6 replies to this topic

[mubarak56]

why does distilation column have different diameter at stripping and rectification section????

why density of binary mixtures increases as the temperature increases in distilation column from top to bottom???

what shuold be the numerical ranges of vapor velocities in distilation column???

Edited by mubarak56, 18 May 2013 - 01:12 PM.

[Raj Mehta]

Read RC-6 and Henry kister. This are basic questions and you will find your answers easily, provided you read carefully.

 

Happy reading. 

[USR]

The reason for different diameters at the stripping and rectification sections are due to the different vapour loads in the sections. Rectifying section has smaller diameter than the stripping section because there is more vapour load in the stripping section than the rectifying section. To have sufficient vapour velocity in the rectifying section the column diameter is kept small so that one doesn't face the problem of weeping at low vapour velocity.

[mubarak56]

i am designing a distilation column for sparation of etanol and water.

my stripping section diameter is smaller than the rectification section which is totally opposite to what you stated so what do you suggest????

[breizh]

Mubarak ,

 

let you consider this resource , among all the data available on internet .

 

http://www.separatio...om/Mainmenu.htm

 

 

 

Breizh

[Raj Mehta]

Follow RC-6, as i previously mentioned. It has solved numericals wherein both the diameters of column top & bottom are calculated, you can check it yourself. It is true that the top dia will be more than bottom dia of the column due to high vapor load at the top. But the difference won't be significant one and usually is not even considered differently while designing. The column bottom dia is taken same as the top dia. 

[katmar]

As stated by others, the vapour and liquid loads vary with height in a distillation column.  The relative sizes of the stripping and rectifying sections will mainly depend on the condition of your feed.  A sub-cooled feed will condense vapours coming up the stripping section, resulting in less vapour in the rectifying section. On the other hand, a super heated vapour feed will result in higher vapour traffic in the rectifying section.

 

The densities are often more a function of composition than temperature.  In your ethanol-water separation the liquid will be more dense at the bottom because it will have a higher fraction of water.  The vapour will be more dense at the top because of the higher molecular mass of ethanol.

 

The superficial vapour velocity is typically in the range of 0.5 to maybe 1.2 m/s, but you should not design on this basis.  The design must be based on a detailed analysis of the tray pressure drop, the downcomer residence time and other parameters.