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Reducing Steam Consumption In Vacuum Packed Distillation

distillation steam packed tower vacuum distillation toluene optimizing rectifying calculation reboiler

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#1 dpunnn

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Posted 30 November 2023 - 08:24 PM

Hello Everyone and Experts,

 

I got a project to study and evaluate distillation packed tower.
 
The purpose of the evaluation was to reduce steam consumption.
 
Operating Conditions:
Feed Temp: 55 C
Top Temp: 45 C (80 mmhg) --> Toluene as Top Product
Bot Temp: 120 C (85 mmhg)
 
It has 1 reboiler (Falling Film Reboiler), 1 distillate condensor, 1 vent condensor.
Packing Type: Structured
Steam Condensate from Reboiler is used for Feed Preheater.
 
Feed  : 5 m3
Distil. : 3.5 m3
Bot.    : 1.5 m3
Reflux: about 1-5 (automatic setting)
 
So far, the purity obtained has always been high (>99%), it's just that the use of steam is too large.
 
I have studied several ways to lower steam consumption such as:
1. Lowering the operating pressure
2. Reducing reflux
3. Increasing feed temperature
 
But I don't think these are applicable to the tower design, because all of them have been carried out in the operation.
 
Is there any way to reduce the steam consumption?
 
Is there any reference that I can use to do a suitable calculation?
 
Thank you,  :)
 

 



#2 breizh

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Posted 30 November 2023 - 08:30 PM

Hi,

If you want to share a P&Id and PFD people will comment.

No indication about flowrates /purity expectation/yield . Good also to give info about the quality of the steam.

Breizh 



#3 dpunnn

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Posted 30 November 2023 - 09:33 PM

Hi,

If you want to share a P&Id and PFD people will comment.

No indication about flowrates /purity expectation/yield . Good also to give info about the quality of the steam.

Breizh 

Hello Mr. Breizh,

 

Thanks for your suggestion, I attached a simple PFD on it.



#4 dpunnn

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Posted 30 November 2023 - 09:42 PM

 

Hello Everyone and Experts,

 

I got a project to study and evaluate distillation packed tower.
 
The purpose of the evaluation was to reduce steam consumption.
 
Operating Conditions:
Feed Temp: 55 C
Top Temp: 45 C (80 mmhg) --> Toluene as Top Product
Bot Temp: 120 C (85 mmhg)
 
It has 1 reboiler (Falling Film Reboiler), 1 distillate condensor, 1 vent condensor.
Packing Type: Structured
Steam Condensate from Reboiler is used for Feed Preheater.
 
Feed  : 5 m3
Distil. : 3.5 m3
Bot.    : 1.5 m3
Reflux: about 1-5 (automatic setting)
 
So far, the purity obtained has always been high (>99%), it's just that the use of steam is too large.
 
I have studied several ways to lower steam consumption such as:
1. Lowering the operating pressure
2. Reducing reflux
3. Increasing feed temperature
 
But I don't think these are applicable to the tower design, because all of them have been carried out in the operation.
 
Is there any way to reduce the steam consumption?
 
Is there any reference that I can use to do a suitable calculation?
 
Thank you,  :)
 

 

Here I attach the simple PFD of the process.

Attached Files



#5 Bobby Strain

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Posted 30 November 2023 - 11:39 PM

What is the bottom product? I presume that it is subject to degradation at higher temperature. Or, the steam is waste. Otherwise, no one would design a column to operate under vacuum to recover toluene. And, you don't show a vacuum pump or steam jet ejector.

 

Bobby



#6 breizh

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Posted 01 December 2023 - 12:12 AM

Hi,

You should supply information like a Chem Eng will do: Mass or mole balances with mol or mass composition to reconciliate the balances.

Are the heavies subject to generate tars at high temperature?

Why toluene is still at 1% in the bottom of the column, far too much.

Structured packing means BX? Who is the supplier of packing? Do you inspect the packing, the distributors regularly? When did you replace the packing for the last time?

You should have a simulation of your process from packing vendor.

How your operation is versus the start up in term of process parameters?

You mean R=1.5 not within a range [1 to 5]

Note :

BP toluene 110.6 C 

BP heavies about 200 C

It should be easy to separate those products.

My guess ,issues with packing and or distributors. Check the traffic in the column and talk to packing vendors. 

Get in touch with Sulzer as an example after you prepare a spec sheet..

All are very basic questions you should answer.

Note : To improve your fuel consumption (bill) you should route your condensate back to the boiler house not the WWT. Unfortunately, very common practice in China, Indonesia, Thailand, Asia Pacific .

My view

Breizh 

Attached Files



#7 shvet1

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Posted 01 December 2023 - 05:50 AM

Stripping tar by a low MW gas (hydrogen, methane, nitrogen, steam). 

Note that for low capacity (your case) a stirring jacketed vessel is more common than a falling film evaporator.


Edited by shvet1, 01 December 2023 - 05:52 AM.





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