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[krishna unni]

I have 3 HP nitrogen storgage vessels 2m3 each with pressure of 295 bars (1680 kg of nitrogen). The purpose of nitrogen storage is for purging(PDP) of process piping and vessels systems before hand over to maintenance in order to bring down ethylene content in it to below LEL.

 

The total volume of process systems is  72.34 m3.  The purging is done at 50 bar at 40 deg C. The total required nitrogen is  3895 kg.

 

The HP nitrogen supply compressor is having rated capacity of 629 kg/hr (design MAX) at 295 bar. 

 

I want to calculate total hours required to run the compressor to purge the process system twice at 50 bar.

 

And I have reached to a value of 9.6 hours. Please let me know is it correct or not

 

 

[P.K.Rao]

Irrespective of the time needed for purging with nitrogen to free the lines and vessels from ethylene, a more fruitful way is checking the exit nitrogen for  ethylene content by gas chromatography. Tell your lab to use just an empty column in GC and FID. You can detect hydrocarbons gases down to below LEL.