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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 Swamp s, which produce Swamp Gas ; Marsh es, which produce Marsh Gas ; Landfill s, which produce Landfill Gas , as well as Sewage Sludge and Manure , by way of Anaerobic Digester s, in addition to Enteric Fermentation particularly 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 is oxidised, 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 Carbon Dioxide than more Carbonaceous fuel sources, such as Coal . Significant biological sources of methane are Termite s, Ruminant s and cultivation. Estimated emissions are 15, 75 and 100 million tons per year respectively. Chemical composition The primary component of natural gas is Methane ( C H 4), the shortest and lightest Hydrocarbon molecule. It may also contain 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 containing only methane is "dry", otherwise it is referred to as "wet". Organosulfur Compounds and Hydrogen Sulfide ( H 2 S 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 Thiol s, to assist in leak detection. Natural gas is, in itself, harmless to the human body -- unlike Carbon Monoxide , for instance, it is not a poison. 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 buldings. 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 nonexistent, 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 Combustion of one Cubic Metre of commercial quality natural gas yields 38 Megajoule s (10.6 KWh ). Equivalently, one Cubic Foot of natural gas produces 1031 British Thermal Unit s (BTUs). In the USA, at retail, natural gas is often sold in units of Therm s (th); 1 therm = 100,000 BTU. Wholesale transactions are generally done in Decatherm s (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 The major difficulty in the use of natural gas is Transport ation and storage. Natural gas Pipelines are economical, but are impractical across Ocean s. 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 Carrier s can be used to transport Liquefied Natural Gas (LNG) across oceans, while Tank Truck s 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 facitilies or into a pipeline. In the past, the natural gas which was recovered in the course of recovering Petroleum could not be Profit ably sold, and was simply Burned at the oil field (known as Flaring ). This Waste ful 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- Inject ed back into the formation for later recovery. This also assists oil Pump ing by keeping underground Pressure s 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 land-fills 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 practical. 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 , former Chairman of the Federal Reserve Alan Greenspan , and former 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 are put into the ground, about the same amount of natural gas is recovered each year). But because of the continuing growth in demand, and the temporary but dramatic hit to production that came from Hurricane s 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. 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 California Energy Commission Frequently Asked Questions About LNG — Harbor , as well as being sheltered from wind and waves. These "suitable" sites are thus deep in well populated Seaport s, 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 River s 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 Tugboat s 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 put substantial, new liquification 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 Carrier s also must occur to move the huge 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 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 around the year 2085. Hydrogen Natural gas can be used to produce Hydrogen that can be used in Hydrogen Vehicle s. 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 Vehicle s 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 ). Residential domestic use 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 Pipe d-in Public Utility services, or with portable Grill s. 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 Fabric s, Glass , Steel , Plastic s, Paint , and other products. SOURCES Natural gas is commercially produced from Oil Field s and Natural Gas Field s. Gas produced from oil wells is called casinghead gas or associated gas. The largest two natural gas fields are probably South Pars Gas Field in Iran and Urengoy Gas Field in Russia , with reserves on the order of 1013 m³. See also List Of Natural Gas Fields . Qatar also has 25 trillion cubic meters of natural gas (5% of the world's proven supply), enough to last 250 years at current production levels. Town Gas is a mixture of methane and other gases which can be used in a similar way to natural gas and can be produced by treating Coal chemically. This a historic technology still used as 'best solution' in some local circumstances, although coal gasification is not usually economic at current gas prices, depending upon infrastructure considerations. Possible future sources One experimental idea is to use the methane gas that is naturally produced from Landfill s 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 gases 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 usable energy. This can be improved by adding other organic material (plants as well as slaughter house waste) to the digester. A speculative source of enormous quantities of methane is from Methane Hydrate , found under sediments in the oceans. At present (2006), no technology has been developed to recover this source of energy economically. SAFETY In any form, a minute amount of Odorant such as Methyl Mercaptan , with a rotting-cabbage-like smell, is added to the otherwise Color less and Odor less gas, so that leaks can be detected before a fire or Explosion occurs. Sometimes a related compound, Ethyl Mercaptan 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. Although concentrated thiols are extremely toxic, it is considered non-toxic in the extremely low concentrations in which it occurs in natural gas delivered to the end user. For example, a safe exposure level to ethyl mercaptan at 5 Parts Per Million over an eight-hour period has been established by the American Congress of Government and Industrial Hygienists (ACGIH). Actual concentrations used by gas companies are on the order of 5 Parts Per Billion (5 parts in 109), one-thousandth the maximum safe limit. In Mine s, where methane seeping from rock formations has no odor, Sensor s 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 Home s, Small Business es 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 . 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 Ecosystem s, Waterway s, Sewer and Water Supply systems, Foundation s, etc. REFERENCES SEE ALSO
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