Hydraulic flame arrester

FIGURE 5-7. John Zink Bubble Screen hydraulic flame arrester. (Source John Zink Company.)... 

NAO has successfully tested hydraulic flame arrester designs for detonations of hydrogen and oxygen (Mendoza 1999). The NAO hydraulic arresters also have an internal detonation inhibitor (shock absorber) upstream of the gas exit nozzle. See the article by Overhoff et al. (1989) for discussion of shock effects in hydraulic flame arresters. 

Some designs of hydraulic (liquid seal) flame arresters have been sric-cesshilly tested for hydrogen service. NAO has designed and snccessfully tested and provided a hydraulic flame arrester for hydrogen-air applications (Straitz 1999). This design is for detonations and has dual liquid seal chambers with shockwave breakers. Rao (1980) also provides information... 

Schwartz (2000) reports the successful use of the John Zink bubble-screen hydraulic flame arrester in acetylene service. 

A vacuum pump seal drum design which provides a liquid seal (hydraulic flame arrester) to mitigate flame propagation backward into the vacuum system. The seal liquid is an organic stream (mostly Cg aromatics) that comes from the vacuum pump discharge drum overflow. 

Tests are needed to verify the design criteria of nonstandard flame arresters (hydraulic flame arresters, packed bed arresters, etc.). 

Hydraulic Flame Arrester A flame arrester consisting of a vessel filled with a seal flnid (often water) and a distribntor which breaks np the incoming gas into discrete bnbbles, thns facilitating qnenching of the flame and preventing flame transmission. 

Liquid Seal A device for preventing the passage of flame by passing the gas mixture through a suitable liquid. See Hydraulic Flame Arrester. 

Hydraulic (Liquid Seal) Flame Arresters Hydraulic (liquid seal) flame arresters are most commonly used in large-pipe-diameter systems where fixed-element flame arresters are either cost-prohibitive or otherwise impractical (e.g., very corrosive gas or where the gas contains solid particles that would quickly plug a conventional arrester element). These arresters contain a liquid, usually water-based, to provide a flame barrier. Figure 23-62 shows one design. Realistic tests are needed to ensure performance, as described in EN 12874 [15]. Note that hydraulic flame arresters may fail at high flow rates, producing a sufficiently high concentration of gas bubbles to allow transmission of flame. This is distinct from the more obvious failure mode caused by failure to maintain adequate liquid level. 

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. 

FIGURE 5-6. Linde hydraulic valve flame arrester. (Source CCPS 1993.)... 

It should be pointed out that the hydraulic diameter method does not work well for laminar flow because the shape affects the flow resistance in a way that cannot be expressed as a function of the ratio of cross-sectional area to wetted perimeter (Green and Maloney 1997). However, some flame arrester manufacturers use this method for noncircnlar flame arrester passages. 

Table 5-2 shows the equations for calculating the hydraulic diameter for various flame arrester passageways. 

Equations for Calculation of Hydraulic Diameter for Various Flame Arresters... 

Deflagration and detonation flame arresters should be inspected annually until operating experience indicates otherwise. Also, the need for frequent inspection and maintenance may affect the selection of one type of flame arrester over another type for a specific application. For example, a hydraulic (liquid seal) flame arrester may be more suitable than a dry, fixed-element, flame arrester if the latter requires frequent inspecdon and maintenance because of persistent plugging problems. 

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). 

Sutherland and Wegert (1972) describe the successful use of the Linde hydraulic valve arrester in stopping an acetylene decomposition detonation. As previously noted, these flame arresters are no longer being made by Linde (now Praxair Inc,), but are still available from ESAB Welding Sc Cutting Products of Florence, SC. 

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

FIG. 23-62 Tested and approved hydraulic (liquid seal) flame arrester. (Courtesy of PROTEGO .)... 

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