Many methods to stop flashbacks have been devised. Broadly the Interruption Methods can classify the Flashback Arrestors into two types :
Types of Flash Back ArrestorÂ
“Active” methods require maintenance of certain parameters, such as liquid level or gas velocity.
“Passive” methods require only routine inspection and typically have no moving parts or instrument requirements.
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Venture type flashback Arrestors (active)
Venture flashback arrestors simply create a restriction in the hydrocarbon/air mixture delivery pipe so that the gas velocity is faster than the flame speed, preventing progression of a flashback upstream.
Flashbacks in the direction of flow can still happen. Even a partly closed valve can create a high velocity for flashback prevention, but a venture shape creates much lower pressure drop. If gas flow stops, the venture is no longer effective, so methods to measure flow and add makeup gas (nitrogen, for instance) are often included.
Online flame arrestors (passive)Â
(most commonly used) :
Mechanical flame arrestors are filled with metal or water or ceramic, which absorbs heat from a flashback, quenching it to a temperature below what is needed for ignition.
This stops the flame. With a low enough hydrocarbon/air mixture flow rate, if a flame travels to the face of the arrestor, it can become stable at that point.
Heating of the arrestor body and internals results. Once the arrestor temperatures increase enough, ignition temperature can be reached on the upstream side of the arrestor and the flashback can proceed.
For this reason, a temperature switch is often installed on the flame side of each arrestor (adding an “active” element).