

MillStar – Advanced Process Control to optimise grinding efficiency and throughput
MillSlicer Mill Vibration Technology

Mill Vibration Technology

MillSlicer – detects liner strike position and help control the mil fill levels
Stone Three - Particle Size Distribution

Particle Size Distribution

Particle Size Distribution (PSD) of bulk material ie. mineral ore

CyLas

Hydrocyclone Flare Angle Measurement

CyLas – Hydrocyclone underflow flare angle measurement and optimise classification and detect roping

Process IQ offers the MillStar Advanced Process Control System to stabilise mill feed, discharge and optimise the circuit.

 

Milling Optimisation

Optimisation of milling needs a systematic approach. One has to ensure the stable operation of the milling circuit before you can aim to optimise power input. Bear in mind that SAG and Ball mills are the highest power consuming equipment in the plant. All Mineral Processing plants have some form of comminution, but SAG and Ball milling is the most common. Comminution is required to liberate valuable minerals from gangue (waste), and then upgrade to a more concentrated form from which the ultimate product is made. Every day millions of dollars are spent breaking big rocks into smaller rocks. It is not a trivial problem and any improvement in these processes can provide a very high rate of return.

SAG Mill Power

SAG milling can be optimised to achieve maximum breakage and throughput (or any other number of objectives). The relationships between the key variables are highly non-linear and shift as the ore hardness, steel load and liner conditions change. Traditional and basic control and modelling techniques are therefore not very effective.

A Model Predictive Control System such as MillStar can continuously seek the optimum mill operation by changing the solids feed or load setpoint, e.g. by continuously determining whether the mill is overloaded or under-loaded. Safety controllers can be used to change the solids feed rate and feed water to prevent mill overloads.

Advanced Control Process

A good advanced control system (APC) can make a big difference in efficiency of operation and throughput optimisation.

The APC system will improve power control, throughput and efficiency of grinding mills. If this is done successfully, then internal liners and lifters in the mill be protected, less grinding media will be used per ton, power consumption per ton of material grounded will be reduced while throughput is increased.

 

Advanced Process Control (APC) should address the following areas:

  • Mill feed stabilisation
  • Mill discharge stabilisation
  • Mill throughput optimisation

Controlling the feed and discharge of a mill is mostly a stabilisation exercise. For example, you need a good fast responding control of the mill feed rate. If the mill feed setpoint is changed, then the actual feed rate needs to stabilise at the new target in a short period of time. The feed rate setpoint can then be tied into a SAG mill power optimisation strategy.

Sag Mill Discharge

Controlling the feed and discharge of a mill is mostly a stabilisation exercise – you need to be able to quickly and accurately control the mill feed rate. If the mill feed setpoint is changed, then the actual feed rate needs to stabilise at the new target in a short period of time. The feed rate setpoint can then be tied into a SAG mill power optimisation strategy.

 SAG mill discharge control is quite involved due to few interactive variables, such as mill discharge sump level, classification hydro-cyclone variables (feed density, flow and pressure) and water feed rate to the sump. Model predictive control (MPC), which is a multi-input multi-output (MIMO) controller, is very suitable for this purpose. If a particle size analyser is installed it can be included in the control strategy to ensure an optimal particle size for flotation or other downstream processes.

This strategy will ensure significant increases in throughput, typically anywhere from 5% to 16% has been observed.

Each milling circuit is unique, and as such the goals and most optimal control strategy might differ for individual cases. Process IQ is an expert in implementing control systems for SAG and Ball milling circuits, making use of advanced stabilisation and optimisation strategies developed by Mintek.

And last, but not least, one should estimate the power load curve and optimum load operating point for maximum productivity in real time.

Watch this video to get an idea of how the power-load relationship in a SAG mill can change over a period of 24 hours.

Want to know more?  Get in touch with us today info@processiq.com.au

 

Process IQ Pty Ltd

Unit 1 / 23 Gibberd Road Balcatta, WA 6021 Western Australia Tel: +61 (0) 8 9240 4357 Fax: +61 (0) 8 6316 0486 Email: info@processiq.com.au

Unit 1 / 23 Gibberd Road Balcatta, WA 6021 Western Australia Tel: +61 (0) 8 9240 4357 Fax: +61 (0) 8 6316 0486 Email: info@processiq.com.au