7 replies to this topic

[Clau]

Hello engineers,

 

I hope someone can help me.

I was wondering how to check weeping in columns with valve trays. The calculations proposed in Coulson&Richarson  text book volume 6 4th ed, refers to sieve trays and I don't know if it's correct to apply them in my case.

 

As a first trial, I follow this comparison ( 2x Dry Tray Pressure Drop > Tray Pressure Drop).

 

Thansk for your help in advance....
 

Clau

[PingPong]

Valve trays weep less than sieve trays. That is the whole point of having valves.

 

Why would you want to waste your time trying to estimate weeping of valve trays? Probably even the vendor is not able to accurately estimate that.

[PingPong]

It is not feasible to estimate the amount of weeping, but vendor software (Sulzer, Koch-Glitsch) will warn you if the vapor load is too low for your given amount of valves and tray type.

 

The good old Glitsch Ballast Tray Design Manual gives the minimum required vapor load, expressed as V_H._√(D_v/D_L) for standard valves of type V-1 as function of liquid level on the tray (including crest over outlet weir):

 

Liquid       V_H ._√(D_v/D_L) 

Level

 

1                   0.35

1.5                0.45

2                   0.53

2.5                0.59

3                   0.69

3.5                0.75

4                   0.82

 

V_H is vapor velocity in valve hole, feet/sec

D_v and D_L are vapor and liquid density respectively

Liquid level is in inch

 

Glitsch is now part of Koch-Glitsch and Ballast type V-1 valve trays are nowadays called Flexitray type A

[Clau]

Thank you very much for your valuable and prompt response.

 

For sure, you are right that the vendor will "ensure" that point. But just to have an alarm about the design.

[Chemical Ag2O]

I believe that you can use a correlation that Norm Liebermen developed empirically which is defined as follows:

K = 28*dP / (TS*NT*SG)

where dP = pressure drop in psi
TS = tray spacing in inches
NT = number of trays
SG = specific gravity of the flowing liquid on the trays at temperature

If the K value is less than 0.15 then the trays are weeping. The trays best efficiency point has a K valve in the range of 0.18-0.25

[Chemical Ag2O]

PingPong,

I'm not sure about your statement. If you read some of the work that FRI has published - I believe that they found that valve trays weep almost as bad as sieve trays at low turndowns.

[Zubair Exclaim]

It is still better to use tray sizing softwares from vendor such as sulcol or KG tower....  there correlations are more accurate

 

 

Chemical Ag2OValve trays should give you less weeping ... they do so by closing down ... however there may be leakages since these valve are simply discs of metal resting over metal without any sealing mechanism, but that should be a concern with a very low turn down  ... however they still have a fairly better trun down capability as compared to conventional sieve tray ...

[Ajay S. Satpute]

 

Chemical Ag2O:

 

If the K value is less than 0.15 then the trays are weeping. The trays best efficiency point has a K valve in the range of 0.18-0.25

Hi,

 

Isn't Norman Lieberman equation for checking the tray flooding?

 

My 1996 copy states;

 

K = 0.18 to 0.25: tray op. close to its BEP

K = 0.35 to 0.40: tray suffering from entrainment

K => 0.5: tray is in fully developed flood

K = 0.10 to 0.12: tray deck leaking

K = 0.00: Liquid level on the tray is zero

 

 

 

Regards.

 

Ajay S. Satpute