In order to reduce the NOx emission during the low-quality blended coal combustion, a novel technique combining an additional separated over fire air ( SOFA) and boiler combustion system retrofit was carried out in a 300 MW tangential-fired boiler. Through three low-quality blended coals firing experiments, the impacts of SOFA, the tertiary-air and shrinked-middle wind on NOx emission and boiler efficiency were obtained. The results indicated that with the increase of air damper opening degree of SOFA, the NOx emission firstly decreased and then increased, while the boiler efficiency decreased. Meanwhile, by comparison with using the tertiary-air, the NOx emission reduced rapidly, but the unburned carbon slowly increased without the tertiary-air. Furthermore, the proper shrinked-middle wind could not only improve the coal combustion efficiency, but also reduce the NOx emission. Hence, air staging combustion adjustment should obtain a proper point for both the low NOx emission and the optimal boiler efficiency.%针对燃用劣质混煤的300 MW四角切圆燃烧锅炉, 通过低氮燃烧系统改造与增设燃尽风 ( SOFA) 相结合的方式, 用于降低氮氧化物 ( NOx ) 排放浓度. 通过三种劣质混煤的实炉燃烧试验获得了SOFA风率, 三次风投、 退, 缩腰配风方式对NOx排放浓度与锅炉燃烧经济性的影响规律. 试验结果表明, 随着SOFA风率增加, 锅炉热效率随之下降, 而NOx排放浓度呈现出先下降后上升的趋势; 制粉系统三次风退出时, NOx排放浓度明显降低, 而飞灰含碳量有所升高; 此外通过优化缩腰配风, 有助于提高锅炉热效率和降低NOx生成浓度, 从而实现低氮燃烧的同时, 兼顾锅炉燃烧经济性.
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