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Natural Gas + Water Vle, Which Thermodynamics ?

natural gas water dew point peng robinson soave cpa gerg

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#1 frpe

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Posted 26 September 2014 - 11:07 AM

for phase equilibria in mixtures of natural gas + water I have read here (in different posts) that ISO 18453 and GERG 2008 models are very accurate,
indeed ISO 18453 does a good job fitting my GPA chart.
 
However recently I have compared ISO 18453 and GERG 2008 against the modified Peng Robinson and Soave Redlich Kwong (with temperature dependent BIPs) for a few natural gas mixtures,
results (dew points) are within 1-1.5 K (with some exceptions for GERG 2008 at very high pressures).
Considering the different models available in Prode

ISO 18453 is limited to only a few components
GERG 2008 has similar limits, less than 20 components (in addition to be quite slow and showing some problematic convergence)
CPA has been described to be accurate for HC+water however it is slow (compared with PR or SRK)
SAFT has similar features
EOS with complex mixing rules (Wong-Sandler, Michelsen etc.) are slow and can show problematic convergence at high pressures (in phase envelope)

it seems that Peng Robinson (and Soave Redlich Kwong) with std. mixing rules but temperature dependent BIPs are good for phase equilibria in natural gas mixtures including water,
do other users agree on this point ?
Do you suggest some different thermo option available in Prode ?



#2 marchem

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Posted 26 September 2014 - 01:29 PM

in my opinion GERG 2008 (and related models based on a Helmholtz free energy function)

are the most accurate but in many cases one doesn't need that accuracy ...

I agree that one can obtain acceptable accuracy from extended

versions of Peng Robinson or Soave Redlich Kwong,

the PR and SRK models included in PRODE have 5 parameters calculated for each

component in database plus three temperature dependent BIPs,

as said the results are quite good in a large number of cases.



#3 serra

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Posted 13 October 2014 - 04:55 AM

I  agree with marchem about densities, enthalpies, ehtropies etc...

models such as GERG 2008 are very accurate

and if you need, for example, to calculate very accurately vapor & liquid

densities of natural gas mixtures GERG 2008 is the best option,

AGA gives similar accuracy but it is limited to vapor phase.

However for phase equilibria in mixtures a std EOS

such as Peng Robinson or Soave Redlick Kwong with

std. mixing rules and temperature dependent BIPs

or complex mixing rules can be competitive

in terms of accuracy and speed,

with a proper tuned EOS you can get errors

below 1 K in water and HC dew points...






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