煤粉再燃还原NOx动态过程试验研究

通过固定床对煤粉再燃还原NO_x的微观动态变化过程,以及不同φ(O₂)条件下的再燃脱硝效果进行了试验研究,结果表明,煤粉再燃过程存在典型的3阶段分布特性,分别是再燃煤粉早期NO生成阶段、挥发份的均相还原阶段和焦炭的非均相还原阶段.再燃粉煤早期NO生成阶段和焦炭的非均相还原阶段对φ(O2)变化不敏感,挥发份的均相还原阶段对φ(O₂)变化非常敏感,NO还原效率随φ(O₂)的增加而降低,φ(O₂)=8％是NO还原有效与否的分界线,当φ(O₂)>8％时,再燃煤粉非但不能对来流NO进行有效还原,而且还生成了新的NO.要获得理想的脱硝效果,需要φ(O₂)<5％,对应挥发份化学当量比SRV<0.8. 通过对不同φ(O₂)条件下的NO动态曲线进行定量积分分析,发现挥发份是富燃还原性气氛下还原NO的主要贡献成分,同样在贫燃氧化性气氛下也是NO生成的主要贡献成分.同时还给出了神华煤再燃还原NO的效率与氧量气氛之间的经验公式.

Experimental study on coal reburning dynamic process for NOx reduction

The microscale process of NOx reduction by coal reburning was investigated on a fixed-bed reactor and the NOx reduction efficiencies at different oxygen levels were studied.The results showed that there are three stages in the coal reburning process.The first stage is the early NO formation of reburning coal,the second one is the NO homogeneous reduction by volatile matter and the last one is the NO heterogeneous reduction by coal char.The first stage and the third stage are insensitive to the change of oxygen fraction in the main stream,while the NO homogeneous reduction by volatile matter is very sensitive to the change of atmosphere composition.With the increase of oxygen fraction in main stream during coal reburning,NO reduction efficiency decreases.The oxygen fraction of 8% is the critical value for determining the effectivity of NO reduction.When oxygen fraction is larger than 8%,NO will be formed by the reburning coal other than reduced in the main stream.In order to obtain valuable NO reduction efficiency by coal reburning,oxygen fraction should be smaller than 5%,and the corresponding stoichiometric ratio of volatile(SRV) should be smaller than 0.8.Quantitative analysis by integral of the NO curves at different conditions shows that the volatile matter is the main contributor to the NO reduction under fuel-rich condition and to the formation of NO under fuel-lean condition.An empirical equation of NO reduction efficiency at different atmosphere for Shenhua coal reburning was also presented.