Flare Header Capacity

[maddocks]

ok, this one's interesting. I'm trying to establish the rate at which we can blow down a pig receiver to the main flare header. The line is 410' of 4" Sch 80 and is rated for 600# ANSI and ties-in to the 16" main header.

Based on using say 0.50 mach, the rate looks like about 7 MMSCFD. However, why can't I force this rate up to say 20 MMSCFD and have a standing pressure wave in the line? The line will simply pressure up to the point where the outlet velocity is at mach 1. Since the line is rated for 600# ANSI, can I use the line as a restriction orifice up to where the downstream pressure is at critical flow?

Thoughts anyone?

 

[dcasto]

no reason you can't. Think about having the pressure drop or control point at the point where the 4" ties to the 16". The 4" is just another piece of the pipeline you are blowing down.

 

[EGT01]

The negative aspects of going to Mach 1 are noise, vibration and any additional stress on your piping system.

 

[maddocks]

I agree, but given that this is a short duration event, manually controlled by the operator, I think the noise will be acceptable.

I think I'll put an orifice or choke nipple in the line to limit system flow to a preset # if the operator cranks the globe valve wide open. I'll review pipe supports and clamps to make sure we're covered on the vibration issue.

 

[JoeWong88]

For high pressure drop and flow would results acoustical (high frequency) induced vibration and risk to the mechanical integrity of downstream piping (150# ?) especially the 16" header (hope it is not a thin wall pipe).

Other than the pipe support & clamp, suggest to review the piping integrity as well.

 

[EGT01]

Of course you'll need to make sure your blowdown rate doesn't exceed your flare capacity or present any other concerns in case you've had to model a release from the flare without it burning.