Energy, exergy, economic and environmental analysis and optimization of an adiabatic-isothermal compressed air energy storage coupled with methanol decomposition reaction for combined heat, power and hydrogen generation system

Compressed air energy storage technology is one of the key technologies for integrating renewable energy generation into the grid. Efficient utilization of compression heat is an important means to enhance the performance of compressed air energy storage systems. Therefore, this paper proposes an adiabatic-isothermal compressed air energy storage coupled with methanol decomposition reaction for combined heat, power and hydrogen generation system. During energy storage, the first stage employs adiabatic compression, where the generated compression heat provides a heat source for methanol decomposition reaction. The produced hydrogen and carbon monoxide are separated, with hydrogen stored in hydrogen refueling stations and carbon monoxide in gas storage tanks for future use. The second stage uses isothermal compression to reduce the generation of compression heat. During energy release, the carbon monoxide produced from the decomposition reaction combusts to reheat the air. This system reduces the generation of compression heat while fully utilizing the compression heat, improving system performance through the principle of energy cascading and incorporating hydrogen production functionality. By developing mathematical models for each component of the proposed system, the variations in the system's 4E (Energy, Exergy, Economic, Environmental) performances with key parameter changes are investigated. The results show that under design conditions, the proposed system achieves a round-trip efficiency of 87.04 %, an exergy efficiency of 74.05 %, an investment payback period of 7.75 years, a levelized cost of energy of 137.28 $/MWh, and a carbon dioxide emission index of 155.93 kg/MWh. Notably, the exergy losses in the combustion chamber and the methanol decomposition reactor are significant, accounting for 27.58 % and 18.06 % of the total exergy losses, respectively. The results of sensitivity analysis indicate that air-to-methanol ratio, liquid piston cycle duration, compressor pressure ratio and efficiency are the key parameters affecting the performance of the system. The simultaneous optimization of a system's thermal, economic, and environmental performance is not achievable. Therefore, in this paper, the system is optimised at six different liquid piston cycle durations. When the liquid piston cycle duration is 1200 s, the optimal operating point exergy efficiency, levelized cost of energy and carbon dioxide emission index of the system are 73.04 %, 135.74 $/MWh and 150.20 kg/MWh, respectively. These findings provide valuable insights for the engineering application of the proposed system.