Percent O2 in N2 mix permited into flare line

[jsummerfield]

Startup operators use nitrogen to inert vessels and piping during the initial startup operations. Some amount of air would normally remain in the equipment during this process. We have a number in mind and plan to use a number smaller than that. However, we need an authoritative and independent third party document such as an API standard to certify the startup procedures.

What accepted standard documents the oxygen level permitted in the nitrogen where the mix could or would be released into a flare line with a fuel-gas sweep?

Thanks for your input.

John Summerfield, PE
Control Systems

 

[Flareman]

I've worked around flares for a lot of years and I'm not aware of any specific standard for the operations you describe. Each plant or corporate entity seem to have their own in-house standards. Common sense is the rule of the day. I don't have the code to hand right now but I recall that NFPA 86 suggests that the oxygen level should be greater than 25% of the LEL or less than (UEL - 3%) to stay "safe"
I have a curve of my own in a paper on Flare safety, which I'd be happy to send you if you drop me an email at flareman_xs@netzero.net.


David

 

[Rocco8]

Stay below the Minimum oxygen of Combustion (MOC) and there is no issue.

I believe flareman meant to says fuel level should be less than 25% of the LEL.

Using the two criteria above will keep you safe

The firm below prepares custom full range composite flammability diagrams to help you pinpoint where you should be operating.

http://www.rccostello.com/explode.html

 

[Flareman]

I posted a page which will estimate the flammable envelope for you, together with the effect of a diluent, based on published data for the flammable gas.

http://www.geocities.com/flareman_xs/Gases/Flammability_calc.html

I just posted it today so there has been no feed-back yet. If it needs 'tweaking' let me know.

David