4 replies to this topic

[-G-]

Hello

I'm currently designing a continuous distillation column for the recovery of solvent from a mixture of acrylic acid and other components.
It will be operatuing under vacuum (13 kPa) with a feed vapour fraction of about 80%.
Based on this I decided a packed distillation column would be suited for this type of separation.

I'v gone through the procedures for calculating the column dimensions (Packed Colum Design, Cheresources / Coulson & Richardson volume 6) but I'm getting crazy dimensions. I'v come out with a column diameter of 58 meters and a height of 12.5.

I'v attached a diagram of this column and a snapshot of my spreadsheet, perhaps someone will spot what the problem is and lead me in the right direction.

 Solvent Recovery Column - Paint.JPG   24.66KB   104 downloads  column dimensions excel.JPG   201.77KB   147 downloads

Note: Area = mass vapour flow in rectifying section / V*w

I can't find anything wrong with my calculations so I'm guessing it's to do with my high flowrates?

This is my feed to the column

 feed.JPG   39.42KB   101 downloads

Regards

Greg

Edited by -G-, 03 March 2011 - 03:32 PM.

[katmar]

I really don't like blaming errors like this on mistakes in text books, especially ones that I respect as much as Coulson & Richardson. But I strongly suspect that the book is wrong. I have a copy of the 4th edition of Volume 6 with me here and it gives the same version of Equation 11.118 (page 604) that you have quoted here. I have a newer version in the other office, and I will check that when I get a chance.

This equation comes from the original work by Eckert, Leva etc and in their articles they never had a term like ( liquid viscosity / liquid density )^0.1

What (I think) some of them had was ( liquid viscosity / water viscosity )^0.1

If I remove the liquid density from the bracket with the 0.1 exponent then I get a diameter very similar to what my software gives. The diameter is still huge - about 16m and still impractical - but this is because of the low system pressure and low pressure drop specified.

[-G-]

Ah! I think you're onto something here. I used the version in C&R volume 6 (I have the 4th edition also) because it's all metric and it's what our department advises on using for design work such as this.

Anyway, I took a look at the example from cheresources (http://www.cheresour...packcolzz.shtml) and it takes the form that you described katmar. Here it is here:

 cheresources graph.JPG   84.64KB   15 downloads

Likewise, this gives me a diameter of around 16 meters

I think I'm leaning towards just dividing the feed up for several columns, maybe 2 or 3 to get a reasonable result.

Many thanks

Edited by -G-, 05 March 2011 - 08:29 AM.

[katmar]

I telephoned a colleague at the other office to check in the 5th edition of C&R Vol 6 and it has exactly the same equation. I wonder how many puzzled students and wrongly built columns this has resulted in? The terms inside the bracket must result in a dimensionless quantity, so I am sure it is wrong to have the liquid density in there.

[breizh]

Hi ,

Let you try this resource :

http://www.chemsof.c...ower_Sizing.xls


Breizh