NOx Production from Premixed Hydrogen/Methane Fuel Blends
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Abstract
Hydrogen (H2) fuel is a promising means for long duration energy storage and dispatchable utilization of intermittent renewable power, which can be combusted without CO2 emissions. However, combustion of any fuel in air can still lead to NOX production. This whitepaper summarizes recent analyses of NO emissions of premixed H2/CH4 blends, demonstrating how fundamental drivers of NOX production change with hydrogen addition. Three major findings are presented: (1) At constant temperature, NO emissions decrease with the addition of H2 for typical gas turbine conditions; (2) Although NOX emissions are typically quoted as parts per million (ppm), it is not appropriate to use ppm as a comparison between different hydrogen blended compositions; one must use mass based comparisons (e.g., ng/J or lbm/MMBTU); (3) atmospheric pressure fuel sensitivity NOX studies will not capture the controlling NO production physics that are present in practical applications, such as gas turbines.
These results provide important context for several experimental studies that have been reported. First, they are consistent with several recent demonstrations of fielded gas turbines with hydrogen blending, that show constant to declining NOX levels with hydrogen addition. Second, some lab studies have noted that hydrogen blended systems have elevated NOX emissions relative to natural gas, but these appear to be for nonpremixed systems and it is not entirely clear what is being held constant for these comparisons (temperature, power, etc.). Given the strong temperature sensitivity of NOX production, these results cannot be applied more generally to understand NOX emissions tendencies.
Taken together, we conclude that utilization of modern premixing combustion technologies with hydrogen blending should lead to constant or decreasing NOX emissions, but use in older, diffusion type burners can lead to elevated NOX.
item_description: This whitepaper summarizes recent analyses of NO emissions of premixed H2/CH4 blends, demonstrating how fundamental drivers of NOX production change with hydrogen addition. Three major findings are presented: (1) At constant temperature, NO emissions decrease with the addition of H2 for typical gas turbine conditions; (2) Although NOX emissions are typically quoted as parts per million (ppm), it is not appropriate to use ppm as a comparison between different hydrogen blended compositions; one must use mass based comparisons (e.g., ng/J or lbm/MMBTU); (3) atmospheric pressure fuel sensitivity NOX studies will not capture the controlling NO production physics that are present in practical applications, such as gas turbines.
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This study has been partially supported by the Electric Power Research Institute (EPRI) and the University Turbine Systems Research (Grant DE-FE0032079) program under project manager Mark Freeman.
Date
2023-09-01
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White Paper