A calcium looping system powered by renewable electricity for long-term thermochemical energy storage, residential heat supply and carbon capture

Affordable long-term energy storage and CO₂ capture technique are imperative to developing the future carbon–neutral energy system. This paper proposed a calcium looping system powered by excess renewable electricity to achieve long-term thermochemical energy storage, residential heat supply and carbon capture. The system can be constructed with industrial equipment and exploit natural, abundant and cheap limestone as the circulating material. The electrical calciner is designed to charge the energy and produce the high-pressured CO₂ during the valley of the electricity grid, while the carbonator side is primarily driven by the discharged thermochemical energy and on-demand coordinates the heat network along with the carbon capture. The HEATSEP framework is adopted to optimize heat transfer processes and operating conditions for deriving the most favorable system configuration in the energy and economic aspects. Compared to the reference plant with electric boilers and short-term heat storage tanks, an energy penalty of around 32.3% total energy percentage points should be paid to drive long-term energy storage and carbon capture. The energy penalty is attributed to thermal losses in the calciner and heat exchanger networks, chemical energy lost by the make-up flow of fresh limestone, CO₂ compression for storage and auxiliary power for solid/fluid circulations. Due to a comparable total plant investment cost to the reference plant, the proposed system achieves the CO₂ avoidance cost of 111.1 RMB/ton_CO2, showing some competitiveness over current post-combustion carbon capture techniques. The techno-economic competitiveness of the proposed system can be further strengthened by replacing natural or synthetic Ca-based materials with high cycling performance instead of limestone, as well as extending applicable occasions to achieve almost year-round operation.