1 reply to this topic

[dgillott]

Just wondering about two alternative approaches to inerting a pipeline for mothballing.  I need to purge methane from a 10 inch six mile pipeline to flare, and leave it N2 filled.  Two approachs being considered.  First, to depressure to flare then flow N2 into the other end to slowly sweep the pipeline.  Can't flow too fast due to limits on the re-gasification from liquid N2.  Or, depressure to flare, close off the valves and re-pressure the line to about 50 psi with N2 from the far end.  Then send to flare again.  Then have a reduced slow purging flow again until .  Discussion has been that the faster depressurisation will carry more of the methane out to flare faster and more thoroughly than the slow purge, which would allow more mixing in the pipe.  What do others think?  Economic drivers are overall time, and N2 usage.  We are going to need to purge until we have no more than barely detectable traces of methane at the flare end. 

[Zauberberg]

Pressurization does not work so well in long distance pipelines - keep in mind that the pressurized end will see very low velocities upon initiation of purge. That may keep a lot of Methane stuck in the front end.

 

You should definitely start with a continuous sweep after depressurization and once when you push Hydrocarbon gas towards the vented end, you may apply a few pressure pops to reduce Methane concentration further.