【作者】 刘定平；

【导师】 陆继东；

【作者基本信息】 华南理工大学 ， 电站系统及其控制， 2012， 博士

【摘要】 随着电力需求的加快增长，能源保障和环保形势日益严峻。为了满足电力需求，我国火力发电机组正向着大容量、高参数的超临界和超超临界燃煤机组发展。这使得发电设备工作环境更加恶劣，设备安全性和技术要求更高，操作控制也变得更加复杂。据现场调研可知，近年来我国在运的大型超临界和超超临界机组普遍出现了高温受热面管内氧化皮问题，有些氧化皮剥落并引发了堵塞爆管和汽轮机叶片冲蚀。高温受热面管内氧化皮问题已严重困扰火力发电机组安全运行。本文紧紧围绕超（超）临界锅炉高温受热面管内氧化皮的生成、剥落机理和防爆关键技术等方面展开研究。通过在现场对超（超）临界锅炉高温管道常用管材（TP347H、T91、T23）及其管内氧化皮进行样本采集，分别进行成分和结构分析，系统地研究了超（超）临界锅炉管内氧化皮的形成机理；通过对氧化皮应力、厚度和温度变化率的关系研究，揭示了变工况运行时高温管道内部氧化皮大量剥落的规律。结合电厂DCS数据库，分析了氧化皮堵塞与壁温变化的耦合关系，建立了基于数据挖掘技术的超（超）临界锅炉氧化皮堵管预警模型。从氧化皮生成、剥落、堵塞各环节系统地提出了预防超（超）临界锅炉因氧化皮剥落和防止氧化皮堵塞而引起爆管的关键技术。氧化皮生成与剥落机理的揭示为超临界锅炉运行优化控制与管内氧化皮堵塞监测提供了理论基础；防爆关键技术可有效地减少因氧化皮问题而带来的长期困扰大型火电机组安全运行的问题，提高了燃煤机组的可靠性。其主要研究结论如下：（1）通过对超（超）临界锅炉高温管道常见受热面材料成分与结构分析，得到了不同成分对材料抗氧化性能的影响。为不同温度区域的受热面材料选择及运行温度优化调整奠定了基础。（2）在对超（超）临界锅炉高温管道常用的TP347H、T91、T23三种代表性的管材及其产生的氧化皮进行取样和成分、结构、形貌的分析，揭示了高温蒸汽管内氧化皮的形成机理及发展过程。研究表明，在正常运行状况下，超（超）临界锅炉管内存在原生层和延伸层两层氧化皮，该状态氧化皮与金属基体结合牢固不易剥落；在高温运行状况下，基体中的铁与渗透进来的氧反应生成以FeO为主要成分的内层高温氧化层，使氧化层由原来的双层膜转变为三层膜。因内氧化层粘附性差且易分解，使氧化皮与金属基体之间产生不稳定层，在热应力的作用下易使氧化皮从内层发生剥落。通过能量色散谱仪（EDS）和PhilipsX’pertMPD型X射线衍射仪对氧化皮进行的成分和结构分析，其结果验证了该演变过程的正确性。（3）通过研究超（超）临界锅炉氧化皮生长增厚变化过程，揭示了氧化皮剥落规律。研究表明，超(超)临界锅炉高温蒸汽侧氧化皮生长速度与材质、管壁温度、运行时间及管内氧化气氛等因素有关。在实际运行中起主导作用的因素为管壁温度和运行时间。在各因素的作用下，氧化皮厚度不断增长，氧化膜内应力不断变化而导致失效。基于断裂力学理论，分析了基于裂纹生长机理及界面结合能的氧化皮剥落模型，提出了利用临界应力及临界温度变化率来预测氧化皮失效的方法。（4）提出了基于安全经济运行温度控制域的超（超）临界锅炉管内氧化皮生成速度控制技术。研究表明，超临界锅炉不同的高温受热面采用了不同的管材，不同的管材各自存在相应最高运行温度点。通过对超（超）临界锅炉不同工况点管壁温度分布情况的研究，得到了不同负荷下的安全运行温度控制线（A线）。综合考虑机组效率及管壁温度对氧化皮生成速度的影响，通过安全和经济校核，得到了超（超）临界锅炉经济运行的高温受热面的温度控制线（B线）。根据上述A、B二线所确定的区域得到超（超）临界锅炉高温受热面安全经济运行温度控制域。实践表明，上述安全经济运行温度控制域的确立，对生产现场满足经济运行，优化控制超（超）临界锅炉管内氧化皮生成速度具有明确的指导意义。（5）提出了基于安全运行周期的超(超)临界锅炉变工况温度变化率控制的防爆技术。研究表明，超（超）临界锅炉氧化皮随着运行时间的加长而不断增厚，呈现一定的规律，根据其规律可以得到相应运行周期可能的氧化皮厚度；再根据Armitt方法计算出一定厚度的氧化皮相应的拉、压应力的承受范围；最后根据相应氧化皮所能够承受的极限拉、压应力的大小，得到超（超）临界锅炉变工况温度变化速率的大小。经过推导计算，得到直接根据机组运行时间的长短来决定机组启停炉及变负荷时的温变速率。简化了超临界机组启停炉及变负荷时的温变速率确立的难题。实践表明，上述运行周期与机组变工况温度变化速率的大小对生产现场控制超（超）临界锅炉管内氧化皮脱落具有实际的指导意义。（6）设计了基于磁场强度的超临界电站锅炉高温管道氧化皮自动校准双探头探测仪。该探测仪有效地解决了氧化皮探测中的基准值问题。同时，应用该仪器研究了磁场强度探测法对不同合金管内氧化皮检测的适应性，实验研究了探头与管道的间隙、偏角、相对位置等因素对磁场强度探测结果的影响，得到了间隙小于1.07mm、角度偏离中法线25.9°内、永磁体相对氧化皮位置在26.4°内，其测量误差可控制在5%的工程误差以内，且探头与管道的间隙是影响磁场测量结果的主要因素；随着探头与管径的偏角、永磁体与管内氧化皮相对位置的增大，测量强度变化呈指数增长。现场检测得到该仪器对奥氏体不锈钢管内氧化皮的探测效果显著。实践证明该仪器对提前探测氧化皮的状况，对及时采取相应措施预防爆管十分有效。（7）建立了基于数据挖掘技术的超(超)临界锅炉管内氧化皮堵塞预测模型，并提出了基于该模型的吹管防爆技术。通过对超（超）临界锅炉因管内氧化皮堵塞而出现的爆管前后现场运行参数的研究，通过数据挖掘技术，揭示了超（超）临界锅炉管壁温度与管内氧化皮堵塞存在强烈的耦合关系，建立了管内氧化皮预测模型。应用该模型能够及时预测管道出现的氧化皮堵塞现象。通过研究提出了采用在线吹管技术对氧化皮进行吹扫，直到预测模型显示氧化皮已被吹净为止。实践表明，通过该模型预测和及时吹管，能有效地预测超（超）临界锅炉管内氧化皮堵塞，防止锅炉由此而出现的超温爆管事故的发生，大大地提高了机组运行的安全性和可靠性。超（超）临界锅炉在球范围广泛的使用，在长时间运行中出现管内氧化皮是一个普遍问题。如何应用本研究理论及技术方法准确判断超（超）临界锅炉高温管道氧化皮状况，及时开展不同管材内氧化皮探测，加强运行控制，减少超温爆管事故，是下一步需要努力的方向。该成果的推广也将为超（超）临界机组的安全运行发挥重要的指导作用。更多还原

【Abstract】 As the demand for power is growing faster, the importance about energy security and environmental situation is increasing. The development of China’s thermal power units is toward the larger capacity and higher parameter of supercritical and (ultra-)supercritical coal-fired units. With the improvement of equipment structure and thermal system technology, the equipment safety need to be improved too, and the operation and control have become more complicated. According to widely investigation, in recent years China’s the large supercritical and ultra supercritical units generally appear the high temperature of heating tube oxide skin generation and spalling by blocking pipe explosion and eroding of steam turbine blades.This paper closely around (ultra-)supercritical boiler heating tube high temperature oxidation of generation of skin, spalling mechanism and key technology of explosion-proof aspects. Through collecting samples about (ultra-)supercritical boiler pipe commonly used pipe (T23, TP347,T91) and tube oxide skin in production field, analyze the composition and structure respectively, study the (ultra-)supercritical boiler tube the formation mechanism of the oxide skin systematically. Through study the relationship between temperature change rate and the oxide skin stress, thickness and temperature, we can reveal the spalling rule of the high temperature oxide skin when operation changes. Combined with the power plant’s DCS database, analyze the coupling relationship oxide skin jam and wall temperature change, we constructed a (ultra-)supercritical boiler oxide skin blocking tube early warning model based on data mining technology. We have put forward key technology for preventing (ultra-)supercritical boiler’s pipe explosion caused by oxide skin peeling from oxide skin growing, spalling, blocking every link.Oxide skin formation and spalling mechanism supply supercritical boiler operation optimization control and tube oxide skin jams monitoring for theoretical foundation Explosion-proof key technology effectively reduces the long plaguing large thermal power unit safe operation problem which is brought by the oxide skin, improves the reliability of coal-fired units. The results are as follows:(1) Through analyzing (ultra-)supercritical boiler high temperature pipe common heating surfaces material composition and structure, obtain the results about the different components influencing on the material oxidation resistance. It laid a foundation for choosing different temperature of heating area material, optimizing and adjusting operation temperature.(2) Analyzing the (ultra-)supercritical boiler pipe commonly used three high temperature representative pipe materials(such as T91, T23, TP347)and it’s oxidation of the composition, structure and skin appearance, the paper reveals that the high temperature steam tube oxide skin formation mechanism and development process. Researches show that, in the normal operation conditions, it exists the original layer and extend layer oxide skin in (ultra-)supercritical boiler tube, the oxide skin and metal substrate combine firmly and is not easily spalling in this state. In high temperature operation conditions, the iron in metal matrix reacts with infiltrated oxygen atoms to generate for the inner FeO oxidation layer, so that oxide film change from the2-layer into3-layer membrane. Because the inner layer has poor adhesion and decompose easily, it leads to produce unstable layer between the oxide skin and base metal. The oxide skin spalls easily from inner under the action of thermal stress. Through using the energy dispersive spectrometer(EDS) and Philips X’pert MPD type X ray diffraction to analyze the composition and structure of oxide skin, the results show the process is correct.(3) Through the research the process about (ultra-)supercritical boiler oxide skin growing and thickening, this paper reveals the oxide skin spalling law. Based on this the model of the oxide skin spalling. Researches show that, the high temperature steam oxide skin growth rate of the (ultra-) supercritical boiler is related to the factors, such as, the material, wall temperature, running time and the oxidation atmosphere. In the actual operation of the factors play a dominant role for wall temperature and running time. In all the factors, the oxidation film thickness increasing and oxide skin internal stress changing lead to be failure. Based on the theory of fracture mechanics, the oxide skin spalling is established, and then propose to predict the oxide skin of criterion of failure which is use of critical stress and critical temperature alteration ratio.(4) Based on the safe and economic operation of the temperature control field (ultra-)supercritical boiler tube oxide skin generating speed control technology was put forward. Researches show that, different high temperature heating surfaces of supercritical boiler use different pipe material, different pipes correspondingly exist the highest operating temperature points. Through researches on the (ultra-)supercritical boiler under different conditions of temperature distribution point wall, the temperature control line (A line) of safe operation under different load is obtained. Considering the unit efficiency and wall temperature the influence on the oxide skin generating speed, through checking the security and economy, the temperature control line (B line) of high temperature heating surfaces of the (ultra-)supercritical boiler under economic operation is got. According to the areas determined by the A, B lines,(ultra-)supercritical boiler heating temperature safe and economic operation temperature control field is got. Practice shows that, establishing the above safe and economic operation temperature control field has a clear guidance significance which optimizes and controls the oxide skin formation rate of the (ultra-)supercritical boiler tube in production field.(5) Based on the operation cycle (ultra-)supercritical boiler temperature alteration ratio control variable condition of explosion protection technology is put forward. Researches show that, with running time increasing, the (ultra-)supercritical boiler oxide skin continuously thickening, and presents certain law. According to the rules, can get the probable thickness of oxide skin corresponding operation cycle. Again according to the Armitt method, calculate the bearing boundary of certain thickness of oxide skin corresponding pull, compressive stress. Finally, according to the ultimate tensile and compressive stress size which the corresponding oxide skin can bear, get the size of the temperature change rate of (ultra-)supercritical boiler under changing conditions. After computation, temperature change rate can been directly determined according to the unit operation time when the boiler starts up, blows out and changes load. The practice shows that, the operation cycle and the size of temperature alteration ratio control variable condition have a clear guidance significance which controls the oxide skin spalling of the (ultra-)supercritical boiler tube in production field.(6) Based on the magnetic field strength, designed a scanner to detect the oxide skin of heat pipe in supercritical power station boiler. Through this scanner, researches the adaptability of the method of the magnetic field strength to detect different alloy tube oxide skin. The experimental study of the clearance between probe and the pipeline, the deflection Angle, the relative position, and other factors affect the results of the magnetic field detection, get the conclusion that the clearance is less than1.07mm, the deflection angle within25.9°, the relative position of permanent magnet and scale inside26.4°, the measurement error can control under5%. And the measured results that the clearance between probe and pipeline is the main factor in which affects the magnetic field, Along with the increase of the deflection angle of probe and the pipe diameter,and the increase of relative position of Permanent magnets and scale, the increase of measuring strength variation is increased. On-site test shows that the result of the scanner to detect the oxide skin in austenitic stainless steel is obvious. As experience proves, through this scanner, detected the oxide skin ahead of time,it is effective to prevent pipe explosion by taking appropriate measures in time.(7) Based on data mining technique, a predicting model of the oxide scale plugging has been built for the (ultra-)supercritical boiler. Meanwhile, the technology of steam blow is proposed for preventing explosion of the tubing according to this model. The strong coupling relationship of tube wall temperature and the oxide scale plugging is revealed by the field running parameter of explosion before and after, because of the oxide scale plugging in the (ultra-)supercritical boiler. The predictive modeling of oxide scale is built. The application of the model can forecast promptly the phenomenon of oxide scale plugging. Sweeping the oxide scale by the technology of steam blow online was present through system research. Combined with the technology, the predictive modeling could display the oxide scale swept clearly. This shows that the oxide scale plugging inside the tubing could be effectively predicted through the modeling and the steam blow in time. Over-temperature, even tube explosion in the heating surface of superheater might be effectively controlled. These are very important and significant to improve the security, reliability of power station boilers.The (ultra-)supercritical boiler has widely operated in the world, a large number of oxide tube is a common problem in the long operation. How to apply the theory and techniques to accurately determine the super (super) critical boiler heat pipe oxide scale conditions in a timely manner different pipe oxide detection, enhance operational control, and reduce the over-temperature tube rupture is the next step is to work towards. The achievement of the promotion will play an important role in guiding for the units’ safe operation.更多还原