5 replies to this topic

[PooM]

I am currently using ASPEN to model distillation columns to separate acetone, butanol, ethanol, and water. I'm moving about 93,000 gallons of ABE and water (bulk of it being water).
Right now with this flow rate my first column will be around 60 ft with a diameter of 17 ft. I assumed a superficial velocity of 2 ft/s through my column to calculate the diameter with a known volume metric flow rate of the vapor through the column. As of right now this would be a sieve tray column.

I have found plenty of heuristics stating the diameter of a tray column should be at least three feet. However I have not found any upper limits. I have read that the trays are more efficient as the diameter increases due to cross flow, but nothing that suggests any downfalls of having a column with a large diameter. Could anyone point me to a good source where I can found how to determine a reasonable upper limit to the diameter of a distillation column?

Thanks

[omarax]

Hi PooM
I can recommend this book : coulson & richardson's chemical engineering design Vol. 6.

To be specific it is chapter 11

[Art Montemayor]

Poo:

I’m afraid yours is yet another example of ChE students armed with powerful simulation programs that can calculate the most complex of problems, but without any idea of the BASICS of Chemical Engineering and the necessary fundamentals that go into the algorithms that solve the problem.

The Mott Souders – George Granger Brown relationship for determining the diameter of a distillation column has been around a very long time and is found in ALL respectable and recognized Unit Operations textbooks (M. Souders and G. G. Brown (1934). “Design of Fractionating Columns, Entrainment and Capacity”. Industrial & Engineering Chemistry, 38 (1): pages 98–103). It is also used extensively to determine the diameter of vapor-liquid separation vessels. Read and study:

http://en.wikipedia....-Brown_equation

and,

http://www.cbu.edu/~rprice/lectures/distill7.html#diam

If you are located in the USA, you should have already been taught this in your Unit Operations lectures or in your text books. No Chemical Engineering student is exempt from this relationship. If you want more discussion and references, simply use the Search Feature in our Forums with the key word and you will find numerous threads showing you how this equation is used to determine the diameter of vessels. If you are smart and want to be a Chemical Engineer, you would be wise to follow this advice.

Right now, you are, analogously, using a Caterpillar front-end loader to fill a flower pot with garden soil - when all you need is a spoon. Computers are not solutions. They are merely sophisticated and expensive TOOLS. If you don’t know how to use a tool, you hurt yourself.

[UNMESH BISWAS]

Mr Art,

You are definately a respected engineer, but surely not a good engineering professor.
The things you have said can be done in a different way also.

Regards

[katmar]

[Edit] I see that I have fallen into the same old trap of replying to an ancient thread that has been resurrected without first checking the date. The original poster is sure to never see my reply, but I will leave it here in case it can help some other person with a similar situation.


This is a very real problem, and if I think back to my student days it very often happened that even some of the lecturers did not have the industrial experience to give that sort of guidance. Once I started working I found a very good supplement to my theoretical knowledge was the library of supplier catalogs we had. The catalogs gave an excellent summary of what was actually available and what engineers really used.

Today's students have a huge advantage because all these catalogs are available on the internet for online viewing or downloading. If you search for "tray manufacturers" you will find references, product lists and photographs showing real-world applications. For example the summary catalog from Koch-Glitsch (probably the worlds largest tray manufacturer) lists standard trays up to 20 ft diameter, and from years of being out there I know that even larger columns exist. See http://www.koch-glit...y/FLEXITRAY.pdf

In your travels around the internet you will find some gems amongst the supplier catalogs and they are well worth bookmarking or even downloading and creating your own library.

Edited by katmar, 14 January 2012 - 01:36 AM.

[kkala]

1. Having no knowledge on the subject, it was useful to know that standard trays can have a diameter up to 6 m (post No 5).
2. Book "Unit Operations" by G G Brown (Willey, 1950), Chapter 24 - Design and control of Fractionating Columns, has a typo on formula (283) of allowable superficial mass velocity of vapor (G). Correct formula is G=C*sqrt((ρl - ρv)/ρv), where ρl, ρv = liquid or vapor density, C=parameter depending on liquid surface tension and tray spacing. This was traced due to post No 3.
3. The "different way" should have been specifically shown in post No 4. General allegations had better be avoided, and at any case broadly documented.

Edited by kkala, 14 January 2012 - 05:19 AM.