Clean Coal Technology

2022, (06) 135-142

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Emissions and flow field studies of swirl premixed flames stabilized using displacement bluff-body

HAN Delin;WANG Tiantian;ZOU Jun;ZHANG Hai;ZHANG Yang;LYU Junfu;WANG Suilin;School of Environment and Energy Engineering,Beijing University of Civil Engineering and Architecture;Department of Energy and Power Engineering,Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Department of Energy and Power Engineering,Tsinghua University;

Abstract:

In a π-type boiler, the low NO_x coal-to-gas transition may result in the problems of the "wall brush" of the flame torch and carbon deposition, and the swirl premixed combustion method is attractive as it provides short flame length and fast burn-out. Combining the advantages of both lean premixed swirl combustion and bluff-body combustion, a lean premixed swirl burner integrated with a displacement bluff-body was designed. By moving the position of the bluff-body, the burner outlet flow velocity could be tuned. The swirl premixed flames pollutant generation characteristics under different swirl numbers, thermal power and bluff-body position conditions were studied and the flow field at the outlet of the burner nozzle was measured using particle image velocimetry technology. Results show that the amount of NO_x generated first decreases and then increases with the increase of the swirl number, the NO_x concentration is lowest at the swirl number of 0.25. When the bluff-body height is fixed, since the flow velocity increases with the increase of thermal power at this time, the NO_x concentration decreases while the CO concentration increases as a function of the thermal power. If the bluff-body position is varied to keep a fixed outlet flow velocity, both the NO_x and CO concentrations are maintained at a relatively low level, as NO_x<12 mg/m3,CO<7 mg/m3,CO<7 mg/m3,and only a small amount of CO is generated at the lowest thermal power. Based on the flow field and flame analysis, as the swirl number increases from 0 to 0.25,the flame width increases, strengthening the flue gas entrainment, and resulting in a decrease in the NO_x emission. As the swirl number further increases from 0.25 to 0.83,the width of the flame hardly changes but the axial flue gas recirculation is enhanced, increasing the residence time of the hot flue gas and the NO_x formation. Therefore, optimized bluff body position and swirl number lead to a reasonable flow field and flame structure, and thereby keep the emissions at a relatively low level.

Key Words: displacement bluff-body;lean premixed combustion;swirl combustion;load change;flow field;NO_x

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Foundation: 国家科技重大专项资助项目(2019-III-0018-0062);; 国家自然科学基金资助项目(52176116)

Authors: HAN Delin;WANG Tiantian;ZOU Jun;ZHANG Hai;ZHANG Yang;LYU Junfu;WANG Suilin;School of Environment and Energy Engineering,Beijing University of Civil Engineering and Architecture;Department of Energy and Power Engineering,Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Department of Energy and Power Engineering,Tsinghua University;

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