The blade is the key part of the steam turbine and one of the most delicate and important parts. It bears the combined effects of high temperature, high pressure, huge centrifugal force, steam force, steam exciting force, corrosion and vibration and water droplet erosion in wet steam area under extremely harsh conditions. Its aerodynamic performance, processing geometry, surface roughness, installation clearance, operating conditions, scaling and other factors all affect the efficiency and output of the turbine; Its structural design, vibration intensity and operation mode have a decisive impact on the safety and reliability of the unit. Therefore, the world’s most famous manufacturing groups have made unremitting efforts to apply the most advanced scientific and technological achievements to the development of new blades, and constantly introduce new blades with superior performance from generation to generation to defend their advanced position in the field of turbine manufacturing.
From 1986 to 1997, China’s power industry has been developing continuously and at a high speed, and the power turbine is realizing high parameter and large capacity. According to statistics, by the end of 1997, the installed capacity of steam turbines including thermal power and nuclear power had reached 192 GW, including 128 thermal power units of 250-300 MW, 29 320.0-362.5 MW units and 17 500-660mw units; The units of 200 MW and below have also developed greatly, including 188 units of 200-210 MW, 123 units of 110-125 MW and 141 units of 100 MW. The maximum capacity of nuclear power turbine is 900MW.
With the large capacity of power station steam turbine in China, the safety and reliability of blades and the maintenance of their high efficiency become more and more important. For 300 MW and 600 MW units, the power converted by each stage blade is as high as 10 MW or even 20 MW. Even if the blade is slightly damaged, the reduction of thermal economy and safety reliability of the steam turbine and the whole thermal power unit cannot be ignored. For example, due to scaling, the area of the first stage nozzle of the high pressure will be reduced by 10%, and the output of the unit will be reduced by 3%. Due to the damage caused by foreign hard foreign matters hitting the blade and the damage caused by solid particles eroding the blade, the stage efficiency may be reduced by 1% ~ 3% depending on its severity; If the blade breaks, the consequences are: light vibration of the unit, dynamic and static friction of the flow passage, and loss of efficiency; In serious cases, forced shutdown may be caused. Sometimes, it takes several weeks to several months to replace blades or repair damaged rotors and stators; In some cases, the blade damage is not found or handled in time, causing the accident to extend to the whole unit or the unbalanced vibration of the unit due to the fracture of the last stage blade, which may lead to the destruction of the whole unit, and the economic loss will be in the hundreds of millions. Such examples are not rare at home and abroad.
The experience accumulated over the years has proved that whenever a large number of new steam turbines are put into operation or when the power supply and demand are unbalanced and the steam turbines are operating for a long time in deviation from the design conditions, the blade failure damage caused by improper design, manufacturing, installation, maintenance and operation will be fully exposed. As mentioned above, the installed capacity of large-scale steam turbines in power stations in China has increased rapidly for more than 10 years, and the new situation of long-term low load operation of large units in some areas has begun to appear. Therefore, it is necessary to investigate, analyze and summarize all kinds of damage to blades, especially the last stage and regulating stage blades, and find out the rules, so as to formulate preventive and improvement measures to avoid large losses.
Post time: Sep-01-2022