'The Times They Are A-Changin’, sang Bob Dylan. In this instance, the tune could be sung directly in reference to the underground mining environment, which for many years has employed energy-intensive pneumatic rockdrills. The pneumatic rockdrill is now facing serious competition from the energy- efficient electric rockdrill.
AngloGold Ashanti’s TauTona mine, situated 70 km south-west of Johannesburg, near Carletonville, in Gauteng, has been 100% electric- powered within the stoping environment since January of this year, with electric rockdrills from technological products and systems company Hilti.
The electric tools were first rolled out to the stoping environment at the mine in mid-2006.
Hilti’s drill is a 240-v, 2,2-kW water-cooled, flameproof system that uses natural electricity as the drive for the machine, and water to thrust it. It is fully enclosed in terms of electronics and operates with the blessing of both the South African Bureau of Standards and the Department of Minerals and Energy.
AngloGold Ashanti vice-president for engineering Iain Menzies says that owing to the power crisis that the mining industry is facing, it is the perfect time to press ahead with a technological innovation such as electric rockdrilling.
“With Eskom imposing widespread power restrictions, the opportunity to roll out electric drilling and remove compressed air and compressors is as good as it has ever been,” he states.
From an ergonomics perspective, Menzies notes, the drill has many benefits, including improved face advance and productivity, and lower noise levels and vibration. Further, he says, pneumatic drills have a lot of oil mist associated with their exhaust air, while this problem does not occur with electric drills.
AngloGold Ashanti TauTona GM Frans Agenbag says that Hilti’s tools provide the opportunity for increased and quicker mine production, as long as there is orebody flexibility. The drilling time at TauTona, he notes, has been reduced by half.
Agenbag says that AngloGold Ashanti decided to convert completely to electric rockdrills for three reasons – lower cost, better energy efficiency, and better safety, as noise levels are much lower with Hilti tools. As reported in Mining Weekly, in April 2007, an independent CSIR-Natural Resources and the Environment survey found that the Hilti TE MD 20 had lower noise and vibration levels than four pneumatic rockdrills tested. The tests also showed that the drills consume far less energy.
“With the Eskom power curb, and the substantial amount of power that had to be cut, we did not lose production, because we were able to shut down the compressors and carry on with the Hilti machines, which are more efficient than pneumatic machines. Also, as far as productivity on the mine is concerned, crew efficiency has improved, and that has resulted in an increase in labour productivity,” he notes.
TauTona engineering manager Japie van Antwerpen says that the ultimate objective of the drill is to eliminate compressed air as an energy medium in the underground environment. He adds that the technology has been well accepted by AngloGold Ashanti’s underground miners, owing to the reduced noise levels from a limited percussion sound, and improved environ- mental and physical conditions, with less oil vapour in the air.
Van Antwerpen says that electric drilling is substantially cheaper than pneumatic drilling, with compressed air normally costing R10,43/m2 while the Hilti machines’ energy costs 10c/m2. This is especially so when one reduces a full compressor on the ring, and drops the air pressure from 5 bar to 4,4 bar, he says.
Ironically, although the electric drills’ main drive is electricity, they actually consume considerably less electricity than pneumatic drills, the compressors for which are electrically powered.
“The Hilti machines run at 92% efficiency. Normally, if pneumatic drillers run on 40% efficiency, you’re doing well,” he says.
“It boils down to an energy-in, energy-out equation, because compressed air drills are using a compressible medium, while Hilti drills directly use electricity to drive the motor with only the efficiency loss of the motor,” Van Antwerpen explains.
Hilti executive vice-president for Africa, the Mediterranean, the Middle East and Central Asia Heinz Felber tells Mining Weekly that AngloGold Ashanti approached Hilti some years ago to develop an improved rockdrill, owing to energy, health and safety problems, and, with former AngloGold Ashanti executive Dave Hodgson leading the way, Hilti worked together with the mining industry to develop a solution. That solution is the electric rockdrill.
Hilti GM for mining Wayne Sterley says that owing to a measured approach, it took a while to introduce the drills to the whole of TauTona’s stoping environment.
“The project teams from Hilti and TauTona wanted to give the drill every chance of succeeding, so a cautious approach was taken in the initial stages and the drills were restricted to one mine overseer’s section.
“The successes achieved in this section were so positive that the remainder of the mine took six more months to complete and, to date, it has not only not lost a blast but has actually shown a considerable increase in productivity,” he says.
Hilti leases rather than sells the tool, as leasing enables the company to offer a full service package that is aligned with its value proposition.
“We were informed by the mining industry that it faces difficulties when technologies that require new processes and a high level of service and maintenance are introduced. As we are a service- orientated company, we took up those concerns, to provide trouble-free blast-hole drilling in the stoping environment,” says Felber.
“As there is only a short window of opportunity to blast underground, the preparation of the blast holes has to be completed in a limited amount of time. We believe, therefore, that it is critical for the mining industry to have a partner that makes sure that the drilling of the blast holes is completed on time and with the highest level of accuracy, and, for that, the mines need service backup,” he says.
Felber says that Hilti is currently in the technology phase of its larger drill, to complement its stoping drill. This drill, he says, will be considerably larger for use in development ends, adding that the timing of the release of the drill will largely depend on the approval and customer requirement process. The responsiveness of the market to the existing tool will also play a role in the timing of the release, he states.
Sterley says that owing to the major compressed air constraints that TauTona faced, they were eager to give the drill an opportunity. Their eagerness and the approach of their management team, combined with their corporate colleagues, made it the right place to introduce the electric rockdrill, he notes.
While the electric drills are currently only in use in the stoping environment, Agenbag says that the TauTona mine has already conducted a risk assessment, looking at the possibility of implementing the drills in tunnelling operations.
“We have identified a test site, which we will probably start on within the next few weeks. Depending on the results from the test site, we will also roll out the machine to all the tunnelling operations. Once we have reached that goal, all operations on the mine will run on electric drills,” he says.
Menzies says, however, that while AngloGold Ashanti wants to introduce the electric rockdrills to its other operations, and is currently doing tests at Moab Khotsong as well as other mines, no firm decision has been made yet on their introduction to other operations. However, all life-of-mine extension projects are being planned with Hilti.
He acknowledges that AngloGold Ashanti is busy conducting tests on the development side, so that the electric drills can be rolled out to the whole mine. However, he concedes, there are safety issues to consider, as restrictions are greater owing to the higher risk of methane gas.
Sterley explains, however, that this problem is being attended to.
“When we initially developed the product, we did not have competences in terms of flameproofing, so when we decided, with AngloGold, to launch the product, we looked in the market for the availability of plugs and accessories, and had to redesign the whole system. However, this challenge has been overcome, and we now have a class 2A approval on the machine, and it can be used in a full methane product,” he notes.
Sterley says that the current gully box is not flameproof. Reef Switchgear, which has been instrumental in the design of the electrical switchgear system, is adapting the box to make it compliant, by placing sniffers and methane detectors inside the box.
Menzies admits that, as with any new project, many issues have had to be resolved, and AngloGold Ashanti has been working with Hilti for many years to resolve issues relating to the performance of the drill, including the drill string, the drilling bits, and electrics.
Sterley notes that the drill performs well in all mining operations, and platinum mines, such as Twickenham and Atok, have proved the unit successful in both types of platinum reef. The perception that it performs better in gold is largely owing to the aggressive roll-out of machines within AngloGold Ashanti and Gold Fields, he says.
Sterley says that Hilti has been supplying drills to the TauTona mine since 2002. The decision to do so was driven from a corporate perspective by Menzies and Robbie Lazare, he says. Kopanang and TauTona were nominated as the two pilot mines.
Sterley says that in early 2002, the drill was not operating at Kopanang at the level desired, and was, therefore, discontinued. However, Hilti persevered with the use of the drill at TauTona, and, when the drill was running optimally, it decided to go for a full-scale roll-out in the stoping environment.
The company decided to make TauTona the pilot mine for full-scale electric rockdrill oper- ations, and, overall, Menzies is satisfied with what has been achieved.
Sterley admits that since Hilti is not a recognised mining company, it was a “learning experience” developing a prototype that could operate efficiently underground. He says that there has been a lot of research and development in the process, from the first time it was tested to the first time it was used in 2002, with a migration from a 1,8-kW tool to a 2,2-kW tool.
The drill was developed at Hilti’s corporate headquarters in Liechtenstein. Sterley says that the technological progress of the drill can be attributed to a joint approach between AngloGold Ashanti, TauTona and Hilti. He states that Hilti believes that its drill is the only patented, fully flameproof, electrical rockdrill in the world.
The tool is specifically designed for narrow-vein mining operations, and is applicable only to South African mining conditions.
In Hilti’s fleet maintenance model, it is respons-ible for the maintenance of the tool. Included in the monthly tool rate, it also makes provision for back-up tools for when the tools are in for pre-maintenance service. It also establishes work- shops on the mine premises and in real terms becomes part and parcel of the mine’s daily mining operations.
Sterley says that the company has an ongoing continuous improvement process with TauTona, whereby it is constantly monitoring the drill’s performance. He adds that it is a constant optimisation process to improve the productivity of the tool and consumables such as drill bits and drill steel.
TauTona Mine History
In 1943, Anglo American Corporation (AAC) acquired the options over a strike length of 17 km to the south of the Blyvooruitzicht and West Driefontein mines, and a new company, Western Deep Levels, was registered. By 1950, nine exploratory holes had been drilled and, in 1956, a mining lease was applied for. In the following year, it was granted and ceded to Western Deep Levels. In June 1957, AAC’s chairperson, Sir Ernest Oppenheimer, set the pregrouting drills in motion on the site of the planned No 3 shaft (now known as the TauTona mine). The mine came into production in 1962.
The mine will celebrate a historic moment on October 9, 2009, when TauTona becomes the deepest mine in the world at 3 771 m, the 120 Carbon Leader project taking the mine to a depth of 3 902 m.
The mine has a main shaft system as well as a secondary and a tertiary shaft. TauTona is predominantly a longwall operation and shares a processing plant with the Savuka mine. The processing plant uses conventional milling to crush the ore and feeds the crushed ore into the carbon-in-pulp circuit. Once carbon has been added to the ore, it is transported to the plant at Mponeng for electrowinning, smelting and the final recovery of gold.
Hilti describes the mine as an underground ‘tower of Babylon’, as it goes down rather than up, with tunnels and galleries extending to more than 1 700 km. Three to four further kilometres are added each month and several thousand tons of ore are extracted every day. A ton of ore from the main reef at TauTona – which runs north to south at a 21° angle – yields an average of 30 g of gold – a little more than an ounce.
Hilti is a partner for construction professionals worldwide, supplying technologically leading products and systems. It was founded in 1941 in Schaan, in the Principality of Liechtenstein, by Martin Hilti.
It is a 100% family-owned company that is globally active in more than 120 countries, with 20 000 employees in total, most of whom are active in sales and marketing. It serves one-million customers worldwide and, in 2007, recorded sales of 4,7-billion Swiss francs.