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.
The device operating in a closed cycle can utilize nuclear energy. It uses a high temperature gas-cooled reactor as a heater, and the coolant (æ°¦ or nitrogen, etc.) of the reactor acts as both a compressor and a turbine.
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