# FOSSIL FUELS Please click to step through this presentation.

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FOSSIL FUELS Please click to step through this presentation

Fossil Fuels Fossil fuels consist generally of the combustible elements: hydrogen, H 2, carbon, C, and sulphur, S. They often also contain the incombustible element nitrogen, N 2, moisture, H 2 O, and minerals.

Fossil Fuels When combusted, the carbon oxidises to carbon monoxide, CO, (if insufficient air is present) and carbon dioxide, CO 2, the hydrogen oxidises to water (steam), H 2 O, and the sulphur (in coals and liquid fuels) becomes sulphur dioxide, SO 2.

Fossil Fuels The carbon and sulphur dioxides dissolve in water to form carbonic, H 2 CO 3, and sulphuric, H 2 SO 4, acids, which contribute to acid rain.

Fossil Fuels When combustion temperatures are high, nitrogen in air can combine with oxygen to form the NOx gases, e.g. nitrous oxide, N 2 O, which dissolved in water forms nitric acid, HNO3. The action of sunlight on exhaust fumes can also form nitrous oxides and ozone. O 3, the main contributors to photochemical smog.

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.

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.

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

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).

Typical Compositions of Liquid Fuels Oil%C%H%S Motor Petrol85.514.40.1 Vapourising Oil86.812.90.3 Kerosene86.313.60.1 Diesel (gas) Oil86.312.80.9 Light Fuel Oil86.212.41.4 Heavy Fuel Oil86.111.82.1 Orimulsion84.010.24.15

Typical Compositions of Liquid Fuels These all approximate to CH 2 but the higher the proportion of Hydrogen, the higher the calorific value %C%H%S Motor Petrol85.514.40.1 and the higher the proportion of Sulphur, the dirtier the fuel is. %C%H%S Orimulsion84.010.24.15

GASES Hydrogen, H 2, 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

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.

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 2n+2.

Samples of Alkanes AlkaneFormulaBoiling PointState at STP MethaneCH 4 -161 o CGas EthaneC 2 H 6 -89 o CGas PropaneC 3 H 8 -42 o CGas ButaneC 4 H 10 -0.5 o CGas PentaneC 5 H 12 36.1 o CLiquid HexaneC 6 H 14 69.0 o CLiquid HeptaneC 7 H 16 98.4 o CLiquid OctaneC 8 H 18 18 compoundsLiquid NonaneC 9 H 20 DecaneC 10 H 22 Note: STP = Standard Temperature and Pressure, 25 o C and 1 atmosphere Fossil Fuels

Alkenes are unsaturated hydrocarbons having the general formula C n H 2n E.g. AlkeneFormulaBoiling PointState at STP Ethene, EthyleneC 2 H 4 -105 o CGas Propene, PropyleneC 3 H 6 -48 o CGas

Fossil Fuels Alkynes are unsaturated hydrocarbons having the general formula C n H 2n-2 E.g. AlkyneFormulaBoiling PointState at STP Ethyne, AcetyleneC 2 H 2 -83.4 o CGas Propyne, C 3 H 4 -23,3 o CGas

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 %H 2 %S %N 2 %O 2 %H 2 O %CO 2 66.0 23.0 0.0 4.0 0.0 1.5 6.0

Other Gases % Gases H 2 CO CH 4 C 2 H 4 C 4 H 8 O 2 N 2 CO 2 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

FOSSIL FUELS