Control of NOx and other emissions in micro gas turbine combustors fuelled with mixtures of methane and ammonia

Ekenechukwu C. Okafor, K. D. Kunkuma A. Somarathne, Rattanasupapornsak Ratthanan, Akihiro Hayakawa, Taku Kudo, Osamu Kurata, Norihiko Iki, Taku Tsujimura, Hirohide Furutani, Hideaki Kobayashi

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Methane–ammonia mixtures have potentials as low-carbon fuels for gas turbines, however significantly high fuel NOx production in their flames present challenges to their application. This study aims to provide deep insight into the physical and chemical processes involved in the formation and control of emissions from the combustion of CH4–NH3–air with up to 30% ammonia by heat fraction in gas turbine combustors. Hence, laser diagnostics techniques such as Particle Image Velocimetry (PIV), and Planar Laser Induced Fluorescence (PLIF) imaging, in addition to Fourier Transform Infrared (FTIR) gas analysis were employed to study the flow field, flame structure and emissions characteristics of a micro gas turbine swirl combustor fuelled with CH4–NH3–air mixtures. The control of emissions from the flames was further studied using Large Eddy Simulation (LES) of a model swirl combustor. The results show that NOx emissions from premixed CH4–NH3–air in single-stage combustion were more than 5000 ppmv at equivalence ratios, Φ = 0.8–1.1, which is about twice more than the values already reported for NH3–air. Trends in NOx emissions correspond with the trends in OH radicals concentration in the combustor owing to the relevance of OH radicals in fuel NOx production. Emissions control leading to significantly low emissions such as 49 ppmv of NOx, 2 ppmv of CO and approximately zero N2O, HCN and NH3 emissions with a 99.8% combustion efficiency was achieved using rich-lean combustion. An optimum Φ of the primary combustion zone for low NOx emission was identified, which varied from 1.30 to 1.35 depending on the ammonia fraction. For Φ richer (leaner) than the optimum Φ, NOx emission increased due to an increase in NOx production in the secondary (primary) combustion zone. Rich-lean combustion of CH4–NH3–air emitted less NOx than that of NH3-air because the higher flame speed of CH4–NH3–air mixtures ensured lower NOx production in the secondary combustion zone.

Original languageEnglish
Pages (from-to)406-416
Number of pages11
JournalCombustion and Flame
Volume211
DOIs
Publication statusPublished - 2020 Jan

Keywords

  • Ammonia
  • Emissions control
  • Fuel NOx
  • Micro gas turbine
  • Rich-lean combustion

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Physics and Astronomy(all)

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