Control valve vibration

[pomeranz]

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?

Thanks!

 

[mk3223]

IMO, the Process needs to confirm these design parameters, including the vapor pressure value (in psia), for the control valve, and then contact the valve vendor to verify the valve sizing for proper velocity flow and noise level, etc.

 

[georgeverghese]

Vapor pressure input is correct.
What do you understand by cavitation coeff of 1.0?
Also check input for exit pressure, currently stated to be 50psig, this sounds like it is the pressure at the rich amine flash drum inlet nozzle, and not at the CV exit? Also account for any elevation difference - line may be slugging also at low flow.

 

[marcsant]

if the valve works with a max 80% aperture probably it has the capacity to pass the required flow (at operating conditions),
in case of doubts, for two-phase flow (flashing liquid) there are specific (I mean adapted to control valves) models as HEM or HNE-DS (Diener and Schmidt) available in tools as Prode Properties or some valve sizing software.
About noise, vibrations etc. I would suggest that you consult the manufacturer,
they could propose different plug(s), piping, supports etc. in order to reduce vibrations and noise,
see IEC 60534-8-3 for a general discussion about these aspects,
see also the comment by georgeverghese, probably you can pass your data to the manufactureer for a review.

 

[hacksaw]

Check the piping layout, you may be dealing with slugging events.

 

[0707]

If your valve is close to an ellbow or any kind of restriction for sure it will be submitted to ultrasonic vibrations. The valve shall be in a horizontal place long way, 12 or more diameters minimum distance from any kind of restriction.

luis

 

[georgeverghese]

If flow is slugging in the 2 phase section, common practice is to locate the control valve as close as possible to the flash drum ( and not immediately downstream of the absorber)