Thermal-mechanical coefficient analysis of adiabatic compressor and expander in compressed air energy storage systems

• Published in: Energy (Oxford) 2022-04, Vol.244, p.122993, Article 122993
• Main Authors: Guo, Huan, Xu, Yujie, Zhu, Yilin, Zhou, Xuezhi, Chen, Haisheng
• Format: Article
• Language: English
• Subjects: Adiabatic; Adiabatic flow; Compressed air; Compressed air energy storage system; Compression; Compression process; Conversion ratio; Cooling effects; Coupling; C–P diagram; Distributed generation; Energy storage; Enthalpy; Exergy; Expansion process; Heat exchangers; Inlet pressure; Inlet temperature; Pressure; Pressure loss; Renewable energy; Storage systems; Thermal expansion; Thermal-mechanical coefficient
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2021.122993

Compressed air energy storage (CAES) technology can play an important role in large-scale utilization of renewable energy, the peak shaving and valley filling of power system, and distributed energy system development. Multi-stage compression and expansion units are key components in CAES systems, while the two key processes exist insufficient study, such as a lack of considering the coordination of temperature and pressure, ignoring coupling relationship between compressor and expander when typically being analyzed independently. To cope with the above critical issues, the new concept of thermal-mechanical coefficient is put forward based on the coupling relationship between temperature and pressure in adiabatic compression and expansion processes, and a C–P diagram (C is thermal-mechanical coefficient, and P is a function of pressure) is established to illustrate the thermodynamic processes concentrating on their work transfer. Besides, the expression of change rate of exergy to enthalpy for adiabatic compression and expansion processes is revealed. By depicting the C–P diagram of single-stage CAES system, it highlights that the thermal-mechanical coefficient of expander is higher compared with that of compressor, but with shorter change in the x-coordinate representing P that results in smaller work output for expander. In addition, it is found that the change of thermal-mechanical coefficient is generally accompanied with thermal-work conversion or heating/cooling effect. When drawing the C–P diagram of a multi-stage CAES system, the influence of heat exchanger's heat/pressure loss and the reduction of expander stage number on system's work transfer process is clearly shown. Significantly, results show that increasing the inlet temperature of expander is beneficial to enhance thermal-mechanical coefficient, which enables the thermal-work conversion ratio to be improved especially at higher inlet pressure and lower outlet pressure. •A new concept of thermal-mechanical coefficient for compressor/expander is proposed.•C–P diagram is proposed to depict thermodynamic processes of CAES systems clearly.•Heating the inlet temperature of expander improves the thermal-mechanical coefficient.•Changing rate of exergy to enthalpy of adiabatic compression/expansion is achieved.