鼓泡床焦炭型氮氧化物生成的试验与模型研究

循环流化床（CFB）锅炉密相区是焦炭型氮氧化物（NOx）生成的主要区域，利用小型鼓泡流化床实验台比拟CFB锅炉密相区，在850 ℃床温和10% O 2浓度下，进行了单颗粒焦炭的燃烧实验，对不同床料粒度、制焦煤种、焦炭粒径和流化风速条件下焦炭氮向NOx的转化比例进行了研究。针对3种原煤制得的焦炭，均发现床料粒度增大后，鼓泡床乳化相内传质系数增加而传热系数降低，导致焦炭颗粒表面氧化性气氛增强，燃烧进程加快，焦炭氮向NOx转化率上升。初始焦炭粒径越大，焦炭氮向NOx转化率越低。流化风速的增大对焦炭氮向NOx转化有一定的促进作用，但并不显著。实验中对焦炭颗粒内部温度进行了测量，验证了前述的实验结果。同时，基于密相区传质传热特性与简化反应机理，建立了单颗粒焦炭燃烧及焦炭氮转化模型，计算结果与实验匹配良好，为CFB锅炉整体NOx排放模型的建立奠定了基础。

Experimental study and modeling of NOx generation from char nitrogen in the bubbling bed

Char-NOx is mainly generated in the dense bed of circulating fluidized bed (CFB) boilers.A small-scale bubbling bed test rig was used to model the dense bed and single char particles were burnt in the 850 ℃ bed temperature and 10% O2.The influences of bed material size，pyrolysis coal type，char particle diameter and fluidization velocity on the conversion ratio of char-nitrogen to NOx were investigated.For three different types of char，the conversion ratio of char-nitrogen to NOx increases with the increase of bed material size due to the subsequent increase of mass transfer coefficient and the decrease of heat transfer coefficient in the emulsion phase of bubbling bed.Meanwhile，the burning process of chars was accelerated.The conversion rate decreases with the increase of initial char particle diameter，but is not significantly influenced by fluidization velocity.The char temperature was also measured，which verified the previous experimental results.Furthermore，the model of NOx generation from single char particle was established based on the mass and heat transfer mechanism in the dense bed，and the simplified chemistry mechansim.The model was proved to be reliable to match the experimental results and would benefit for the modelling of NOx emission in a practical CFB boiler.