31 replies to this topic

[latexman]

peruanolimense,

 

That is not 100% correct, but it's not 100% wrong either, IMO.  Draw the full theoretical plates, they come in integer values.  I would not worry about exceeding the y_D spec a bit.  That is the actual practice.

[peruanolimense]

latexman,

 

Yeah, that is something that breaks my mind a bit,  What my professor told us is:

 

"When asked for theoretical plates, draw from one net flow to the other net flow, even if you obtain 1/4 of plate; it is not wrong.  When asked for the real number of plates, draw from one net flow to the other, but do not cut a plate.  Finish your response with a round number of plates (if you get 4.6, then 5. If you get 3.2, then 4)"

 

Because we do not have a net flow in the upper sector of the column, I draw from the stripping net flow to the y_D, and that is what I do not know if it is correct

 

Thanks!

[breizh]

Hi ,

In addition to other documents supplied ,

Consider this ppt document to support your work .

Breizh 

[peruanolimense]

Breizh,

 

Thanks very much.  Very, very useful!

[Art Montemayor]

Carlos:

 

I’m interjecting myself into this thread because:

 

1. I want to emphasize the importance of reading and studying the literature that Breizh has submitted for your perusal;
2. I feel that there is a misinterpretation in applying your process description and submitted sketch, resulting in not describing all involved stream flows correctly.

 

As Latex has noted, I also believe that your use of the English language is far superior to many of our fellow citizens here in the U.S.A.  Although your written description and supplied sketch are well done, I find that both are not complementary in fully supporting each other.  Please refer to the attached Excel workbook where I show your simplified flow diagram next to my quick sketch of what I interpret as a description of your written process explanation.

 

Having lived, married, and worked in Peru I fully respect your use of the word “partial” condenser and believe you know what that describes.  You will note in my sketch that I depict the introduction of the “extra” vapor feed stream as going directly to the partial condenser.  By definition, this condenser will condense only sufficient vapor (that produced by the distillation column as well as the feed vapor stream) so as to produce sufficient saturated liquid reflux.  The excess vapor emitted from the partial condenser enters the reflux drum where it is separated from the liquid reflux and it exits the reflux drum as a vapor product going elsewhere.  Normally, there is no liquid overheads product when a partial condenser is used.  If this is the case, it should be stated as such.  However, a vapor overheads product is always produced – that is the reason for using a partial condenser.

 

I believe that your mass balances are not defining the correct process and that is why you are having problems.  And that is also the reason I emphasize Breizh’s astute and experienced advice: read and study the literature given.

 

If my comments are wrong, then please let me know.  The McCabe-Thiele method may not be a very accurate solution in designing a distillation column, but it is a marvelous method in explaining and defining what is happening in the process.

 

Saludos y Que Viva el Peru, Carajo!

Attached Files

•  Croquis de Distilacion.xlsx   82KB   10 downloads

[Art Montemayor]

Carlos:

 

If you continue to be interested in the McCabe-Thiele Distillation method of studying how a distillation column can be studied, go to:

 

http://facstaff.cbu....es/distill.html

 

Professor Price has always been one of my Internet favorites in presenting and explaining Unit Operations in Chemical Engineering.  In this presentation he clearly explains the function of a partial condenser and how it works in a heat and mass balance.  You may find the whole lecture very interesting.  I have copied and transcribed the entire lecture to a Word for Windows document for detailed study and reference.  Unfortunately, I' m presently on my way to Church to hear Mass and I have not formatted the entire resulting document.  I am attaching the unfinished product here for your perusal and perhaps study.  I think you would find the lecture helpful.  Professor Price has produced other lectures on Chemical Engineering at Christian Brothers University and you may want to follow his work.

 

Saludos.

Attached Files

•  Distillation.docx   39.73KB   12 downloads

[Art Montemayor]

Carlos:

 

You have not replied to my comments indicating that your explanations and heat - mass balances for the case of a partial condenser do not seem to be correct.  I still maintain that the recommended book that Breizh submitted contains vital information on learning the methods employed in the McCabe-Thiele method.  Because of this, I have compiled a copy of the book's section that I consider important for you to understand and know regarding the employment of a partial condenser.

 

I apologize for using the cut & paste way of putting the text into a readable Word for Windows format, but the .pdf copy submitted does not allow direct copying of the contents.  If you study this document, I believe you will understand what I have tried to bring out.  I hope this helps you know and dominate this distillation calculation method.

 

I am also including some additional information that might be of interest.

 

Saludos.

Attached Files

•  Separation Processes - 2nd Ed - C. Judson King.docx   2.6MB   5 downloads
•  Reflections on the use of the McCabe-Thiele method.pdf   343.29KB   4 downloads
•  McCabe-Thiele Method.docx   258.62KB   4 downloads