Dynamic Performance Analysis of a Thermochemical Resorption System for Low-grade Heat Storage and Cogeneration of Power and Cold

Thermochemical Sorption Systems can provide multiple functions, including storage of low-grade thermal energy, heat upgrade, cold production and provision of power when coupled with adequate turbomachines. As such, they have the potential to play a significant role in the decarbonization of industrial processes whose energy demand is dominated by thermal needs. Thermochemical Resorption Systems exploit two reversible solid-gas chemisorption reactions to store thermal energy in the form of chemical potential during the charge phase, while producing cold and/or heat during the discharge phase. This work investigates the performance of a thermochemical resorption system for recovery and storage of low-grade heat and cogeneration of cold and power (TRSC), by means of a scroll expander. The work focuses the study on the dynamic performance, and it addresses the relationship between components behavior and system performance. A series of Metal Chlorides – NH_3 reactions to be employed in the TRSC under investigation have been evaluated. The performance analysis of different suitable TRSC configurations to meet the requirements of cold and work production of 120 kWh and 12 kWh respectively, with a hot source temperature in the range of 100-200 ℃ has been carried out. Firstly, the efficiency of the ideal thermodynamic cycle was investigated. Subsequently, the system performance including the effective thermal masses of the sized reactors was analyzed in the steady state case. A dynamic model comprehending the effects of chemical reaction kinetics within such a system was implemented for the first time. The dynamic model was used to explore the transient behavior of relevant quantities, as well as the impact of operating parameters on the cycle time. The thermodynamic efficiency of the ideal cycle revealed to be higher for TRSC configurations adopting lower hot source temperature and higher expander pressure ratio. The system energy efficiency ranges between 0.19 and 0.57, with a maximum energy density of 91.7 kWh/m3. It resulted that the intrinsic property of the solid/gas reaction which mostly affects the efficiency loss between ideal and sized system due to thermal masses is the specific adsorption capacity. The dynamic analysis showed that selecting an expander pressure close to the maximum admissible value causes the reaction charge time to increase drastically. Moreover, imposing a higher pressure difference between the two reactors prior to adsorption/desorption allows to reduce the reaction discharge time