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

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The present problem simulates two-step mechanism combustion in a gas flare in the presence of wind flow using ANSYS Fluent software.

This product includes a Mesh file and a comprehensive Training Movie.

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Gas Flare Project Description

The present problem simulates two-step mechanism combustion in a gas flare in the presence of wind flow using ANSYS Fluent software. 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 in offshore platforms. Gas flares are responsible for burning the natural gases released during oil extraction in a completely controlled manner. In fact, during the oil extraction process, some natural gas accumulates in a mass on top of the oil in the reservoirs. Therefore, it is better to try to collect and store natural gas, but if this is not possible, they burn it.

The combustion of these gases using the flare system causes, firstly, to prevent 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. To define chemical reactions, the reaction mode must be activated in volumetric mode. 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.

gas flare

Gas Flare Geometry & Mesh

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 to reduce the computational cost, only half of it has been modeled. 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.

gas flare

We carry out the model’s meshing using ANSYS Meshing software. The mesh type is unstructured. The element number is 1546925. The following figure shows the mesh.

gas flare

CFD Simulation

We consider several assumptions to simulate the present model:

  • We perform a pressure-based solver.
  • The simulation is steady.
  • The gravity effect on the fluid is ignored.

The following table represents a summary of the defining steps of the problem and its solution:

Models (Gas Flare)
Viscous k-epsilon
k-epsilon model realizable
near wall treatment standard wall functions
Species Species Transport
mixture material methane-air-2step
reactions volumetric
number of volumetric species 6 (CH4,CO2,CO,O2,H2O,N2)
Energy On
Boundary conditions (Gas Flare)
Inlet – Wind Velocity Inlet
velocity magnitude 0.2 m.s-1
temperature 300 K
O2 mass fraction 0.23
N2 mass fraction 0.77
other specied 0
Inlet – Fuel Velocity Inlet
velocity magnitude 0.1 m.s-1
temperature 300 K
CH4 mass fraction 1
other species 0
Outlet Pressure Outlet
gauge pressure 0 Pascal
Wall of Flare
wall motion stationary wall
thermal condition coupled
Symmetry Symmetry
Methods (Gas Flare)
Pressure-Velocity Coupling SIMPLE
Pressure second order
momentum first order upwind
turbulent kinetic energy first order upwind
turbulent dissipation rate first order upwind
all species first order upwind
energy second order upwind
Initialization (Gas Flare)
Initialization methods Standard
gauge pressure 0 Pascal
x-velocity & z-velocity 0 m.s-1
y-velocity 0.1 m.s-1
CH4 mass fraction 1
other species 0
temperature 500 K


At the end of the solution process, two-dimensional and three-dimensional contours related to the pressure, temperature, velocity and mass fraction of each of the 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.

There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.


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