Air Ingress to Flare Stack with No Purge Flow

[mrcaptainplanet]

Hello all

I have a question dealing with what will occur if the purge gas to flare system (nitrogen) has a supply failure. The flare is equipped with velocity seal. I see from John Sink and API521 that this describes oxygen levels below the seal as they will rise almost immediately after purge stops when using velocity seal but how quick will the stack fill with air? Approximately. The reason I ask is currently for the flare when nitrogen supply is encountered a small flow of natural gas will be started at the flare base but this must be done by operator who travels to the flare and could take a while. Therefore worries arise about making an explosive mixture ourselves. Thank you.

 

[TD2K]

Why don't you install a line and valve to add the natural gas into the flare header in the main plant where the Operators can get to it quickly? The flare header is full of gas so as soon as you start a flow, you have flow through the header pretty quick.

I don't have a time for you and I'm not sure John Zink would provide a hard number but I would suspect it's less than 15 minutes and I wouldn't want to have to take credit for operator intervention.

 

[mrcaptainplanet]

Thank you for the reply. I think that if the time is so short my preference is to install a switch for low flow or pressure in that will automatically start the flow of natural gas. As you said better to not take credit for operator intervention.