Parkstone's Highwall Miner Hit
Parkstone Energy successfully reworks residual coal resources in West Virginia with two highwall miners.
No one disputes that West Virginia is coal country. Lying in the center of the eastern US Appalachian coal field, the state has long been host to both surface and underground coal production, and while today’s industry is concentrated in a few specific areas, historical mine sites abound. Where these have involved contour mining in the past, sandstone highwall outcrops often mark the only trace of previous activity, the rock faces standing proud within the surrounding forests that are such a feature of the rugged mountain landscape here.
Since the passing of the Surface Mining Control and Reclamation Act (SMRCA) in 1977, the requirements placed on mining companies relating to the restoration of mined-out land have changed dramatically. In particular the need is for much better restoration practice than was typically applied in the past, such that the outcrop that marks the top of the highwall is now much less intrusive in the landscape.
However, while “pre-law” highwalls (those created before the SMRCA came into force) remain the focus of ongoing restoration by both the federal and state agencies, current regulations permit companies to rework the residual coal resources, opening up a major market opportunity for highwall miner systems.
With a new operation located on steep valley hillsides about 10 miles
south of the state capital, Charleston, Parkstone Energy is one of the
companies that has grasped this opportunity with both hands.
Parkstone has been working at its Siata mine since the middle of 2005,
and now has not one but two Terex SHM Highwall Miners in operation there.
Parkston president Shannon Keeran explained the sequence of events that
led to the decision to select Terex SHM Highwall Miner for this specific job.
“You have to have the right application for this type of system,” he
said, “and we have miles and miles of pre-law highwall on our
properties." Within about 60 miles, Parkstone Energy has a number of
underground and conventional surface operations, and our acquisition of
this property has added the highwall miner to our production portfolio.
“As well as that we have the luxury that the Siata mine is less than
four miles by truck to our wash plant, which in turn is a mile from the
dock (on the Kanawha River) where we load our coal onto barges for
direct shipment to our customers. With diesel prices the way they are now, that makes a big difference in terms of our transport costs.”
A Four-Seam Resource
Parkstone is now producing coal from a four-seam sequence, contained
within the Upper Carboniferous Kanawha Formation, close to the
geological hinge between the state’s Northern and Southern coal fields.
Of the four seams, resources in the lower three are contained in
pre-law benches; only for the top seam in Parkstone having to produce
coal first in order to open up a new bench on which its highwall miner
can operate.
Nonetheless, as Keeran noted, merely reopening the old benches can
present some challenges in terms of ground clearance. “After
clearcutting the regrowth timber on the benches,” he said, “we clean
down to the old bench level using an excavator. One of the operational
battles we have is keeping enough bench open ahead of the Terex SHM
machines.”
Another operational constraint is imposed by the narrowness of the
existing pre-law benches. Keeran said Parkstone has to live with the
bench widths used by the company that mined here initially although, as
always, challenges such as this can present opportunities for technical
solutions.
“We helped Terex SHM to develop its new return conveyor system on its highwall miner,
which takes cut coal from the rear of the miner back to the center of
the bench,” he said.
“That way, we have much more flexibility for our stockpile and loader
operation there.”
The top, previously unmined seam, the Upper Coalburg, averages around
40 inches in thickness, and is separated from the Lower Coalburg below
by around 50 feet of sandstone and shale interburden. A further 35 ft
of waste separates the 40-42 in Lower Coalburg from the underlying
Winefrede seam, which here averages around 38 in thick.
The bottom seam in the sequence, the Chilton Rider, lies 30 ft below
this, but is thicker than the others, averaging 46-48 in. All four lie
well within the operating range of Terex SHM’s low-seam cutterhead
module, which is fitted to both the highwall miners onsite.
Deeper into the wall
Parkstone’s first Terex SHM Highwall Miner came onsite in July 2005. The
acquisition of additional resource blocks later in the year more than
doubled the mine’s reserves, and this, together with the buoyant coal
market led to the company placing an order with Terex SHM for a second highwall miner. This was delivered in March 2006.
Both highwall miners feature Terex SHM’s rear discharge configuration which,
as the company’s director of engineering Stewart Myers explains, has
been a key to increasing the machine’s production capability.
“Moving from the original vertical-discharge design to rear discharge,
and then introducing the right-angle conveyor concept to take cut coal
from there to the stockpile, was a major advance,” he said.
“Now we have taken the idea a stage further with the second right-angle
conveyor, bringing the coal back to the center of the bench without the
potential for any bottlenecking at the transfer points.”
Parkstone has scheduled its production such that the first highwall miner
is dedicated to mining in the upper two seams – the Coalburgs – while
the newer unit works in the Winifrede and Chilton Rider seams below.
Each highwall miner moves from bench to bench in sequence, with a new stretch
of one bench being prepared while mining is taking place on the other.
That way, as Keeran explained, the two operations can be managed
properly without either getting too far ahead or behind the mine’s
production requirements.
Operating on the top seam involves stripping waste back to a new
highwall, then loading out the seam to leave a working bench for the
miner.
Waste stripped from the top bench is backfilled for restoration
there, and is also used for reclamation on the lower benches. Since it
is a new (rather than reworking) operation, Parkstone is able to create
a wider bench for the Upper Coalburg seam, at around 100 ft, whereas
the pre-law benches below are narrower, ranging from 60-80 ft wide.
Hence the incentive to develop the return-conveyor system, Keeran
noted.
While the full operating depth of the current generation of Terex
SHM Highwall Miners is at least 1000 ft, Parkstone has found that individual
seam conditions at Siata mean that its penetration ability is typically
between 600 ft per hole until the seam begins to roll,” he said.
“In the lower Coalburg we are constrained by the soft shale roof, but
in the Winifrede we can get to 800 ft. For the Chilton Rider, it’s too
early to tell what the maximum might be, although from our experience
in this seam in another of our (underground) mines, it doesn’t seem to
roll too much so we’re looking to go in 800 ft or more.”
Reworking
Aside from the seam geology, previous auger-mining is another
factor that has to be taken into consideration. The three lower seams
on the property were worked to a depth of 80 ft at some time in the
past, using a twin-auger machine that produced pairs of 24
inch-diameter holes in the seam center. While this has clearly depleted
the in-situ resource significantly over this distance, it presents no
problems for the Terex SHM Highwall Miners, which mine out a 9 ft 6 in wide
rectangular entry over the full seam thickness before continuing on
into the deeper untouched resource.
Keeran said the presence of the auger holes does, however, have
implications from a mine engineering point of view.
“Although ideally we would want to follow the contour profile of the
bench – keeping the miner square on to the highwall – for stability
reasons we have to follow the line of the old auger holes,” he said.
“Where the auger mining left barriers, we maintain these and miss out
every 10th entry to provide an additional safety pillar.
“We don’t have that constraint on the top bench so we can plan the
extraction pattern to relate better to the highwall line and to
optimize our coal recovery.”
Conditions are such that Parkstone can mine entries at 13 ft centers,
leaving a 4 ft pillar between entries and achieving a nominal 70%
extraction rate for the in-situ resource.
All the coal produced by the Terex SHM Highwall Miners is hauled by truck to
Parkstone’s wash plant in the bottom valley. Here, the company has
recently invested in a new 600 ton per hour facility, replacing an old
jig plant with dense-medium cyclones that have helped to improve the
recovery of saleable coal by around 10% since they came onstream. In
addition, it is now installing a column-flotation unit to increase the
recovery of fine coal, for which there is a ready market.
Overall, the two Terex SHM Highwall Miners are producing around 110,000 t per
month run-of-mine, leading to an output of some 50,000 tpm of saleable
coal. The entire Siata mine’s output is steam coal that is sold to
electricity utilities. Other units within the Parkstone Energy family
produce metallurgical and stoker coal as well, with the company having
a total production of between 3 and 3.5 million tons of coal annually.
Cost Expectations Met
According to Keeran, highwall mining has
different planning requirements than conventional surface coal
production. “Scheduling is critical to the success of the operation,”
he said, adding that having a highly skilled operating crew is also a
key factor here. “With the control and operating systems built into the Terex SHM Highwall Miners, you need a different skill set to be able to optimize their
performance.”
With skilled operators in short supply, Parkstone has set up incentive
schemes to attract suitable people and training program to ensure that
they are up to speed on the miners’ operating systems.
The two Terex SHM Highwall Miners run round the clock, 11 days out of 14, with a
14-man team for each unit working three eight-hour shifts a day.
Maintenance is vital to keeping the machines operating at full
capacity, with daily preventative maintenance backed up by spot checks
between holes and weekend overhauls.
“We have a meticulous maintenance program,” Keeran said, “and we take
maintenance as seriously as producing coal. If we don’t do the one, the
other suffers.”
In terms of Terex SHM’s reputation for its miners producing low cost
coal, he confirmed that the equipment has met Parkstone’s expectations
in this respect.
In addition, he was generous in his appreciation of the level of
service support the company has received: “Terex SHM is the best of our
vendors in terms of support.”
With the Siata mine currently holding enough permitted reserves to keep
both Terex SHM Highwall Miners operating at current production rates for
three-and-a-half to four years, Parkstone is already seeking further
highwall-mineable resources.
Notwithstanding the fact that the US coal market peaked in 2005 and
that high prices then brought a flood of new products in their wake,
Keeran is confident that the company will continue
to be successful.
With an order already having been placed with Terex SHM for a third
miner to be delivered once the permitting of new reserves has been
completed, there seems little doubt that highwall mining using Terex
SHM Highwall Miners will continue to delivery low cost coal for Parkstone well
into the future.
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