【作者】 李辉；

【导师】 周昊； 李卫东；

【作者基本信息】 浙江大学 ， 工程博士能源与环保（专业学位）， 2024， 博士

【摘要】 我国能源结构特点是“富煤贫油少气”,以煤炭为主体的能源生产和消费结构对于保障能源安全以及促进经济发展等方面有着巨大作用。新疆煤炭资源总储量超过2.19万亿吨,约占我国煤炭总储量的40%,准东、吐哈、伊犁煤田均为储量超过3000亿吨的特大型煤田,其中准东和吐哈煤田分布有大量高碱煤。高碱煤具有易开采、热值高、灰分低以及含硫量低等优点,但赋存多种形态高含量的钠、钾等碱金属元素,直接燃烧会导致锅炉受热面出现严重沾污结渣等问题。十二五以来,新疆地区投产了多台以高碱煤为设计煤种的机组,均为固态排渣锅炉,通过炉膛与燃烧系统的优化设计、掺烧高岭土、增加吹灰器等针对性技术措施,可有效提高锅炉燃用高碱煤的比例,但仍难以做到100%全烧高碱煤。液态排渣锅炉具有燃烧强度高、捕渣率高、烟气含尘量少等优势,它克服了固态排渣锅炉燃用易结渣煤种时受热面沾污结渣严重等缺点,对于易结渣煤种尤为适宜。采用液态排渣锅炉燃烧技术,不仅大幅提高炉内捕渣率、降低炉膛出口飞灰浓度,还通过锅炉熔渣与气相碱金属间的多相反应实现对钠、钾等元素的捕捉,是解决高碱煤燃烧导致沾污结渣难题的一种技术手段。基于上述背景,本文结合国家重点研发计划项目,重点围绕高碱煤在液态排渣锅炉中燃烧的飞灰颗粒迁移及沉积特性、灰渣熔融及钠捕集特性、液渣流动特性、NO_x的生成与控制等方面,开展机理分析和试验研究,最终将研究成果集成应用到一台300MW级机组开展工业示范,并通过168小时的试验验证。首先基于OpenFOAM提出并开发了一种结合动网格技术、颗粒温度模型、侵蚀模型、颗粒粘附模型和热泳力模型的液渣颗粒沉积算法耦合模型,利用模型研究了液渣颗粒的热泳力行为和沉积颗粒性质。结果表明,热泳力会扩大结渣颗粒的输送范围,颗粒浓度、粒径分布和流速都会影响撞击和沉积效率;利用PCA和BP神经网络建立了最大沉积厚度和沉积形貌的预测模型;基于耦合模型求解得到液态排渣炉内飞灰沉积厚度仅为固态排渣炉的25%,从机理上说明液态排渣炉全烧高碱煤时,受热面不会出现严重的沾污结渣问题。第二,选用高碱煤为研究对象,以1400℃时的熔融灰渣作为对照组,采用钠捕获实验装置来进行灰渣的钠捕获实验,利用场发射扫描电子显微镜（SEM）拍摄实验后的灰渣显微结构,研究了不同Na₂CO₃添加量、不同反应温度下的钠元素质量分数,得到了灰渣的钠捕获规律。结果表明,温度对钠的捕获有促进与抑制两种作用,温度在1450℃左右时,钠捕捉效果较为明显。以全烧高碱煤及掺烧不同比例Na₂CO₃后的灰渣为研究对象,探究不同温度下灰渣的热熔融特性以及流动特性,结果表明,Na₂CO₃的加入能够提高灰渣的流动性,10%左右的添加比例时流动状态最佳。第三,提出模拟倒挂灰渣块的方法获得流动参数,以研究不同煤种灰渣熔融流动特性。通过计算我国45种典型煤种的临界流动温度和临界流动速度并拟合数学公式,模拟结果和实验结果在形貌和数据方面均吻合较好。结果显示,添加Na₂CO₃可以提高灰渣流动性并降低临界流动温度。模拟计算新疆十余种典型高碱煤的临界流动温度,证实国内液态排渣锅炉可以全烧大部分新疆高碱煤,为液态排渣锅炉选择适用煤种提供参考。第四,基于对杨柳青电厂三期液态排渣锅炉的运行现状、相关试验结果以及设备特性的分析研究,制定了低氮改造和试验方案。通过对6号300MW等级机组的优化改造,并开展系统调试及燃烧优化调整试验,省煤器出口NO_x平均排放浓度由试验前的600mg/m³降至434.5 mg/m³,降低了150 mg/m³左右。结果表明,通过增强初期燃烧以及加强锅炉空气分级的方式,液态排渣锅炉具备通过低氮改造降低NO_x排放浓度的能力。最后,综合本文对高碱煤燃料特性及液态排渣锅炉设备特性的研究成果,在杨柳青电厂5号300MW等级机组液态排渣锅炉进行了全烧高碱煤工业化示范,并顺利完成168小时试验验证。结果表明:液态排渣锅炉全烧高碱煤后,制粉、燃烧、烟风、汽水、环保等系统运行正常,受热面沾污情况良好,液态排渣系统工作正常,且液态渣中钠钾金属捕集率为54.8%,省煤器出口NO_x排放浓度在300 mg/m³以下,说明液态排渣锅炉能够安全清洁的全烧高碱煤。随着我国西北大型能源基地的开发力度不断加大,紧邻高碱煤田的新疆准东、甘肃河西走廊等地区的发展潜力巨大,本文的工程博士研究成果可以为大规模利用高碱煤提供有力支撑。更多还原

【Abstract】 China’s energy structure is characterized as"rich in coal,poor in oil and low in gas",and the energy production and consumption structure mainly based on coal plays a great role in ensuring energy security and promoting economic development.The total coal resources of Xinjiang exceed 2.19 trillion tons,accounting for about 40%of China’s total coal reserves,and the Jundong,Tuha and Yili coal fields are mega-coal fields with more than 300 billion tons of reserves,among which the Jundong and Tuha fields have a large amount of high-alkali coal.High-alkali coal has the advantages of easy mining,high calorific value,low ash and low sulfur content,but endowed with a variety of forms of high content of sodium,potassium and other alkali metal elements,direct combustion will lead to the serious staining slagging and other problems.of boiler heating surface.Since the Twelfth Five-Year Plan,Xinjiang has put into operation a number of high alkali coals for the design of coal units,are solid slag boilers,through the optimization of the design of the furnace and combustion system,mixing kaolin,increase soot blower and other targeted technical measures,can effectively improve the boiler combustion ratio of high alkali coal,but it is still difficult to achieve 100%of all burning high alkali coal.Liquid slagging boiler has the advantages of high combustion intensity,high slagging rate and low dust content in the flue gas.It overcomes the drawbacks of solid slagging boilers,such as severe fouling and slagging on heating surfaces when burning coal prone to slagging,making it particularly suitable for such coal types.The use of liquid slag boiler combustion technology,not only greatly improve the furnace slagging rate and reduce the concentration of fly ash at the furnace exit,but also through the boiler slag and gas-phase alkali metal multi-phase reaction between the capture of sodium,potassium and other elements,is the solution to the problem of burning high alkali coal slagging problems caused by staining a technical means.Based on the above background,this paper combines the project of the National Key Research and Development Program of China,focusing on the migration and deposition characteristics of fly ash particles,ash melting characteristics and sodium trapping characteristics,liquid slag flow characteristics,and NO_x generation and control of high alkali coal combustion in liquid slag boilers,to carry out mechanistic analyses and experimental research,and finally integrate and apply the results of the research to a 300MW class unit for industrial demonstration,and pass the 168 hours of experimental validation.Firstly,a coupled model of liquid slag particle deposition algorithm combining dynamic mesh technique,particle temperature model,erosion model,particle adhesion model and thermophoretic force model is proposed and developed based on Open FOAM,and the thermophoretic force behavior of liquid slag particles and the properties of deposited particles are investigated using the model.The results show that the thermophoretic force will expand the transport range of slag particles,and the particle concentration,particle size distribution and flow rate will affect the impact and deposition efficiency;the prediction model of maximum deposition thickness and deposition morphology is established by using PCA and BP neural network;based on the coupled model solution,the thickness of the fly ash deposition in the liquid slag discharge furnace is only 25%of that in the solid slag discharge furnace,and it is shown that the liquid slag discharge furnace will not have serious staining on the heated surface when it burns all the high alkali coals from a mechanical point of view.When the liquid slagging furnace burns high alkali coal,the heating surface will not have serious contamination and slagging problems.Secondly,the high alkali coal was chosen as the research object,and the molten ash at 1400℃was used as the control group,and the sodium capture experimental device was utilized to carry out the sodium capture experiments of ash,and the microstructure of ash after the experiments was photographed by field emission scanning electron microscope（SEM）,and the sodium mass fraction at different Na₂CO₃ additions and different reaction temperatures was investigated,and the sodium capture law of ash was obtained.The results show that temperature has both promoting and inhibiting effects on sodium capture,and the sodium capture effect is more obvious when the temperature is around 1450℃.Taking the ash slag after burning high alkali coal and mixing different proportions of Na₂CO₃ as the research object,the hot melt characteristics and flow characteristics of the ash slag under different temperatures were investigated,and the results showed that the addition of Na₂CO₃ could improve the fluidity of the ash slag,and the flow state was the best when the proportion of Na₂CO₃ was added at about 10%.Thirdly,the method of simulating the inverted ash block is proposed to obtain the flow parameters in order to study the melt flow characteristics of different coal types of ash.The critical flow temperatures and critical flow velocities of 45 typical coal types in China were calculated and fitted with mathematical equations,and the simulation results and experimental results were in good agreement in terms of morphology and data.The results show that the addition of Na₂CO₃ can improve the ash flowability and reduce the critical flow temperature.The simulation calculates the critical flow temperatures of more than ten typical high-alkali coals in Xinjiang,which confirms that most of the high-alkali coals in Xinjiang can be fully burned in domestic liquid slag discharge boilers,and provides a reference for the selection of suitable coal types for liquid slag discharge boilers.Fourth,a low-NO_x retrofit and test program was formulated based on the analysis and research of the operational status of the liquid slag discharge boiler at Yangliuqing Power Plant Phase III,relevant test results and equipment characteristics.Through the optimization and modification of the No.6 300MW class unit and the system commissioning and combustion optimization and adjustment test,the average NO_x emission concentration at the coal economizer outlet was reduced from 600mg/m3 before the test to 434.5 mg/m³,which is about 150 mg/m³ lower.The results show that by enhancing the initial combustion as well as strengthening the boiler air classification,the liquid slag discharge boiler has the ability to reduce the NOx emission concentration through low-NO_x modification.Finally,by synthesizing the research results of this paper on the fuel characteristics of high alkali coal and the equipment characteristics of liquid slag discharge boiler,an industrial demonstration of all-fired high alkali coal has been carried out in the liquid slag discharge boiler of the No.5 300MW unit of Yangliuqing Power Plant,and the 168-hour test verification has been successfully completed.The results show that:after the liquid slag boiler burns high alkali coal,the systems of pulverizing,combustion,flue gas,steam,environmental protection and so on operate normally,the heating surface is well polluted,the liquid slag discharge system works normally,and the capture rate of sodium and potassium metal in the liquid slag is54.8%,and the concentration of NO_x emission from the economizer outlet is below300 mg/m³,which indicates that the liquid slag boiler can burn high alkali coal safely and cleanly.With the increasing development of China’s northwest energy base,the development potential of Xinjiang Jundong、Gansu Hexi Corridor and other regions,which are adjacent to the high alkali coal field,is huge,and the results of the engineering doctoral research in this paper can provide strong support for the large-scale utilization of high alkali coal.更多还原