2 replies to this topic

[go-fish]

Hi,

 

Please could any one advise under what scenarios is nitrogen blanketing required on spheres storing services like liquid mixed C4s, butene etc.

 

I have come across two projects. In one, the spheres have nitrogen blanketing and in another, there is no nitrogen blanketing. Both of them are for intermediate/buffer storage between two process units. If it is to allow for breathing and outbreathing due to liquid inflow and outflow, then it should be required for both the projects.

 

Thanks

[Art Montemayor]

What are the storage conditons (pressure, temperature) for the liquid butanes-butenes?  Are you storing at saturated conditons under ambient temperatures?  If so, then your vapor pressure inside the sphere should be 26 to 70 psia for temperatures 60 to 120 ^oF.  For iso-butane, it would be higher.

 

The point here is that there can be no such thing as “in-breathing” or “out-breathing” of a combustible gas.  You either flare it or you recover it.

 

You normally store such condensed gases in the saturated state, at their vapor pressure.  Unless you have a special reason, an inert gas (such as nitrogen) is not used in the vapor space.  One reason would be that the nitrogen will dissolve in the liquefied gas.

 

Please furnish complete process information and a detailed P&ID for further comment(s).

[go-fish]

Art,

 

Thanks for your response. I do not have the complete process data and P&IDs available with me. Just reviewing a PFD which has a sphere and pump along with nitrogen blanketing on sphere.  It’s a C4 fraction from a cracker and feed for the butadiene extraction unit. The buffer storage is part of a circulation loop so it receives from and transfers back to a circulation cooler in the Cracker on continuous basis.  Only when the cracker is not working, it will provides buffer storage for BEU.  The operating flow conditions are 15 deg C and 7 barg.