煤粉炉高温还原性氛围下NH_3还原NO_x

NO_x Reduction with NH_3 Reagent Injected into High Temperature and Reducing Atmosphere in PC-boiler

在一台75,t/h煤粉炉上采用炉内空气分级和低氮燃烧器进行改造,在主燃区创造高温强还原性氛围,在该区域喷入氨还原剂,通过实验研究在高温强还原性气氛下NH_3还原NO_x的影响因素及效果,结果表明:当主燃区过量空气系数(37)1<1时,喷入尿素溶液后,NO_x体积分数明显低于仅采用空气分级时的工况,当(37)1>1.15时,则得到相反结果,在富氧条件下NH_3易生成NO_x;在(37)1=0.9时,四角处和侧墙处沿喷枪轴线方向氧体积分数均小于0.4%,,温度在1,200~1,300,℃,该氛围下NH_3可有效降低NO_x;喷射位置在炉膛四角时NO_x排放浓度明显低于在侧墙处,最佳氨氮摩尔比为1.73,且在侧墙处喷入尿素溶液,随着氨氮摩尔比的增加NO_x排放有明显上升趋势;在主燃烧区喷入尿素溶液((37)1=0.9,氨氮摩尔比为1.73)NO_x还原效率为66.5%,,比单独采用空气分级高35.27%,,零氨逃逸.

This paper aimed at demonstrating an industrial retrofit to decrease NOx emission in a 75 t/h PC-boiler by adopting such approaches as ove fire air（OFA） and low NOx burners. A high temperature and reducing atmosphere was created in the main combustion zone with the air-staging configuration, in which NH3 was injected to further reduce NOx. The reduction of NOx by NH3 was investigated through a series of experiments. The main conclusions were shown as follows. When the stoichiometric ratio in the main combustion zone（37）11, NOx concentration was obviously reduced compared with that when only air staging was adopted. When（37）11.15, the opposite result was obtained, with more NOx emission generated. When（37）1=0.9, the oxygen concentration was less than 0.4% in the axis direction of injectors and the temperature range was within 1 200—1 300 ℃, NH3 could effectively reduce NOx emission. The NOx reduction was more obvious when NH3 reagent was injected from the four corners near the burner than that from the middle of the side walls. The optimum normalized stoichiometric ratio（NSR）was 1.73. The NOx showed a rising tendency with the increase of NSR when NH3 was injected from the side walls.When NH3 was injected into the main combustion zone, with（37）1=0.9 and NSR was 1.73, the NOx reduction efficiency was 66.5%, 35.27% higher than that when only air staging was adopted, with no escape of ammonia.