32 replies to this topic

[PaoloPemi]

mdepeche,
the methods are described in these papers
Darby, Self, Edwards, "Properly Size Pressure-Relief Valves for Two-Phase Flow", Chemical Engineering, 2002
Leung, "Easily Size Relief Devices and Piping for Two-Phase Flow", Chemical Engineering Progress, 1996
both (the numerical integration included in nozzle.xls and Leung Omega) are based on HEM (homogeneous Equilibrium Model) where vapor and liquid have equal velocities (no slip), Leung Omega is an attempt to define a simplified model capable to represent both equilibria and internal energy, it works fine in many cases.
The numerical integration is more reliable, it is applicable to both vapors and liquids (two-phase) but it takes a lot of time to solve all the flash operations...
You may solve the HEM model in a different way, Prode Properties has a specific function ISPF() to model nozzles (relief valves), ISPF() offers the option to choose HEM, HNE-DS and HNE-NH (?) , Prode adopts specific procedures which take less time yet giving (in the case of HEM) results more accurate than nozzle.xls.
i

[PaoloPemi]

mdepeche,
recently I have read "Case Studies of Sizing Pressure Relief Valves for Two-Phase Flow" authors Schmidt & Egan
but I am sure a search with google will return many documents discussing this topic ...

[Bobby Strain]

You might want to consult with your relief valve supplier. If you size it yourself, you might be taking on a lot of liability for your employer. But, you also want to be sure that it is done to acceptable standards.

Bobby

[deltaChe]

Could anyone please kindly help to explain how to use Aspen Plus to calculate the PSV relief load fire case @ supercritcal pressure, such as relief load with time ?
And how to calucated the enthalpy, relief rate at different temperature and different time ?

Thank you very much.

[PaoloPemi]

deltaChe,
I am afraid I am not familiar with Aspen Plus, perhaps you may find the answer in the operating manual of your software or open a specific thread,
I can only say that the simulation of a fire case should not be too difficult with a simulator,
I do that with Prode Properties (which has specific methods to model a blow down or a fire case) but these procedures are available in almost all process simulators,
of course if you have data we can compare the results (which could be of interest for the readers)

Edited by PaoloPemi, 07 October 2012 - 09:57 AM.