Optical non-intrusive measurements of internal recirculation zone of pulverized coal swirling flames with secondary swirl intensity

• Published in: Energy (Oxford) Vol. 103; pp. 61 - 74
• Main Authors: Sung, Yonmo, Lee, Sangmin, Eom, Seongyong, Moon, Cheoreon, Ahn, Seongyool, Choi, Gyungmin, Kim, Duckjool
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.05.2016
• Subjects: Combustion; Downstream effects; Expansion; Flame structure; Internal recirculation zone; Optical diagnostics; Particle image velocimetry; Pulverized coal; Pulverized coal combustion; Reduction; Stagnation point; Swirl stabilized flame; Swirling; Flame structure; Particle image velocimetry; Internal recirculation zone; Pulverized coal combustion; Optical diagnostics; Swirl stabilized flame
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2015.12.095

The most favorable condition for NOx reduction in the swirl burner of wall-fired type boilers is to increase the residence time of pulverized coal particles in the internal recirculation zone which should be fuel-rich environments. The purpose of this study is to elucidate fundamental mechanisms for NOx reduction in pulverized coal swirling flames by means of the detailed observation of the flow field of the oxygen lean internal recirculation zone. The structure of pulverized coal swirling flames with secondary swirl intensity is studied experimentally by particle image velocimetry and local flame colors based on OH∗, CH∗, and C2∗ chemiluminescence intensities. The results show that the internal recirculation zone is enlarged with increasing the outer swirl intensity because the location of the stagnation point moves toward downstream. Also, the exhaust tube vortex is observed along the centerline in the flames, and started from near the stagnation point. For the combustion characteristics, the maximum temperature reduces as the outer swirl intensity increases, and the flame then moves downstream. The higher outer swirl intensity would be more effective in the low NOx swirl burner systems because of enhancing a dimension of the internal recirculation zone and reducing a local rate of chemical reaction. •The structure of pulverized coal swirling flames with burner air staging was studied.•The possibility of PIV without additional seeding particles was clearly proven.•The internal recirculation zone and exhaust tube vortex were observed.•Combustion reaction processes could be classified by the flame color measurements.