Low-priced stable SrCl2@SG composite sorbents for low-grade solar heat storage application in open sorption systems

Abstract

The combination of thermal energy storage (TES) unit and solar air heater is one of the most efficient methods for long-term utilization of solar energy. In this study, a series of stable SrCl 2 @SG composite sorbents were prepared based on silica gel (SG) pellets and strontium chloride hexahydrate (SrCl 2 ·6H 2 O) to store low-grade solar thermal energy for space heating application. Composite characteristics, kinetic hydration/dehydration performance of SG and SrCl 2 @SG sorbents were thoroughly studied. Results demonstrated that the SrCl 2 @SG_10 sorbent has the largest sorption capacity of 0.34 g/g at the temperature of 25 °C and relative humidity (RH) of 90% without any liquid leakage. Additionally, kinetic hydration experiments showed that RH has a great impact on the water sorption performance of the TES materials, while the temperature effect is relatively insignificant. The TES performance of sorbents was further investigated in a laboratory prototype reactor with a multilayer structure, which was designed following an open sorption system concept. 800 g of sorbent pellets were evenly distributed on each layer of the sieve. Maximum instant output power and energy storage density of the SrCl 2 @SG_10 sorbent at 70% RH are 19.7 W and 100 kWh/m 3 respectively. Furthermore, the open TES system still maintains a comparatively high TES performance after fifteen charging/discharging cycles. • Preparation of stabilized SrCl 2 @SG composite sorbent for low-grade thermal energy storage. • Kinetic hydration/dehydration behavior of reversible SrCl 2 ⸱6H 2 O are investigated. • Sorption mechanism of SrCl 2 @SG composite sorbents is proposed. • Thermal energy storage performance of SrCl 2 @SG_10 sorbent is tested in an open sorption system. • SrCl 2 @SG_10 sorbent has discharging efficiency of 58.5% and can be recycled stably.