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Flare Purge and Seal Design

asked May 19, 2016 in Engineering by russelbraley (435 points) | edited May 20, 2016 by russelbraley
Hello all, can you please help with providing an equation to estimate the purge gas rate required for an open pipe flare?

Thanks very much in advance for any inputs.

2 Answers

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answered May 20, 2016 by AngelPenavega (1,025 points)

You can use the following equation as an initial estimate of the purge gas rate required for an open pipe flare.

PG = BD3 / M0.565

Where:
PG   =  purge gas, m3/h (ft3/h)
B     =  constant for flare stacks 457–914 mm (18–36 in.) in diameter (1.2 x 10-5 [metric]; 7.0 [customary])
D     =  stack diameter, mm (in.)
M     =  molecular weight of purge gas

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answered May 30, 2016 by Lana Hajovsky (340 points)

Purge Gas should be configured to supply a continuous flow and should be fitted in the main flare header as far away from the flare as possible in order to sweep the flare header.

When purge gas is used in conjunction with a buoyancy seal or kinetic seal, a smaller amount of gas is needed.

Purge requirements for proprietary flare tips and seals should be established with the supplier.  The purge rate should be specified to prevent internal burning up stream of the air seal device (kinetic, molecular, water) and premature tip degradation.

After startup, a small stream of continuous purge gas need only be injected into the main header at the point farthest from the flare.  A flow meter with a low-flow alarm should be installed at the purge gas injection point.

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