Reflux Vessel Question

[zamakaze]

In a typical fractionation column with a total condenser, does the liquid going to the reflux drum remain fully in the saturated liquid phase? Is any vapor formed in the reflux drum? Is the reflux drum usually just an accumulator or does it also act as a separator? If the reflux drum has a boot, does this mean there's another liquid phase, making it a three-phase separator?

 

[Latexman]

Besides the equipment, it also depends heavily on the process (components, concentrations, temperature, pressure, etc.) and operation inside the equipment. Not enough detail.

Good Luck,
Latexman

 

[LittleInch]

As shown all mass entering the drum as a liquid exits the drum as a liquid via only one line. How this liquid reacts and separates in the drum is not clear or relevant.

But there will be a lot more to it than shown

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

This sketch is only a PFD type arrangement. The full details would be seen on the PID.

a)does the liquid going to the reflux drum remain fully in the saturated liquid phase?
Often, the liquid going to the reflux drum is slightly subcooled for a total condensor application. This is the only way one can be sure the overhead vapor stream is completely condensed. Some portion of the reflux condensor HX tubes are fully submerged in the condensed liquid to enable this subcooling and process controls will be in place for this

b) Is any vapor formed in the reflux drum?
No additional vapor is formed. But there is often a hot vapor vapor bypass around the reflux condensor leading into the reflux drum to enable pressure control. This is necessary to prevent the reflux drum pressure from going too low since liquid here is partly subcooled. See PID for full details - often a dPIC controller performs this function

c)Is the reflux drum usually just an accumulator or does it also act as a separator?
Since vapor flow into the drum has only a small flow of hot bypass vapor going to it, it acts more as an accumulator than a separator

d)If the reflux drum has a boot, does this mean there's another liquid phase, making it a three-phase separator?
That is usually the case. To be sure, see the PID.

 

[pierreick]

HI,
To add to George's reply consider reading the document attached.
Good luck
Pierre

 

[georgeverghese]

Further to response to (b), pls note it is preferable to enable a small purge to flare or LP fuel gas( or similar) at the condensor vapor space for total condensors, usually by manually loading a field control valve by HIC at DCS, or by FIC-FCV - this is to avoid buildup of non condensibles (even if the feed composition doesnt show any) in the vapor space of the HX.
As you can see from @pierre's link to the Kister article, there are many variations to process controls for ovhd total condensors, and there are some more not described in this link.