Design of reactive particle fluidized bed heat exchangers for gas–solid thermochemical energy storage

Concentrated solar power (CSP) systems integrated with a supercritical carbon dioxide (sCO2) Brayton power cycle are regarded as the primary future direction for CSP technologies. Calcium-based particles can be a suitable storage medium to achieve high temperatures exceeding 750 ℃. However, there have been few studies on reactive particle/sCO2 heat exchangers (HXs) to drive high-performance power cycles with high energy storage efficiencies. In this paper, the mechanisms by which chemically reactive particles release energy in a fluidized bed (FB) heat exchanger has been investigated to evaluate the performance of thermochemical storage systems. A 1-MWt thermal duty fluidized bed heat exchanger with sCO2 as the working fluid operating at 988 K was designed in different configurations, featuring single stage and multistage counter-flow HXs. A detailed shell and tube model combining the chemical reaction kinetics and the heat transfer between the fluidized particle and sCO2 FB HX design was developed. A comparison of sensible and chemical heat materials shows that thermochemical energy storage is advantageous due to the relatively short tube length and slow particle mass flow rate. The tube length and particle mass flow rate are reduced by 3.5 and 11.5 times, respectively. The average chemical conversion is 97.30 % for a one-stage heat exchanger, which is lower than the 99.95 % conversion achieved by the two-stage heat exchanger. Additionally, a sensitivity analysis was carried out to understand the impacts of key operating parameters on the process performance. These findings provide insights into the operational stability and efficiency of the system, contributing to the development of advanced heat exchangers for thermochemical energy storage applications.