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Associate

Join Date: Oct 2006
Posts: 49

# hydrocarbon dewpoint calculation

08/14/2007 4:41 PM

I need to write a procedure which calculates the hydrocarbon dewpoint for typical natural gas mixtures.

The purpose of the procedure is to provide our customers with additional guidance to operate the compressors we manufacture. It will be offered as a new feature of our compressor sizing program.

Does anyone have any equations to work with? I expect to use Peng-Robinson Equation Of State as a starting point but I am not sure how to proceed from there.

I will also need to calculate the water dewpoint.

A typical gas analysis looks like the following:

Gas Name: Natural Gas

Specific Gravity: 0.902
Mole Weight: 26.141

Cp/Cv: 1.238
Gas Analysis:

Component

Methane 50.435%

Ethane 18.261%

Propane 13.913%

I-Butane 4.348%

CO2 4.348%

H2O 6.087%

H2S 2.609%

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Anonymous Poster
#1

### Re: hydrocarbon dewpoint calculation

08/15/2007 3:54 AM

H2O 6.087% will predominate as it has the highest boiling point.

Power-User

Join Date: May 2007
Posts: 101
#2

### Re: hydrocarbon dewpoint calculation

08/15/2007 7:59 AM

The easiest way is to use the HYSYS or PRO II process simulator. The dew point can be obtained by reducing the temperature in small steps until you see a liquid phase.

Associate

Join Date: Oct 2006
Posts: 49
#3

### Re: hydrocarbon dewpoint calculation

08/15/2007 8:31 AM

>>Guest

>>H2O 6.087% will predominate as it has the highest boiling point.

I agree. However, there are many gas streams that our customers see that have very little H2O. In those cases, the hydrocarbon dew point will dominate.

>>Slong

>>The easiest way is to use the HYSYS or PRO II process simulator. The dew point can be obtained by reducing the temperature in small steps until you see a liquid phase.

This might be the easiest approach if I needed this for my own purposes but I need to write a procedure into our existing software so our customers can use it. Any guidance regarding formulas or references would be helpful.

Anonymous Poster
#4

### Re: hydrocarbon dewpoint calculation

08/05/2008 12:04 PM

JohnB

For water dewpoint calculation, you can go to www.amsystems.com and click "moisture calculator". It will request personal information before. Then when the calculation form appeas, you can click on Source code of the explorer and have all the procedure for moisture calculation. For moisture in natural gas, you must specify 17-18 molecular weight according to the fraction sum of your type of gas. Other source of calculation is the standard ASTM D1142-95. Email me and I will reply with formulas written in Pascal.

As to hydrocarbon dewpoint, I do not have any information about a procedure but I am still looking all over. I also have the need to implement this procedure since we work with chromatographs and develop software solution.

If you have any news respect to hydrocarbon dewpoint I will appreciate to let me know. My email address is lwsegovia@yahoo.com

Best regards, Walter