Using Reactor Networks for Predicting the Impact of Turbine Expansion on Gas Turbine Emissions

The goal of this study is to develop a chemical reactor network model to understand the impact of turbine expansion on engine-out emissions. Historically, experimental studies and network models measure combustor-out emissions, but the rapid expansion in the turbine, which results in dramatic reductions in temperature and pressure, could have an impact on kinetics with slow timescales, including pollutant formation and recombination reactions. The combustor model consists of a series of perfectly stirred reactors representing the primary, recirculation, and dilution zones of a gas turbine combustor. The test case used in this study is based on prior studies that considered the use of exhaust gas recirculation (EGR) with carbon capture and hydrogen enrichment in the fuel as two methods to reduce the carbon emissions from industrial and power generation gas turbines. Different blends of diluents are used to simulate EGR with oxygen from 21% to 15% by volume and carbon dioxide addition up to 15% by volume. Additionally, hydrogen enrichment up to 40% by volume is blended with methane in combination with EGR. The turbine expander is modeled with a plug flow reactor with the profile of temperature, pressure, and velocity calculated using the meanline velocity triangle approach for an ideal turbine. Accuracy of the combustor model was assessed by comparing the network results to prior experimental data and results were within reasonable error. The turbine expander model functions and produces thermodynamic output data that aligns with typical performance of industrial and power generation gas turbines. It can be concluded that the use of a network model for the turbine is an effective method to accurately predict engine-out emissions and analyze critical chemical kinetic pathways.