Quantity of steam for smokeless flaring on elevated flare 1

[Saver2008]

Hi!!!

I´m searching info about the required QUANTITY OF STEAM in smokeless flaring. According to API, it is just one formula that is related the flaring flow (wished % for smokeless intentions), molecular weight but actual researches indicates that we must take other topics but I really do not know. Can you help me with that please?

Thks!!

 

[Flareman]

Saver 2008
The steam needed for smokeless performance will actually vary widely based on many factors.
Smoke forms in the flare flame because the gas in the center of the flow stream gets hot and "cracks" before it meets up with oxygen to convert. The smoke forms initially as atomic carbon but very quickly agglommerates into solid forms which are red hot and give the flame its color and most of the radiant property. If these solids do not fully decay as they run into the oxygen rich zone, they will cool down and leave the flame as visible carbon.
Gases which are intrisically unstable like acetylenes and olefins "crack" very quickly and dump a lot of free carbon. More stable gases like methane, not so much. Side chain isomers are worse than straight chain. The relative heat of formation is a good predictor of smoking potential of the gas. (high, positive = bad; low, negative = good)
A large flame or a large diameter is more prone to make smoke because the dwell time for the free carbon is longer than with small diameters and flames.
The technique of steam addition is basically to cool down the core of the flame and retard the carbon release.
Then you have different methods of steam introduction. Some flare designs use the steam to mix air efficiently into the flame zone thus reducing the time before the carbon meets up with oxygen.
You need to speak to the Flare tip vendor to ask how efficient his tip will be (then allow for the salesman's pitch when you make your own estimate).
Simply as an example, most commercial tips run around 0.5 wt/wt for mid range refinery grade hydrocarbon mixtures up to 1 wt/wt for Butadiene or Benzene rich mixtures. Efficient tips may be a little lower, inefficient tips a little higher.
In practice operators never run flares at these values, which represent a highly visible clean flame. Operators invariably oversteam like crazy to reduce luminosity as well as smoke and may run at 3 - 4 times the actual need, even running the risk of flame extinction.

David