| 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.
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