Impact of rehandling
Rehandling contributes significantly to
the material degradation occurring
during the mining process. Simulating
the rehandling of material, Wirtgen
conducted a study to establish the
amount of material degradation that
does occur. For simulation purposes,
80 t of material was loaded by a wheel
loader and run through a screening
plant several times.
With every throughput, the amount
of fine material increased significantly.
During five test cycles in coal, the
amount of material <4 mm increased
from 19% to 26%, representing an
increase of 34%. A similar result was
found with sedimentary ore: the fine
fraction increased by 24% during five
test cycles (Figure 3).
None of the steps in this rehandling
simulation (loading, transport to the
screen deck, sizing on the screen deck
itself) involves the high material stress
levels that would be induced, for
example, by a dozer moving on
stockpiled material. Nevertheless,
significant material degradation was
measured during the simulation. One
can assume that the material
degradation that takes place during
stockpiling results in an even higher
increase of the fine fractions.
Keeping in mind that even this kind
of ‘soft’ rehandling causes significant
material degradation and that a lot of
rehandling steps occur all along the
mining process, it is important to
minimise the number of rehandling
steps. What is more, every rehandling
step itself results in additional costs.
This is where Wirtgen surface miners
offer a two-fold advantage: material
mined with a surface miner has not
been blasted, but cut out of the ground
by the rotating cutting drum, thus the
level of fines is already low. But as the
material is loaded straight onto a truck,
rehandling is kept to a minimum and
thus the level of fines stays as low as
possible.
Looking at the complete mining
operation, using a surface miner
simplifies operations and reduces the
number of process steps (Figure 4),
resulting in immediate cost savings.
Summary
High levels of coal fines in the
ROM material result in higher
costs for washing, lower recovery,
reduced workplace safety and
negative impacts on the
downstream processes. Knowing
where these coal fines come from
and optimising the procedures
along the process chain can yield
significant savings.
Wirtgen has conducted several
studies to address the fines problem
and proved that it is possible to
reduce the levels of coal fines in the
ROM: mining coal with a Wirtgen
surface miner is a first step toward
substantial savings in the process
chain. Additionally, operating a
Wirtgen surface miner will reduce the
quantity of active equipment required
to load one tonne of coal by
streamlining the mining process.
Furthermore, it will simplify the
interdependence of process steps in
mining operation, reducing costly
time losses between the individual
process steps.
Figure 4. Process steps in the mining of coal using either conventional mining or surface miners.
Figure 3. Increasing level of fines with every rehandling step.
32
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World Coal
|
March 2016
