Hydraulic Liquid Seal Flame Arrester

Wliile all the flame arrester types disenssed above have a solid arresting element (matrix), the hydranlic (liqnid seal) flame arrester contains a liqnid, nsnally water, to provide a flame barrier. It operates by breaking np the gas flow into discrete bnbbles by means of an internal device to qnench the flame. A mechanical nonretnrn valve (check valve) is sometimes incorporated to prevent the displacement of liqnid dnring or after a flame event (deflagration or detonation). 

This arrester is nsnally designed to be effective in one direction only. However, hydranlic arresters exist that are reported to be effective in preventing flame propagation in both directions. Tests to establish this on a particnlar hydranlic arrester design are described by Flessner and Bjorklnnd (1981). 

API RP 521 (1997) disensses the design of hydranlic flame arresters (liqnid seal dmms) for flares. Fignre 5-5 shows a typical flare stack seal dmm. There are some nncertainties abont the effectiveness of the API 

Note The sewer scaJ should be designed for a minimum of 175 percent of the drum s maximum operating pressure. 

FIGURE 5-5. Sketch of a typical API flare stack seal drum. (Source API representative 521, Appendix D. Reprinted courtesy of the American Petroleum Institute.) 

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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. 

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... 

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). 

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. 

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

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. 

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

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