4 replies to this topic

[Chirag Prajapati]

I need to check whether one redudant column having dia 2.4m and having 60 valve trays with 600mm tray spacing can be used for existing 0.8m dia column having 26 trays with 450mm valve tray spacing.
As per perlimnary analysis i think it may lead to weeping due very low vapor velocity.
I wanted to know how to calculate minimum vapor velocity below which column should not be operated.

[Bobby Strain]

Download software from Koch-Glitsch. Or use one of the process simulators. It's quite unlikely that the larger column would function for the small one.

 

Bobby

[ahmadikh]

 Chirag,

 

As far as weeping is concerned, please note that vepour flowrate (a better term to evaluate rather than vapour velocity) is not the only parameter which determines whether weeping on a tray occurs or not. Actually, weeping is a result of excessive downward force from liquid on the tray which overcomes the force exerted by the vapour. As such, the other main parameter which results weeping is the liquid static head on the tray. Also, remember some specific design parameters such as the valve net rise (depends whether the valve is fixed type or not), valve slot area and valve density (other term to express number of valves on a tray) have an impact on weeping. You can try the available free of charge software such as the one for K-G, but in order to certainly determine whether weeping occurs or not, you have to consult the internal/tray vendor and ask them to check or provide you the tray performance diagram which gives you the operability range of your tray.

 

Also, remember that each tray vendor offers various types of valve trays with different designs. If you want to check the vapour velocity you can use the formulas given in H. Kister's book, but you won't be able to find specific and independent threshold for the minimum vapour velocity above which tray operates perfectly.

 

Hope this helps.

 

Best,

Milad

Edited by ahmadikh, 29 January 2015 - 03:29 PM.

[rahulavyas]

The better thing will be to simulate the column with given feed conditions and desired product specifications. you can use simulation softwares like "ASPEN" or "HYSIS".

[Chirag Prajapati]

Thanks to all for reply.