Exergy analysis of a CAES with thermal energy storage

A Compressed Air Energy Storage (CAES) with thermal energy recovery is presented. The latter recovers thermal energy in the compression phase and delivers it to the expanding air, eliminating the need for a combustion chamber and therefore avoiding local pollutant emissions. Seeking for maximum system flexibility, reference is made to an artificial storage and compressed air pressure is seen as a design variable. The proposed system has a multistage design with variable configuration, in order to handle the increasing /decreasing pressure in the storage. Hence each compression/expansion stage works in a relatively narrow range of pressure ratio throughout the energy storage and recovery phases. In order to raise its energy recovery efficiency, the proposed system is analyzed in terms of exergy destruction minimization. Some of its design parameters are optimized.