Stable Combustion under Carbon Dioxide Enriched Methane Blends For Exhaust Gas Recirculation (EGR)

Abstract

Exhaust gas recirculation (EGR) is one of the main techniques to enable the use of oxyfuel combustion for carbon capture and storage (CCS). However, the use of recirculated streams with elevated carbon dioxide poses different challenges. Thus, more research is required about the cumulative effects on the desirable outcomes of the combustion processes such as thermal efficiency, reduced emissions and system operability, when fuels with high CO2 concentration for CCS exhaust gas recirculation or biogas are used. Therefore, this study evaluates the use of various CO2 enriched methane blends and their response towards the formation of a great variety of structures that appear in swirling flows, which are the main mechanism for combustion control in current gas turbines systems. The study uses 100 kW acoustically excited swirl-stabilised burner to investigate the flow field response to the resultant effects of the variation in the swirl strength, excitation under isothermal condition and the corresponding effects during combustion with different fuels at various CO2 concentrations. Results show changes in size and location of flow structures as a result of the changes in the mean and turbulent velocities of the flow field, consequence of the imposition of different swirl and forcing conditions. Improved thermal efficiency is also observed in the system when using high swirl and forcing while the blend of CO2 with methane balanced the heat release fluctuation with a corresponding reduction in the acoustic amplitudes of the combustion response, suggesting that certain CO2 concentrations in the fuel can provide more stable flames. Concentrations between 10 to 15% CO2 volume show great promise for stability improvement, with the potential of using these findings in larger units that employ CCS technologies.