Temperature of upstream piping. Blowdown utility HYSYS

[enguest]

Dear all,

Now I am working on the project which involves blowodown calcualtion using HYSYS utility.

We need to blow down a small inventory (piping spool with volume of 0.3 m. cub)and concerned about the minimum temperature upstream of the restriction orifice because the design temperature of upstream piping is only -20°C. Hysys provides us with two temperature - vessel fluid (-26C) and inner wall temperature (-12C).

Could you please advice which of these temperature do I need to use as a basis to protect upstream piping?

Please see the file attached.

Thanks in advance.

 

[hianbotech]

The temperature to be checked is: the minimum inner wall temperature. That's the temperature that the vessel/pipe will reach during the blowdown.

To get the right inner wall temperature you must be carefull in hysys with the following information:
* the weight and material of the vessel and piping in contact with the fluid usptream of the restriction orifice.
* minimum ambient temperature.
* Insulation properties, if this is applicable (thickness, material, etc).

 

[MortenA]

In short the upstream temperature is lower because the decompression here is more isentropic while its isenthalpic downstream.

With regards to wall temperature read what hianbo says.

Best regards

Morten

 

[SNORGY]

It will all probably be immaterial because of the allowances available to you for low temperature excursions without impact tested materials in the piping Code (presumably B31.3). Unless you have DBTT issues I wouldn't even worry about this at -26 C.

However...the "valve outlet" temperatures of -86 C...what's that all about? That's cause for concern.

Regards,

SNORGY.