By Steve Fiscor, Editor-in-Chief
Mines rely heavily on conveyors to transport coal. Similar to the mines, the size, number and complexity of conveyors systems vary from site to site. Availability is where they find common ground. Whether it’s serving a small single-section deep mine or a massive train loadout facility, when the conveyor system goes down, the mining company loses money.
Properly engineered conveyors are able to meet the mines needs today and anticipated future needs with the highest availability. Many large, established mining companies can project future production plans 10 to 15 years and they invest in the infrastructure accordingly. New, small- to medium-sized mines, however, require some level of flexibility as the price and demand for the coal they mine may vary. A mining company must be able to realistically predict future production requirements; otherwise they risk seeing the conveyor system become a limiting factor.
Coal demand is a function of electricity and steelmaking, which is based on the economy. During the last few years, the coal business has seen dramatic swings in pricing and demand. From 2006- to mid-2008, coal was not only in high demand, new projects were competing with projects in other industries for men and materials. It was during this period that Thunder Basin Coal built the first train loadout that stretches across the BNSF-UP jointline. The facility had to meet today’s needs, production from pits on the east side of the jointline, and future mining on the west side. In addition to high throughput and availability, Thunder Basin had a strict timeline for completion.
Similar to many sectors, the coal business suffered a setback when the economy bottomed out. The one exception would be the metallurgical coal market. Met coal mines are often accessing deep reserves and mining in difficult conditions. In many cases, the mine or property owner would like to take advantage of high spot prices, which means they have to bring production online quickly. Some have found that outside engineers and service firms can assist in those efforts.
Thunder Basin’s High Volume Installation
The scale of coal mining operations at Arch Coal’s Black Thunder mine is staggering. Six draglines, 22 electric shovels and 150 haul trucks operate continuously to produce nearly 110 million tons per year. Every day, approximately 24 trains cycle through the mine’s three loadout facilities, which load trains in as little as 75 minutes.
The newest of the three loadouts was completed in 2008 as part of $100 million coal handling expansion project. The project consisted of a nearly 2-mile long overland conveyor system that transported coal from a near-pit 7,000-tph crushing installation to two 17,500-ton silos, and a rail turnout from the main line with a five-track yard and a loop that totaled 12.5 miles of rail.
Thunder Basin Coal selected Roberts & Schaefer (R&S) to design the near-pit crushing station and the overland conveyor. At the truck dump, a McLanahan triple roll, two-stage crusher reduces raw coal from 60 inches to 2- x 0-inch. It has a 1,000-ton hooded hopper, which is designed to handle 360-ton haul trucks. From the crusher station, the coal is loaded onto an overland conveyor traveling at 1,150 feet per minute; it is also rated for 7,000 tph. The conveyor crosses the jointline and rises 341 ft to the top of the silos. The elevated portion of the overland conveyor is enclosed in long-span tubular gallery.
The belt is powered by a single drive station with three drive units at a mid-belt location (just as the conveyor is elevated to go to the top of the silos). The total motor horsepower to the drive is 6,750 hp (3 x 2,250 hp). Control systems allow equal drive sharing of the load during all starting, running and stopping conditions. Fenner supplied the belting. Sandvik and Continental Conveyor (now Joy Mining Machinery) supplied the hardware, and the motors and drives are Dodge Reliance (Baldor).
At the loadout, a Kanawha Scales & Systems batch weigh system flood loads the railcars. The system is rated for 12,500 tph and each silo has its own system. The system also uses an HSS Sampling System and a Thermo Gamma-Metrics ash analyzer to monitor product quality.
The rail yard has the capacity to store any combination of five trains empty or loaded.
Coal first ran across the belt in November 2008. Ken Miller, director process improvement, Thunder Basin Coal Co., worked on the project from the early stages of engineering in January 2006 through to completion. It has been in continuous operation ever since. “We refer to this project as the Black Thunder West Loadout,” Miller said. “Right now we are shipping about 3 million tons per month through that facility.”
Thunder Basin had performed some conceptual design work and was in the processing of selecting a location. “We reviewed three possible locations and ultimately decided on this location,” Miller said.
The Black Thunder West Loadout would serve as a replacement for the former North Rochelle facility. Prior to January 2006, Arch Coal sold the North Rochelle facilities to Peabody Energy’s Powder River Coal with a two- to three-year turnover time. “This provided Black Thunder with a facility more centrally located for the rest of the reserves,” Miller said. “From the existing reserves, the pits are advancing to the West. So we were able to position this facility for the future continued westward advance.”
As far as design considerations, the Black Thunder West Loadout would obviously have to be as robust if not more so than the existing loadouts. “All of the Black Thunder overland conveyor systems were 72-inch belts,” Miller said. “We were operating comfortably in the 6,000 tph range and we were convinced that this crushing system could now achieve 7,000 tph. We used that as our basis for this project.”
Today, availability for the system currently stands at more than 97%. The entire system has a high degree of automation, especially with in-pit crushing, conveying, sampling and unit train loading. Miller says he is very satisfied with the outcome of the project. “The Black Thunder West Loadout pushes the envelope on capacities here in the basin,” Miller said. “It’s created a new average by which to operate conveyor/crusher systems for coal.” This system will serve Thunder Basin for the next 20 years.
Managing a Major Construction Project in the PRB
This expansion was the first to extend across the jointline and the rest of the mining community was watching as the Black Thunder West Loadout was constructed. Considering the high degree of availability at all temperatures, high tonnage rates, long spans (including the 280 ft span across the jointline) and the height of the silos, this project presented opportunities for a number of firsts, all of which R&S accomplished, explained Bruce Hale, senior vice president, R&S.
“At its heart, R&S is a materials handling company,” said Hale. “Regardless of the application—a mine, a power plant or a transloading terminal—our expertise is in moving bulk materials from one place to another. We are particularly skilled at loading, conveying and storing coal.”
At the time of construction (2006-2007), the U.S. economic engine was running full throttle. Scheduling work and getting steel delivered was difficult at times. R&S used its network of quality suppliers throughout the United States to source the steel and platework supply. Steel details were provided by both R&S direct as well as steel fabricators. “The design maximized shop assembly where it made sense to minimize field assembly requirements. Many of these procedures reduced the time workers were exposed to the elements.”
As an example, the construction crews chose to pre-assemble the head house on the ground and then lift it as a unit into place atop the silos, mitigating high wind construction conditions. Similarly, the tubular galleries were pre-fitted with conveyor stringers, walkways, wash down piping, and lighting to maximize pre-assembly. The conveyor tube support towers used standardized sub-assemblies to capture the ability to reuse steel fabrication details and shop assemblies on multiple towers.
The challenges of this and any major project required that R&S engineers work closely with the owner, suppliers and erectors through each stage of the project.
“R&S worked closely with Thunder Basin and the contractors, reviewing the challenges of the major structural lifts and designing support points and connections that provided the necessary flexibility to allow each connection to be made safely and accurately at the heights required by this installation the normal tolerances of industrial construction,” Hale said.
Conveyors are an R&S specialty. R&S believes it has unmatched design experience for conveyor systems operating in extreme weather conditions with high tonnage rates and high availability requirements. “Our team approach with the owners, contractors and suppliers allows each critical element to be analyzed and designed to meet the critical requirements of this most important project,” Hale said.
Static and dynamic design analysis of the overland conveyor was performed by AC-Tek, which provided for all design considerations over the operating range and conditions of the conveyor.
The 1,000-ton ROM dump uses a passive dust hood with a fogging system to control fugitive dust emissions. The original passive dust hoods designed by R&S in 1988 for Black Thunder, form the basis for the current state-of-the-art design. In addition to being considered BACT, passive dust hoods eliminate the requirement for baghouse collection systems at the ROM Dumps.
Communications on the project was key. On-line design communications were used to shorten design reviews and delivery of designs to fabricators, Hale explained.
“Few other coal mines ship as much coal as Black Thunder and not having coal available for the continuous stream of unit trains was simply not an option,” said Hale. “We used our proven designs to meet Black Thunder’s high demand requirements.”
Engineering an Existing Met Facility
A couple of hundred miles to the south on the Front Range of the Rocky Mountain is in Colorado, an older met coal mining operation is being restored. While the company’s long-term projections are uncertain as to how far they will ultimately grow production, they needed a dependable conveyor system now and turned to Fenner Dunlop Conveyor Services.
With all of the acquisitions Fenner has made recently, the company is in a somewhat unique position to offer technical support and application engineering. In addition to supplying all conveyor components, they can construct conveyors from initial the design work through to fabrication and installation. The company will even operate and maintain the belts.
The Colorado company recently enlisted Steve West, senior vice president, Fenner Dunlop Loadout Service/Facilities Management, to help in the operation of the surface facilities. Once on site, West recognized this group of miners could use some help regarding conveyors. He called Terry Rafferty, senior vice president, Fenner Dunlop Classic Conveyor, who is based in Pennsylvania, and they put forward a plan for a new slope belt that should serve the mine well for immediate future.
“We have not only had the ability to engineer the slope belt within the scope that was presented to us, but Rafferty and his group have offered assistance to the mine regarding its future plans and conveyor needs,” West said. “They lend expert opinion to develop the best plan for the conveyors.”
The mine, working with Fenner, recently completed a 1,000-ft 17˚ slope belt. “This is a good sized slope belt, with dual 2,000-hp drives capable of hauling 6,500 tph,” Rafferty said. “It has a [variable frequency drive] VFD that runs from 300 fpm up to 900 fpm.”
The mine originally had a 48-inch belt that was upgraded to 60-inch steel cord belt (ST 3150). “The amount of horsepower for the length of the belt is significant,” Rafferty said. “We took the best of the best and put all of that into one steep conveyor system.”
Rafferty believes this is the first slope belt a conveyor company has built in its entirety, the structure, drives, main frames, etc. Ordinarily, several vendors supply several components. “We use brand name motors and gearboxes, but we build the rest,” Rafferty said.
The mine owner gave Fenner the latitude to get more involved in the process, and that’s where Rafferty’s resources with the engineering and fabrication group were able to assist on the project. The plans for the mine’s conveyor system evolve along with the mine plan.
One of the challenges with the project was to tie the slope belt into an existing facility on the surface. “We had to tie into a facility that was an upgrade rather than new installation,” West said. “In doing so, they upgraded the old structure, which was not structurally adequate for this new conveyor.” Rafferty and his team had to engineer and design a self-supporting structure cantilevered into the building.
The difficult part was making sure everything tied in from the slope to the old building and with adequate steel work to handle the new higher tensions on the conveyor. “We didn’t have much real estate to work with—the distance between the slope and the old building was tight,” Rafferty said. “The initial truss work was a tie-in, but as the system developed and volumes grew, it became a stand alone system.” Fenner had to engineer the structure and beams.
Another interesting aspect of this project is it had to be designed as a secondary escape route. “We had to slow the conveyor down so miners could safely ride it and we had to provide areas to get on and off of the belt.” Because of the steepness of the slope, the mine had to offer a mechanical means of exiting the mine. Rafferty acknowledges they are rarely asked to design a system for miners to ride, but they did and it is MSHA compliant.
Fenner recently introduced its Life Cycle Management program to several customers. “We have offered to run, manage and maintain the belts for them,” Rafferty said. “Similar to an equipment leasing program, they pay a fee for the service and we hold costs to a minimum and guarantee availability at more than 97%.” With this program, each mine will have a dedicated Fenner beltman committed to that conveyor system.
Fenner Dunlop Conveyor Services would use the latest in technology to track components and belting along with complete conveyor maintenance including splices, scrapers, servicing the drives, structure maintenance and replacement etc. “With this particular customer we have been involved from the beginning with this mine,” West said. “We understand what they need and we have been able to advise them accordingly.”
The mine is currently a room-and-pillar operation, but the company eventually hopes to install a longwall. The long-term plans call for a new set of slopes with 72-inch conveyors and this would be a great opportunity for Fenner. “This slope belt is a great testing ground,” West said. “This is a case where the mine relied a little more on the supplier and working together the two have established a good relationship.”