how to size a kettle reboiler 1

[EngineeringPS]

How do you size a kettle reboiler? The reboiler will have a fire tube as the heating medium, and is intended to boil dirty ethylene glycol and water. The EG-water as the tops, and waste as the bottoms.

Thanks

 

[Montemayor]

I have to presume you're a ChE and when you say "size", you mean process design - not mechanical design.

If you are going to use a direct-fired reboiler (I assume you'll burn natural gas) then it would depend if you're doing this for a client, for your own company, or for yourself. When "sizing" the fire tube - which is all you are really going to have to do - use only an empirical heat flux value as your sizing tool. If you are doing it for a client and for max profit, use 10,000 Btu/hr-ft²; if you're doing it for your company, use 8,000 Btu/hr-ft²; and if you're doing it for yourself, use 6,000 Btu/hr-ft².

Bear in mind that you said "dirty" glycol solution, & you alone know how dirty it can get. Therefore, use the appropriate contingency amount of extra surface to allow for fouling.

There are a lot of other items that you must take into consideration if you're to succeed with a good design. But you haven't furnished specific, detailed basic data so that's all I can contribute.

 

[EngineeringPS]

Yes, I'm looking to determine the size (length, dimensions) of the fire tube and the vessel itself. I would like to have a horizontal vessel, with the firetube at the bottom. A sufficient glycol level will have to cover the firetube during operation, so that the feed (dirty EG/water) vapourizes when it enters the vessel (assuming the liquid glycol holdup is at a temperature and pressure to allow for that).

I wish to operate the drum at 21" Hg, and about 285F. I have determined that this will allow the dirty stuff (iron, phosphates, silica, ashphaltenes, dissolved solids, @ 3-5% of feed rate (1USGPM)) to get knocked out, and just the water and glycol to vapourize.

The firetube will use combusted propane that will be forced through the tube. I was thinking a U-shaped firetube (like a 2 pass) would allow sufficient heat transfer to the fluid (i've calculated about 530000 Btu/h required to vaporize 1USGPM) but this I have yet to determine.

What I'm interested in is how to determine the size of the horizontal drum, and the size of the firetube.

Thanks.

 

[Montemayor]

I believe I responded to all your needs when I gave you the empirical flux rates that everyone uses in this type of application. Once you have (or assume) the acceptable flux, the rest falls like a set of dominoes.

Knowing the heating duty, you can calculate the total area required using the flux.

With the total area and knowing the size of burner & flame, you know the size & length of pipe you require to fabricate the Fire Tube.

Knowing the size and length of Fire Tube and the height of solution you should keep above it, you can easily derive the size of heater shell & weir that you require to maintain the Fire Tube totally submerged and a reasonable level on the outlet side of the weir.

What you are proposing is old stuff. This design has been around so long that I designed and fabricated my first one over 40 years ago - and it was old technolgy then!

Good luck.

 

[Monagas]

Begin your estimations with the information provided by Mr.Montemayor.

The rest of the work and research you can do it by yourself as a good ChE engineer .

Have you ever seen the ASME VIII code, for mechanical design of shell-and-tube heat exchangers?

http://www.edata-center.com/books/bookindex/hedh.html

All the best from venezuela