Flames detonating

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. 

Chemical explosions are uniform or propagating explosions. An explosion in a vessel tends to be a uniform explosion, while an explosion in a long pipe is a propagating explosion. Explosions are deflagrations or detonations. In a deflagration, the burn is relatively slow, for hydrocarbon air mixtures the deflagration velocity is of the order of 1 m/s. In contrast, a detonation flame shock front is followed closely by a combustion wave that releases energy to sustain the shock wave. A... 

This book makes reference to flame arresters, deflagration flame arresters, and detonation flame arresters. Flame arresters is the generic term for both deflagration and detonation flame arresters. Deflagration flame arresters are nsed when a flame only propagates at snbsonic velocity, whereas detonation arresters are nsed when a flame can propagate at all velocities inclnding snpersonic velocities. 

It was not nndl the 1950s that detonation flame arresters made of crimped metal ribbon elements were developed and began to be used more freqnendy (Binks 1999). The major impetus for die use of crimped metal ribbon detonation flame arresters in the US was the enactment of clean air legislation (Clean Air Act of 1990) which inadvertently created a safety problem by requiring reductions in volatile organic compound (VOC) emissions. To do this, manifolded vent systems (vapor collection systems) were increasingly installed in many chemical process industry plants which captured VOC vapors and transported them to suitable recovery, recycle, or destruction systems. This emission control requirement has led to the introdnction of ignition risks, for example, from a flare or via spontaneous combustion of an activated carbon adsorber bed. Multiple... 

In Germany, deflagration and detonation flame arresters are tested and approved by the German Federal Physical-Technical Institnte (PTB) in Brannschweig and the German Federal Institnte for Material Research and Testing (BAM) in Berlin. However, once the new Enropean Committee for Standardization (CEN) standard is approved, it will supersede the PTB and BAM procedures. 

The International Maritime Organization (IMO) published a standard in 1984 for the design, testing and locating of deflagration and detonation flame arresters and high velocity vent valves for cargo tanks in tanker ships (IMO 1984). This was amended in 1988 and reissued as Revision I (IMO 1988). A new revised standard was issued in 1994 (IMO 1994). 

EMRC (Eactory Mutual Research Corporation) Class 6061. 1999. Examination Program, Detonation Flame Arresters. Eactory Mutual Research Corporation, Norwood, MA. 

This chapter presents an overview of the varions practices nsed in the chemical process indnstries to prevent and protect against deflagrations and detonations. It inclndes an introdnction to deflagration and detonation flame arresters and also other methods that can he nsed when flame arresters are not practical or are too expensive. 

In almost all cases, if a flame arrester is placed in-line rather than at (or close to) the open end of a vent pipe, a detonation flame arrester is needed. Detonation flame arresters mnst be able to stop both deflagrations and detonations. They require extensive testing and mandatory testing protocols may apply. 

An in-line detonation flame arrester must be used whenever there is a possibility of a detonation occurring. This is always a strong possibility in vent manifold (vapor collection) systems, where long pipe runs provide sufficient run-up distances for a deflagration-to-detonation transition to occur. Figure 3-3 shows the installation of in-line arresters of the detonation type in a vent manifold system. 

FIGURE 3-5. Protego detonation flame arrester with shock absorber. (Source Protego/ Braunschweiger Flammenfilter GmbH)... 

FIGURE 3-6. Westech detonation flame arrester with detonation momentum attenuator (D.M.A). (Source Westech Industrial, Ltd.)... 

FIGURE 3-7. Various types of detonation flame arresters. (Sources Protectoseal Company, NAO, Inc., and Westech Industrial, Ltd.)... 

Dry type deflagration and detonation flame arresters have an internal arrester element (sometimes called a matrix) that quenches the flame and cools the products of combustion. A great number of arrester elements have been developed and used. The most common types currently available are as follows ... 

Other types of deflagration and detonation flame arresters that do not contain an arrester element (matrix) have been used snccessfnlly in various applications where conventional dry type arresters were not suitable or were very expensive. Among these are ... 

Knittel, T. 1993. In Line (Detonation) Flame Arresters—Function, Certification, Selection and Application. Paper 10c. Paper presented at the 27th Annual AlCliE Loss Prevention Symposium, March 30-April 1, 1993, Houston, TX. 

FIGURE 4-3. Differences between deflagration and detonation flame fronts. 

Overdriven detonation is the condition that exists during a DDT before a state of stable detonation is reached. Transition occurs over the length of a few pipe diameters and propagation velocities np to 2000 m/s have been measnred for hydrocarbons in air. This is greater than the speed of sonnd as measnred at the flame front. Overdriven detonations are typically accompanied by side-on pressnre ratios (at the pipe wall) in the range of 50-100. A severe test for detonation flame arresters is to adjust the mn-np distance so that DDT occurs at the arrester, subjecting it to the overdriven detonation impulse. 

Lapp, K. and Werneburg, H. 1999. Detonation Flame Arrester Qualifying Application parameters for explosion Protection m Vapour Handling Systems./. Can. Petrol. TechuoL, Special Edition 1949-1999, Paper 94-58. 

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