flare line study

1. A flare line must NOT have any pockets
2. Most Flare systems will have one or more Flare Knock-Out (KO) Drums
3. To determine the Flare Line find the overall distance from the flare Stack to the farthest Relief Valve.
4. Determine the size of the Flare KO Drum
5. Determine the size of the Flare Header
6. Determine the minimum slope of the Flare Header
7. Establish the height of the Flare KO Drum. Don't forget the NPSH requirements for the Slops Pump off the bottom of the KO Drum.
   
8. Figure the fitting make-up for the flare header piping at the flare drum to establish a starting point
9. calculate the slope (up) from the flare drum to the location of the farthest relief valve including elevation changes at changes in direction
10. Spot check other relief valves
11. If the system does not work you may need to add in a second intermediate Flare KO Drum
12. Make all PSV discharge lines drain to the sub-headers, and all sub-headers drain to the main header and the main header drain to the KO drum
    

dear sir

you can finding john zink handbook and finding all answer of your questions.

and Flare Gas Design by :F. Ghadyanlou -2011 ,andishesara publishing company

If the size of subheader and the header is same ( ex 30") , also should we drain subheader to header or they can join horizentally too?