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RISE OF THE FLOTATION GIANTS...

Higher demand for metals and increasing operational costs have contributed to the introduction of growing numbers of larger equipment in the minerals processing industry. The dramatic increase, for example, in float tank cell sizes over recent years has seen the units grow from 100m3 to cells now with capacities of 300m3 and 500m3. While these larger units reduce capex and opex costs per capacity installed, they also set higher requirements for reliability and quality of cell operation.

Additionally, the geometric dimensions of large flotation cells lower the ratio between froth surface area and cell volume. This promotes higher overall froth stability, but also increases sensitivity to feed variation. These factors, together with the complexities of mining lower grade orebodies, have propelled the need for effective automation technology.

FROTH ANALYSIS FOR PERFORMANCE

For decades typical flotation cell control has consisted of two basic control loops with associated instrumentation for slurry level and flotation aeration rate, with both feedback loops using the PI form of the PID (Proportional, Integral, Derivative) algorithm. However, thick froth beds and variations in slurry

density methods make it difficult to achieve accurate level measurements in the flotation cell for methods that use direct ultrasonic instruments or hydrostatic pressure,

Also, due to capacity margins in the circuit design, control valves often only operate at <30%, below the optimum range of 30-60% and with cells typically in a series, feedback slurry level control loops are highly interconnected, making effective control very difficult. Feed disturbances travel slowly through the cell bank as each cell separately compensates for the disturbance, affecting the set point of the following cell. While flotation aeration rate is less complex than slurry level control, fine tuning needs to be done with care, as operators often adjust the process by changing the set

points of aeration rates in the cells.

On-line froth surface analysis systems, such as FrothSense™, focus on the stabilisation and controllability of the froth bed. The metallurgical performance of the flotation cell is highly dependent on the froth bed and its properties, with froth stability being one of the key factors for the successful operation of a cell.

Froth analysis systems constantly analyse the high quality image data of froth and determines important information, such as froth speed, bubble size, colour and stability. Continuous and on-line froth speed measurements allows significant stabilization for the cell operation, as froth flow rate can be automatically controlled by manipulating air and level, and thus removing subjectivity

MAXIMISING RECOVERY WITH FROTHSENSE™ IMAGE ANALYSIS

Author: Brian McPherson

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and reducing operator error. Often froth speeds can be correlated with grades and recoveries obtained in the circuit. The other information has proved valuable at least from process monitoring and diagnostics perspective, in order to faster identify emerging change in ore feed to process, for instance.

FROTHSENSE™ SYSTEM

Launched in 2011, FrothSense™, a third generation on-line froth surface analysis system, provides real-time measurements and statistics of froth speed and direction, bubble size distribution, froth stability and froth colour (RGB and CIE-LAB). Measurements are updated each second. Statistical data related to these variables provides consistent information 24 hours a day, enabling operators to achieve total process control and optimization.

A typical FrothSense™ installation has several froth imagers mounted on top of flotation machines. The imagers feature an advanced Power over Ethernet (PoE) solution that makes it possible to transmit all data and power for both the camera and the LED lights with just one standard ethernet cable.

Due to high performance analysis and modularity, there is practically no restriction for the number of imagers that a system can have. Imagers connect to field connection cabinets (FCC), each of which can host up to 16 imagers. FCCs are networked to an analysis server, or servers which runs the necessary machine vision algorithms and acts as an interface to the plant automation network using OLE for Process Control.

stabilising effect on cell performance. (Macraes was the first site in the world to install and successfully operate ‘large’ flotation cells - in this case, 3 x TankCell - 300s, each with over 300m3 active capacity.) Further details on Macraes can be found in the paper ‘Optimising large flotation cell performance through advanced instrumentation and control’ from Proceedings p 299-304, AusIMM Tenth Mill Operators’ Conference.

SIMPLE UPGRADING

Built on the success of its predecessor, FrothMaster 2™, the new FrothSense™ system offers improved reliability, performance and maintenance, as well as faster, simpler installation.

Current FrothMaster users upgrading to FrothSense™ will benefit from enhanced features such as the high quality digital camera, improved software and system architecture, as well as parallel computing for faster update rates, (updated each second for each measurement). Dual LED lights have replaced the single light to provide increased stability and

By default, FrothSense™ includes control of froth speed with air and level.

In addition to the online analyses of FrothSense™, the captured image data can be saved for future inspection. This feature is especially useful in process studies, or if the need arises to develop new algorithms in FrothSense™.

The system supports virtually any network topology, such as the star or ring configurations with copper or optical fibre and is equipped with IP67-rated connectors that eliminate the need for opening the cabinet when connecting cameras. For smaller systems, (up to 4 imagers), a wireless Wi-Fi option is also available.

FROTHSENSE™ SYSTEM SPECIFICATION

The system is delivered as an operational package containing froth imager assemblies, connection cabinets, analysis server and software license. For technical specifications, visit www.outotec.com and go to downloads to get the latest FrothSense™ brochure.

AUTOMATION IN ACTION

At Macraes Gold Mine, for example, a FrothMaster 2 image analysis system (predecessor of FrothSense™) was installed in December 2007. Apart from this system, a froth velocity control and a level control system which utilises adaptive feedforward compensation were also installed at the rougher-scavenger flotation circuit there. The results from this installation show significant

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reliability in the lighting conditions, crucial for accurate image analysis.

The unit’s new, lighter mechanical design, with self-supporting module, makes optimum use of the footprint and offers user-friendly inspection of equipment and installation, reducing maintenance and inspection time.

LOW INVESTMENT FOR MASS PULL AND RECOVERY

Having larger cells means there are fewer cells to control and monitor, resulting in lower capital cost for instrumentation. A FrothSense™ system is a relatively small investment in comparison to the

overall project outlay, yet will ensure optimal operation of the key process section of the concentrator. With lower installation costs than in previous years and faster commissioning, installing a new automation system will provide the necessary fine tuning to process control, resulting in consistent mass pull and increased recovery from the flotation cells.

To further enhance the capabilities and stabilizing effect of real-time

About the author...Brian McPherson is currently Applications Engineer - Automation for Outotec in Perth, Australia. Brian has over 20 years experience in minerals processing and worked previously in the Service Department dealing with mills, thickeners, flotation, automation and training. In this current role Brian helps customers optimize automation and sampling installations in both new projects and brownfield operations.

froth analyses, the FrothSense™ system is embedded with Outotec ACT froth speed control application, readily configured to control froth speed by manipulation of air and level. The same ACT platform makes it also possible to expand one step more towards optimization, by implementing a comprehensive grade-recovery system for the optimisation of the entire flotation circuit.

Invitation to the 2012 series of the AusIMM Metallurgical Society GD Delprat Distinguished Lecture

Co-sponsored by

To be presented by Emeritus Professor Alban Lynch AO HonFAusIMM

Mineral processing during the 20th Century - The highlights, why they occurred, what comes next?

MELBOURNE: Thursday 25 October, CQ Functions, 113 Queen Street, Melbourne (between Bourke Street and Little Collins), 5.30pm for 6pmPERTH: Tuesday 23 October, the Celtic Club, 48 Ord Street, West Perth, 5.30pm for 6pm HOBART: Sunday 28 October, Hotel Grand Chancellor, 1 Davey Street, Hobart, 5.30pm for 6pm preceding the AusIMM Mill Operators’ Conference. The lectures are free; refreshments will be available prior to lectures.

ENQUIRIES: David Pollard, Chair Metallurgical Society: david.pollard@internode.on.net or Peter Tilyard, Vice Chair MetSoc: Peter.Tilyard@MMG.COM

If you would like more information, click here to contactbrian.mcpherson@outotec.com