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Two Parallel Condensers


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#1 RDENG

RDENG

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Posted Yesterday, 08:26 AM

Hi all!

 

First I want to thank you all for this excellent forum.

 

We are designing a distillation system which has two parallel condensers. I’m looking for your help to get an certainty of how we should design it so that vapor flows through each condenser as desired proportions.

 

Requirements:

  • Two parallel total condensers operating at vacuum. One of which is operated at cooling water and one of which is cooled by process fluid. CW operated should be designed for full capacity because of start-ups.
  • Overhead system has low pressure drop. I.e. no control valve in the overhead vapor line.
  • Heat integrated condenser duty is about half of CW operated one.
  • Stable pressure control
  • Some non-condensables are present in the overhead vapor, but exact amount is not known.

 

At the moment we considering two options (Please see sketch attached). Option 1:

  • Condensing capacity is controlled by flooding the condensers. After start-up cooling water operated condenser is partly flooded and heat integrated condenser is set in motion.
  • Preventing vapor to flow just through one condenser is done by putting valve in pressure equalizing line. By throttling the valve pressure drop of both condensers + equalizing line is set equal (at desired condensing rates)
  • Pressure equalizing line valve is controlled by flow meters that measures condensate flow rate from each condenser.
  • Column pressure is controlled by vacuum line control valve connected to the reflux drum.

 

Option 2:

 

The other option is to use same configuration and regulate column pressure on condensers surface levels and to use these ‘equalizing lines’ just for venting.

 

Can You comment on these scenarios? Waiting for your valuable replies.

 

RDENG

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#2 Bobby Strain

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Posted Yesterday, 03:10 PM

Probably neither of these is satisfactory. Talk to your suppliers for the vacuum system. They will probably help. Or pay some practicing engineer to design the system for you.

 

Bobby



#3 RDENG

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Posted Today, 01:30 AM

Thanks for your quick reply Bobby. We consider your suggestions.

 

Can you be little more specific? What are the deficiencies of options 1 and 2 presented?

 

RDENG 



#4 breizh

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Posted Today, 02:06 AM

hi RDENG ,

Consider reading the document attached . 

I'm worried about how  you want to manage the vacuum on your system .Performance of your distillation depends on the quality of the vacuum ..... 

 

Good luck 

Breizh 

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#5 RDENG

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Posted Today, 02:47 AM

Thanks Breizh for the article. Got some valuable tips how to proceed with this issue.

 

Vacuum is greated by Liquid ring vacuum pump. Column pressure is controlled in option 1 by vacuum line valve which is, based on my experience, quite fast and reliable method. In option 2 column pressure is controlled by changing the heat exchange area in condensers, which more sluggish.

 

RDENG



#6 breizh

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Posted Today, 03:59 AM

Hi ,

In addition to my previous answer a document about Pressure management on distillation column.

good luck

Breizh

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#7 RDENG

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Posted Today, 04:40 AM

Breizh,

 

Document you sent is a good summary about the control of single condenser. Instead I found very few documents which deals with parallel condensers...

 

RDENG



#8 breizh

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Posted Today, 05:14 AM

http://www.distillat...question015.htm

 

Take a look , from the same vein.

Good luck

Breizh



#9 RDENG

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Posted Today, 06:52 AM

Thanks again Breizh for sharing documents.

 

We can't use control valve in vapor inlet lines of the condensers, because overhead system should have low pressure drop.

 

RDENG






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