Numerical investigation of pressure and H2O dilution effects on NO formation and reduction pathways in pure hydrogen MILD combustion

Shunta Xu, Liyang Xi, Songjie Tian, Yaojie Tu, Sheng Chen, Shihong Zhang and Hao Liu

Applied Energy, 2023, vol. 350, issue C, No S0306261923011005

Abstract: Pure hydrogen moderate or intense low-oxygen dilution (MILD) combustion offers a potential solution to meet low NO emission needs while achieving rapid decarbonization for gas turbines. This paper reports a numerical investigation of the pressure (1–25 atm) and H2O dilution (0–60%vol, including its physical and chemical effects) influences on NO formation and reduction pathways in opposed-flow pure hydrogen diffusion MILD combustion, where the present NO sub-pathway analysis method is also evaluated. Results show that, the present NO sub-pathway analysis method with Glarborg2018 can respectively predict thermal NO, prompt NO, NO formed via NNH and N2O-intermediate, and NO reduced via CHi and H reburning reasonably well. In pure hydrogen MILD combustion, NO emission reaches its peak with the pressure up to about 6 atm due to more NO formed via N2O-intermediate, and then decreases as the pressure is further raised, which is mainly attributed to less NO formation via NNH and more NO reduction by H radicals, finally causing the dominant NO formation pathway to transform from NNH to N2O-intermediate at high pressure. The addition of H2O, mainly because of its chemical effect to inhibit the NNH and N2O-intermediate pathways via the channels NNH + O → NO and N2O + H/O → NO, results in further NO emission reduction. The top NO contributor is changed from NNH to N2O-intermediate with H2O dilution at atmospheric pressure, while at high pressure, NO formation is invariably dominated by the N2O-intermediate pathway even when H2O is added up to 60%vol. NO reduction, which is initiated by the channel NO+H(+M)⇌HNO(+M), behaves more actively at high pressure, constituting 21% of the total NO produced at 25 atm, while its importance is weakened with H2O dilution.

Keywords: MILD combustion; Opposed-flow flame; Hydrogen; Pressure; H2O dilution; NO reaction pathway (search for similar items in EconPapers)
Date: 2023
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Citations: View citations in EconPapers (1)

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DOI: 10.1016/j.apenergy.2023.121736

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