Reflux Condensation 2

[luke7203]

For tubeside reflux condensation, do you typically have multiple tubeside nozzles (i.e. a vapor inlet and a liquid drain) or is the same nozzle typically used for inlet and outlet?

 

[Montemayor]

Luke:

What do you mean by "multiple tubeside nozzles"? Please describe the type of condenser you are referring to by stipulating the TEMA letter descriptions and the orientation (i.e., vertical or horizontal?). I assume you mean a shell-and-tube type of construction and one-pass in the tubeside. We need an intelligent description to give an intelligent and helpful response.

Otherwise, everyone who responds has a different idea of what you are referring to. It doesn't cost you anything to be specific and detailed in describing your problem or question in something more descriptive than one sentance; the quality of the responses are proportionately related to the quality of the query.

Art Montemayor
Spring, TX

 

[luke7203]

I am refering to a vertical tubeside reflux condenser, where the vapor enters at the bottom and flows up. As the vapor condenses, the condensate flows back down inside the tubes and back out the header.

I am trying to determine if this is arrangement typically has one tubeside nozzle on the bottom head that serves both as the entrance for the vapor and the exit for the condensate or if having two nozzles is more typical.

 

[25362]

These are sometimes called dephlegmators and are frequently mounted directly above a boiling vessel. Flooding imposes a limit in their design, thus most vertical units use downflow condensation. Ludwig's Applied process design to chemical and petrochemical plants, Volume 3, deals with this subject under the heading "Condensation Inside Tubes".

 

[Montemayor]

Luke:

Thanks for the additional information. The reason I asked for the basic data is that there are differenct uses for a "reflux" - which you are probably aware of:

1. A total reflux condenser on a reactor;
2. A partial condenser on a distillation column;
3. A Sub-cooling condenser on a distillation column;
4. A saturated reflux condenser on a distillation column.

You haven't stated the TEMA type, so I'll assume its a variation of the BEM - one end without a bonnet and mounted directly on a reactor to serve as a total reflux condenser.

You can also mount the vertical unit externally and on top of the reactor, complete with a bottom bonnet. However the vapor nozzle from the reactor has to penetrate the bottom nozzle directly upwards and have a "chinese hat" on it internally within the bottom bonnet. The total condensed product is collected around the vapor nozzle and removed through another, smaller nozzle in the bottom bonnet. As you can visualize, the bottom bonnet has to be customized and designed to serve as a vapor distributor into the bottom of the vertical tubes and also as a liquid container and reservoir for the produced condensate. A level controller or a "goose-neck" liquid seal can be employed to effect the necessary condensate seal.

Note that it is very difficult to obtain a defined and calculated degree of sub-cooling in this mechanical arrangement. The product reflux may be slightly sub-cooled, but I always calculate on the basis of it being saturated.

As 25362 states, you can easily flood the vertical tubes if you don't design and control the vapor rate accordingly - for a given number of tubes and diameter. There are usually definite reasons for using this condenser configuration because it entails several trade-offs: the flooding problem(s), the head room requirement, the structural vertical requirements, the piping and nozzle design, etc. The main (& sole) reason I have used this orientation is to have the process vapor in the tubes and available for easy cleaning ("rodding") and rapid evacuation of gases or non-condensables. Otherwise, I normally would opt for a conventional horizontal configuration with the process vapor on the shell side - with very clean, clear fluids such as THF, CCl4, Acetone, etc.

I believe this responds to your original question and points out the many variations and problems that accompany the assumptions taken.

Art Montemayor
Spring, TX

 

[25362]

From my long-ago-student-days I recall the use of the traditional vertical glass Liebig (19th century?) condenser in laboratory bench work.
I think such, and variations thereof, are still used in pilot plants batch distillations as total reflux condensers until "equilibrium" is reached prior to withdrawal of distillates.
On continuous operations, they are probably used much more in the chemical industry than in petroleum refineries.

 

[luke7203]

Thank you very much for your comments. They are greatly appreciated.