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From Wikipedia, the free encyclopedia

Flare stack at theShell Haven refinery in England.

A gas flare, alternatively known as a flare stack, is a gas combustion device used inindustrial plants such as petroleum refineries, chemical plants,natural gas processingplantsas well as at oil or gas production sites havingoil wells,gas wells,offshore oil and gas rigsandlandfills.

North Dakota Flaring of Gas

In industrial plants, flare stacks are primarily used for burning offflammable gas released bypressure relief valves during unplanned over-pressuring of plant equipment.[1][2][3][4][5]During

plant or partial plant startups and shutdowns, flare stacks are also often used for the plannedcombustion of gases over relatively short periods.

A great deal of gas flaring at many oil and gas production sites has nothing to do withprotection against the dangers of over-pressuring industrial plant equipment. Whenpetroleumcrude oil is extracted and produced from onshore or offshore oil wells, raw natural gasassociated with the oil is produced to the surface as well. Especially in areas of the worldlackingpipelines and other gas transportation infrastructure, vast amounts of suchassociatedgas are commonly flared as waste or unusable gas. The flaring of associated gas may occur atthe top of a vertical flare stack (as in the adjacent photo) or it may occur in a ground-levelflare in an earthen pit.

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Contents

1 Overall flare system in industrial plants

2 Impacts of waste flaring associated gas from oil drilling sites and other facilities 3 See also 4 References 5 External links 6 Media

Overall flare system in industrial plants

Schematic flow diagram of an overall vertical, elevated flare stack system in an industrialplant.

Whenever industrial plant equipment items are over-pressured, the pressure relief valvesprovided as essential safety devices on the equipment automatically release gases andsometimes liquids as well. Those pressure relief valves are required by industrial design

codes and standards as well as by law.

The released gases and liquids are routed through largepiping systems calledflare headerstoa vertical elevated flare. The released gases areburned as they exit the flare stacks. The sizeand brightness of the resulting flame depends upon the flammable material's flow rate interms ofjoulesper hour (orbtuper hour).[4]

Most industrial plant flares have a vapor-liquid separator (also known as a knockout drum)upstream of the flare to remove any large amounts of liquid that may accompany the relievedgases.

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Steam is very often injected into the flame to reduce the formation of black smoke. When toomuch steam is added to the flame, a condition known as "over steaming" can occur resultingin reduced combustion efficiency and higher emissions. In order to keep the flare systemfunctional, a small amount of gas is continuously burned, like a pilot light, so that the systemis always ready for its primary purpose as an over-pressure safety system.

The adjacent flow diagram depicts the typical components of an overall industrial flare stacksystem:[1][2][3]

A knockout drum to remove any oil and/or water from the relieved gases.

A water seal drum to prevent any flashback of the flame from the top of the flarestack.

An alternative gas recovery system for use during partial plant startups and/orshutdowns as well as other times when required. The recovered gas is routed into thefuel gas system of the overall industrial plant.

A steam injection system to provide an external momentum force used for efficient

mixing ofair with the relieved gas, which promotes smokeless burning.

Apilot flame (with itsignition system)that burns all the time so that it is available toignite relieved gases whenever needed.[6]

The flare stack, including a flashback prevention section at the upper part of the flarestack.

Impacts of waste flaring associated gas from oil drilling

sites and other facilities

Flaring of associated gas from an oil well site in Nigeria.

Flaring gases from an oil platform in the North Sea.

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Flaring is a contributor to the worldwide anthropogenic emissions of carbon dioxide.Improperly operated flares may emit methane and othervolatile organic compounds as wellas sulfur dioxide and other sulfur compounds, which are known to exacerbate asthma andother respiratory problems. Other emissions from improperly operated flares may include,aromatic hydrocarbons (benzene, toluene,xylenes)andbenzapyrene,which are known to be

carcinogenic.

Flaring can impact wildlife by attracting birds and insects to the flame. Approximately 7,500migrating songbirds were attracted to and killed by the flare at the liquefied natural gasterminal in Saint John, New Brunswick, Canada on September 13, 2013.[7]Similar incidentshave occurred at flares on offshore oil and gas installations.[8] Moths are known to beattracted to lights. A brochure published by the Secretariat of the Convention on BiologicalDiversity describing the Global Taxonomy Initiative describes a situation where "ataxonomist working in a tropical forest noticed that a gas flare at an oil refinery was

attracting and killing hundreds of these [hawk or sphinx] moths. Over the course of the

months and years that the refinery was running a vast number of moths must have been

killed, suggesting that plants could not be pollinated over a large area of forest".[9]

As of the end of 2011, 150 109cubic meters (5.3 1012cubic feet) of associated gas areflared annually. That is equivalent to about 25 per cent of the annual natural gas consumptionin the United States or about 30 per cent of the annual gas consumption in the EuropeanUnion.[10] If it were to reach market, this quantity of gas (at a nominal value of $5.62 per1000 cubic feet) would be worth $29.8 billion USD.[11]

Also as of the end of 2011, 10 countries accounted for 72 per cent of the flaring, and twentyfor 86 per cent. The top ten leading contributors to world gas flaring at the end of 2011, were(in declining order):Russia (27%),Nigeria (11%),Iran (8%),Iraq (7%),USA (5%),Algeria(4%),Kazakhstan (3%),Angola (3%),Saudi Arabia (3%) andVenezuela (3%).[12]

That amount of flaring and burning of associated gas from oil drilling sites is a significantsource of carbon dioxide (CO2) emissions. Some 400 10

6 tons of carbon dioxide areemitted annually in this way and it amounts to about 1.2 per cent of the worldwide emissionsof carbon dioxide. That may seem to be insignificant, but in perspective it is more than halfof the Certified Emissions Reductions(a type of carbon credits) that have been issued underthe rules and mechanisms of the Kyoto Protocol as of June 2011.[10][13]

Satellite data show that from 2005 to 2010, global gas flaring decreased by about 20%. The

most significant reductions in terms of volume were made in Russia and Nigeria.

[10][14]

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