Does anyone know...

[svv]

Hi,

I am looking at purge rates for flare systems.
I looked up API 521 for purge rates to flare and it suggested a purge rate (if there is a liquid seal before the flare). I could not find a value for purge rate if you did not have a liquid seal before the flare.
Does anyone know where I could obtain more information on purge rates to flare systems?

Another question is: what kind of gas can be used for purging purposes? Raw gas could be one because it is fairly combustible and cheap. Could you please state a site or other gases that can be used for purging purposes to the flare.

Thanks

svv

 

[rbcoulter]

If you do not have a seal then do you have any sort of
backflash protection?

 

[svv]

Hi rbcoulter,

There is a disentrainment drum and then an ESD valve before it gets to the ground flare.

 

[ChemLover]

Either a seal or a Gravel Box must be used, you can use N2 for purging provided you have good flare Pilot system .

 

[SooCS]

Pity, I thought the flareman would help you out on this. He must be taking vacation or something.

Natural gas purse is most common though some countries/company disallow it. N2 is the most common alternative but requires investment for N2 generator.

The purge rate depends on the diameter of the flare nozzle. Flare vendor is your best consultant. Try Kaldair. If not, I have a chart with me on the purge rate vs diameter of the flare. So if you tell me what is the diameter of you flare I can tell you the purge rate.

Alternative to purge gas, especially if your local authority disallow it, you can design your flare system against flash back explosion. The maximum internal pressure of an enclosed system at perfect stoichoimetric hydrocarbon gas and air mixture explosion is 7 bar. API RP 521 recommends the flare system to be designed for 3.5 bar.