4 replies to this topic

[dgoyal]

have system (gas compressor station) having volume almost 500 cubic meter this need to be depressurized by a common vent in emergency like gas leak , fire etc. The station condition would be as below ;

Blow down initial pressure =65 Barg
Blow down initial temperature = 30 Deg C
Final pressure required = 6.89 Barg ( 100 PSIG )
Maximum allowable blowdown time = 5 Min
As this is automatic blow down and can be activated in case of LEL alarm , so its suggested to consider adiabatic depressurization .
As this is a compressor station major volume is of piping.
MOC of system component is Carbon steel.

By using hysis Iam getting very low temperature in system so i want to make sure whether this blowdown time is achievable or not.
Normally in actual practice the temperature drops only after orifice not in upstream of orifice.
Please suggest is hyssy is right tool for determing this or not.

DGOYAL

[Zauberberg]

Yes, it can be done in HYSYS, and it is done in HYSYS by many engineering companies I know.
Temperature profile depends on several factors (you should use the "Search" feature in ChE forums and look for similar threads), and if you get quite a big difference as compared to applying Joule-Thomson principle in expansion calculations, the software may not be very accurate.

As witnessed by many operators, if you have 100% vapor in the system volume, the minimum temperature should be very close to the minimum Joule-Thomson expansion temperature. For systems containing liquid phase, the temperature profile is a bit more different.

[JoeWong]

Dgoyal,

You have opened another post in " Depressurisation Of Compressor Station". Please try not to do that.

[sabahboyz]

have system (gas compressor station) having volume almost 500 cubic meter this need to be depressurized by a common vent in emergency like gas leak , fire etc. The station condition would be as below ;

Blow down initial pressure =65 Barg
Blow down initial temperature = 30 Deg C
Final pressure required = 6.89 Barg ( 100 PSIG )
Maximum allowable blowdown time = 5 Min
As this is automatic blow down and can be activated in case of LEL alarm , so its suggested to consider adiabatic depressurization .
As this is a compressor station major volume is of piping.
MOC of system component is Carbon steel.

By using hysis Iam getting very low temperature in system so i want to make sure whether this blowdown time is achievable or not.
Normally in actual practice the temperature drops only after orifice not in upstream of orifice.
Please suggest is hyssy is right tool for determing this or not.

DGOYAL

May i know what is your blow down pipe size? what is the process gas? temperature too low may be you had create JT effect because small nozzle of discharge...

[Andrei]

Yes, Zauberberg was right. I'm working for an engineering company and we did very recently such study for and entire gas plant using Hysys, probably one of the biggest in the world.

We noticed the same thing like you.
I don't think you are right, on the paper in steady state, we consider temperature drop only downstream of the oriffice. In reality, not steady state, you will see a pressure decrease upstream of the riffice, so a temperature drop is justified.
And yes, we determined lower temperatures occuring than we previously estimated using steady state methods.