Abstract

Achieving carbon neutrality and sustainability has prompted research efforts into reducing carbon dioxide and carbon monoxide emissions in combustion systems without significantly increasing nitrogen oxides (NOx). Because of its high specific energy density, hydrogen is a prime candidate to eventually replace natural gas. Presently, using renewable hydrogen mixtures in natural gas turbines can reduce carbon dioxide and carbon monoxide emission as a step towards carbon neutrality. In the present effort, a commercial natural gas 200kW microturbine generator produced by Capstone Green Energy Corporation is used to study the impact of hydrogen addition to natural gas. Exhaust emissions, injector temperatures, and power output are evaluated for increasing levels of hydrogen in the fuel mixture. Relative to emissions on 100% natural gas, the experimental results show that, for full load, carbon monoxide and carbon dioxide emissions decrease as the amount of hydrogen in the fuel mixture increases while the NOx emissions increase. This is attributed to the increased reactivity of hydrogen resulting in a jet flame stabilized closer to the injector exit as the amount of hydrogen is increased. While the injector tip temperatures increased modestly with additional hydrogen, visual inspection of the injectors following hydrogen addition tests indicate that flashback or combustion inside the injectors was not occurring. This is consistent with the modest changes in NOx with hydrogen addition. If flashback were occurring, the emissions levels would be expected to be significantly higher. The results also demonstrate that added hydrogen to the fuel does not have a statistically significant impact on overall system efficiency. In general, the results show that the injectors can withstand the temperature increase from hydrogen addition while maintaining low emissions at full load, indicating that addition of hydrogen is possible without any modification to this gas turbine engine which has been optimized for performance on natural gas. Parametric studies were carried out to demonstrate how modest changes in engine operating points and fuel injectors can be incorporated to attain single digit NOx levels with up to 30% hydrogen.

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