Distillation Tower Flooding 1

[Falcon03]

Hello there,

What are the symptoms (sign) of distillation tower flooding (such as Crude tower) beside the DP cell indication? And

How we can tell that the tower is flooded if we have suspected DP indication?

 

[gregq8]

Flooding = accumulation of liquid within the column.
If liquid accumulation occurs below the feed you could observe erratic level in the column sump. If liquid accumulation occurs near top of column, you may see erratic level in reflux drum. A further symptom of flooding is poor separation due to poor vapor/liquid contact. Depending on how many of the trays are flooded, you may be able to see that the temperature profile is flat in the region where flooding has occured. Consider also the value of the total column pressure drop. Typical tray DP's are 0.7 to 1 kPa/tray. If average tray DP is much higher than this it would also be indicative of tray flooding.

A good check to see if your column DP is faulty or if the problem is flooding would be to back-off on column loads to see if DP behaves better at lower loads. DP should increase proportionately with loads and at flood point there should be a sudden sharp increase in gradient.

Flooding could also be liquid or vapor sensitive. There are tests you can perform to determine which it is and also what the flooding mechanism is (i.e. downcomer backup flooding / downcomer choke flooding / jet flooding). For more on these techniques refer to "Distillation Operation" by H.Z. Kister.

Lastly, you could take column hydraulic data from steady state column simulation and ask a reputable tray vendor to rate the column internals.

Hope this helps..

Greg

 

[July]

I agree with Greg. You will see poor separation in the flooded sections as well as minimal temperature differences.

 

[mur]

First check your DP indication
Best method I have found is to use two seperate (Independent) pressure transmitters & do the DP calulation via a moore card in your DCS.
Your are basically going to have to do a set of trials to map a pressure profile of your tower.(ensure the readings are taken directly off the tower at sample connections etc and not at a common header at the base of the tower)This chould give you a "magic number" the operators can keep the DP below. (also give them a simple mass balance spreadsheet)

 

[eyadamk]

b4 flooding level rises ... as level rises ... as level increased (if the distillation tower has a side draw-off's) the properties of draw-off's differs (if petroleum industry the collours become darkers @the upper trays) & down trays become colder...
the main indication for level increasing is the increase of pressure.

by the way under any adoubt of flooding watch:
1-High levels of bottom..
2-Pressure increase of the collumn.
3-Temp.'s of trays become colder.

 

[DMcMahan]

All points well made. Another thing you could do...there are many companies out there that can perform external scans over the length of your column. They can map out tray by tray characteristics over the column.

 

[scanguy]

DMcMahan is right, this service can and will fast and accurately pinpoint flooding as well as many other process related problems and internal damage. check it ouit here for more info.

http://www.towerscan.com

maybe we can help.