Natural gas

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Natural gas (commonly refered to as gas in many countries, but note that gas is also an American and Canadian shortening of gasoline) 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 cattle.)

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. Also, natural gas, when burned, produces much less greenhouse gas than more carboniferous fuel sources, such as coal. As a pollutant, significant biological sources of methane are termites, cattle (ruminants) and cultivation (estimated emissions are 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 it to remove the entrained VOCs. Usually, treatment is by combustion of the landfill gas. Because of the remoteness of landfill sites, it is sometimes 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 sulphur containing 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 significant amount of sulfur impurities is termed "sour".

Natural gas is tasteless and odorless. However, before gas is distributed to end-users, it is odorized by adding mercaptans, to assist in leak detection. Natrual gas is, in itself, harmless to the human body -- unlike carbon monoxide, for instance, it is not a poison. Natural gas can kill, however if it is present in large concentrations -- and thus reduces the amount of oxygen available in the air, such that the amount of oxygen remaining won't sustain life.

Natural gas can also kill through an explosion. Natural gas is lighter than air, and so tends to dissipate. But when natural gas is contained, such as within a house or in a tent (perhaps put over a house for fumigation) gas concentrations can reach explosive proportions and trigger very powerful blasts that can level houses, and even neighborhoods. 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-existant, due the the escaping nature of the gas, and the need to maintain concentrations between 5% and 15% to trigger explosions.

Energy content and statistics

Combustion of one cubic metre of commercial quality natural gas yields 38 MJ (10.6 kWh). Equivilently, one cubic foot of natural gas produces just over 1000 British Thermal Units (BTUs).

In the USA, at retail, natural gas is often sold in units of therms (th), which equals 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.

The US uses roughly 60,000 billion cubic feet, or 60 tera decatherms (TDth), each year.

Storage and transport

Image:Polyethylene gas main.jpg 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 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 earth's atmosphere, and since a profitable method may be found in the future. Instead, the gas is instead re-injected back into the formation for later recovery. This is known as Underground Gas Storage (UGS). It 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.

Natural gas is often stored in underground caverns formed inside salt domes as Compressed Natural Gas (CNG), or in tanks as 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 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. Indigenous supply has not truly fallen -- but it has leveled off (no matter how many new straws we put into the ground, we still get about the same amount of natural gas each year). But because of the continuing growth in demand, and the temporary but dramatic hit to production that came from Hurricanes Katrina and Rita, 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 importation of 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 9/11 terrorist attacks in the United States. The U.S. Department of Homeland Security is responsible for maintaining their security, and the security arrangements during the 2004 Democratic Convention in Boston, Massachusetts, home to one of only six LNG terminals in the United States, were extraordinarily tight.

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 spacious—at least 38.5m deep—harbor, 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 harbor 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 tugs 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 harbor 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 but substantial, new liquification stations in Indonesia, the Middle East, and Afreca, in order to concetrate the gas generally assoicated with oil production in those areas. A substantial explansion of the fleet of LNG tankers also must occur to move the hugh amount of fuel needed to make up for the coming shortfall in North America.

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 fewer 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] 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, Natural gas 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 finish in the mid 2080's(2085).

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. 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 engine function using the Otto Cycle, but research is on its way to improve the process (Westport-Cycle).

Here is a link to a general discription of this technology.

http://www.nesea.org/greencarclub/factsheets_naturalgas.pdf#search='explosion%20ratio%20natural%20gas'

Residental domestic use

Image:Gas burner on stove.JPG 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. Gas produced from oil wells is called casinghead gas or associated gas. Natural gas can also be produced by treating coal chemically, although coal gasification is not economic at current gas prices. The biggest natural gas field is located in Urengoy, Russia, with a reserve of 10.0 · 1012 m³. See also List of 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 biogas, 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 anaerobic 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 concentrated, rotten-egg like scent (such as mercaptan/ethanethiol) is deliberately added to the otherwise colorless and odorless gas, so that leaks can be detected by 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, 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.

Contrary to popular belief, natural gas and the odorant that's added to it 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

ca:Gas natural cs:Zemní plyn cy:Nwy naturiol da:Naturgas de:Erdgas es:Gas natural eo:Tergaso fr:Gaz naturel id:Gas alam it:Gas naturale he:גז טבעי lt:Gamtinės dujos ms:Gas asli nl:Aardgas ja:天然ガス no:Naturgass nn:Naturgass pl:Gaz ziemny pt:Gás natural ru:Природный газ simple:Natural gas sk:Zemný plyn fi:Maakaasu sv:Naturgas zh:天然气

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