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Nitrogen Blanket On Cryogenic Tank


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#1 alameehs

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Posted 19 January 2017 - 06:59 AM

good day gentlemen

 

in my plant there is tank which is store the liquid ethylene product. A small portion of the liquid flashes to vapor during the transfer. The vapor rises through the liquid and exist the tank overhead to ethylene compressor. the liquid is transfer to other unit by utilizing pumps. there is a nitrogen line on the tank which is open to pulling a vacuum on the tank and to protect compressor and pump.

 

I want to calculate the required nitrogen flow to protect the pump and compressor if there is low pressure on the tank . Is there any way to calculate it

 

thanks for help  



#2 Bobby Strain

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Posted 19 January 2017 - 10:47 AM

Please provide complete information about the tank, pumps, and compressor. And, it seems that nitrogen is to protect the tank, and is unrelated to the pumps and compressor.



#3 Saml

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Posted 19 January 2017 - 12:19 PM

Please check the discussion on this link.

It is about ammonia, but for a cryogenic tank (I assume yours is cryogenic and the compressor is the boiloff recompression / refrigeration) the same physical phenomena are at play.

 

http://www.cheresour...gen-blanketing/



#4 Bobby Strain

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Posted 20 January 2017 - 09:38 PM

Sami,

     We often misuse the term cryogenic. It does, in fact, refer to temperature less than -150 C. Liquid ethylene at atmospheric pressure is only around -150 F.

 

Bobby



#5 alameehs

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Posted 22 January 2017 - 12:23 AM

good day Booby

 

yes you are right. the nitrogen line is to protect the tank from collapse. if the feed flow to the tank is stopped while the compressor and pump are running, the tank pressure will be decreased. there will be potential to collapse the tank. what I need to know how to calculate the required nitrogen flow ( nitrogen blanketing)  to maintain minimum pressure on the tank. the minimum allowable pressure on tank is 0.01 kg/cm2 and the nitrogen line is 3'' with upstream pressure of 10 kg/cm2.

 

the normal tank temperature is -99 C    

 

thanks for help


Edited by alameehs, 22 January 2017 - 12:50 AM.


#6 Saml

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Posted 23 January 2017 - 06:03 AM

Sami,

     We often misuse the term cryogenic. It does, in fact, refer to temperature less than -150 C. 

Thanks. You are right.  As you say, it is quite usual to misuse the word "cryogenic" to refer to refrigerated LPG, ammonia and ethylene tanks.






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