By Russell A. Carter, Western Editor
As the oldest noncaptive operation in Wyoming’s Powder River Basin, the Belle Ayr mine has seen many changes during its 38-year history, including numerous market cycles, advances in mining technology—and ownership, starting with original owner Amax Coal, followed by Cyprus Amax Coal, RAG, Foundation Coal Holdings, and current owner Alpha Natural Resources following the merger of Foundation with ANR in 2009.
The mine, located south of Gillette, Wyo., has maintained its reputation as a strong performer for all of its owners since it began shipping coal in 1972. By mid-year 2010, Belle Ayr had produced 11.9 million tons of thermal coal which, when combined with 11.4 million tons from Eagle Butte, ANR’s other PRB mine, put both mines on track to reach the company’s projected 2010 production range of 47 million to 50 million tons from its western U.S. operations. At that production rate, Belle Ayr moved approximately 92 million yd3 of material last year.
Another enduring characteristic has been its mining method: Belle Ayr began as a truck/shovel operation and has stayed with that approach while many other PRB mines have transitioned to dragline operations to meet the challenges of increasing overburden thickness. At least part of Belle Ayr’s commitment to truck/shovel mining has been dictated by local conditions: In the earlier years of its operation, its pit dimensions were limited by the presence of a stream that crossed the property. And as mining moved to the property’s high-ratio reserves, overburden depth would have required pre-stripping and spoil rehandling to maintain adequate production from even a large dragline.
Currently, the mine’s average strip ratio is 3.5:1. Coal is extracted from a single main seam that varies between 70–90 ft thick. Although it has looked at cast blasting and occasionally uses it, the mine’s bulldozer fleet is not large enough to support the method full-time while carrying out other necessary tasks.
Over the years, mine management hasn’t been timid about adopting new technology; Belle Ayr was quick to buy Caterpillar’s largest road grader, the Model 24, when it was introduced in 1996, for example, and was the first PRB mine to pass 120-ton shovel loads. In 2007, after haul distances had grown to uneconomical lengths, it installed a $40-million, near-pit crusher station and 2.5-mile overland conveyor system that reduced the average haul length to a mile or less and which now handles about 95% of coal delivered to its load-out facilities. The overland conveyor installation freed up several trucks to switch to overburden removal while alleviating the rising costs of truck tires and diesel fuel.
Belle Ayr has been an active partner with its major equipment vendors in various field-development and field-follow programs, said Belle Ayr/Eagle Butte Operations Superintendent Shane Durgin. “These programs give us a fresh look at new technology.”
In fact, asset utilization is specifically addressed in the mine’s mission statement, said Durgin. “Our goal is to achieve world-class asset utilization—to select, buy and use mining equipment better than any other operation can.”
To support that effort, the mine conducts a continuous improvement program across the entire operation, administered by a dedicated coordinator and employing Six Sigma principles to identify and reduce variances from specified standards and goals. Another tool is its Coal Management Planning Process (CMPP) which encompasses everything from annual budgeting down to monthly forecasting and daily scheduling. The process enables Belle Ayr operations and maintenance management, for example, to track haulage performance and costs down to the last ton hauled per truck per year and the amount of fuel used to haul it, in tenths of a gallon.
Mechanical Drive Measures Up
The mine currently uses a fleet of nine Caterpillar 797B mechanical-drive trucks for overburden haulage, and 360-ton-capacity Bucyrus (formerly Terex) MT4000 trucks, along with a Cat 793, for coal haulage. Also part of the equipment fleet are three Cat 797F pre-production model trucks, and the mine plans to acquire more of these 400-ton-capacity ultra-class haulers. All of the Caterpillar trucks are fitted with Cat MSD II bodies.
Although the demands placed upon trucks in typical Powder River Basin applications—where haul routes are generally straight and flat to mildly inclined—aren’t as extreme as with, say, trucks hauling copper ore or waste out of a quarter-mile-deep pit, there are still operating challenges to overcome: higher speeds can wear out brakes and other components prematurely; suspensions can break, and tires can overheat if speed and payload aren’t closely controlled, or incur cuts from loose rock; and extreme weather conditions can make service and maintenance work tougher to perform. In Belle Ayr’s case rain, not snow, causes more traction and handling problems, and intermittent layers of wet and dry sand in the upper portions of its overburden strata pose additional traction problems for trucks. In fact, said Durgin, the soft ground is probably the top problem for haulage at Belle Ayr. “For us, mechanical drive trucks are the most appropriate choice. There are situations here where electric drive trucks can’t operate,” he said.
After almost four decades of truck/ shovel mining, it might be expected that Belle Ayr’s staff and workforce has developed considerable expertise in this type of operation. One of the key elements in its efficient use of large, rigid-body haul trucks and electric rope shovels is a comprehensive approach that combines maintenance and repair contract agreements (MARCs) from its major vendors with a large measure of on-site, do-it-yourself maintenance work covering a wide range of equipment types. One of the major dividends from the mine’s investment of time and money in maintenance is its ability to regularly wring high operating hours out of its haulage trucks.
Last year, Belle Ayr reported that two of its Cat 793Bs had almost reached or exceeded 8,000 operating hours over a 12-month operating period. This is not an uncommon event at the two ANR mines, according to management: Eagle Butte also has racked up more than 8,000 hours/year from some of its 793Bs, with six-year-old trucks reaching between 50,000-52,000 total operating hours. For the two high-hour Belle Ayr trucks, vital statistics include a total of 8,069 operating hours, utilization of 92.8%, mechanical availability of 92.3% and 11,528,000 tons hauled during the year for one; and 7,699 hours, 92.7% utilization, 92.2% availability and 11,198,768 tons hauled for the other.
“Those are ‘meter’ hours, with the engine running,” said Ken Ferguson, maintenance superintendent for both mines. Ferguson said reaching the 8,000-hour mark at Belle Ayr represented 10.53 operational hours per shift, with 1.73 hours of idle time. “In other words, our trucks are scheduled to operate every hour of the year, and then that number is reduced by any necessary downtime or delays.”
Ferguson orchestrates the activities of an 83-person department that handles maintenance at both mines, and is principal architect of the maintenance program that enables their trucks to operate at consistently high productivity levels. It’s not just a matter of pride-of-accomplishment for the maintenance crews to achieve consistently high mechanical availability throughout the truck fleet, Ferguson noted; it makes solid economic sense. Benefits include fewer trucks needed to accomplish production goals—and fewer operators—along with better return on equipment investment, among others.
Throughout the mining industry, well-planned equipment maintenance is commonly regarded as offering the greatest potential for achieving high mechanical availability. At Belle Ayr, one of the cornerstones of the mine’s truck maintenance program is a “pre-PPM” inspection, typically conducted three days before a truck is scheduled for its regular preventive-maintenance shop visit. During the pre-PPM, a maintenance inspector thoroughly examines the truck in the field and interviews the operator to identify any mechanical problems that might require service beyond routine PM items. Parts can then be ordered to arrive in time to perform the needed repairs while the truck is in the shop for PM service.
Because total costs of unscheduled downtime can be as much as 15 times that of planned maintenance, Belle Ayr’s Planned Component Replacement (PCR) program schedules required component replacement for its production equipment five years ahead, with replacements that will take place over the next two years scheduled down to the month.
Shovel buckets are rebuilt in-house and spares are always available, but no bucket is rebuilt until the year in which it is scheduled for replacement.
Similarly, the mine handles all truck-body rebuilds in-house—actually, out in the open, year-round, carried out by a two-man crew that employs a portable welding trailer. Overburden bodies average about 20,000 hours before a rebuild is needed, but body condition is monitored during PM jobs to confirm that no repairs are required before the scheduled rebuild date. The mine also keeps one rebuilt coal body ready for installation at all times.
Over the shorter term, the mine attempts to keep unplanned repair time to a minimum on all of its production equipment by various measures that include maintaining a full hose inventory for its 793/797 trucks—thereby reducing what could be four to five hours out-of-service, as mechanics wait for a hose to be delivered from the dealer, to a 90-minute remove-and-replace operation. Spare trip ropes are carried on all shovels, with backup supplies stored in the maintenance yard. Shovel ropes are scheduled for changeout on a cubic yard/tons-loaded basis, not according to time elapsed since the last changeout, and generally last for about 3.6 million yd3 before replacement is needed.
Primary loading equipment includes P&H 4100 XPB, Bucyrus 495HR, and Dresser-Marion 301 shovels for overburden and two 47-yd3-capacity Bucyrus 295 shovels for coal loading. The 120-ton-capacity 4100XPB, according to mine management, loaded 36 million yd3 of material in its second year of operation at the mine, and typically moves 60,000 yd3 during a shift, filling 797s in three passes.
Road Care Keeps Trucks Rolling
When it comes to mining productivity, even top-notch mechanical-availability performance can be undercut by a wide-ranging set of factors that might include, for example, casual haul-road maintenance, poorly planned refuel/lunch breaks or less-than-optimal shift-change management. Maintaining consistently high productivity levels generally requires a concerted effort from all mine departments, using the tools available to them to maximum advantage.
At Belle Ayr, getting “the basics” right from the start is important to management, and given the close relationship between overall productivity and haulage conditions—average haul length, road surface and profile, etc.—the mine’s 150-ft-wide haul roads receive a lot of attention. Although the roads are engineered and built using best practices, constant pounding from trucks with 250-, 360- and 400-ton payload capacities makes regular care a necessity. Road surfaces are maintained with a grader fleet comprising Cat 16H and 24H models. “We couldn’t really function with these ultra-class trucks without the 24,” said Ken Ferguson. To reduce road repair time, piles of crushed scoria (local volcanic rock) are strategically placed around the mine site; when repairs are required, a scraper is used to cut out any soft spots and resurface as needed, spreading material from the scoria piles.
Adhering to the philosophy that the haul road begins at the face and ends at the dump, the mine uses Cat 854 wheel dozers in both areas to clean up spillage and other loose material that can cause tire problems.
Belle Ayr also employs Caterpillar’s Road Analysis Control (RAC), a system that monitors racking (twisting due to uneven load on diagonally opposite tires) and pitch (force on frame front to rear from bumps and dips) that road and load conditions impose on haulers—and which, incidentally, was developed and tested at Belle Ayr before commercial introduction. Road-related “high RAC” events are relayed to dispatchers for attention.
These measures, combined with a operator-education program that focuses on proper driving techniques, attention to changing road conditions and tire-care issues, also has enabled the mine to increase average tire life from 5,300 hours to 11,800 hours, said Ferguson.
To minimize truck downtime, shift changes are combined with overburden-truck refueling. Because they are considered a Key Process Indicator-level item, they are tightly managed, with the goal being a full changeover within 32 minutes, including the refueling operation. At the shift change, dispatchers coordinate to perform a staged shutdown, grouping trucks assigned to overburden haulage as advantageously as possible to allow quick refueling from the mine’s 8,000- and 4,500-gallon-capacity tankers. The larger fuel truck, built by support-equipment specialist Ground Force Mfg. of Post Falls, Idaho, can fill a fuel tank in 4.5 minutes. Coal haulers are driven to an in-pit fuel station for refilling during the lunch break.
All diesel fuel is filtered upon delivery and when being dispensed. The inclusion of the 797Fs in the haulage fleet makes it mandatory to provide filtration down to the 6-micron level—a requirement that’s now almost universal on newer diesels such as the Cat C175-20 that employ high-pressure common rail fuel systems. Even with this high level of filtration, Ferguson said the injector units on all haulage engines are replaced at the midway point in engine service life just to maintain fuel efficiency. And, speaking of fuel efficiency, he noted the three 797Fs in field-follow service at the mine, when operating in “economy” mode, actually provided lower fuel consumption rates than the mine’s older 793s.
Worth the Cost
At operations as tightly scheduled as Belle Ayr, where the goal is to load an unending procession of 150-car unit trains in less than four hours each, high equipment utilization rates as well as mechanical availability figures in the plus-90% range are mandatory in maintaining production levels. Preventive, and predictive, maintenance programs for the mine’s primary production equipment are key to achieving these goals, and although thorough PM servicing takes a certain amount of time away from potential operating hours, it’s a cost that mine management seems willing to bear. “You really can’t argue with success. We’re getting 8,000 hours out of our trucks,” said Durgin.
