Enhancement of turbulent scalar mixing and its application by a multihole nozzle in selective catalytic reduction of NOx |
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Authors: | Hang Seok Choi Seock Joon Kim Kwan Tae Kim |
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Institution: | (1) Environmental Systems Research Center, Environmental and Energy Research Division, Korea Institute of Machinery and Materials, 171 Jang-dong, Yuseong-gu, Daejeon, 305-343, Korea;(2) Environmental and Energy Research Division, Korea Institute of Machinery and Materials, Daejeon, Korea |
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Abstract: | The mixing characteristics of a passive scalar in the turbulent flow of a selective catalytic reduction process were numerically
and experimentally investigated, focusing especially on an injection nozzle with multiple holes for the reducing agent. The
multihole injection nozzle studied has six holes that are perpendicular to the ambient flue gas flow and are located near
the tip of the nozzle. Large eddy simulation was applied to the turbulent flow and mixing fields to elucidate the mixing mechanism
of the proposed nozzle compared with the single-hole nozzle that is commonly used in the conventional selective catalytic
reduction process. From the results, there exist broader regions of higher turbulent intensities for the multihole nozzle
than for the conventional single-hole nozzle. These regions are well matched with the positions of high vorticity in the near
upstream region of the jet flow issuing from the multiple holes of the nozzle. Consequently, the high turbulent intensities
and vorticity magnitudes lead to intensified mixing between the flue gas and the reducing agent. Hence, the most suitable
molar ratio between NOx and the reducing agent for the catalytic reaction can be easily obtained within a shorter physical
mixing length as a result of the enhanced scalar mixing. Finally, the numerical results were applied to a trial design version
of a multihole nozzle, and this nozzle was experimentally tested to confirm its mixing performance. |
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Keywords: | NOx SCR Turbulent mixing Vortices |
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