pressure pumping with N2 to remove other gases from equipment and pipe

[Jacqueaux]

I'm looking for an engineering approach or calculation to determine the effectiveness of nitrogen pressure pumping to remove air or other gases from equipment and dead ended pipes. Is there a paper of link to serve as a reference? By "nitrogen pressure pumping," I mean pressuring with N2 to a certain pressure and depressurizing through the same opening.

Other engineers have said that if the upper pressure is 3X the lower pressure in the cycle, you can assume perfect mixing in the dead ended piping for up to 75 linear ft. Some have doubted the expansion and contraction in the dead end is energetic enough to mix the line thoroughly. There is debate on whether stagnate diffusion is significant or not. No one so far has produced a document or reference.

Sure- it is more effective to sweep long pipe lines from one end to the other instead of pressure pumping, but there is the trade off of higher cost for valves and fittings and fugitive emmision points.

similar to...
thread135-15647: Nitrogen Purge Rates For "Atmospheric" Vessels
thread135-161047: Tank Purging Calculations

 

[JimCasey]

It is not uncommon in "filled" systems to pull a hard vacuum on them and then to fill the system with an uncontaminated fluid of choice. The fluid can be a gas or a liquid. Certainly more efficient to do this than what you describe.

 

[Longinthetooth]

We have never had much success purging dead head piping like this. Trying to get below the LEL is a nightmare. Flow through purging or vacuum purging is the way to go as JimCasey says.