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Influence of Staged-Air on Airflow, Combustion Characteristics and NOx Emissions of a Down-Fired Pulverized-Coal 300 MWe Utility Boiler with Direct Flow Split Burners

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journal contribution
posted on 01.02.2010, 00:00 by Zhengqi Li, Min Kuang, Jia Zhang, Yunfeng Han, Qunyi Zhu, Lianjie Yang, Weiguang Kong
Cold airflow experiments were conducted to investigate the aerodynamic field in a small-scale furnace of a down-fired pulverized-coal 300 MWe utility boiler arranged with direct flow split burners enriched by cyclones. By increasing the staged-air ratio, a deflected flow field appeared in the lower furnace; larger staged-air ratios produced larger deflections. Industrial-sized experiments on a full-scale boiler were also performed at different staged-air damper openings with measurements taken of gas temperatures in the burner region and near the right-side wall, wall heat fluxes, and gas components (O2, CO, and NOx) in the near-wall region. Combustion was unstable at staged-air damper openings below 30%. For openings of 30% and 40%, late ignition of the pulverized coal developed and large differences arose in gas temperatures and heat fluxes between the regions near the front and rear walls. In conjunction, carbon content in the fly ash was high and boiler efficiency was low with high NOx emission above 1200 mg/m3 (at 6% O2 dry). For fully open dampers, differences in gas temperatures and heat fluxes, carbon in fly ash and NOx emission decreased yielding an increase in boiler efficiency. The optimal setting is fully open staged-air dampers.