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[process chemical]

Dear Members,

I have a problem in executing dynamic depressurization using Aspen HYSYS for the scenario of isometric pressure depressurisation.
Following are the input conditions,
I have to depressurise a test separator contaning hydrocarbon fluid
Operating pressure of the vessel = 375 psia
Operating Temperature of the vessel = 169 - 180°F
PAHH pressure of the vessel = 534 psia
Ambient temperature =48°F
The vessel is letdown to cool to ambient temperature from PAHH pressure. Due to cooling there is pressure reduction in the vessel, Can any one help me how to find out the isometric pressure when the vessel attains ambient temperature?

thanks in advance

[Zauberberg]

The first thing - what does it mean "isometric pressure"? I know there are piping isometric drawings, but I have never heard of the term "isometric pressure". Where did you encounter this one?

Secondly, the calculation is fairly simple if you follow this logic:

- Volume of the system (vessel) is constant;
- Mass inside the vessel is constant (no relief during vessel cooldown, if I understood you well);
- Therefore, actual mass density (total mass inside the vessel divided by vessel volume) has to be constant as well.

In order to calculate the final pressure after cooldown, set the final temperature and use the "Adjust" operation in Hysys to find the pressure at which the actual mass density ("Parameters" tab) will be equal to the actual mass density at initial conditions (known P, T, composition). Easy as that.