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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, these values of temperature and pressure can be compared with the MAWP and MAWT and decide if a depressuring system is required.
The basis of the procedure is the flash operation at specified volume and pressure.
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 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
psvsimul.xls

Tags: depressurization, psv, rating, vessel

Categories

Safety And Environment , Oil And Gas Production , Oil And Gas Process , Petrochemical , Engineering Codes, Standards & Certifications

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, these values of temperature and pressure can be compared with the MAWP and MAWT and decide if a depressuring system is required.
The basis of the procedure is the flash operation at specified volume and pressure.

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 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

Tags: depressurization, psv, rating, vessel

Categories

Safety And Environment

for additional information see this thread
'http://www.egpet.net/vb/threads/27092-Excel-library-for-process-calc-s-including-distillation'

Prode Properties allows to size / rate a PSV for critical or two-phase flows with different models including HEM (Homogeneous Equilibrium Model)
The HEM model for the nozzle applied in Prode Properties solves

hin+1/2*vin^2 = ho+1/2*vo^2

(in = inlet, o = orifice)
where vo (for a critical flow) is the speed of sound
ho, vo calculated at vena contracta conditions

this model works well for critical and two-phase flows,
it is also applicable for subcritical flows within certain limits.
For subcritical flows Prode calculates the area solving a constant energy operation but since usually for a nozzle we do not specify the internal area of pipe (which is required for calculating vin in above formula the procedure estimates the value, this may generate errors when the rate vo/vin is low.
For such cases it is suggested to use as alternative to ISPF() the method EPF

double t = EPF(integer stream, double p, double E, double aout, double et)

this method allows to specify both inlet and outlet condition thus modeling a adiabatic, irreversible expansions when the contribute of kinetic energy cannot be neglected.

Tags: hem, nozzle, psv, safety, sizing

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Uncategorized

I have found several papers discussing this topic, one is "Improved control valve sizing for multiphase flow" from Hydrocarbon Processing March 200, the authors say "HNE-DS method basically assumes that the flow pattern in the control valve is homogeneous but gas and liquid are not in equilibrium – a non-equilibrium factor N represents the boiling delay"
your comment agrees with this statement.
By the way I found also an interesting thread comparing API PSV formulation for gas flow here

'http://www.cheresources.com/invision/topic/16104-psv-discharging-temperature'

the author has provided a Excel page to compare different procedures

Discharging temperature (PSV outlet)
1) calculated with isentropic + adiabatic flash (the default in nozzle.xls)
2) calculated with adiabatic flash
3) calculated with isentropic flash

Calculated Area
1) rigorous numerical solution of isentropic nozzle
2) API formulation for gas and vapors, ideal cp/cv
3) API formulation for gas and vapors, real cp/cv
4) API formulation for gas and vapors, real cp/cv, Zv = 1

all the required properties are calculated by Prode library , for personal/academic use you can download a free -with limited number of components- copy from 'www.prode.com'

I recommend to read this thread to everyone interested in PSV sizing.
psvcompare1.xls

Tags: flow, gas, hem, liquid, psv

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Uncategorized

cbadia wrote
for a two phase discharge I am sizing a relief valve with the isentropic Nozzle unit available in Prode Properties,
the procedure allows to specificy the HEM (Homogeneous Equilibrium Model) and NHNE (Non-Homogeneous Non-Equilibrium Model) for isentropic flow.
While the HEM model gives results consistent with those calculated by Excel page nozzle.xls distributed with the program the NHNE model requires specific settings and may give results quite different.
Which is the best option (HEM or NHNE) for modeling a PSV discahrge ?

I think it depends from several factors as for example the size of the valve and the physical properties of the fluid,
my version of Prode Properties has three models
HEM (Homogeneous Equilibrium Model)
HNE-DS (Homogeneous Non Equilibrium, simplified model)
NHNE Non Homogeneous Non Equilibrium)
the last two require a specific parameter which for HNE-DS is available in several papers while for NHNE you have to estimate the value, generally I select HEM and I do a test with HNE-DS

Tags: hem, hne-ds, psv, two-phase

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Uncategorized