6 replies to this topic

[GeorgeEls]

Hi All

 

I am currently designing the high pressure distillation column for a cryogenic air separation plant. I am doing the preliminary design using the McCabe Thiele method, using the method shows that the feed stage is at 'stage 1', which would normally be the reboiler. 

 

I have read in the literature that the high pressure distillation columns do not have a reboiler. I would like someone to either confirm what i believe or correct:

 

There is no need for a reboiler on the high pressure distillation column as the upwards vapour flow for the column is provided from the feed, which is at a point below the first tray of the distillation column. 

 

Thank you

 

George 

[Art Montemayor]

George:

 

You don’t reference your source of information nor do you give a basis.  I have furnished a sketch of a typical Linde twin air separation Column in another thread.  You can download this workbook by finding the thread using our SEARCH engine.

 

I have always seen the high pressure column operating with a reboiler coil instead of the way you describe it.  Otherwise, the HP column would be nothing more than a flash chamber with no refluxing because you wouldn’t have the ability to rectify the reflux liquid (pure liquid nitrogen) descending.

 

Look carefully at my sketch and try to visualize how Linde carried out the basic distillation requirements to fulfill the specified product purities.  You need reflux in both columns ensure the purity at the top.

 

[Bodhisatya]

You are wrong in interpreting the HIGH Pressure Column operation of an Air Separation unit.A HP Column always consist a Reboiler-Condenser either once through or Bath Type depending upon the Configuration.For a HP Column it's generally a condenser,condensing the upcoming vapour and sending back a part of that into the Column as a reflux,until a reflux is available you can't have a proper distillation and hence Pure Product.The upcoming vapour gives away it's heat to a boiling liquid and inturns cool.With time this upcoming vapour becomes richer in Gaseous nitrogen and the liquid collected in bottom sump in Oxygen.

 

Cheers.

[Bodhisatya]

Am attaching a distillation Column predominately a HP column used in a Nitrogen Generation Unit.Hope it helps.

Attached Files

•  REBOILER CONDENSER DESIGN.xls   22KB   70 downloads

Edited by Bodhisatya, 08 April 2013 - 10:51 AM.

[Art Montemayor]

George:

 

I don't know if you have already gone to the following thread:

http://www.cheresour...eparation-unit/

 

and downloaded the workbook found there.  That is the detailed drawing of what a typical Linde Double Column looked like before recent modifications were made to it, using welded plate exchangers to act as the Nitrogen condenser.  The original columns were lead and silver soldered.  Today, there are few (if any) skilled solderers left on this planet and the columns are made of stainless alloys anyway, so plate heat exchangers are now used.  But the basic principles and operations are exactly the same.

 

If you are serious about being a Chemical Engineer and doing good work, you should read all the information in our Forums regarding air separation.  I operated and maintained a lot of air separation units in my younger years, so I am speaking from an experienced, hands-on level.  Cryogenic air separation is not a complex subject.  However, the understanding and knowledge involve work input and labor.  It is just like anything else: you have to earn it.

[GeorgeEls]

Thank you very much for your responses.

 

I am only designing the high pressure column, for which i am clear on the condenser/reboiler which is located at the top of that section. It was mainly the reboiler of the high pressure section i was querying about and i am aware that the reboiler generates the upwards flow of vapour so the column can operate. I was wondering if locating the feed stream below the first tray of the distillation column would completely remove the need for a reboiler at the bottom of the high pressure column. 

[junaid8942]

Location of  the feed stream below the first tray of the distillation column the pressurized super saturated steam (4 tray down feed tray (added in existing no. of trays) as flasing zone)is used instead of reboiler . so according to the installed utilities you can choose must feasible option for reboiling the feed.