Flame propagation decomposition flames

Fig. 1. Pressure required for propagation of decomposition flame through commercially pure acetylene free of solvent and water vapor in long horizontal pipes. Gas initially at room temperature ignition by thermal nonshock sources. Curve shows approximate least pressure for propagation (0), detonation,...

The pressure developed by decomposition of acetylene in a closed container depends not only on the initial pressure (or more precisely, density), but also on whether the flame propagates as a deflagration or a detonation, and on the length of the container. For acetylene at room temperature and pressure, the calculated explosion pressure ratio, / initial > deflagration and ca 20 for detonation (at the Chapman-Jouguet plane). At 800 kPa (7.93... 

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

Decomposition Flame Arresters Above certain minimum pipe diameters, temperatures, and pressures, some gases may propagate decomposition flames in the absence of oxidant. Special in-line arresters have been developed (Fig. 26-27). Both deflagration and detonation flames of acetylene have been arrested by hydrauhc valve arresters, packed beds (which can be additionally water-wetted), and arrays of parallel sintered metal elements. Information on hydraulic and packed-bed arresters can be found in the Compressed Gas Association Pamphlet G1.3, Acetylene Transmission for Chemical Synthesis. Special arresters have also been used for ethylene in 1000- to 1500-psi transmission lines and for ethylene oxide in process units. Since ethylene is not known to detonate in the absence of oxidant, these arresters were designed for in-line deflagration application. 

There is a need in many chemical processes for protection against propagation of nnwanted combnstion phenomena snch as deflagrations and detonations (inclnding decomposition flames) in process eqnipment, piping, and especially vent manifold systems (vapor collection systems). 

Acetylene may propagate decomposition flames in the absence of any oxidant above certain minimum conditions of pressure, temperature, and pipe diameter. Acetylene, unlike most other gases, can decompose in a detonative manner. Among the different types of flame arresters that have proven successful in stopping acetylene decomposition flames are hydraulic (liquid seal) flame arresters, packed beds, sintered metal, and metallic balls (metal shot). 

A most successful application of the approximate theory has been performed for the ozone decomposition flame, where the flame velocity has been estimated over the entire 02-03 composition range in which the flame is propagated (V2). A comparison of the calculated flame velocities and the experimental values is made in Fig. 4. 

A list of substances which have been used or considered to support decomposition flames is shown in Table I. Almost all of these substances have been studied at one time or another to provide fundamental information for the evaluation of the theory of flame propagation. As previously mentioned, the ozone decomposition has proved most useful as the basis of a flame which is amenable to both theoretical and experimental study. The NO decomposition flame provided a situation where a clear-cut prediction was made possible by flame theory (P2). On the basis of a flame calculation it was predicted that a strong preheat would permit the stabilization of this flame at a measurable flame velocity, since it was known that a flame would not propagate into the gas at room temperature. Subsequent experimental work confirmed the prediction by stabilizing a flame with approximately the predicted value. This places a great deal of... 

The liquid material in cylinders (which contains around 30% of propadiene) is not shock-sensitive, but a wall temperature of 95°C (even very localised) accompanied by pressures of about 3.5 bar, will cause a detonation to propagate from the hot spot [1], Induced decomposition of the endothermic hydrocarbon leads to flame propagation in absence of air above minimum pressures of 3.4 and 2.1 bar at 20 and 120°C, respectively [2]. Application as a monopropellant and possible hazards therefrom (including formation of explosive copper propynide) have been discussed [3]. Although the pure material is highly endothermic (A/// (g) +185.4 kJ/mol, 4.64 kJ/g), the commercial mixture with propadiene and propane (MAPP gas) is comparable with ethylene for handling requirements and potential hazard [4]. 

Fast flame propagation occurs on heating the powder moderately. See entry HIGH RATE DECOMPOSITION... 

CA 50, 12482 (1956) (Flame propagation in ozone) 29)Sax (1957), 161-61 (Destruction of expls) 30)F.C.Ikle, "The Social Impact of Bomb Destruction , Univ of Oklahoma Press, Norman, Okla (1958) 3l)Anon, Ordnance Service in the Field , US Army Field Manual FM 9-1 (1959) (Destruction of ammo) 32)Anon, Ordnance Ammunition Service , FM 9 5 (1959) (Destruction of ammo) 33)A.B.Amster, "Relationship Between Decomposition Kinetics and Sensitivity (U), Stanford Research Institute, Menlo Park, California,Repts (1962), Contract No Nonr 3760(00) (Conf, not used as a source of info) 34)P.W.M.Jacobs A.R.T.Kureishy, Kinetics of Thermal and Photochemical Decomposition of Some Alkali Metal Azides , Imperial College, London, England, Final Tech Rept (1964) Contract DA-91-591-EUC-2059 34a)Anon, Care, Handling, Preservation and Destruction of Ammunition , TM 9-1300-206 (1961) 35)-Anon, Investigations of the Mech-... 

There is no direct experimental evidence for this complex decomposition and it may well occur by several steps [107]. However, substantial yields of unsaturated carbonyl compounds are formed particularly at high pressures [78] under initial reaction conditions where cool flames propagate. For example, the cool-flame oxidation of 2-methylpentane at 525 °C and 19.7 atm in a rapid compression machine [78] yields no less than 14 unsaturated carbonyl compounds viz acrolein, methacrolein, but-l-en-3-one, pent-2-enal, pent-l-en-3-one, pent-l-en-4-one, trans-pent-2-en-4r one, 2-methylbut-l-en-3-one, 2-methylpent-l-en-3-one, 4-methylpent-l-en-3-one, 2-methylpent-l-en-4-one, 2-methylpent-2-en-4-one, 2-methyl-pent-2-enal and 4-methylpent-2-enal. Spectroscopic studies of the preflame reactions [78] have shown that the unsaturated ketones account for ca. 90 % of the absorption which, occurs at 2600 A. At lower initial temperatures and pressures acrolein and crotonaldehyde are formed from n-pentane [69, 70] and n-heptane [82], and acrolein is also formed from isobutane [68]. 

The velocity of the decomposition flame was first measured by Gerstein et al. [62] using upward flame propagation in a tube. The experimental value of 12.5 cm. sec , corrected to 1 atm and room temperature, was in reasonable agreement with values calculated from theories of flame propagation using the Arrhenius parameters obtained by Mueller and Walters [63] for the first-order pyrolysis of ethylene oxide at much lower temperatures. 

The decomposition of ozone has been of great interest to those concerned with combustion, because of the apparent simplicity of the reaction and the fact that there is only one product gas, oxygen. Lewis and von Elbe (13) developed a theory of flame propagation in ozone-oxygen mixtures on the basis of their burning velocity studies. They (13) derived high-temperature specific heat values for oxygen from their explosion data. 

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