March 2016
|
World Coal
|
29
M
ost coal mines measure the particle size
distribution (PSD) of their plant feed to obtain
information about the suitability of the feed for
their process, especially regarding the fines
content. But few mines know where these fines come from
exactly, and few still actually measure the fines content at the
face to compare it to the plant feed data and to optimise the
processes in between – although optimising the fines content
of the ROM coal offers numerous savings and benefits:
n
The cost of washing coal fines is higher because of
the processes used and the product losses that occur
(resulting – as well – in a lower recovery).
n
With increased losses, more tailings have to be disposed
in a suitable facility.
n
Coal that does not meet the customer’s size
requirements cannot be sold.
n
A lower level of fines in the ROM results in a lower
level of respirable and airborne dust, increasing
workplace safety and reducing the risk of coal dust
explosions.
n
Coal fines have the tendency to retain moisture, which
causes disadvantages in the downstream processes.
The breakage of coal occurs throughout the process
chain, from extraction at the face to the point where it is
used. Some of this breakage is intentional, e.g. extraction
and crushing, and some is unwanted, occurring when the
coal is transported, stockpiled, sized or washed. Generally,
breakage behaviour greatly depends on the geology, but
mining technology offers a chance to affect the amount of
fines generated along the process chain. It is of the utmost
importance to use this chance and reduce the level of fines
to the greatest possible extent.
Wirtgen has conducted several large-scale field tests on
material degradation recently. It was found that Wirtgen
surface miners offer significant advantages when it comes
to the reduction of fines.
Wirtgen surface miners
AWirtgen surface miner is a crawler-mounted mining
machine with a rotating cutting drum for rock penetration
mounted at the centre of gravity. This ensures that the full
machine weight of the miner can be transformed into rock
penetration force. The cutting drum transfers the material
onto a conveyor belt (Figure 1) from which it is directly
loaded onto a dump truck.
Wirtgen surface miners – here the power pack 4200 SM – cut and crush the rock with
a special cutting drum and load it onto dumpers in a single pass via a conveyor system.
Wirtgen is the only manufacturer that can offer a performance range up to 3000 tph
with direct loading by conveyor belt.
