Thermodynamic analysis and parameter optimization of a Chemical Looping Electricity Storage system

Abstract

In this study, a novel Chemical Looping Electricity Storage (CLES) system which integrated thermochemical energy storage into the Pumped Thermal Energy Storage (PTES) system was investigated and the corresponding thermodynamic models considering the temperature difference between charge and discharge were developed. Then, the exergy flow distribution characteristics of the Chemical Looping Electricity Storage system using Ca(OH)2 and CaO working pair were revealed. The influence of the key thermodynamic parameters on the system's round-trip efficiency was investigated. Finally, approaches to further improve the round-trip efficiency were briefly discussed. The results show that the existence of the charge-discharge temperature difference will reduce system round trip efficiency as a result of the changing of the heat balance between the charge and discharge processes. Taking Ca(OH)2/CaO working pair as an example, when the charge temperature ranges from 750 to 850 K and the discharge temperature ranges from 650 to 750 K, the system can achieve a round-trip efficiency of 43.38–61.45 %, lower than that of the Pumped Thermal Energy Storage system at the same temperature range. The discharge temperature variation will influence the round-trip efficiency more significantly than the charge temperature. Adoption of a turbomachine with high isentropic efficiency, reducing the pressure loss within the reaction vessel and the heat exchange temperature difference within the recuperator, and optimizing the temperature ratio can all effectively improve the system round-trip efficiency.