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.