In 1791, the British Barber first described the working process of the gas turbine; in 1872, the German Stolzer designed a gas turbine and tested it from 1900 to 1904, but was unable to disengage the starter independently. The operation failed; in 1905, the French Lemmel and Amango made the first gas turbine capable of outputting work, but the efficiency was too low, so it was not practical.
In 1920, the German Holzwat made the first practical gas turbine with an efficiency of 13% and a power of 370 kW. It was operated according to the equal-volume heating cycle, but was heated by intermittent deflagration due to the isovolumic heating cycle. There are many major shortcomings that have been abandoned.
With the development of aerodynamics, people have mastered the characteristics of gas diffusion flow in compressor blades, and solved the problem of designing high-efficiency axial flow compressors. Therefore, in the mid-1930s, axial flow with an efficiency of 85% appeared. Compressor. At the same time, turbine efficiency has also improved. In the case of high-temperature materials, there is a heat-resistant steel such as chrome-nickel alloy steel that can withstand temperatures above 600 °C, so that a higher gas initial temperature can be used, and the gas turbine of the isostatic heating cycle is finally successfully applied.
In 1939, a four-megawatt gas turbine for power generation was built in Switzerland with an efficiency of 18%. In the same year, the test flight of a jet made in Germany was successful. From then on, the gas turbine entered a practical stage and began to develop rapidly.
With the continuous development of high-temperature materials, and the use of cooling blades by the turbine and continuous improvement of the cooling effect, the initial temperature of the gas is gradually increased, so that the efficiency of the gas turbine is continuously improved. Single-machine power has also increased, with several 100-megawatt gas turbines in the mid-1970s, up to 130 megawatts.
At the same time, the application field of gas turbines continues to expand. In 1941, the first gas turbine locomotive made in Switzerland passed the test; in 1947, the first British-made gas turbine-equipped ship was launched, which was powered by a 1.86 MW gas turbine; in 1950, the first British made it. Gas turbine car. Since then, gas turbines have gained traction in more sectors.
At the same time that gas turbines are widely used, there are also composite devices that combine gas turbines with other heat engines. The earliest appeared was the combination of the piston-type internal combustion engine; in the 1950s and 1960s, a free-piston gas turbine device consisting of a free-piston gas generator and a gas turbine appeared, but due to the cumbersome and complicated system, production stopped in the 1970s. . In addition, diesel engine gas turbine composite devices have been developed; another type of full energy system that utilizes gas turbine exhaust heat supply (or steam) can effectively save energy and has been used in various industrial production.
The working process of the gas turbine is that the compressor (ie, the compressor) continuously draws in air from the atmosphere and compresses it; the compressed air enters the combustion chamber, mixes with the injected fuel, burns, becomes high-temperature gas, and then flows into the gas turbine. The medium expansion work pushes the turbine impeller to rotate together with the compressor impeller; the function of the heated high-temperature gas is significantly improved, so that the gas turbine drives the compressor while still having the remaining work as the output mechanical work of the gas turbine. When the gas turbine is started from a standstill, it needs to be rotated with the starter. After it is accelerated to be able to operate independently, the starter will be disengaged.
The working process of a gas turbine is the simplest, called a simple cycle; in addition, there are regenerative cycles and complex cycles. The working fluid of the gas turbine comes from the atmosphere, and finally to the atmosphere, which is an open cycle; in addition, there is a closed cycle in which the working fluid is closed and recycled. The combination of a gas turbine and other heat engines is called a compound cycle device.
The initial temperature of the gas and the compression ratio of the compressor are the two main factors affecting the efficiency of the gas turbine. Increasing the initial temperature of the gas and increasing the compression ratio accordingly can significantly increase the efficiency of the gas turbine. In the late 1970s, the compression ratio reached a maximum of 31; the initial gas temperature of industrial and marine gas turbines was up to 1200 °C, and that of aviation gas turbines exceeded 1350 °C.
The gas turbine is composed of a compressor, a combustion chamber, and a gas turbine. Compressors are available in axial flow and centrifugal, and axial flow compressors are highly efficient and suitable for high flow applications. At low flow rates, axial flow compressors are shorter due to the latter stages and are less efficient than centrifugal. Among the gas turbines with several megawatts of power, some compressors use axial flow and a centrifugal type as the final stage, thus achieving higher efficiency and shortening the axial length.
The combustion chamber and the turbine not only have high operating temperatures, but also withstand the thermal shock caused by the drastic changes in temperature during the start and stop of the gas turbine, and the working conditions are bad, so they are the key components that determine the life of the gas turbine. In order to ensure sufficient life, the worst-working parts of the two components, such as the flame tube and the blades, must be made of high-temperature materials such as nickel-based and cobalt-based alloys, and air cooling is required to lower the operating temperature.
For a gas turbine, in addition to the main components, there must be a complete adjustment security system, in addition to the need for a good auxiliary system and equipment, including: starter, fuel system, lubrication system, air filter, air intake and Exhaust muffler, etc.
Gas turbines are available in both heavy and light versions. Heavy-duty parts are thicker, have a longer overhaul period, and have a lifespan of more than 100,000 hours. The light weight is compact and light, and the materials used are generally better. The structure of the aircraft is the most compact and lightest, but the life is short.
The main advantage of gas turbines is that they are small and light compared to piston-type internal combustion engines and steam power plants. The quality of unit power, heavy-duty gas turbines are generally 2 to 5 kg / kW, while aircraft are generally less than 0.2 kg / kW. The gas turbine has a small footprint. When used in transportation machinery such as cars and ships, it can save space and can also be equipped with gas turbines with higher power to increase the speed of vehicles and ships. The main disadvantage of gas turbines is that the efficiency is not high enough, the efficiency drops rapidly under partial load, and the fuel consumption at no load is high.
Different application departments have different requirements and usage conditions for gas turbines. Most gas turbines with a power of more than 10 MW are used for power generation, and almost all of 30 to 40 MW or more are used for power generation.
The gas turbine generator set can be quickly started without external power supply, and has good maneuverability. It is used in the power grid to drive the peak load and serve as an emergency backup, which can better ensure the safe operation of the power grid, so it is widely used. In mobile power stations such as automobile (or trailer) power stations and train power stations, gas turbines are widely used due to their small size. In addition, there are many portable power supplies that utilize gas turbines, with a minimum power of less than 10 kW.
The future development trend of gas turbines is to improve efficiency, use high temperature ceramic materials, utilize nuclear energy and develop coal combustion technology. The key to improving efficiency is to increase the initial temperature of the gas, that is, to improve the cooling technology of the turbine blades, and to develop high-temperature materials that can withstand higher temperatures. The second is to increase the compression ratio and develop a compressor with fewer stages and a higher compression ratio. Again, it is to improve the efficiency of each component.
High-temperature ceramic materials can work at high temperatures above 1360 °C. When used as high-temperature parts such as turbine blades and flame tubes of combustion chambers, the initial temperature of the gas can be greatly improved without air cooling, thereby greatly improving the gas turbine. effectiveness. High-temperature ceramic materials suitable for gas turbines include silicon nitride and silicon carbide.
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