3 replies to this topic

[LSUgolfer23]

I am trying trouble shoot an issue with a C5 splitter.   Specifically, high temperature of the liquid leaving the reflux drum.

 

The attached drawing shows the installed control scheme. 

 

1.  The site previously used a liquid full reflux drum controlling column pressure by varying the distillate rate.  The overhead system was converted to the schematic shown in the drawing by adding the pressure control valve between the condenser and the reflux drum and adding the equalization line.

 

2.  The condenser is a total condenser and subcools the overhead vapor to ~10F above ambient temperature.

 

3.  The reflux drum is getting quite hot.  The liquid product leaving is close 130F.  My understanding is that this temperature should exceed the condenser outlet temperature by no more than 2-3F.  

 

4.  There is a lot of "banging" occuring in the reflux drum.  I assume this to be shock condensation.

 

5.  The overhead line is 6".  The equalization line is 2".  The equalization line itself is only about 10ft long and ties into the vapor space on the drum.  The equalization line take off from the overhead line is approximately 1/3 of the way down the line running to the condenser.  

 

6.  I don't have drawings of the reflux drum internals.  I have seen pictures taken by inspectors and it appears the feed pipe has a down leg that

goes to the bottom of the drum (i.e., I don't believe there is subcooled liquid contacting the vapor space).  

 

7.  The boiling range of the overhead product is pretty tight (around 1F).

 

Any thoughts / ideas?

 

 

 

 

Attached Files

•  OH CONTROL SCHEME.pdf   154.94KB   22 downloads

[Bobby Strain]

What are the controls at the tower bottom, including reboiler duty? And can you provide a drawing of the column sump, reboiler, and reboil return arrangement? You might have introduced some instability when you changed the control scheme. It's possible that the problem is created by instability in the tower bottom operation. And you won't be able to detect the cause. Vapor condensation in the reflux drum is probably pretty steady. You might want to share operating data for flows; feed, bottoms, overhead, reflux, and reboil.

 

Why was the control modified? You might also explain the operation of the column overhead pressure controller and the one on the reflux drum. What happens when you vary the reflux drum level? Change fan speed/pitch? Troubleshooting takes lots of data. Colum sump drawings can rule out some things. Along with flow data.

 

Bobby

Edited by Bobby Strain, 28 June 2021 - 10:13 PM.

[Pilesar]

The equalization line should keep the reflux drum pressure equal to column overhead line pressure. Do the pressure controllers on the overhead and on the reflux drum fight each other? I would watch the reflux drum pressure in real time to see if there is much swing that might be masked in a historian.

[Bobby Strain]

So, did you fix it? We expect feedback.

 

Bobby