Energy storage technology is a key technology for realizing large-scale access to renewable energy such as wind energy and solar energy, peaking and filling valleys in power systems, and distributed energy supply systems. It is currently an important way to solve energy and environmental problems. Among all energy storage technologies, compressed air energy storage systems have the advantages of large energy storage capacity, long energy storage cycle, and low investment ratio. They are considered to be one of the most promising large-scale energy storage technologies and have been subjected to domestic and international The scholars are highly concerned. The conventional compressed air energy storage system has the problems of relying on large-scale gas storage rooms, dependence on fossil fuels, and low system efficiency.
In response to these problems, researchers at the Research Center for Energy Storage R&D of the Institute of Engineering Thermophysics of the Chinese Academy of Sciences proposed a new type of supercritical compressed air energy storage system. The system flow is shown in Figure 1. The system has a very high energy density, about 18 times the energy density of a conventional compressed air energy storage system, which significantly reduces the volume of the system storage tank, frees up the restrictions on the geographical conditions; the system recovers heat and cold, and gets rid of the Reliance on fossil fuels; using the supercritical state flow and heat transfer characteristics of air to improve system efficiency.
The decompression and liquefaction of air in the system can be achieved by means of a throttle valve or a liquid expander. By analyzing the thermal performance of these two types of supercritical compressed air energy storage systems, the supercritical compressed air energy storage using a liquid expander is found. The efficiency of the system (LE-SC-CAES) can be as high as 67.2%, which is 7 percentage points higher than that of a system using a pressure reducing valve (V-SC-CAES), and much higher than that of a conventional compressed air energy storage system (48%~54 efficiency) %). Turbulence analysis of the system, as shown in Figure 2, shows that the loss of helium in the display system is mainly concentrated in the compressor, expander and cold storage heat exchangers and other key components, thus improving the performance of the key components of compressors, expanders, and cold storage heat exchangers. Improve the overall system performance has an important role. Through the sensitivity analysis of the system parameters, researchers at the R&D center found that there is a certain matching relationship between the energy storage pressure and the energy release pressure in the supercritical compressed air system, as shown in Figure 3, because the air is in the cold storage heat exchanger. The heat transfer process is a transcritical heat transfer process, and the aerodynamic parameters of the air change drastically. Therefore, under the condition of a certain energy storage pressure, the system efficiency increases first and then decreases with the increase of the release pressure, and there is an advantage.
At the same time, the researchers studied the effect of parameters such as isentropic efficiency of the compressor, isentropic efficiency of the expander, pressure loss of the intercooler/reheater, and temperature difference of the heat exchanger/reheater intercooler on the system efficiency. Provide theoretical guidance for the design and optimization of critical compressed air energy storage systems. The above research work has been supported by the National Natural Science Foundation of China and the National “863” Program. The relevant research results have been published in international academic journals (Energy Conversion and Management, 115:167-177, 2016).
