Analysis of low-temperature thermochemical heat transformer system based on hydrated salt: Dynamic modelling and performance evaluation

Abstract

Low-grade and mismatch issues result in large amounts of renewable energy/waste heat not being utilized. Thermochemical heat transformer (THT) is a novel heat storage technology integrating energy storage and energy upgrade, which can address these issues. Hydrated salts, particularly SrBr₂·6H₂O, have emerged as compelling thermochemical storage media due to their low charging temperature requirements, which can be met by low-grade renewable energy/waste heat. This paper establishes a lumped parameter model of a low-temperature THT system based on SrBr₂·6H₂O which couples a thermochemical reactor and an evaporator/condenser. Based on the verified mathematical model, the dynamic characteristics of the system and its performance under different working conditions are studied, and special attention is paid to the effects of reactor heating water temperature, condensation cooling water temperature and reactor cooling water mass flow rate on the THT system. The results suggest that increasing the reaction driving force or reactor cooling water mass flow rate causes the energy storage efficiency to monotonically decrease or increase, while the exergy efficiency first increases and then decreases. As heating water temperature increases, the energy storage efficiency decreases from 0.654 to 0.573. Conversely, as condensation cooling water temperature decreases, the energy storage efficiency increases from 0.558 to 0.652, and the exergy efficiency reaches the peak value of 0.617 at a heating water temperature of 65 °C. Moreover, A lower heating water temperature can drive the THT system as the cooling water temperature decreases. Similarly, as the reactor cooling water mass flow rate increases, the energy storage efficiency increases from 0.376 to 0.573, and the exergy efficiency reaches the peak value of 0.653 with a mass flow rate of 0.006 kg/s. Compared with the thermochemical heat storage (TCES) system, the exergy efficiency of the THT system is 1.93 times as much. The results of this study provide a theoretical reference and technical guidance for THT technology in the field of utilizing low-grade renewable energy/waste heat.