User:Milton Beychok/Sandbox

(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. 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).

Function

On oil production rigs, in refineries and chemical plants, 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.

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.

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.

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%).

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. 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.

See also

• Environmental issues in the Niger Delta (The Delta is the greatest gas flaring site on Earth.)
• Flue-gas stack
• Relief valve

External links

• Flare Gas Recovery - An option to stop flare gas being burned to atmosphere.
• Flare Stack sizing calculator
• Modelling industrial flares environmental impacts