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Estimating Steam Flow For Blown Condensate Seal In Reboiler


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#1 bh123

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Posted 06 March 2019 - 05:33 AM

Hello,

 

We have a thermosyphon reboiler with steam (10 bar; 210 deg C) as a heating media. The steam flow to the reboiler is controlled by a control valve located on condensate outlet from reboiler. We want to increase the steam flow through reboiler to get more heaty duty out of it. However, I suspect that a blown condensate seal (steam flowing through exchanger without condensation) might cause a problem. So I wanted to ask if there is a way we can estimate at what flow the condensate seal is likely to blow?

 

Thanks.



#2 Pilesar

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Posted 06 March 2019 - 07:54 AM

At some valve opening your exchanger will reach its maximum exposed surface area. Your steam is not excessively superheated. What problem do you think might happen if you have a blown condensate seal? 



#3 bh123

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Posted 06 March 2019 - 10:43 PM

At some valve opening your exchanger will reach its maximum exposed surface area. Your steam is not excessively superheated. What problem do you think might happen if you have a blown condensate seal?

In my understanding, a blown condensate seal would result in loss of heat duty from the reboiler, the reboiler return temperature would fall and consequently column will be disturbed.



#4 Bobby Strain

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Posted 06 March 2019 - 11:40 PM

And, where did you develop this understanding? It seems flawed to me. What all good process engineers learn early is that with condensate control as such, one needs a small condensate pot to detect and avoid low level. It's quite elementary.

 

Bobby



#5 Sharma Varun

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Posted 07 March 2019 - 03:07 AM

 

At some valve opening your exchanger will reach its maximum exposed surface area. Your steam is not excessively superheated. What problem do you think might happen if you have a blown condensate seal?

In my understanding, a blown condensate seal would result in loss of heat duty from the reboiler, the reboiler return temperature would fall and consequently column will be disturbed.

 

I think you are looking at using steams latent heat which can not be ensured in case seal is blown.

 

you need to carry out proper hydraulics for pressure drop in heat exchanger & outlet line. This will be compared with available head between exchanger bottom nozzle & condensate pot liquid level.



#6 bh123

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Posted 10 March 2019 - 11:48 PM

And, where did you develop this understanding? It seems flawed to me. What all good process engineers learn early is that with condensate control as such, one needs a small condensate pot to detect and avoid low level. It's quite elementary.

 

Bobby

There were previous instances where operators have observed reboiler return temperature to fall at high condensate valve openings. I developed the understanding about broken condensate seal from one of Lieberman's book.

 

As for the condensate pot, I agree that it should be used to detect and avoid low level. However, the system does not have a condensate pot for this purpose.



#7 Bobby Strain

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Posted 11 March 2019 - 10:11 AM

You may not have interpreted the operators observation correctly. I would expect that the fall comes before the opening. Which is exactly the desired control. One would normally compare the operation to the design to evaluate exchanger performance. There is nothing to be done with the operating exchanger.

 

Bobby



#8 bh123

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Posted 03 May 2019 - 05:25 AM

You may not have interpreted the operators observation correctly. I would expect that the fall comes before the opening. Which is exactly the desired control. One would normally compare the operation to the design to evaluate exchanger performance. There is nothing to be done with the operating exchanger.

 

Bobby

You were right that the fall comes before the opening.

 

When a higher duty was required, the reboiler condensate return valve was at 99% and even the valve's bypass was opened to increase the steam flow and no such problem  (blown condensate seal) occurred.

 

P.S. I apologize for a late response, I was away for a while.






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