Flare Capacity Calculation
Flare Capacity Calculation
(OP)
Any thoughts on how to calculate the capacity of a flare? I know how much natural gas I can feed and the dimensions of the flare and piping, as well as the waste gas composition. I would like to know the max capacity of the flare. Thanks!





RE: Flare Capacity Calculation
Then there is the question of radiation on surrounding equipment, property lines, operating areas that needs to be checked out.
Capcity of the flare drum should also be checked, that method is summarized in API 520/521.
If it's a sonic type type, I suggest getting the vendor involved.
RE: Flare Capacity Calculation
RE: Flare Capacity Calculation
Also - should not we include the ability to disperse the gas to a safe ground level concentration if the flare is extinguished?
The more you learn, the less you are certain of.
RE: Flare Capacity Calculation
I've seen several company specifications which limit flare head velocities to 50% of mach. When I've done any calculations, the 50% mach limit at the header outlet quickly results in back pressure building up upstream of this point which in turns reduces the velocity and even more quickly, reduces the pressure drop upstream of that point. The effect is that only the end of the flare header (or ends if you have increasing diameter flare header) will see the 'high' velocities.
I have not routinely seen vapor dispersion calculations done on a flare to prevent ground level gas concentrations from exceeding the LEL or some portion of the LEL. I've done radiation calculations for 'cold' vents which were designed only to disperse the gas into the atmosphere but not the other way around and the only gas dispersion calculation I was involved with was on a ground level open vent to atmosphere. Other experience out there?
RE: Flare Capacity Calculation
The more you learn, the less you are certain of.
RE: Flare Capacity Calculation
Nevertheless API RP521 4th raise that issue in paragraph 4.4.3.5.
As exposed there, if flared gases are toxic, pilot monitoring is critical to ensure flare is always ignited.
Hope this helps
RE: Flare Capacity Calculation
Rough rules of thumb are,
- if the gas is a rich flammable, (natural gas or better) then 20% sonic is probably just fine; 50% sonic needs good pilots and flame stabilizers, and anything over than (yes there a lot of sonic discharge flares) needs a special design,
- if the gas is leaner than natural gas, go to the rules of 40CFR60.18 http://www.gpo.gov/su_docs/aces/aces140.html
They're a reasonable guide (albeit very poorly crafted and badly misapplied .. in my opinion)
Look at API RP-521 for other guidelines and I'll send you a paper of my own if you drop me an email at flareman_xs@netzero.net
David