Flue Gas Condensation
Flue Gas Condensation
(OP)
I am hoping someone can help me out. I have a flue gas stream that has the following composition.
vol% mol%
CO2: 10.5% 26%
H20: 28.82% 12%
SO2: 0.006% ~0%
O2: 4.01% 5%
N2: 56.67% 57%
I have searched this site and found this thread (amongst others)
http://eng-tips.com/viewthread.cfm?qid=118571
The section thread has a link to a PDF that is pretty good. However, I do not understand where this line comes from:
yv = 18.6/ 100 +18.6 = 0.157
Can anyone explain to me what that mole fraction line means and if it correct or not? Its seems pretty straightforward to follow this process except for that one line.
vol% mol%
CO2: 10.5% 26%
H20: 28.82% 12%
SO2: 0.006% ~0%
O2: 4.01% 5%
N2: 56.67% 57%
I have searched this site and found this thread (amongst others)
http://eng-tips.com/viewthread.cfm?qid=118571
The section thread has a link to a PDF that is pretty good. However, I do not understand where this line comes from:
yv = 18.6/ 100 +18.6 = 0.157
Can anyone explain to me what that mole fraction line means and if it correct or not? Its seems pretty straightforward to follow this process except for that one line.





RE: Flue Gas Condensation
I believe that there is something wrong with your data. Mol percent means volume percent. The other composition method is by weight percent. In a mixed gas, the components with the higher molecular weights will have higher weight fractions than volume fractions.
For a gas including water vapor and other non-condensables, (that is, with only one condensable component) it can be treated as a simple binary mixture of water vapor and everything else. You can use a steam table to find out at what temperature the water vapor will condense based on its mol (volume) fraction of the total mixture and the total pressure of the mixture.
However, when you have H2S present there is a sulfuric acid dew point which is a bit higher than the water vapor dew point. I would check a reference such as B&W's Steam Book for that. The big issue is generally corrosion when any surface of the equipment goes below the acid dew point.
Regards,
speco (www.stoneprocess.com)
RE: Flue Gas Condensation
I did also use a steam table to find my dew point and got similar numbers. But, I used the mol% figures I had posted which then would cause the same problem.
If I use a steam table and 28.82% as my mol % than I get a dew point of about 155F. As you mentioned though with the sulphur this would actually be a bit higher. I assume Cl- has the same effect which could explain the corrosion we are seeing quite easily.
Cheers
RE: Flue Gas Condensation
The calculation represents the amount of water as a mole fraction, or 18.6 parts of water in 118.6 parts of stuff
Mole Fraction = 18.6/118.6 = 0.157 or 15.7% moisture by volume
Brian
RE: Flue Gas Condensation
Jack
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com