Numerical analysis of combustion characteristics and emissions of recycled flare gas in ethylene cracking furnaces

Flaring hydrocarbon gases is a common practice in petrochemical plants, contributing to significant greenhouse gas (GHG) emissions and resource wastage. This study investigates the combustion characteristics and emissions of recycled flare gas mixtures in an industrial burner for petrochemical applications using computational fluid dynamics (CFD) simulations in ANSYS Fluent. The research examines the behavior of three flare gas mixtures with varying compositions (10–40 %) and the influence of excess air levels (10–50 %) on temperature profiles, flame stability, and emissions. Results indicate that Mixture 1, rich in hydrocarbons, stabilizes combustion at 30–40 % flare levels, achieving peak temperatures, while instability occurs at 10–20 % flare levels. Mixture 2, with high methane content, performs optimally at 40 % flare, enhancing heat retention, but lower levels reduce stability due to turbulence. Mixture 3, containing lighter hydrocarbons, remains unstable overall but shows improved combustion performance at 30 % and 40 % flare levels due to delayed energy release. Introducing 10–20 % excess air enhances stability, but levels beyond 30 % impair thermal efficiency. Emission trends indicate methane-rich mixtures increase CO₂ and NO_x, while lighter mixtures reduce NO_x but encounter stability challenges. These insights inform strategies for optimizing flare gas utilization in petrochemical burners.