Compression performance optimization considering variable charge pressure in an adiabatic compressed air energy storage system

In an adiabatic compressed air energy storage system (A-CAES), the storage pressure persistently increases during the energy storage process causing deteriorate of the charge performance under off-design operating conditions. The compression performance with variable backpressure is essential for the energy storage efficiency and density of A-CAES. A thermodynamic model with energy loss analysis is built up to investigate the performance of a multi-stage centrifugal compressor used in an A-CAES (about 6.0 MW). By energy loss analysis, the blade inlet angle is first focused on to improve the disadvantages of narrow operating conditions and low efficiency at large mass flow rate of the original compressor. Then, the variable rotating speed study is applied on to increase the energy charge efficiency with a wide storage pressure range. Using the thermodynamic model, the available rotating speed is determined to be 0.85-1.05 of design value. Furthermore, the rotating speed is optimized to achieve the best efficiency under variable storage pressures and the corresponding correlation is fitted. Using the optimal rotating speed, the compression efficiency can be kept above 80% while the exergy efficiency is above 82% during the whole energy storage process with a wider storage pressure.