Thermodynamic analysis of a novel pumped thermal energy storage system with waste heat integration

Abstract

Pumped thermal energy storage (PTES) system is a large-scale electricity storage technique, and the thermally integrated PTES system has been brought forward to raise the energy storage efficiency and extend feasible ways to utilize the low-grade waste heat (<100 °C). The solutions to raise the power-topower efficiency of the thermally integrated PTES system have aroused much attention worldwide. This paper presents an innovative thermally integrated PTES system, in which the two-stage heat pump with an economizer is incorporated into the PTES system. Despite utilizing the waste heat at charge time, the low-grade waste heat is also poured into the discharging process innovatively. The simulation model of the thermally integrated PTES system is established in the software MATLAB, and the physical properties of the substances are acquired from the software Refprop 10. The parameters of the PTES system are displayed and the power-to-power efficiency of the PTES system is investigated under various thermal storage temperatures. The results indicate that the power-to-power efficiency increases first and then declines as the low heat storage temperature rises when the high heat storage temperature is deemed. However, the energy storage density of the system dwindles with the increment of low heat storage temperature. The rise of the component efficiency contributes to the improvement of the powerto- power efficiency obviously, which can reach 87.3% as the isentropic efficiencies are 90%. The exergy destruction in the heat exchangers and mechanical components occupy a large proportion of the overall exergy destruction, which infers that the modification of the heat transferring and expansion/ compression processes are viable for performance enhancement.