Optimization of thermal performance of high temperature sensible heat thermal energy storage system for direct steam generation: A simulation work

Abstract

The high temperature sensible heat thermal energy storage (TES) system for direct steam generation (DSG) has wide prospects in efficiently utilizing waste heat recovery. Improving the charging/discharging efficiency under a large working temperature range is one of the key issues in optimizing the high-temperature sensible heat TES system performance. This paper focuses on the optimal thermal performance of a high-temperature TES system for DSG by using solid graphite for high-temperature flue gas recovery in a gas turbine. The working performance of the high-temperature TES for DSG was simulated by APROS, which is a physics-based advanced dynamic process modeling and simulation software. The effects of the number and mass distribution of thermal storage cell units on the discharge efficiency were investigated. The results show that the effects of cell unit number on discharging efficiency can be neglected when the cell unit number reaches 10. Based on that, an optimized mass distribution based on the local enthalpy matched method was obtained, and the discharging efficiency can reach up to 0.665. Moreover, the thermal performance of the TES system during the charging and discharging process was also analyzed, especially the effects of flow distribution in parallel modules. Further, the performance of TES was analyzed by integrating it into the CCGT start-up process. The results show that the initial charging rate of TES has opposite effects on waiting time and system efficiency for the CCGT start-up process. And a proper initial charging rate for the start-up process of the CCGT system in this work is suggested to be 0.4.