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Distillation Column Design

#distillation #design #sizing #pressure #process #equipment #vessel

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#1 AakashChem

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Posted 15 June 2021 - 09:25 AM

Should pressure drop per tray be revised for both rectification and stripping section in distillation column design, if slight difference is observed only in one section?

My column diameter for the top section is also coming almost twice that of the bottom section due to the superheated feed condition using the column sizing method given in RC Vol.6. So is it okay to have a larger upper section?


Edited by AakashChem, 15 June 2021 - 09:29 AM.


#2 Pilesar

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Posted 15 June 2021 - 11:29 AM

For a student project, I would not adjust pressure drop per tray for slight differences unless it makes a significant impact in the result, such as in vacuum service. Perhaps check the sensitivity of the result after you finish the rest of the column design. As for designing a column with a larger top section diameter, it can be done and is most often seen in vacuum distillation. If this diameter change is caused only by superheated feed, then consider whether an exchanger to cool the feed would be useful. Column diameter is costly for large scale commercial applications. If you were to supply more details, you might get more specific responses.



#3 AakashChem

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Posted 15 June 2021 - 02:05 PM

Thanks for your response @Pilesar.

The calculated top diameter is 750 mm and bottom diameter is 450 mm.

Assumed pressure drop per tray was of 120 mm WC for a tray plate spacing of 600mm taken. Though a total pressure drop of 112 mm WC & 135mm WC  was observed in rectifying and stripping section respectively. Every other constraint of operating range was satisfied for the calculations. 



#4 Pilesar

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Posted 15 June 2021 - 03:20 PM

Your supplied data indicates you only have one tray in the rectifying section and one tray in the stripping section. Did you report the data correctly? Clear reporting of data is an important feature of engineering. Trayed columns have a practical minimum diameter for construction - research this diameter on your own. Think of how trays could be installed inside a narrow column and imagine the difficulty. You should most likely choose the calculated larger diameter for the entire tower. Transitions between diameters are a costly addition and not justified for such small diameter changes. It is common for sections of distillation towers to have larger diameters than the minimum required by calculation.



#5 AakashChem

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Posted 15 June 2021 - 03:45 PM

I apologize for the miscommunication on my part...read this corrected paragraph:

The calculated top diameter is 750 mm and bottom diameter is 450 mm.

Assumed pressure drop per tray was of 120 mm WC for a tray plate spacing of 600mm taken. Though a total pressure drop per plate of 112 mm WC & 135mm WC  was observed in rectifying and stripping section respectively. Every other constraint of operating range was satisfied for the calculations. 

 

5 real trays are there in each rectification and stripping section.  






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