Proposal and thermodynamic analysis of a steam methane reforming system integrated with thermochemical energy storage and a SCO₂ brayton cycle

Solar energy is a promising alternative to fossil fuels for providing heat in steam methane reforming (SMR) hydrogen production. However, the variability of solar energy requires effective storage solutions. This study presents a new SMR hydrogen production system that integrates thermochemical energy storage (TCES) utilizing a CaO/CaCO₃ cycle with a SCO₂ Brayton cycle. The system converts fluctuating solar energy into the stable chemical energy of CaO by calcinating CaCO₃ in the solar calciner, with the SMR reaction mainly heated by the exothermic reaction of CaO and CO₂. The SCO₂ Brayton cycle efficiently recovers heat from the high-temperature SMR products. Comprehensive thermodynamic analysis and evaluation models are developed. Results show that the proposed system performs well, achieving energy and exergy efficiencies of 73.49 % and 78.46 %, respectively, under benchmark conditions. The energy storage efficiency of TCES is 81.55 %, and the solar-to-chemical energy efficiency is 48.21 %. Integrating TCES significantly enhances the system's steady operation under fluctuating solar energy conditions. The calciner accounts for the largest share of exergy destruction at 31.63 %, followed by the carbonator at 17.50 %. Sensitive analyses of key operating parameters indicate that higher CaO conversion rate and storage temperature enhance energy storage, energy, and exergy efficiencies. Besides, the energy and exergy efficiencies decrease with the increasing SMR reaction pressure but increase with rising reaction temperature. When the S/C is 2.0, these efficiencies reach their maximum values of 75.42 % and 78.63 %, respectively.