The large-scale development and utilization of new energy is one of the important strategies for coping with the fossil energy crisis and the resulting environmental pollution problems worldwide. Due to the volatility and randomness of new energy generation such as wind energy and solar energy, large-scale new energy grid brings severe challenges to the safe and stable operation of power systems and power quality. There are a lot of wind and light abandonment in actual operation. The utilization rate of new energy sources has been at a low level for a long time. 13. Therefore, how to realize the safe, efficient and economical utilization of large-scale new energy sources has become a key issue to be solved urgently in the construction of smart grids.
As we all know, energy storage technology is an important means to solve the above problems. However, large-scale engineering storage of electrical energy has always been a major problem for power technology workers around the world. To a certain extent, there is no real smart grid in the absence of large-scale energy storage.
In terms of large-scale energy storage, the more mature technologies are mainly pumped storage, battery storage and compressed air energy storage. H. Pumped storage power station is a good way to store large amounts of electrical energy, but its construction Strictly limited by geographical conditions, it is difficult to meet the needs of large-scale promotion. The battery energy storage technology is relatively mature, and the energy conversion efficiency of the above three energy storage parties is the highest, but its working life is often only 2 to 3 years, which not only has high replacement cost, but also has serious environmental pollution in the later treatment. In contrast, the construction of compressed air energy storage systems has fewer restrictions, is environmentally friendly, and has high comprehensive efficiency. It is expected to be the best choice for solving many problems in large-scale new energy development and utilization.
This paper first puts forward the concept of electric energy grade and energy storage benefit, introduces the basic principle of compressed air energy storage and the development of domestic and foreign development, and focuses on non-compensated compressed air energy storage power generation technology and its characteristics. Finally, the broad application prospects of this technology in smart grid and the key issues that need to be solved to realize large-scale industrial application are discussed.
2 Electrical energy grade and energy storage efficiency For thermal energy, we have the concept of taste. For example, steam turbines have high inlet steam temperature and high pressure, which can convert their thermal energy into electrical energy with high efficiency, so they belong to high grade thermal energy. However, shallow geothermal (shallow water or wet mud at around 14 °C) and waste heat generated during industrial production, even with large volume, are difficult to utilize and are low-grade heat.
Electric energy is the same as thermal energy, and there are objectively high and low grades.
Due to the characteristics of the power system, the production and consumption of electricity is basically completed at the same time. Most of the electric energy produced during the peak load period is used to meet people's large-scale production and living needs, and it belongs to high-grade electric energy, and its price is often high. The electric energy produced during the period of low load has to sell at a low price or even abandon electricity because it far exceeds actual demand, and it belongs to low-grade electric energy. The important role of various energy storage methods is to store low-grade electric energy and convert it into high-grade electric energy, thus reflecting the benefits of the energy storage method.
The author believes that for a given energy storage method, the economic benefit of the energy storage method can be roughly calculated by the following formula: Value; Vl is the cost of using the energy storage method to produce high-grade electric energy; The total amount of low-grade electric energy; n is the electric energy conversion efficiency of the energy storage mode; Ph and Pl are the peak-to-valley electricity price respectively; C is the equal-cost construction cost and operation and maintenance cost for producing the high-grade electric energy.
The effect of compression, compression series (such as single-stage high-pressure ratio and multi-stage compression) on compression efficiency. In the high-pressure gas storage subsystem, it is necessary to consider the effect of heat dissipation in the gas storage space and gas leakage on system efficiency. In the turbine power generation subsystem, the effect of the reducer on system efficiency needs to be considered. In the regenerative utilization subsystem, it is necessary to consider different heat exchange media (such as the use of water storage heat and molten salt heat storage) and the effect of heat exchange temperature on thermal energy utilization efficiency.
Optimized configuration of subsystem interface parameters The compressed air energy storage system involves multiple subsystems, and each subsystem is coupled with each other. The overall efficiency of the system is closely related to the interface parameters. In addition to designing appropriate processes for each subsystem, the interface parameters of each subsystem should be optimally configured to achieve overall efficiency gains.
6.2 Key Technologies for Improving CAES Economics (1) The underground cave gas storage technology and the external parameters (wind, light, water output and load demand) are constrained, and it is urgent to study the optimized control and scheduling technology of compressed air energy storage. Give full play to its role in the economic operation of the power grid.
6.3 Key Technologies for Improving the Safety of CAES Under normal circumstances, the medium used in the compressed air energy storage system is conventional air. When the gas contains a large amount of moisture or dust, it is easy to form dust agglomeration in the gas storage space and corrode the gas wall. What is more serious is that when the air expands and works, the temperature is lowered to form water droplets or even ice particles, which will bring serious safety hazards to the high-speed rotating air turbine.
Therefore, air drying and dust removal technology is an important basis for the safe promotion of compressed air energy storage technology.
The detection and repair technology of high-pressure gas storage space is the most important part of the system with the highest bearing pressure and the longest pressure-bearing time. It is very important to ensure the safety of high-pressure gas storage subsystem. To this end, it is necessary to optimize the design of the key parameters such as volume, shape, size and material of the gas storage space according to the performance indexes of the energy storage system, the energy storage capacity, the storage pressure, and the storage temperature. In addition, the long-running gas storage space may undergo fatigue damage due to the reciprocating change of the air pressure, resulting in deformation of the gas storage space or even gas leakage, thereby causing a large safety hazard. Advanced flaw detection technology and repair technology are important support for ensuring the safety of compressed air energy storage systems.
Turbine Power Generation Subsystem Control and Protection Technology The parameters such as the pressure and temperature of the turbine inlet air in the compressed air energy storage system directly affect the smoothness of the output power of the turbine power generation subsystem. Considering that the pressure and temperature of the gas storage space will gradually decrease during the power generation process, the advanced turbine valve opening control technology will be an important basis for ensuring the stable operation of the system. In addition, when the external power grid is disturbed by active power or reactive power, the control center of the turbine power generation subsystem should still be able to give correct control commands to enhance the robustness of the grid to disturbances. In extreme cases, such as the three-phase short-circuit fault and sudden no-load, the protection device of the turbine's power generation subsystem should be able to operate quickly to ensure safe shutdown of the unit.
7 Conclusion Large-scale industrial storage of electrical energy is a major problem facing humanity. Compressed air energy storage has great potential for development. This paper focuses on the basic principles and application prospects of large-scale non-compacting compressed air energy storage technology for smart grids. The progress of the State Grid 500kW compressed air energy storage project is briefly introduced. Under the background of vigorously promoting smart grid construction and energy saving and emission reduction, with this major science and technology project as the carrier, through the cooperation of politics, production, learning and research, it is expected to build China's first non-combustion compressed air energy storage power generation. Demonstration system, which will play a positive role in promoting the development of China's compressed air energy storage industry.
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