ANALYSIS OF DIFFERENT EMISSION METRICS FOR POWER GENERATION MACHINERY IN FLEXIBLE CO-GENERATION ENERGY SYSTEMS

There are many different metrics used for characterizing the emission behavior of power generation units, making it difficult to compare different technologies, fuels, and cycle layouts comprehensively. The present study analyses and evaluates different metrics for emission quantification (e.g., relative, absolute, or performance-based values). Mixtures of conventional fuels (natural gas, represented by methane) and alternative, carbon-neutral fuels (hydrogen and ammonia) are compared. Different cycle adaptations of power generation systems (exhaust gas recirculation, water and steam injection) are addressed. Both NOx and CO2 emissions are investigated using a gas turbine model and a chemical reactor network for a state-of-the-art industrial gas turbine. The results show that by using common metrics (i.e., ppmvdr) the emission behavior is significantly and moderately exaggerated for H-2 and NH3, respectively. Performance-based metrics, however, are found to be most suitable for emission quantification across different fuels and cycle layouts: for example, if a standard gas turbine NOx emission limit of 15 ppmvdr is applied, lower NOx are found for fuel substitution with H-2 than with NH3. Additionally, introducing the equivalent NOx emission limit of 150 mg/kWhel for gas turbines (considering full load efficiency of 39 %) as a regulative limit enlarges the suitable hydrogen addition rate from 47 vol.% up to 60 vol.% H-2 from an emission perspective.