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A gas flare, alternatively known as a flare stack, flare boom, ground flare, or flare pit is a gas
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
device used in places such as petroleum refineries, chemical plants and natural gas processing plants, oil or gas extraction sites having oil wells,
gas well An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas m ...
s, offshore oil and gas rigs and landfills. In industrial plants, flare stacks are primarily used for burning off flammable gas released by
safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds ...
s during unplanned over-pressuring of plant equipment. (See Chapter 11, ''Flare Stack Plume Rise''). 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. In a practice known as production flaring, they may also be used to dispose of large amounts of unwanted
associated petroleum gas Associated petroleum gas (APG), or associated gas, is a form of natural gas which is found with deposits of petroleum, either dissolved in the oil or as a free "gas cap" above the oil in the reservoir. The gas can be utilized in a number of ways ...
, possibly throughout the life of an oil well.Global Gas Flaring Reduction Partnership (GGFR), World Bank
October 2011 Brochure.


Overall flare system in industrial plants

When industrial plant equipment items are over-pressured, the
pressure relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is re ...
is an essential safety device that automatically release 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 Within industry, piping is a system of pipes used to convey fluids (liquids and gases) from one location to another. The engineering discipline of piping design studies the efficient transport of fluid. Industrial process piping (and accompa ...
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
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...
s per hour (or
btu The British thermal unit (BTU or Btu) is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is also part of the United States customary units. The modern SI u ...
per hour). 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 "over steaming" can occur resulting in reduced combustion efficiency and higher emissions. To keep the flare system functional, a small amount of gas is continuously burned, like a
pilot light Merker Tankless water heating, tankless gas-fired water heater from the 1930s, with pilot light clearly visible through the aperture in the front cover. The large opening allowed for the manual lighting of the pilot light by a lit match or taper ...
, 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 or water from the relieved gases. There may be several knock out drums: high pressure and low pressure drums taking relief flow from high pressure and low pressure equipment. A cold relief drum which is segregated from wet relief system because of the risk of freezing. *A water seal drum to prevent any flashback of the
flame A flame (from Latin '' flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density they ...
from the top of the flare stack. *An alternative gas recovery system for use during partial plant startups and 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 The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
with the relieved gas, which promotes smokeless burning. *A
pilot flame Merker Tankless water heating, tankless gas-fired water heater from the 1930s, with pilot light clearly visible through the aperture in the front cover. The large opening allowed for the manual lighting of the pilot light by a lit match or taper ...
(with its
ignition system An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engines, oil-fired and gas-fired boilers, rocket engines, etc. The widest application for spark i ...
) that burns all the time so that it is available to ignite relieved gases when needed. *The flare stack, including a flashback prevention section at the upper part of the stack. The schematic shows a pipe flare tip. The flare tip can have several configurations: * a simple pipe flare * a sonic tip – upstream pressure > 5
bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar * Chocolate bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a layer of cloud * Bar (u ...
* a multi nozzle tip, sonic or subsonic * a Coanda tip – a profiled tip using the Coanda effect to entrain air into the gas to improve combustion.


Flare stack height

The height of a flare stack, or the reach of a flare boom, is determined by the
thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
that is permissible or tolerable for equipment or personnel to be exposed to. 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: * 4.73 kW/m2 (1500 Btu/hr.ft²) would limit exposure to 3 to 4 minutes * 6.31 kW/m2 (2000 Btu/hr.ft²) would limit exposure to 30 seconds.


Ground flares

Ground flares are designed to hide the flame from sight and to reduce
thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...
and noise. They comprise a steel box or cylinder lined with
refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
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).


Crude oil production flares

When petroleum 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 (as in the adjacent photo). Preferably, associated gas is reinjected into the reservoir, which saves it for future use while maintaining higher well pressure and crude oil producibility. 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. 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 The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been de ...
. At market, this quantity of gas—at a nominal value of $5.62 per 1000 cubic feet—would be worth US$29.8 billion.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.
Also, the waste is a significant source of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(CO2) and other
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
.


Biogas flares

An important source of anthropogenic methane comes from the treatment and storage of
organic waste Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane or simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digesti ...
material including
waste water Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industrial ...
,
animal waste Manure is organic matter that is used as organic fertilizer in agriculture. Most manure consists of animal feces; other sources include compost and green manure. Manures contribute to the fertility of soil by adding organic matter and nu ...
and landfill. Gas flares are used in any process that results in the generation and collection of
biogas Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...
. As a result, gas flares are a standard component of an installation for controlling the production of biogas. They are installed on landfill sites, waste water treatment plant and
anaerobic digestion Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to Waste management, manage waste or to produce fuels. Mu ...
plant that use agriculturally or domestically produced
organic waste Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane or simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digesti ...
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 Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
quality biogas for vehicle fuel or for heating in buildings, drying
Refuse Derived Fuel Refuse-derived fuel (RDF) is a fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste. The World Business Council for Sustainable Development provides a definition: ''"Selected waste ...
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. 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 Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
temperature and are usually supplied to conform to a specific
residence time The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distributi ...
of 0.3s within the chimney to ensure complete destruction of the toxic elements contained within the biogas. 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.


Adverse health effects

Flares release a cocktail of chemicals known to be harmful to human health, including
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
,
particulates Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The t ...
, nitrogen oxides, heavy metals,
black carbon Chemically, black carbon (BC) is a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter). Black carbon consists of pure carbon in several linked forms. It is formed through the incomplete combustion of fossil fuel ...
, and
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
. Several of these pollutants correlate with
preterm birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 2 ...
and reduced newborn
birth weight Birth weight is the body weight of a baby at its birth. The average birth weight in babies of European descent is , with the normative range between . On average, babies of South Asian and Chinese descent weigh about . As far as low birth weigh ...
. Pregnant women living near flaring natural gas and oil wells experienced a 50% greater premature birth rate. Flares may emit
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
and other
volatile organic compounds Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure at room temperature. High vapor pressure correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a t ...
as well as sulfur dioxide and other sulfur compounds, which are known to exacerbate
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
and other
respiratory disease Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, bro ...
. A 2021 study found that a 1% increase in flared natural gas increases the hospitalization rate by 0.73%.


Environmental impacts

The natural gas that is not combusted by a flare is vented into the atmosphere as methane.
Methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
's estimated
global warming potential Global warming potential (GWP) is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (). GWP is 1 for . For other gases it depends on the gas and the time ...
is 28-36 times greater than that of CO2 over 100 years, and 84-87 times greater over 20 years. 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. However, flaring emissions contributed to 270 Mt (
megatonnes The tonne ( or ; symbol: t) is a unit of mass equal to 1000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
) of CO2 in 2017 and reducing flaring emissions is key to the
mitigation of global warming Climate change mitigation is action to limit climate change by reducing emissions of greenhouse gases or removing those gases from the atmosphere. The recent rise in global average temperature is mostly caused by emissions from fossil fuels bur ...
. An increasing number of governments and industries have pledged to eliminate flaring. Th
Global Methane Pledge
signed at
COP26 The 2021 United Nations Climate Change Conference, more commonly referred to as COP26, was the 26th United Nations Climate Change conference, held at the SEC Centre in Glasgow, Scotland, United Kingdom, from 31 October to 13 November 2021. The ...
, 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 Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
(
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
,
toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...
,
xylenes In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...
) and benzo(a)pyrene, which are known to be carcinogenic. A 2013 study found that gas flares contributed over 40% of the
black carbon Chemically, black carbon (BC) is a component of fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter). Black carbon consists of pure carbon in several linked forms. It is formed through the incomplete combustion of fossil fuel ...
deposited in the Arctic, thus further increasing the rates of snow and ice melt. 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 Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the vol ...
terminal in Saint John, New Brunswick, Canada on September 13, 2013. Similar incidents have occurred at flares on offshore oil and gas installations. Moths are known to be attracted to lights. A brochure published by the Secretariat of the
Convention on Biological Diversity The Convention on Biological Diversity (CBD), known informally as the Biodiversity Convention, is a multilateral treaty. The Convention has three main goals: the conservation of biological diversity (or biodiversity); the sustainable use of its ...
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 awk or sphinxmoths. 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".The Global Taxonomy Initiative - The Response to a Problem
(scroll down to the section entitled "Pollinating moths")
The
Bhopal disaster The Bhopal disaster, also referred to as the Bhopal gas tragedy, was a chemical accident on the night of 2–3 December 1984 at the Union Carbide India Limited (UCIL) pesticide plant in Bhopal, Madhya Pradesh, India. Considered the world's ...
exemplifies the consequences of a failure to flare escaping
methyl isocyanate Methyl isocyanate (MIC) is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane and methyl carbylamine. Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides (such as carbaryl, ...
gas. The gas was released from an over-pressured tank to a detached flare tower by a
safety valve A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds ...
, and flooded the surrounding area.


See also

*
Blowdown stack A blowdown stack is an elevated vent or vertical stack that is used to vent the pressure of components of a chemical, refinery or other plant if there is a process problem or emergency. A blowdown stack can be used to complement a flare stack or a ...
*
Flue-gas stack A flue-gas stack, also known as a smoke stack, chimney stack or simply as a stack, is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. Flue ...
*
Relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is re ...
* Gas venting *
Environmental issues in the Niger Delta Environmental issues in the Niger Delta are caused by its petroleum industry. The delta covers within wetlands of formed primarily by sediment deposition. Home to 20 million people and 40 different ethnic groups, this floodplain makes up 7.5% of ...
*
Waste Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor economic value. A waste prod ...


References


Further reading

*
Flare and Vent Disposal Systems on PetroWiki


Media

{{DEFAULTSORT:Gas Flare Fuels Oil refining Air pollution Air pollution control systems Volatile organic compound abatement Gas technologies