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Invisible Nitrogen Gas Barrier


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#1 wbic1

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Posted 06 January 2017 - 04:02 AM

A few refining operators still wrongly believe that an invisible nitrogen gas barrier can be created if they can maintain a positive pressure differential between the nitrogen and another gas, i.e, hydrocarbon gases in a gas pipe.

In my opinion, this is a dangerous belief which can lead to industrial accidents.  Since nitrogen and hydrocarbon gas are compressible gases and that gases are simply particles it is ridiculous to even think that such a nitrogen gas barrier can be created.  The nitrogen gas will mix with the hydrocarbon gases in a pipe.   

 

Im looking for any information regarding this issue

 

Thank you in advance, Harry



#2 sgkim

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Posted 06 January 2017 - 06:50 AM

Hi,

The word 'barrier' reminds us a 'wall', 'barricade' or 'membrane' to separate one thing from the other.  But 'nitrogen gas barrier' does not mean such a physical material or state.  Nitrogen is used for the purging of container or conduit by replacing the gas and providing a positive pressure compared with surrounding atmosphere.   So the nitrogen gas drop the concentration of combustible gas much below the lower limit of explosion, and prohibits explosion by preventing the air from infiltration into the system. This kind of roles are called "nitrogen barrier effects".  Nitrogen mixes with gas or vapor completely and 'builds and happens nothing' as you might think, no physical 'barrier' would be made anywhere between molecules.  

 

Stefano G. Kim



#3 wbic1

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Posted 06 January 2017 - 11:31 AM

Kim, Thanks for your reply. Would your reply be similar if the operators were to use steam instead of nitrogen gas? No barrier can be created between steam,i.e. 300# steam and another gas, i.e, hydrocarbon gas flowing at 10psi ?

Edited by wbic1, 06 January 2017 - 11:35 AM.


#4 Art Montemayor

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Posted 06 January 2017 - 11:40 AM

Stefano is precisely correct.  The effect that is being described by the OP seems to be nothing more than plain, old-fashioned, nitrogen purging of a system containing hydrocarbon gases or vapors for the sake of safe operation.

 

The misleading term "barrier" has been adopted by someone who undoubtedly has little or no engineering (or language) background in why and how nitrogen (an inert gas) is used to displace a flammable/explosive vapor in a safe and orderly manner.  What has been left out is that blowers or vacuum jets are sometimes used in addition to nitrogen injection to assist in evacuating hydrocarbon vapor systems in a faster and orderly manner.



#5 wbic1

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Posted 06 January 2017 - 01:32 PM

Thanks for your reply Art,

 

would your reply and Kim's apply similarly to steam as well?   there is no such thing as steam barrier either?   some refinery operators are still using steam as a barrier for the purpose of blocking out hydrocarbon gas in piping.


Edited by wbic1, 06 January 2017 - 01:39 PM.


#6 Art Montemayor

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Posted 06 January 2017 - 08:36 PM

wbic1:

 

You have not stated what unit operation you are referring to.  I have stated that I suspect you are referring to a pipe (and/or vessel) purging operation where you are using an inert gas (nitrogen) to "sweep" away and out any hydrocarbon vapors residing in the system in order to avoid a flammable/explosive atmosphere.  This would allow you to have a subsequent inspection and/or repair of the system.  Am I correct?  Or are you referring to something else?   Please be explicit, because we don't need to waste time, words, and effort on something that is that simple and direct.

 

I have used steam in the past to purge out hazardous gases from a piped system.  I've used steam in order to economize.  A nitrogen sweep can be expensive if the system is relatively large.  However, in using steam you will create a lot of water condensate within the system and you will subject the entire system to a heat-up - which will necessitate a cool-down.  Subsequent water removal is always a problem - and sometimes may not be tolerated or allowed.

 

​I still don't understand why you persist in using the term "barrier".  There is no such thing as a barrier in a purging operation.  I have a problem visualizing how one can "maintain a positive pressure differential between the nitrogen and another gas".   What do you mean by "blocking out hydrocarbon gas in piping"?  How is this done?   Why don't you just tell us what the actual operation is?



#7 wbic1

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Posted 07 January 2017 - 07:00 PM

I do not believe in nitrogen or steam "barrier" because they do not exist and they go against all chemical engineering concepts. The operators i work with,however, have been wrongly (in my opinion) embracing the concept of gas barriers, and are still practicing it.
Gases behave as particles which will disperse anywhere from high to low pressures. Two or multiple gases in a pipe,vessel or any containers will mix and there is no such thing as molecular boundary or barrier between these gases. I agree with you about the practice of gas purging; however gas monitoring must be closely watched for presence of flammable gases during purging to see effectiveness of purging.
I went on this board to see if there may be a black magic concept of nitrogen or steam barrier that I may not be aware of, but as I thought, such belief of gas barier is a misconcept which goes against laws of science.
Thank you for everyone's input.


Edited by wbic1, 07 January 2017 - 09:37 PM.





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