【作者】 王学栋；

【导师】 程林；

【作者基本信息】 山东大学 ， 机械设计及理论， 2009， 博士

【摘要】 本文针对电站锅炉燃煤污染物排放浓度高的现状,通过大量的现场测试和实验,研究了多种容量燃煤锅炉的NOx排放特性,以及低NOx燃烧技术和低NOx燃烧器在这些锅炉上的应用效果;采用理论分析和实验研究相结合的方法,研究了颗粒状催化剂的成分对活性的影响、添加剂的成分和含量对催化剂活性的影响,以及催化剂的成分和制作工艺对成型性能和活性的影响,利用挤出成型法制备了峰窝状成型催化剂;通过测试成型催化剂在中型燃烧实验台上的活性,研究了烟气成分和实验参数对催化剂活性的影响;通过研究筛选出了成型性能好、活性高的催化剂,为开发具有自主知识产权的选择性催化还原反应（SCR）催化剂打下了良好的基础。1、系统地研究了山东电网不同容量、不同型式、不同煤种、不同时期低NOx燃烧技术和燃烧器锅炉的NOx排放浓度。早期投产的小容量机组锅炉的NOx排放浓度在800～1200mg/m³之间;300MW机组锅炉的NOx排放浓度在600～1100mg/m³之间,其中烧贫煤的300MW机组锅炉的NOx排放浓度达800～1100m/m³;近几年新投产的大容量机组燃煤锅炉,引进利用新型炉内低NOx燃烧技术和燃烧器,NOx排放浓度可控制在300～700mg/m³之间,由于燃烧调整不及时等原因,个别贫煤锅炉和烟煤锅炉的NOx排放浓度仍然高达800～1000mg/m³。2、分析了燃煤锅炉NOx排放浓度与燃烧煤种、锅炉结构、燃烧器型式、锅炉运行工况和运行参数的关系。在所有因素中,煤种对NOx排放浓度的影响最大;在所有锅炉运行参数中,炉膛内平均氧量以及氧浓度分布对NOx排放浓度的影响最明显。“W”火焰锅炉燃烧贫煤,其NOx排放浓度最高,达1000～1500mg/m³;其次是四角切圆直流燃烧器锅炉;燃用相同煤种时,采用新型低NOx旋流燃烧器锅炉的NOx排放浓度低于四角切圆燃烧锅炉;循环流化床锅炉的NOx排放浓度最低,一般不超过200 mg/m³;烧烟煤的四角切圆燃烧锅炉的NOx排放浓度比贫煤锅炉低约50%;随过量空气系数和锅炉负荷的降低,烟煤锅炉NOx排放降低的量比贫煤锅炉大;锅炉运行工况和运行参数对NOx排放浓度有较大影响,及时地调整锅炉燃烧工况和运行参数,NOx排放浓度可降低10～20%。3、研究了浸渍法制备的V₂O₅-WO₃-MoO₃/TiO₂颗粒状催化剂在固定床反应器上的活性。钒是催化剂中的主要活性成分,钒的含量增加,SCR反应的脱硝效率增加;当钒的含量增加到1%时,催化剂具有较高的活性,且温度窗口拓宽到了200～300℃之间;随着钒的含量进一步增加,催化剂的活性降低,活性温度窗口范围减小。钨在催化剂中主要起促进作用,增强催化剂在高温区域的活性;但当钨的含量超过7%时,WO₃抢占钒在载体表面的位置,造成V₂O₅活性中心数目下降,催化剂活性下降。钼的存在改善了催化剂在高温区域的活性,增强了催化剂的表面酸性和NH₃的吸附性,反应的选择性增加;当钼的含量达到7%以上时,钼的含量进一步增加,催化剂的性能改善不大。以钒、钨、钼的含量分别为1%、5%和5%的催化剂活性最好,该配方的颗粒状催化剂的脱硝效率达到95%以上。4、通过实验对催化剂活性成分、添加剂成分及含量对催化剂成型性能和活性的影响进行了研究,利用挤出成型法,制备了蜂窝状催化剂。研究结果表明:添加剂加入到催化剂中,对成型性能和活性产生了不利的影响;添加剂成分和含量改变,催化剂的活性和最佳焙烧温度也改变,同时活性和最佳焙烧温度的关系也改变;通过调整各种添加剂成分及其含量,改变催化剂的成型工艺,对各物料的成型性能进行了研究,最终获得了成型性能好、活性高的蜂窝状成型催化剂。5、分析了催化剂样品的表征及其影响因素。催化剂的孔结构特性受活性成分、载体本身、添加剂成分、成型过程和制作工艺影响较大。混合法制得的颗粒催化剂的孔体积和比表面积都比浸渍法制得的颗粒催化剂的孔体积和比表面积小;合适的添加剂有利于改善催化剂的孔结构;成型过程中的挤压作用导致催化剂的孔体积和比表面积减小;随着焙烧温度的升高,成型催化剂的比表面积下降,活性降低;在所有成型催化剂中,经350℃焙烧后的催化剂的比表面积最大,催化剂的活性最高。分析扫描电镜结果得到:在成型性能好、活性高、经350℃焙烧后的催化剂表面,添加剂和活性成分、TiO₂载体结合良好,形成了形状规则的颗粒,颗粒表面孔上又分布着许多类似蜂窝的细小微孔结构。催化剂孔结构特性的差异最终导致了催化剂脱硝活性的差异,而且这种孔结构上的差异和催化剂的脱硝活性具有良好的对应关系。6、研究了成型催化剂在中型燃烧实验台上的催化活性。实验结果表明,催化剂的活性受各种因素影响较大:脱硝效率随氨氮比的增加而增加,氨氮比大于0.85时,脱硝效率达到90%以上,增大氨氮比会使脱硝效率提高,但当氨氮比大于1.1时,脱硝效率增长趋势平缓,在SCR催化剂还原反应中,维持氨氮比为1;在NO浓度为250～830ppm的实验范围内,NO初始浓度对脱硝效率的影响不明显;空速增大时,脱硝效率降低,在中型燃烧实验台上,反应空速为2000/h左右;反应温度对脱硝效率有较大影响,在100～200℃低温下,催化剂的活性很低,脱硝效率不到70%,随温度升高,脱硝效率急剧升高,温度升至315℃时,脱硝效率达到90%以上,在375℃左右,脱硝效率达到95%以上,随后脱硝效率随温度的升高而下降,催化剂的活性温度窗口较宽,从300℃到425℃。本课题得到国际科技合作重点项目（大气中氮氧化物NOx控制技术应用研究,NO.2004DFA07700）和山东电力集团科技项目（大容量燃煤锅炉氮氧化物NOx排放控制技术实验研究,NO.2008ZB-19）的资助。更多还原

【Abstract】 Concentrating on the higher emission of pollutant in the gas exhausted from power station,the NOx emission characteristics,the effects of low NOx combustion technology and low NOx burner were investigated.With theory analyse and experiment, the influence of compositions,additives and the molding technologies on the catalytic activity and molding performance were first investigated in laboratory.The molding honeycomb catalyst was obtained by extruding method.The influences of gas compositions and experimental parameters on catalytic performance of honeycomb catalyst were investigated by simulated SCR reaction on middle-sized combustion test-bed.All these analysis and tests lead to a kind of honeycomb catalyst with excellent molding and catalytic performances,which can be used for SCR reaction.1.The investigation of NOx emission of boilers with different types,capacities, coal types,low NOx technologies and burners was systematically done in Shandong electric network.As the low NOx technologies early used were in low level,the low capacity boilers all have high NOx emission from 800 to 1200mg/m³.The 300MW units put into production early have NOx emission from 600 to 1100mg/m³,and the value increases to 800-1100mg/m³ for boilers burning lean coal.The NOx emission of the boilers with big volume installed recently was reduced to 300-700mg/m³,due to the new low NOx technologies and burners in these units.However the NOx emission value would still reach to 800-1000mg/m³ if low NOx technologies and burners could not work sufficiently due to the delay of combustion regulation for boilers burning lean coal or bituminous coal.2.The influences of coal type,boiler configuration,burner mode,boiler operational conditions and parameters on NOx emission were studied.Among all the influencing parameters,coal type is the most important factor.Among all the operational parameters,the oxygen content and distribution in furnace have the most obvious influence on NOx emission.W-flame boiler burning lean coal has the highest NOx emission from 1000 to 1500mg/m³.Boiler with quadrilateral tangential straight-flow burner comes next.The emission of boiler with low swirl-flow burner is lower than that of quadrilateral tangential straight-flow burner when the same coal is burnt.CFB boiler has the lowest NOx emission no more than 200mg/m³.Boiler with quadrilateral tangential straight-flow burner burning bituminous coal has about 50% NOx emission lower than that of boiler burning lean coal.With excess air coefficient and boiler load decreasing,the reduction rate of NOx emission of boiler burning bituminous coal is larger than that of boiler burning lean coal.The result shows that the NOx emission is largely impacted by boiler operational conditions and parameters,and it can be reduced about 10-20%by adjusting combustion condition with boiler operational conditions and parameters changing.3.Much regularity was obtained by investigation on the catalytic performance of V₂O₅-WO₃-MoO₃/TiO₂ powder catalyst:the reaction rate and activity of SCR increases with the content of primary ingredient V₂O₅ growing.When the V₂O₅ content grows to 1%,there is high activity and a wide active temperature range from 200℃to 300℃. However,with the content of V₂O₅ increasing further,the catalytic activity decreases, its active temperature range becomes cabined.The W in catalyst mainly increases the activity at high temperature.But WO₃ would take the place of V₂O₅ active sites when the W content is higher than 7%,which will reduce the V₂O₅ active sites and consequently decrease the catalytic activity.The Mo in catalyst also improves the catalytic activity at high temperature,meanwhile it increase the surface acidity and NH₃ adsorption,which improves the selectivity of the reaction.But these benefits would not be remarkable when the Mo content is higher than 7%.Finally a kind of catalyst composing of 1%V,5%W,5%Mo was obtained,having the highest activity above 95%.4.The influences of active substances,additive species and their contents on molding performance,as well as the activity of catalyst have been investigated.The molding honeycomb catalyst was obtained by extruding method.The result of research shows that additives have some influences on the molding performances and activity of the catalyst.Both additive species and their contents have large impacts on the molding performances and activity of the catalyst.Through adjusting additives and their contents, changing the molding technologies,a recipe of one honeycomb catalyst with good molding performance and high activity was obtained finally.5.The characterizations of the catalyst and the influences factors on them were investigated by MPI（mercury intrusion porosimetry） and SEM（scanning electron microscope）.The pore characterizations are largely impacted by active compositions, carrier characterizations,additive species and molding technologies.Catalysts made by mechanical blend method have bigger pore volume and pore area than those of catalysts made by dipping method.Appropriate additives can benefit molding performance and pore structure of the catalyst.Extruding process has slight negative impacts on pore structure for honeycomb catalyst resulting in the decrease of pore volumn and pore area. With the calcining temperature increasing,the decreasing pore area induces the drop of activity for honeycomb catalyst.The catalyst calcined at 350℃has the biggest pore volume and pore area among all of the honeycomb catalyst,so it has the highest activity. The investigations by SEM show that:For catalyst with good molding performance and high acitivity,calcined at 350℃,additives and active substances and TiO₂ carrier bond well on its surface,which form regular granules and honeycomb pores on surface of granules.Catalysts with different pore structures represent different catalytic performances.6.Tests on catalytic performance of the honeycomb catalyst were done by simulation SCR reaction on middle-sized combustion test-bed.The results show that: The NOx conversion is impacted by input ratio of NH₃ and NO,initial NO concentration,reaction temperature and space velocity.When the input ratio of NH₃ and NO is higher than 0.85 while lower than 1.1,the NOx conversion increases with the ratio growing,but this effect would not be remarkable if the ratio is above 1.1.For consideration of NH₃ escape,the ration is preferably fixed at 1.Within the NO concentration between 250 and 830ppm,the NOx conversion is not affected obviously by the initial NO concentration.The NOx conversion decreases with space velocity growing.For middle-sized combustion test-bed,the space velocity is 2000/h.Reaction temperature has large impact on NOx conversion,the NOx conversion is less than 70% when the temperature is between 100℃and 200℃.When the reaction temperature is above 200℃,the NOx conversion rapidly increases with temperature growing.The NOx conversion is above 90%at 315℃,and exceeds 95%around 375℃,then it slightly decreases with temperature growing.Therefore the active reaction temperature ranges from 300℃to 425℃,which is qualified for SCR reaction.This project is co-sponsored by International Science Cooperation Major Project （Technology for the control of nitrogen oxides emissions,NO.2004DFA7700） and Shandong Power Group Science Project（Experimental study on NOx emission and control technology of high-capacity boilers,NO.2008ZB-19）.更多还原