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40 Cfr Section 60.18 U.s. Epa - Flare Tip Exit Velocity And Flare Tip Diameter

The United States Environmental Protection Agency provides several guidlelines as well as codes for environmental protection.

A code of federal regulations (CFR) with the title CFR 40 Section 60.18 provides guidelines for determining the flare exit or tip velocities as a function of the calorific value of the flared gas.

The flare exit velocity is calculated based on two different equations for steam-assisted flares and air-assisted flares. The following are the equations:

Steam-Assisted Flares:

log10(vmax) = (Bv + 1212) / 850.8

vmax = maximum permissible velocity at the flare tip, ft/s
Bv = Heating value of the gas being flared, Btu / scf

Air-Assisted Flares

vmax = 28.56 + 0.087*Bv

where Vmax and Bv are defined as above

1. vmax not to exceed 60 ft/s for flare gas having heating value of 300 Btu/scf
2. vmax to be calculated based on above equations for flare gas having heating value between 300-1000 Btu/scf
3. vmax up to 400 ft/s is permitted for flare gas having heating value >1000 Btu/scf

The flare tip is designed considering a velocity of 80% of the max. permitted velocity i.e. 0.8*vmax

Based on the calculated maximum velocity vmax the flare tip daimeter can be easily calculated as follows:

Q = A*V


V = 0.8*Vmax, ft/s
Q = Volume flow rate of the total gas passing through the flare tip (sum of the main flare gas plus the purge gas), scfm
A = cross-sectional area of the tip, ft

Simplifying the above equation in terms of flare tip diameter we get the following equation:

Dtip = 1.95*(Q / Vmax)0.5


Dtip = diameter of the flare tip, inches
Q = flow rate, scfm
Vmax = maximum velocity as calculated above, ft/s

If you know the flare gas composition you can calculate the calorific value using any simulator or using the law of proportions calculate the calorific value of the gas for each component and multiply it with the individual mole fraction and add up the individual values to get the total calorific value.

The following links are given for further reading and guidance on "40 CFR Section 60.18"



Hope this proves useful to the esteeemed readers of this forum.

Comments are welcome.


Feb 15 2011 12:02 PM
Its Very good sir
Sep 04 2011 07:40 PM
why we should limit the velocity?

As you might have noticed that the velocity is a function of the calorific value of the gas being flared as per EPA. Higher the calorific value higher the velocity you can maintain. For low calorific values higher velocities will cause a flameout or which means the flame will get extinguished. High velocities can also cause flame detachment where the flame lifts off from the flare tip which ultimately leads to a flameout.

Some linkls for velocity limits are as follows:




Hello Sir, 

My name is AHMED and I'm a student in Chemical engineering but my advisors asked me to do research in gas flare area (especially gas flare tip), I need help in finding books title or papers title or websites or anything that provide information about flare tip ( types, design, flare tip diameter, purge gas velocity, wind effect, and effect of purge (flare gas) velocity on combustion efficiency) . I did some research on line but did not find any good information.

Please help me

thank you very much, 

email :Mama6002@yahoo.com 
Ahmed Jasim

Dear Ankur, thanks a lot for sharing such invaluable information, actually I have previously worked in oil production plants, there are two different scenarios regarding flaring associate gas 1- normal flaring excess gas comparing to capacity of adjuscent gas processing plant which was about 10 mmscfd 2- flaring of all associte gas when gas processing plant goes for anual overhaul. my question is which of the mentioned scenarios have to be cosidered as the basis of design?
thanks in advance for your precious help

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