N2 Gas purging calculation

[Nasreddine]

Hi All
I am wondering how calculate N2 volume needed for shutdown activities?
Thank you

 

[Latexman]

I recommend you use Search (between Forum and FAQs). There are 131 threads with the word "purge" in the title. This topic has been discussed many times.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[BenjaminM]

There are a few different cases. For pressure purging:

yf = yi(PL/PH)^n

yf = final concentration
yi = initial concentration (presumably 0.21)
PL = Pressure low (presumably 14.7 PSIA)
PH = Pressure high (in PSIA)
n = number of cycles

For vacuum purging, it is similar except PH is 14.7 PSIA and PL is lowest you pull in PSIA.

 

[Compositepro]

It is dangerous to hand out equations to inexperienced engineers without giving the underlying assumptions. In this case I would assume that the assumption is perfect mixing of gases between purge cycles. Mixing can be difficult to achieve in any number of circumstances, such as long pipes. Nitrogen is slightly less dense than air, so that can inhibit or help with mixing. These details are important to understand.

 

[choack]

Refer to AGA Purging Principles and Practices