Natural gas rig
Natural gas (commonly refered to as
gas in many countries) is a
gaseous fossil fuel consisting primarily of
methane. It is found in
oil fields and
natural gas fields, as well as - in smaller quantities - in
coal beds.
When methane-rich gasses are produced by the
anaerobic decay of non-fossil
organic material, these are referred to as
biogas. Sources of biogas include
swamps (swamp gas),
marshes (marsh gas),
landfills (landfill gas), sewage sludge and
manure (by way of
anaerobic digesters) and
flatulence (most notably in
cows.)
Methane is an extremely efficient
greenhouse gas which may contribute to enhanced
global warming when free in the atmosphere, and such free methane, would then be considered a
pollutant rather than a useful energy resource. However, methane in the atmosphere reacts with ozone, producing carbon dioxide and water, so that the greenhouse effect of released methane is relatively short-lived. As a pollutant, significant biological sources of methane are termites, cows (ruminants) and cultivation (estimated emissions 15, 75 and 100 million tons per year respectively.
(Landfill gas), which is approximately equal parts
methane and carbon dioxide, also contains trace volatile organic compounds (VOCs), many of which are known to be precursors to photochemical smog. Because landfill gas contains these trace compounds, The US Federal Clean Air Act (Part 40 of the Federal Code of Regulations) requires
landfill owners to estimate the quantity of VOCs emitted. If the estimated VOC emissions exceeds 50 metric tons, then the landfill owner is required to collect the landfill gas, and treat the landfill gas to remove the entrained VOCs. Usually, treatment is by combustion of the landfill gas. Because of the remoteness of the landfill sites, it is often not economically feasible to produce electricity from the gas.
Chemical composition and energy content
Chemical composition
The primary component of natural gas is
methane (
CH4), the shortest and lightest
hydrocarbon molecule. It may also contain heavier gaseous hydrocarbons such as
ethane (
C2H6),
propane (
C3H8) and
butane (
C4H10), as well as other gases, in varying amounts, see also
natural gas condensate.
Organosulfur compounds and
Hydrogen sulfide (
H2S see
acid gas) are common contaminants, which must be removed prior to most uses. Gas with a signifcant amount of sulfur impurities is termed "sour."
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).
Storage and transport
Natural gas line
The major difficulty in the use of natural gas is
transportation and storage. 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 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 in underground caverns formed inside salt domes, or in tanks as
Compressed Natural Gas ('''CNG'''), or
Liquefied Natural Gas ('''LNG''').
Natural gas crisis
Many politicians and prominent figures in North America have spoken publicly about a possible natural gas crisis. This list includes former Secretary of Energy
Spencer Abraham, Chairman of the Federal Reserve
Alan Greenspan, Ontario Minister of Energy
Dwight Duncan.
The natural gas crisis is typically described by the increasing price of natural gas in the U.S. over the last few years due to the decline in indigenous supply and the increase in demand for
electricity generation. The price has become so high that many
industrial users, mainly in the
petrochemical industry, have closed their plants causing loss of jobs.
Alan Greenspan has suggested that a solution to the natural gas crisis is the importation of liquified natural gas, or LNG.
This solution is both
capital intensive and
politically charged due to the
NIMBY syndrome and the public perception that LNG terminals are explosive risks, especially in the wake of the 911 terrorist attacks in the USA. (The security arrangements during the 2004 Democratic Convention in Boston, one of only six LNG terminals in the USA were extraordinarily tight; and are maintained at a high state year round by the US Dept. of
Homeland Security.)
Infrastructure issues to establish new or expanded LNG terminals are non-trivial, to say the least, especially when taken together with high capitalization needs of each subsystem. LNG terminals require a very spaceous (large) deep (42 ft (38.5 m) or better) harbor well sheltered from wind and wave. These
suitable sites are thus deep in well populated seaports, which are also burdened with right of way concerns for LNG pipelines (inland through your backyard, not mine!), or conversely, required to also host the LNG expansion plant facilities and end use (Petrochemical) plants amidst the high population densities of major cities (with the associated fumes, multiple serious risks to safety).
Typically, to attain
well sheltered waters, suitable harbor sites are well up rivers or estuaries, whereas these same sites are unlikely to be dredged deep enough. Since these superlarge vessels must move slow and ponderously in restricted waters - by definition in all and any harbor - the transit times to and from the terminal become costly, as multiple tugs and security boats shelter and safewguard these gargantuan behemoths. Operationally, LNG tankers are (Boston) effectively given sole use of the harbor, forced to arrive and depart in the wee hours of the night-morning cycle, and precluded from occupying the same harbor until the first is well departed. These are not factors that aide profitability and attract capital investment.
Uses
Power generation
Natural gas is important as a major source for
electricity generation through the use of
gas turbines and
steam turbines. Particularly high efficiencies can be achieved through combining gas turbines with a steam turbine in
combined cycle mode.
Environmentally, natural gas burns cleaner than other
fossil fuels, such as oil and coal, and produces less
greenhouse gases. For an equivalent amount of heat, burning natural gas produces about 30% less
carbon dioxide than burning
petroleum and about 45% less than burning
coal.
http://www.naturalgas.org/environment/naturalgas.asp#greenhouse Combined cycle power generation using natural gas is thus the cleanest source of power available using fossil fuels, and this technology is widely used wherever gas can be obtained at a reasonable cost.
Fuel cell technology may eventually provide cleaner options for converting natural gas into electricity, but as yet it is not price-competitive.
Natural gas vehicles
Compressed natural gas (and
LPG) is used as a clean alternative to other
automobile fuels. As of 2003, the countries with the largest number of
natural gas vehicles were
Argentina,
Brazil,
Pakistan,
Italy, and
India.
Residental domestic use
Many [[stoves use natural gas.]]
Natural gas is supplied to homes where it is used for such purposes as
cooking and heating/cooling. CNG is used in
rural homes without connections to
piped-in
public utility services, or with portable
grills.
Fertilizer
Natural gas is a major feedstock for the production of
ammonia, via the
Haber process, for use in
fertilizer production.
Other
Natural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, and other products.
Sources
Natural gas is commercially produced from
oil fields and
natural gas fields.
Possible future sources
One experimental idea is to use the methane gas that is naturally produced from
landfills to supply power to cities. Tests have shown that methane gas could be a financially sustainable power source.
There are plans in Ontario to capture the methane gasses rising from the manure of cattle caged in a factory farm and to use that gas to provide power to a small town.
There is also the possibility that with the source separation of organic materials from the waste stream that by using an anerobic digester, the methane can be used to produce useable energy. This can be improved by adding other organic material (plants as well as slaughter house waste) to the digester.
Safety
In any form, a strong bad scent (such as
ethanethiol) is deliberately added to the otherwise
colorless and
odorless gas, so that leaks can be detected by the
smell before an
explosion occurs. In
mines,
sensors are used and mining apparatus has been specifically developed to avoid ignition sources (e.g. the
Davy lamp). Adding scent to natural gas began after the 1937
New London School explosion. The buildup of gas in the school went unnoticed, and killed three hundred students and faculty when it ignited.
Explosions caused by natural gas leaks occur a few times each year. Individual
homes and
small businesses are most frequently affected when an internal leak builds up gas inside the structure. Frequently, the blast will be enough to significantly damage a building but leave it standing. In these cases, the people inside tend to have minor to moderate
injuries. Occasionally, the gas can collect in high enough quantities to cause a deadly explosion, disintegrating one or more buildings in the process. The gas usually dissipates readily outdoors, but can sometimes collect in dangerous quantities if
weather conditions are right. Considering the tens of millions of structures that use the fuel, the risks of using natural gas are very low.
Contrary to popular belief, natural gas is non-toxic, though some gas fields yield
acid gas or
sour gas containing
hydrogen sulfide. This untreated gas is toxic.
Extraction of natural gas (or oil) leads to decrease in
pressure in the
reservoir. This in turn may lead to
subsidence at ground level. Subsidence may affect
ecosystems,
waterways,
sewer and
water supply systems,
foundations etc.
See also
External links
Natural gas vehicles
North America
South Asia
Pollution and allergy
Category:Fuels
Category:Hydrocarbons
Category:Natural gas
Category:Petroleum
Category:Natural resources
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