外文翻译天然气Word格式文档下载.docx

1、From Wikipedia, the free encyclopediaJump to: navigation, search For other uses, see Natural gas （disambiguation）.Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, with up to 20 percent1 concentration of other hydrocarbons （usually ethane） as well as small

2、 amounts of impurities such as carbon dioxide. Natural gas is widely used and is an important energy source in many applications including heating buildings, generating electricity, providing heat and power to industry and vehicles and is also a feedstock in the manufacture of products such as ferti

3、lizers.Natural gas is found in deep underground natural rock formations or associated with other hydrocarbon reservoirs, in coal beds, and as methane clathrates. Most natural gas was created over time by two mechanisms: biogenic and thermogenic. Biogenic gas is created by methanogenic organisms in m

4、arshes, bogs, landfills, and shallow sediments. Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material.2Before natural gas can be used as a fuel, it must undergo processing to clean the gas and remove impurities including water in order to m

5、eet the specifications of marketable natural gas. The by-products of processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons, hydrogen sulphide （which may be converted into pure sulfur）, carbon dioxide, water vapor, and sometimes helium and nitrogen.In the 19t

6、h century, natural gas was usually obtained as a byproduct of producing oil, since the small, light gas carbon chains came out of solution as the extracted fluids underwent pressure reduction from the reservoir to the surface, similar to uncapping a bottle of soda pop where the carbon dioxide efferv

7、esces. Unwanted natural gas was a disposal problem in the active oil fields. If there was not a market for natural gas near the wellhead it was virtually valueless since it had to be piped to the end user. In the 19th century and early 20th century, such unwanted gas was usually burned off in the oi

8、l fields. Today, unwanted gas （or stranded gas without a market） associated with oil extraction often is returned to the reservoir with injection wells while awaiting a possible future market or to repressurize the formation, which can enhance extraction rates from other wells. In regions with a hig

9、h natural gas demand （such as the US）, pipelines are constructed when economically feasible to move the gas from the wellsite to the end consumer.Another possibility is to export the natural gas as a liquid. Gas-to-liquids （GTL） is a developing technology that converts stranded natural gas into synt

10、hetic gasoline, diesel, or jet fuel through the Fischer-Tropsch process developed during World War II by Germany. Such fuel can be transported to users through conventional pipelines and tankers. Proponents claim GTL burns cleaner than comparable petroleum fuels. Most major international oil compani

11、es are in an advanced stage of GTL production, with a world-scale （140,000 barrels （22,000 m3） a day） GTL plant in Qatar scheduled to be in production before 2010.dated infoNatural gas can be associated （found in oil fields） or non-associated （isolated in natural gas fields）, and is also found in co

12、al beds （as coalbed methane）. It sometimes contains significant amounts of ethane, propane, butane, and pentaneheavier hydrocarbons removed for commercial use prior to the methane being sold as a consumer fuel or chemical plant feedstock. Non-hydrocarbons such as carbon dioxide, nitrogen, helium （ra

13、rely）, and hydrogen sulfide must also be removed before the natural gas can be transported.3Natural gas is commercially extracted from oil fields and natural gas fields. Gas extracted from oil wells is called casinghead gas or associated gas. The natural gas industry is extracting gas from increasin

14、gly more challenging resource types: sour gas, tight gas, shale gas, and coalbed methane.The worlds largest proven gas reserves are located in Russia, with 4.7571013 m （1.681015 cubic feet）. With the Gazprom company, Russia is frequently the worlds largest natural gas extractor. Major proven resourc

15、es （in billion cubic meters） are world 175,400 （2006）, Russia 47,570 （2006）, Iran 26,370 （2006）, Qatar 25,790 （2007）, Saudi Arabia 6,568 （2006） and United Arab Emirates 5,823 （2006）.It is estimated that there are about 900 trillion cubic meters of unconventional gas such as shale gas, of which 180 t

16、rillion may be recoverable.4 In turn, many studies from MIT, Black & Veatch and the DOE - see natural gas - will account for a larger portion of electricity generation and heat in the future.5s largest gas field is Qatars offshore North Field, estimated to have 25 trillion cubic meters6 （9.01014cubi

17、c feet） of gas in placeenough to last more than 420 yearscitation needed at optimum extraction levels. The second largest natural gas field is the South Pars Gas Field in Iranian waters in the Persian Gulf. Located next to Qatars North Field, it has an estimated reserve of 8 to 14 trillion cubic met

18、ers7 （2.81014 to 5.01014 cubic feet） of gas.Because natural gas is not a pure product, as the reservoir pressure drops when non-associated gas is extracted from a field under supercritical （pressure/temperature） conditions, the higher molecular weight components may partially condense upon isothermi

19、c depressurizingan effect called retrograde condensation. The liquid thus formed may get trapped as the pores of the gas reservoir get deposited. One method to deal with this problem is to re-inject dried gas free of condensate to maintain the underground pressure and to allow re-evaporation and ext

20、raction of condensates. More frequently, the liquid condenses at the surface, and one of the tasks of the gas plant to collect this condensate. The resulting liquid is called natural gas liquid （NGL） and has commercial value.Town gasTown gas, a synthetically produced mixture of methane and other gas

21、es, mainly the highly toxic carbon monoxide, is used in a similar way to natural gas and can be produced by treating coal chemically. This is a historical technology, not usually economically competitive with other sources of fuel gas today. But there are still some specific cases where it is the be

22、st option and it may be so into the future.Most town gashouses located in the eastern US in the late 19th and early 20th centuries were simple by-product coke ovens which heated bituminous coal in air-tight chambers. The gas driven off from the coal was collected and distributed through networks of

23、pipes to residences and other buildings where it was used for cooking and lighting. （Gas heating did not come into widespread use until the last half of the 20th century.） The coal tar （or asphalt） that collected in the bottoms of the gashouse ovens was often used for roofing and other water-proofin

24、g purposes, and when mixed with sand and gravel was used for paving streets.BiogasMain article: biogasWhen methane-rich gases are produced by the anaerobic decay of non-fossil organic matter （biomass）, these are referred to as biogas （or natural biogas）. Sources of biogas include swamps, marshes, an

25、d landfills （see landfill gas）, as well as sewage sludge and manure8 by way of anaerobic digesters, in addition to enteric fermentation, particularly in cattle.Methanogenic archaea are responsible for all biological sources of methane, some in symbiotic relationships with other life forms, including

26、 termites, ruminants, and cultivated crops. Methane released directly into the atmosphere would be considered a pollutant. However, methane in the atmosphere is oxidized, producing carbon dioxide and water. Methane in the atmosphere has a half life of seven years, meaning that if a tonne of methane

27、were emitted today, 500 kilograms would have broken down to carbon dioxide and water after seven years.Other sources of methane, the principal component of natural gas, include landfill gas, biogas, and methane hydrate. Biogas, and especially landfill gas, are already used in some areas, but their u

28、se could be greatly expanded. Landfill gas is a type of biogas, but biogas usually refers to gas produced from organic material that has not been mixed with other waste.Landfill gas is created from the decomposition of waste in landfills. If the gas is not removed, the pressure may get so high that

29、it works its way to the surface, causing damage to the landfill structure, unpleasant odor, vegetation die-off, and an explosion hazard. The gas can be vented to the atmosphere, flared or burned to produce electricity or heat. Experimental systems were being proposed for use in parts of Hertfordshir

30、e, UK, and Lyon in France.Once water vapor is removed, about half of landfill gas is methane. Almost all of the rest is carbon dioxide, but there are also small amounts of nitrogen, oxygen, and hydrogen. There are usually trace amounts of hydrogen sulfide and siloxanes, but their concentration varie

31、s widely. Landfill gas cannot be distributed through utility natural gas pipelines unless it is cleaned up to less than 3% CO2, and a few parts per million H2S, because CO2 and H2S corrode the pipelines.9 It is usually more economical to combust the gas on site or within a short distance of the land

32、fill using a dedicated pipeline. Water vapor is often removed, even if the gas is combusted on site. If low temperatures condense water out of the gas, siloxanes can be lowered as well because they tend to condense out with the water vapor. Other non-methane components may also be removed in order to meet emission standards, to prevent fouling of the equipment or for environmental considerations. Co-firing landfill gas with natural gas improves combustion, which lowers emissions.Gas generated in sewage treatment plants is commonly used to generate elec