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Natural gas

2007 Schools Wikipedia Selection. Related subjects: Business; Chemical
compounds

                        Natural gas
                 Natural gas Natural gas
                          General
   Other names              Marsh gas, Swamp gas
   Molecular formula        CH[4]
   Appearance               Clear Gas, Blue Flame
                        Properties
   Density and phase        0.717 kg/m^3, gas
   Melting point            −182.5°C (90.6 K) at 1 atm

                            25 °C (298 K) at 1.5 G Pa
   Boiling point            −161.6°C (111.55 K)
   Triple point             90.7 K, 0.117 bar
                          Hazards
   MSDS                     External MSDS
   EU classification        Highly flammable (F+)
   NFPA 704

                            4
                            1
                            0

   R-phrases                R12
   S-phrases                S2, S9, S16, S33
   Flash point              −188°C
   Autoignition temperature 537°C
   Maximum burning
   temperature:             2148°C
   Explosive limits         5–15%
                     Related compounds
   Related alkanes          Ethane
                            Propane
   Related compounds        Methanol
                            Chloromethane
     Except where noted otherwise, data are given for
   materials in their standard state (at 25 °C, 100 kPa)
   Infobox disclaimer and references
           See methane for a more complete list.

   Natural gas is a gaseous fossil fuel consisting primarily of methane.
   It is found in oil fields and natural gas fields, and in coal beds.
   When methane-rich gases are produced by the anaerobic decay of
   non-fossil organic material, these are referred to as biogas. Sources
   of biogas include swamps, marshes, and landfills (see landfill gas), as
   well as sewage sludge and manure by way of anaerobic digesters, in
   addition to enteric fermentation particularly in cattle. Natural gas is
   often informally referred to as simply gas, especially when compared to
   other energy sources such as electricity.

Chemical composition

   The primary component of natural gas is methane (CH[4]), the shortest
   and lightest hydrocarbon molecule. It also contains heavier gaseous
   hydrocarbons such as ethane (C[2]H[6]), propane (C[3]H[8]) and butane
   (C[4]H[10]), as well as other sulphur containing gases, in varying
   amounts, see also natural gas condensate. Natural gas also contains and
   is the primary market source of helium.
                   Component                 wt. %
   Methane (CH[4])                           80-95
   Ethane (C[2]H[6])                         5-15
   Propane (C[3]H[8]) and Butane (C[4]H[10]) < 5

   Nitrogen, helium, carbon dioxide and trace amounts of hydrogen sulfide,
   water and odorants can also be present . Mercury is also present in
   small amounts in natural gas extracted from some fields. The exact
   composition of natural gas varies between gas fields.

   Organosulfur compounds and hydrogen sulfide are common contaminants
   which must be removed prior to most uses. Gas with a significant amount
   of sulfur impurities, such as hydrogen sulfide, is termed sour gas and
   often referred to as " acid gas". Processed Natural gas that is
   available to end-users is tasteless and odorless, however, before gas
   is distributed to end-users, it is odorized by adding small amounts of
   thiols, to assist in leak detection. Processed Natural gas is, in
   itself, harmless to the human body, however, natural gas is a simple
   asphyxiant and can kill if it displaces air to the point where the
   oxygen content will not support life.

   Natural gas can also be hazardous to life and property through an
   explosion. Natural gas is lighter than air, and so tends to dissipate
   into the atmosphere. But when natural gas is confined, such as within a
   house, gas concentrations can reach explosive mixtures and, if ignited,
   result in blasts that could destroy buildings. Methane has a lower
   explosive limit of 5% in air, and an upper explosive limit of 15%.

   Explosive concerns with compressed natural gas used in vehicles are
   almost non-existent, due to the escaping nature of the gas, and the
   need to maintain concentrations between 5% and 15% to trigger
   explosions.

Energy content and statistics

   Quantities of natural gas are measured in normal cubic metres
   (corresponding to 0° C at 1 atm) or in standard cubic feet
   (corresponding to 60° F and 30 inHg). The gross heat of combustion of
   one normal cubic metre of commercial quality natural gas is around 39
   megajoules (≈10.8  kWh), but this can vary by several percent. In US
   units, one standard cubic foot of natural gas produces around 1000
   British Thermal Units (BTUs).

   The actual heating value when the water formed does not condense is the
   net heat of combustion and can be as much as 10% less.

   The price of natural gas varies greatly depending on location and type
   of consumer, but as of 2006 a price of $10 per 1000 cubic feet is
   typical in the US. This correponds to around $10 per million BTU's, or
   around $10 per gigajoule.

   In the USA, at retail, natural gas is often sold in units of therms
   (th); 1 therm = 100,000 BTU. Wholesale transactions are generally done
   in decatherms (Dth), or in thousand decatherms (MDth), or in million
   decatherms (MMDth). A million decatherms is roughly a billion cubic
   feet of natural gas.

Storage and transport

   Polyethylene gas main being laid in a trench.
   Enlarge
   Polyethylene gas main being laid in a trench.

   The major difficulty in the use of natural gas is transportation and
   storage because of its low density. 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.

   LNG carriers can be used to transport liquefied natural gas (LNG)
   across oceans, while tank trucks can carry liquefied or compressed
   natural gas (CNG) over shorter distances. They may transport natural
   gas directly to end-users, or to distribution points such as pipelines
   for further transport. These may have a higher cost, requiring
   additional facilities for liquefaction or compression at the production
   point, and then gasification or decompression at end-use facilities or
   into a pipeline.

   In the past, the natural gas which was recovered in the course of
   recovering petroleum could not be profitably sold, and was 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 earth's atmosphere. Additionally, companies now
   recognize that value for the gas may be achieved with LNG, CNG, or
   other transportation methods to end-users in the future. The gas is now
   re- injected back into the formation for later recovery. This also
   assists oil pumping by keeping underground pressures higher. In Saudi
   Arabia, in the late 1970s, a "Master Gas System" was created, ending
   the need for flaring. The natural gas is used to generate electricity
   and heat for desalinization. Similarly, some landfills that also
   discharge methane gases have been set up to capture the methane and
   generate electricity.

   Natural gas is often stored in underground caverns formed inside
   depleted gas reservoirs from previous gas wells, salt domes, or in
   tanks as liquefied natural gas. The gas is injected during periods of
   low demand and extracted during periods of higher demand. Storage near
   the ultimate end-users helps to best meet volatile demands, but this
   may not always be practicable.

Natural gas crisis

   Blue flames of a burner on a natural gas stove.
   Enlarge
   Blue flames of a burner on a natural gas stove.

   Many politicians and prominent figures in North America have spoken
   publicly about a possible natural gas crisis. This includes former
   Secretary of Energy Spencer Abraham, former Chairman of the Federal
   Reserve Alan Greenspan, and 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. Indigenous supply has fallen from 20,570,295 MMcf in 2001
   to 19,144,768 MMcf in 2005. Because of the drop in production
   (exacerbated by the dramatic hit to production that came from
   Hurricanes Katrina and Rita) and the continuing growth in demand, the
   price has become so high that many industrial users, mainly in the
   petrochemical industry, have closed their plants causing loss of jobs.
   Greenspan has suggested that a solution to the natural gas crisis is
   the import of LNG.

   This solution is both capital intensive and politically charged due to
   the public perception that LNG terminals are explosive risks,
   especially in the wake of the 9/11 terrorist attacks in the United
   States. The U.S. Department of Homeland Security is responsible for
   maintaining their security.

   New or expanded LNG terminals create tough infrastructure problems and
   require high capital spending. LNG terminals require a very spacious—at
   least 40 feet (12.2 m) deep— harbour, as well as being sheltered from
   wind and waves. These "suitable" sites are thus deep in well-populated
   seaports, which are also burdened with right-of-way concerns for LNG
   pipelines, 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 harbour sites
   are well up rivers or estuaries, which are unlikely to be dredged deep
   enough. Since these very large vessels must move slowly and ponderously
   in restricted waters, the transit times to and from the terminal become
   costly, as multiple tugboats and security boats shelter and safeguard
   the large vessels. Operationally, LNG tankers are (for example, in
   Boston) effectively given sole use of the harbor, forced to arrive and
   depart during non-peak hours, and precluded from occupying the same
   harbour until the first is well-departed. These factors increase
   operating costs and make capital investment less attractive.

   To substantially increase the amount of LNG used to supply natural gas
   to North America, not only must "re-gasification" plants be built on
   North American shores -- difficult for the reasons stated above --
   someone also must put substantial, new liquefaction stations in
   Indonesia, the Middle East, and Africa, in order to concentrate the gas
   generally associated with oil production in those areas. A substantial
   expansion of the fleet of LNG carriers also must occur, to move the
   huge amount of fuel needed to make up for the coming shortfall in
   Northeast America.

Uses

Power generation

   Natural gas is 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. Natural gas burns cleaner than other fossil fuels,
   such as oil and coal, and produces less greenhouse gas per unit energy
   released. 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 . 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. Also, the natural gas supply is said to
   peak around the year 2030, 20 years after the peak of oil. It is also
   projected that the world's supply of natural gas should be exhausted
   around the year 2085.

Hydrogen

   Natural gas can be used to produce hydrogen that can be used in
   hydrogen vehicles. One common method is the Hydrogen reformer.

Natural gas vehicles

   Compressed natural gas ( methane) is used as a clean alternative to
   other automobile fuels such as gasoline (petrol) and diesel. As of
   2005, the countries with the largest number of natural gas vehicles
   were Argentina, Brazil, Pakistan, Italy, and India. The energy
   efficiency is generally equal to that of gasoline engines, but lower
   compared with modern diesel engines, partially due to the fact that
   natural gas engines function using the Otto cycle, but research is on
   its way to improve the process ( Westport Cycle).

   Liquified petroleum gas (a propane and butane blend) is also used to
   fuel vehicles. LPG and CNG vehicle fuel systems are not compatible. CNG
   also requires higher pressure tanks which are typically much heavier
   than those used for LPG.

Residential domestic use

   Natural gas is supplied to homes, where it is used for such purposes as
   cooking in natural gas-powered ranges and/or ovens, natural gas-heated
   clothes dryers, and heating/ cooling. Home or other building heating
   may include boilers, furnaces, and water heaters. 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.

Safety

   In any form, a minute amount of odorant such as t-butyl mercaptan, with
   a rotting-cabbage-like smell, is added to the otherwise colorless and
   odorless gas, so that leaks can be detected before a fire or explosion
   occurs. Sometimes a related compound, thiophane is used, with a
   rotten-egg smell. Adding odorant to natural gas began in the United
   States after the 1937 New London School explosion. The buildup of gas
   in the school went unnoticed, killing three hundred students and
   faculty when it ignited. Odorants are considered non-toxic in the
   extremely low concentrations occurring in natural gas delivered to the
   end user.

   In mines, where methane seeping from rock formations has no odour,
   sensors are used, and mining apparatus has been specifically developed
   to avoid ignition sources, e.g., the Davy lamp.

   Explosions caused by natural gas leaks occur a few times each year.
   Individual homes, small businesses and boats 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. Also, considering the tens of millions of
   structures that use the fuel, the individual risk of using natural gas
   is very low.

   Some gas fields yield sour gas containing hydrogen sulfide (H[2]S).
   This untreated gas is toxic. Amine gas treating, an industrial scale
   process which removes acidic gaseous components, is often used to
   remove hydrogen sulfide from natural gas.

   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.
   Retrieved from " http://en.wikipedia.org/wiki/Natural_gas"
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