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Psv Dynamic Simulation

psv dynamic aspen hysys buckle pin

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#1 walid.nahhas

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Posted 27 March 2019 - 03:57 AM

I want to simulate the opening of a PSV (buckle pin device) which is on the bypass of an MOV (upstream a two phase separator). when the MOV accidentally closes, the Buckle Pin has to open to prevent overpressurization of the upstream pipe.

 

In Aspen Hysys, the PSV is opening in 20 seconds minimum, which is not the real case as the buckle pin open instantaneously.

Can Aspen hysys simulate the fast opening of the PSV? or is there an extension to Aspen hysys that can be used in this regard?

 

Thanks



#2 PaoloPemi

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Posted 27 March 2019 - 12:33 PM

which is the scope of your work ?
If , given volumes and flows,  you wish to simulate the increase of pressure vs time (in your separator with blocked output) there are simple procedures (based on direct integration method, see several threads at cheresources.com),
a dynamic simulation does that (i.e. calculate pressure profile vs. time to identify when a PSV / Protection Device opens)



#3 walid.nahhas

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Posted 30 March 2019 - 06:59 AM

The scope of this simulation is like you have said, to simulate the increase of the pressure vs time in the vessel which already is half-full liquid and contain gas.

 I attached an snapshot of the buckle pin, mov and the vessel.

 



#4 PaoloPemi

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Posted 01 April 2019 - 01:20 AM

you can solve these problems in different ways,
for example, being the volume of container (vessel + piping) constant,
solve a series of flash operations with specified volume, as result you obtain the temperature / pressure values vs. time which allow to identify when the PSV opens,
from post #1 it appears that PSV opens after 20 seconds, in your opinion, is that value not correct ?  
You can adopt a different method (see above) in order to test the result.



#5 walid.nahhas

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Posted 05 April 2019 - 11:14 PM

I think you got my idea wrongly, I will try to make more clear to you. The PSV doesn't open after 20 seconds, the opening time is 20 s (the time required for the PSV to opening from 0 % to 100 %). The fluid is flowing to the vessel in normal operation, suddenly the MOV upstream the vessel closes. The liquid now undergoes an over-pressurization due to blocked outlet. After it reaches a specific set point (for ex. 100 psig), a PSV which bypass the MOV open to prevent rupture of the pipe. When that PSV opens (should be very fast opening, less than 1 second), the fluid is again flowing to the vessel. I want to know the increase in pressure inside the vessel immediately after the opening of the PSV.

 

Thank you.



#6 PaoloPemi

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Posted 08 April 2019 - 07:25 AM

as said, you should evaluate volumes and flows, from these you can calculate the different conditions, including the PSV opening, (normally) pop-acting relief valves do not immediately open completely (to 100% lift) , being the opening dependent from pressure, it may be that your model predicts a slow increasing of pressure, check pressure Pressure vs Time values,
for simple applications I prefer to define myself the models (see post #2) with tools as Python or Excel (plus a thermodynamic library for solving phase equilibria and fluid properties), in that way I have some additional control over intermediate results...






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