INDUSTRY EQUIPMENT: MINING
it is not that economical to mine with a
surface miner,” Fennell adds.
Frequent questions are about fuel
consumption and maintenance, especially
replacing tips on the milling drum. “It all
depends on how hard the material is that
you are mining, how fast you are driving
the machine and how deep you are milling.
There is a lot of variation. You cannot say that
because you change one or two tips at 200+
hours in Botswana harvesting salt, which is
a very soft material (although very corrosive)
the same would apply to an iron ore mine
in Australia, for example. In a coal mining
operation, you will have to change tips more
often than in the salt mines for example, but
less than in an iron ore operation,” Fennell
explains. “If compared to the cost of a
traditional surface mining operation, and all
the steps in the process that the surface
miner eliminates, the machine is more fuel
efficient per ton,” he adds.
Coal mining’s potential
The biggest potential for the surface
miners lies in the coal mining industry. It
is ideal for the way Australian and India
mines their coal deposits, however, South
African coal mines seems to be battling
in breaking the traditional way of mining,”
says Fennell.
Fennell says that surface miners offer
significant advantages in the reduction of
contamination experienced in normal open
cast mining methods. In the coal mining
industry, the breakage of coal occurs
throughout production, from extraction at the
face to end use. While some of this breakage
is intentional, such as during extraction
and crushing, breakage occurring during
transportation, stockpiling, sizing or washing
Lingering questions
The surface miners are ideal for large coal mining operations.
is not desired. Generally speaking, breakage
behaviour depends heavily on geology, but
mining technology of today offers the option
to reduce the amount of fines generated
during production to maximise coal
recovery for optimised operation as well as
minimising contamination of mined coal to
increase yields.
Most coal mines measure the particle
size distribution (PSD) of their plant feed
to obtain information about the suitability
of the feed for their processes, especially
with regards to fines content. However,
few mines know precisely where these
fines come from and even fewer measure
the fines content at the face to compare it
with the plant feed data and to optimise the
connecting processes.
“There are a number of challenges
associated with failing to optimise this
connecting process. The cost of washing
coal fines is higher because of the intensive
processes used and the product losses
that occur, all resulting in a lower rate of
recovery. With increased losses, more
tailings must be suitably disposed of and
coal that does not meet the customer’s size
requirements cannot be sold. Furthermore,
coal mines have the tendency to retain
moisture, which can cause problems in the
downstream process,” says Fennell.
“On the other hand, optimising fines
content and reducing contamination of the
run-of-mine (ROM) coal offers numerous
savings and benefits, such as a lower level
of respirable and airborne dust, increasing
workplace safety, reducing the risk of coal
dust explosions and improving yields,”
adds Fennell.
PSD field tests
The material can be loaded directly from the conveyor into the haul truck.
22
JANUARY/FEBRUARY 2020
In Wirtgen’s many field tests over the
years on PSD and material degradation,
coal and sedimentary ore from eight
different pits were analysed to obtain
their PSD. Close to 8 000 tons of material
was screened to compare the material
produced by surface miners versus
conventional mining methods.
In one coal mine, Wirtgen surface
miners operated alongside dozers that
employed the conventional rip-and-stack
method and in view of the coal prices
at the time, the mine was optimising
every step of the operation. This included
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