Hello, I'm a little confused on what the depressuring utility actually calculates. I essentially want to calculate the time it will take to blowdown an entire flowline, that is initially at some pressure Pi to atmospheric. I set the initial pressure, and other prop of gas as the stream inlet, and the back pressure being atmospheric; and the depressuring utility as a general valve with a Cd of 0.86 and an RO size of 50mm^2. My final pressure should be atmospheric, and I want to calculate time required for blowdown. Can anyone help with this?

And can someone please explain the difference between the Vapour outlet and Vapour streams.

Thanks in advance,

Youssef

Also, if someone can explain why the vessel pressure drops to 0kPa instead of the back pressure of 1 Atm.

Thanks,

Youssef

The pressure with decay from initial pressure to a few barg (e.g. 3 barg) in short period, however it will take INFINITE time to reach ATM. Theoritically is impossible.

I don't think any operator will blowdown to ATM. Normally they will blowdown to 2-3 barg and follow by purging for maintenance blowdown.

For emergency blowdown, API STD 521 only demand to blowdown as low as 6.9 barg.