MAE 5310: COMBUSTION FUNDAMENTALS

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MAE 5310 COMBUSTION FUNDAMENTALS

• Lecture 7 Adiabatic Combustion Equilibrium
  Examples
• September 8, 2009
• Mechanical and Aerospace Engineering Department
• Florida Institute of Technology
• D. R. Kirk

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ADIABATIC COMBUSTION EQUILIBRIUM

• Previously we have considered
• Known Stoichiometry 1st Law (Energy Balance) ?
  Adiabatic Flame Temperature
• Problems 1-4
• Known P and T 2nd Law (Equilibrium Relations) ?
  Stoichiometry
• Problems 5-9
• Now we can combine these
• 1st Law (Energy Balance) 2nd Law (Equilibrium
  Relations) ? Adiabatic Flame Temperature
  Stoichiometry
• Problems 10-14
• Solution Scheme
• Guess a TTguess
• Do equilibrium calculation to solve for species
  concentrations at Tguess
• Plug into 1st Law
• We want F(Tguess)0
• If F(Tguess) gt 0, then initial guess was too high
• If F(Tguess) lt 0, then initial guess was too low
• Increment Tguess

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PRACTICAL APPLICATION RECUPERATION

• A recuperator is a heat exchanger in which energy
  from a steady flow of hot combustion products,
  called flue gases, is transferred to the air
  supplied to the combustion process

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SOME COMMON TYPES OF RECUPERATORShttp//www.hardt
ech.es/hgg_tt_hrt.0.html
Tubes cage radiation recuperator
Tubes cage radiation recuperator working at
1,200ºC
Double shell radiation recuperator
Installation consisting of a tubes cage
recuperator and a double shell one, series-connect
ed
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EXAMPLE RECUPERATION (TURNS)

• A recuperator, as shown in figure, is employed
  in a natural-gas-fired heating-treating furnace.
  The furnace operates at atmospheric pressure with
  an equivalence ratio of 0.9. The fuel gas enters
  the burner at 298 K, while the air is pre-heated.
• Determine the effect of air preheat on the
  adiabatic flame temperature of the flame zone for
  a range of inlet air temperatures from 298 K to
  1,000 K.
• What fuel savings result from preheating the air
  from 298 K to 600 K? Assume that temperature of
  flue gases at furnace exit, prior to entering
  recuperator, is 1700 K, both with and without
  preheat.

Radiant-tube burner with coupled Recuperator for
indirect firing. Note that All flue gases pass
through the recuperator Source Turns, An
Introduction to Combustion
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STANJAN PRACTICE PROBLEM

• Consider combustion of a methane-air mixture at
  10 atm (both fuel and air are at 10 atm).
• Plot mole fractions, ci, for the species CO2, CO,
  H2O, H2, OH, O2, N2, NO vs. temperature for f1
  for a temperature range from 1000 to 2500 K.
• Calculate Tflame and mole fractions as a function
  of f for adiabatic combustion. Plot these results
  vs. f and discuss at what value the peak flame
  temperature occurs. Comment on this value in
  light of the discussion found in Chapter 1, Part
  2 of Glassman.
• Compare Tflame from part (2) to what would be
  obtained assuming complete oxidation (burning in
  only oxygen) and what would be obtained assuming
  complete combustion (burning in air).