【作者】 吕刚；

【导师】 陆继东；

【作者基本信息】 华中科技大学 ， 热能工程， 2011， 博士

【摘要】 随着水泥工业的快速发展及其产量的日益提高,水泥生产已是我国NOx排放的重要来源之一,仅次于火力发电和汽车尾气之后居第三位。水泥预分解窑技术(干法水泥星产技术)是当今世界水泥工业的主流生产工艺,分解炉是干法水泥生产工艺中降低NOx排放的有效设备。国内外研究者注重降低水泥预分解窑NOx排放的实际效果,而对炉内NOx生成和还原的机制研究较少。所以,开展水泥分解炉这一特殊工况条件下NO转化机制研究对水泥工业的NOx减排具有重要的意义。本论文总结和分析了水泥分解炉内NO生成与还原反应机理的国内外研究现状。采用理论分析、模拟实验和计算机模拟相结合的方法对分解炉内NO生成和还原反应规律,以及全尺度分解炉内NO的分布特征进行了系统的研究。本论文主要从以下几个方面开展研究工作：利用模拟分解炉悬浮及喷腾条件的高温气固悬浮实验系统,对分解炉内不同类型的水泥生料、生料的各种配料及高CO2浓度对煤粉和煤焦燃烧过程中NO生成反应的影响规律进行了实验研究。结果表明,水泥生料及其配料对煤粉和煤焦燃烧NO的生成反应均具有一定的催化作用,不同类型的生料对煤燃烧NO生成反应的催化作用差异不大,生料配料中石灰石对NO生成反应的催化作用最强。气氛中CO2浓度升高,煤粉和煤焦燃烧过程中NO的生成反应速率降低,NO排放总量减少。升高温度对煤粉和煤焦燃烧NO的生成有一定的促进作用；气氛中C02浓度升高,添加生料及升高温度对煤粉和煤焦燃烧NO生成的促进作用减弱。分析了水泥分解炉内煤粉和煤焦对窑尾烟气中NO的还原作用机制,得到了不同温度条件下水泥生料及CO2浓度对煤粉和煤焦还原NO的影响规律；探讨了煤焦及生料对CO还原NO反应的影响作用。研究表明,煤粉和煤焦对NO的还原作用差异较大；挥发分与NO的反应速率更快,焦炭与NO反应的速率较慢,但与NO反应的时间相对较长；生料对挥发分和焦炭还原NO的反应均有一定的催化作用,且生料对挥发分含量高的煤粉还原反应的催化作用更强；温度升高,生料对NO还原反应的催化作用也逐渐增强。气氛中C02浓度升高,煤粉和煤焦对NO的还原能力均增强,而生料对NO还原反应的催化作用减弱。煤焦和生料对CO还原NO的反应均有一定的催化作用,但CO2浓度升高时,生料对CO还原NO反应的促进作用降低。在模拟分解炉的悬浮实验系统上,研究了分解炉内煤粉及煤焦在氧气存在的条件下对窑尾烟气中NO还原的动态变化特性,得到了挥发分和焦炭在燃烧过程中NO生成和还原的动态转化规律。研究表明：在氧气存在条件下,煤粉还原NO的转化过程分为均相还原和异相氧化两个阶段。添加水泥生料、变化温度及O2浓度,煤焦及煤粉与NO反应的动态转化过程均会发生一定的变化。分解炉内NO生成及还原的动态转化机制实验研究,揭示了分解炉内窑尾烟气中NO被大量还原的本质。在煤焦燃烧及水泥生料分解耦合作用研究的基础上,对分解炉条件下煤焦燃烧过程中NO生成反应的动力学模型进行了理论分析及实验研究,得到了适用于水泥工业常用的几种煤样的煤焦燃烧过程中NO生成反应动力学模型与参数,并将各模型和参数应用于分解炉NO排放模拟的计算机辅助试验平台。在此基础上,从动力学的角度探讨了分解炉内煤焦燃烧过程中NO生成及实际排放之间的关系。分析了分解炉内NO生成及还原的主要途径及数值模拟的数学模型,在原有分解炉热态模拟计算机辅助试验平台基础上,建立了分解炉NO排放数值模拟计算机辅助试验平台,在此基础上模拟分析了某5000吨/天生产能力的全尺寸三喷腾分解炉的NO分布规律。研究结果表明,在三喷腾分解炉三次风入口上部区域的NO浓度最高,温度对炉内NO排放的影响较大；分三次风可以降低炉内的燃烧温度及主燃区的O2浓度,从而有效的减少预分解窑系统的NO排放。多工况模拟结果与现场测量的数据偏差较小,验证了所建立的试验平台的适用性,为开发低NO分解炉提供了一套完备的试验平台。更多还原

【Abstract】 In China, with the rapid development of cement industry, the total amount of NOx produced from the cement industry has been the third largest resources, besides the power plant and automobile. The precalciner technology(new type processing cement with daily output), in which precalciner is an important equipment for the reduction of NO emission, is the main technology for cement production in China now. Most of attentions about the researches of NOx emission in precalciner systems were paid to the actual results of NO reduction, however, the study of the mechanisms about NO formation and reduction in precalciner has been rarely concerned on up to now. Therefore, it is necessary and significant to study the conversion of NO for the reduction of NO emission from cement production.Therefore, the Characteristics of NO formation and reduction in precalciner and the NO distribution in 3-D precalciner have been studied with the methods of simulated experiments, theoretical analysis and CFD simulation. The researches have been carrid out mainly on the several following respects:A suit of equipment simulated the suspension and spray condition of precalciner was established in this dissertation, in which the experiments of NO fornation on different CO2 concentrations and with the catalysis of cement raw were carried out. It was shown that different types of raw meal had significant effect on the formation of NO. However, the catalytic capacity between different kinds of raw meal was almost the same. For different ingredients of cement raw meal, the catalysis of limestone on the formation of NO was the strongest. With the increase of CO2 concentration, the rate of NO emission and the total amount of NO emission during coal and char combustion decreased. The conversion of fuel-N and char-N to NO increased with the rise of temperature, however, the effect of temperature and cement raw meal on the NO emission reduced with the increase of CO2 concentration.The mechanism of NO reduction by coal and char in precalciner was discussed, and the effects of cement raw meal and CO2 concentration on the reduction of NO by coal and char at different temperatures were discussed, the mechanism of NO reduction by CO with the catalysis of char and cement raw meal was also concerned. It was found that the rates of NO reduction by volatiles was much higher while the reaction time of NO-C was longer. The amount of NO reduction by coal and char incresed with the addition of raw meal, which indicated that cement raw meal had positive catalysis on the reduction of NO. The catalysis of cement raw meal on the reduction of NO by higher volatile coal was more stronger, and the catalysis of the cement raw meal became stronger with the increase of the reaction temperature. With the increase of CO2 concentration, the NO recuciton capacity of coal and char became stronger. Char and cement raw meal could promote the reaction of CO and NO, however, the effect of cement raw meal decreased with the increase of CO2 concentration.The dynamic processes of NO reduction by coals and char at different O2 concentrations were firstly investigated on the suspension condition of precalciner. The effects of cement raw meal, temperature and O2 concentration on NO formation and reduction by coal and char were discussed. It was shown that there were two stages in NO reduction process at the presence of O2. The first stage was the early homogeneous NO reduction by volatiles, while the second one was the heterogeneous oxidation of char-N. Cement raw meal, temperature and O2 concentration could affect the dynamic processes of NO conversion by coals and char. The mechanism that lots of NO from kiln rotary was reduced in precalciner was revealed by the analysis of NO conversion with the presence of O2 in precalciner.The kinetics of NO formation during char combustion with raw meal presence in the suspension reactor was investigated. The influences of reaction conditions (species, temperature and cement raw meal) on the kinetics of NO formation during char combustion were discussed in this paper. The models and parameters have been applicated to the computer aided test platform for NO simulation in precalciner. The effect of cement raw meal on the kinetics of NO formation during char combustion as well as the correlation between the formation and reduction of NO during char combustion was also discussed.The emission of NO in precalciner was analyzed by numerical simulation, and the relevant mathematical models were developed. The numerical simulation method was combined to develop the computer aided test platform for NO simulation in precalciner, which could provide an experimental platform for design and development of low-NO precalciner. NO transformation and distribution in a 3 D-precalciner with the production capacity of 5000t/d was analyzed in this dissertation. The results indicated that the NO concentration on the top of the inlet of the tertiary air was the highest, and the distribution of NO in precalciner could be affected by temperature significantly. The emission of NO could be reduced by staged combustion effectively because of the reduction of O2 concentration in main combustion zone. It could be found that the platform was reliable through the comparison between the simulation results and the actual measurements.更多还原