%mol - CO2 1

[RussellJB]

Struggling with some very basic composition math...

I'm looking to calculate the percentage of CO2 in a volume flow based on %mol CO2.

Information is as follows:

Rate: 128,865 Nm3/hr
Composition (vol%): 4.3%mol CO2

Calculation:

Is it as simple as 128,865 * .043 =5,541 Nm3/hr - CO2.

Which can than be converted to kg/hr as follows:

5,541 Nm3/hr * 1977 kg/m3 ~= 10,955kg/hr

 

[Latexman]

Yes, it's that simple, but 1977 kg/m3 for CO2 does not make sense. From wiki:

1562 kg/m3 (solid at 1 atm and −78.5 °C)
1101 kg/m3 (liquid at saturation −37°C)
1.977 kg/m3 (gas at 1 atm and 0 °C)

See what I mean?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[RussellJB]

Thank you for the quick response.

Sorry, fat finger mistake. I was going for 1.977kg/m3.

 

[IRstuff]

That seems more like it. "Air" is something like 1.3 kg/m^3

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[MortenA]

A "safer" Way would be to convert Nm3 to kmol directly and Them ude CO2 molweight to calc massflow

5541/22.414*44=

 

[25362]

Just to clarify. The factor 22.414 L/mol refers to an ideal gas at 1 atmosphere of pressure
and at 0 °C. At 1 bar, it would be ~ 22.711 L/mol.

 

[MortenA]

Disagree with your clarification (or splitting hairs dont really know), Nm3 is in reality a unit that refers to no. of mols (for any gas). A Nm3 can in really be any given number of moles since there is no universal definition, but following the most common definition: 0ºC, 0 barg (1.01325 bar a) this is 22.414 l/mol

 

[25362]

22.414 L/mol is for an ideal gas at 0 [sup]o[/sup]C and 1 atm. At these conditions, the factor for CO[sub]2[/sub] is ~22.263 L/mol.

 

[MortenA]

@25362, and this is where i disagree. A Nm3 CO2 has the same no. mols as any other Nm3 of any other gas!

 

[25362]

Here are some examples of "real" gases at 0[sup]o[/sup]C and 1 atm, conditions usually referred as normal, in L/mol:

SO[sub]2[/sub] 21.856
H[sub]2[/sub]S 22.187
CH[sub]4[/sub] 22.361
O[sub]2[/sub] 22.392
N[sub]2[/sub] 22.404
Ne 22.425
H[sub]2[/sub] 22.428

One can see the differences, however small, because of their cuasi-ideality at normal conditions..

 

[MortenA]

true, but when you refer to 1 Nm3 of SO2 you have just as many mol SO2 as when you refer to 1Nm3 of CH4 (and that would be 44.6158)

 

[25362]

Wrong! With 1 Nm[sup]3[/sup] at 0[sup]o[/sup]C and 1 atm, of each gas, the numbers of moles are not the same, for example:

CH[sub]4[/sub] 44.722
SO[sub]2[/sub] 45.755
and for n-butane
C[sub]4[/sub]H[sub]10[/sub] 46.518 (in this case the deviation from ideality is more than 4%)

 

[MortenA]

No you are wrong! The fastes ref i have is the Danish Energy Authorities, i could trawl NIST or UIPAC for a while but its not the easiest sites to navigate:

https://ens.dk/sites/ens.dk/files/OlieGas/oil_and_gas_in_denmark_2013.pdf

page 104

 

[ione]

MortenA,

Your statement would imply all real gases have the same Z compression factor, which is not the case.

 

[EmmanuelTop]

25362 is referring to actual (real) gases while MortenA refers to the ideal gas case.
Is it sunny outside? No, I want a hamburger for dinner.

Dejan IVANOVIC
Process Engineer, MSChE

 

[25362]

EmmanuelTop, MortenA postings tell a different -erroneous- story. Bon appetit!