A flame arrester (also spelled arrestor), deflagration arrester, or flame trap is a device that stops fuel combustion by extinguishing the flame.
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Usage and applications
Flame arresters are used:
- to stop the spread of an open fire
- to limit the spread of an explosive event that has occurred
- to protect potentially explosive mixtures from igniting
- to confine fire within an enclosed, controlled, or regulated location
- to stop the propagation of a flame traveling at sub-sonic velocities
They are commonly used on:
- fuel storage tank vents
- fuel gas pipelines
- safety storage cabinets for paint, aerosol cans, and other flammable mixtures
- the exhaust system of internal combustion engines
- the air intake of marine inboard engines
- Davy lamps in coal mining
- overproof rum and other flammable liquors.
Principles
A flame arrester (also called a deflagration arrester) functions by absorbing the heat from a flame front traveling at sub-sonic velocities, thus dropping the burning gas/air mixture below its auto-ignition temperature: consequently, the flame cannot survive. The heat is absorbed through channels (passages) designed into an element. These channels are chosen and measured as the mesg (Maximum Experimental Safe Gap) of the gas for a particular installation. These passages can be regular, like crimped metal ribbon or wire mesh or a sheet metal plate with punched holes, or irregular, such as those in random packing.
The required size of the channels needed to stop the flame front can vary significantly, depending on the flammability of the fuel mixture. The large openings on a chain link fence are capable of slowing the spread of a small, slow-burning grass fire, but fast-burning grass fires will penetrate the fence unless the holes are very small. In a coal mine containing highly explosive coal dust or methane, the wire mesh of a Davy lamp must be very tightly spaced.
For flame arresters used as a safety device, the mesh must be protected from damage due to being dropped or struck by another object, and the mesh must be capable of rigidly retaining its shape during the propagation of a flame front. Any shifting of the individual wires that make up the mesh can create an opening large enough to allow the flame to penetrate and spread beyond the barrier.
On a fuel storage vent, flame arresters also serve a secondary purpose of allowing air pressure to equalize inside the tank when fuel is added or removed, while also preventing insects from flying or crawling into the vent piping and fouling the fuel in the tanks and pipes.
Safety
Flame arresters should be used only in the gas group and conditions they have been designed and tested for. Since the depth on an arrester is specified for certain conditions, changes in the temperature, pressure, or composition of the gases entering the arrester can cause the flame spatial velocity to increase, making the design of the arrester insufficient to stop the flame front ("propagation"). The deflagration may continue downstream of the arrester.
Flame arresters should be periodically inspected to make sure they are free of dirt, insects using it as a nest, or corrosion. The U.S. Chemical Safety and Hazard Investigation Board concluded that an uninspected and badly corroded flame arrester failed to prevent a 2006 explosion at a wastewater treatment plant in Daytona Beach, Florida.
Source of the article : Wikipedia
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