Gas Flare, 2-step Air-Methane Mechanism Combustion, ANSYS Fluent Tutorial

Description

Description

The present problem simulates a two-step combustion mechanism in a gas flare in the presence of wind flow using ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

The flare system, also known as a gas flare, is a combustion device used in industrial units such as oil and gas refineries and the production of oil and gas wells, especially on offshore platforms.

The present model is designed in three dimensions using Design Modeler software. The present model is related to the construction of a gas flare due to symmetry, and only half of it has been modeled to reduce the computational cost.

This flare has a cylindrical structure with four outlet ducts located in a certain computational domain with the wind flow. This computational domain is also semi-designed due to symmetry, and the symmetry boundary condition is used.

The meshing of the model has been done using ANSYS Meshing software. The element number is 1546925.

Gas Flare Methodology

Gas flares are responsible for burning the natural gases released during oil extraction. In fact, during the oil extraction process, some natural gas accumulates in a mass on top of the oil in the reservoirs.

Therefore, collecting and storing natural gas is better, but they burn it if this is not possible. The combustion of these gases using the flare system causes, firstly, prevents the combustion and burning of these gases dangerously and uncontrollably.

Secondly, burning and converting methane to carbon dioxide and releasing them in the open space has less damage than the methane release.

Therefore, for this project, the species transport model has been used. The reaction mode must be activated in volumetric mode To define chemical reactions. The eddy dissipation model is also used to estimate the reaction rate.

In this simulation, a mixture of methane and air is burned in a two-step mechanism; they produce a chemical reaction in two consecutive stages.

Initially, methane and oxygen react to produce carbon monoxide, and then carbon monoxide combines with oxygen to produce carbon dioxide. The air enters the domain with a velocity of 0.2 m/s and a temperature of 300K.

Also, the fuel enters with a velocity of 0.1 m/s and a temperature of 300K. Moreover, the realizable k-epsilon model and energy equation are enabled to solve the turbulent fluid equation and calculate temperature distribution within the domain.

Gas Flare Conclusion

t the end of the solution process, two-dimensional and three-dimensional contours related to the pressure, temperature, velocity, and mass fraction of each gas species modeled in this simulation are obtained. Two-dimensional contours are displayed on the geometry symmetry plane.

The mass fraction contour of gaseous species indicates the occurrence of a chemical reaction.

For example, the carbon dioxide and carbon monoxide contours indicate that a chemical reaction produces these gaseous products, or the methane contour indicates that the hydrocarbon is used as a chemical reaction agent.

Another noteworthy point is that the defined wind flow in the computational region causes the gases from the chemical reaction, such as carbon dioxide and carbon monoxide or NO pollutants, to be released into the environment around the flare.