Stratified and Hydrogen Combustion for Higher Turndown and Lower Emissions

This chapter provides an overview of the combustion methods used in industrial gas turbines to reduce emissions and improve fuel efficiency. As a low-temperature combustion strategy to control NOx emissions, lean premixed combustion (LPM) technology is presented. One of the most promising LPM-based combustion systems for reducing NOx emissions is the Dry Low NOx (DLN) system. However, DLN combustors struggle to separate CO2 from the exhaust stream in order to lessen the carbon footprint of gas turbines. This is especially true while running at low load (near blowout). In an effort to solve these challenges, gas turbine manufacturers created enhanced-design burners, such as the Dual Annular Counter Rotating Swirl (DACRS) and Enhanced-Vortex (EV/SEV/AEV) burners, for higher turndown and reduced NOx emissions. The DACRS combustors have nearly twice the volume of traditional burners, giving the fuel plenty of time to burn completely. In EV-burners, the mixing efficiency is increased, leading to enhanced flame stability at low load or start-up conditions. The idea of flame stratification, or heterogenization of the overall equivalency ratio, was first established to increase the operability, regulate the emissions, and improve the turndown ratio of gas turbine combustors. The stability range of current LPM flames for industrial applications can be expanded with this technology. A step forward that could lead to perfect control of gas turbine emissions with a greater operability turndown ratio is the integration of stratified combustion technique with oxy-fuel combustion technology. The most recent advancements and difficulties with using hydrogen gas turbines are described.