Composition of flue gases by volume on a wet basis and dry basis

  • #1
dbomb1203
1
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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 25ºC, 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 90ºC

(e) Determine the composition of the flue gases by volume (assuming the inlet air is dry) :
(i) on a wet basis
(ii) on a dry basis.

I'm aware that there is a similar question already posted from 6+ years ago. I have read that particular forum and seem to still struggle.
Relevant Equations
Balanced reactions
Butane C4H10 + 6.5O2 = 4CO2 + 5H20
Propane C3H8 + 5O2 = 3C02 + 4H2O
Butene C4H8 + 6O2 = 4CO2 + 4H20
Butane
0.75mol of C4H10

0.75 x C4 = 3mol of CO2
0.75 x H5 = 3.75mol of H2O
0.75 x 6.5O2 = 4.875mol of O2

Propane
0.10mol of C3H8

0.10 x C3 = 0.3mol of CO2
0.10 x H4 = 0.4mol of H2O
0.10 x 5O2 = 0.5mol of O2

Butene
0.15mol of C4H8

0.15 x C4 = 0.6mol of CO2
0.15 x H4 = 0.6mol of H2O
0.15 x 6O2 = 0.19mol of O2

We know, Oxygen = 6.3mol + 10% excess air = 1.1 x 6.3mol = 6.93mol.

I know I need to find the value of Nitrogen. I've seen on other threads, that they have got a value of 26.07mol...but I'm struggling to understand how they've achieved this.

This is as far as I can manage to get...Please help me with some advise!!
 
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  • #2
This problem has appeared previously in PhysicsForums. Please use Search.
 

FAQ: Composition of flue gases by volume on a wet basis and dry basis

1. What is the difference between wet basis and dry basis in flue gas composition?

The wet basis includes the moisture content in the flue gas, representing the total volume of gases including water vapor. The dry basis excludes the moisture content, representing the volume of gases after all water vapor has been removed. This distinction is important for accurate analysis and reporting of gas concentrations.

2. How do you convert flue gas composition from a wet basis to a dry basis?

To convert flue gas composition from a wet basis to a dry basis, you need to remove the water vapor content from the gas mixture. This is typically done by using the formula: Dry gas concentration = (Wet gas concentration) / (1 - Water vapor fraction). The water vapor fraction can be determined through measurements or calculations based on the combustion process and conditions.

3. Why is it important to know the composition of flue gases on both wet and dry bases?

Knowing the composition of flue gases on both wet and dry bases is crucial for several reasons. It allows for accurate emissions reporting and compliance with environmental regulations, helps in optimizing combustion efficiency, and aids in the design and operation of pollution control equipment. Different applications and regulatory requirements may specify the need for either wet or dry basis data.

4. What are the typical components of flue gases analyzed on wet and dry bases?

Typical components of flue gases analyzed on both wet and dry bases include carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), nitrogen (N2), sulfur dioxide (SO2), and water vapor (H2O). On a dry basis, the water vapor is excluded from the analysis, while on a wet basis, it is included.

5. How does moisture content affect the analysis of flue gas composition?

Moisture content affects the analysis of flue gas composition by diluting the concentrations of other gases when reported on a wet basis. This can lead to lower apparent concentrations of pollutants and other components. Accurate determination of moisture content is essential for converting between wet and dry basis measurements and for ensuring that emissions data are correctly interpreted and reported.

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