enggcyclopedia.com http://www.enggcyclopedia.com/vent-flare-systems/ V ent and Flare Sys t ems Buoyancy seals and velocity seals - Buoyancy seal typi cal ly uses t he diff erenc e in densities o f the purge ga s and ambient air to keep the air f rom entering f lare system. V elocity seal is a cone- shaped obst ruction place d inside the f lare tip so as to o bst ruct the inf iltrating ai r f rom ‘huggi ng the inner wall’. T he purg e gas f low comi ng through t he cone is a f ocused s tream which sweeps away the inf iltrating air along wi th it. Continuo us purge gas f low require ment in flare networks – One of the ways to avoid ai r ingress into t he f lare stack, vent KO drum, f lare network and subsequent catast rophic consequences, i s t o cont inuously purge a smal l f low rate of hydrocarbon gases. T his continuous hydrocarbon gas purge f low in the f lare network helps t o build up some pos itive backpress ure at t he vent kno ck out drum. Emissivity coefficient for flare tip – Emissivi ty coef f icient f or a f lare tip i s t he fraction of heat generated at t he f lare tip that is radiated to surro undi ngs. Not all the heat that is generated by burning hydrocarbon gases at the ti p of a f lare i s radiated. Major f raction o f the heat generated by a f lare i s carried to t he surroundi ngs in the f orm of hot gases by c onvection and the f raction of this heat is simp ly radia ted to surroundings. Flar e radiation plots / isople ths – Radiatio n pl ot s are representative of the incident radiated heat f rom f lare reaching at dif f erent locations in the surroundings. Radi ation plot s t ypi cal ly consist of iso pleths. Iso pleths are curves o n a map of the f lare surroundings whi ch connect geographi cal points recei ving the same intensity of heat radi ated f rom the f lare. Flar e tip burn back – Burn bac k of the f lare tip is caused b y low exit vel ocities o f the gas at f lare tip. T he f lare tip and f lare stack diam eter are designed handli ng f or the maximum p os sible f low in the f lare network. However , the no rmal gas f low in the f lare stack is much lower than t he design f low rate, res ulting in l ow exit gas velocities at t he f lare tip. L ow gas velocities mean that t he 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 – liqui d seal at the f lare stack base is ess entiall y a cyl indri cal volume o f liq uid in to whi ch the gas inlet t o f lare stack is dipp ed. T his volume allows the flow of f lared gas f rom inlet pipe to the stack in f orm of bubbles rising thro ugh the liqu id. L iqui d seal volume does not perm it any air f low entering the gas inl et pipe, thus preventing a ir ingress into the f lare network.

Vent and Flare Systems

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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.