Numerical comparison of two operating modes of thermal energy storage tank for compression heat storage in adiabatic compressed air energy storage

Abstract

• Thermal performance of multi-PCM energy storage tank is numerically analysed. • A thermodynamic comparison of two charging configurations is implemented. • A parametric study of PCM packing height is performed. • Results indicate that correct arrangement of PCM packing height is critical. • Preheating air after compression with part of excess electricity improves performance Two different charging modes of a thermal energy storage tank (TEST) system employing multi-phase change material for compression heat storage in an adiabatic compressed air energy storage process was simulated to compare their performance. The modes are mod1 with higher mass flow rate and low temperature and mod2 with higher temperature and low mass flow rate of heat transfer fluid respectively. A mathematical formulation of the energy interactions in the HTF and the PCM filling the TEST was discretized using implicit finite difference technique and solved in Matlab using a matrix inversion technique. The developed model showed good agreement with experimental data of temperature profile of heat transfer fluid during the charging mode. The two modes were compared using metrics such as charging rate, discharging rate, charging efficiency, discharging efficiency, charging and discharging exergy efficiency, and overall exergy and energy efficiency. It was found that mod2 performs better than mod1 in both the charging and discharging cycle. The round trip efficiency of mod1 ranges from 0.87 to 0.77 with a mean value of 0.76 whereas that for mod2 ranged from 0.97 to 0.79 with an average of 0.78. Moreover, the overall exergy efficiency ranges from a peak value of 0.48 and 0.55 to the least value of 0.33 and 0.44 in mod1 and mod2 respectively, corresponding to average efficiencies of 0.45 and 0.51 in mod1 and mod2 respectively. The numerical results show that using some part of the excess electricity of wind turbine to preheat air after compression is a promising solution to improve performance of A-CAES plants.