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Performance assessment of staged-air declination in improving asymmetric gas/particle flow characteristics within a down-fired 600 MWe supercritical utility boiler

1 January 2013
Publication year: 2013
Source:Energy, Volume 49

By using phase-Doppler anemometry (PDA) measurements within a cold small-scale model for a down-fired 600-MW e supercritical utility boiler, gas/particle flow characteristics were acquired at various staged-air declination angle settings (i.e., 0°, 15°, 30°, and 45°) so as to assess the availability of a staged-air declination method in improving the strong asymmetric gas/particle flow field. Detailed comparisons made in the mean velocity, particle volume flux, particle number concentration, gas/particle flow decays, and trajectories of the downward gas/particle flows with respect to different staged-air angle settings, revealed that enlarging the staged-air angle essentially did not change the strong asymmetric patterns in gas/particle flow characteristics. From measurements taken within a real furnace equipped with a designed horizontally-fed staged air (i.e., 0° for the staged-air angle), strong asymmetric combustion characterized by gas temperatures being much higher near the rear wall than near the front wall, low burnout, and particularly high NO x emissions, were found. By considering the appearance of a similar strong asymmetric gas/particle flow field at various staged-air angle settings in this study and at different staged-air ratios in a previous study, staged-air declination and staged-air ratio reduction are very likely to be inapplicable if applied in real furnaces to deal with these problems (i.e., strong asymmetric combustion, low burnout and high NO x emissions). Retrofitting a boiler with deep-air-staging combustion technology developed in our recent investigation is recommended if symmetric combustion, high burnout, and low NO x emissions are to be achieved.


► No essential improvement in the severely asymmetric flow field pattern with enlarging the staged-air angle. ► Asymmetric combustion, low burnout, and high NO x emissions in the real furnace. ► Both the staged-air declination and staged-air ratio reduction being inapplicable in dealing with these problems. ► Recommending a down-fired technology based on the concept of multiple injection and multiple staging for the furnace.

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