Calculate the Flame temperature

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Discussion Overview

The discussion revolves around calculating the maximum flame temperature for a fuel gas mixture consisting of butane, propane, and butene, which is to be combusted with excess air. The context includes the application of thermodynamic principles to determine heat input and output in a combustion process.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents the composition of the fuel gas and the conditions for combustion, seeking to determine the maximum flame temperature.
  • Another participant suggests a method involving summing heat capacities and performing division to find the solution.
  • A participant calculates the heat released by the fuel mixture based on the combustion of butane, propane, and butene, providing specific enthalpy values for each component.
  • Questions arise regarding the products of combustion and their respective heat capacities, indicating a need for clarity on these values.
  • One participant lists the moles of flue gases produced and calculates the heat content based on assumed flame temperature, providing a total heat value.
  • Participants seek feedback on their calculations and whether there is agreement on the presented values and methods.

Areas of Agreement / Disagreement

The discussion shows a lack of consensus, with participants providing different calculations and seeking validation of their approaches. There are multiple competing views on the correct method and values to use for the calculations.

Contextual Notes

Participants have not fully resolved the assumptions regarding heat capacities and the products of combustion, which may affect the calculations. The flame temperature remains an open question pending further agreement on these details.

GeorgeP1
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Homework Statement


A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume.
It is to be fed to the combustion chamber in 10% excess air at 25°C, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to generate 5 bar steam from water at 90°C.

Determine the maximum flame temperature ?.

Homework Equations


[/B]
heat input to process = heat out of process
Heat out of process = ∑ (mass × mean specific heat capacity × TF ) for each product of combustion

The Attempt at a Solution


[/B]
2581 Kj

1987°C

This answer is incorrect.
Any help is much appreciated.
 
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C'mon --- you know the "drill" --- sum the heat capacities, do the division, ...
 
butane = -2660 kj/mol
propane = -2046 kj/mol
butene = -2540 kj/mol
heat released by 1 mole of fuel
= (0.75x2660)+(0.1x2046)+(0.15x2540)
=2581 kj (heat in)

is this correct so far?
 
Last edited:
What are the products, and what are their heat capacities?
 
Flue gas =

H2O = 4.75 moles
CO2 = 3.9 moles
O2 = 0.63 moles
N2 = 26.06 moles
Total = 35.34 moles

assuming a flame temperature of 2000°C

Heat content = enthalpy x no. of molesFor N2, 66.10 x 26.06 = 1722.6 kJ

CO2, 108.32 x 3.9 = 422.5 kJ

O2, 69.65 x 0.63 = 43.9 kJ

H2O, 86.24 x 4.75 = 409.6 kJ

Total = 2598.6 kJ

 
how does this look?
 
GeorgeP1 said:
how does this look?
George - looks good to me, did anyone agree?
 

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