A Reactor-Network Framework to Model Performance and Emissions of a Longitudinally-Staged Combustion System for Carbon-Free Fuels

Abstract

Abstract Hydrogen and ammonia are considered crucial carbon-free energy carriers optimally suited for seasonal chemical storage and energy system balance. In this context, longitudinally-staged combustion systems (LSC) represent an attractive technology for achieving low emissions while conserving high load and fuel flexibility at high efficiency. While these two-stage combustion systems have been successfully implemented for natural gas and hydrogen firing of gas turbines, optimal operation with ammonia-based fuel mixtures not yet established. Recent works have shown that ammonia can be combusted with low emissions in gas turbines by employing a Rich-Quench-Lean operational concept where a slightly rich fuel-air mixture is burnt in the first-stage followed by dilution air addition, which completely oxidizes the remaining unburnt fuel. However, an optimal operational strategy to efficiently combust all three fuels within the same system is yet to be established. In this work, we exploit a reactors-network framework to efficiently investigate the emissions performance of a LSC system fired with natural gas, hydrogen and ammonia. Firstly, the framework is validated with experimental and computational emission results in the literature. Secondly, the optimal operational strategy (in terms of fuel- and air-split between the stages) for clean and efficient ammonia-firing operation is found. Thirdly, the consequences of such ammonia-optimized operational strategy on flame stabilization and emissions with natural gas- and hydrogen are considered. Finally, the air and fuel distribution for optimal performance and minimal emissions for all three fuels is found for the LSC system.