A Novel Solar-Hybrid Gas Turbine Combined Cycle With Inherent $CO2$ Separation Using Chemical-Looping Combustion by Solar Heat Source

In this paper we propose a novel $CO2$-recovering hybrid solar-fossil combined cycle with the integration of methane-fueled chemical-looping combustion, and investigate the system with the aid of the Energy-Utilization Diagram (EUD). Chemical-looping combustion (CLC) consists of two successive reactions: first, methane fuel is oxidized by metal oxide(NiO)as an oxygen carrier (reduction of metal oxide); and second, the reduced metal (Ni) is successively oxidized by combustion air (the oxidation of metal). The oxidation of methane with NiO requires a relative low-grade thermal energy at $300°C-500°C$⁠. Then concentrated solar thermal energy at approximately $450°C-550°C$ can be utilized to provide the process heat for this reaction. By coupling solar thermal energy with methane-fueled chemical-looping combustion, the energy level of solar thermal energy at around $450°C-550°C$ can be upgraded to the chemical energy of solid fuel Ni for better utilization of solar energy to generate electricity. The synergistic integration of solar thermal energy and chemical-looping combustion could make the exergy efficiency and the net solar-to-electric efficiency of the solar hybrid system more than 60% and 30%, respectively, at a turbine inlet temperature (TIT) of $1200°C$⁠. At the same time, this new system has an extremely important advantage of directly suppressing the environmental impact due to lack of energy penalty for $CO2$ recovery. Approximately 9–15 percentage points higher efficiency can be achieved compared to the conventional natural gas-fired combined cycle with $CO2$ separation. The results obtained here are promising and indicate that this novel solar hybrid combined cycle offers the new possibility of $CO2$ mitigation using both green energy and fossil fuels. These results also provide a new approach for highly efficient use of solar thermal energy to generate electricity.