In-pit crushing and conveying saves more than just fuel
Transporting ore and waste in the most economic, efficient and environmentally friendly way is critical to the operation of any open-pit mine. Can in-pit crushing and conveying provide a solution?
Operational costs, worker safety and CO2 emissions are challenges faced by most mines and quarries today. While there certainly isn’t a silver bullet that would solve all problems overnight, in-pit solutions, such as in-pit crushing and conveying (IPCC) are widely recognized as a good place to start.
In an in-pit crushing and conveying system, the primary crushing takes place in the pit and then the crushed material is conveyed to the following process phases.
Why is this more economical, safer and less harmful to the environment? One important factor is the drastic reduction in dump truck traffic.
No drivers or exhaust pipes
In a conventional open-pit mine or quarry, primary crushing is often synonymous with a parade of loud dump trucks driving around, generating dust, noise and consuming excessive amounts of fuel. A drill-and-blast team blasts the shot and develops a muck pile. A front-end loader, hydraulic shovel or backhoe excavator at the muck pile loads the dump trucks, which transport the rock to a fixed primary crusher. This translates to a large number of trucks and people moving between the blast site and the fixed crushing plant, generating unnecessary CO2 and dust emissions as well as exposing the workers to potential injuries caused by the traffic.
In a fully mobile in-pit crushing and conveying system, an excavator located on the muck pile loads material directly into the hopper of a mobile crushing plant, instead of feeding a dump truck. Crushed rock is then transported to an in-pit belt conveyor via mobile conveyors. The conveyor carries crushed rock from the mobile crusher to the fixed secondary crushing plant for further processing – no dump trucks required. This cuts operational costs, reduces emissions and helps prevent traffic-related injuries: a conveyor has no exhaust pipe, nor does it need a driver.
And when blasting is performed, the mobile primary crusher and the mobile conveyors move to a safe distance. After the blast, a wheel loader cleans the floor and the crusher moves to the new muck pile. Operation resumes with minimal production downtime.
Invest now, save later
Given the obvious benefits, one might wonder why aren’t all companies in the industry around the world eagerly adopting and embracing in-pit solutions.
The University of Queensland in Australia has identified a number of presumed barriers to IPCC implementation; it names high capital cost, orebody characteristics, mine planning and operational reliability as the most common objections cited by mines and quarries.
None of these need to be real showstoppers, however.
“An IPCC system does require a higher initial capital investment and takes a bit more planning, but in the long run, the pros clearly prevail over the cons and the investment and planning really pay off,” explains Veikko Kuosa, In-pit Bid Manager at Metso.
Kuosa does not recognize the arguments for the supposedly lower operational reliability, either.
“It’s a question of mindset. Yes, with a truck-and-shovel system you might be able to get away with neglecting preventative maintenance, but that doesn’t mean that it’s a good way to run your business,” he says.
“With proper maintenance and planning, IPCC is by no means any less reliable,” he continues.
Save fuel – save money
According to Scott McEwing, Principal Consultant with SRK Consulting, mining companies often overlook the use of an IPCC because of a desire to get a rapid return on their investment.
“A lot of mining companies put in place a traditional operation because they are looking for low risk, early payback on their investment and to make hay while the sun shines,” McEwing states in an SRK paper from 2012, titled The economic and environmental case for IPCC.
“While an IPCC requires an investment, in the long-term it helps mining companies reduce their capital and operating costs. Your traditional truck-and-shovel mining operation is equipment-intensive and has a heavy reliance on diesel fuel. You have loaded trucks travelling up and out of the mine 24 hours a day, so you need a fleet of trucks and a roster of drivers. You’re burning up huge amounts of diesel and wearing tires at a time when there is a worldwide shortage of them,” writes McEwing.
“Studies have demonstrated that operating costs can be significantly reduced. This shows that if you’re prepared to outlay that extra money upfront, there is the potential for large savings in the long run,” he states.
The safety aspect should not be overlooked, either. Veikko Kuosa recalls that site traffic is the cause of most accidents in the industry. Thus, less traffic not only saves fuel – it can save lives.
Ideal for high capacity
In-pit solutions are applicable both to greenfield projects and expansions of existing mines. They lend themselves especially well to deep, high-capacity open-pits where the orebody is homogenous and the pit is located relatively close to the processing plant. As the conveying system is the most expensive part of an IPCC solution compared to a traditional process – the primary crusher has to be bought anyway – it generates the biggest savings in applications where the transportation route is short but steep.
According to Veikko Kuosa, in these types of cases, the payback time can be just a few years.
”If you double the capacity, you usually need to double the number of dump trucks as well. But with in-pit crushing and conveying, doubling the capacity only requires about a 30 percent larger investment in conveyors upfront,” he explains.
“When comparing conveyors to dump trucks, you should also keep in mind that, with trucks, you’re constantly paying for the truck to carry its own weight in addition to the material. With a conveyor, well, it just simply moves the material,” Kuosa adds.
In mining operations where the orebody is more heterogeneous and trucks offer the advantage of flexibility to move quickly between different ore zones, IPCC systems can still be used to significantly reduce operating costs by doing the ‘heavy lifting’ of the ore out of the pit.
Consider IPCC for waste rock handling
Both the ore and the waste rock can becrushed and conveyed in the pit. The design of the IPCC solution depends on a variety of factors, such as stripping ratio and ore blending requirements, which means that the solutions for waste handling and ore handling are individually designed and normally very different. For waste, crushing takes place only to make the material transportable on the conveyor; for ore, in-pit crushing is a part of the total comminution process.
Crushing waste rock in the pit has several benefits.
“If the waste rock has to be crushed, crushing it in the pit and conveying it out is the most economical solution. You save in operational costs by not spending money on hauling waste,” Veikko Kuosa iterates.
Crushing and properly sorting the waste rock in the pit also enables its use as backfill and for other site infrastructure purposes. In addition, preventing it from entering the following phases of the process, such as grinding, has significant impacts on the profit per ton.
SRK: The economic and environmental case for IPCC (press release, 2012)
University of Queensland, School of Mechanical and Mining Engineering: http://www.mechmining.uq.edu.au/mining-methods-and-equipment (website, referenced January 2015)