风口前端氧煤燃烧NOx生成行为分析及控制

 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/m3增加到12 942 mg/m3,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/m3增加至7 486 mg/m3,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/m3;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/m3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。

NOx formation behavior analysis and control of oxygen coal combustion at front end of tuyere

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_xproduction increases from 4 056 mg/m3 to 12 942 mg/m3, 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/m3 to 7 486 mg/m3, 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/m3 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 NOx 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/m3, 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.