June 4th, "From May 2017, we started the technical renovation of turbine bolts for 600,000 kilowatts or more of coal-fired generating units. Now the five units have been transformed and put into operation. This is the nation's first technological transformation. It not only solves the hidden dangers of early bolt breakage, but also creates good economic benefits. Only Zheneng Group's system generator set can achieve a cost reduction of approximately 50 million yuan after all such bolt replacements are completed.” June 3, Zhe Neng The Institute of Materials Technology of the Institute of Technology has introduced the reporter to the reporter.
“This technical achievement is the first one we put forward and put into practice in China, and we have made new breakthroughs in the study of imported bolt domestic substitution projects. At the same time, we also provide experience for the development of the industry.” Vice Dean of Zhejiang Energy Group Technology Research Institute Tong Xiaozhong said. After the success of this technology research, the institute invited more than 10 senior experts from the State Power and Electric Power Research Institute, Zhejiang University, and manufacturing companies to analyze and demonstrate that the technology is at the forefront among domestic counterparts. At present, this research achievement won the second prize of Zhejiang Electric Power Science and Technology Progress Award in 2018.
Small bolt hide big risk
The parameters of steam temperature and pressure of ultra-supercritical units in large-scale thermal power plants are very high, and the requirements for the sealing performance of the valve body are rather severe. The bolts play a key role in providing sealing and fastening forces. Long-term operation of bolts at high temperatures can easily cause fractures, causing serious crew accidents and endangering power production safety and power supply safety.
"In April 2016, the General Affairs Department of the National Energy Administration issued a circular on the "Implementation of Inspection and Control of Hidden Troubles in Imported Units", requesting all thermal power plants throughout the country to fully implement the bolts and partitions of imported steam turbine valve covers and parts. When the notice was announced, Zhenneng Group had conducted a thorough investigation of the potential safety hazards, and the entire requirement was more than half a year ahead of the national requirements.” said Lou Yumin, Senior Engineer, Material Specialist, Zengneng Group Technology Research Institute. .
The time goes back to October 2015, when a coal-fired generating unit in Zhejiang was found to have broken valve bolts during maintenance. The occurrence of this incident made the Zenn Group technicians who were present at the time feel puzzled. Because the price of the bolt is very expensive, the price of an imported bolt exceeds 50,000 yuan.
“The use of steam turbine bolts for a few years was so ‘vulnerable’ and the material of the bolts was the top material for the introduction of technology,” recalls the staff responsible for on-site repairs. After the incident, Zhejiang Energy Group immediately asked all subsidiaries to carry out special investigations. "We must know that 600,000 kilowatts or more of coal-fired units are the main models for power generation in Zhejiang and even in China. Once an accident occurs, it will not only directly affect production safety and endanger workers, but it will also affect the safety of power supply to the power grid, and it will affect thousands of households." Lou Yumin Say.
Import substitution saves money
"Because the material is imported technology, the technical data of this material is very limited. The domestic production companies and related research institutions only stay in the primary stage for the understanding of the material." Lou Yumin introduced.
Problems lie ahead. It's harder to fight. Zhejiang Energy Group set up a technology research group and carried out a series of research, statistical analysis and experimental research. Feng Yumin, who is responsible for this technology, said that on the one hand, through a large number of basic experimental analysis and computational studies, on the other hand, he investigated the fracture conditions of more than 10 domestic power plants and the turbine manufacturers. In this way, relying on a step-by-step analysis and accumulation, the reasons for the breakdown of steam turbine bolts began to surface gradually, to determine the original imported materials used in steam turbine bolts - Alloy783, processing performance and material properties are somewhat dissatisfied with the soil, not meet the domestic production and processing environment It is not suitable for the high-load production environment of domestic power generation companies. There are hidden dangers and the need to replace suitable materials.
"After full comparison and certification studies, we finally established a replacement domestic material (Co3W3B) that has a wide range of applications in domestic ultra-supercritical steam turbines, reliable long-term service performance, and bolts of this material. It is able to process and produce in China and solve the monopolized production situation of the original bolt material by foreign companies and joint ventures. The key is that the cost is much lower than the original material,” said Qin Ganghua, Dean of the Zengneng Group Technology Institute.
After fully demonstrating the feasibility of material replacement, in May 2017, the technology was successfully applied to the turbine of the 600,000-kilowatt unit of Zhejiang Energy Group, which successfully achieved the import substitution of bolt materials, saving money and peace of mind. At present, after the technical innovation of the bolts has been put into use, the operation is in good condition, and many domestic operators of the same type of large-scale generator sets have come to Zhejiang to view it.
In recent years, ZNEC has always attached importance to technological innovation and independent R&D work. It has closely integrated science and technology with enterprise development. From 2011 to 2017, it has invested 2.88 billion yuan in total for scientific and technological innovation. Among them, the “Key R&D and application of ultra-low emission coal-fired generators” invented by the Zhanneng Group was awarded the first prize for national technology invention. The promotion and application of this technology has made the emission of each major pollutant of the coal-fired unit better than that of the gas turbine unit. Standards have greatly reduced the occurrence of haze in the country.