Vapour pressure of flashing liquid in pipe 1

[PetroBob]

I have a 3 phase separator (Vap, liquid hydrocarbon & water). There is a control valve in the liq HC line just downstream of the separator. At the control valve inlet, vapour pressure P(VAP) = fluid system pressure 300 psig (since it is a boiling liquid). Downstream of the control valve the pressure is reduced to 150 psig producing a 2 phase flashing mixture. Is vapour pressure of the mixture downstream of the control valve equal to system pressure ie P(VAP) = 150 psig?

Further downstream is an exchanger heating the mixture, and therefore more flashing. Is the vapour pressure at exchanger outlet equal to system pressure (150 psig minus losses) at this point?

Thanks and have a Merry Christmas!

 

[mbeychok]

PetroBob:

If we can assume there is no air or nitrogen and no water in the HC liquid outlet line, then the vapor pressure of the liquid in the flashed mixture downstream of your control valve is indeed 150 psig since there is nothing in the line except the hydrocarbon liquid and its equilibrium vapor at the temperature and pressure existing in the line. (Sorry for the long sentence.)

If there is some water present, the situation is somewhat more complicated.

Milton Beychok
(Visit me at www.air-dispersion.com)
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