Lifecycle Management

Automation keeping underground workers safe at LKAB Malmberget Mine


Underground mining companies and equipment manufacturers have been cooperating at an unprecedented level to ensure the safety of underground workers. A considerable degree of this effort has been directed — with the aid of computers, sensors and video-links — toward the removal of workers from either a danger zone or the underground environment altogether.

Today, virtually every modern mining operation has been automated to some degree. While some have benefited only marginally, others have seen a dramatic change with regard to remote working due to the size, structure or character of the ore body.

TAILOR-MADE FOR AUTOMATION

Nowhere have these efforts been more visible than with the autonomous drilling and load-haul-dump (LHD) work at LKAB’s Malmberget operation. In many ways this ore body could have been tailor-made for extraction by sub-level caving and, therefore, mechanical automation.

The Malmberget mine, owned and operated by Luossavaara-Kiirunavaara Aktiebolag (LKAB), started production in 1888 and since then has produced over 350 million metric tonnes (386 million short tons) of iron ore.

Malmberget’s iron ore reserves, spread over an underground area approximately 5 by 2.5 kilometers (3 by 1.5 miles), have been estimated as 187 million metric tonnes (206 million short tons), with its measured, indicated and inferred resources accounting for a further 176 million metric tonnes (194 million short tons) with the ore bodies remaining open at depth. Furthermore, with its reserves grading at 43.6 percent Fe, Malmberget is among the world’s purest metal deposits. Its current annual extraction rate is over 12 million metric tonnes (13 million short tons). Located at Gallivare in northern Sweden, the mine contains approximately 20 ore bodies, of which 10 are currently being exploited. LKAB employs about 1,000 people at Malmberget; about 900 work in mining processing and administration.

MALMBERGET’S MINING METHODS

Large-scale sub-level caving is the method of mining. Production drilling (at the access level) is undertaken by five electric-powered automated rigs, with each rig drilling approximately 10,000 meters (33,000 feet) of 11.5-centimeter (4.5-inch) diameter holes per month. Each hole averages 50 meters (165 feet) in length and, while the direction and number of holes varies depending on the structure and orientation of the ore at that location, most “production fans” contain 10 holes resulting in 10,000 metric tonnes (11,000 short tons) of ore being blasted per 3.0- to 3.5-meter (10- to 11.5-foot) slice. The emulsion explosives are pumped down-hole by two trucks for production charging and four trucks for drift development. All drifts are supported by roof bolts and shotcreting.

The blasted rock, now funnelled by the unfractured host rock, percolates down toward a series of pre-prepared production draw points, from where it is loaded by 20- to 25-metric-tonne (22- to 27-short-ton) capacity LHDs. The LHDs, which include Cat® R2900s, work from the production sub-levels. The ore is trammed at a daily rate of approximately 50,000 metric tonnes (55,000 short tons) to the haulage level, from where it is transported in 120-metric-tonne (132-short-ton) capacity trucks to the underground crusher stations. After crushing, the ore is skip-hoisted to the surface for magnetic-separation processing and onward shipping.

It is the very nature of the ore body (i.e., massive and slightly inclined) and therefore the mining operation (i.e., sub-level caving) at Malmberget that lends itself to the automation of both the drilling and LHD work. “We are employing sub-level caving because it is the most productive mining method for this ore body,” says Bjorn Koorem, Malmberget’s mine manager. “But perhaps our biggest surprise is that during recently completed LHD trials, automation has been shown to increase productivity by between 10 and 20 percent.”

AUTOMATION EVOLUTION

The original remote working of LHDs, termed line-of-sight remote, involved an operator employing a chest-mounted console from which to control the LHD while its bucket was loaded and then backed away from the ore pile. Once this task had been completed, and the machine had been moved away from the danger zone, the operator returned to the cab and manually drove the machine to the dump point. Once emptied, the operator drove the machine back to the loading location.

While remote working met many of the criteria for removing the operator from the most dangerous area of operation, accidents continued to occur when safety procedures were not observed. Therefore, mining companies concurred that the goal was to remove human exposure to injury. This bold decision was the initiative that eventually led to the development of the MINEGEM™ system.

Caterpillar formed a joint venture with Lateral Dynamics to develop the MINEGEM Automation system as an attachment to standard LHDs. The system offers two levels of control: co-pilot, with operator-assisted automatic steering, and auto-pilot, under which the loader can automatically tram, dump and return to the load point.

The initial refinement of the remote system to the co-pilot mode removes the physical need for the operator to steer the machine. The operator, based at a console in a control room (often at the surface), monitors the machine’s location on a mine plan while using a joystick to instruct the machine in which direction to travel. On-board scanners and a radio network mounted along the journey route ensure the machine self-drives along a safe path.

MALMBERGET TRIAL

The Malmberget mine was chosen as one of the locations for MINEGEM development, recently completing a successful 12-month trial using the Cat R2900G XTRA LHD.

“We knew that there were going to be two significant advantages to be achieved by employing the MINEGEM system,” explains Ola Soderholm, technical specialist at Cat dealer Pon Equipment AB. “Firstly, removal of the operator from a potentially dangerous environment, and secondly, the ergonomic advantages to an operator being able to work from a chair in a control room rather than from an uncomfortable seat underground. The purpose of the trial was to show that the practice matched the theory. What we hadn’t quite appreciated was the extra advantages we would be uncovering: an increase in utilization and productivity, and less machine damage. I think we will find that with time, other advantages will emerge.”

Based on the trial results, a 12-plus month “production-result” based rental agreement was set up between Caterpillar and LKAB. The next generation of the MINEGEM system is due to be launched in 2009 as the Mk3.0 model with newly developed software. LKAB is currently progressing plans to increase its annual production to 20 million metric tonnes (22 million short tons) of crude ore and 9 million metric tonnes (10 million short tons) of pellets. It is anticipated that a significant part of this production increase will be achieved through the implementation of the MINEGEM system.

AUTO-PILOT AND BEYOND

The MINEGEM auto-pilot mode allows the operator to select a goal for the machine and send it there using its own self-guidance system. A normal routine for the MINEGEM operator is to fill the bucket in remote mode, then set the mode to auto-pilot with the ore pass as the goal. The machine will then tram to the dump point, empty the bucket and return to the draw point automatically using its own self-guidance system, without any input from the operator.

While a manually operated LHD may achieve greater tramming speeds than one fitted with the MINEGEM system, it cannot do so without the risk of striking the sidewalls. Additionally, production over a 24-hour period may be improved with an automated LHD.

Operating under auto-pilot, several machines can be operated by a single operator. Available options include traffic management, production statistics capture, and data sharing.

The actual hardware setup (i.e., line-of-sight aerials, a radio and repeater network, security gateways and a leaky-feeder cable) is easily achieved. In fact, at the Malmberget mine, LKAB technicians took only a few days to successfully complete the setup for the second MINEGEM production trial area. In addition, all the equipment can be moved and re-used in another location if necessary.

SCANNERS AND LADARS

In the late 1990s, when faster and more powerful computers were combined with other developments in the field of scanning technologies, MINEGEM LHD automation became a true solution for underground mining operations.

“Scanning provided the definitive ‘Eureka!’ factor as far as autonomous hauling was concerned,” explains Stuart Burridge, a product specialist with Caterpillar Underground Mining. “Now we can visually scan and recognize the sidewalls and their profilers.” To do this, the system employs the LADAR (laser-radar range sensing) system, which provides spatial information to the machine by comparing these profiles to an existing database provided from the mine map. The system is then programmed to make a decision that it transmits to the machine as a command: left, right, forward, backward, steady speed, accelerate or break.

“It has been these two inter-related developments — high-speed computers and scanning technology — that have enabled underground automation to become a reality, and subsequently a commercial success,” says Burridge.

“In addition to constant machine status and engine monitoring, the operator also receives audio feedback from the machine. Machine health status is also displayed on the remote operator’s console.”

ADVANTAGES OF MINEGEM

Originally designed to be employed in dangerous areas, the MINEGEM system has since proved to have additional advantages: speed-efficiency, a reduction in damage to the LHDs, and virtually continuous equipment utilization, uninterrupted by shift changes and the need to evacuate the area for ventilation after blasting. It is estimated that the overall shift speed-efficiency increases productivity by approximately 25 percent, while side-wall collisions resulting in LHD damage and the need to repair both the equipment and the collision zone are reduced to zero. Additionally, the ability to tram regardless of shift patterns or blasting schedules has been estimated to increase the daily production period by between four and six hours.

The MINEGEM system already has been employed at several world-class operations, including Rio Tinto’s Northparkes Mine, where the system attained more than 95 percent availability, while operating an average of 10 hours per 12-hour shift.

“As one would expect, some LHD operators are strongly opposed to any change, while others see this as a positive step forward, which will remove them from a dangerous, hot, dusty and humid environment,” says Soderholm. “It was a little easier for some of the younger men, who have more computer experience, to get used to the console and joystick workings. To them it is a little like running a video game.”

Automation has removed operators from areas of potential danger, as well as reduced the fatigue they suffer when performing the repetitive and “bone-rattling” tasks associated with running LHDs.

Soderholm explains that computer skills are not nearly as important as knowledge of the way an LHD operates. “Experienced LHD operators do not necessarily have the computer skills, but they do have a better understanding of what is happening to the machine, what it is being asked to do, and more importantly what can go wrong and the indicators that all is not right,” he says. “In my opinion, traditional understanding of the way the machine works, how to make it perform to its best advantages and the very special conditions in underground mining operations, far outweigh any computer skill argument.”

MOVING FORWARD

While computers and scanners are often considered the two tools that provided the step-change necessary for the automation of LHDs, Burridge has predicted that the next significant step will follow the development and commercial availability of the self-learning computer.

“Once this has been achieved, the auto-dig program will become more capable, which will be the final phase toward achieving the fully automated loader,” he says. “Following this it will be possible for 12 to 15 machines to work simultaneously servicing a block caving area with associate fleet management and traffic control systems to allow them to safely work side-by-side.”

While some mines will always require people to work underground, the MINEGEM system is making it possible for some hazardous, repetitive and fatiguing tasks associated with the operation of LHDs to be done from the comfort and safety of a remote control room. The fact that this method of controlling and supervising an LHD has been shown to be efficient, effective and more productive, simply adds to its value.

MALMBERGET MINE TESTING ROCK FACTORY CONCEPT

The very shape and massive size of its ore deposit has led to Malmberget becoming a classic example of the sub-level caving mining method. However, more recently the mine was selected as a testing ground for a new generation of underground loader automation systems being pioneered by Caterpillar as part of the industry’s loosely-termed “rock factory” concept.

“The rock factory concept involves taking the large open-pit mines of the world today and turning them into the successful underground operation of tomorrow,” explains Burridge, a product specialist with Caterpillar Underground Mining. “Over 80 percent of the world’s known ore-bodies today were discovered by examining surface outcrops. Once you get to the bottom of the open-cut — usually dictated by the prohibitive cost of hauling the ore from the bottom of the pit to the surface and the extra amount of overburden removal required to expose a smaller and smaller quantity of ore — there is still ore to be extracted by switching to an underground operation.”

The rock factory concept began as a grass-roots re-evaluation of mining and its traditional extraction methods. This initiative intended to pursue the notion that underground deposits could produce the same tonnages that previously had been possible only from open pit operations. To realize this vision it has been necessary to harness the power and versatility of computerization and its associated technology. Although only in its infancy, the rock factory concept has already achieved some tremendous results.

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