Annex IV
AIV-1. Adiabatic Flame Temperature At Lower Flammability Limit The AFTLFL is explained as an example in which the fuel gas is methane, CH4. Let’s consider the chemical reaction of methane where its concentration is 5% (value of LFL).
(
0.05CH 4 + (1 − 0.05)·( 0.21O2 + 0.79N2 ) → Pr oducts CO2 , H2O, O2 and N2
)
(AIV-1) Dividing through by 0.05 gives: CH 4 + 3.99O2 + 15.01N2 → CO2 + 2H2O + 1.99O2 + 15.01N2
(AIV-2)
As the original mixture was fuel lean, the excess of oxygen will contribute to the total thermal capacity of the product mixture. For obtaining the AFTLFL, the method of section must be applied. Considering an initial temperature of 25ºC, the AFTLFL is 1200 ºC.
AIV-2. Adiabatic flame temperature at upper flammability limit The AFTUFL is also explained as an example in which the fuel gas is methane, CH4. Let’s consider the chemical reaction of methane where its concentration is 15% (value of UFL). Stoichiometric combustion XCH4 + CH4 + 2O2 + 7.52N2 → CO2 + 2H2O + 7.52 N2 + XCH4 (AIV-3) For obtaining what is the fuel non burnt:
UFL =
X +1 = 0.15 X + 1 + 2 + 7.52
(AIV-4)
Therefore, X is equal to 0.68.
0.68CH4 + CH4 + 2O2 + 7.52N2 → CO2 + 2H2O + 7.52 N2 + 0.68CH4 (AIV-5) As the original mixture was lack of oxygen, the excess of fuel will contribute to the total thermal capacity of the product mixture. For obtaining the AFTUFL, the method of clause must be applied. Considering a initial temperature of 25ºC, and a thermal capacity of methane equal to 81.3 J/molK the AFTUFL is 1565 ºC.
A-45