富氧燃烧系统中NO的还原及其排放

Reduction and emission of NO in oxy-fuel system

富氧燃烧方式具有排烟中的CO2浓度高、CO2捕捉回收处理容易等优点,是很有前途的新型清洁煤燃烧方式。通过实验得出了富氧燃烧过程中燃料氮生成NO的转化率随CO2浓度的变化、循环NO在挥发分燃烧火焰中的还原率、循环NO对燃料氮生成NO的转化率的影响,并得出了相应的定量关系式。结合实验结果和系统物质平衡理论分析,得出了整个系统的燃料氮向排放NO的总体转化率。结果表明,由于干式循环的烟气循环倍率大于湿式循环,干式循环的NO排放减少幅度大于湿式循环的减少幅度。采用富氧燃烧,NO排放量可以降低到常规空气燃烧的1/7左右。循环NO的还原是NO排放大幅度减少的主要原因。随煤的含氮量增加,排放烟气的NO浓度增加,但增加幅度小于煤的含氮量的增加幅度。随煤的含氮量增加,系统的燃料氮生成NO的总体转化率降低。

Oxy-fuel combustion has an advantage of easy CO2 recovery due to its high CO2 concentration in exhausted gas.It is a promising combustion method for coal.In this work,the change of conversion ratio of fuel-N to NO with CO2 concentration,reduction ratio of recycled NO in the reducing zone of volatile matter combustion,and the influence of recycled NO on conversion ratio of fuel-N to NO were investigated,and corresponding correlations were obtained.With these experimental results and theoretical analysis on the material balance in the system,the conversion ratio of fuel-N to NO in the system was derived.The results revealed that much less NO was released in a dry-recycle system than in a wet-recycle system,due to a higher gas recirculation ratio in the dry-recycle system.With oxy-fuel combustion,NO emission can be reduced to about only 1/7 of conventional air combustion.This effect is mainly attributed to the reduction of recycled NO.NO concentration increases with nitrogen content,but the increase in NO concentration is less than that in nitrogen content.As nitrogen content increases,the conversion ratio of fuel-N to NO of the system decreases.