风口前端氧煤燃烧NO_(x)生成行为分析及控制

NO_(x) formation behavior analysis and control of oxygen coal combustion at front end of tuyere

以高炉风口前端煤粉燃烧过程为研究对象,通过热力学计算系统分析了不同约束条件下煤气成分及NO_(x)的生成规律,探讨了温度、煤种比例及煤粉成分、富氧、喷煤等不同工况参数对NO_(x)生成行为的影响,并提出降低NO_(x)生成的方向性建议。研究结果表明,高炉风口前端煤粉燃烧生成NO_(x)兼具热力型、快速型、燃料型3种途径。温度是影响热力型NO_(x)生成的重要因素,温度大于2 000℃时,温度每升高100℃,高炉风口前端NO_(x)生成量增幅大于30%以上,计算温度范围内(2 000~2 400℃),NO_(x)生成量由4 056 mg/m^(3)增加到12 942 mg/m^(3),NO_(x)生成量远超传统燃煤锅炉;其他工况条件不变,高炉烟煤配比由0提高至50%,NO_(x)的生成量由4 152 mg/m^(3)增加至7 486 mg/m^(3),增幅达到80%;高炉煤比为80 kg/t时,即使不富氧,NO_(x)生成量依然达到了18 006 mg/m~3;喷吹煤粉中1 mol碳素供氧量由2.0 mol降至1.2 mol,NO_(x)生成量显著减少了68%。综上所述,高炉通过采取调整理论燃烧温度、减少烟煤配比、使用低挥发分煤种、合理匹配富氧喷煤水平等措施,可以实现NO_(x)生成的源头控制。此外,就高炉NO_(x)排放角度而言,炉顶煤气中NO_(x)的含量水平亦显著受高炉内部还原作用的影响。正常冶炼条件下,生成的NO_(x)在炉内能够被充分还原,高炉炉顶煤气NO_(x)量通常为50 mg/m^(3)以下,但应关注亏尺、悬料、休送风等特殊工况时高炉煤气及下游煤气用户NO_(x)的排放水平。

Taking pulverized coal combustion process at the front end of blast furnace tuyere as the research object,the formation rules of gas composition and NO_(x) under different constraints were analyzed by thermodynamic calculation systematically.The effects of different operating parameters such as temperature,ratio of coal species,pulverized coal composition,oxygen-enriched and coal injection on NO_(x) formation behavior were discussed,and several directional advices to reduce NO_(x) formation were proposed.The results show that there are three ways to generate NO_(x) by pulverized coal combustion at the front end of blast furnace tuyere,thermal,prompt and fuel.Temperature is an important factor affecting the formation of thermal NO_(x),when the temperature is higher than 2 000 ℃,the NO_(x) production at the front end of blast furnace tuyere increases by more than 30% for each 100 ℃ increase.Within the calculation temperature range(2 000-2 400 ℃),NO_(x)production increases from 4 056 mg/m^(3) to 12 942 mg/m^(3),which is far more than the traditional coal-fired boiler.The ratio of bituminous coal increases from 0 to 50%,NO_(x) production increases from 4 152 mg/m^(3) to 7 486 mg/m^(3),and the production content of NO_(x) increases by 80%.The ratio of bituminous coal increased from 0 to 50%,and production content of NO_(x) increased by 80%.When the coal ratio is 80 kg/t,NO_(x) production still reaches 18 006 mg/m^(3) even without rich oxygen.NO_(x) generation is significantly reduced by 68% when the oxygen supply for 1 mol carbon in pulverized coal decreased from 2.0 mol to 1.2 mol.Therefore,source control of NO_(x) generation can be realized by adjusting the theoretical combustion temperature,reducing the ratio of bituminous coal,using low volatile coal,reasonably matching the level of oxygen-enriched and coal injection.In addition,from the perspective of blast furnace NO_(x) emission,the content level of NO_(x) in the top gas is also significantly affected by the internal reduction of the blast furnace:under normal smelting conditions,the generated NO_(x) can be fully reduced in blast furnace,and the NO_(x) content of the top gas of the blast furnace is usually below 50 mg/m^(3),but attention should be paid to the NO_(x) emission level of blast furnace gas and downstream gas users,when it is in the special operating mode such as low stock line,hanging,blowing-off,blowing-in,and so on.