Knight Hawk Coal Age
With the help of Terex SHM Highwall Miners, the surface coal mining company is experiencing productive coal recovery with consistent machine availability.
There’s a new sound coming from under the Illinois flat lands today, a new buzz deep in the pit. Knight Hawk Coal, LLC – the little project dreamed up by F.D. Robertson, James Bunn, and James Bunn, Jr., and ex-Arch V.P. Steve Carter has quietly become one of Illinois’ largest producers, its success further cemented by Arch Coal’s recent 33% buy-in to the little upstart. Following the general implosion of the high sulfur IB market in the 1990s, Knight Hawk has cautiously grown from little gopher hole to a medium size surface miner operating simultaneously in several regional pits.
A few years ago, while planning for their first underground operation and trying to decide what to do with their “tweener” reserves—seams too shallow for the new mine and with ratios too high for another surface job—Knight Hawk took a chance and purchased a Terex Superior Highwall Miner (Terex SHM). Ever since, this small, innovative company has been pioneering the use of highwall mining in a trenching application—learning how on the go, while steadily producing coal in what remains a tough cool market.
Currently, while in advanced development of what will be Knight Hawk’s second underground operation, their Terex SHM steadily and reliably adds to their bottom line, monetizing those tweeners.
Red Wheel Turning at Prairie Eagle
Josh Carter, Steve’s son who has taken over much of the day-to-day
operations at Knight Hawk walked into the conference room adjacent to
his office with the morning’s production report—the dirt still drying
on his boots. He had just returned from his newest operation, the
Prairie Eagle mine where the company’s Terex SHM-32 is punching holes
in a trench, a few thousand feet from where Knight Hawk’s first
continuous miner unit is boring further underground. The Terex SHM’s
signature red wheel slowly pays out more protected cable as the
cutterhead advances with every minute.
Combined, the underground and highwall miner pulled about 1 million
tons of 11,300 Btu coal out of the ground last year. In a cautiously
optimistic tone, Josh allows that there’s a bit of capacity within both
sides of the operation to ramp up the production if the market allows
it. “We did about 3 million last year, all of the operations combined,”
said Josh. “We just do our thing, nothing crazy, trying to keep up with the coal
demand.”
To Strip or Not to Strip, That is the Question
For decades, highwall mining for coal has been something undertaken at the
end of a mine’s economic life, when the average stripping ratios of a
surface mine are getting too high or jump. In Appalachia, it’s
practiced as contour mining. When surface mining reaches its effective
limits, highwalling is the perfect way to go around a mountain.
While new to the Illinois Basin in its more modern form, in the
right conditions highwall mining is one of the most efficient and
cheapest methods of extracting coal. It allows an operator to remotely
control an extendable cutting head which extracts coal from the exposed
seam at the base of the highwall, typically from a series of parallel
entries driven to a significant depth within the seam horizon. Highwall
mining is a hybrid system capable of accessing reserves for
substantially less capital cost and lead time than a full underground
mine, especially from coal resources that would otherwise be unmineable.
Some statistics suggest that with a Terex SHM machine a coal mining
company could expect to add anywhere from 75,000 to 150,000 additional
tons per month depending on the coal thickness and cutterhead required
for the operation.
One of the biggest selling points for highwalling in general is its
inherent safety over other methods. This is mainly due to its lowered
labor requirements and that no one has to travel underground. Most
Terex SHM owners use so four to five-man crew consisting of an
operator, a ground man who is responsible for inserting the pushbeams
into the mainframe, a forklift operator who sets the beams onto the
machine, an electrician, and a superintendent or a foreman.
To maintain a safe highwall mining system, operators try to stay
away about 40 feet back from the highwall in case of its sudden
collapse. Equally important is ensuring that the pillars remaining
between individual entries and the barrier pillars that have to be left
between panels of entries, are strong enough to support the highwall
above. However, over-designing these pillars will reduce the recovery
rates, so it is critical from both the safety and economic viewpoints
to make sure that pillar design is optimized.
Over the past 20 years there have been numerous improvements in
highwall technology, especially in terms of understanding how the
forces of nature act on a highwall mining layout. But no matter what,
by all accounts, the first thing an operator will do is make sure they
thoroughly understand the local geology of the coal reserves they plan on
going after. “Do your homework,” said John Harman, vice president of
Vigo Coal, an Indiana-based operation, who rented Knight Hawk’s Terex
SHM while Knight Hawk was preparing for it. “While highwall mining is
site specific and its success is mainly dependent on good roof
conditions, it’s a no brainer if you’ve got the right geologic
conditions that will allow you to have high penetration depth,” said
Harman.
It’s also critical that an operator keep enough face open for the
highwaller at all times. Pretty common on the learning curve is the
realization that the miner can out-perform what’s initially expected of
it. But if the face is exceeded, the miner’s out of production until
another one can be prepared. Terex SHM recommends that 1,000 linear
feet of highwall be maintained in front of the miner as consistently as
possible; and that as it’s operating, more face be exposed in front of
it, or, in trench mining, another trench be prepared simultaneously.
Trench mining with a Terex SHM miner is the preferred option in the
Illinois Basin. Mining companies use heavy equipment to extract coal
while forming a trench anywhere from 100 to 300 feet wide. After
extracting the coal from the trench cut, they would insert a highwall
miner to work both sides of the open wall penetrating another 1,000
feet with a deep mining cutterhead. Knight Hawk has been very
successful in this application with a Terex SHM miner.
Another of the major benefits of today’s highwall mining systems is
its flexibility. In a surface coal mine, an excavator is limited by its
reach—any coal that lies beyond that stays where it is unless the
machine can be moved safely. With a highwall miner, the machine can be
positioned well back from the highwall, leaving the transport
connection between the cutterhead and the miner as the only piece of
equipment vulnerable to falling rock if the wall should fail. Where
this is not an issue, the machine can be positioned closer, but in each
case the operator remains in a safe working environment. No other coal
mining method—in pit or underground—provides that level of security.
Mining underground but with control from the surface also provides
opportunities for coal recovery where in-seam methane would otherwise
be a problem. Today’s highwall miners can be equipped with effective
ventilation equipment to dilute any methane that is released during the
coal cutting process. The cutterhead itself is equipped with methane
monitors that automatically kill the power to the drive if the gas
concentration reaches pre-determined limits.
For small operations that need to maximize resources, highwalling,
according to Harman, is an important option. “Vigo is a small coal
company with a limited amount of reserves,” Harman said. “Anyway we can
use them, we will. We’re mining a pocket of coal along the periphery of
our reserve where stripping wasn’t economical. What we decided was to
construct a box cut and mine off each side.”
Why It’s Superior
Not all highwall miners are created equally. The number of Terex
SHM’s mining systems in use today outnumber their rivals in large part
due to their ability to operate in lower seams with more challenging
roofing and flooring conditions. The extracted coal is protected within
a series of reinforced steel push beams that safely surround a pair of
augers tasked with conveying raw coal to the surface. Because of the
armor, the Terex SHM system can sustain minor roof falls while mining.
The Addcar system, Terex SHM’s main competitor, instead uses a belt in
an open conveyed system that is more prone to getting stuck or cut when
sustaining a roof fall. Its availability suffers as they then have to
retract and fix the belt and start the mining process over.
“With the coal boom, folks were looking to mine coal reserves they hadn’t
otherwise considered,” said Harman. “One thing that’s superior with
their system is that it can mine thinner seams. That’s Terex SHM’s
niche. With Addcar you’re more susceptible to production slowdowns
caused by roof falls, whereas, with their pushbeams being enclosed, you
don’t have that problem with Terex SHM’s system.”
The Terex SHM system itself has been upgraded in many ways as well.
Four main design improvements now allow for an increase in the system’s
seam thickness cutting capabilities by using interchangeable thin,
medium, and thick-seam cutterheads; the introduction of a
higher-capacity rear-discharge system for cut coal; building in anchor
points to increase the machine’s drive force; and providing
gamma-detection systems to improve the control of the cutter head
position within the seam. With its modular construction, today’s
highwall miner can still be moved from mine to mine quickly and
effectively.
Roof collapses continue to be one of the common risks of this
technology. After determining that many of these events are caused by
the miner being positioned in the pit incorrectly and cutting through
the previously mined hole, Terex SHM is now equipping all new miners
with a GPS system. Mounted on the front of the machine, GPS guidance
greatly aids in the alignment of the miner.
In the very near future Terex SHM will offer on its miner as
standard equipment the ability to move the miner out of the pit through
a wireless remote control system. This may prove to be a tremendous
safety feature for the crew of the miner as, in the event of a highwall
fall, the crew will be able to move the miner out of the pit without
actually getting into the cab of the miner. The manufacturer indicates
that “there is strong belief that this also will reduce the insurance
rate on a Terex SHM as well.”
Terex SHM is also in the final stages of placing a remotely operated
camera on the cutterhead as standard equipment as well. This will allow
the coa; operator to view the top to better understand where the cutterhead
is located in regards to the coal seam. The camera is fully protected
inside the framework of the cutterhead and telescopes out when the
operator requests. Terex SHM is currently deploying new gamma detectors
which enable operators to mine cleaner coal requiring less
washing, or in some cases, eliminating the need altogether.
The Knight Hawk Learning Curve
When Knight Hawk decided to purchase their Terex SHM, they were
accepting the challenge of learning how to use it in an area where it
had not yet been proven. “We’ve definitely gone through our learning
phases with it,” Josh said. “For the last 18 months, we’ve had some
good success with it. But when we started, we weren’t set up properly.”
Initially the company was surprised by the volume the miner would
extract and in their initial phase, were unable to keep enough face in
front of it. “But over the last year we’ve found that it’s a really
efficient machine.”
Set up, said Josh, is all about timing, “You have to make sure that
you’ve got highwall in front of it and the right conditions for the
machine. We’ve also learned that, given the amount of fireclay in our
pit floors, we’ve got to give the machine a deeper drilling rig than
Terex SHM offers to get anchored into the bedrock better. That’s a
unique feature for us in the IB. We did install Terex SHM’s upgrade
accessory for deeper drilling,” said Josh. “It has made a big
difference and helps us achieve full penetration.”
Maintenance was one of the most important components in Knight
Hawk’s choice of operating platform. “It’s maintenance friendly,” said
Josh. “Most of your service and mechanical points are out in the open,
as opposed to being buried in a hole. It’s also really flexible. If we
run into trouble, we do something different.”
"At the end of the day, the Terex SHM functions as a great compromise
between a full fledged underground or surface operation. If the ratios
become marginal, trench mine, get some of it and go on,” said Josh.
“It’s a way of getting as much of the coal underground without the
expense of moving all the overburden. You leave some coal behind, but
you don’t have to go through the entire process of stripping. The
trench only needs one box cut. We go down about 95 to 100 feet to where
the Herrin No. 6 seam outcrops.”
On average, Josh said, they’re recovering 60%-70%, depending on the
size of the pillar left between holes, “For us, mostly it’s a 5- to
6-ft pillar, which is more than 100% what many rock mechanics might
say, but we decided that’s right for us.” But no matter what you leave,
you still have to pay for the machine. “None of these units are cheap.
But we’ve found that it’s a good investment up front, especially as
opposed to a fleet of trucks. We feel that over the long run we’ll save
on their associated costs. With the nature of the reserves in the IB,
there are opportunities for this machine and others will start to pick
up on it.”
Today, with well over a century of coal mining behind it, most of
the easy, low ratio surface coal reserves across the nation, and certainly
in the Illinois Basic, have been depleted. In their operating
environment, highwall mining becomes a very feasible and logical step.
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