E&MJ looks at some recent developments in both traditional and unconventional systems for moving rock in underground mines
By Simon Walker, European Editor
|High-tonnage underground mines can benefit from using a fixed rail-based transport
infrastructure, as at LKAB's Kiruna operation. (Photo courtesy of Schalker Eisenhütter)
In many respects, the choice of haulage system for an underground mine is dictated by the orebody geometry. Narrow-vein systems or orebodies that are elongated vertically lend themselves to an LHD-based system centered around a series of orepasses. For ore zones that are more tabular, or are geographically spread out, using LHDs to load mine trucks that then transport material either to an orepass or directly to surface via a ramp may be a better option. High-capacity, bulk-tonnage mines, by contrast, may find that a fixed infrastructure network using either high-tonnage trucks or rail-bound haulage is the most economical way of moving their ore. And, while conventional belt conveyors are less-commonly used in hard rock mining than in coal, for instance, there are always innovations being developed and trialed that offer an alternative means of rock transport.
In this article, E&MJ samples some of the recent technological developments in each of these areas, showing just how versatile the various systems now available can really be.
Locomotive Haulage: Still a Major Option
Earlier this year, German specialist locomotive manufacturer Schalker Eisenhütte Maschinenfabrik announced it had won a further order from Sweden's LKAB for heavy-duty mining locomotives. With three out of an initial five of the 108-metric ton (mt) machines already delivered, and two scheduled to arrive in northern Sweden this year, the new order brings the total number of locomotives Schalke will be supplying to LKAB to nine.
|Sandvik's new TH551 underground mine
truck has a 51-mt payload and can be
fitted with a low-emission Tier
4i-compliant engine. (Photo courtesy
Specially designed and tailor-made for use at the new 1,365 m level at the Kiruna iron ore mine, the trolley-wire locos can handle a non-braked load of up to 1,500 mt per train from the loadout to the primary crushing station. Schalker has also equipped them with technology that allows fully automated operation throughout the complete loading, haulage, dumping and return cycle.
With each wheelset being powered by a 225-kW, IGBT-controlled AC traction motor, the locos feature electro-dynamic service braking that uses dynamic retarding to bring the train to a complete standstill. An automatic train protection (ATP) system provides for additional safety during operation, even at haulage speeds of up to 25 km/h, Schalker said.
Meanwhile, during 2012 the company received an order from Freeport-McMoRan Copper & Gold (FMCG) for 10 40-mt mining locomotives for the Grasberg mine in Indonesia. With the transition from open pit to underground mining, FMCG has been developing a "common infrastructure" network that will handle all of the production from the DOZ, DMLZ, Big Gossan, Kucing Liar and Grasberg block cave operations from 2017. The Schalker locos will be used to transport all production from the mining areas to the treatment facilities, with the first units scheduled for delivery next year.
Two-axle, compared with the four-axle LKAB locos, the FMCG units will be powered by a 135-kW AC traction motor on each wheelset. A fully loaded train will run to just more than 700 mt, with haul speeds of up to 25 km/h. Again, the locos are equipped for electro-dynamic braking and carry an ATP system, although the Grasberg units have been designed with an operator's cab at each end whereas the LKAB machines are single-ended in this respect, reflecting the one-direction system of operation at Kiruna.
The Rubber-tired Alternative
Since the time that heavy locomotives became available, long-distance underground haulage has largely remained the domain of rail-bound systems, and for good reason. Although expensive to install, rail networks are relative cheap to maintain, whereas haul roads need constant cleaning to remove spillage as well as regular repairs to the wearing surface.
|The latest version of the Kiruna truck concept, the 50-
mt-capacity Electric Minetruck EMT50 is part of Atlas
Copco's new Green Line. (Photo courtesy of Atlas
Nonetheless, a few operations—such as LKAB's Malmberget mine—recognized the potential for using high-capacity haul trucks underground to give additional flexibility in terms of routing from drawpoint to dump. The use of the 120-mt-capacity Sisu SRH450 Mammut paved the way, although only six were ever built, while Sandvik took a Sisu concept for a side-tipping hauler and developed it into its current top-of-the-range model, the five-axle 80-mt-capacity TH680.
However, there is only a limited number of mines for which machines of this size would be suitable, and Sandvik's most recent hauler introductions have been the 51-mt-capacity TH551, designed for 5 × 5-m declines, and the 63-mt-capacity TH663, designed for 6 × 6-m declines. Both machines, which were announced at last year's MINExpo show in Las Vegas, are scheduled for official launch in September. Meanwhile, a TH551 has been undergoing mine-site trials at Wolfram Bergbau und Hütten's Mittersill underground tungsten mine in Austria, and the first TH663 is scheduled to begin moving rock at Barrick Gold's Darlot mine in Western Australia this month.
According to Sandvik, the new trucks have the highest haulage capacity in their class and "envelope size." Other key features include higher ramp speeds for increased productivity, the use of more than 60 safety features that are designed to protect the operator, maintenance crews and the trucks themselves, and careful matching to Sandvik's underground loaders to ensure precise three-pass loading for optimum loading speed and efficiency. The TH663 has been matched to the company's LH621 underground loader, which carries a 10.5-14 yd3 (8-10.7 m3) bucket, while the TH551 is matched to the 8.5-11 yd3 (6.5-8.6 m3) LH517.
In addition, the TH551 has an option of a Tier 4i low-emission engine that eliminates the need for a diesel particulate filter, while both machines have the option of an on-board jacking system for faster and safer tire changes that will help minimize production holdups.
The TH551 has a 51-mt payload with a standard body capacity of 28 m3 (36-yd3) and can haul at speeds of up to 37.5 km/h. The 63-mt-payload TH663 has a 36-m3 (47-yd3) body, and a top speed of 42.5 km/h provided by a Cummins QSK19 engine rated at 567 kW (760 hp). The standard engine on the TH551 is a 515 kW (690 hp) Volvo TAD1642VE-B, while the option- al lower-emission Tier 4i power unit is a Volvo TAD1662VE, also rated a 515 kW.
According to Sandvik's product manager for trucks, Mark Ryan, the Tier 4i-compliant engine will significantly reduce underground ventilation costs and help improve underground working conditions, as well as combining good torque characteristics with low fuel consumption.
Felix Gaul of Wolfram Bergbau und Hütten added, "All our heavy machines have to be equipped with diesel particulate filters for underground operations. With the Tier 4i engine, this is not necessary, resulting in savings of about €100,000 ($130,000) over the lifetime of the machine."
Atlas Copco Goes GreenerAt the end of April, Atlas Copco launched its new Green Line of electric-powered LHDs and haulers, aimed at reducing mines' fuel costs and environmental footprint. "With these new products, we are ready to be part of the global solution for reduced environmental impact," said David Shellhammer, president of the company's underground rock excavation division. "We are especially proud to be the only supplier of underground electric trucks, and I believe this development marks the beginning of a change in the mining industry."
|The key elements of Caterpillar's Rock Flow system.
Above: an RF300 Rock Feeder. Below: An RM900
Rock Mover unit. (Images courtesy of Caterpillar)
The Green Line includes two new electric underground trucks, the Electric Minetruck EMT35 and EMT50, with load capacities of 35 and 50 mt, respectively. There is, of course, some history here, since Atlas Copco acquired the former Kiruna Electric truck with its acquisition of GIA at the end of 2011, with the Kiruna Electric truck concept having been available since the 1980s. Now Atlas Copco claims that the new versions are about twice as fast as any diesel truck in these capacity ranges, making them the world's most productive underground haul trucks.
At the time of the Green Line launch, Product Manager Erik Svedlund said, "Looking at the cost per ton, using an electric underground truck can almost double the productivity while decreasing the total cost of ownership by up to 50%."
According to Atlas Copco, the electric trucks reduce energy consumption by up to 70%. High-efficiency electric motors drive the axles directly, minimizing transmission losses, while regenerative braking returns energy to the grid—meaning that about 30% of the energy consumed up the ramp is regenerated going back down.
The EMT trucks operate from fixed trolley lines with a small diesel engine used to maneuver the vehicle when it is out of reach of the main power supply. The truck draws its power through a patented trolley arm and trolley car, which automatically connects to or disconnects from the trolley line. The arm is flexible enough to allow the center of the truck to deviate by up to 2 m from the center of the line. Looking specifically at the EMT50, auxiliary power is provided by a 107-kW (145-hp) Mercedes engine, while the truck itself can be supplied with 17, 21, 24 or 28 m3-capacity boxes, depending on the characteristics of the rock being handled.
Atlas Copco points out that the advantage gained by using an electric truck over its diesel counterpart increases as the ramp depth—and hence length of haul—increases, with an electric vehicle needing a power input of around 3 kWh/mt over a 400-m vertical lift compared with around 8 kWh/mt for a diesel truck. The company told E&MJ that an EMT50 was being delivered to a mine in Canada in May.
Caterpillar's Radical Approach
As featured in this year's Best of Germany supplement to the April edition of E&MJ, Caterpillar's German-based underground mining equipment operations have been working on a radical new concept for handling ore in block-caving operations. The Rock Flow system essentially transfers armored face conveyor concepts from coal mining to the hard rock sector, offering mines the opportunity to do away with LHD operations completely in the block-cave production system.
The concept centers on the use of an RF300 Rock Feeder beneath each drawpoint, each with a capacity of up to 300 mt/h, to push broken ore on to a 900-mt/h RM900 Rock Mover conveyor. This in turn moves the ore to a primary crusher, with belt conveyors being used for rock transport after that. Caterpillar said the Rock Feeder replaces the LHD at the drawpoint, so personnel are not exposed to the hazards of the loading area, even where remote control of the vehicle is being used.
Major benefits claimed for the system include higher production, lower costs, a high level of automation, and a better working environment since all of the equipment is electric-powered. In addition, Caterpillar said the Rock Feeders are easy to remove for maintenance or clearance work, while the system has low maintenance requirements and high resistance to wear.
One Rock Flow unit has been on trial at Codelco's Salvador mine since 2007, with a second, more extensive system scheduled for installation at the company's Andina operation this year. Caterpillar suggests that by using the Rock Flow system, mining companies can cut development costs for drawpoint-level infrastructure in block-cave operations, then achieve continuous, high-performance production that is supervised from a surface control room without the need for on-site operators.
An Award for Thinking Outside the Box
In May, the Canadian company Rail-Veyor received the 2013 Bell BEA Innovation Award. Sponsored by NORCAT (the Northern Center for Advanced Technology) and Cambrian College of Applied Arts and Sciences, the award recognizes Rail-Veyor's innovative approach to bulk materials handling in underground operations.
|A Rail-Veyor 'train' discharging material
from underground into a surface hopper.
(Photo courtesy of Rail-Veyor)
As described in detail in E&MJ (December 2012, pp.86–87), Rail-Veyor is an electrically powered series of two-wheeled interconnected mini rail cars that travel along a light rail track at speeds up to 8 m/s (18 mph). Operated by remote control, the technology comprises simple components that allow continuous material haulage without diesel emissions, and with significantly less capital and maintenance costs than other options, the company said.
"Rail-Veyor has the ability to maneuver through complex track geometries, transport through difficult topography and easily stop and start on gradients up to 20%," said the company's CEO, Ron Russ. "Its efficiency as an automated system with a small environmental footprint is something heavy rail can't touch."
According to Rail-Veyor, its system eliminates the need for underground infrastructure such as ore passes, crusher stations and large bins. It enables mines to go deeper and easily transport far below the shaft within a 2.4×2.4 m (8 ft square) opening, and integrate with existing mobile equipment if necessary.
Vale installed a Rail-Veyor at its Copper Cliff 114 orebody in December 2011, with the system becoming operational last June, doubling the mine's advance and production rates.
"Lead time to production for any project is extremely critical for the return on investment," said Alex Henderson, Vale's general manager for underground mine technology. "If we can develop twice as fast as we currently do to bring an ore zone into production, and reduce it from four years of pre-capital expenditures to two, this has a huge impact on the ROI."
"It's an honor to be recognized by our peers in business," said Russ at the Bell Excellence Awards. "It is rewarding to see so much interest in our technology from so many industries worldwide."
With mines getting deeper, investment financing harder to come by and energy prices rising, operators need to chose an underground haulage system that will help them cut costs and reduce their environmental footprint. There are more options available today than ever before. Some are suitable for specific applications; others are more generic; others still offer a radical approach to an age-old requirement. Somewhere in there is the right choice, but it needs to be made early so the appropriate infrastructure can be built into the mine design.