7 replies to this topic

[mb23]

What is the significance of sensitive tray temperature in a column?

How is sensitive tray chosen in a column
?

What is the logic behind establishing temperature control on sensitive tray instead of reboiler outlet temperature?

[breizh]

Hi,

For you to understand, you need to perform simulation or monitor on an existing column a temperature profile. Monitoring the sensible temperature on this specific tray will guarantee you the performance of your column (split and yield)

Good luck

Breizh

[mb23]

Dear breizh,
Thank you for your reply. I was actually looking to understand the more fundamental concept behind selective sensitive tray temperature and it's control.

[Pilesar]

Columns have a temperature profile which changes when the composition of the trays change. Some tray temperatures are affected by the composition of the key components more than others. It is good to control the process using the measurements that best indicate the performance desired. The reboiler outlet temperature should have very little of the light key component. If the reboiler outlet temperature was used for column control, there may be a very flat temperature curve once enough heat is input. Reboiler temperature might signal 'add more heat' but could not easily signal 'enough heat has been added so don't add any more heat.'

[latexman]

Early in my career (1980's) I dabbled in this subject.  My company had special distillation subroutines within our in-house simulator that could:

establish a converged base case,

perturb a single parameter set by user (feed conc., distillate conc., bottoms conc, reflux ratio, etc.),

establish a converged perturbed case,

determine many parameters of (base case - perturbed case) / base case, like ΔT/Δx for every stage,

point out where the most sensitive (largest differentials) were located.

 

Reboiler outlet temperature would always be there as Stage n (or 1) depending on numbering convention chosen.

 

This assisted greatly in analyzing a column for control.

 

I haven't used this methodology in decades, but I bet Aspen+ and HYSYS can do it.

[Bobby Strain]

You can find the answer in one of Kister's books. It's not complicated. Use your favorite search engine.

 

Bobby

[SilverShaded]

You should control a tray that has a good temperature/product composition response.  You will need a simulation to determine that.

[breizh]

Hi,

Consider this document to support your work,

For a temperature at a given pressure composition is related (equilibrium stage).

EDIT :Good to read:

https://www.osti.gov...ets/purl/780447

 

https://www.eng.uc.e...000477-main.pdf

 

https://www.scienced...959152405000569

 

Good luck

Breizh