Steam turbine is a power machine for thermal power generation, which drives the engine to generate electricity. Steam turbine is a rotating power machine that converts steam energy into mechanical work, and it is one of the main equipment of steam power plant. Steam turbine is a kind of turbine machinery, also known as steam turbine. In the first century, Herod of Alexandria described the steam spinning ball, also known as Fengshen wheel, as the prototype of the earliest reactive steam turbine. In 1629, Blanca, Italy, proposed a runner that rotates by steam impacting blades. At the end of 19, Laval in Sweden and Parsons in Britain built practical steam turbines respectively. Laval built the first 5 HP (3.67 kW) single-stage impulse turbine in 1882, which solved the problems related to nozzle design and strength design. Single-stage impulse turbine has little power and is rarely used now. At the beginning of the 20th century, France Lato and Switzerland Zolai made multi-stage impulse steam turbines respectively. Multi-stage structure has opened the way for improving steam turbine power, and has been widely used, and the unit power is also increasing. Parsons obtained the British patent in 1884, and manufactured the first 10 horsepower multistage reactive steam turbine, which was in a leading position in power and efficiency at that time. At the beginning of the 20th century, Curtis made a multi-speed steam turbine, and each speed stage generally had two rows of moving blades. After the first row of moving blades, guide blades are installed on the cylinder to guide the steam flow to the second row of moving blades. At present, speed-class steam turbines are only used for small steam turbines, mainly driving pumps and blowers. , often used as the first stage of small and medium-sized multistage steam turbines. Compared with the reciprocating steam engine, the steam flow in the steam turbine is continuous and high-speed, and the flow rate per unit area is large, so it can generate more power. High-power steam turbines can use higher steam pressure and temperature, so the thermal efficiency is higher. /kloc-since the 20th century, the development of steam turbines has been to increase the single unit power and improve the thermal economy of the unit on the basis of continuously improving safety, reliability and durability and ensuring convenient operation. The appearance of steam turbine promoted the development of electric power industry. By the beginning of the 20th century, the power of a single steam turbine in power station had reached 10 MW. With the increasing application of electric power, the peak load of power stations in new york and other big cities in the 1920s approached 65,438+000 MW. If the power of a single machine is only 10 MW, it is necessary to install nearly 100 units. Therefore, in the 1920s, the unit power was increased to 60 MW, and in the early 1930s, 1.65 MW and 208 MW steam turbines appeared. Since then, the economic recession and the outbreak during the Second World War have made the increase of single turbine power stagnate. In 1950s, with the post-war economic development, the demand for electricity increased by leaps and bounds, and the single unit power began to increase continuously, and large steam turbines with 325-600 MW appeared one after another. In 1960s, a 1000 MW steam turbine was built. A 1300 MW steam turbine was built in 1970s. At present, the single machine power widely used in many countries is 300 ~ 600 MW. Steam turbines are widely used in various sectors of social economy. There are many types of steam turbines and different classification methods. According to the structure, there are single-stage steam turbines and multi-stage steam turbines; Single-cylinder steam turbines installed in one cylinder at all levels, and multi-cylinder steam turbines packaged in several cylinders at all levels; Single-shaft steam turbines installed on one shaft at all levels, and double-shaft steam turbines installed on two parallel shafts at all levels. According to the working principle, there is an impulse turbine, and its steam mainly expands in nozzles (or stationary blades) at all levels; Reactive turbine with steam expanding in stator and rotor blades; And the kinetic energy of the steam expanded in the nozzle is utilized on several rows of moving blades. According to the thermal characteristics, there are condensing steam turbine, heating steam turbine, back pressure turbine, extraction steam turbine and saturated steam turbine. The steam discharged from condensing turbine flows into the condenser, and the exhaust pressure is lower than the atmospheric pressure, so it has good thermal performance and is the most commonly used turbine. The heating turbine not only provides power to drive generators or other machinery, but also provides heat for production or life, with high heat utilization rate; Back-pressure turbine The exhaust pressure of which is greater than the atmospheric pressure; Extraction steam turbine is a steam turbine that can extract steam from the intermediate stage for heating; Saturated steam turbine is a steam turbine with saturated steam as new steam. The steam of steam turbine expands from the inlet to the outlet, and the volume of steam per unit mass increases by hundreds or even thousands of times, so the height of blades at all levels must be lengthened step by step. The exhaust area of high-power condensing steam turbine is very large, and the last stage blades must be made very long. The thermal economy of steam turbine device is expressed by the heat consumption rate or thermal efficiency of steam turbine. The heat consumption rate of steam turbine is the steam heat consumed per unit output mechanical work, and the thermal efficiency is the ratio of output mechanical work to steam heat consumed. For the whole power station, the boiler efficiency and power consumption of the power station should also be considered. Therefore, the heat consumption rate of the power station is higher than that of a single steam turbine, and the thermal efficiency of the power station is lower than that of a single steam turbine. A power station with a total power of 1000 MW turbine generator consumes about 2.3 million tons of standard coal every year. If the absolute value of thermal efficiency can be increased by 1%, 60,000 tons of standard coal can be saved every year. Therefore, the thermal efficiency of steam turbine devices has been paid attention to. In order to improve the thermal efficiency of steam turbine, in addition to continuously improving the efficiency of steam turbine itself, including improving the blade profile design at all levels (reducing flow loss) and reducing the loss of valves and exhaust pipes, measures can also be taken from the perspective of thermodynamics. According to the principle of thermodynamics, the higher the new steam parameters, the higher the thermal efficiency of thermal cycle. The pressure and temperature of new steam used in early steam turbines are low, and the thermal efficiency is lower than 20%. With the increase of single machine power, the fresh steam pressure has increased to 3 ~ 4 MPa and the temperature is 400 ~ 450℃ in the early 1930s. With the continuous improvement of high-temperature materials, the steam temperature is gradually increased to 535℃, the pressure is also increased to 6 ~ 12.5 MPa, and some of them have reached 16 MPa, and the thermal efficiency is above 30%. In the early 1950s, a steam turbine with a fresh steam temperature of 600℃ was used. Then there was a new steam turbine, and the steam temperature reached 650℃. Modern large steam turbines usually adopt supercritical parameters, such as fresh steam pressure of 24 MPa, fresh steam temperature and reheat temperature of 535 ~ 565℃, or subcritical parameters, fresh steam pressure 16.5 MPa, fresh steam temperature and reheat temperature of 535℃. The thermal efficiency of power plants using these turbines is about 40%. In addition, the lower the exhaust pressure of steam turbine, the higher the thermal efficiency of steam cycle. However, the exhaust pressure mainly depends on the temperature of cooling water. If the exhaust pressure is too low, it is necessary to increase the cooling water flow or increase the cooling area of the condenser, and the last stage blades are also longer. The common exhaust pressure of condensing turbine is 0.005 ~ 0.008 MPa. In order to reduce the weight and size of marine steam turbines, the exhaust pressure of 0.006 ~ 0.0 1 MPa is often used. In addition, the measures to improve the thermal efficiency of steam turbine include regenerative cycle, reheat cycle and heating steam turbine. Improving the thermal efficiency of steam turbine is of great significance to energy saving. Developing large-scale steam turbines is an important direction for the development of steam turbines in the future, in which developing longer last stage blades is the key to further developing large-scale steam turbines. The research on improving thermal efficiency is another direction of steam turbine development, and it is an important trend to adopt higher steam parameters and secondary reheating, develop peak shaving units and popularize the application of heating steam turbines. The number of steam turbines in modern nuclear power plants is increasing rapidly, so it is of great significance to study steam turbines with good performance suitable for different reactor types. 1983 The installed capacity of steam turbines using geothermal energy in the world has reached 3 190 MW, but the utilization of deep geothermal resources with higher temperature such as lava remains to be explored. Steam turbine power station using solar energy is already under construction, and ocean temperature difference power generation is also under study. All these new energy turbines have yet to be tested and studied. In addition, in the process of steam turbine design, manufacture and operation, it is also an important content of steam turbine research in the future to adopt new theories and technologies to improve the performance of steam turbines. For example: three-dimensional flow theory in gas dynamics, wet steam two-phase flow theory; Finite element method of strength and fracture mechanics analysis: fast Fourier transform, modal analysis and laser technology in vibration: computer technology in design, manufacturing technology, test and measurement and operation monitoring; Ultrasonic detection and loss calculation in life monitoring. In addition, the application of new working fluids such as freon, as well as new structures, new processes and new materials will be developed.
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