Flashback Arresters

When a catalytic recombiner is included in a system, flashback arresters are required on either side of the recombiner. Some flashback arresters can be reset and used again after a flashback occurrence. Other types must be replaced after a flashback occurrence. We used an arrester that could not be reset, but was inexpensive compared to the types that can be reset. These are widely available through welding shop suppliers. 

This particular arrester has a brass body, as most do, which is not appropriate for long term use in a system with a KOH electrolyte. Stainless steel arresters are preferred, but are more expensive than the brass. Since our system is experimental and is frequently assembled and disassembled, any corrosion problems can be monitored, so we opted for brass. 

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For the simple system without recombiner, flashback arresters and filter, simply connect the coalescer to the tank. 

Catalytic recombiners also require a filter, located after the second flashback arrester, to collect the water formed by the catalyst. 

A system for inspecting workplace precautions is essential in any proactive monitoring programme. On many occasions it can form part of an organisation s arrangements for the planned preventive maintenance of plant (e.g. electrical maintenance and testing) and equipment (e.g. flashback arresters for oxy/fuel systems) which are also covered by legal requirements. 

Maintenance of equipment under the fire prevention plan. Certain equipment is often installed in workplaces to control heat sonrces or to detect fuel leaks. An example is a temperature limit switch often found on deep-fat food fryers found in restaurants. There may be similar switches for high-temperature diptanks, or flame failure and flashback arrester devices on furnaces and similar heat-producing equipment. If these devices are not properly maintained or if they become inoperative, a definite fire hazard exists. Again, employees and supervisors should be aware of the specific type of control devices on equipment involved with combustible materials in the workplace and should make sure, through periodic inspection or... 

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. 

Flashback tests incorporate a flame arrester on top of a tank, with a large plastic bag surrounding the flame arrester. A specific gas mixture (for example, propane, ethylene, or hydrogen at the most sensitive composition in air) flows through and fills the tank and the bag. Deflagration flames initiated in the bag (three at different bag locations) must not pass through the flame arrester into the tank. On the unpro-tec ted side, piping and attachments such as valves are included as intended for installation a series of tests—perhaps ten—is conducted. 

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. 

Howard, W. B. 1982. Flame Arresters and Flashback Preventers. Plant/Operations Progress, 1(4), 203-208 2(1), 71-72 (January 1983). 

The single 30-mesh stainless steel flame arrester was effective in arresting flashback flames from all eight fuel-air mixtures tested. 

The dual 20-mesh stainless steel arrester was effective in arresting flashback from all eight fnel-air mixtures tested except in some ethylene-air tests. It failed in three out of three tests where the flame speed was 4.86 m/s (15.94 ft/s) or greater. 

A proprietary sintered metal arrester was made by the Linde Division of Union Carbide Corporation (now Praxair) for rise in processes handling acetylene, but is no longer made by Praxair (Dickerman 1999). A sintered metal flashback flame arrester for rise on an acetylene cylinder is made by Western Enterprises of Westlake, OH. Figure 5-4c shows a sintered metal flame-arresting element. 

Bjorklund, R. A., Kushida, R. O., and Flessner, M. F. 1982. Experimental Evaluation of Flashback Flame Arresters. Plant/Operations Progress, 1(4), 254-262. 

Appendix B to Part 154 is a standard specification for tank vent (end-of-line) deflagration flame arresters. It does contain test procedures for these types of flame arresters. An end-of-line flame arrester mnst be able to arrest three atmospheric deflagrations as well as to withstand two honrs of continnons bnrning withont flashback. 

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. 

Flashback Undesired flame propagation opposite to the direction of flow. It is also used to describe failure of a flame arrester element. 

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