Stratified and Hydrogen Combustion Techniques for Higher Turndown and Lower Emissions in Gas Turbines

This review overviews combustion technologies for reduced emissions and better fuel economy in the industrial gas turbine. Lean premixed combustion (LPM) technology is introduced as a low-temperature combustion technique to control NO_x emissions. The dry low NO_x (DLN) is one of the most promising LPM-based combustors for controlling NO_x emissions. However, DLN combustors suffer from limited flame stability, especially under low load (near blowout) operating conditions, in addition to the difficulty of separating CO₂ from the exhaust stream for reducing the gas-turbine carbon footprint. Trying to overcome such difficulties, the gas turbine manufacturers developed enhanced-design burners for higher turndown and lower NO_x emissions, including the Dual Annular Counter Rotating Swirl (DACRS) and environmental-vortex (EV) burners. The volume of the DACRS combustors is almost twice the conventional burners, which provide ample residence time for complete combustion. The mixing effectiveness is improved in EV-burners resulting in higher flame stability at low load or startup conditions. To widen the operability, control the emissions, and improve the turndown ratio of gas turbine combustors, the concept of flame stratification, i.e., heterogenization of the overall equivalence ratio, was introduced. This technique can widen the stability range of existing LPM flames for industrial applications. Integrating stratified combustion techniques with oxy-fuel combustion technology is a way forward that may result in complete control of gas turbine emissions with a higher operability turndown ratio. The recent developments and challenges toward the application of hydrogen gas turbines are introduced.