The Resources of the Earth - Thanatia: The Destiny of the Earth's Mineral Resources - page 149

350000

Distribution of coal proved reserves in the world

Mt

300000

250000

106,517

200000

211,614

132,253

150000

100000

159,326

112,835

50000

92,990

174

5,618

32,721

6,890

0

North America S. & Cent. America Europe & Eurasia Middle East & Africa Asia Pacific

Anthracite and bituminus Sub-bituminous and lignite

Fig. 6.5 Coal proved reserves at the end of 2010. Values in million tonnes. Elaborated from data
included in WEC (2010)

processes begin to break down the organic matter into what is called kerogen, a
precursor of oil and gas. The second stage is marked by the thermal alteration
of kerogen to hydrocarbons as the deposit is buried deeper by younger, overlying
sediments. The production of hydrocarbons begins at a temperature of around 50
to 60 o C and at a depth of 2 to 2.5 km. Hydrocarbon formation continues to depths
of 6 to 7 km and temperatures of 200 to 250 o C. Formation of oil dominates in the
lower temperature ranges and gas in the higher.
The British standard BS2869:1998 classifies fuel oil into six classes according to
its boiling temperature, composition and purpose. No. 1 and No. 2 are referred to
as distillate fuel oils, while No. 4, No. 5 and No. 6 are labelled residual fuel oils. In a
more commercial sense: No. 1 fuel oil is kerosene; No. 2 is diesel oil and No. 4, 5 and
6 are heavy fuel oils. Table 6.5 shows the chemical composition, density and HHV
of classes 1, 2, 4, 5 and 6. Low molecular weight petroleum has an exergy content
between 40 to 46 MJ/kg. Higher molecular weight petroleum and the hydrocarbon
portion of inorganic mixtures have a chemical exergy close to 40 MJ/kg (Hermann,
2006).
Natural gas consists primarily of methane but includes significant quantities of
ethane, butane, propane, carbon dioxide, nitrogen, helium and hydrogen sulphide.
The main properties of natural gas are listed in Table 6.6. The specific exergy of
natural gas is around 50 MJ/kg (Hermann, 2006).