3 replies to this topic

[KeJoSa2010]

Hello,

 

I was recently involved as the junior engineer on a project that required us to rate an existing low pressure flare header for size over various plant overpressure scenarios. Each storage tank is connected to the Low Pressure flare line through a PVSV that will "pop" if the maximum allowable pressure in the tank is met. It was clear from the beginning that in the case of a fire the "current" low pressure flare header does not have the capacity to relieve the storage tank vapours. The end result is that we made sure that the the EPRV and the thief hatch on each tank was sized correctly for the fire case but, we didn't size the LP flare header for the fire case. So in the case of a fire the tank vents to atmosphere.

 

I am just curious to see if this is standard practise? It seems obvious (but with my limited experience I could be wrong) that most LP Flare headers would not be able to handle tank vapour due to fire (unless they have a very large header). Anyway, I will appreciate any discussion I could have about this with anyone......I am just trying to increase my knowledge base.

 

Thanks!

Edited by KeJoSa2010, 08 August 2013 - 10:28 AM.

[proinwv]

Have you reviewed API 2000 ?

[KeJoSa2010]

Yes, I have reviewed API 2000....I haven't read it cover to cover though and, I don't recall seeing anything about the destination of venting (although I could be wrong).... I will review it further.

Edited by KeJoSa2010, 08 August 2013 - 12:50 PM.

[Robert Montoya]

Dear, I guess they are light products in the tank  (NH3, propane, etc.). In case external fire on a refrigerated tank (low pressure) the vapor  in the tank can be sent to the atmosphere if and only if the vented gas dispersion does not mean any additional risk during fire. But I can indicate that the most suitable in this case is to relieve to the Flare is safer because there is no risk of accumulation of gases around the tank in the event of any excess pressure which is the cause. Also I can see that not only during the fire event can ease into the atmosphere, the tank can alleviate even when multiple tanks while alleviating relief and the head is not large enough, ie when the head  this limited capacity.

My recommendation is not to relieve the atmosphere, send vapors in case of overpressure to flare