FOSSIL FUELS

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FOSSIL FUELS
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• Fossil Fuels
• Fossil fuels consist generally of the combustible
  elements
• hydrogen, H2, carbon, C, and sulphur, S.
• They often also contain the incombustible element
  nitrogen, N2, moisture, H2O, and minerals.

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• Fossil Fuels
• When combusted, the carbon oxidises to carbon
  monoxide, CO, (if insufficient air is present)
  and carbon dioxide, CO2,
• the hydrogen oxidises to water (steam), H2O,
• and the sulphur (in coals and liquid fuels)
  becomes sulphur dioxide, SO2.

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• Fossil Fuels
• The carbon and sulphur dioxides dissolve in water
  to form carbonic, H2CO3,
• and sulphuric, H2SO4, acids,
• which contribute to acid rain.

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• Fossil Fuels
• When combustion temperatures are high, nitrogen
  in air can combine with oxygen to form the NOx
  gases, e.g. nitrous oxide, N2O, which dissolved
  in water forms nitric acid, HNO3.
• The action of sunlight on exhaust fumes can also
  form nitrous oxides and ozone. O3, the main
  contributors to photochemical smog.

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• Fossil Fuels
• Moisture present in a fuel absorbs sensible heat
  from the flame to supply the latent heat needed
  to change phase from liquid to vapour.
• Any minerals present form the residual ash.

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• Fossil Fuels
• Smoke is a dispersion in air of small solid
  particles of uncombusted fuels (carbon and
  sulphur) with some airborne ash.
• Volatile organic compounds (VOCs) are
  non-combusted organic liquids, such as petrol and
  benzene.

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• COAL
• Fossilised reserves of coal emanate from
  land-based vegetable matter
• (wood converting to peat and then to coal over
  time).

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• OIL and GAS
• Both Oil and Gas reserves emanate from marine
  creatures
• (plankton reducing to methane (major component of
  natural gas) and then forming oil over time).

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• Typical Compositions of Liquid Fuels
  
• Oil C H S
• Motor Petrol 85.5 14.4 0.1
• Vapourising Oil 86.8 12.9 0.3
• Kerosene 86.3 13.6 0.1
• Diesel (gas) Oil 86.3 12.8 0.9
• Light Fuel Oil 86.2 12.4 1.4
• Heavy Fuel Oil 86.1 11.8 2.1
• Orimulsion 84.0 10.2 4.15

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• Typical Compositions of Liquid Fuels
  
• These all approximate to CH2
• but the higher the proportion of Hydrogen, the
  higher the calorific value
• C H S
• Motor Petrol 85.5 14.4 0.1
• and the higher the proportion of Sulphur, the
  dirtier the
• fuel is.
• C H S
• Orimulsion 84.0 10.2 4.15

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• GASES
• Hydrogen, H2, having no carbon content, has the
  highest calorific value of the gaseous fuels and
  produces only water when combusted.
• It is therefore a totally clean fuel.
• Unfortunately, it does not occur naturally and is
  therefore not a Fossil Fuel

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• Fossil Fuels
• Hydrocarbons are compounds containing hydrogen
  and carbon only.
• Most hydrocarbons in petroleum deposits occur
  naturally as liquids, but a few exist in the
  gaseous phase at atmospheric temperatures and
  pressures.

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• Fossil Fuels
• Alkanes form the major constituents of crude
  petroleum and are also present in natural gas
  from underground wells.
• The general formula for this homologous series of
  saturated hydrocarbons is
• C n H 2n2.

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• Fossil Fuels

Samples of Alkanes Alkane Formula Boiling
Point State at STP Methane CH4 -161
oC Gas Ethane C2H6 -89 oC Gas Propane C3H8
-42 oC Gas Butane C4H10 -0.5
oC Gas Pentane C5H12 36.1 oC Liquid Hexane C6H
14 69.0 oC Liquid Heptane C7H16 98.4
oC Liquid Octane C8H18 18 compounds Liquid Nona
ne C9H20 Decane C10H22 Note STP
Standard Temperature and Pressure, 25oC and 1
atmosphere
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• Fossil Fuels
• Alkenes are unsaturated hydrocarbons having the
• general formula C n H 2n
• E.g.
• Alkene Formula Boiling Point State at STP
• Ethene,
• Ethylene C2H4 -105 oC Gas
• Propene,
• Propylene C3H6 -48 oC Gas

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• Fossil Fuels
• Alkynes are unsaturated hydrocarbons having the
• general formula C n H 2n-2
• E.g.
• Alkyne Formula Boiling Point State at STP
• Ethyne,
• Acetylene C2H2 -83.4 oC Gas
• Propyne, C3H4 -23,3 oC Gas

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• Natural Gas
• Natural Gas is comprised mainly of methane, but
  also contains carbon dioxide as well as small
  percentages of ethane, propane, butane, pentane,
  hexane, and nitrogen and oxygen.
• Typical Composition of Natural Gas
• C H2 S N2 O2 H2O CO2
• 66.0 23.0 0.0 4.0 0.0 1.5
  6.0

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• Other Gases
• Gases H2 CO CH4 C2H4 C4H8
  O2 N2 CO2
• Coal Gas 49.4 18.0 20.0 0.0
  2.0 0.4 6.2 4.0
• Producer Gas 12.0 29.0 2.6 0.4
  0.0 0.0 52.0 4.0
• Blast Furnace Gas 2.0 27.0 0.0 0.0
  0.0 0.0 60.0 11.0

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FOSSIL FUELS