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Flare Header Sizing

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#1 Sara Owens

Sara Owens

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Posted 07 February 2019 - 02:13 PM

i am sizing the relief valve outlet lines. The outlet lines are connected to a flare header where the battery limit back pressure is minimum 2 psig and max of 65 psig.

how do i determine the relief valve outlet lines? At 65 psig max backpressure, this will be used to determine what type of relief valve selection, bellows, conventional, etc. when i make the flare backpresssure to 2 psig, i get a mach number of 1, which forces me to increase the line size. (when i use the 65 psig backpressure, I had no problem with the line size) what is the general practice to size the outlet lines to flare header? what is the rule of thumb for mach number on header and flare outlet lines? for the flare header and subheader, i want 0.5, and for the lateral outlet lines, i want to keep a mach number of 0.7. please let me know. 

#2 Emamoke


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Posted 25 February 2019 - 10:39 AM

Try Using a simulation. In some cases, Clients specify which Simulation software you should use. Yo can use ASPEN Flare System Analyzer. There are other out there too. 


As per the header size, you need to consider using the larger pipe size because that would be your worst scenario. 


Ideally, when we size Flare Header, its the most stigent scenario that governs the header size. 


Hope this input helps. 

#3 AlertO


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Posted 27 February 2019 - 04:36 AM

Hi Sara


I think what you stated above has already answered you question. So I just left my feedback below.


- Typically, to determine the outlet line size, you need to achieve both mach no and backpressure.

- It is normal to have high mach no when the relief fluid is discharged to low pressure.

- Your criteria seems being general practice. Any concern to use them?


May I ask you a question? How you get the number of minimum and maximum pressures you referred to?

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