3 replies to this topic

[gecos]

I have a question concerning the phase diagram calculated by Prode Properties with GERG 2008 AGA 2017 model for the mixture (stream 4) with composition

C1 0.78 C2 0.1 C3 0.05 CO2 0.02 IC4 0.03 H2O 0.02

 

the diagram (see attached image) shows a red line, a black line, the critical point, the lines are not connected,
I think the red line is the water condensation line, the black line the bubble line and blue line that with specified liquid fraction, correct ?
Also, can someone explain why the lines are not connected ?

Thanks.

Attached Files

•  phaseenvelope_HC+Water.jpg   88.86KB   4 downloads

[PaoloPemi]

For a mixture of hydrocarbons + water, the lines are not connected because the water forms a separate phase.

 

You are correct :

red line = water incipient condensation 

black line = bubble line (hydrocarbons + water)

blue line= specified liquid fraction

 

N.B. Fugacity calculated according GERG 2008 procedure (actual AGA 2017 std. doesn't specify that)

[staffel]

I think that for mixtures of HC+water models such as PRX (Peng Robinson Extended in Prode) produce more realistic phase diagrams,

probably due to complexity of GERG model (many roots etc.)

what do you think Paolo ?

[PaoloPemi]

I presume that solving GERG 2008 is more difficult than working with a EOS such as Peng Robinson or Soave,
GERG 2004 monograph says there are many roots (compared with max 3 in EOS),
anyway I think Prode does a decent job with phase diagrams,
it can solve even three phase separations (see for example the three phase area detected on stream 1 C1 0.7 CO2 0.15 H2S 0.15),
also there is a volume solver available (as alternative to std. solver) in Extended Version,

however in many cases, for phase diagrams, I prefer Peng-Robinson (std. or Extended) with suitable mixing rules (Prode includes many different options),

I adopt CPA (Cubic Plus Association) and SAFT models available in Prode only for specific applications (examples are Hydrates, Wax, Oils ....)