water hydrocarbons dew point in natural gas pipelines

[hcostello]

I appreciate the help,
actually we are considering for measuring water content different devices, however that value (within a limited range) should not influence water dew point, do you know how much the water dew point (temperature) can change in the range, say, 500-3000 ppm for water , composition C1 72% C2 18% ....

[dbert]

IMO for water contents in the range 500-3000 ppm the water dew point should change little, I can do the calc's with ISO 18453 to verify.

[carlo.stenali]

you may do these calc's with Prode Properties , the student's version includes ISO 18453...
In my opinion the main advantage of ISO 18453 over Peng Robinson or Soave Redlick Kwong (with extended Alpha function) is the range of application below 0 (water freezing point), a water dew point spec. in the range -20/-6 C is quite common.

[hcostello]

thanks,
I did a test with the software from Prode, for the mixture C1 0.8 C2 0.1 C3 0.04999 CO2 0.05 H2O !.0E-4 (100 ppm) molar fractions I calculated these dew points

P 3 Bara 239.94 K
P 5 Bara 244.77 K
P 10 Bara 251.6 K
P 50 Bara 268.149

I have some data collected in the past which confirm the accuracy in low pressure range, what is the expected unceartainty of the method ?

[carlo.stenali]

the (max error) should be 2-3 K in the permitted range of application (see the standard for additional information).
When calculating water dew point make sure that liquid phase is almost all water, in your example if you reduce the water amount to 50 ppm (C1 0.8 C2 0.1 C3 0.049995 CO2 0.05 H2O 5.0E-5 ) then at 20 Bar.a , dew point 231 K , the condensate includes water and all other components (i.e. the gas can contain that amount of water)

[hcostello]

if I understand correctly :

1) water dew point, the dew point when a incipient pure (all water) phase begins to condense

2) hydrocarbons dew point, when a phase with mixed composition begins to condense

is that definition generally accepted ?

[carlo.stenali]

hcostello wrote:

>1) water dew point, the dew point when a incipient pure (all water) phase begins to condense
>2) hydrocarbons dew point, when a phase with mixed composition begins to condense

that is my understanding of the process, for a natural gas mixture including water usually the dew point (i.e. the temperature ai which the liquid begins to condensate as pure water or mixed phase) is higher than hydrocarbon's dew point (calculated without water),
do not forget that all general rules may have exceptions...

[hcostello]

thanks,
actually water content is very low so I do not expect water to condense before hydrocarbons, most probably we'll obtain some water and hydrocarbons.

[mpor]

does the interface allow multiphase (gas+liquids+water) ?
I need to include in DCS a realtime evaluation (given composition and operating conditions) of a multiphase stream.

[carlo.stenali]

yes,
Prode Properties can do rigorous (not water decant or separated) multiphase,
in Prode Properties you can select the (thermodynamic) models for gas, liquid and solid fugacities.
I would suggest to open a new thread if you have specific questions not related to this thread.