分解炉空气分级燃烧及排放特性研究 -

随着我国经济的飞速发展,作为重要基础材料的水泥产品需求量极大且趋于稳定。水泥生产过程中的NO_x排放与燃煤火电厂和汽车尾气产生的NO_x排放已成为空气污染的主要来源,而分解炉是降低水泥生产工艺中NO_x排放的有效设备。笔者在引入高温烟气的模拟分解炉内进行空气分级燃烧试验,研究配风位置、配风比例以及石灰石/煤比例对分解炉内燃烧和NO_x排放特性的影响规律。试验稳定过程中,高温烟气发生装置的给煤量和配风量保持不变。此时,高温烟气发生装置的时间平均温度为911℃,其产生的高温烟气温度稳定在750℃左右,高温烟气中NO_x主要以NO和N_2O的形式存在,其浓度分别为261.49×10~(-6)和12.96×10~(-6)。该股高温烟气将模拟实际回转窑产生的烟气进入分解炉内。在分解炉的上部区域(距离顶部0～2 000 mm区域)的温度为800～1 000℃,与实际分解炉运行温度一致,排放烟气中NO_x主要以NO和N_2O形式存在。随着中间配风位置的下移,煤粉燃烧放热区域下移,而顶部区域的石灰石吸热量变化较小,则原有热量平衡被打破且原有吸热量高于现有放热量,导致顶部区域内燃烧温度降低。此时,还原气氛中煤粉燃烧和石灰石分解反应时间均变长,导致NO_x的还原反应更加充分。但石灰石分解产生的氧化钙(CaO)作为中间产物会促进NO的生成反应,其反应时间增加也促进了NO的生成;另一方面,石灰石作为催化剂参与焦炭和挥发分还原NO的反应过程,分解炉顶部区域的温度下降使得该还原反应变弱。综上,NO的最终排放浓度是以上反应的综合结果。随着配风位置的下移,该变化对NO的生成作用更加明显,故NO的排放浓度逐渐升高。当一级风量与二级风量的配风比例降低时,分解炉上部区域的煤粉燃烧份额减少和石灰石分解量降低,而分解炉下部区域的煤粉燃烧份额增加和未分解的石灰石份额增加,但石灰石的吸热增加量高于燃烧增加份额的放热量,因此分解炉内整体温度均降低。分解炉内NO浓度是由石灰石催化的氧化过程和还原过程综合决定的。一级风量变小时,尾部CO浓度随之增加,烟气中NO浓度呈现降低的趋势。当石灰石/煤比例增加时,分解炉内沿程温度逐渐下降。随着石灰石给粉量增加,分解炉内石灰石受热分解产生的CaO浓度增加,CaO催化NO还原反应更剧烈,从而NO浓度逐渐降低。而石灰石给粉量增加和分解炉温度降低的过程导致尾部的CO浓度升高。 With the rapid development of China's economy,as an important basic material,the demand for cement products is huge and tends to be stable. The NO_x emission from cement production process and coal-fired power plants and automobile exhaust has become the main source of air pollution,and decomposition furnace is an effective equipment to reduce NO_x emission in cement production process.The air-staging combustion experiments were carried out in a simulated precalciner with high-temperature flue gas,and the effects of air distribution position,air distribution ratio and limestone/coal ratio on combustion and NO_xemission characteristics in cement precalciner were investigated. During the stable test,the coal feeding and air distribution of the high-temperature flue gas generator remain unchanged.At this time,the time-average temperature of the high-temperature flue gas generator is 911 ℃,and the temperature of the high-temperature flue gas produced is stable at approximately 750 ℃ . The NO_x in the high-temperature flue gas mainly exists in the form of NO and N_2O,and the concentration is 261.49×10~(-6) and 12.96×10~(-6),respectively. The high-temperature flue gas will simulate the actual flue gas from the rotary kiln into the decomposition furnace. The temperature in the upper part of the calciner( 0-2 000 mm