Flare Radiation Shielding calc and hot spot temperature 1

[jocelynmak]

Does anyone know how to calculate the hot spot temperature of an object (for example a tank) if the flare radiation intensity is given? And, how does the object temperature decreases if a shield is being put to protect the object from flare radiation?

 

[JKEngineer]

If I understand your question correctly:
A heat transfer analysis including conduction through the bodies, convection to the surroundings, and radiation between the flare and the object and between the object and the surroundings would be necessary. If you know enough about the system, you might justify ignoring some of these. That allows calculation of the T for the case without the shielding. A similar calculation including the shielding would be needed. The shielding would impact the radiative transfer between the flare and the object and would also play a role in the other forms of transfer. I would be inclined to set this up in an FEA calculation, after, perhaps a simple hand calc.

Be glad to work through it for you if you would like me to.
Jack Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[Flareman]

As indicated by JKEngineer, thermal temperature calcs based on heat transfer and radiant imput are the usual manner in which this is done. I have some formulae in a paper which I would be glad to send you if you drop me an email to flareman_xs@netzero.net.

I have to caution that this calculation has to be very "iffy" because the radiant profile from the flare flame itself is almost a "wet finger" calculation and you have to make so many assumption about emissive surfaces and convective conditions in the temperature calcation that your final condition is only accurate (maybe) +/- 50 degrees (C or F .. doesn't matter). Then you realise that there are a lot of other conditions you haven't investigated which can give you other temperature ranges.

Any shield dramatically reduces the radiant load because the flame is radiating based on a mean temperature somewhere around 3000 degF whereas, behind the shield, you can only receive radiation based on the shield temperature which is much less.

The biggest real world temperature concern has to be exposure time. The thermal mass of much (metal) equipment slows down the temperature rise so that it can easily tolerate high radiant profiles over the short term but it will achieve a high equilibrium over the longer term (several hours), and that's when the problems arise. Plastics and electrical wiring suffer much more quickly because they don't have the ability for internal conductive transfer of heat away from the heated face.

With storage tanks you are probably most concerned that exposed metal edges which are not convectively cooled by the wind, can reach temperatures which are incedive for the vapors in the tank. I'm not convinced that anyone has successfully made this calculation and, in my experience, most people go with about 1500 btu/sq.ft_h as a limit because it probably can't generate temperature above (about) 300 degF even in the extreme case and it is also the "safe" personnel limit (that's a whole other story).

Good luck

David

 

[Flarenuf]

If you are still struggling take a look at FLARESIM from

http://www.softbits.co.uk,

I think this may help