Study of NO_x from Different Natural Gas and Hydrogen Fuel Compositions in Combustion Applications

摘要

NO_x emissions from stationary power generation sources such as gas turbines continue to present air quality concerns. Many studies on formation of NO_x, and investigation of different formation pathways have been carried out, yet uncertainties and inconsistency in NO_x formation levels in different applications is noted. This is especially an issue with alternative fuels. The literature indicates conflicting results regarding how fuel composition impacts emission levels for different applications. In an effort to address this question, NO_x emissions from a lean premixed swirl stabilized combustor operated at relatively low combustion temperatures are measured in different testing conditions for different fuel compositions. The fuel composition in this study includes a wide range of hydrogen and natural gas blends, starting from pure natural gas as a conventional fuel, to pure hydrogen as an alternative fuel. Moreover, the influence of residence time on NO_x emission levels is studied. To investigate the reason why emission levels change with fuel composition and residence time, a chemical reaction network (CRN) was developed. The CRN development requires detailed knowledge of flow field, thus computational fluid dynamic (CFD) simulations were conducted to facilitate the construction of the CRN. The CRN was then used to evaluate the details of the NO_x formation. For the present configuration with reaction temperatures below 1800 deg-K, NNH is the dominant NO_x formation pathway which corresponds to the observed increase in NO_x with higher hydrogen concentrations and shorter reaction times, both of which lead to higher H radical concentrations.