Investigation on the impact of size and form variation of sorption material pellets on heat storage efficiency in an adsorption thermal energy storage system

摘要

Growing global energy demand and rising concerns about environmental problems have increased the worldwide attention to thermal energy storage (TES), trying to improve the currently inefficient utilization of energy (especially primary energy sources e.g. fossil or renewable). A major part of the energy consumption could be considered as low temperature thermal energy (below 200°C). Thus, a better management of this energy by thermal energy storage could provide a significant contribution to improve the overall efficiency in industrial economies. Thermal energy can be stored by means of different methods (e.g. sensible heat, latent heat or thermo-chemical storage). Compared to sensible heat and latent heat, thermo-chemical heat storage has in general a higher heat storage density (up to 10 times more that sensible heat storage) and lower heat losses, especially for long storage period. The principle of the adsorption storage system is based on a gaseous working fluid (e.g. water) which gets adsorbed by a highly porous material (e.g. zeolite). This adsorption process is an exothermal one, thus the released heat, can be extracted and used. In order to recharge the heat storage system, desorption of the working fluid is done by heating the porous material. The whole process occurs under vacuum pressure. In this investigation, a thermo-chemical method was used with a reversible adsorption/desorption process in order to improve the operation conditions for different shapes of Zeolite pellets. Hence to achieve this aim, an experimental sorption unit has been set to measure the invested and stored heat in the adsorbent packed bed. The experimental results show that both shape and size of the pellets have an influence on the heat efficiency and capacity, where a maximum specific heat storage capacity of 120 Wh/kg was achieved.