November 2013

In-pit innovation

In-pit crushing and conveying advances make the most of increased maneuverability and enhanced equipment monitoring

By Eavan Moore

In-pit crushing and conveying (IPCC) experts say, with the technology proven, the challenge now is to integrate the systems into mine plans that acknowledge and make use of the special constraints IPCC imposes – in ways that are unique to each site, lending variety to the solutions demanded of suppliers.

The fuel savings, reduced traffic, lower road maintenance costs and fewer diesel emissions that in-pit crushing and conveying offer are persuasive arguments for surface mine planners considering this technology. However, IPCC, whether truly truckless or a hybrid of truck and conveyor use, is still rare compared to truck-based set-ups, especially in hard rock mines.

Basic IPCC equipment – shovel, crusher and conveyor – has been in place for a while, points out David Tutton, consultant mining engineer, but the design specifications and capabilities have changed over time. Conventional semi-mobile crushers can be extremely expensive to move, with relocation costs in the hundreds of millions of dollars not unprecedented. This has prompted suppliers to move away from semi-mobile systems that require concrete and instead adopt steel structures.

Glenn Davis, system solutions manager at FLSmidth Global Material Handling, says FLSmidth’s customers are asking for smaller, lighter, more easily relocatable equipment. Moreover, Davis says there are regions where mines need to keep it light, as in Indonesia, Malaysia, and other places where competent road-building material is scarce. That means relatively small, low-speed sizers, like FLSmidth’s ABON twin-roll sizer, have widened their scope. “These low-speed sizers have generally been soft rock applications,” he says. “Well, now they’re getting bigger and more robust, and we’re starting to get those into the hard rock application.”

Maneuverability, elimination of cantilevered shock loading, and stability needs also drove the development of Sandvik Mining Systems’ PF300 fully mobile crushing station in 2007, according to Karl Ingmarsson, Sandvik’s product line manager of continuous mining and IPCC. “The main difference is that the discharge boom was completely removed to instead be a part of the conveyor bridge or belt wagon,” he says. “This has made the crushing station substantially more maneuverable.”

Diverging development paths

David Morrison, manager of integrated mining systems at Sinclair Knight Merz, believes there will be an industry-wide trend toward small crushing equipment with output in the 4,000- to 5,000-tonne-per-hour range to match large hydraulic excavators. “The current cost paradigm in mines is that the big rope shovels, serving the biggest trucks you can buy, have the lowest unit operating cost,” he says. “Now, that’s true in the Western world. It’s not quite true in places like South Africa, where they’ve started looking more at the productivity of the units because labour is not such a large part of the cost structure. And the iron ore industry typically uses smaller equipment as well. The second-tier miners producing 20 or 30 million tonnes a year will probably drive the definition of IPCC equipment in the next 10 to 15 years.”

But Morrison’s suggestion is still larger than some mines prefer. Jorma Kempas, business manager, in-pit crushing solutions, mining and construction at Metso, says the company added a 3,000-tonne-per-hour, fully mobile crusher to its Lokotrack line last year. He says the LT200 jaw crusher platform, which can be moved as often as twice per shift, could be boosted to 5,000 tonnes on softer iron ores. But for harder ores, a large primary gyratory crusher would be required, cutting down on mobility. Metso will develop whatever proves feasible, but, Kempas says, “Our motto is ‘Bring the crusher to the rock,’” adding that “so far the call has been for multiple smaller units.”

On the other end of the spectrum, John McCarthy, project manager, IPCC systems at Joy Global, says his customers want larger wares. “Mine operators are looking to reduce the number of vehicles and people in the pit,” he says. “To move 10,000 to 20,000 tonnes per hour or more, smaller equipment is not economically viable. Smaller equipment would require more active benches and the conveyor system becomes more complex.”

Joy Global is working on a 9,000- to 11,000-tonne-per-hour mobile crushing station that would be integrated with an electric shovel, using an automated swing-to-hopper sequence running on its Centurion control system.“It maximizes production because you’re optimizing that swing cycle,” he explains. “If you’re careful and come in slow, you’re not doing the optimal production. In addition to improved cycle times, the system also prevents impacts between the dipper and crusher, and minimizes spillage, which reduces time and effort required for cleanup between relocating the crusher.”

McCarthy says basic engineering on the 4107C has been completed, but the company is still seeking a customer to partner with. Despite a wave of interest in fully mobile crushing four years ago, there have been “a minimal number of fully mobile mining crusher tenders,” he says.

Regardless of the manufacturer, the legacy of past mistakes will have to be overcome, says Scot Szalanski, director of IPCC solutions at Peck Tech Consulting Ltd.

He explains, “One of the historical problems with high-tonnage mobile crushers was that they were often being built using undercarriages based on spreaders or bucket-wheel excavators, which do not experience the same cantilever loads that high tonnage mobile crushers experience. A mobile crusher using an undercarriage designed for the digging demands of an electric shovel has proven to be more durable, and has been an important model for new high tonnage mobile crusher designs.” The other issue relates to performance expectations. “Mines will perform their total cost of operation analysis, comparing IPCC and a truck fleet, and select the IPCC option,” Szalanski points out. “But what is forgotten is that IPCC is a series operation, and if any one component is not available or not operating at full capacity the entire process suffers.”

Remote health monitoring is gaining traction industry-wide and, suggests Szalanski, will both improve availability of IPCC and give mine operators the information they need to better optimize the technology. McCarthy agrees that building in sensors that could predict failures ahead of time is a useful trend. “This is something that we do currently on our shovel and we’re applying it towards our other products, which include crushers and conveyors,” he says. Metso’s Lokotrack equipment also logs and transmits performance data.

Future course

But no one, Szalanski included, thinks the reason for slow uptake can be pinned on technology. Doug Turnbull, vice-president continuous mining and IPCC at Sandvik Mining Systems, comments: “The pace of change in technology is not the issue. The real issue is the ability for change in mine planning techniques to cater for a different mining methodology that is accepted by industry in general. It does not help that IPCC as a mining methodology is not even taught at mining universities globally and is one reason Sandvik is creating such a curriculum due out for start of university year 2014. It took more than 30 years for underground longwall technology to be accepted by industry. IPCC can either wait 30 years for similar acceptance levels or learn from the underground coal implementation program, or, better still, learn from the more than 200 existing operational IPCC sites in the world today.”

Miners have to resist thinking that they can treat IPCC like the off-the-shelf truck it is potentially replacing, suggests Turnbull. “Mine planning is different, mine layout is different, dump development is different, conveyor relocation is different, planning needs to be actually adhered to, which some call inflexibility,” he says. “There are existing mines in the world with IPCC that are exceedingly good at relocating cheaply, quickly and easily – yet there are industry personnel who refuse to accept this is possible.” Part of the problem, he adds, is that the term “semi-mobile” is too broad to be very useful when comparing current systems with those of the past.

Tutton and Morrison agree that the specifics of the mine plan make or break IPCC. “Most suppliers generally look at the benefits of IPCC from a unit operating cost point of view, while what drives operating mines is net present value, and that’s very much dictated by the mine plan,” says Tutton, pointing out that the conveyor system cannot move with the vertical development rate usually dictated in copper and gold mines.

Morrison proposes that careful, original thinking could help – as well as software better tailored to IPCC. “Because in IPCC cases, the capital cost is a very large component of the total life of mine cost, and because a large portion of the total life of mine cashflow is actually spent before the operations start, this is a substantial problem. Most of the analysis software that’s available for this sort of early-phase study doesn’t give you an answer that reflects this situation,” he says. “It often gives you the wrong answer, in fact. Until that situation’s sorted out, it’s really going to struggle to gain any traction. And so there’s a whole knowledge base that needs to be created in the support industry.”

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