Performance Study On Novel Compressed Air Energy Storage System

With the rapid development of power industry, the peak-valley gap is increasing greatly, which make the peak load regulation of electricity grid more and more difficult. In the meanwhile, the access of intermittent renewable energy sources, such as solar energy and wind power, also bring a great challenge to the power grid. Given the safety of the power grid, it is crucial to apply the energy storage technology. The advanced adiabatic compressed air energy storage (AA-CAES) technology, which provides with high efficiency, low cost, zero-emission and high compatibility with renewable energy, can be used for large-scale energy storage. This paper has made some research from the aspects of thermodynamic modeling, software simulating, varying conditions analysis and multiple systems comparing.First, the thermodynamic models of AA-CAES system, including compression, expansion, heat transfer, thermal storage and air storage processes, were built in this paper. Then the performance of a two-stage compression and expansion system was simulated by using Aspen Plus Software. The simulation results show a high charging efficiency of 69.3% while a charge-discharge cycle. In addition, several measures could contribute to higher efficiency, for instance, designing a proper pressure ratio between two stages to ensure the exits of air compressors having approximately the same temperature, equal expansion ratio of turbines, higher discharging pressure in a reasonable range, reducing the temperature difference of heat exchangers and so on.In order to further improve the charging efficiency, a novel system combined AA-CAES and solar energy was designed and explored in this paper. Along with the increasing load of solar thermal collector, the turbine inlet temperature, total output power and charging efficiency were rising. It had a higher charging efficiency of 83.5% comparing with traditional AA-CAES system.Furthermore, it is innovative to design a cascade thermal storage subsystem with three oil tanks of high temperature, middle temperature and low temperature, respectively. Organic Rankin Cycle (ORC) was added to increase the generating capacity. Comprehensive measures, such as energy efficiency, primary energy efficiency and roundtrip efficiency were used to evaluate the systems. Based on the study, one can draw a conclusion that the AA-CAES system with solar energy and ORC had the minimum energy loss and the best thermal performance while providing sufficient cooling fluid.A series of formulas about air chamber were deduced at the end of paper. On the basis of that, the pressure, temperature and gross air storage could be calculated in real time by knowing mass flow rate, charging or discharging time and polytropic exponent of the process. Energy density of the air chamber was considered. This study, which can also be applied to CAES system, had an important significant for the design of air chamber.