Vent and Flare Systems

Buoyancy seals and velocity seals- Buoyancy seal typically uses the difference in densities of the purge gas and ambient air to keep the air from entering flare system. Velocity seal is a cone-shaped obstruction placed inside the flare tip so as to obstruct the infiltrating air from ‘hugging the inner wall’. The purge gas flow coming through the cone is a focused stream which sweeps away the infiltrating air along with it.

Continuous purge gas flow requirement in flare networks - One of the ways to avoid air ingress into the flare stack, vent KO drum, flare network and subsequent catastrophic consequences, is to continuously purge a small flow rate of hydrocarbon gases. This continuous hydrocarbon gas purge flow in the flare network helps to build up some positive backpressure at the vent knock out drum.

Emissivity coefficient for flare tip - Emissivity coefficient for a flare tip is the fraction of heat generated at the flare tip that is radiated to surroundings. Not all the heat that is generated by burning hydrocarbon gases at the tip of a flare is radiated. Major fraction of the heat generated by a flare is carried to the surroundings in the form of hot gases by convection and the fraction of this heat is simply radiated to surroundings.

Flare radiation plots / isopleths - Radiation plots are representative of the incident radiated heat from flare reaching at different locations in the surroundings. Radiation plots typically consist of isopleths. Isopleths are curves on a map of the flare surroundings which connect geographical points receiving the same intensity of heat radiated from the flare.

Flare tip burn back - Burn back of the flare tip is caused by low exit velocities of the gas at flare tip. The flare tip and flare stack diameter are designed handling for the maximum possible flow in the flare network. However, the normal gas flow in the flare stack is much lower than the design flow rate, resulting in low exit gas velocities at the flare tip. Low gas velocities mean that the gas begins to burn much closer to the flare tip than desired, thus causing burn back of the flare tip.

 Liquid Seals on Flare/Vent Stack - liquid seal at the flare stack base is essentially a cylindrical volume of liquid into which the gas inlet to flare stack is dipped. This volume allows the flow of flared gas from inlet pipe to the stack in form of bubbles rising through the liquid. Liquid seal volume does not permit any air flow entering the gas inlet pipe, thus preventing air ingress into the flare network.

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