Question about the Fluid Recombination

[141175]

I did recombine the condensate and the dry gas to find out the recombination of fluid at reservoir condition. However, my phase envelope did not show the critical point. Is that a resonable result? And if the fluid has not a critical point, could you guys explain for me?

 

[TD2K]

What software are you using and what thermodynamic correlation are you using? There WILL be a critical point, it's just a matter of getting it out of your software if your software supports this.

 

[141175]

I use the PVT sim to recombine the fluids and i think the correlation in my situation is SRK standard. Do i answer exactly your correlation question? Seem i dont get close to your thermodynamic correlation. I brought the recombined fluid into the Pipesim also, but it still showed no critical point. Do you think in the world existing a fluid w/o critical point?

 

[MortenA]

I have also experienced that PVT sim could not detect the critical point. I think it vers 8.

HYSYS also had problems with this fluid i recall - but im sure if it actually could determine the critical point.

I think the problem occurs if the PT curve becomes very steep near the CP.

I just tried to skim through the pages of Smith & Van Ness on the subject but im still not sure if a defined CP has to exists for all mixtures or not.

Best rgards

Morten

 

[141175]

Could you guys try to draw a phase diagram for this composition below? I know the PVTsim limits the range of lower temperature and pressure. However, in my opinion the appearance of the critical pt does not depend on the software.
Recombined Comp
C1 0.8228
C2 0.0952
C3 0.0464
iC4 0.0064
C4 0.0096
iC5 0.0035
C5 0.0029
C6 0.0029
C7+ 0.0103

For C7+
MW= 113lb/lb mole
spgr= 0.794

 

[TD2K]

Sure. Got a fax number or something I can send the phase envelope to you if you want it?

 

[TD2K]

Okay, I used Pro/II and the Simsci SRK thermodynamic correlation. The heavy fraction (MW = 113) is about octane, I cheated and simply did a case with the heavy fraction being C7, C8 and C9 to see what the variation is rather than bringing it in as a pseudo component. There wasn't much change as you can see.

I also assumed your compositions were mol%

C7 as heavy, Tc = -64.2F, Pc = 662.2 psia
C8 as heavy, Tc = -66.9F, Pc = 663.3 psia
C9 as heavy, Tc = -69.4F, Pc = 664.4 psia

 

[141175]

Thx for your usefull help. I think it's not a great ideal when you assumed the compositions of C7,C8,C9 because the C7+ includes not only the C7,C8,C9 but also the C10 to C40. That's why your phase envelope will not correct 100%( i guess)Anyway, could you pls send the phase diagram via my email. Mine is haint@pidc.com.vn

 

[MortenA]

Did the calc in HYSYS usign PR and the data for heavy fration given above.

I got Tc:-35 deg C=-31F
Pc=91 bar=1320psia

Changing to pure nC8 i got:

Tc=-49 deg C=120F
Pc=93 bar=1199 psia

That quite different fro your finding TD2C

 

[141175]

Thank all you guys. If i use pure C7, my result is
Crit Point --47.38F 1267pisa pure C8
Crit Point -46.35F 1316psia
pure C9
No Crit Point found.
I used PR correlation also. When i changed to SRK
No crit pt found for C8, C9.
However, i still think we cant ignore the C10...C40 for heavy component.

 

[141175]

Ah I got the Crit pt for C7+ (PR correlation)
Ct=-52.63C Pt=76.39bar.
Still have a big gap b/w u guys results.