Hybrid thermochemical Carnot battery with calcium looping, methane dry reforming, and supercritical carbon dioxide cycle: thermodynamic and techno-economic optimization

This study proposes a polygeneration hybrid thermochemical Carnot battery that integrates calcium-looping thermochemical storage with methane dry reforming in an electrically heated calciner, coupled to a supercritical CO₂ Brayton cycle for power discharge. Operating the calciner in a methane atmosphere lowers the calcination temperature by ∼200 °C, mitigates sorbent deactivation, and enables in situ CO₂ utilization for synthesis-gas coproduction. A steady-state system model combined with multi-objective optimization is developed to examine efficiency–cost trade-offs. The Pareto-optimal compromise achieves a levelized cost of electricity (LCOE) of 0.94 ¥ per kWh, with a simplified recuperated cycle delivering 22.6 MW net output at a round-trip efficiency of 20.5%. Accounting for synthesis gas coproduct and ∼90% CO₂ capture increases the overall energy and exergy efficiencies to 88.0% and 85.0%, respectively. Sensitivity analyses identify favorable operating windows of 30–50% CaO conversion and 5–10 °C minimum temperature approach in recuperators. Economies of scale are evident: as capacity expands from 1 to 100 MW, the LCOE declines from 2.37 to 0.83 ¥ per kWh. These findings demonstrate that incorporating methane dry reforming into calcium looping enables long-duration storage with inherent CO₂ capture and valuable syngas coproduction, offering attractive thermo-economic trade-offs for grid-scale applications.