Combustion in a Boiler

Combustion Inside the Boiler, ANSYS Fluent CFD Simulation Training

Description

This project simulates combustion inside a boiler using ANSYS Fluent. The 3D geometry was designed in SpaceClaim, with airflow entering through the boiler's side panel and a combination of fuel streams entering through narrow pipes at the boiler's lower section, while the outlet connects to the upper pipe. The domain was meshed in ANSYS Meshing, totaling 4,694,637 elements.

Methodology

Boilers are pressurized tanks designed to boil or heat a working fluid, raising its temperature to the boiling point — a process that depends on sustaining a combustion reaction within the boiler itself. This combustion reaction occurs throughout the boiler's computational domain, with the relevant chemical species defined using the Species Transport model. Nine distinct species were defined to represent the combustion chemistry, governed by five volumetric combustion reactions between them.

The boiler features two inlets: an airflow inlet entering from the side at 303.15 K with a mass flow rate of 3.375 kg/s, and a fuel inlet — a combination of several different fuel species — entering through the lower narrow pipes at 300 K with a mass flow rate of 0.6135 kg/s. Turbulence was resolved using the Realizable k-epsilon model, with the energy equation enabled to capture temperature variation throughout the domain as combustion progresses.

Conclusion

Results include 2D and 3D contours of temperature, velocity, and mass fraction for each defined species, including oxygen, carbon dioxide, water vapor, CH₄, C₂H₄, C₃H₄, and C₄H₁₀. The results show that as the hydrocarbon fuel species combine with oxygen, a combustion reaction takes place, driving a clear rise in temperature throughout the boiler's interior.

As this reaction proceeds, hydrocarbon and oxidant concentrations decline near the boiler's inlet region, while carbon dioxide and water vapor — the primary combustion products — correspondingly increase in concentration, confirming that the fuel-oxidizer mixture is being consumed and converted into combustion products as expected throughout the boiler.