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Liquid Levels In Distillation Columns

distillation column level hll nll lll

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#1 miguel29chem


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Posted 04 June 2017 - 10:45 AM



I am trying to set the operating levels for a distillation tower to design the control loops. Which criteria should I adopt to define the HLL, NLL and LLL of the tower?


Thank you.


#2 Bobby Strain

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Posted 04 June 2017 - 10:53 AM

Whatever your client requires.



#3 gegio1960


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Posted 04 June 2017 - 10:55 AM

which kind of distillation tower?

which kind of reboiler?

have you developed a preliminary sketch?

#4 miguel29chem


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Posted 04 June 2017 - 11:00 AM



There's no client, this is a project for college. We have already designed the tower with its diameter, height, amount of trays and type, etc.   


The proyect we are working on is Air Distillation, production of Oxygen. We have two integrated towers in a cryogenic temperature. There is a high pressure tower with a condenser, and a low pressure tower with reboiller which is integrated to the condenser of the first one. 


We have every single aspect of the towers designed, but we are having trouble in defyning the HLL, NLL and LLL since we don´t know the residence time in the bottom of the column.


I don´t know if that is enough data for you to help us.


Thank you.

#5 Art Montemayor

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Posted 04 June 2017 - 02:40 PM



Use your common sense.  You are dealing with a student design project - not a real-world project.


You may think you know the required physical dimensions of the Linde double column you have designed, but you really don't.  What is expected of you is to give the relative heights of the liquids in the sumps - enough to cover the reboilers.  You may think you have covered every aspect - but you really haven't.  Believe me, I've worked too many years working with air separation columns and know the internals well.


Make sure you know the type of reboiler you have designed and how it is expected to work.  You're doing submerged boiling, so common sense tells you you should have the bundle totally submerged.


Where you set the Low-Low level depends on how you design and pipe up the tower sumps were the reboilers are located.  You should have already prepared a detailed sketch of the towers - complete with dimensions.  Refer to my simplified profile of how a typical Linde double column is built and operates.  You should have generated and submitted this to our members if you are seeking help and advice.



Attached File  Air Separation - Lindes Double Column.xlsm   37.38KB   27 downloads

#6 breizh


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Posted 04 June 2017 - 09:38 PM

Hi ,

To add to the previous post , let you consider this resource .

Good luck


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