This study reports an experimental investigation on the nitrogen oxide (NO_x) emissions in pulverized fuel (coal and char) combustion through preheating with a circulating fluidized bed. The high-temperature preheated fuel particles obtained from the circulating fluidized bed would be burned in the down-fired combustor. The focus of this research is the trend of NO_x emissions with different air distribution through varying secondary air nozzle structures and air ratios as well as tertiary air positions along the down-fired combustor. Under stable operation, the burning temperature was uniform and the combustion efficiency was high. When the fuel was pulverized coal, the NO_x emissions with the secondary air center nozzle structure were almost twice of that with ring nozzle structure. Furthermore, the NO_x emissions increased with an increase of secondary air ratio when the nozzle structure was in the center. However, there was a minimum NO_x concentration when the nozzle structure was a ring. And, the lower NO_x emissions were achieved through arranging the tertiary air distribution rationally. In addition, the trend in NO concentration along the down-fired combustor was almost the same irrespective of the fuel (coal or char). But, the char combustion efficiency should be paid more attention when the tertiary air position changes.

中文翻译：

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空气分布对循环流化床预热煤粉和焦炭燃烧NO _x排放的影响

这项研究报告了通过循环流化床预热对粉状燃料（煤和焦炭）燃烧过程中氮氧化物（NO _x）排放的实验研究。从循环流化床获得的高温预热燃料颗粒将在向下燃烧的燃烧器中燃烧。本研究的焦点是NO的趋势_X具有不同的空气分配排放通过改变二次空气喷嘴的结构和空气比以及三次空气位置沿向下烧制燃烧器。在稳定运行下，燃烧温度均匀，燃烧效率高。当燃料是煤粉时，NO _x二次空气中心喷嘴结构的排放几乎是环形喷嘴结构的两倍。此外，当喷嘴结构处于中心时，NO _x排放随着二次空气比的增加而增加。但是，当喷嘴结构为环形时，NO _x浓度最小。并且，下侧NO _X的排放量是通过合理安排三次空气分布来实现的。另外，不管燃料（煤或焦炭）如何，沿着向下燃烧的燃烧器中NO浓度的趋势几乎相同。但是，当第三级空气位置改变时，焦炭的燃烧效率应引起更多的重视。