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Reboiler And Condenser Duty Calculation

distillation duty condenser reboiler

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#1 Prashkrans

Prashkrans

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Posted 29 June 2016 - 05:46 AM

How can I calculate the condenser and reboiler duties for a distillation column given the following data without using any simulation or software i.e by hand calculations.

 

                                    Feed 1 (To Distillation Column)       Stream 2 (Distillate)               Stream 3   (Residue)

Temperature                    35                                                  71.5174                                   172                              C

Pressure (absolute)         2280                                              250                                          250                         mmHg

Mass Flow                      10000.0008                                    999.7895                                 9000.2113               kg/h

Molar Flow                      172.9571                                        55.4976                                  117.4595                 kmol/h

Mixture Density              1651.6539                                       0.2091                                     370.6435                kg/m3

Mixture Molar Weight     57.8178                                          18.015                                      76.624                    kg/kmol

Flow Energy (Stream)   -1.8213*10^7                                  -3.7406*10^6                            -1.364*10^7            kcal/h

Mass Flow (kg/hr)        

Water                              1000.0001                                       999.7895                                 0.2116                     kg/h

Ethylene glycol                5500.0004                                           0                                         5500.0028               kg/h

Diethylene glycol             2000.0002                                           0                                         2000.0025               kg/h

Triethylene glycol            1500.0001                                           0                                         1499.9945               kg/h

 

 

 

 

Please suggest any method or procedure to carry out the calculations.

A small example would be helpful too.

 

 

Thanks


Edited by Prashkrans, 29 June 2016 - 06:09 AM.


#2 Pilesar

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Posted 29 June 2016 - 08:55 AM

If your heat and material balance boundary only cuts across these three streams, you can determine the net external heat into the system, but not the individual hot and cold duties. You cannot calculate the condenser and reboiler duties solely from the information provided. If there is a condenser, there is probably a reflux stream. Is there no more information?



#3 Bobby Strain

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Posted 29 June 2016 - 09:04 AM

So, you must have a textbook for your course. Or class notes. Are you looking for someone to do your work for you?

 

Bobby



#4 breizh

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Posted 29 June 2016 - 10:47 PM

https://escholarship...96n0xv#page-489

 

Hi,

Consider the resource above to support your work . A lot of data are missing to perform balances !

 

 

Good luck

 

Breizh



#5 Prashkrans

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Posted 30 June 2016 - 12:13 AM

Thank you all for replying. 

 

I am very sorry for providing less information. I think we can assume a total condenser with a reflux ratio of 2. Also I used the steam tables for the vapour and liquid water enthapies at Temp = 71 deg and press. = 250mm Hg.

I found these equations in Treybal :- Qc = D[(R+1)Hg1 - R*HLo-HD] and   (assumed HLo = HD

                                                     Q= DH+ WH+ Q- FHF         where L= Refluxed liq.   D=Distillate  and R = Lo/D (Reflux ratio)

Using this I was able to get Qc and Q.

 

But I wanted to confirm that in general, does the condenser operate at the same temp. and press. as the distillation column ( at top ) i.e. I wish to know that condenser only absorbs latent heat of vaporization (m*lambda) and stays at same temp. and press. as the top of distillation column. 

 

Also is it right to assume HLo = HD

 

These are my only doubts now that I can use the above equations.

 

Again please confirm that my method is correct or not, since I have no answer book to check it from.


Edited by Prashkrans, 30 June 2016 - 12:26 AM.


#6 breizh

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Posted 30 June 2016 - 01:38 AM

Hi ,

Yes you need to perform mass and heat balances and you will get your answer .

As long it's a  total condenser you assume that the energy removed  is the product of vapor time the latent heat of the product  . It's true that some delta P will occur when the gas will converted to liquid in the condenser .

 

For QB , apply your equation ( mass and heat balance) over the column .

 

Note : Take a look at the resource supplied above.

 

Hope this helps

 

Breizh






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