Flare detonation

[mflr]

Have anyone expirience detonation in your flares?

I have been researching about detonation problems but all the information I found mention air entering into the system as a cause of the problem, however the gas that we are flaring is 95% methane so we need a more or less a 95% air vs 5% gas in order to have a posible explosive mixture.

Could be posible that something like a buble of air travel through the pipe? maybe created after a maintenance of a valve?

Now, because of the fear of detonation, we are using aproximatly 15 times of the purge gas we suppose to use.

 

[Guidoo]

You wrote:

"the gas that we are flaring is 95% methane so we need a more or less a 95% air vs 5% gas in order to have a posible explosive mixture."

Since the Upper Flammable Limit of methane in air at standard conditions is 16.5 vol% this is not correct. You probably used the Lower Flammable Limit of 4.4%!

Now, to be on the safe side you should prevent ever coming near this value of 16.5%. Again, to be on the safe side, you should have a purge rate that prevents air ingress.

Whether you are currently using too much purge gas we can not assess since you didn't mention sufficient details (e.g. tip diameter, molecular weight of gas, flowrates).

 

[mflr]

Guidoo,

I take the worse case as you mention. The brand of our flare is Callidus, following their indications the amoun of gas that we need for purge is 75SCFH, at this moment we are using 1000SCFH what is more than 10 times the requirement. How could be posible to have a detonation with that quantity of gas?

 

[sshep]

Some of our flare systems have O2 measurement on the header near the knock-out drum. Since we have a negative pressure systems in all our flares, there is always the concern that air could leak in somehow. This has happened during maintenance on rare occassion (including being the contributing cause of a fatality 20+ years ago during a plant shutdown). Current practices regarding breaking into flare lines are very stringent, but mistakes are always possible.

Oxygen monitoring is by no means a practice being used in all of our plants, but may give you another option to consider. Just a thought, sshep