Find the adiabatic flame temperature for a stoichiometric methane/air flame if the initialtemperature of the fuel and air is 10°C. Take the net calorific value of methane as 50.14 MJ/kg.CH,f= Final stateAhActual path10 °C, 1 atmCO2H,01 atm N2T| Ah,CombustionT,Constant PchamberState i- + 2Constant PAir100%Percentagecompletionof reaction10°C, 1 atm

Adiabatic flame temperature: During combustion process the the energy is released to the combustion products. If there is no heat loss during the process, the final temperature of the combustion products is known as adiabatic flame temperature.Assumptions for the given problem: 1 Steady operating conditions exist. 2 Air and combustion gases are ideal gases. 3 Kinetic and potential energies are negligible. 4 There are no work interactions. 5 The combustion chamber is adiabatic. Analysis Under steady-flow conditions the energy balance Ein − Eout = ΔEsystem applied on the combustion chamber with Q = W = 0 The stoichiometric equation for combustion of methane is CH4+ath(O2+3.76N2)→CO2+2H2O+ath×3.76N2 ath=theoretical oxygen required to complete the combustionFrom the oxygen balanceath=1+1=2Therefore the stoichiometric equation becomes CH4+2(O2+3.76N2)→CO2+2H2O+2×3.76N2 Now from the table shown below Substance hf0, kJ/kmol h283k, kJ/kmol h298k, kJ/kmol CH4 -74850 - - O2 0 8350 8682 N2 0 8461 8669 H2O -241820 9854 9904 CO2 -393520 9156 9364 Thus, (1)(-393520+hCO2-9364)+(2)(-241820+hH2O-9904)+(7.52)(0+hN2-8669)=(1)(-74850)+0+0or, hCO2+2hH2O+7.52hN2=896672.88 kJ The adiabatic flame temperature is obtained from a trial and error solution. A first guess is obtained by dividing the right-hand side of the equation by the total number of moles, which yields 896672.8/(1 + 2 +7.52) = 85235.06 kJ/kmol. This enthalpy value corresponds to about 2500 K for N2. Now at 2300k hCO2+2hH2O+7.52hN2=870695.21 kJ (lower than 896672.88 kJ) At 2350 k hCO2+2hH2O+7.52hN2=915289.58 kJ (higher than 896672.88 kJ) By interpolation, TP=2329 k Answer: The adiabatic flame temperature is 2329k.

Answered: Find the adiabatic flame temperature…

Introduction to Chemical Engineering Thermodynamics

8th Edition

ISBN:9781259696527

Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart

Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart

Chapter1: Introduction

Section: Chapter Questions

Problem 1.1P

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Find the adiabatic flame temperature for a stoichiometric methane/air flame if the initial
temperature of the fuel and air is 10°C. Take the net calorific value of methane as 50.14 MJ/kg.
CH,
f= Final state
Ah
Actual path
10 °C, 1 atm
CO2
H,0
1 atm N2
T
| Ah,
Combustion
T,
Constant P
chamber
State i
- + 2
Constant P
Air
100%
Percentage
completion
of reaction
10°C, 1 atm

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