Published in the December 2009 Coal USA Magazine
Amid the rich seams of the Illinois Basin sits Knight Hawk Coal’s Prairie Eagle complex, where the Prairie Eagle underground operation takes center stage. The boxcut/drift mine commenced production in August 2006 and its short life thus far has made quite an impact on the region through favorable conditions and its use of perimeter mining methods.
A relatively small crew of 87 workers gather at the portal in Cutler, Perry County, for the short trip underground to the mine’s active sections that sit under just 110 feet of overburden. Though significantly shallower than its neighbors, Prairie Eagle is quite roomy with a seam height average of 78 inches (range is 5-8 feet) in the Illinois Herrin No. 6 and a cutting height of 80-84in.
Operations are led by Knight Hawk founder Steve Carter and vice president of operations Josh Carter. The underground management team includes mining operations manager Dale Winter, maintenance manager Mike Followell, mine manager Gary Chaney, and mine operations engineer Tom Hasenstab.
The group proudly notes the mine is running two super-sections: each fleet consists of two Joy 14CM15 continuous miners, two Fletcher Roof Ranger II roof bolters, four DBT-Bucyrus 816 battery coal haulers, one Fairchild 35C-WH battery scoop and one Cogar CF56-A1-C-DH feeder breaker. Both sections use extended cuts.
The mine’s layout consists not just of panels with rooms but also a more atypical feature for the area, perimeter mining, which was chosen in the mine’s design to maximize the reserve and mining efficiency.
“It is a modified room and pillar layout making perimeter cuts on the outside ends of each set of rooms,” Winter noted. “This would be considered partial recovery and has proven to be a very effective and productive method of mining at PE with no planned subsidence.”
While uniquely shallow, the mine has diverse cover that includes competent Brereton limestone as well as Anna and Energy shale; total consolidated overburden is approximately 70-80 feet thick. The Brereton is found throughout the entire reserve, while the Anna – a hard black shale – and the softer grey shale Energy are more infrequent but are accompanied by slickenslides.
“Prairie Eagle has good to very good geology,” Steve Carter said. “There are no real main challenges at this property as far as geology is concerned.”
Roof bolt spacing underground at Prairie Eagle is 4.5ft row to row and bolt to bolt, standard spacing for the southern Illinois region of the Illinois Basin.
The mine utilizes Excel/Minova roof bolts that range from 30in conventional to resin-assisted double-lock bolts measuring 72in, the former much more prevalently seen in the main anchor zone of the Brereton limestone. It also installs wire mesh throughout the mine’s key areas, including escapeways and travelways, belt drive areas, and the sections where electrical installations and battery charging barns are placed.
In its development, the operation leaves a typical entry width on mains and 19ft on submains; typical panel and room entry widths are 20ft. Main pillar sizes are a stable 60ft by 80ft, and once in the panels pillar sizes are just slightly smaller at 60ft by 60ft.
As coal is pulled from the mine at an average 2637 raw tons per unit shift (advance rate of 377ft), it travels along a series of panel and mainline belts, both 48in in width and rated for 1800 tons per hour. All belt applications at Knight Hawk use Goodyear three-ply 600 PIW belting.
AMS-Bucyrus has supplied all of the mine’s belt terminal groups. Mainline drives are 250hp alignment-free and the panel belts are dual 200hp. Continental Conveyor was the chosen original equipment manufacturer for the rigid roof-hung infrastructure that can be seen on both the mains and panels.
The intricate, well-planned setup can easily handle current output rates, and is ready for whatever crews can throw at it.
“The current conveying system is more than adequate for the existing production capacity,” Steve Carter noted. “[It] would handle an additional 33 to 50 per cent increase is needed.”
Winter noted that, because gas was not a significant issue for the new kid on the Illinois Basin block, there was no need for pre-drainage.
“Prairie Eagle has very little methane liberation,” the two Carters said, explaining that the shallow cover is part of the reason that just 50,000 cubic feet per minute is liberated daily.
The mine’s ventilation circuit is also a reflection of the favorable conditions; the system consists of a Joy (Howden Buffalo) 7ft exhaust fan. Management explained that because the underground workings included just the two operating sections, it used just a single set of overcasts to split the air.
Blowing line curtain and scrubbers aboard its Joy CM units comprises the face ventilation plan. Crews record typical last crosscut readings of 35,000cfm.
The mine devotes the entire owl shift, an idle period, to maintenance. It conducts preventative schedules determined by its various equipment OEMs for servicing, oil changes and filter changes, while computed tonnage levels and past experience are the basis for other items such as component, pin and bushing exchanges.
Prairie Eagle’s maintenance program is overseen and monitored by Followell. It uses no maintenance planners or software programs for any component. However, its maintenance crew is extensive and includes the manager, a supervisor, four mechanics on nights, five on day and five more on evenings.
The complex does not have an equipment downtime/availability tracking system. While management said availability estimates would be in the high nineties, the absence of a formal program was thanks to its excellent preventive program and the fact that the mine’s entire fleet was brand new when mining commenced.
Also on the operation’s side was its high level of support from its OEMs, the Carters said.
“Since all of the production equipment was purchased new, we went through a considerable time when the equipment was under warranty,” Winter noted. “We saw excellent support through that period and continue to see the same support now.”
Once coal arrives at the surface of Prairie Eagle, it travels to an onsite heavy-media wash plant constructed by Taggart in 2005, which it shares with the highwall and surface portions of Knight Hawk’s complex.
The facility is rated at 550tph and uses heavy media cyclones to separate the coal. Output is typical high-sulfur that the Illinois #6 contains, and has a content near 3% as received and 11,200 British thermal units after washing is completed. About three-quarters of the total product produced from all of the complex’s mines, are shipped by barge from the company’s Mississippi River loading dock while the balance is either truck-delivered or sent on smaller railroad pulls originating on the Illinois Central/Canadian National.
“Knight Hawk has over 40 customers shipping to 12 different states in the US,” the two noted. “The size of KHC customers range from smaller contracts of 5000tpa to larger contracts of nearly one million tons annually.”
Despite a small crew (92 with support personnel), even its largest customer commitments are easily managed with Prairie Eagle underground budgeted to produce 1,634,0006 tons this year (just over 2.4 million tons raw). In September, it was well on its way with 1.323Mt clean already extracted (2Mt raw).
Working hard and working safe are two things the crews of this operation do well. In 2009 it had an accident frequency rate of 3.95, notably lower than the national average. Steve Carter said he believed the mine led its MSHA district for the lowest number of citations issued per inspection day.
This small but mighty team of experienced staff also has the best years of Prairie Eagle’s life ahead of them, as the operation has an extensive reserve base of about 30Mt in place – and that’s just the beginning.
“The existing property is contiguous with considerable reserves that could be accessed from this mine, depending upon ownership. Prairie Eagle is, without a doubt, considered to be a 20-year-plus mine,” he said. “The long-term future of the mine is excellent in the fact that there is a very nice reserve with an excellent workforce.”
Prairie Eagle details
Mine: Prairie Eagle
Owner: Knight Hawk Coal
Location: Perry County, Illinois
Start: August 2006
Seam: Illinois Herrin #6
Depth: 110 feet
Seam height: 78 inches
Cutting height: 80-84 inches
Staff: 87 underground, 5 support
Prairie Eagle runs two super-sections with two Joy 14CM15 continuous miners, two Fletcher Roof Ranger II roof bolters, four DBT-Bucyrus 816 battery coal haulers, one Fairchild 35C-WH battery scoop and one Cogar CF56-A1-C-DH feeder breaker.
