Flashback explosion

Internal flashback explosion, i.e., 1055 kPa design pressure at normal... 

Combustion. The burning of soHd, Hquid, and gaseous fuels as a source of energy is very common. Using sufficient and reHable combustion controls, this process seldom causes serious problems. However, some combustion processes are deHberately carried out with an inadequate oxygen supply in order to obtain products of incomplete combustion. Explosive mixtures sometimes occur, and then flashback is a serious problem. 

Deflagration Arrester Testing For end-of-line and tank vent flame arresters, approval agencies may require manufacturers to provide users with data for flow capacity at operating pressures, proof of success during an endurance burn or continuous flame test, evidence of flashback test results (for end-of-hne arresters) or explosion test results (for in-line or tank vent arrester applications), hydrauhc pressure test results, and results of a corrosion test. 

Alternatives to Arresters Alternatives to the use of flame arresters include fast-ac ting isolation valves, vapor suppression systems, velocity-type devices in which gas velocity is designed to exceed flashback velocity, and control of the flammable mixture (NFPA 69 standard, Explosion Prevention Systems ). The latter alternative frequently involves reduction of oxygen concentration to less than the limiting oxygen concentration (LOC) of the gas stream. 

Flare systems are subject to potential flashback and internal explosion since flammable vapor/air mixtures may be formed in the stack or inlet piping by the entry of air, and the pilot constitutes a continuous ignition source. Flares are therefore always provided with flashback protection, which prevents a flame front from travelling back to the upstream piping and equipment. Design details are described later. 

The deflagration flame arrester must he subjected to a series of at least 10 explosion (deflagration) tests in a rig with a pipe at least 5 feet (1.5 meters) long with various mixtures of propane in air and different test conditions to test the entire spectrum of possible deflagrations. Also, a series of 3 flashback tests, using a mixture of 4.2 volume percent of propane in air, must be conducted. 

If the release forms a vapor cloud that premixes with air before ignition occurs, and turbulence is developed (for example, by the flame front propagating through a process structure), the flame speed can accelerate sufficiently to cause a blast. This event is referred to as a vapor cloud explosion. In addition to blast effects, radiant heat and flame contact effects may also occur. Flashback to the source may cause a pool and/or jet fire. 

Air seals (also called purge reduction or gas seals) are often recommended to prevent air from entering the stack, which could possibly cause flashbacks and explosions. More information about air seals can be found in API RP 521 (2007) and the AIChE-CCPS book Guidelines for Pressure Relief and Effluent Handling Systems. 

Liquid seal drums Emergency vent streams are usually passed through a liquid seal, commonly water, before going to the flare stack. The liquid seal drum is usually located downstream of the knockout drum, and some vendors designs include them in the base of the flare stack. A liquid seal drum is used to maintain a positive pressure in the vent header system and upstream system. It also reduces the possibility of flame flashbacks, caused when air is inadvertently introduced into the flare system and the flame front pulls down into the stack it also acts as a mechanical damper on any explosive shock wave in the flare stack. Figure 23-58 is a schematic of a typical flare stack liquid seal drum, designed per API RP 521 criteria. 

When YBa2Cus07 x is heated to 1000°C in a flowing atmosphere containing H2, [CAUTION The H2 should be diluted with 10 volumes of Ar to reduce the hazard of an explosion. A 10-turn 5-cm-diameter coil of glass tubing should be inserted next to the H2 tank to prevent flashback of the tank. The thermal analyzer must be purged completely so there are no dead volumes of air and the exit gas must be exhausted carefully.] reduction to BaO, Y2Os and Cu occurs (10)(25)... 

Fuze, Spitback or Fuze, Flashback. A fuze located in the forward part of a shaped charge munition. When initiated by impact it produces a detonation which is directed toward the element located in the base of munition and this, in turn, detonates the main explosive charge. The combination of point impact fuze and base element is referred to as point initiating base detonating" (PIBD) fuzing system... 

Flashback (or Spitback) Tube. A tube attached to the truncated apex of a shaped charge liner, ordinarily extending thru the the explosive charge. Thru this tube the detonating impulse is transmitted from the point of initiation to a detonator at the base of the explosive charge Ref Glossary of Ordn(1959), 270-R(Spit-back Tube)... 

The flow of fuel and oxidant mixture through a premix burner orifice must be kept above a minimum rate, depending on the fuel, to avoid flashback. Flashback occurs when the mixture inside the burner barrel ignites with an explosion, which extinguishes the flame. 

Laminar flow burners of the type shown in Figure 28-11 provide a relatively quiet flame and a long path length. These properties tend to enhance sensitivity for atomic absorption and reproducibility. The mixing chamber in this type of burner contains a potentially explosive mixture, which can be ignited by flashback if the flow rates are not sufficient. Note that the burner in Figure 28-11 is equipped with pressure relief vents for this reason. 

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