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Natural gas

From Academic Kids

Natural gas rig
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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.

Contents

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

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Natural_gas_line.jpg
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. [1] (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

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Gas_burner_on_stove.JPG
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

  • Pakistan: Conversion to CNG up 64% from last year (http://www.dailytimes.com.pk/default.asp?page=story_18-1-2004_pg5_4)
  • Pakistan: Daily Times stories about cheap ($2000 - $3000) CNG cars: [2] (http://www.dailytimes.com.pk/default.asp?page=story_27-12-2003_pg5_9) [3] (http://www.dailytimes.com.pk/default.asp?page=story_20-3-2004_pg5_5)
  • India: How New Delhi used CNG to ease pollution (http://cities.expressindia.com/fullstory.php?newsid=85665)

Pollution and allergy

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