Efficient conversion of CO₂ to CH₄ through supercritical water gasification of plastic with calcium looping

Calcium looping (CaL) is a promising technology with significant implications for carbon capture. However, the traditional CaL requires a high temperature of 950 °C for CaCO₃ decomposition, posing challenges for further development due to stringent temperature conditions. This study leverages the advantages of a hydrogen-rich reaction environment in a supercritical water gasification (SCWG) system to develop a thermodynamic model of a solar-driven SCWG system incorporating CaL. This innovation reduces the high-temperature requirement of traditional CaL by 41 %, lowering it to 560 °C, and simultaneously alleviates the coupling difficulty of solar-driven systems. The system utilises waste carbide slag (CS) to convert waste plastics into combustible CH₄ and other industrial products, achieving thermochemical elimination of CO₂ into CH₄. Results indicate that CH₄ production in traditional gasification systems increases with temperature, whereas the inclusion of CaL shows a trend of initial increase followed by a decrease, peaking at 560 °C with a 19.12 % increase compared to systems without CaL. Both energy and exergy efficiencies decline with temperature, while the impact of pressure on gasification performance and system efficiency remains below 10 %. Increasing the plastic-to-water ratio enhances CH₄ production and energy and exergy efficiencies but reduces the gas yield per unit of plastic.