Flare Gas Purge Rate Impacted by new Sub Header Addition

[ChemEngSquirrel]

I'm adding a new 10" flare sub header with multiple smaller sub headers. The new header will connect to the existing 14" flare header. Otherwise, the 14" flare header, downstream flare drum and 14" flare stack are unchanged.

Will the addition of a 10" flare header alter the required flare gas purge rate in any way?

Thanks.

 

[TD2K]

I wouldn't think so. Flare header purges are usually to achieve a few objectives:

1. Ensure air/oxygen doesn't build up to dangerous levels
2. Provide sufficient flow up the flare stack to keep air infiltration down the stack at safe limits, this is typically provided by the flare tip vendor and is dependent on the type and size of flare stack and the flare header purge gas density.
3. Prevent backflow into the flare system due to the cooling of hot gases.

Which ones apply? Typically if I'm installing a new lateral I'm usually concerned about preventing air/oxygen from building up in that header. The purge rates are quite low, 0.1 ft/sec or so is more than sufficient to have a significant number of volume changeovers each hour.