Z factor (compressibility factor) 7

[processengineer1998]

I want to know how can I calculate Z factor for natural gas including c1-c5 and c6+ to c+20 cuts and also H2S and CO2.
I tried to use HYSYS but the Z factor field is empty.
Is there somebody to explain the method for such calculation in HYSYS or any other method or reference for such cases.

 

[jmw]

Google: "Z factor compressibility calculation"
10seconds:

http://www.lmnoeng.com/Flow/GasFlow.htm

Or was there something more to the question?

JMW

http://www.ViscoAnalyser.com

 

[zdas04]

JMW,
You might have spent 15 seconds on it, that link is singularly unhelpful.

ProcessingEngineer1998,
"Compressibility" is a fudge factor to account for non-ideal behaviour in real gases. The calculation of the "Z Factor" has a number of different EOS and empirical methods. The Standing and Katz Chart is widely used. The Hall Yarborough EOS can generate the Standing and Katz chart pretty well, NIST REFPROP does a good job. Beggs and Brill do ok, Shell and Amoco have variations of these, etc. There is a pretty good write up at

http://etd.lib.ttu.edu/theses/avail...613/unrestricted/NeerajKumarMastersThesis.pdf

Some equations are pretty simple, some are devilishly complex. I use the Hall Yarbourough equations which are somewhere in the middle. I've found that simpler versions don't match the NIST predictions very well at all.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[jmw]

Yes, sorry, but it was an example.

I just grabbed one off the top of a basic search.
A bit more time and effort and links like this come up:

http://pubs.acs.org/doi/abs/10.1021/i260068a009

My point was that it seems like a question to be first addressed by a search, and then if the search does not give the answers, to come and seek the answers.

Did your link come from google?




JMW

http://www.ViscoAnalyser.com

 

[zdas04]

It did, but a while back. I'm geek enough to save stuff like that, it is a really good review of the subject even if you don't buy into his version of the equations.

I don't disagree with your assertion that Google should be the first step. When I Google a tech subject these days, eng-tips.com is usually represented several times on the first page--a lot of people's first view of this site is on Google so it seems common to say "I got here through Google, I've done my due dilligence". It's wrong, but pretty common.

I've been noticing that there are an awful lot of long-time contributers to eng-tips.com who have been really snarky this week. Seems like a real unwillingness to give anyone the benefit of the doubt (one guy asked a question about fence supports which are pipe-looking in the Pipeline forum and everyone climbed down his throat and started line dancing, his question wasn't really stupid and he made an important typo, but no one was giving him any slack. I saw the same kind of thing on a half dozen threads this week). Not sure what is going on.

David

 

[dcasto]

Here is the quickest way to get Z

T = Temp in deg F
P = Pressure in psia
G = specific gravity
Criticle Temp (CT)= 169.01+314.001*G
Criticle Press (CP) = 708.75-57.5*G
Reduced P (PR) = P/CP
reduced Temp (RT) =(460+T)/CT
Z = 1 + (0.0703 * PR / TR) * (1 - 6 / TR ^ 2)


For gases with less than 5% N2 and CO2 and pressures under 1500 psig.

 

[jmw]

You could have a point Zdas04, its a long hot summer.....we've had several days of it in the UK.

And, well, I got jumped on by a first timer in another thread.
Some justification for part of the response but not for the rest and none for attitude.
So maybe I jumped too quick here.

JMW

http://www.ViscoAnalyser.com

 

[zdas04]

Just noticing a pattern. Maybe it is a long hot summer in the whole Northern hemisphere (doesn't explain the folks from Oz that are being snarky too, but maybe being in Oz is enough by itself?).

David

 

[JohnGP]

Hey, fair go, mate!

 

[ione]

David,

Thanks for sharing that thesis

 

[PaoloPemi]

processengineer1998,
if your simulator calculates the gas density it would be easy to derive the compressibility factor from that (PV=ZRT), if at specified (t,p,composition) properties for gas phase are not available it could be that VLE routine detects only a liquid phase, you mention a "c1-c5 and c6+ to c+20 cuts and also H2S and CO2" I don't think easy to calculate by hand properties for that mixture however you can get a rough approximation by considering only a few elements, to do this simple procedures as that suggested by Dcasto, compressibility diagrams as those of Standing and Katz or the closed form solution proposed by Hall and Yarborough (which however requires a iterative solution) etc. should be Ok.
Don't forget that accurate results require the full composition and properties, you should be able to use your simulator or an equivalent tool to do that.

 

[processengineer1998]

friends
thanks for your nice recommendations.
just for calrification, I should declared that before opening this thread I searched a lot about this matter but I got no where.so I asked it here

 

[chemjock]

The Z factor in Hysys is 0 for a saturated vapor. If you move away from the saturation point, ie raise the temperature a bit, a degree or two, then then Hysys should report the Z factor.

 

[mbeychok]

processengineer1998:

Want an article that includes a hyper link to an online graph used to obtained the compressibility factor Z of natural gases?

That also includes the calculation of the Z factor of pure gases by the van der Waals equation, Redlich-Kwong equation, Soave-Redlich-Kwong equation, Peng Robinson equation and the virial equation of state?

Then read this article in the online Citizendium encyclopedia: Compressibility factor of gases

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[processengineer1998]

Dear friends
I am really pleased to be here in eng-tips among such strong experts.
This is my first thread.I should appreciate all of you especially zdas04,dcasto,PaoloPemi,chemjock and mbeychok .
I also shall thank eng-tip admins and stuff.