Purge Gas Line

Fuel gas for purging is preferably introduced into the main flare header upstream. Requirements are readily estimated. One or more 3/4-inch fuel gas lines may be required, particularly for start-up purging. 

In start-up it is desirable to purge the headers with fuel gas to remove the air prior to igniting the pilots at the flare tip. The purge time should be at least V/cfh hrs, where V is the total volume of headers (cubic feet), including knockout drum and flare stack, and cfh is the flow rate of fuel gas (cubic feet per hour). 

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A Check Valve (CV501) must be installed in the purge gas line immediately upstream of the fire wall per NFPA 86 (sect. 4-4.3.8). The purpose of the check valve is to prevent backflow of any gases into the purge gas pipeline. 

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