Performance enhancement of thermochemical energy storage system through heat recovery and reutilisation

This work is concerned with sorption based thermochemical energy storage (TCES) for heating applications. Despite significant efforts in the past, the system level efficiency of such TCES remains relatively low. This work aimsto significantly enhance the efficiency. Silica gel-water pair is used as an example for the work and a packed bed is used as the reactor. With a basic open TCES system, hot air flowing through the bed is directly rejected to the ambient, leading to a low system efficiency. Through the inclusion of a heat exchange unit, we recover and reuse the heat from the outlet of the reactor to preheat inlet air during desorption (charging) to reduce the energy consumption. Our results show that the charging efficiency, defined as ratio of desorption heat to input energy, ranges only from 13% to 17% for the basic open TCES system; whereas the use of a single stage heat exchanger increases the charging efficiency to 77%~85%. The use of a two-stage heat recovery process is shown to enhance further the efficiency up to ~90%. Additionally, an optimal charging flowrate is found which corresponds to the lowest input energy. The system efficiency (ratio of discharged heat to the total input energy) is found to increase from ~10% to ~59% by using the single heat exchange unit, while can be further increased up to ~63% if the two-stage heat recovery is used.