Water Saturation at low temperatures & high temperatures

[Mrepp]

At 450 PSIG and -60 F what is the saturation concentration/ partial pressure of water? We trying to reduce the water content of a stream to prevent hydrate formation. It our understanding that water needs to be present to create hydrates. The HYSYS model runs out of significant figures for lowering water content and doesn't register at PPB. The goal is to not drop liquid in the pipeline, with the design conditions of 450 PSIG and -60 stated above. Is there any literature or insight out there?

 

[25362]

Water at -60 deg F is solid ice. Its vapour pressure is 0.0004972 psia (Perry VI, table 3-300). Its mol fraction in the vapour would be 0.0004972/(450+14.7)=1*10^-6.
Is this what you were looking for ?

 

[MortenA]

If your model shows taht all water has left the HC stream then no water can drop out... Did you ever include water in your model? If your original composition assumed that the water was removed by drying (e.g. a glycol unit) then an interesting case would be to simulate what would happen if the drying unit was down - would you have to shut down the pipeline or could you continue - maybe at reduced capacity???


Best regards

Morten

 

[Mrepp]

Thanks 25362, that is the data I needed. I was looking at crane (which is most of the time), and it has limited data, my Perry's has some dust on it.

Morten, good point, we should consider providing guidance for operating when the mol sieve drying unit is down in the winter time. We already have addressed winter and summer operating modes, the summer not needing as dry of a stream.

 

[krossview]

Mrepp

A word of caution here using Hysys and the hydrate prediction model. Your dewpoint temperature of -60°F is not in the range of the model as the temperature is far below the freezing point. On a previous project with high 22% H2S content at 1,000 Psig and 95°F the hydrate model found two water dewpoints in the range of +14°F and -4°F. To my knowlegde, Hyprotech never solved this problem, when I reported it.

In summary, be aware of the Hysys produced by Hysys.

Krossview/OK

 

[krossview]

Oops, correction on last line..
In summary, be aware of the results produced by Hysys.

Krossview/OK