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Final Temperature of Combustion Gases

  1. May 31, 2012 #1
    Hopefully one of you guys can help me out..

    I'm designing a burner that will run off powdered biofuel and I'm trying to calculate the resulting temperature after combustion. I have a higher heating value (HHV) of around 10,000 BTU/lb for the biofuel and for a complete stoichiometric combustion will need 6.2 pounds of air per pound of fuel.

    My thinking is, that burning one pound of fuel will release 10,000 BTU's of energy which will heat the air. Using a simple heat balance and assuming constant specific heat:

    10,000 (BTU)= 6.2 (pounds of air) * .24 (BTU/lb/F) * (T_final - 75F)

    And solving for T_final...

    T_final = 6645.43F

    This seems way too hot so I'm pretty sure I'm doing something wrong here. I'm just looking for a rough approximation of the final temperature which I feel should be around 2000F. I'm probably using the heating value wrong and I think the final temperature might have something to do with the adiabatic flame temperature but I'm not sure. Anyone have any thoughts or recommendations?

    Any help would be greatly appreciated!

    Thank you
     
  2. jcsd
  3. Jul 1, 2012 #2

    etudiant

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    Gold Member

    You are quite right, the 6600F estimate is way too high.
    You come close to that in an internal combustion process, where near stoichiometric conditions can be approximated, but a powdered biofuel burner will run with a huge excess of air with peak temperatures limited by the combustor linings.
    I would be surprised if you get much over 2000F, reflecting the air flow through your combustor.
     
  4. Jul 2, 2012 #3
    With a great deal of time, money, and effort the gas turbine industry has hit a limit of 3500-4000 degrees F. That requires the use of high temperature super alloys and propriety coatings. Since that is much higher than the melting point of the alloys, they also use very creative methods to cool them.

    A practical limit for your application would be as stated in the last post.
     
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