water dew point in natural gas

[cosh]

for a stream containing hydrocarbons (C1-C9) and water (< 1000 ppm) I am calculating water dew point and hydrocarbon dew point, my reference tools GPSA manual and process simulator (Aspen) give very different results, I think process simulator is wrong, I selected Peng Robinson model as suggested in the manual but changing the model doesn't reduce the difference between the two methods.
My question is, how large errors one should expect when estimating water dew point and hydrocarbons dew point values ?
Could you suggest a more reliable method ?

 

[zdas04]

Buy a copy of ASTM D1142. Costs a couple of hundred dollars and if you can afford Hysys you can afford the basis for all the calculations.

The data in GPSA (I'm assuming you are talking about the McKenna graph on figure 20-3) comes from the referenced ASTM document. You can use the technique in ASTM to get the theoretical "right" answer. If Aspen is far from that then Aspen is "wrong".

David

 

[PaoloPemi]

that is a quite common problem.
For dew point of water in natural gas I suggest the standard ISO 18453 (GERG 2004), expected errors are within 2 K in the area of application, this method is available in the student's edition of Prode Properties (see

http://www.prode.com),

you can easily compare the results.
Generally I calculate water dew point with ISO 18453 and hydrocarbons dew point with Peng Robinson (or Soave) after having removed the water content.

 

[cosh]

Thanks a lot both of you,

zdas04
yes, it is the GPSA graph, actually I have not the ASTM standard but I think the GPSA graph is reasonably reliable (altough not much accurate, see my comment below)

PaoloPemi
I have tested ISO18453 and it seems to give accurate values, I think I'll adopt the ISO standard as it is mentioned in client's accepted standards.

 

[dcasto]

Calculation of Gross Heating Value,
Relative Density, Compressibility and
Theoretical Hydrocarbon Liquid
Content for Natural Gas Mixtures for
Custody Transfer
GPA Standard 2172–09
API Manual of Petroleum Measurement Standards
Chapter 14.5


is the US standard