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N2 Requirement


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#1 aanita

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Posted 15 May 2017 - 06:59 AM

A vessel of 25 Am3 to be purged with N2 at 2 barg pressure before hand over to maintenance. How much N2 will be required? Am3= Actual m3(Volume of the vessel).

 

I try with the following steps, please correct me if I am wrong:

 

PV=nRT  to get n= moles of N2, and then convert it to Nm3 with

1 mol gas=22.414 Nm3 of gas(ideal gas assumption for simplicity).

 

Warm regards,



#2 Saml

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Posted 15 May 2017 - 11:04 AM

1 mol of gas (28 grams in this case) is 22.414 liters, not cubic meters. That is 1 kmol.

But you don't need to do that conversion, since N2 is purchased, and measured in Nm3.

So for a 25 m3 vessel at 2 barg  you will need 75 Nm3 (plus temperature correction) for each volume renewal.

 

However, not knowing the purpose of the Maintenance intervention, the contents of the tank and disposal system availability, it is impossible to tell how many volume renewals you need.



#3 Art Montemayor

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Posted 15 May 2017 - 11:33 AM   Best Answer

aanita:

 

This is a vessel purging application.  It can be continuous or batch operated.  It does not involve calculation of the gas quantity needed.

 

What is needed is an experienced indication - either empirical or recommended - regarding the quantity of vessel volumes or nitrogen needed to purge out the vapors or gas originally in the vessel down to the level you require.  We don't know what the parameters are.

 

As Saml has indicated, you can use a 3:1 ratio of purge volume to vessel volume - but that is no guarantee that you will achieve what you need or want (which you haven't defined).  A lot depends on the location of the injected purge, the method used, and the the particular gas or vapor in the vessel as well as the vessel's geometry and configuration.  If this is a homework assignment or class problem, the nature and specifics of the purging operation should have been explained by your instructor or professor.  If not, shame on them.  As a student, you should always question any operation specified or mentioned by your instructor that hasn't been studied or fully explained.



#4 Pronab

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Posted 15 May 2017 - 01:39 PM

Check the below link, it may be helpful:

 

http://www.glocalecl...essure-purging/



#5 breizh

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Posted 17 May 2017 - 06:55 AM

Hi,

Take a look at the document attached .

Hope this helps

Breizh






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