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Natural gas is a gas produced by the anaerobic decay of organic material. It is usually found in oil fields and natural gas fields, but is also generated in swamps and marshes (where it is called swamp gas or marsh gas), in landfill sites, and during digestion in animals (see flatulence). 1 Chemical composition and energy content
1.1 Chemical composition
The primary component of natural gas is methane ( C H4), the shortest and lightest hydrocarbon molecule. It may also contain heavier gaseous hydrocarbons such as ethaneProperties General Name Ethane Chemical formula C HCH Formula weight 30. 07 amu Synonyms Dimethyl, Ethyl hydride, Methylmethane CAS number 74-84-0 UN number 1035 Phase behavior Melting point 90. 34 K (-182. 76 °C) Boiling point 184. 6°C) Triple point 91 K ( C2 H6), propaneProperties General Name Propane Lewis Structure: H H H | | | H-C-C-C-H | | | H H H Chemical formula C HCHCH or CH Formula weight 44. 10 amu Synonyms Dimethylmethane, LPG, Propyl Hydride CAS number 74-98-6 UN number 1978 Phase behavior Melting point 85. ( C3 H8) and butaneButane is an alkane hydrocarbon with the empirical formula C H. It has the following display formula: H H H H | | | | H C C C C H | | | | H H H H It is a flammable, colorless, easily liquefied gas that is used extensively as a fuel for cigarette lighters ( C4 H10), as well as other gases, in varying amounts. Hydrogen sulfide ( H2 S) and mercury (Hg) are common contaminants, which must be removed prior to most uses.
1.2 Energy content
Combustion of one hundred cubic feet (1 ccf) of commercial quality natural gas typically yields approximately 1 therm (100,000 british thermal units, 30 kWh). One cubic meter yields 38 MJ (10.6 kWh).
2 Storage and transport
The major difficulty in the use of natural gas is transportation. Natural gas pipelines are economical, but are impractical across oceans. Many existing pipelines in North America are close to reaching their capacity prompting some politicians in colder climates to speak publicly of potential shortages. Liquefied natural gas ( LNG) tankers are also used, but have higher cost and safety problems. In many cases, as with oil fields in Saudi Arabia, the natural gas which is recovered in the course of recovering petroleum cannot be profitably sold, and is simply burned at the oil field (known as flaring ). This wasteful practice is now illegal in many countries, especially since it adds greenhouse gas pollution to the atmosphere, and since a profitable method may be found in the future. The gas is instead re- injected back into the ground for possible later recovery, and to assist oil pumping by keeping underground pressures higher.
Natural gas is often stored as Compressed Natural Gas or CNG.
