User:Milton Beychok/Sandbox: Difference between revisions

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However, a great deal of gas flaring at many oil and gas production sites has nothing to do with protection against the dangers of over-pressuring industrial plant equipment. When [[Crude oil|petroleum crude oil]] is extracted and produced from onshore or offshore oil wells, [[Natural gas|raw natural gas]] associated with the oil is produced to the surface as well. In areas of the world lacking pipelines and other gas transportation infrastructure, vast amounts of such associated gas are commonly flared as waste or unusable gas. The flaring of associated gas may occur at the top of a vertical flare stack (as in the adjacent photo) or it may occur in a ground-level flare in an earthen pit. Such flaring constitutes a hazard to human health and also significantly contributes to the worldwide anthropogenic emissions of [[carbon dioxide]] (CO<sub>2</sub>).  
However, a great deal of gas flaring at many oil and gas production sites has nothing to do with protection against the dangers of over-pressuring industrial plant equipment. When [[Crude oil|petroleum crude oil]] is extracted and produced from onshore or offshore oil wells, [[Natural gas|raw natural gas]] associated with the oil is produced to the surface as well. In areas of the world lacking pipelines and other gas transportation infrastructure, vast amounts of such associated gas are commonly flared as waste or unusable gas. The flaring of associated gas may occur at the top of a vertical flare stack (as in the adjacent photo) or it may occur in a ground-level flare in an earthen pit. Such flaring constitutes a hazard to human health and also significantly contributes to the worldwide anthropogenic emissions of [[carbon dioxide]] (CO<sub>2</sub>).  


== Function ==
== Overall flare system in industrial plants ==
On [[drilling rig|oil production rigs]], in [[oil refinery|refineries]] and [[chemical plant]]s, its primary purpose is to act as a safety device to protect vessels or pipes from over-pressuring due to unplanned upsets. Pressure control valves are set at predetermined pressures to release excess gas,  thus allowing continued operation during upset conditions. Whenever plant equipment items are over-pressured, the pressure relief valves on the equipment automatically release gases (and sometimes liquids as well) which are routed through piping runs called ''flare headers'' to the flare stacks. The gases and/or liquids are separated in a flare knock out drum with the gas piped to the flare stacks for burning or for lighter gases venting. The size and brightness of the resulting flame depends upon how much flammable material was released. Typically there may be more than one flare system handling high pressure gas, low pressure gas, sour or corrosive gas, cold gas and wet gas. Vents (unignited flares) are used typically on gas plants for emergency gas disposal and are designed to operate in an emergency at sonic velocity. Flare gas recovery systems are occasionally used to collect low flows of waste gas and return it to the Process Plant as opposed to burning the gas. Steam can be injected into the flame to reduce the formation of black smoke. The injected steam does however make the burning of gas sound louder, which can cause complaints from nearby residents. Compared to the emission of black smoke, it can be seen as a valid trade off. In order to keep the flare system functional, a small amount of purge gas flows  continuously, whilst there are continuously  burning pilots, so that the system is always ready for its primary purpose of burning as an over-pressure safety system. Enclosed ground flares are engineered to eliminate toxic and corrosive components, reduce smoke, and contain the flame within the enclosure. Burn pits are used to dispose of waste hydrocarbon liquids and are increasingly being designed out due to their unacceptable dirty appearance.
Whenever industrial plant equipment items are over-pressured, the [[pressure relief valve]]s provided as essential safety devices on the equipment automatically release gases and sometimes 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 large [[Piping (engineering)|piping]] systems called ''flare headers'' to a vertical elevated flare. The released gases are [[Combustion|burned]] as they exit the flare stacks. The size and brightness of the resulting flame depends upon the flammable material's flow rate in terms of [[Joule|joules]] per hour (or [[U.S. customary units|btu]] per hour).<ref name=Beychok/>
 
Most industrial plant flares have a [[Vapor-liquid separator|vapor-liquid separator]] (also known as a knockout drum) upstream of the flare to remove any large amounts of liquid that may accompany the relieved gases.
 
[[Steam]] is very often injected into the flame to reduce the formation of black smoke. In order to keep the flare system functional, a small amount of gas is continuously burned, like a pilot light, so that the system is 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 stack system:
 
*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 the top of the flare stack.
*As alternative gas recovery system for use during partial plant startups and/or shutdowns as well as other times when required. The recovered gas is routed into the fuel gas system of the overall industrial plant.
*A steam injection system to provide an external momentum force used for efficient mixing of air with the relieved gas, which promotes smokeless burning.
*A pilot flame (with its ignition system) that burns all the time so that it is available to ignite relieved gases whenever needed.
*The flare stack, including a flashback prevention section at the upper part of the flare stack.


== Climatic effects ==
== Climatic effects ==

Revision as of 10:58, 2 June 2012

(CC) Photo: Ari Frede
An industrial flare stack in a petroleum refinery.

A gas flare, alternatively known as a flare stack, is a combustion device (see the adjacent photo) used in industrial plants such as petroleum refineries, chemical plants, natural gas processing plants as well as at oil or gas production sites having oil wells, gas wells, offshore oil and gas rigs and landfills.

In industrial plants, flare stacks are primarily used for burning off flammable gas released by pressure 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 planned combustion of gases over relatively short periods.

However, a great deal of gas flaring at many oil and gas production sites has nothing to do with protection against the dangers of over-pressuring industrial plant equipment. When petroleum crude oil is extracted and produced from onshore or offshore oil wells, raw natural gas associated with the oil is produced to the surface as well. In areas of the world lacking pipelines and other gas transportation infrastructure, vast amounts of such associated gas are commonly flared as waste or unusable gas. The flaring of associated gas may occur at the top of a vertical flare stack (as in the adjacent photo) or it may occur in a ground-level flare in an earthen pit. Such flaring constitutes a hazard to human health and also significantly contributes to the worldwide anthropogenic emissions of carbon dioxide (CO2).

Overall flare system in industrial plants

Whenever industrial plant equipment items are over-pressured, the pressure relief valves provided as essential safety devices on the equipment automatically release gases and sometimes 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 large piping systems called flare headers to a vertical elevated flare. The released gases are burned as they exit the flare stacks. The size and brightness of the resulting flame depends upon the flammable material's flow rate in terms of joules per hour (or btu per hour).[6]

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 relieved gases.

Steam is very often injected into the flame to reduce the formation of black smoke. In order to keep the flare system functional, a small amount of gas is continuously burned, like a pilot light, so that the system is 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 stack system:

  • 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 the top of the flare stack.
  • As alternative gas recovery system for use during partial plant startups and/or shutdowns as well as other times when required. The recovered gas is routed into the fuel gas system of the overall industrial plant.
  • A steam injection system to provide an external momentum force used for efficient mixing of air with the relieved gas, which promotes smokeless burning.
  • A pilot flame (with its ignition system) that burns all the time so that it is available to ignite relieved gases whenever needed.
  • The flare stack, including a flashback prevention section at the upper part of the flare stack.

Climatic effects

Flaring and venting of natural gas from oil and gas wells contribution to greenhouse gases has declined by three-quarters in absolute terms since a peak in the 1970s of approximately 110 million metric tons/year of CO2 and now accounts for 0.5% of all anthropogenic carbon dioxide emissions.[7]

Recently, under the Kyoto Protocol, garbage collecting companies in some developing nations have received a carbon bonus for installing combustion devices for the methane gas produced at their landfills, preventing methane from reaching the atmosphere. When burned, the methane is converted to heat, water and CO2. (According to the IPCC Third Assessment Report report of the IPCC, Methane is 23 times more powerful a greenhouse gas than CO2)

Volume

The World Bank estimates that over 134 billion cubic metres of natural gas are flared or vented annually, an amount equivalent to more than 20 percent of the United States’ gas consumption or 33 percent of the European Union’s gas consumption per year.[8]

This flaring is highly concentrated: 10 countries account for 70% of emissions, and twenty for 85%. The top ten leading contributors to world gas flaring in 2010, were (in declining order): Russia (26%), Nigeria (11%), Iran (8%), Iraq (7%), Algeria (4%), Angola (3%), Kazakhstan (3%), Libya (3%), Saudi Arabia (3%) and Venezuela (2%).[9]

Russian flaring

Russia has announced it will stop the practice of gas flaring as stated by deputy prime minister Sergei Ivanov on Wednesday September 19, 2007.[10] This step was, at least in part, a response to a recent report by the National Oceanic and Atmospheric Administration (NOAA) that concluded Russia's previous numbers may have been underestimated. The report, which used night time light pollution satellite imagery to estimate flaring, put the estimate for Russia at 50 billion cubic meters while the official numbers are 15 or 20 billion cubic meters. The number for Nigeria is 23 billion cubic meters.[11]

See also

References

  1. ↑ EPA/452/B-02-001, Section 3.0: VOC Controls, Section 3.2: VOC Destruction Controls, Chapter 1: Flares. (A U.S. Environmental Protection Agency report, dated September 2000.)
  2. ↑ A. Kayode Coker (2007). Ludwig's Applied Process Design for Chemical And Petrochemical Plants, Volume 1, 4th ed. Gulf Professional Publishing, pp. 732-737. ISBN 0-7506-7766-X. 
  3. ↑ Sam Mannan (Editor) (2005). Lee's Loss Prevention in the Process Industries: Hazard Identification, Assessment and Control, Volume 1, 3rd ed. Elsevier Butterworth-Heinemann, pp. 12/67-12/71. ISBN 0-7506-7857-1. 
  4. ↑ Milton R. Beychok (2005). Fundamentals of Stack Gas Dispersion, Fourth ed. self-published. ISBN 0-9644588-0-2.  (See Chapter 11, Flare Stack Plume Rise).
  5. ↑ A Proposed Comprehensive Model for Elevated Flare Flames and Plumes, David Shore, Flaregas Corporation, AIChE 40th Loss Prevention Symposium, April 2006.
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Beychok
  7. ↑ Global, Regional, and National CO2 Emissions. In Trends: A Compendium of Data on Global Change, Marland, G., T.A. Boden, and R. J. Andres, 2005, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee.Template:Dead link
  8. ↑ The World Bank, World Bank, GGFR Partners Unlock Value of Wasted Gas", World Bank 14 December 2009. Retrieved 17 March 2010.
  9. ↑ Global Gas Flaring reduction, The World Bank, "Estimated Flared Volumes from Satellite Data, 2006-2010."
  10. ↑ News.yahoo.com
  11. ↑ The Boston Globe: Russia top offender in gas-flare emissions.

External links

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