To wet basis...
To wet basis...
(OP)
Hello
I am doing energy balances to cracking furnaces.
I have the %vol O2 at dry basis and I want to convert it to wet basis.
What is the best way to do it?
Thanks
AndreChE
I am doing energy balances to cracking furnaces.
I have the %vol O2 at dry basis and I want to convert it to wet basis.
What is the best way to do it?
Thanks
AndreChE





RE: To wet basis...
Best regards
Morten
RE: To wet basis...
Otherwise, if you wish to estimate it, assuming perfect and complete combustion with excess (xs) air, knowing the % CO2 on a dry basis you obtain y/x (i.e., the H/C atomic ratio) of your fuel in CxHy.
Since the volumes of CO2 and H2O aren't affected by xs air, and the volume of water from combustion is equal to (y/2x) times the vol of CO2, one can estimate the volume of combustion water from that ratio.
For example, assume one is burning a hydrocarbon fuel with 20% xs air (about 3.5% oxygen in the flue gases) and measures 11% CO2 on a dry basis, it would result in y/x=2.9 (a typical refinery gas). And y/2x=1.45, meaning water volume would be 1.45*11=15.95. Added to 100% dry gas results in 115.95 volumes of wet gas, and any % expressed on a dry basis should be divided by 1.1595 to get the % on a wet basis.
BTW, the xs air on a perfect and complete combustion of a hydrocarbon can be determined just by knowing the % O2 with little appreciable error for any hydrocarbon fuel, as follows:
1% oxygen ~ 5% xs air; 2%, ~10% xs air; 3.5%, ~20% xs air; 5%, ~30% xs air, etc.
Don't forget that any fuel oil atomizing steam would have to be accounted for. I sincerely hope to be understood.
RE: To wet basis...
RE: To wet basis...
where
n, is the xs air coefficient, for 10% xs air, 1.1; for 20% xs air, 1.2, and so forth.
p = %CO2, dry basis.
The above formula is derived from the stoichiometric one giving all (wet) products of combustion of CxHy with xs air:
RE: To wet basis...
See Thread798-103509
Milton Beychok
mbeychok@xxx.net (replace xxx with cox)
(Visit me at www.air-dispersion.com)
RE: To wet basis...
Summarizing, when the composition of the hydrocarbon fuel CxHy is not known, the (approximate) procedure is as follows:
1. From %O2 (dry basis), A, find the excess
air coefficient n.
2. Measure %CO2 (dry basis) = p.
3. From n and p determine y/x.
4. Find %H2O, H = p(y/2x).
5. Find %O2 (wet basis), B=A/(100+H).
All the % are volume or mol %.
I invite comments from experts in combustion engineering.