4 replies to this topic

[Sherif Morsi]

Hi All,

 

I am reviewing the sizing of Methanol Vessel PSVs again. The PSVs will be sized for fire case.

In an effort to determine the temperature at relieving pressure using HYSYS for the mixture, I generated the envelope utility curve from the "stream attachment" and got a temperature of 136 C corresponding to the relief pressure of 948 KPa.

 

Another way is to force-input the relief pressure of 948 KPa and the vapor fraction as zero degree C and let HYSYS calculate the temperature. The calculated temp in this case is 143.6 C

 

Which one is the accurate way?

 

Sherif

[serra]

With Prode Properties in Excel I follow this procedure

 

http://prodesoftware...ns.blogspot.com

 

perhaps you may adopt a equivalent methodology

[Bobby Strain]

What you really want is temperature and properties at relieving conditions. Which pressure is equal to set pressure x 1.21.

 

Bobby

[Sherif Morsi]

Bobby,

 

The set pressure x 1.21 is 948 KPa.

 

To get HYSYS calculate the temperature, you must supply it with pressure and vapor fraction. Should I set the vapor fraction to zero or 1?

[serra]

you can solve with a phase equilibria spec. for a single component (pure fluid)

If you have a mixture you may solve a V-P flash

(with specified volume and pressure inside vessel at relieving condition, in your case set pressure*1.21)

as discussed in my post #2

that keeps in account for vapor/liquid equilibria,

an exception being the tank full of liquid (not clear),

for that case you can consider the isothermal compressibility

of mixture and solve directly,

hoping this helps to clarify the point

Edited by serra, 04 June 2014 - 08:03 AM.