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TOPIC: pocket in flare header

6 years 8 months ago #8263

  • Er.piping
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Flare headers shall be free draining towards knock out drum
without any pocket, this was my concept till yesterday..!
In a new project i am working on a unit flare header is tapped to main header
unit flare header is at 6 mtr. tier & main header is at 10 mtr. tier. The vertical leg at battery limit
is having a drip leg kind of arrangement.

I raised this issue with my boss and he told me that process people has no objection
to it.
My question is .. How is it possible..??

Re: pocket in flare header 6 years 8 months ago #6745

  • Jop
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I need more information before I can offer any comments.
Information such as:
- What kind of plant is this? Please be very specific. (example: Small Gas Treating Unit being added in an existing refinery)
- The size of the new Flare Header?
- The size of the existing Flare Header?
- How about a sketch or verbal description of how the tie-in is going to be made? (Here I want to know how they are going to keep a BIG slug of liquid from back-flooding the new header.)
- In what country is this work being done?
- What kind of experience does your Boss really have?
Do it once and Do it Right

Re: pocket in flare header 6 years 8 months ago #6746

  • Er.piping
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Dear Jop,
This is a greenfield power project in SA using coal gasification technology.
The unit i have been assigned to is called "Rectisol" in which impure gas is purified (H2s, Co2, HCN recovery) using
methanol as a solvent.
Size of main header is 24".
Size of unit header is 8".
Unit flare header (8") is sloped and supported outside the rack on cantilever. WP. EL. of unit header at B/L is approx. 6 mtr. At B/L it is raised vertically upward and tapped at 45^ to the main header (24") which is at 10 mtr. level.

At B/L vertical leg of approx 4 mtr. is provided with a drip leg and drain is routed to U/G system.

I hope this clarifies the situation. (No comments about the Boss..!! )

Re: pocket in flare header 6 years 8 months ago #6747

  • Jop
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Just my opinion.
When the situation was recognized the Project Management of your company should have met with the Client and made them aware of the problem and the potential danger. The situation should have also raised red flags during the HAZOP reviews of the P&IDs.
The solution (I have seen on projects) is to add a Unit Flare Knock-Out Drum inside the Battery Limits of the Unit.
Thus the Unit Flare Header would dump into the Unit Flare KO Drum and then the Drum would be piped to the Main Flare Header. Any fluids from the Unit or back flooding from the main header would go into the Unit KO Drum and would protect the Unit Flare relief capabilities.
Do it once and Do it Right

Re: pocket in flare header 6 years 8 months ago #6748

  • Er.piping
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Your resolution is no doubt the best possible way to do it sir,
But i was told to route drain of the unit header to U/G slope methanol
System and I wonder how it would work..? Since their is no KO drum in this perticular unit.

Re: pocket in flare header 6 years 7 months ago #6756

  • Peter Pyper
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I have had this problem from time to time. Jop's method of a secondary KO Drum is best and safest and should be the first choice.
I have however had to install a drain and barrel/pot at the low point. When I first encountered this I challenged the process engineer as I thought this was an unsafe practise. He said it was allowed according to code (API 520 Part II Section 6 - Installation Conditions that require Drain Piping) but it must be written into the operating procedures so that the plant operator can drain the line frequently. This of course requires client approval as it places responsibility and onus on their operations for safety.
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