Dew Point - Pressure Relationship
Dew Point - Pressure Relationship
(OP)
Hi all,
Looking at some hydrate curves for gas and was wondering if there is a quick formula for calculating the dew point with pressure change.
Hydrocarbon gas in the line with dew point of -20DegC at 35bar.
What would be the dew point at 110bar?
Gas temperature is 40DegC.
Thanks,
Ryan
Looking at some hydrate curves for gas and was wondering if there is a quick formula for calculating the dew point with pressure change.
Hydrocarbon gas in the line with dew point of -20DegC at 35bar.
What would be the dew point at 110bar?
Gas temperature is 40DegC.
Thanks,
Ryan





RE: Dew Point - Pressure Relationship
If you wish to calculate dew point temperatures (at different pressures) but about the same composition you may calculate the entire dew point line (phase envelope) then calculate the parameters for a curve, fitting the calculatecd data (quite easy with Excel or similar tools)
If composition changes are important then you need a more complex approach.
RE: Dew Point - Pressure Relationship
only change is the pressure
RE: Dew Point - Pressure Relationship
RE: Dew Point - Pressure Relationship
CO2 1.39 44.00 0.0139 0.0139 #DIV/0!
N2 1.78 28.00 0.0178 0.0178 #DIV/0!
C1 77.25 16.00 0.7725 0.7725 #DIV/0!
C2 8.47 30.00 0.0847 0.0847 #DIV/0!
C3 6.10 44.00 0.061 0.061 #DIV/0!
iC4 1.31 58.00 0.0131 0.0131 #DIV/0!
nC4 2.28 58.00 0.0228 0.0228 #DIV/0!
iC5 0.54 72.00 0.0054 0.0054 #DIV/0!
nC5 0.01 72.00 0.0001 0.0001 #DIV/0!
C6 0.40 86.00 0.004 0.004 #DIV/0!
C7 0.06 100.00 0.0006 0.0006 #DIV/0!
C8 0.02 114.00 0.0002 0.0002 #DIV/0!
C9 0.03 128.00 0.0003 0.0003 #DIV/0!
C10+ 0.02 142.00 0.0002 0.0002 #DIV/0!
Composition is shown above... does anyone have the links to the required graphs for the xi at the stated P&T?
RE: Dew Point - Pressure Relationship
RE: Dew Point - Pressure Relationship
What formula do I use to find the dew point of the gas?
Do I need to vary the temperature to find new Ki values?
Thanks
RE: Dew Point - Pressure Relationship
1) calculate Gas & Liquid fugacities (at p,t)
2) Ki=Fli/Fvi
3) correct t to find (for the dew point) SUM(Wi/Ki) = 1
a simple procedure should work with p , t far from critical conditions.
To learn more on the subject I would recommend a good textbook.
RE: Dew Point - Pressure Relationship
RE: Dew Point - Pressure Relationship
you get
SUM(Wi/Ki) = 1
solving Rachford and Rice
SUM (Ki-1)*Wi/((Ki-1)*vf+1)
putting vf (vapor fraction) as 1.0 (dew point specification)
You may read a good textbook for additiona information.
RE: Dew Point - Pressure Relationship
I have assumed that the vapour fraction is equal to the compositonal anlaysis (which was taken at 35bar and 40degC)
using this composition I have looked up the charts and determined the xi based on the K value and now my xi is equal to one which means that my due point is 40degC which is wrong...
Can someone have a look at the attached and help please...
I have put a guess temperature section where I would move on but I dont know what to do...
Thanks again...