4 replies to this topic

[marb]

how accurate is extended Peng Robinson to calculate liquid densities of hydrocarbons (C5-C13) + water (mole fraction 13-60%) at different p,t conditions ?
I am comparing the values calculated with extended Peng Robinson against tables of values (from volumetric flowmeters) and errors are high...
Which methods do you suggest as alternative to extended Peng Robinson ?
Thank you for help,
Mark

[PaoloPemi]

with non-ideal fluids as water standard Peng Robinson gives high errors for density and other properties, most simulators include variants or "extended" versions of Peng Robinson but the results (in terms of accuracy) are quite different from software to software, to give you some data I have calculated the values of liquid density for water at different conditions with IAPWS 1995 (best standard actually available for properties of water) and the different variants of Peng Robinson available in Prode Properties (you can download a copy from www.prode.com and test yourself accuracy at different conditions) ,
as you may notice the errors with the extended versions of Peng Robinson available in Prode Properties are very low, about 1% at tested conditions, compared with 15-20% errors of standard version.
I think that 1-2% error is acceptable in my usual engineering practice so I use extensively the extended versions of Peng Robinson (or Soave Redlich Kwong).


legenda
IAPWS 95 IAPWS 1995
PR std Peng Robinson standard
PR PEN Peng Robinson with Peneloux correction
PR EXT Peng Robinson Extended
CPA PR Cubic Plus Association Peng Robinson

water 15 C , 1 Atm
IAPWS95 999.1 Kg/m3

PR std 854 kg/m3 15% error
PR PEN 870 kg/m3 13% error
PR EXT 1015 kg/m3 1.5% error
CPA PR 1010 kg/m3 1% error

water 200 C , 20 Atm
IAPWS95 865 Kg/m3

PR std 709 kg/m3 18% error
PR PEN 720 kg/m3 16% error
PR EXT 857 kg/m3 1% error
CPA PR 851 kg/m3 1.5% error

[marb]

thanks for providing those results which appear much more accurate than those I am getting from my simulator,
I guess I have to update my knowledge about "extended" EOS :-)

[serra]

thanks PaoloPemi,
the data provided about water density are very interesting,
do you know if the extended EOS models included in prode Properties are able to fit enthalpy data (cp, cv, latent heat), too ?

[PaoloPemi]

the extended versions of Soave Redlich Kwong and Peng Robinson in Prode Properties have custom parameters calculated for best fitting of vapor pressure, liquid density and enthalpy experimental data points.
Soave Redlick Kwong and Peng Robinson are quite accurate with hydrocarbons but the extended versions included in Prode Properties produce accurate values also for non-hydrocarbons,
for example for water at equilibria
393.15 K
198671 Pa

IAPWS 95 (steam tables)
Latent Heat 2202.114 Kj/Kg

Soave Redlich Kwong standard
Latent Heat 2320 Kj/Kg

Soave Redlich Kwong (extended, Prode Properties)
Latent Heat 2188 Kj/Kg

Peng Robinson standard
Latent Heat 2276 Kj/Kg

Peng Robinson (extended, Prode Properties)
Latent Heat 2213 Kj/Kg

a similar accuracy you can expect for non ideal chemicals as for example glycol solutions etc.