vapor pressure higher than the critical pressure

[chemiind]

I am trying to size a control valve located on the outlet of a condensate pump recycle cooler. For sizing the control valve I need to determine the Critical pressure of the process stream. I generated the phase envelope using HYSYS. However, this shows that the Vapor pressure of the stream at the valve inlet pressure is higher than the critical pressure.
Reading through couple of other posts on this forum, I think this might be possible in the case of this stream as it is a Hydrocarbon mixture.

http://www.eng-tips.com/viewthread.cfm?qid=160034&page=1

Is this possible?

 

[PaoloPemi]

the pressure in two phases area can go up to cricondenbar (cricoP), the temperature up to cricondentherm (cricoT), there can be one (or more) critical points at pressures below cricoP, see for example

http://www.prode.com/en/phaseenvelope.htm

in any point of two phase area you have some amount of liquid which can change of state when pressure changes through a control valve, when p > Pc the Masoneilan (now ISA) formulation (for pure fluids) could not be suitable, there are different solutions, for example if there is a change of phase (easy to verify with a flash) you can sum areas, define a safety factor, etc. etc. in these cases better to ask the manufacturer