Natural gas is found in association with oil and coal deposits. It is primarily methane with small amounts of other hydrocarbons. It is usually refined to give almost pure methane (CH4) prior to use as a fuel or chemical feedstock. If used as a fuel it is given a characteristic odor for safety reasons.
There are two ways by which natural gas is produced subterraneally:
- microbial action on decaying vegetation (methanogenesis)
- action of hydrogen on carbon under high temperature and/or pressure
Having a lower density than oil or water, natural gas will rise within the Earth's crust until stopped by an impermeable layer. Thus, it is often found in "domes" above oil deposits. The pressure of the gas under these conditions may be considerable.
Natural gas is transported either using tankers, in a liquified form by cooling and using high pressures, for international and large distances; or via pipelines direct to the end user. It is used in electrical power stations, or as a compressed gas for use in vehicles and as fuel for ovens and stoves. For household use, natural gas has almost entirely replaced the use of "coal" (produced by heating coal) gas as it is more efficient and cleaner burning.
Safety and environmental aspects
Methane is a "clean burning" gas, in that it produces only carbon dioxide and water when burnt with sufficient oxygen and waste gases are generally free of toxic elements such as excess carbon monoxide, or worse, sulfur oxides. As an alternative to burning coal or oil, it produces less pollution. However, by virtue of it still being a fossil fuel, it is still a source of CO2, a well-known greenhouse gas, although it produces less of the gas per unit of energy produced than other fuels. Methane itself is also a greenhouse gas, approximately 24 times more powerful per mole than CO2. "Fugitive" emissions during the extraction process may also offset much of the benefit of natural gas, as a study by the National Center for Atmospheric Research concluded.
America has vast reserves of natural gas, which has led to some experts calling for a shift to its use. Critics in that country point out that this will be a stopgap maneuver, serving only until the natural gas runs out, and further that the funds spent on developing the infrastructure necessary to extract, move, and use the gas might be better spent on renewable resources. But still, it seems as though any path towards energy independence in America, an important goal for many, will involve the use of natural gas at least in those areas where it is locally available.
- ↑ Additional chemicals (usually sulphides) are added as odorants to make leak detection easier, as methane itself is a colorless, odorless gas. The same is true of higher alkane gases like propane and butane - the chemical combinations are also different for each, so someone who nose the difference can tell which gas it is by sniffing it. Mostly what this does is add a characteristic "stinky gas smell" to odorless but dangerous gasses.
- ↑ Tom Wigley. Coal to gas: the influence of methane leakage. Climatic Change (2011) 108:601–608. Press release.
- ↑ http://www.thedailyshow.com/watch/wed-november-12-2008/t--boone-pickens