Development status and prospects of compressed air energy storage technology
Introduction
Energy storage technology is an urgent need to solve the large-scale access of renewable energy and improve the efficiency, safety and economy of conventional power systems and regional energy systems. It is called the supporting technology and strategic emerging industries of the energy revolution. As of the end of 2017, my country's installed energy storage capacity was 28.9 GW, accounting for about 1.6% of the country's total installed capacity, which is far below the world average of 2.7%. It is estimated that by 2050, my country's installed energy storage capacity will reach more than 200 GW, accounting for 10% to 15% of the total power generation. The market demand is huge and urgent. Compressed air energy storage has the advantages of large scale, high efficiency, low cost, and environmental protection, and is considered to be one of the most promising large-scale energy storage technologies.
Traditional compressed air energy storage technology
The traditional compressed air energy storage system is an energy storage system developed based on gas turbine technology. In the low power consumption valley, the air is compressed and stored in the air storage chamber, so that the electric energy is converted into air and stored in the air; at the peak power consumption, high-pressure air is released from the air storage chamber, enters the combustion chamber and burns with the fuel, and then drives the turbine Power generation, as shown in Figure 1.
It has been commercialized in Germany (Huntorf 290 MW) and the United States (McIntosh 110 MW). However, traditional compressed air energy storage systems have three main technical bottlenecks. One is that they rely on fossil fuels such as natural gas to provide heat; the other is that they need to rely on large gas storage caves, such as rock caves, salt caves, and abandoned mines, and the third is that the system is inefficient , Huntorf and McIntosh power stations have efficiencies of 42% and 54%, respectively.
New compressed air energy storage technology
In order to solve the technical bottleneck problem of traditional compressed air energy storage, in recent years, domestic and foreign scholars have carried out research and development of new compressed air energy storage technology, including adiabatic compressed air, thermal storage compressed air energy storage and isothermal compressed air energy storage (not used Fuel), liquid air energy storage (not using large gas storage caves), supercritical compressed air energy storage and advanced compressed air energy storage (not using large gas storage caves, no fuel), etc. At present, there are a total of 4 institutions that have built a new megawatt-level compressed air energy storage system demonstration in the world, namely, the British Highview company (2 MW liquid air energy storage system, 2010), the United States SustainX company (1.5 MW isothermal compression Air Energy Storage System, 2013), GeneralCompression Corporation (2MW regenerative compressed air energy storage system, 2012) and Institute of Engineering Thermophysics, Chinese Academy of Sciences (1.5MW supercritical compressed air energy storage system, 2013) And 10 MW advanced compressed air energy storage system, 2016). Among them, the Institute of Engineering Thermophysics of the Chinese Academy of Sciences completed the world’s first 10 MW advanced compressed air energy storage demonstration system in 2016, with a system efficiency of 60.2%. It is currently the world’s most efficient and largest new compressed air energy storage system. The Institute of Engineering Thermophysics of the Academy of Sciences is developing the world's first 100 MW advanced compressed air energy storage demonstration system, which is expected to be completed around 2020.
Representative new compressed air energy storage technologies include:
(1) Adiabatic compressed air energy storage system
When the system is storing energy, the air is compressed to a high temperature and high pressure state by a compressor, and the heat storage system is used to store the compressed heat, and the air is cooled and stored in a storage tank. When discharging energy, the high-pressure air is released, the stored compression heat is used to heat the air, and then the expander is pushed to generate power, as shown in Figure 2.
The system recovers the compression heat and reuses it to improve efficiency. At the same time, the combustion chamber is removed and zero emissions are achieved. However, the energy consumption of the compression process is relatively high. Due to the high temperature of the air at the compressor outlet, high requirements for equipment materials are required.
(2) Regenerative compressed air energy storage system
The difference between this system and the adiabatic compressed air energy storage system is that the system exchanges and stores heat between stages in the compression process, and the adiabatic compressed air energy storage stores heat after the entire compression process, as shown in Figure 3.
Compared with adiabatic compressed air energy storage, the thermal storage compressed air energy storage system has lower heat storage temperature and energy storage density, but its compressor energy consumption is reduced, and the requirements for compressor materials are not high. The disadvantage of this system is that it adds multi-stage heat exchange and heat storage, and the initial investment of the system has increased.
(3) Isothermal compressed air energy storage system
The system adopts certain measures (such as piston, spray, bottom gas injection, etc.) to provide an approximately constant temperature environment through a liquid with a large specific heat capacity (water or oil), increase the gas-liquid contact area and contact time, and make the air compress and expand The process is infinitely close to an isothermal process, which minimizes heat loss and improves system efficiency, as shown in Figure 4.
In addition, the system does not require supplementary combustion, and gets rid of the dependence on fossil fuels, but it does not get rid of the dependence on large gas storage caves.
(4) Liquid air energy storage system
This system is a technology that converts electrical energy into internal energy of liquid air to achieve energy storage. When storing energy, the system drives the air separation and liquefaction device to produce liquefied air, which is stored in a low-temperature storage tank; when the energy is released, the liquid air in the low-temperature storage tank is pressurized to absorb heat, and then the turbine is driven to generate electricity, as shown in Figure 5.
Due to the liquefied storage of air, the size of the storage device is greatly reduced, thereby eliminating the need for a large air storage chamber.
(5) Supercritical compressed air energy storage
In 2009, the Institute of Engineering Thermophysics of the Chinese Academy of Sciences originally proposed advanced supercritical compressed air energy storage technology internationally, which can simultaneously solve the three major technical bottlenecks of traditional compressed air energy storage systems. Its working principle is: when storing energy, the system uses electric power to drive the compressor to compress the air to a supercritical state, and after recovering the compression heat, the stored cold energy is used to cool and liquefy it and store it in a low-temperature storage tank; The liquid air is pressurized to recover the cold energy to reach a supercritical state, and further absorbs the heat of compression and then drives the motor through a turbo expander to generate electricity. The system uses liquid air storage to increase the energy storage density and solves the dependence on large air storage chambers; the use of compressed heat recovery solves the dependence on fossil fuels and further improves the system efficiency.
The main application areas of compressed air energy storage
(1) Power system peak shaving
At present, the daily electricity load fluctuates, and the peak-to-valley difference is increasing day by day. Compressed air energy storage, as a large-scale capacity energy storage technology, can store and release the electricity generated during the peak of electricity consumption, realize the peak and fill valley of the power system, reduce the installed power generation and grid capacity, and improve the efficiency and efficiency of the power system. Economy.
(2) Renewable energy
Renewable energy is intermittent and unstable. Direct power generation and grid connection have a great impact on the grid, so the phenomenon of abandoning wind and light is serious. Compressed air energy storage can store intermittent, unstable, and uncontrollable renewable energy for power generation, and then release it in a stable and controllable manner according to demand. It has functions such as smooth fluctuations, tracking and dispatching output, peak and frequency modulation, and achieves large renewable energy power generation. Scale grid connection.
(3) Distributed Energy System
Distributed energy system is the main development trend of high-efficiency, low-carbon and high-safety energy systems in the future. However, compared with large power grids, it has disadvantages such as large load fluctuations, poor system regulation ability, and high failure rate. Compressed air energy storage can be used as a load balancing device and backup power source to effectively solve the above problems, improve the reliability and stability of the power supply of the system, and realize black start and isolated grid operation.
(4) Frequency modulation of power system
Compressed air energy storage power station can perform the same function of power system frequency regulation as gas turbine power station, thermal power station or pumped storage power station. When the power station is combined with other energy storage technologies such as super capacitors, flywheels, chemical batteries, etc., the frequency modulation speed will be faster and more effective.
(5) Other applications
Compressed air energy storage is also widely used in other fields, such as providing power for mobile devices such as automobiles and golf carts; as an uninterruptible power supply (UPS), providing guaranteed power for data room, precision instrument manufacturing, medical facilities, defense facilities, etc. ; The air released after power generation by the expander is low in temperature and purified, and can be used in the air conditioning system to provide fresh air and cooling for the building.
Compressed air energy storage challenges and prospects
(1) Technical performance needs further improvement
At present, the maximum efficiency of the new compressed air energy storage is about 60%, which has room for improvement compared with the 70% to 75% efficiency of the 300 MW pumped energy storage; the maximum scale of the system is 10 MW, which has not yet reached the traditional compressed air The scale of energy storage is 100 megawatts; its unit cost is about 6000~10000 yuan/kW and 1500~2500 yuan/kWh, there is still room for decline.
(2) The scale of the system needs to be further increased
Large-scale is the development trend of compressed air energy storage technology, and it is also the main way to reduce costs and improve performance. The scale of the new compressed air energy storage technology that has been applied is relatively small (1-10 MW), and cannot meet the requirements of scale and economy. Therefore, there is an urgent need to launch a larger-scale (100 MW class) new compressed air energy storage technology research and development. It is expected that the efficiency of the 100 MW new compressed air energy storage technology can be increased to 70%, and its unit cost can be reduced to about Around 4,000 yuan/kW and around 1,000 yuan/kWh.
(3) Demonstration and application urgently need to be strengthened
The number of demonstration systems for new compressed air energy storage technology is small, which cannot meet the demonstration needs of technological development and large-scale application. It is urgent for the government and enterprises to strengthen policy guidance and increase financial support. At present, no systematic electricity price compensation and incentive policies have been formed, and the relevant policies for pumped storage are not applicable to compressed air energy storage. There are few power stations in commercial operation worldwide, which affects the promotion and application of compressed air energy storage technology to a certain extent.
With the gradual deepening of the energy revolution, the continuous development of energy storage technology, and the successive completion of large-scale compressed air energy storage demonstration projects, the compressed air energy storage industry will also enter the fast lane of development. It is believed that under the correct organization and leadership of the government, under a good policy environment, and with the joint efforts of scientific research institutions and enterprises, compressed air energy storage technology will surely develop continuously and healthily, and achieve large-scale applications quickly.
