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A gas flare, alternatively known as a flare stack, is a gas combustion device 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.〔(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.)〕〔 (See Chapter 11, ''Flare Stack Plume Rise'').〕〔("A Proposed Comprehensive Model for Elevated Flare Flames and Plumes" ), David Shore, Flaregas Corporation, AIChE 40th Loss Prevention Symposium, April 2006.〕 During plant or partial plant startups and shutdowns, flare stacks are also often used for the planned combustion of gases over relatively short periods. 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. 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 (as in the adjacent photo) 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.〔Leffler, William (2008). Petroleum Refining in Nontechnical Language. Tulsa, OK: PennWell. p. 9.〕 == Overall flare system in industrial plants == When industrial plant equipment items are over-pressured, the pressure relief valve 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 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).〔 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, 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 top of the flare stack. *An 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 when needed.〔(Product Overview Ignition Systems ), Smitsvonk, November 2001. Eexcellent source of information about flare stack pilot flames and their ignition systems.〕 *The flare stack, including a flashback prevention section at the upper part of the stack. There is also a safe method to divert the flare gas which is insertion of Liquid U seal with Liquid Hold up vessel. The Liquid U seal is designed to take pressure up to permitted back pressure of the system. This helps to divert the flare gas to recovery system. In case of plant upset, pressure rises and liquid in the U seal will move into Liquid Hold up vessel. On normalization, the Liquid U seal will start diverting the gas again.〔(KP Engineers & Contractors )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gas flare」の詳細全文を読む スポンサード リンク
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