Ejector-based performance enhancement and power regulation in compressed air energy storage systems under high backpressure conditions

Although compressed air energy storage (CAES) systems play a vital role in grid peak shaving, turbine output is often limited by inlet pressure constraints. This study proposes using an ejector with a regulating needle valve to draw in low-pressure exhaust for a 10 MW CAES demonstration project in China's Guizhou Province. This would enhance the turbine's inlet flow and pressure. Numerical simulation and response surface analysis were used to investigate the effects of nozzle outlet position, main gas flow pressure, ejector exhaust pressure and outlet backpressure on ejector performance. The results indicate that the central-jet entrainment configuration adapts well to high backpressure conditions, with optimal performance being achieved at a nozzle outlet position of 22.5 mm. For the CAES system with a gas storage tank volume of 2.2 × 103 and a full load pressure of 12.0 MPa, under the working condition of back pressure of 8.0 MPa, the ejector injects low-pressure exhaust gas of 5.6 MPa into the turbine again to realize the energy release cycle. At this time, the system benefit evaluation shows that the introduction of the ejector increases the power generation of the system by 2.04%, the best comprehensive energy efficiency is 16.67%, and the power regulation capacity is as high as 107.0 kW. This study provides the theoretical foundations and optimization strategies for the design and operation of ejectors within high-backpressure CAES systems, thereby facilitating the efficient recovery of energy and the flexible regulation of power.