Heavy HC from breathing valve during pipeline pigging

[rob5377]

Dear all,

There is a pig receiver at a natural gas plant. Condensate from a pipeline is taken to the vessel through the condesate line with PRV installed. The flashing condensate will get into the vessel causing some HC getting out of the vessel through the breathing valve to the atmosphere. The breathing valve releases the vapour directly to the atmosphere but to the safe localization. There is no flare at the plant only a cold vent stack at remote location.
The guys from the plant claims that it is not possible to vent the vapours directly to the atmosphere because heavy HC released during the pigging may accumulate and cause the explosive atmosphere around the vessel. In my opinion it is pointless to have few hundreds of pipe to hook it up to the vent. Is there any example in the literature that my solution (breathing valve directly to the atmosphere) is acceptable. Are there are any calculations that can be done to prove that it is safe?
Or maybe guys from the plant are right and my solution is not acceptable at all.
Thanks for any comments.
Rob

 

[Rickyherb]

Rob: Remember the primary rule in Engineering ethics- social safety, I believe these guys may be correct but for own proof you can do the following:
- Material balance for the escapes at the vent.
- Check the explosive safe and trigger limits for this HC over a known volume around the vessel- (depending on worst conditions of no winds- there will be an accumulation, i.e non-steady state flow) which could trigger an explosion (read on explosive dusts, causes, protections and preventions- flares are usually a cheap prevention).
- Compare your findings and always assume worst case scenario in design. (in my opinion- I wouldn't sweat the extra piping to avert the vent fumes away from the vessel). Let me know your findings- good luck.

 

[MortenA]

Do a dispersion analysis! This can involve some work including CFD calculations. How high i the tail pipe? Normally it would be 3 metres (10 ft i guess) here i Europe anyway.

Best regards

Morten

 

[maddocks]

MortenA is right - if your stack is high enough, you can induce a fair amount of draft. As long as there is no possibility of an ignition at the tip - you should be fine.

The other approach may be to install a flare stack with some assist gas like fuel gas to be burned during pigging operations. Most of the sweet ones I've worked on have only had short vent pipes similar to yours.

 

[SNORGY]

I would like to see the P&ID before trying to comment in an informed way.

I will say this, though...

If the "guys from the plant" are uncomfortable about something, pay very, very close attention to it.

If it looks like a duck, walks like a duck, smells like a duck, quacks like a duck...

Regards,

SNORGY.

 

[maddocks]

and in conclusion to snorgy's post, if the guys at the plant are not convinced it's going to work, it NEVER will. No matter how hard the engineers try to convince them. Trust me.

 

[rob5377]

Maddocks, this is what I have already found. It is really hard to convince them. Not only in this matter (they may be right) but sometimes they are really stuck to only one solution (theirs solution). The thing is, in the BOD, the cold stack vapors disposal solution was approved. Now at the end of the project they would like to have "ignition tool" at the cold vent stack to to safe dispose heavy HC during pigging. "or other safe solution"
It seems like there is no other option than hook it up to vent stack. I hope they will accept this...
The stack is 10m high.
cheers

 

[SJones]

CCPS Safe Design & Operation Of Process Vents & Emission Control Systems will walk you through the considerations and analysis (and then follow the operators' gut feel!).

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[dcasto]

Put is a small packaged combustor and get it over with. Plant guys are always right and pipeline guys are just idiots. I'm one of the idiots and I learned to just live with it. Take the pilot fuel from thier side of the meter.