Publication: Numerical analysis of non-premixed biogas combustion in model gas turbine combustor with static swirler.
Date
2024-07
Authors
Alvin Hasan
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Abstract
Biogas, primarily composed by methane gas (CH4) and carbon dioxide (CO2), is a versatile renewable energy resource produced through a biological mediated process, known as anaerobic digestion (AD). Biogas has lower calorific value, flame velocity and flammability range compared to natural gas due to its CO2 richness as a fuel. With emerging needs of fossil fuel replacement due to its environmental issues due to the pollution produced as the product of its combustion, biogas stands as one of the leading reliable substitutes. In this project, a non-premixed combustion of biogas in stoichiometry condition inside a gas turbine (GT) combustor model with the application of a static swirler will be simulated using a CFD software, ANSYS FLUENT 2024 R1 (Student Version), where the 3D geometry is imported from SOLIDWORKS 2023. The main objectives of the study are to know the effect of addition of CO2 on the flame characteristics of the biogas combustion. The flame temperature and velocity will be observed, while at the same time the product of combustion such as carbon monoxide, carbon dioxide, as well as thermal NOx emission will be monitored. Swirler is introduced in the system to produce a better mixing of flame and air in the combustor chamber, thus creating a more stabilized and uniform flame. In this study, three concentrations of fuel will be used, such as 10%, 20% and 30% of carbon dioxide with 90%, 80% and 70% of methane respectively. Moreover, three different types of turbulence model will be used in this study, namely k-ε standard, k-ε RNG and k-ε realizable. The results produced by each turbulence model will then be compared with the combustion of methane only. After testing, it is found that the standard model gives the most relevant result compared to the other turbulence models. It is found that the addition of CO2 can lower the flame temperature of biogas combustion. Thus, reducing the production of thermal NOx emission significantly since it is highly dependent on the temperature. However, the amount of CO2 inside the combustor will definitely increase. The temperature difference between biogas and fully methane combustion can reach up to 50K. In addition, the amount of carbon monoxide produced by biogas combustion is similar with the methane combustion. Furthermore, due to the bluff body blocking the airways to the chamber and with the help of chemical reaction, the maximum velocity of the flame is around 35m/s inside the combustor.