NOx formation characteristics were studied under air-staged combustion by numerical simulation, during which the NOx formation rate around the burner and in the whole furnace was analyzed, so as to obtain the NOx formation characteristics at different over-fire air rates. Results show that NOx is mainly generated at the initial stage of combustion; NOx reduction will occur when the fuel and O2 are mixed insufficiently; seen from the whole furnace, the formation rate of fuel NOx is significantly higher than that of thermal NOx; fuel NOx is formed in both the main combustion zone and the burn-out zone, while thermal NOx produced almost only in the main combustion zone where the temperature is extremely high; moreover, the sensitivity of thermal NOx to the O2 volume fraction is weaker than that of fuel NOx ; the major control factors on NOx formation rate in the main combustion zone and burn-out zone are respectively the O2 volume fraction and the coke combustion rate; with the rise of over-fire air rate, both the NO., formation rate and NOx formation region reduce in the main combustion zone, with an increased reduction region and a decreased mass concentration of NOx emission.%利用数值模拟方法对空气分级燃烧下NOx的生成特性进行了研究,分析了燃烧器附近局部区域和炉膛整体区域NOx的反应速率,得到了不同燃尽风率下NOx的生成特性.结果表明:NOx主要产生于燃烧初期,当燃料与O2混合不充分时会发生NOx的还原反应；从炉膛整体来看,燃料型NOx的生成速率明显大于热力型NOx,主燃区和燃尽区均生成燃料型NOx,而热力型NOx几乎只在温度很高的主燃区生成,且对O2体积分数的敏感性弱于燃料型NOx；主燃区和燃尽区NOx反应速率的主要控制因素分别为O2体积分数和焦炭燃烧速率；燃尽风率增大,主燃区NOx生成速率和生成区域减小,还原区域增大,NOx排放质量浓度明显减小.
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