5 replies to this topic

[Ryanfog1]

Hi,

 

I am completing my design project in my final year at University and have to design a node containing a vacuum distillation column. The column must operate under vacuum conditions as it requires the separation of FAEE (biodiesel) from minor components, and so the column's operating conditions must not go over ethyl oleate's degradation temperature of 275 degrees Celsius, whilst some of the other components boiling points are a lot higher than this. For reference, the stream includes ethyl oleate (72.5wt%), oleic acid (13.5 wt%), beta-sitosterol (9.2wt%), and triolein, diolein, and alpha-tocopherol in minor compositions.

 

I am following the design book by Sinnott and Towler and they state that one of the first decisions to be made is to define the operating conditions of the column. I have found an optimal range of 0.004 - 0.007 bar and 165 - 215 degrees Celsius from an online source, however I am unsure how they calculated this and it seems pretty vague. It appears as though they have calculated the boiling points of the different components at different pressures using the Clapeyron - Clausius equation however I am unsure of how they derived the optimal conditions from these figures. A friend of mine also stated that I need to use vapour pressures but could not explain further than this.

 

This is my first time designing a piece of equipment and I am pretty lost - any help with how to define operating conditions and any other tips for what I should be considering in the early stages of design of a vacuum distillation column would be much appreciated. 

Edited by Ryanfog1, 20 February 2021 - 09:38 AM.

[PingPong]

I have found an optimal range of 0.004 - 0.007 bar and 165 - 215 degrees Celsius from an online source

What is the url of that online source ?

[Pilesar]

The 'optimal range' you found is probably not correct for a plant application. Such a tight vacuum will be very difficult to maintain. I suggest you use the vacuum required to stay just below the maximum temperature. It will make plant easier to design and your project more feasible.

[latexman]

3-5 mm Hg! That’s going to be a big, expensive system!

[breizh]

https://www.research...l_Bio-Additives

 

HI,

I believe this is the paper the OP is referring to !

 

 

Breizh 

Edited by breizh, 20 February 2021 - 07:40 PM.

[SilverShaded]

You need to be able to calculate the vapour pressure of the light components (those you want in the overhead), use that to calculate the boiling point at low pressures, and have the heat sensitive components stay below the degradation temperature.  The vacuum should not go lower than is neccesary as it will increase capital costs (tower diameter, vaccum equipement etc).