Reacting Flow: Flare System Combustion

Description

This project simulates combustion in a gas flare system using ANSYS Fluent, investigated through CFD analysis. The model was built in 3D using Design Modeler. Owing to the symmetrical structure of the flare and to reduce computational cost, only a 120-degree segment of the geometry was modeled.

The flare has a cylindrical structure situated within a cylindrical computational domain. Several distinct sections — steam, gas flow, and pilot — are defined at the tip of the flare. Meshing was performed in ANSYS Meshing, producing 1,043,138 elements.

Methodology

A flare system, or gas flare, is a combustion device used in industrial facilities such as oil and gas refineries and at oil and gas production wells, particularly on offshore platforms, to safely burn off surplus hydrocarbon gases. The Species Transport model was used to carry out this simulation.

The reacting mixture is defined as an n-butane–air blend consisting of nine gaseous species: C₄H₁₀, O₂, CO₂, H₂O, H₂, CH₄, C₂H₆, C₃H₈, and N₂. The volumetric reaction model was activated to enable the chemical reactions and, in turn, the combustion process, which is represented by five distinct chemical reactions.

At the flare tip, a stream of hydrocarbon gas enters the environment at a flow rate of 0.09259 kg/s. Simultaneously, a methane flow from the pilot and a steam flow from the steam inlet — both at velocities of 2.479 m/s — enter the domain to ignite the mixture. The standard k-epsilon model was used to solve the turbulent flow equations, together with the energy equation to compute the temperature variation within the combustion region.

Conclusion

On completion of the solution, three-dimensional contours of velocity and of the mass fraction of each modeled gas species were obtained.

For instance, examining the three-dimensional contour of carbon dioxide clearly shows that the combustion reaction and the resulting production of CO₂ are taking place. As the results also demonstrate, the mass fractions of the fuel species decrease with distance from the fuel inlet, while the mass fractions of the reaction products correspondingly increase along the same direction — confirming the progress of combustion through the domain.