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We use air to regenerate caustic in our LPG sweetening units. And we send the off gas to heater chamber to decompose hydrocarbon content and bad odor materials in it. We install frame arresters and skin temperature elements in the piping system of these off gas lines for safety consideration.
Fuel gas supply to heater burners, we use typical design (i.e. two blocks and one bleed design initiate by ESD of heater), we do not install flame arresters in these lines.
We found one plant outside our refinery, they installed flame arresters in fuel gas lines. Since the oxygen content in fuel gas is trace and well controlled and monitored, we do not think flame arrester is necessary. Please advise.
 
Answers
14/03/2012 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
The off gas from the LPG sweetening units is observed to be mainly the excess air (air with low oxygen levels) with a disagreeable odour with hydrocarbon traces and moisture. These typically are the ingredients that form a sticky film on the surface of the Flame arrestors very quickly and make the system out of service msot of the time. In one of the location we have just routed this gas to the comustion air duct (Forced Draft fan discharge). The gas will get diluted in the large volume of Combustion air, turns relatively harmless and gets incinerated in the radiation chamber of the furnace. Flame arrestors in the Fuel Gas supply to burners is mainly to prevent flame backing up to the Fuel Gas headers from the burner tips.
14/01/2012 A: G KAMALAKANNAN, Foster Wheeler India Ltd, siddhukamal@yahoo.co.in
Installing flame arrestor in fuel gas line is required if fuel gas is flowing into the radiant box directly through a pipe (without burners). This system is followed if the fuel gas is rich in oxygen and having very low battery limit pressure. Since the battery limit pressure is very low, installing burner in this line is not feasible. Also, the flow rate is very small and there are no temp controls by this off gas line. For normal fuel gas line going through burners does not require flame arrestor as per my experience. However, I request you to check API-560 (Fired heaters for general refinery service) and local regulations for deciding the requirement of flame arrestor in fuel gas line.