Coal Mining Methods
Overview
 Coal
is mined by two main methods -
The choice of method is largely
determined by the geology of the coal deposit,
in particular the depth of the seam below the
surface.
The majority of the world's coal reserves are
recoverable by underground mining. Currently,
almost two-thirds of hard coal production worldwide
comes from underground mines, but in certain important
coal producing countries, such as the USA and
Australia, this proportion is significantly lower.
Underground
Mining
There are two main methods
of extracting coal by underground mining: room-and-pillar
(or, bord-and-pillar) and longwall mining.
Cutaway of underground mine, south coast New South
Wales, Australia (room and pillar method)
Room-and-pillar mining involves cutting
a network of 'rooms' or panels into the coal seam
and leaving behind 'pillars' of coal to support
the roof of the mine. Initially, recoveries are
reduced (to 50-60 per cent) because of the coal
left in the pillars - however, this coal can sometimes
be recovered at a later stage of mine life.
Longwall mining involves the use of mechanised
shearers to cut and remove the coal at the face,
which can vary in length from 100-250 m.
Self-advancing, hydraulic-powered supports temporarily
hold up the roof whilst the coal is extracted.
The roof over the area behind the face, from which
the coal has been removed, is then allowed to
collapse. Over 75 per cent of the coal in the
deposit can be extracted using this method.
Open-Cut (Surface)
Mining
Surface mining, economic only when the coal seam
is relatively close to the surface, recovers a
higher proportion of the coal deposit than underground
methods.
 The
equipment used includes: draglines, which remove
the overburden (the term given to the strata between
the coal seams and the surface); power shovels;
large trucks, which transport overburden and coal;
bucket wheel excavators; and high capacity conveyors.
Surface mining equipment has increased dramatically
in size over recent years. However, in some countries,
the high capital cost of importing this equipment
can favour the selection of underground mining.
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