a rotary power machine that converts steam energy into mechanical work. Also known as steam turbine. Mainly used as the prime mover for power generation, it can also directly drive various pumps, fans, compressors and ship propellers. You can also use the exhaust steam or intermediate extraction of steam turbine to meet the heating needs in production and life.
The steam turbine is a rotary 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 AD, Hero of Alexandria described the steam rotating ball, also known as Fengshen wheel, which was the prototype of the earliest reactive steam turbine. In 1629, Blanca, Italy, proposed a runner that was rotated by a steam hitting the blades.
at the end of 19th century, Laval in Sweden and Parsons in England respectively created practical steam turbines. Laval made the first single-stage impulse turbine with 5 horsepower (3.67 kW) in 1882, and 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 2th century, France lato and Switzerland zolai made multi-stage impulse steam turbines respectively. Multi-stage structure has opened the way for increasing steam turbine power, and has been widely used, and the unit power is increasing. Parsons obtained a British patent in 1884, and made the first 1-horsepower multistage reactive steam turbine, which was in the leading position in power and efficiency at that time.
at the beginning of the 2th century, Curtis of the United States made steam turbines with multiple speed stages, and each speed stage generally had two rows of moving blades. After the first row of moving blades, guide blades were 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-scale steam turbines, mainly driving pumps, blowers, etc., and are often used as the first stage of small and medium-sized multi-stage 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. Since the 19th century, the development of steam turbine is to increase the power of a single machine and improve the thermal economy of the device on the basis of continuously improving safety, reliability and durability and ensuring convenient operation.
The appearance of steam turbines promoted the development of power industry. By the beginning of the 2th century, the single power of steam turbines in power stations had reached 1 MW. With the increasingly extensive application of electric power, the peak load of power stations in new york and other big cities in the United States was close to 1 MW in the 192s. If the single machine power was only 1 MW, nearly 1 units needed to be installed. Therefore, the single machine power was increased to 6 MW in the 192s, and 165 MW and 28 MW steam turbines appeared in the early 193s.
the subsequent economic recession and the outbreak during the second world war brought the increase of single turbine power to a standstill. In 195s, with the post-war economic development, the demand for electric power increased by leaps and bounds, and the single unit power began to increase, and large steam turbines with 325-6 MW appeared one after another. In 196s, a 1 MW steam turbine was built. In the 197s, a 13 MW steam turbine was built. At present, the stand-alone power commonly used in many countries is 3 ~ 6 MW.
steam turbines are widely used in various sectors of social economy. There are many kinds of steam turbines, and there are 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 are impulse turbines whose steam mainly expands in nozzles (or stationary blades) at all levels; Reactive turbine with steam expanding in both stator and rotor blades; And the kinetic energy of 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, which has high heat utilization rate; Steam turbines with back-pressure turbine exhaust pressure greater than 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 the steam turbine unit is expressed by the heat consumption rate or thermal efficiency of the steam turbine. The heat consumption rate of steam turbine is the steam heat consumed per output unit of mechanical work, and the thermal efficiency is the ratio of output mechanical work to steam heat consumed. For the whole power station, boiler efficiency and power consumption in the plant should also be considered. Therefore, the heat consumption rate of power station is higher than that of single steam turbine, and the thermal efficiency of power station is lower than that of single steam turbine.
a power station with a total power of 1 MW of turbo-generators consumes about 2.3 million tons of standard coal every year. If the absolute value of thermal efficiency can be increased by 1%, 6, 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 the steam turbine, in addition to constantly improving the efficiency of the steam turbine itself, including improving the blade profile design of all levels (to reduce flow loss) and reducing the loss of valves and exhaust pipes, measures can also be taken from the thermodynamic point of view.
according to the thermodynamic principle, the higher the new steam parameters, the higher the thermal efficiency of the thermal cycle. The pressure and temperature of new steam used in early steam turbines are low, and the thermal efficiency is lower than 2%. With the increase of single machine power, the pressure of fresh steam has increased to 3 ~ 4 MPa and the temperature is 4 ~ 45℃ in the early 193s. 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 over 3%. In the early 195s, steam turbines with new steam temperature of 6℃ were used. Later, there was a new steam turbine with a steam temperature of 65℃.
modern large-scale steam turbines usually adopt supercritical parameters with fresh steam pressure of 24 MPa, fresh steam temperature and reheat temperature of 535 ~ 565℃, or subcritical parameters with fresh steam pressure of 16.5 MPa and fresh steam temperature and reheat temperature of 535℃. The thermal efficiency of power plants using these turbines is about 4%.
in addition, the lower the exhaust pressure of the steam turbine, the higher the thermal efficiency of the steam cycle. However, the exhaust pressure mainly depends on the temperature of the 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 .5 ~ .8 MPa. In order to reduce the weight and size of marine steam turbines, the exhaust pressure of .6 ~ .1 MPa is often used.
in addition, the measures to improve the thermal efficiency of steam turbines include regenerative cycle, reheat cycle and heating turbine. Improving the thermal efficiency of steam turbine is of great significance to saving energy.
The research and development of large steam turbines is an important direction for the future development of steam turbines, among which the research and development of longer last stage blades is a key to further develop large steam turbines. Research on improving thermal efficiency is another direction of steam turbine development, and adopting higher steam parameters and secondary reheating, developing peak shaving units and popularizing the application of heating steam turbines are important trends in this development.
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.
The installed capacity of steam turbines using geothermal energy in the world was 3,19 MW in 1983, but the utilization of deep geothermal resources with higher temperature such as lava has yet to be explored. Steam turbine power station using solar energy has been 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, adopting new theories and technologies to improve the performance of steam turbines is also an important content of steam turbine research in the future. For example: three-dimensional flow theory in gas dynamics, wet steam two-phase flow theory; Finite element method and fracture mechanics analysis of strength; Fast Fourier transform, modal analysis and laser technology in vibration; Computer technology in design, manufacturing technology, test measurement and operation monitoring; Ultrasonic inspection 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.