dewpoint of water at tempratures less than 32¦F

[timbones]

I have a natural gas stream that contains a very small amount of water vapour. The concentration is about 45 ppmv and the line pressure is at 600 psia.

Assuming I've got my science right, the partial pressure of the water vapour works out to 45x10^-6 x 600 psia = 0.027 psia.

Now the problem...at that partial pressure, the saturation temperature is less than 32°F which is the lowest temperature on every steam table I have. How do I figure out what the water dew point actually is? Presumably I can have dew points less than 32°F?

thanks,
tim

 

[SooCS]

Based on the 45 ppmv of water content, which is about 2.5 #/MMSCF at 600 psia, the due point is about -10 oF.

Check it out in GPSA Engineering Data book.

 

[25362]

The vapour pressure of 0.027 psia corresponds to about +7^oF and relates to ice (solid water). See Perry VI, table 3-300.

 

[hacksaw]

the vapor pressure of water (for all temperatures) is listed in several references and textbooks.

Perry's as previously mentioned, Lange's, Felder & Rousseau, you name it....

 

[timbones]

Thanks everyone. GPSA really does have most everything, provided you know what section to look under. I never thought to look in the section headed "Dehydration, Treating and Absorption" for dew points of natural gas.

tim