Development of SrBr2 composite sorbents for a sorption thermal energy storage system to store low-temperature heat

Abstract

A composite material was developed as sorbent for sorption thermal energy storage (TES) which was used to recycle the low-temperature heat in industry and life fields in this study. The composite sorbent was formed by strontium bromide (SrBr2) and the additive of expanded natural graphite treated with sulfuric acid (ENG-TSA). Sorption characteristics, kinetic sorption performance, thermal conductivity and permeability of 15 samples were studied. The material test results indicated the following: (1) the composite SrBr2 is of high energy density and good mass transfer performance; (2) it can be regenerated below 100 °C; (3) the additive of ENG-TSA greatly improves the heat transfer performance, while no degradation is observed on sorption water uptake; (4) the optimal composite sorbent is of 743 kg/m3 and with 10 wt% ENG-TSA.An lab-scale sorption TES system with 1 kWh design capacity was established and investigated. Under the conditions in winter seasons: charging temperature Tcha is 80 °C, discharging temperature Tdis is 35 °C, condensing temperature Tc is 15 °C, evaporating temperature Te is 15 °C, the heat storage capacity can reach 1.02 kWh. The heat storage density obtained is 242 Wh/kg composite sorbent and the heat discharging power is 67.4 kW/m3 composite sorbent.