flame surface temperature 1

[Tigon]

does anyone have an idea on how to obtain/calculate the surface temperature of a flame, especially during gas flaring?

 

[davefitz]

laser anemometry

 

[AbbyNormal]

A lot of fuels have the theoretical flame temperatures published for stoichiomtetric combustion. Perhaps allow for the specific heat of the excess air, methane be 3600F or cooler

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[Lalbatros]

The actual flame temperature will depend on the boundary conditions.

The adiabatic flame temperature can be used if there is no losses which means that your flame does not heat up some heat sink.

If you are not in adiabatic conditions, then you need to evaluate the heat transfer. Usually, in such an analysis, you do not only get the flame temperature but also the boundary (wall) temperature. This wall temperature is obviously depending on the system considered: boiler, oven, kiln, ...

If you are able to evaluate the wall temperature independently (like a measurement), then you can calculate the heat losses from the flame from the usual radiation formula. The emissivity of the flame will be the main parameter and will depend on several aspect: is there a lot of dust in your flame, the amount of water and CO2, the geometry of the flame, the mixing of the gas and all profiles within the flame. This may get so complicated that a full combustion code maybe needed.

Fortunately it is sometimes made easier by some empirical knowledge. For example, by doing many simulation of a given kiln, I could conclude that the radiation losses were typically 25% of the heat value (taking into account the combustion air preheating). Therefore, it became easy for me to make a rough evaluation of the flame temperature of different fuel mixes and to use that for some optimisation.

So, this is a rather complicated question, but simple answers are possible sometimes.

Michel

 

[unclesyd]

Here is a calculator just based on the fuel and the oxidizer that might give you a place to start.

http://astronautics.usc.edu/utility/flame_temperature/

 

[MortenA]

The actual temperature of the flame from the flare is usually of little interest - however for flare tip design it may matter?

I think that you can get reference data for the temperature of various gasses in the litterature. Check for "worst case" amongst the gasses in you flare gas and of this does not cause severe problems dont go any further.

Best regards

Morten

 

[Flareman]

Tigon
I can't think why on earth you might need this data unless you're hoping to use it to calculate radiant output.

The truth is that the "surface" of the flame doesn't exist in flaring. It's a constantly changing mixture of pre-reaction gases, reacting mixture and post reaction flue gases. The closest you will come to getting a realistic temperature of the reaction zone (in my opinion) is to calculate the adiabatic flame temperature at the LEL, which is the condition which defines the outer limits of the flame because the reaction stops when it cools any further.

If you are hoping to use it for radiant output, you will need a pretty fancy model to determine how much "surface" you have altogether, and the shape of that surface.
You might want to check a paper through AIChE "A comprehensive model for flare flames and plumes" (Spring meeting 2006) and look at dispersion theory to define a possible flame shape.

For radiant values, most people in industry "wet finger" it as a proportion of the total heat in the flame (see standard API RP-521 models)
For large hydrocarbon flames, the radiant surface tends to vary in output anywhere between 20 and 200 kW/sq.m depending on the amount of transient carbon in the reaction zone and the amount of cold, unburned carbon beyond the reaction zone.

Good luck
I love to hear if you have success with a model.

David