09-10-2012, 10:42 AM
THE COAL RESOURCE
THE COAL.pdf (Size: 2.39 MB / Downloads: 27)
The build-up of silt and other sediments,
together with movements in the earth’s crust
(known as tectonic movements) buried these
swamps and peat bogs, often to great depths.
With burial, the plant material was subjected
to high temperatures and pressures. This
caused physical and chemical changes in the
vegetation, transforming it into peat and then
into coal.
Coal formation began during the
Carboniferous Period – known as the first
coal age – which spanned 360 million to 290
million years ago.
The quality of each coal deposit is determined
by temperature and pressure and by the length
of time in formation, which is referred to as its
‘organic maturity’. Initially the peat is converted
into lignite or ‘brown coal’ – these are coaltypes
with low organic maturity. In comparison
to other coals, lignite is quite soft and its
colour can range from dark black to various
shades of brown.
Types of Coal
The degree of change undergone by a coal as it
matures from peat to anthracite – known as
coalification – has an important bearing on its
physical and chemical properties and is
referred to as the ‘rank’ of the coal.
Low rank coals, such as lignite and subbituminous
coals are typically softer, friable
materials with a dull, earthy appearance. They
are characterised by high moisture levels and
low carbon content, and therefore a low energy
content.
Finding Coal
Coal reserves are discovered through
exploration activities. The process usually
involves creating a geological map of the area,
then carrying out geochemical and geophysical
surveys, followed by exploration drilling. This
allows an accurate picture of the area to be
developed.
The area will only ever become a mine if it is
large enough and of sufficient quality that the
coal can be economically recovered. Once this
has been confirmed, mining operations begin.
Underground Mining
There are two main methods of underground
mining: room-and-pillar and longwall mining.
In room-and-pillar mining, coal deposits are
mined by cutting a network of ‘rooms’ into the
coal seam and leaving behind ‘pillars’ of coal to
support the roof of the mine. These pillars can
be up to 40% of the total coal in the seam –
although this coal can sometimes be recovered
at a later stage. This can be achieved in what is
known as ‘retreat mining’, where coal is mined
from the pillars as workers retreat. The roof is
then allowed to collapse and the mine is
abandoned.
Coal Preparation
Coal straight from the ground, known as runof-
mine (ROM) coal, often contains unwanted
impurities such as rock and dirt and comes in a
mixture of different-sized fragments.
However, coal users need coal of a consistent
quality. Coal preparation – also known as coal
beneficiation or coal washing – refers to the
treatment of ROM coal to ensure a consistent
quality and to enhance its suitability for
particular end-uses.
The treatment depends on the properties of
the coal and its intended use. It may require
only simple crushing or it may need to go
through a complex treatment process to
reduce impurities.
To remove impurities, the raw run-of-mine coal
is crushed and then separated into various size
fractions. Larger material is usually treated
using ‘dense medium separation’.
Safety at Coal Mines
The coal industry takes the issue of safety very
seriously. Coal mining deep underground
involves a higher safety risk than coal mined in
opencast pits. However, modern coal mines
have rigorous safety procedures, health and
safety standards and worker education and
training, which have led to significant
improvements in safety levels in both
underground and opencast mining (see graph on
page 11 for a comparison of safety levels in US
coal mining compared to other industry sectors).
There are still problems within the industry.
The majority of coal mine accidents and
fatalities occur in China. Most accidents are in
small scale town and village mines, often
illegally operated, where mining techniques are
labour intensive and use very basic equipment.
Coal Consumption
Coal plays a vital role in power generation and
this role is set to continue. Coal currently fuels
39% of the world’s electricity and this
proportion is expected to remain at similar
levels over the next 30 years.
Consumption of steam coal is projected to
grow by 1.5% per year over the period 2002-
2030. Lignite, also used in power generation,
will grow by 1% per year. Demand for coking
coal in iron and steel production is set to
increase by 0.9% per year over this period.
The biggest market for coal is Asia, which
currently accounts for 54% of global coal
consumption – although China is responsible
for a significant proportion of this. Many
countries do not have natural energy resources
sufficient to cover their energy needs, and
therefore need to import energy to help meet
their requirements. Japan, Chinese Taipei and
Korea, for example, import significant
quantities of steam coal for electricity
generation and coking coal for
steel production.