5 replies to this topic

[hysyshunter]

Hi, 

 

I've done a preliminary design of a distillation column and now im trying to find the diameter, however all the equations to calculate this involves a vapour flow rate. But the problem is i only have glycerol in the bottoms at 225C, so it would still be a liquid and the distillate (Propylene Glycol) is at 134C, so i have no vapour in my distillation column. 

 

So i was wondering if there was a way to calculate the diameter with these conditions, or would i have to make an educated guess and adjust based on the type of packing and my pressure drop?

 

Anything would help

 

Thanks

Edited by hysyshunter, 07 March 2024 - 11:41 AM.

[breizh]

Hi,

"i have no vapor in my distillation column." weird.

Please explain your process. I've the feeling that distillation process is not understood.

https://patents.goog.../EP2540692A2/en

https://www.chemengg...ter-estimation/

 

Underneath a e book about separation process.

https://escholarship...96n0xv#page-489

 

Breizh 

[Pilesar]

The vapor rate for sizing distillation columns is the internal vapor. Even though you have liquid products at top and bottom, there will be internal traffic which may have very different flowrates than the products. The reflux stream adds liquid to the column and the reboiler adds vapor. In general, there is a trade between the number of column stages and the amount of internal traffic required to get the same product qualities. Optimization involves determining a reasonable compromise between reflux rate and number of stages. The vapor traffic will vary inside the column. Usually the column diameter is determined by the vapor just above the reboiler if the feed stream is liquid. Liquid traffic sometimes affects diameter also. Size the bottom of the column with your equations and then size the top of the column. If the calculated diameters are close, then it is usually cheaper to make the column one diameter all the way from top to bottom.

[hysyshunter]

The vapor rate for sizing distillation columns is the internal vapor. Even though you have liquid products at top and bottom, there will be internal traffic which may have very different flowrates than the products. The reflux stream adds liquid to the column and the reboiler adds vapor. In general, there is a trade between the number of column stages and the amount of internal traffic required to get the same product qualities. Optimization involves determining a reasonable compromise between reflux rate and number of stages. The vapor traffic will vary inside the column. Usually the column diameter is determined by the vapor just above the reboiler if the feed stream is liquid. Liquid traffic sometimes affects diameter also. Size the bottom of the column with your equations and then size the top of the column. If the calculated diameters are close, then it is usually cheaper to make the column one diameter all the way from top to bottom.

Thanks, would this vapour at either side be comprised of the top and bottom products at the condensor and reboiler respectively, because i've used hysys and it's told me my net vapour and my net liquid at each stage including the condensor and reboiler, but im not sure on what the densities would be

[hysyshunter]

Hi,

"i have no vapor in my distillation column." weird.

Please explain your process. I've the feeling that distillation process is not understood.

https://patents.goog.../EP2540692A2/en

https://www.chemengg...ter-estimation/

 

Underneath a e book about separation process.

https://escholarship...96n0xv#page-489

 

Breizh 

Thanks this has helped a lot

[Pilesar]

There are lots of details in column design. I suspect you just want diameter and height for your student project. Look further into your Hysys calculations and you should be able to get the software to show detailed profile properties in the column including temperatures, pressures, compositions, flowrates and densities for vapor and liquid at each stage. There is likely a way to get the software to size the column diameter also with just a simple user parameter requesting that! If you cannot find a knowledgeable Hysys user in person, there are probably internet videos showing column sizing with Hysys.