7/27/2019 Vent and Flare Systems

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Vent and Flare Systems

Buoyancy seals and velocity seals- Buoyancy seal typically uses the diff erence

in densities o f the purge gas and ambient air to keep the air f rom entering f lare

system. Velocity seal is a cone-shaped obst ruction placed inside the f lare tip soas to o bstruct the inf iltrating air f rom ‘hugging the inner wall’. The purge gas f low

coming through the cone is a f ocused stream which sweeps away the inf iltrating

air along with it .

Continuous purge gas flow requirement in flare networks – One of the ways

to avoid air ingress into t he f lare stack, vent KO drum, f lare network and

subsequent catast rophic consequences, is to cont inuously purge a small f low

rate of hydrocarbon gases. This continuous hydrocarbon gas purge f low in the f lare network helps to build

up some positive backpressure at the vent knock out drum.

Emissivity coefficient for flare tip – Emissivity coef f icient f or a f lare tip is the fraction of heat generatedat the f lare tip that is radiated to surroundings. Not all the heat that is generated by burning hydrocarbon

gases at the tip of a f lare is radiated. Major f raction of the heat generated by a f lare is carried to the

surroundings in the f orm of hot gases by convection and the f raction of this heat is simply radiated to

surroundings.

Flar e radiation plots / isopleths – Radiation plot s are representat ive of the incident radiated heat f rom

f lare reaching at dif f erent locations in the surroundings. Radiation plots typically consist of isopleths.

Isopleths are curves o n a map of the f lare surroundings which connect geographical points receiving the

same intensity of heat radiated f rom the f lare.

Flar e tip burn back – Burn back of the f lare tip is caused by low exit velocities o f the gas at f lare tip. The

f lare tip and f lare stack diameter are designed handling f or the maximum possible f low in the f lare network.

However, the normal gas f low in the f lare stack is much lower than the design f low rate, resulting in low exit

gas velocities at the f lare tip. Low gas velocities mean that the gas begins to burn much closer to t he f lare

tip than desired, thus causing burn back of the f lar e tip.

 Liquid Seals on Flare/Vent Stack – liquid seal at the f lare stack base is

essentially a cylindrical volume of liquid into which the gas inlet to f lare stack is

dipped. This volume allows the f low of f lared gas f rom inlet pipe to the stack in

f orm of bubbles rising through the liquid. Liquid seal volume does not permit any

air f low entering the gas inlet pipe, thus preventing air ingress into the f larenetwork.