Installing an Equalization Line on a Condenser (with no vapor bypassing)

[will3496]

Hello,

My facility has a condenser and a reflux drum off the top of a distillation tower. The reflux drum has two outlets.

1. A vapor sent forward to a waste line and
2. A liquid that is returned to the tower as reflux.

The product that we condense in this exchanger condenses at temperatures above ambient. We get complaints if we send any liquid into the vapor waste line.

We are having issues right now because the condenser and reflux drum do not have an equalization line. We will sometimes pull a greater vacuum in the condenser than in the reflux drum. The reflux drum then begins to back up and eventually liquid covers the vent nozzles and we end up getting liquid in the waste line.

One proposed solution is to add an equalization line between the two pieces of equipment but are concerned that if any vapor product that bypasses the condenser it will enter the waste line as a vapor and then eventually condense due to heat loss in the line.

Is there any way to pressure equalize a condenser and a reflux drum without having hot product bypass?

Appreciate the help.

 

[georgeverghese]

One way is to include a differential pressure control valve (and dPIC) on the hot gas bypass line. Set the dPIC for a small differential such that liquid from the reflux drum cannot backup enough to get back into the condensor.
Sometimes, the problem with this hot gas bypass is a lot of vapor bypasses to maintain this differential. The reason for this is that the feed into the reflux drum terminates in the vapor space of the drum and does not dip into the liquid. Hence, the hot gas bypass stream chills down quickly in the vapor space. So check that the liquid line from the condensor dips well down into the liquid space of the reflux drum also.

 

[will3496]

Hi George,

Thanks for the advice. Both the points you made seem really logical!

 

[georgeverghese]

Some details that will help to complete the picture on this current configuration are:

a) Is your condensor a partial condensor or does it condense the entire feedstream from the column overheads? Sounds like a total condensor from your narrative.
b) Do you have a liquid loop seal between the condensor and the reflux drum ?
c) Your narrative seems to indicate that you already have a hot vapor bypass line, which could be the only reason you have a higher pressure in the reflux drum than in the condensor, which then results in the reflux drum liquid backing up into the condensor ?