Columns with two diameters

[thalathb]

Hi every body,

Regarding the distilation cloumns, Why most of the demethanser and Deethanizer has two diameters, for exampel the de-ethanizer has bigger diameter at the bottom and smaller one at the top, vise versa for De-c1.

Thanks and regards

 

[TD2K]

Vapor and liquid traffic are significantly different in the top and bottom of those towers.

 

[katmar]

Consider a simple column with a single feed, and take-off streams only at the very top and bottom. If you feed with a cold liquid near the middle then there will be much more liquid (and vapor) traffic in the lower part of the column. On the other hand, if you feed a vapor then the top part of the column will have a higher vapor traffic than does the bottom part.

If you complicate the issue with multiple feeds and take-offs then the analysis becomes more complicated but the principle is the same.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[JLSeagull]

The wider diameter at the top often applies to a demethanizer in natural gas where the composition is mostly methane. Even in such cases some contractors would provide the demethanizer with one diameter (sized for the methane and oversized for the liquids) because it is cheaper to build.

 

[786392]

It's witnessed for many distillation tower designs employed in industry that where ever liquid/vapor loads vary (or as mentioned above traffic varies) either Due to some streams

1)drawn off from and/or

2)reboiled& fed back into.

the main distillation column thus the requirement of mass transfer intimate contact surface area greatly varies; and consequently the column diameters.



Best Regards
Qalander(Chem)

 

[dcasto]

straight and to the point, with out the proper diameter, the tower would flood or weep and you would not have (almost) equalibrium and therfore no seperation.

The amount of vapour above the feed or the top of a mixed NGL liquids stream de-ethanizer is small. In a gas plant where ther is only a de-ethanizer, the amount of methane and etahne vapours above the feed is very high.