Friday, May 3, 2013

How to calculate fluid conditions inside a vessel when PSV opens

In a vessel protected by a PSV the temperature inside the vessel may reach values higher
than those allowable for vessel's materials,
for these cases a depressuring system is required.
Prode Properties allows to calculate the temperature when the PSV opens.
The basis of the procedure is the flash operation at specified volume and pressure.
In this example we will see how to utilize Microsoft Excel and Prode Properties to
calculate the fluid temperature inside a vessel when the PSV opens.
The example allows to define composition, t, p (operating conditions) and PSV discharge

The procedure calculates the temperature and phase equilibria when PSV opens.
To define the composition from Excel open Prode Editor, select stream 5 (or whichever you prefer) and define the composition.
In cells B1 and B2 enter operating pressure and temperature,
the procedure will calculate specific volume in cell B3,
in B3 set the macro =EStrV(5,$B2,$B1)
in B5 set the macro = VPF(5,$B4,$B3,0)
In cell B4 enter the discharging pressure for PSV,
the procedure will calculate the fluid temperature at specified discharging pressure.
To view compositions at specified discharging pressure open Prode Editor and select the stream

How it works ?
The procedure calculates specific volume (gas + liquid) at initial conditions,
then it solves a flash operation with specified volume and pressure
to find the temperature when PSV opens

Pin, Tin = initial conditions
Pfin = PSV discharging pressure 

For additional information

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