Flare

[jakom]

Hello,

I have a simple question about flare. What could cause a flame out (in a steam smokeless refinery flare)?

I know that if steam to gas ratio is more than required (more steam or less gas) it would cause the flame out. But is there any other possible reason?

 

[25362]

Flame lift-offs can result from combinations of higher gas velocity, flare tip deterioration and lower-than-design gas heating value. Too much steam may cool (quench) flames, and cause instability. Instability can create low-frequency noise which can travel over several kilometers.

High velocities (say, 1000 fps) of low gas heating value (~300 Btu/ft³) can extinguish a flame. Flare tip diameters for normal operation (not emergency flaring) are designed on basis of the maximum allowable (regulated) velocities and the total actual volumetric flow.

I pressume the following site may provide more information:

http://www.johnzink.com/products/flares/html/flar.htm

 

[tkdhwjd]

In addition to what 25362 explained, a loss of pilot flame can also lead to flame out.

 

[jakom]

Thank you guys. It seems to be a control problem. However, also all of our pilot lines are plugged. We tried to purge it with Nitrogen, but no luck. Is any of you aware of anyway to unplug those lines?!

 

[jsummerfield]

Lots of things can happen. Perhaps a slug of liquid that begins up the flare then gravity flows back to the drum could extinguish the flare. Check the historical data saved for the flow meter and pressure meter on the line from the drum to the flare.

John

 

[25362]

According to EPA a flare handling gases with heat content greater than 1,000 Btu/std. ft³ can have a stable flame as long as the exit velocity of the flare gas is below 400 ft/s. Read Design and Operate Flares Safely[/b by Ajay Kumar in the Environmental Manager section of ChE, December 1998.

 

[peteship]

For refinery flares, according to API RP 521, the exit velocity for a stable flame may be as high as Mach 0.5 for intermittent service. Flares for hydrocarbon gases have been tested with a velocity as high as Mach 0.8.

 

[GasProcess]

If the flare tip is having molecular sieve and the liquid accumulated is not drained regularly then the low quantiyt of flare gas may extinguish the flare