Contour's Highwall Miners Control Costs

With the final figures available from one of Contour Mining’s operations, internationally acclaimed mining writer Simon Walker spoke to the company’s vice-president, Dave Bundy, about what had been achieved.

Headquartered in Summersville, West Virginia, Contour Mining Corp. operates two Terex SHM highwall miners, producing low-cost coal on a contract-mining basis for resource owners in the Appalachian coalfield. Having begun highwall coal recovery using augers in 1985, today the company operates two Terex SHM miners with work sites in West Virginia.

Contour Mining’s COO., Dave Bundy, explained the background to the company and its operations. “Our first experience with a Terex SHM highwall miner came with a mining contract that we carried out for Peabody,” he said. “Peabody took the machine over, and we acquired another – Terex SHM No.27 – in April the following year."

“We used it for about 18 months on a couple of mine sites, then in August of 2004 we began a new contract for Amvest Corp. at its Powellton Coal Co. mine near Jodie, West Virginia. We bought our second Terex SHM highwall miner - No.46 - in April 2006,” he went on, “since then it has been working at United Coals’ Century property, located near Buckhannon in the northern part of the state."

Contour’s Powellton site used No. 27 highwall miner which produced a staggering 2,069,696 short tons (1.87 Mt) of coal during 34 months of operation. As Mr. Bundy pointed out, that comes to an average of over 60,873 tons (56,900 t) per month, a figure that does, however, mask some real achievements. “Our maximum monthly production came to 78,862 tons (71,560 t) in March 2007,” he went on, “and that beat our previous monthly record by just over 600 tons. When you consider that the seam was averaging 52 in (1.47 m) in height, it shows just how productive the Terex SHM machines can be, even when we are using a low-seam cutterhead.”

See the Terex SHM Highwall Mining System in action in our new High Definition Highwall Mining Video. 

What the average figure does not take into account as well is the time needed for a major overhaul to the cutterhead that Contour Mining carried out, in-house, in July last year. Involving a total rebuild, this was the first such work that the cutterhead had needed since new, having mined at least 2,250,000 tons (2 Mt) in the mean time.

The Cutting Edge

Terex SHM’s highwall miners have the capability to carry both low-seam and standard-height cutterheads. This gives increased flexibility, especially where operators are working in small reserve areas, or where two or more seams of differing recoverable thicknesses can be accessed. Low-seam cutterhead modules can mine seams from 28 to 64 in (710-1,625 mm) in thickness, medium modules are designed for work in seams 36-90 in (915-2,290 mm) thick, and high-seam cutterheads are used for seams from 50 in (1,270 mm) to 16 ft (4.8 m) thick.

Depending on the individual application, cutterhead drums can be provided with diameters ranging from 22 in (560 mm) to 44 in (1,120 mm). While the company uses Joy 12CM- and 14CM-series cutterheads for thick- and medium-seam applications respectively, its low-seam unit was designed in-house. Just as in a conventional continuous miner, in-seam coal is cut by sumping the cutterhead forward, then raising or dropping it in an arc, allowing the cut coal to fall to the gathering-arm loader below.

Better than predicted

The major overhaul on the cutterhead and the miner that took place last year allowed Contour Mining to get a better idea of the real costs of highwall mining than had been possible before. Dave Bundy admits to having been pleasantly surprised. “Terex SHM expected us to spend around US$100,000 a year on maintenance and repairs to the cutterhead,” he said, “and the real figure has been significantly less than that."

“To give an idea of the costs that we incurred,” he went on, “in 2006, keeping the cutterhead working cost us US¢29/ton, including the rebuild.” To put that into context, the cutterhead’s cost during the first quarter of this year, during which time it only underwent regular maintenance such as the replacement of picks and cutter chains, was US¢15/ton.

The other area with which Mr Bundy has been particularly pleased has been in the lifespan of the cutter chains on the low-seam cutterhead. “When we started at the Powellton site in August 2004,” he said, “we were getting about 25,000 tons of coal from a set of chains. We worked with the chain manufacturer to make improvements to the design, so now we are producing over 125,000 tons from a set, something that we’ve never achieved before. That obviously makes a big difference to the cost of keeping the system running,” he added, pointing out that this was not a soft-coal seam. Its Hardgrove Grinding Index of around 50 confirms that there is a fair proportion of harder rock within the seam itself, making for more abrasive cutting conditions.

With the No. 27 machine now working on a different site with a mid-seam cutterhead, the company has had the opportunity to bring the low-seam unit back into its workshop for another check-up. “There were only minor things to do,” Mr Bundy noted, “and they probably cost us less than US$5,000 in all.”

Pushbeam Maintenance

The cutterhead is by no means the only maintenance item on a highwall miner, with the pushbeams coming a close second in terms of per-ton costs. The pushbeams fulfill two functions: not only do they transmit the sumping force generated by hydraulic rams on the miner vehicle itself to the cutterhead, but they also provide the means of transporting cut coal back along the entry from the cutterhead to the mine bench.

In order to keep the cut coal as clean as possible during its journey to surface, Terex SHM has focused on an enclosed transport system rather than a belt conveyor on which the coal can be contaminated by falling roof rock. Each 20 ft (6.1 m) pushbeam contains two 17 in (430 mm)-diameter augers that interconnect sequentially as each new beam is added during mining, with the augers and their bearings subject to constant abrasion from the damp cut coal as it is fed along.

In addition, the pushbeams themselves have a hard life, with the bottom being pushed and pulled along the entry floor and the top and sides requiring resistance to impact from falling rock as well as to corrosion from any acidic water present. In order to give as long a working life as possible, Terex SHM has its pushbeams constructed from high-tensile corrosion-resistant Cor-Ten steel for the top and sides, and Hardox abrasion-resistant steel for the bottom.

Safety first, second, and third

One of the things that Dave Bundy is most proud of in relation to Contour Mining’s highwalling operations is the company’s safety record. In 2005, its Powellton crews worked over 33,000 hours without a lost-time accident (LTA), resulting in the company achieving a top-three place in the annual Sentinels of Safety awards for small mine operations. Here, four-man teams worked 12-hour shifts on a four days on/four days off roster, with a total of 16 operators on the payroll.

For 2006, however, Mr. Bundy is optimistic of another award, since the team clocked up over 38,000 hours without an LTA while producing 713,000 tons (647,000 t) of coal.

Looking ahead, he is now evaluating potential worksites for the No. 46 Terex SHM machine. While No. 27 is mining in a 2.4 m (8 ft) seam at another Amvest site before its low-seam cutterhead is reinstalled, he expects No. 46 to be moving to a new contract within weeks.

Moving a Terex SHM miner holds no fears for the company, which has already done this several times in the past. Mr. Bundy gave one example of the time-frame involved in such a move, explaining that this particular machine had finished mining on a Saturday morning, was split into its transport modules and completely rebuilt at a new site by the following Friday, and was back at work within two more days.

“It typically takes four to five hours to break down the miner and get it on to trucks ready to move,” he said. “We do all the disconnecting of hydraulic lines and power cables, and unbolt the parts, then the haulage company brings in a 165 st (150t) -capacity crane and loads them onto trucks. At the other end, it’s just the reverse procedure,” he added.

Looking at the current U.S. coal market, Mr. Bundy sees the situation beginning to improve, especially in the coking-coal and industrial steam-coal sectors that have provided much of Contour Mining’s work to date. The company is also helped by its clients often having long-term supply contracts that are not affected by swings in spot-market prices.

Since acquiring its first Terex SHM highwall miner, Contour Mining has been extremely proactive in innovating new design concepts for its machines. Having been the driving force behind the development of the 90 degree rear-discharge system that SHM now fits as standard to all of its miners, it was also instrumental in helping Terex SHM to develop its gamma detector system for accurate in-seam steering of the cutterhead.

The most recent overhaul to Terex SHM No. 27 has brought the machine up-to-date in terms of its operating systems, transducers, and other critical parts, demonstrating just how easy it is to retrofit new technology to the existing design. With this included in the cost of less than US¢50/t in keeping the machine fully operational during 2006, this is proof, if any were needed, of the system’s capabilities of producing low-cost coal.