World Mineral Production - NERC Open Research Archive - Natural ...

COAL
Characteristics
Coal is a combustible sedimentary rock made of lithified plant
remains. A coal seam is formed by the alteration of dead plant
material that initially accumulates as peat on the land surface.
As the peat becomes buried beneath younger sediments the
temperature increases with increasing depth of burial. Peat is
sequentially altered by the process of ‘coalification’, a process
involving the loss of water and volatile components, through
brown coals to black coals.
The physical and chemical properties of coal, that is coal
quality, determine whether a coal can be used commercially.
Calorific value, or the heat energy given off by the combustion
of a unit quantity of fuel is one of the main quality criteria
used by coal consumers. Coal quality is important as it affects
the operation of plant, and thus the costs of generating power,
through its impact on the costs of both maintenance and
conformity with environmental legislation. Chlorine and
sulphur are both detrimental in coal, causing pollution as well
as corrosion in boilers.
Based on the physical properties of different bituminous coals,
a fundamental distinction is made worldwide between steam
coal (or thermal coal), used for burning in boilers, chiefly for
electricity generation, and coking coal, which is used to make
coke for the metallurgical industries. Coking coal produces
coke with sufficient strength to support the loads imposed
within a blast furnace. Steam coal tends to have calorific
values at the lower end of the range.
Uses
Power generation is the primary use for coal. Roughly 40 per
cent of electricity, worldwide, is generated from coal and this
may be considerably higher in many individual countries. In
the US, for example, a little over half of the electricity
generated is through coal-fired power stations and in China, 70
per cent. Approximately 25 per cent of world primary energy
consumption is from coal.
Almost two-thirds of world steel production is made from iron
produced in blast furnaces which use coal, mainly in the form
of coke. Coke is made from coking coals, which are
characterised by their chemical and physical properties: they
are low in sulphur and phosphorus, liquefy when heated in the
absence of air and solidify into hard, porous lumps. The lumps
of coke are produced by processing coal in a series of coke
ovens with an oxygen-deficient atmosphere in order to
concentrate the carbon. The coke has a high energy value and
provides the permeability, heat and gases which are required
to reduce and melt the iron ore, pellets and sinter consumed in
iron-making. Another, less-used, method is pulverised coal
injection, which can utilise a wide range of coals, including
the less-expensive steam coal. About a third of world steel
production is produced from scrap in electric arc furnaces, and
it follows that much of the electricity for this process is
produced from coal.
Liquid fuels derived from coal are sulphur-free and have low
levels of nitrogen oxides and particulate matter. Coal may be
converted into liquid fuel (and other products such as waxes,
lubricants and chemicals) by two methods: direct liquefaction,
where coal is dissolved in solvents at high temperature and
pressure; and indirect liquefaction, which gasifies the coal to
produce a ‘syngas’ which is then condensed over a catalyst
(the Fischer-Tropsch process). The Fischer-Tropsch process
produces a clean, high-quality product, whilst the liquid fuel
produced through the direct process requires further refining.
The South African company, Sasol, is the sole producer of
liquid fuel and chemicals from coal on a commercial scale.
The first coal liquefaction project in China, in the Inner
Mongolia Province of China, is due to commence operation in
2008. Three companies, Shenua Group Corp., Jiali Chemical
Ltd, and Baotou Mingtian Science and Technology Co. Ltd,
invested in this project which will produce liquids from coal
by direct liquefaction. Its aim is to reduce China's reliance on
crude oil imports by 10 per cent or more. Projects are also
under way or planned in the USA and Australia, and projects
are being considered in Indonesia, India and Germany
(Copley, 2007).
Coal is used as an energy source in cement production – a
process that requires a large amount of energy. The coal
consumed is half the mass of cement produced. Coal may also
be gasified to produce a combination of hydrogen and carbon
monoxide, which may be used for a range of purposes such as
industrial heating, electricity generation and manufacture of
chemicals. It is the source of numerous chemicals, as byproducts,
which are used in soap, pharmaceutical products,
solvents, plastics, dyes and synthetic fibres. Coal is used in
alumina refineries and in the production of activated carbon,
carbon fibre and silicon metal.
World production in 2006
World coal production in 2006 was 6194 million tonnes. This
was a five per cent increase on 2005. Production increased
steadily during the period 2002 to 2006, with an overall
increase of 29 per cent. China was the top-producing country
with 2380 million tonnes. This represents a nine per cent
increase on 2005 and a 68 per cent increase since 2002. The
USA was the second largest producer with 1054 million
tonnes and India, third, with production of 462 million tonnes.
For many countries experiencing steady and rapid economic
growth, availability of low-cost coal has been a key factor in
large-scale electrification and this is driving demand and
increased production. China is now 99 per cent electrified, and
77 per cent of the electricity is produced in coal-fired power
stations. The BBC reported that about two large coal-fired
power stations were being built every week in China
(Harrabin, 2007). This raises concerns about emissions,
particularly the raised carbon dioxide concentrations, and
health and safety matters. In 2006, 6000 deaths were officially
recorded in coal mines in China.
Asia showed the fastest increases in coal production. Overall,
there was an eight per cent increase in 2006 compared to 2005,
and 53 per cent since 2002. Although much of this was due to
the Chinese output, other countries have significantly
increased their production. For 2002 to 2006, Indian
production increased by 26 per cent, Indonesia by 71 per cent
and Mongolia by 110 per cent.
Coal production in Europe, excluding Russia, has largely been
stable during 2002 to 2006, falling by only two per cent to 809
million tonnes. Russia, the world’s fifth largest producer, has
increased production by 21 per cent from 256 million tonnes
to 309 million tonnes.
African production is dominated by South Africa, the sixth
largest coal-producing country in the world. Production of 245
million tonnes by South Africa represents an 11 per cent
increase from 2002 to 2006. Coal production in the Americas
has increased by eight per cent over the same time span, with
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