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PLCs and soft control helping to keep Kalgoorlie’s air clean

Kalgoorlie Consolidated Gold Mines (KCGM) is one of Australia’s largest gold producers. KCGM is the managing company of the world famous Super Pit in the Goldfields of Kalgoorlie, Western Australia.  

Metso and Electrical Board Manufacturers designed a complete system that was only required to control the kiln’s operation during testing and commissioning. 
KCGM has recently commissioned a new Metso carbon regeneration kiln as part of its $98 million Emissions Reduction Project that has eliminated sulphur dioxide and significantly reduced mercury emissions from its Gidji and Fimiston Processing Facilities. The project was supported by KCGM’s joint venture owners Barrick and Newmont.

Today KCGM’s Fimiston Open Pit is a massive operation, popularly known as the Super Pit. At 3.5km long, 1.5km wide and over 600m deep, it is so large that it can be seen from space and, despite its remote location, it is a popular tourist attraction. 
Annually, KCGM processes over 12 million tonnes of rock to produce up to 800,000 ounces of gold. The Fimiston Open Pit is mined using the drill-and-blast method, with the ore transported by six-metre high haul trucks. It is crushed down to nominal 300mm size rocks and then ground down to 0.2mm sized particles before it is mixed with flotation reagents. 
This produces a gold-rich froth, which is dewatered in filters to produce a sulphide gold concentrate. A common practice is to roast this concentrate at 650°C which vaporises sulphur dioxide and other impurities like mercury.

As part of its Air Quality Management Plan, the company would stop the roasting process whenever prevailing winds could blow roasting emissions towards the town and residential areas. This resulted in unplanned stoppages and the sacrifice of up to one third of available production time. Improving air quality for the community and avoiding disruptions to production were the key drivers for research into alternatives to the roasting process. This year as part of KCGM’s $98 million ‘Emissions Reduction Project’, a new larger ultra-fine grinding (UFG) Mill was installed at Gidji to replace roasting.
UFG reduces ore down to 12 micron particles, it is then subjected to a cyanidation process followed by adsorption onto activated carbon in a process called Carbon-in-Leach or CIL. Next, the carbon is recovered from the CIL process and transferred to the elution circuit. 

The elution process uses caustic soda and cyanide in a pressurised column at 110°C to strip the gold off the carbon. Once this step is complete, only the spent carbon is left behind. The carbon is then rinsed in water and sent for regeneration via the carbon regeneration kilns. 
KCGM installed two Metso carbon regeneration kilns in 1994 and 1997. Since then, they have relied on the company’s maintenance services and engineering knowledge to ensure that the kilns continued to perform efficiently. Hratch Loussikian, Metso’s National Product Manager – Pyro Systems, played a key role in the supply of the original kilns and has been directly involved in KCGM’s carbon regeneration process for over 10 years

With the carbon at 700°C, great care has to be taken to ensure safe interactions between the kiln and the upstream and downstream processes, particularly in the event of any process malfunction. This means the kiln needs a safety shutdown system, which operates independently of any external systems or power. 

A momentary loss of control by the DCS (Distributed Control System) or a power outage could have catastrophic results. The drum which carries the carbon runs at temperatures of between 850°C and 1000°C. Stopping the kiln drum from rotating, even for a short period of time, will cause the drum to sag under its own weight.

Hratch explained, “Even the smallest changes in tolerances will have dramatic effects on the kiln’s ability to operate correctly; it may not operate at all. With no easy way to rectify damage, it is likely the kiln would be offline for up to 6 months, whilst a new one is constructed and installed. Our design takes care of this problem with a special shutdown operation that is driven by a battery backup system in case of power failure. It keeps the kiln rotating until all the carbon is safely out of the kiln and the drum has cooled down sufficiently to safely stop.” 

Once the kiln had been assembled and tied in with the mechanical and electrical components of the upstream and downstream processes, testing and cold commissioning started. Although the site’s Yokogawa DCS will control the kiln, the kiln’s operation and control needed to be tested and proven independent of the DCS. 

Metso and Electrical Board Manufacturers designed a complete system that was only required to control the kiln’s operation during testing and commissioning. David Merrick, Electrical Board Manufacturers’ automation and control engineer, explained in more detail.
“Once testing was complete, control of the kiln was transferred to the Yokogawa DCS. To ensure that control is exactly the same, our programming and our control interface hardware were integrated into the DCS. This was a complex process, but the cooperation I enjoyed from KCGM and Yokogawa, made the process really simple. ”

With the roasters no longer in operation, atmospheric emissions have been eliminated from the Gidji Processing Plant. 

Everybody wins – with emission reductions the environment and community wins and the process can run 24/7, without the need to halt operations due to prevailing wind conditions.

(02) 8825 1600

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