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ice plug in flare - how to fix that? 2

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eagle1900

Mechanical
Sep 11, 2006
25
Does anybody having experience with ice plugging in flare during winter?

I'm in a plant where we flare gaz from a seal drum of oil-water-h2s-gaz... And me I'm pretty new with process engineering.

Could you tell me what you think about, to add a nitrogen purge in the flare and maybe to try to dry much our vapor?

Is that important if we shoot vapor before to flare and after? Does it has a link with creating ice? Is that better to only use vapor at the end? Does it exist any litterature or norms which show how to adjust everything?

We shoot vapor aroud the tip and not by the middle...

Thanks for your help!

mech eng.
 
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We had a 48" flare with a fluidic seal below the tip. It once froze in winter several years ago. Luckily there was an unused pilot gas line running all the way up and we removed the ice plug by pumping methanol up this 2" line and over the edge into the top. This worked well but it was a very dangerous situation while it lasted. Since very cold winters were the norm, a facility for pumping methanol up there was added to all the flares.
All sub headers leading into the main flare should have a small flow of gas at the very begining to continuously sweep the flare system of tramp gases or air. Normaly this is dry nitrogen or natural gas, whichever is cheaper. There are guidelines for flowrates which I dont have in front of me. All refinery flares I have seen have this. There is often pressure from the management and/or accountants to minimise or remove this flow since it costs money. This should be resisted.

The propensity to freezing obviously depends on tip and seal design, of which there are many.
 
Can't it be traced?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>
 
Couldn't say. I've never seen one traced. Reliability in a location that sees some extreme tempererature excursions might be a problem. Also it might be hard to trace the internals which are remote from the tip wall.
 
eagle1900
On a previous job in a very cold climate we had a constant Fuel gas (natural gas) purge and we had the flare headers traced, only in the bottom section of the header. In this case electrical tracing.
Could be a good idea to spcifically go for electrical tracing here if one experiences a trip while it is cold and steam might not be available at all times.
If it was up to me I would also like to have a facility to add some MeOH.
 
This is all quite scary. I would really focus on keeping the water out, or it will become normal to have water in the flare and you will be one step closer to a major catastrophe.
 
We always have a knock out drum before the flare, nevertheless, the flare line up to the flare is electrically heat traced and insulated. I have yet to experience an iceplug. Even with ambient temps <-40ºC

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>
 
We had a hydrogen flare in about -40 deg F weather and we were venting steam since we did not always have gas to put in the reformer. A big chunk of ice developed around the flare tip. A very smart maintenance person got a crane with an upside down tank on the hook, I suppose about 6 feet diameter tank, and held it just above the flare for a while. The steam melted the ice.

HAZOP at
 
I would be interested in hearing from Geordie87. Click on my website at the bottom of this post, then go to "Contact us". The email function is a popup so you may need to turn your popup stopper off. Howay United!

HAZOP at
 
Thanks guy!!!

As we say I'm in a beautiful chalenge "with the managers".

But what you told me confirm what API say, but the best could be, "maybe", to eliminate all water entering in the flare. But, my seal drum work with water and steam... Here is the bigger problem I see for now.

An other thing is I've read about drying the vapor going in the flare... like to separate exasparating water for keeping only vapor, and by tracing the vapor line.

But OWG, are you telling they have used a crane for un-plugging the flare???? WoW!!! We actually use boiler feedwater for un-plugging.
 
An other option I see, is to inject a sequence of hot gaz in the flare during winter... but my question for now is which gaz??? I flare Hydrocarbone + H2S ++++
 
I don't work in an area that frozen water in the discharge of PSV vents is a problem, BUT water collection in these is. We routinely put a 1/4" dia. weep hole at the bottom of the elbow to drain any accumulation of liquids. I'm guessing this could work for you too. Good Luck!
 
One possible solution is to insulate your stack with high temp rated insulation. That solution worked out quiet well with an exhaust stack of one of our boilers--a little bit different than your situation.
 
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