Gas flare

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Flare stack at the Shell Haven refinery in England Shell haven flare.jpg
Flare stack at the Shell Haven refinery in England

A gas flare, alternatively known as a flare stack, flare boom, ground flare, or flare pit, is a gas combustion device used in places such as petroleum refineries, chemical plants and natural gas processing plants, oil or gas extraction sites having oil wells, gas wells, offshore oil and gas rigs and landfills.

Contents

In industrial plants, flare stacks are primarily used for burning off flammable gas released by safety valves during unplanned overpressuring of plant equipment. [1] [2] [3] [4] [5] During plant or partial plant startups and shutdowns, they are also often used for the planned combustion of gases over relatively short periods.

At oil and gas extraction sites, gas flares are similarly used for a variety of startup, maintenance, testing, safety, and emergency purposes. [6] In a practice known as production flaring, they may also be used to dispose of large amounts of unwanted associated petroleum gas, possibly throughout the life of an oil well. [7]

Overall flare system in industrial plants

Schematic flow diagram of an overall vertical, elevated flare stack system in an industrial plant. FlareStack System.png
Schematic flow diagram of an overall vertical, elevated flare stack system in an industrial plant.

When industrial plant equipment items are overpressured, the pressure relief valve is an essential safety device that automatically releases gases and sometimes liquids. 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 joules per hour (or btu per 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 relieved gases.

Steam is very often injected into the flame to reduce the formation of black smoke. When too much steam is added, a condition known as "oversteaming" can occur resulting in reduced combustion efficiency and higher emissions. [8] 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 overpressure safety system.

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

The schematic shows a pipe flare tip. The flare tip can have several configurations:

Flare stack height

The height of a flare stack, or the reach of a flare boom, is determined by the thermal radiation that is permissible or tolerable for equipment or personnel to be exposed to. [11] For continuous exposure of personnel wearing appropriate industrial clothing a maximum radiation level of 1.58 kW/m2 (500 Btu/hr.ft²) is recommended. Higher radiation levels are permissible but for reduced exposure times:

Ground flares

Ground flares are designed to hide the flame from sight and to reduce thermal radiation and noise. [10] They comprise a steel box or cylinder lined with refractory material. They are open at the top and have openings around the base to allow combustion air to enter. They may have an array of multiple flare tips to provide turndown capability and to spread the flame across the cross-section of the flare. They are generally used onshore in environmentally sensitive areas and have been used offshore on floating production storage and offloading installations (FPSOs). [10]

Crude oil production flares

Ground-level flaring of gas in North Dakota North Dakota Flaring of Gas.JPG
Ground-level flaring of gas in North Dakota

When crude oil is extracted and produced from oil wells, raw natural gas associated with the oil is brought to the surface as well. Especially 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, or it may occur in a ground-level flare in an earthen pit. Preferably, associated gas is reinjected into the reservoir, which saves it for future use while maintaining higher well pressure and crude oil producibility. [12]

Advances in satellite monitoring, along with voluntary reporting, have revealed that about 150 × 109 cubic meters (5.3 × 1012 cubic feet) of associated gas have been flared globally each year since at least the mid-1990s until 2020. [13] In 2011, that was equivalent to about 25 percent of the annual natural gas consumption in the United States or about 30 per cent of the annual gas consumption in the European Union. [7] At market, this quantity of gas—at a nominal value of $5.62 per 1000 cubic feet—would be worth US$29.8 billion. [14] Additionally, the waste is a significant source of carbon dioxide (CO2) and other greenhouse gas emissions.

Biogas flares

Flare stack igniting biogas from sewage sludge digesters at a sewage treatment plant in Ontario, Canada. Sewage Sludge Digester Gas Flare Stack.jpg
Flare stack igniting biogas from sewage sludge digesters at a sewage treatment plant in Ontario, Canada.

An important source of anthropogenic methane comes from the treatment and storage of organic waste material including waste water, animal waste and landfill. [15] Gas flares are used in any process that results in the generation and collection of biogas. As a result, gas flares are a standard component of an installation for controlling the production of biogas. [16] They are installed on landfill sites, waste water treatment plant and anaerobic digestion plant that use agriculturally or domestically produced organic waste to produce methane for use as a fuel or for heating.

Gas flares on biogas collection systems are used if the gas production rates are not sufficient to warrant use in any industrial process. However, on a plant where the gas production rate is sufficient for direct use in an industrial process that could be classified as part of the circular economy, and that may include the generation of electricity, the production of natural gas quality biogas for vehicle fuel [17] or for heating in buildings, drying refuse-derived fuel or leachate treatment, gas flares are used as a back-up system during down-time for maintenance or breakdown of generation equipment. In this latter case, generation of biogas cannot normally be interrupted, and a gas flare is employed to maintain the internal pressure on the biological process. [18]

There are two types of gas flare used for controlling biogas, open or enclosed. Open flares burn at a lower temperature, less than 1000 °C and are generally cheaper than enclosed flares that burn at a higher combustion temperature and are usually supplied to conform to a specific residence time of 0.3s within the chimney to ensure complete destruction of the toxic elements contained within the biogas.[ citation needed ] Flare specification usually demands that enclosed flares must operate at >1000 °C and <1200 °C; this in order to ensure a 98% destruction efficient and avoid the formation of NOx. [19]

Environmental impacts

Flaring of associated gas from a site in Nigeria. Niger Delta Gas-Flares.jpg
Flaring of associated gas from a site in Nigeria.
Flaring gases from an oil platform in the North Sea. First gas from the Oselvar module on the Ula platform on April 14th, 2012.jpg
Flaring gases from an oil platform in the North Sea.
Flare, Bayport Industrial District, Harris County, Texas Flare, Bayport Industrial District, Harris County, Texas.jpg
Flare, Bayport Industrial District, Harris County, Texas

The natural gas that is not combusted by a flare is vented into the atmosphere as methane. Methane's estimated global warming potential is 28-36 times greater than that of CO2 over the course of a century, and 84-87 times greater over two decades. [20] Natural gas flaring produces CO2 and many other compounds, depending on the chemical composition of the natural gas and on how well the natural gas burns in the flare. Therefore, to the extent that gas flares convert methane to CO2 before it is released into the atmosphere, they reduce the amount of global warming that would otherwise occur. [21] [22]

Flaring emissions contributed to 270 Mt (megatonnes) of CO2 in 2017 and reducing flaring emissions is thought to be an important component in curbing global warming. [23] An increasing number of governments and industries have pledged to eliminate or reduce flaring. [23] The Global Methane Pledge signed at COP26, in which 111 nations committed to reducing methane emissions by at least 30 percent from 2020 levels by 2030, is also playing a role in raising the global focus on methane.

Additional noxious fumes emitted by flaring may include, aromatic hydrocarbons (benzene, toluene, xylenes) and benzo(a)pyrene, which are known to be carcinogenic. A 2013 study found that gas flares contributed over 40% of the black carbon deposited in the Arctic. [24] [25]

Flaring can affect wildlife by attracting birds and insects to the flame. Approximately 7,500 migrating songbirds were attracted to and killed by the flare at the liquefied natural gas terminal in Saint John, New Brunswick, Canada on September 13, 2013. [26] Similar incidents have occurred at flares on offshore oil and gas installations. [27] Moths are known to be attracted to lights. A brochure published by the Secretariat of the Convention on Biological Diversity describing the Global Taxonomy Initiative describes a situation where "a taxonomist 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". [28]

Adverse health effects

Flares release several different chemicals including: benzene, particulates, nitrogen oxides, heavy metals, black carbon, and carbon monoxide. Several of these pollutants correlate with preterm birth and reduced newborn birth weight. According to one study from 2020, pregnant women living near flaring natural gas and oil wells have reportedly experienced a 50% greater premature birth rate. [29] Flares may emit methane and other volatile organic compounds as well as sulfur dioxide and other sulfur compounds, which are known to exacerbate asthma and other respiratory disease. [30]

A 2021 study found that a 1% increase in flared natural gas increases the respiratory-related hospitalization rate by 0.73%. [31]

See also

Related Research Articles

<span class="mw-page-title-main">Natural gas</span> Gaseous fossil fuel

Natural gas is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (95%) in addition to various smaller amounts of other higher alkanes. Traces of carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present. Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide. Because natural gas is odorless, odorizers such as mercaptan are commonly added to it for safety so that leaks can be readily detected.

<span class="mw-page-title-main">Biogas</span> Gases produced by decomposing organic matter

Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. Biogas is produced by anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester, biodigester or a bioreactor. The gas composition is primarily methane and carbon dioxide and may have small amounts of hydrogen sulfide, moisture and siloxanes. The methane can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used in fuel cells and for heating purpose, such as in cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.

<span class="mw-page-title-main">Incineration</span> Waste treatment process

Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high-temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, flue gas and heat. The ash is mostly formed by the inorganic constituents of the waste and may take the form of solid lumps or particulates carried by the flue gas. The flue gases must be cleaned of gaseous and particulate pollutants before they are dispersed into the atmosphere. In some cases, the heat that is generated by incineration can be used to generate electric power.

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

<span class="mw-page-title-main">Alternative fuel</span> Fuels from sources other than fossil fuels

Alternative fuels, also known as non-conventional and advanced fuels, are fuels derived from sources other than petroleum. Alternative fuels include gaseous fossil fuels like propane, natural gas, methane, and ammonia; biofuels like biodiesel, bioalcohol, and refuse-derived fuel; and other renewable fuels like hydrogen and electricity.

<span class="mw-page-title-main">Fuel gas</span> Fuels which under ordinary conditions, are gaseous

Fuel gas is one of a number of fuels that under ordinary conditions are gaseous. Most fuel gases are composed of hydrocarbons, hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of energy that can be readily transmitted and distributed through pipes.

<span class="mw-page-title-main">Fossil fuel power station</span> Facility that burns fossil fuels to produce electricity

A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal, oil, or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating gas engine. All plants use the energy extracted from the expansion of a hot gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have their efficiency limited by the Carnot efficiency and therefore produce waste heat.

<span class="mw-page-title-main">Landfill gas</span> Gaseous fossil fuel

Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simple hydrocarbons.

<span class="mw-page-title-main">Global Methane Initiative</span> International partnership to reduce methane emissions

The Global Methane Initiative (GMI) is a voluntary, international partnership that brings together national governments, private sector entities, development banks, NGOs and other interested stakeholders in a collaborative effort to reduce methane gas emissions and advance methane recovery and use as a clean energy source. National governments are encouraged to join GMI as Partner Countries, while other non-State organizations may join GMI's extensive Project Network. As a public-private initiative, GMI creates an international platform to build capacity, development methane abatement strategies, engage in technology transfer, and remove political and economic barriers to project development for emissions reduction.

Renewable natural gas (RNG), also known as biomethane, is a renewable fuel and biogas which has been upgraded to a quality similar to fossil natural gas and has a methane concentration of 90% or greater. By removing CO2 and other impurities from biogas, and increasing the concentration of methane to a level similar to fossil natural gas, it becomes possible to distribute RNG via existing gas pipeline infrastructure. RNG can be used in existing appliances, including vehicles with natural gas burning engines (natural gas vehicles).

<span class="mw-page-title-main">Waste-to-energy</span> Process of generating energy from the primary treatment of waste

Waste-to-energy (WtE) or energy-from-waste (EfW) refers to a series of processes designed to convert waste materials into usable forms of energy, typically electricity or heat. As a form of energy recovery, WtE plays a crucial role in both waste management and sustainable energy production by reducing the volume of waste in landfills and providing an alternative energy source.

<span class="mw-page-title-main">Biodegradable waste</span> Organic matter that can be broken down

Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane, compost, humus, and simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digestion or similar processes. It mainly includes kitchen waste, ash, soil, dung and other plant matter. In waste management, it also includes some inorganic materials which can be decomposed by bacteria. Such materials include gypsum and its products such as plasterboard and other simple sulfates which can be decomposed by sulfate reducing bacteria to yield hydrogen sulfide in anaerobic land-fill conditions.

Landfill gas monitoring is the process by which gases that are collected or released from landfills are electronically monitored. Landfill gas may be measured as it escapes the landfill or may be measured as it is collected and redirected to a power plant or flare.

<span class="mw-page-title-main">Thermal oxidizer</span>

A thermal oxidizer is a process unit for air pollution control in many chemical plants that decomposes hazardous gases at a high temperature and releases them into the atmosphere.

<span class="mw-page-title-main">Greenhouse gas emissions by the United States</span> Climate changing gases from the North American country

The United States produced 5.2 billion metric tons of carbon dioxide equivalent greenhouse gas (GHG) emissions in 2020, the second largest in the world after greenhouse gas emissions by China and among the countries with the highest greenhouse gas emissions per person. In 2019 China is estimated to have emitted 27% of world GHG, followed by the United States with 11%, then India with 6.6%. In total the United States has emitted a quarter of world GHG, more than any other country. Annual emissions are over 15 tons per person and, amongst the top eight emitters, is the highest country by greenhouse gas emissions per person.

<span class="mw-page-title-main">Environmental impact of the energy industry</span>

The environmental impact of the energy industry is significant, as energy and natural resource consumption are closely related. Producing, transporting, or consuming energy all have an environmental impact. Energy has been harnessed by human beings for millennia. Initially it was with the use of fire for light, heat, cooking and for safety, and its use can be traced back at least 1.9 million years. In recent years there has been a trend towards the increased commercialization of various renewable energy sources. Scientific consensus on some of the main human activities that contribute to global warming are considered to be increasing concentrations of greenhouse gases, causing a warming effect, global changes to land surface, such as deforestation, for a warming effect, increasing concentrations of aerosols, mainly for a cooling effect.

<span class="mw-page-title-main">Landfill gas utilization</span> Method of producing electricity

Landfill gas utilization is a process of gathering, processing, and treating the methane or another gas emitted from decomposing garbage to produce electricity, heat, fuels, and various chemical compounds. After fossil fuel and agriculture, landfill gas is the third largest human generated source of methane. Compared to CO2, methane is 25 times more potent as a greenhouse gas. It is important not only to control its emission but, where conditions allow, use it to generate energy, thus offsetting the contribution of two major sources of greenhouse gases towards climate change.

Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% of methane released globally was from human activities, while natural sources contributed about 40%. Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.

<span class="mw-page-title-main">Gas venting</span> Disposal of unwanted methane gas from fossil fuels

Gas venting, more specifically known as natural-gas venting or methane venting, is the intentional and controlled release of gases containing alkane hydrocarbons - predominately methane - into Earth's atmosphere. It is a widely used method for disposal of unwanted gases which are produced during the extraction of coal and crude oil. Such gases may lack value when they are not recyclable into the production process, have no export route to consumer markets, or are surplus to near-term demand. In cases where the gases have value to the producer, substantial amounts may also be vented from the equipment used for gas collection, transport, and distribution.

<span class="mw-page-title-main">Routine flaring</span> Disposal of unwanted gas during extraction

Routine flaring, also known as production flaring, is a method and current practice of disposing of large unwanted amounts of associated petroleum gas (APG) during crude oil extraction. The gas is first separated from the liquids and solids downstream of the wellhead, then released into a flare stack and combusted into Earth's atmosphere. Where performed, the unwanted gas has been deemed unprofitable, and may be referred to as stranded gas, flare gas, or simply as "waste gas". Routine flaring is not to be confused with safety flaring, maintenance flaring, or other flaring practices characterized by shorter durations or smaller volumes of gas disposal.

References

  1. 1 2 "Section 3: VOC Controls, Chapter 1: Flares" (PDF). EPA Air Pollution Cost Control Manual (Report) (6th ed.). Research Triangle Park, NC: U.S. Environmental Protection Agency (EPA). January 2002. EPA 452/B-02-001.
  2. 1 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   978-0-7506-7766-0.
  3. 1 2 Sam Mannan, ed. (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   978-0-7506-7857-5.
  4. 1 2 Milton R. Beychok (2005). Fundamentals of Stack Gas Dispersion (Fourth ed.). self-published. ISBN   978-0-9644588-0-2. (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. ↑ "IPIECA - Resources - Flaring Classification". International Petroleum Industry Environmental Conservation Association (IPIECA). Retrieved 2019-12-29.
  7. 1 2 Global Gas Flaring Reduction Partnership (GGFR), World Bank, October 2011 Brochure.
  8. ↑ "EPA Enforcement Targets Flaring Efficiency Violations" (PDF). Enforcement Alert. Washington, D.C.: EPA. August 2012. EPA 325-F-012-002.
  9. ↑ Product Overview Ignition Systems, Smitsvonk, November 2001. Excellent source of information about flare stack pilot flames and their ignition systems.
  10. 1 2 3 Argo Flare Services. "Argo flare services". argoflares. Retrieved 20 January 2021.
  11. 1 2 American Petroleum Institute (2020). Pressure-Relieving and Depressuring Systems (API Standard 521) (7th ed.). API. pp. Table 12.
  12. ↑ Leffler, William (2008). Petroleum Refining in Nontechnical Language. Tulsa, OK: PennWell. p. 9.
  13. ↑ "Global gas flaring and oil production (1996-2018)" (PDF). World Bank. June 2019.
  14. ↑ Annual Energy Review, Table 6.7 Natural Gas Wellhead, Citygate, and Imports Prices, 1949-2011 (Dollars per Thousand Cubic Feet), United States Energy Information Administration, September 2012.
  15. ↑ "Environmental Impact Of Using Biomass And Biogas Technology". www.biomass.net. Retrieved 2019-03-29.
  16. ↑ "Basic Information about Landfill Gas". Landfill Methane Outreach Program. Washington, D.C.: EPA. 2019-12-18.
  17. ↑ "Alternative Fuels Data Center: Alternative Fuels and Advanced Vehicles". afdc.energy.gov. Retrieved 2019-03-29.
  18. ↑ "Management of landfill gas: LFTGN 03". GOV.UK. Retrieved 2019-03-29.
  19. ↑ "NOx Emissions from Silicon Production". ResearchGate. Retrieved 2019-03-29.
  20. ↑ US EPA, OAR (2016-01-12). "Understanding Global Warming Potentials". www.epa.gov. Retrieved 2022-03-16.
  21. ↑ "Natural gas - Gas flaring and gas venting - Eniscuola". Eniscuola Energy and Environment. Retrieved 23 June 2018.
  22. ↑ "Natural gas and the environment - U.S. Energy Information Administration (EIA)".
  23. 1 2 "Flaring emissions – Tracking Fuel Supply – Analysis". IEA. Retrieved 2020-02-12.
  24. ↑ Stohl, A.; Klimont, Z.; Eckhardt, S.; Kupiainen, K.; Chevchenko, V.P.; Kopeikin, V.M.; Novigatsky, A.N. (2013), "Black carbon in the Arctic: the underestimated role of gas flaring and residential combustion emissions", Atmos. Chem. Phys., 13 (17): 8833–8855, Bibcode:2013ACP....13.8833S, doi: 10.5194/acp-13-8833-2013 , hdl: 11250/2383886
  25. ↑ Michael Stanley (2018-12-10). "Gas flaring: An industry practice faces increasing global attention" (PDF). World Bank. Retrieved 2020-01-20.
  26. ↑ 7,500 songbirds killed at Canaport gas plant in Saint John (online CBC News, September 17, 2013).
  27. ↑ Seabirds at Risk around Offshore Oil Platforms in the North-west Atlantic, Marine Pollution Bulletin, Vol. 42, No. 12, pp. 1,285–1,290, 2001.
  28. ↑ The Global Taxonomy Initiative - The Response to a Problem (scroll down to the section entitled "Pollinating moths")
  29. ↑ HSC News, University of Southern California, 17 Jul. 2020 "Living Near Natural Gas Flaring Poses Health Risks for Pregnant Women and Babies"
  30. ↑ "Frequent, Routine Flaring May Cause Excessive, Uncontrolled Sulfur Dioxide Releases" (PDF). Enforcement Alert. Washington, D.C.: EPA. October 2000. EPA 300-N-00-014.
  31. ↑ Blundell, Wesley; Kokoza, Anatolii (2022-04-01). "Natural gas flaring, respiratory health, and distributional effects". Journal of Public Economics. 208: 104601. doi:10.1016/j.jpubeco.2022.104601. ISSN   0047-2727. S2CID   232350369.

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