3 replies to this topic

[Propacket]

Hi,
I am working on the design of a kettle type reboiler. I have calculated many design parameters like, shell dia, bundle dia, bundle length and liquid height etc. In order to determine the complete length of the reboiler, i need following information:
1) Length past the weir
2) Length of front head
I have consulted literature but it only gives length of bundle. Can anybody help me calculate these lengths?

[Art Montemayor]

P. Engr:

I have designed, built, and operated several kettle reboilers. All worked and functioned as designed.

The basic information required to mechanically design the kettle reboiler is the ultimate U-tube bundle physical dimensions. Once you have decided on this, you can fix the remaining reboiler shell characteristics. The remaining decisions are all mainly common, practical sense. For example, the answers to your questions are:

• The length past the over-flow weir is determined by how much residence time you require or need in that section of the reboiler. Sometimes you may want storage space there – for maintenance or temporary storage of solution. It depends on your needs, scope of work, or requirements. You also may have a liquid level height to consider if you have a minimum static head of liquid there.
• What I assume you mean by “Length of front head” is the straight length of the right frustum that joins the main, cylindrical body of the reboiler with the U-tube bundle flange connection. If that is what you mean, then that length depends on the angle that you give to the frustum section. Some reboiler designs do not incorporate a frustum; they use a conventional cylindrical nozzle welded into the bottom part of an ellipsoidal head or an F&D ASME head. In any event, the length that you allow for has to conform so that the total length of the U-tube bundle fits well within the reboiler and is allowed to expand without any problems once it reaches hot working conditions.

I hope this experience helps.

[Propacket]

Art,
Thanks for the reply.
1) For the length past the weir, I came to know that it is normally designed for residence time 2-3 mins. Further, I have following information:
Weir height= 56.25"
Liquid flow=2000 Usgpm
Can you recommend what method I should use to find the length?

[Art Montemayor]

Please read my first post carefully. I specifically stated that you design and size the reboiler according to what YOU REQUIRE OR NEED - not according to what "is normally designed". What I want to stress here is that you should abide by what the application is and what is required to bring about what you need. This is where common, practical sense comes into play. You may have a liquid level control on the downstream portion of the weir and because of this, you will require a nominal amount of liquid as a minimum reservoir. This is to account for the time that it takes your liquid flow out (presumably it is pumped out) in a reasonable manner. You probably require a minimum residence time based on the pump-out flow rate. A "normal design" will never account for this; you should apply your specifc pump-out rate and other specific application characteristics and needs.

That´s something I or anyone else on the Forum can´t predict or guess at. You are the best, indicated person to decide or calculate that.