With sustainability now being a global buzz-word in a variety of applications, it was perhaps timely that the German-based engineering company, Siemens, chose this as the theme for its fourth media summit, held in Essen in early May. Once at the heart of Germany’s industrial power-base, Essen today epitomizes the greening of the rust-belt, with its coal mines, cokeworks and steel plants now remembered only as part of its heritage.

One focus of sustainability from Siemens’ viewpoint lies in adopting a holistic approach to saving energy and water in industrial processes, including mining and metallurgy. Examples cited by the CEO of the company’s Industry Solutions division, Jens Wegmann, included its Corex steelmaking process, endless strip processing for steel coil production and Siemens’ new design of hybrid flotation cell. This, Wegmann claimed, uses 17% less energy than conventional cells and has a smaller footprint, yet achieves better recoveries.
Water shortages threaten to present a major challenge to societies world wide, Wegmann said, with the potential for conflict between users already recognized. In this context, mining has its own concerns, especially in some of the more arid places that are now being explored. Already, ensuring the security of water supplies for mineral processing can bring a whole new aspect when feasibility studies and mine planning are under way, with desalinization no longer an unacceptable option. However, water treatment by any means is expensive, with a high energy demand that adds to project costs across the board.

The company’s Senior Vice President for Mining and Metals Technologies Bernd Zehentbauer, took up this theme during his own presentation to the media meeting. “The ‘business as usual’ approach is over, and mining companies need more than ever to build up a sustainability strategy,” he said.

Zehentbauer went on to outline some of the technologies that Siemens has developed specifically for mining-industry applications. The company recently upgraded the downhill conveyor system at Antofagasta plc’s Los Pelambres copper-moly mine in Chile, increasing both the carrying capacity and its generating output. The conveyor now produces up to 21 MW of power for the mine and represents, he said, “a fantastic solution to help improve an operation’s energy balance.”

Los Pelambres has also been the location for Siemens to trial its hybrid flotation cell, the company now having supplied a second unit to the operation’s molybdenum plant. This has joined the first 16-m3 cell, installed in 2007, the aim of the design being to improve the floatability of very fine particles while giving lower energy usage. Using what Zehentbauer described as two cells in one, without conventional agitation, column flotation follows pneumatic spray-in of pulp that has been pre-treated with nitrogen. Further nitrogen is blown in to the column cell to improve the floatability of very fine moly, with the tailings being sent for copper recovery.

The second cell has replaced eight conventional cells at Los Pelambres, contributing savings in terms of both water and energy usage, Zehentbauer said, with a pilot unit now undergoing trials in another copper operation. The intention here is to provide data from three separate installations in order to verify the concept’s technical and economic performance.

Since January, Minera Los Palembres has also been operating a new milling section at its concentrator, with both SAG and ball mills equipped with Siemens’ gearless drives. Power ratings for the two mills are 15 MW and 15.5 MW respectively, the company having previously supplied drives for two mills at Los Pelambres in 1999.

Siemens states that, compared with geared motors, gearless drives are more efficient, require less maintenance and have better availability. Last September, it confirmed having received an order from Xstrata Copper for three mill drive systems for an un-named project in Latin America. Including motors, gearless drives and power-supply equipment for a 24-MW SAG mill and two 16.4-MW ball mills, plus transformers, protective equipment and operator control devices, the order followed an almost identical set of equipment for Xstrata’s Las Bambas project in Peru, where a final development decision is scheduled for this year.

Turning to other solutions, Zehentbauer cited trolley-assist systems for haul trucks as having major potential, especially with the prospect of diesel prices continuing on an upward curve. Siemens’ EPC contract for Equinox Resources’ Lumwana copper project in Zambia included a trolley-assist system for Hitachi haulers that are equipped with Siemens’ AC drives, as well as gearless drives for the operation’s 18-MW SAG mill and 15-MW ball mill. The company claims its AC drive systems can save up to 15% on operating costs for mining shovels and haulers by reducing energy usage and providing a better power-usage profile, with trolley-assist providing additional savings. “However, a commitment to using either trolley assist or downhill conveyors to generate power for a mine requires a new approach to mine planning, right from the start,” Zehentbauer said.

In a day-long excursion from the media summit, delegates had the opportunity to see at first hand how Siemens’ Manufacturing Execution Systems (MES) are now used to control mining and transport operations at RWE Power’s Garzweiler II lignite mine near Cologne. Currently some 210 m deep, and designed for an output of 35- to 40-million mt/y of power-station fuel for at least the next 35 years, Garzweiler produces lignite from three seams with a composite thickness of 40 m. A total of seven bucket-wheel excavators feed lignite to the main stockpile and waste to bulk spreaders, via a complex system of belt conveyors that converge in one corner of the operation, immediately beneath the control center.

With the transfer of mining from the earlier Garzweiler I pit to Garzweiler II in 2006, Siemens installed some 85 km of new conveyor lines together with switchgear, overhead power lines and the electric equipment for the belt drives. The entire network is controlled by one of the company’s Simatic PCS7 systems, Siemens having supplied all the automation equipment for operations monitoring as well as the infrastructure for information processing and communication. All control and automation components are linked to each other and with the control centre by fiber-optic cables that carry data and other information under an open transport network (OTN).

A team of four operators on each shift controls all of the production and maintenance operations at the mine, including stacking and reclaiming from the surge lignite stockpile. Given variations in the quality of the lignite at Garzweiler, blending is essential in order to provide a consistent feed for RWE’s nearby Frimmersdorf, Neurath and Niederraußem power stations, which are connected to the mine by a dedicated rail link. The only exceptions to the current level of automation are the bucket-wheels themselves, with RWE and Siemens scheduled to implement a prototype automated control system for the first of these in July.

Describing Siemens’ MES concept as a tool to help management make the right decisions for both production and environmental sustainability, Zehentbauer went on to illustrate other potential applications. With future mines more likely to be developed in increasingly remote parts of the world, management faces a new set of challenges, he said, including having to rely on a labor pool where technical education standards may be low, and a reluctance on the part of senior management to commit to long periods of minesite life. MES can help simplify operational control in these circumstances, he explained, as well as acting as a route for transferring data and operating information between a company’s individual mines. Further opportunities could involve using data from individual plant items, such as haulers or shovels, to assess operator capabilities and to schedule training or refresher needs.

Summarizing the company’s aims for sustainability, Wegmann said, “Rising energy prices, legal requirements and a deeper awareness of ecological responsibility are leading to greater environmental protection and higher energy efficiency. Sustainability and cost-effectiveness are not a contradiction.”

Referring to Siemens’ Eco-Care Matrix, which it uses to assess a plant or product’s environmental compatibility and cost-effectiveness, he pointed out that: “individual products, systems or complete plants can now be evaluated and developed to ensure that they not only meet cost and energy-efficiency targets, but also satisfy important ecological requirements. As a result, we are offering sustainable, cost-effective benefits to our customers and are helping them to remain competitive throughout the world,” Wegmann said.

“It is important to have a comprehensive energy-management system,” Zehentbauer said. “The social challenges and environmental policy requirements regarding energy consumption and water supplies are imposing even greater costs on mining operations, and this calls for additional investment.

“It is not enough just to optimize one area of operations,” he said. “The real-time transparency offered by MES enables management to control operating processes better, and to assess the cost-effectiveness of their various production plants.”

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