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Control Valve Vibration

rich amine letdown valve

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#1 Pomeranz


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Posted 17 April 2020 - 03:01 PM

We are having a vibration problem in a rich amine let-down valve before the stripping tower.
Support problems were identified, at the same time the operating team questions the size of the control valve.
Following the design information that the operation team is using to size the valve with Emerson software:
Liquid:                                                                  Rich Amine
Inlet fluid density (Rho1):                                lb/ft3    66.3
Inlet Pressure (P1):                                            psig     59
Outlet Pressure (P2):                                        psig     50
Inlet Temperature (T1):                                  deg F   227.7
Volumetric Flow Rate Liquid (Ql):                ft3/m    128.6
Pressure Recovery Factor (Fl):                                        0.88
Valve style modifier (Fd):                                                  0.35
Cavitation coefficient (Kc):                                               1
Dynamic Viscosity (Mu):                                  cP        3.215
Vapor Pressure (Pv):                                        psig      58.99
Critical Pressure (Pc):                                      psig      3200.252
Atmospheric Pressure:                                  psi        14.69
Pipe Size Up:                                                      in            10
Pipe Schedule Up:                                                             STD
Pipe Size Down:                                                in            10
Pipe Schedule Down:                                                        STD
Nominal Valve Diameter (dv):                      in            10
Sizing Coefficient (Cv):                                                       456.906
% Open:                                                                              36
Application Ratio (Ar):                                                         1
What I question is the vapor pressure they are using.  Is hard to believe for me that the 8” valve (standard trim) is small, never operating at more than 80% open. I'm not sure that say the amine is in equilibrium at the valve inlet is Ok. I agree that “flashing / degassing” will take place in the valve, but not for the entire flow.
How we size this valve? Which vapor pressure should we use? How we take into account the flashing/degassing? Is better to consider a biphasic flow considering the gas fraction of the stream after the valve of the process simulation without considering the vapor pressure?  

#2 breizh


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Posted 17 April 2020 - 08:38 PM


You may find pointers in the document attached .

BTW why don't you contact the valve manufacturer or representative ?

Good luck


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