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

In summary, the conversation discussed the wet basis for flue gas composition, including the amount of oxygen and various products resulting from the combustion of different compounds. The theoretical oxygen required was determined to be 6.93mol, with a total of 35.35mol in the flue gas. The composition by volume on a wet basis was calculated to be 3.9mol CO2, 4.75mol H2O, 26.017mol N2, and 0.63mol O2. On a dry basis, the composition would be 3.9mol CO2, 26.017mol N2, and 0.63mol O2.
  • #1
PCal
31
2
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. Data: Net calorific value (MJ m–3) at 25ºC of: Butane (C4H10) = 111.7 MJ m–3 Butene (C4H8) = 105.2 MJ m–3 Propane (C3H8) = 85.8 MJ m–3 Air is 21% oxygen, 79% nitrogen by volume and 23.3% oxygen and 76.7% nitrogen by mass. Atomic mass of C = 12, O = 16, N=14 and H = 1.
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 know the main part of the question has been posted before but I cant find any threads about the flue gas analysis. Any help would be greatly appreciated as my lessons don't seem to give much help!
Relevant Equations
Balanced reactions
Butane C4H10 + 6.5O2 = 4CO2 + 5H20
Propane C3H8 + 5O2 = 3C02 + 4H2O
Butene C4H8 + 6O2 = 4CO2 + 4H20
Wet basis

0.75mol C4H10

Requires 4.875 mols O2

Produces 3 mols of CO2 and 3.75 mols of H2O

0.1mol C3H8

Requires 0.5 mols O2

Produces 0.3 mols of CO2 and 0.4 mols of H2O

0.15mol C4H8

Requires 0.9 mols O2

Produces 0.6 mols of CO2 and 0.6 mols of H2O

Theoretical oxygen= 6.3mol +10% excess = 6.93mol

N2= 26.07

Total mol in flue gas = 35.35mol

Flue gas composition by volume (wet basis)

CO2 3+0.3-0.6=3.9mol

H2O 3.75+0.4+0.6=4.75mol

N2=26.017mol

O2=0.63mol

I’m not sure if this is correct and I also don’t have a clue how to work out the composition on a dry basis.
 
Physics news on Phys.org
  • #2
Is the dry basis as simple as saying...

CO2 3+0.3-0.6=3.9mol

N2=26.017mol

O2=0.63mol
 
  • #3
Any help would be massively appreciated please!
 
  • #4
PCal said:
Wet basis

0.75mol C4H10

Requires 4.875 mols O2

Produces 3 mols of CO2 and 3.75 mols of H2O

0.1mol C3H8

Requires 0.5 mols O2

Produces 0.3 mols of CO2 and 0.4 mols of H2O

0.15mol C4H8

Requires 0.9 mols O2

Produces 0.6 mols of CO2 and 0.6 mols of H2O

Theoretical oxygen= 6.3mol +10% excess = 6.93mol

N2= 26.07

Total mol in flue gas = 35.35mol

Flue gas composition by volume (wet basis)

CO2 3+0.3-0.6=3.9mol

H2O 3.75+0.4+0.6=4.75mol

N2=26.017mol

O2=0.63mol

I’m not sure if this is correct and I also don’t have a clue how to work out the composition on a dry basis.
They want the mole fractions of the various species (a) for the flue gas as-is and (b) with the water vapor removed. (In common terminology, volume fraction is the same as mole fraction)
 
  • #5
Fab got it! Thank you!
 

1. What is the difference between wet basis and dry basis when measuring the composition of flue gases?

Wet basis refers to the measurement of flue gases in their original state, with water vapor included. Dry basis, on the other hand, removes the water vapor from the measurement, providing a more accurate representation of the gas composition.

2. Why is it important to consider both wet basis and dry basis when analyzing flue gases?

Flue gases often contain a significant amount of water vapor, which can impact the accuracy of measurements. By considering both wet basis and dry basis, scientists can get a more comprehensive understanding of the composition of flue gases.

3. What are the most common components found in flue gases on a wet basis?

The most common components found in flue gases on a wet basis include water vapor, carbon dioxide, sulfur dioxide, nitrogen oxides, and oxygen. The exact composition may vary depending on the source of the gases.

4. How is the composition of flue gases on a wet basis and dry basis typically measured?

The composition of flue gases is typically measured using a gas analyzer, which can detect and quantify the various components present. The gases are first collected and then analyzed using specialized equipment.

5. Can the composition of flue gases on a wet basis and dry basis change over time?

Yes, the composition of flue gases can change over time due to various factors such as changes in fuel type, combustion efficiency, and environmental conditions. Regular monitoring and analysis are necessary to track these changes and ensure compliance with regulations.

Similar threads

Engineering Composition of flue gases by volume on a wet basis and dry basis
    • Engineering and Comp Sci Homework Help
Replies
1
Views
423
Automotive Loss of gaseous volume because of fuel combustion
    • Mechanical Engineering
Replies
2
Views
200
Heat transfer and combustion
    • Engineering and Comp Sci Homework Help
Replies
9
Views
7K
Calculating CV of Fuel/Air Mixture @ 25°C
    • Engineering and Comp Sci Homework Help
2
Replies
47
Views
7K
Material Balance Problem Involving Ideal Gases- Any ?
    • Engineering and Comp Sci Homework Help
Replies
1
Views
4K
Combustion Analysis: Excess Air, Flue Gas Composition, Dew Point Temp
    • Engineering and Comp Sci Homework Help
Replies
12
Views
5K
Desulfurization, Removing ammonia problem
    • Engineering and Comp Sci Homework Help
Replies
1
Views
2K

Hot Threads

Recent Insights

Back
Top