Geology Reference
In-Depth Information
Nuclear Energy
626.2 5%
Renewables 158.6
1%
Coal 3,555.8 30%
Natural Gas 2,858.1
24%
Hydroelectric
775.6 6%
Oil 4,028.1 34%
Fig. 6.4 Primary world energy consumption by fuel type at the end of 2010. Values in Mtoe.
Elaborated from data included in BP (2011)
6.6.6.1 Coal
Coal is a sedimentary and metamorphic rock. It is formed from plants that grew
in ancient swamps. The remains of the plants accumulated in a non-oxidising en-
vironment and were eventually buried by other sediments, usually sand or mud,
which are now the sandstones and shales typically associated with coal beds. Coal
deposits start off as organic materials made chiefly of carbon, oxygen and hydrogen.
With the rise of temperature and pressure, due to the burial of the deposits, the
hydrogen and oxygen are then gradually lost (Leet et al., 1982).
In addition to carbon, oxygen and hydrogen, coal contains many other elements
in trace amounts. Sulphur is one of its most common impurities, making it a
dangerous pollutant of air and water. Table 6.4 shows the ASTM D388 coal-rank
classification according the HHV. Coal's specific exergy varies from about 20 to
30 MJ/kg (Hermann, 2006), although some low-carbon coals such as lignites may
have specific exergies as low as 15 MJ/kg.
Coal accounts for about 30% of the energy consumption in the world. Proved
global reserves
11
of coal were estimated by the World Energy Council (WEC, 2010)
at 860.9 Gt. Considering the average HHV reported by Eggleston et al. (2006), the
world's proved coal reserves are about 427 Gtoe. The authors will go on to calculate
a resasonable value for the exergy of coal reserves in Chap. 11.
Proven coal reserves are larger than those of oil and natural gas. According to
the World Energy Council (WEC, 2007) the global coal reserves could be multiplied
by more than two. WEC (2010) estimates additional resources amount in place at
11
Proved reserves of coal - generally taken to be those quantities from known deposits that geolo-
gical and engineering information suggests with a reasonable degree of certainty, are “recoverable”
in the future (under existing economic and operating conditions).
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