Two-stage cascading desorption cycle for sorption thermal energy storage

Sorption thermal energy storage is an effective technology for low-grade heat recovery and it could solve the problem of mismatching between thermal energy demand and supply. However, the conventional single-stage cycle couldn't adapt well to the unstable heat source with variable temperature from solar energy or industry. To overcome this problem, two-stage cascading desorption cycles are proposed and compared with conventional single-stage sorption cycle. Under the condition of small temperature variation of heat source, which is divided into 5 stages between 68.2 degrees C and 152.8 degrees C, results show that various working pairs for two-stage cascading desorption cycles adapted to the heat source better than that for single-stage cycle, considering the effect of hysteresis. Under large temperature variation of heat source conditions such as larger than 50 degrees C, the concept of modularization thermal cell is proposed and the guideline for optimal combination between various halides and cycles is summarized. Considering both thermal energy density and grade, the combined two-stage cascading desorption cycle with three halides of optimal filled mass proportion is recommended, with system energy storage density of 879 kJ/kg and the product of temperature increment and thermal energy storage density of 81.1 MJK/kg. (C) 2019 Elsevier Ltd. All rights reserved.