Improving the performance of steam power cycle through thermo-photovoltaic device: A novel combined system and thermodynamic analysis

In this study, a new system consisting of a thermophotovoltaic device and steam Rankine cycle system is proposed to prevent the mismatch between the combustion temperature and the steam maximum temperature to achieve photo-thermal energy cascade utilization and improve the fuel conversion efficiency. The energy balance model of the proposed system is established, and the influence of parameters such as emitter area and heat exchange coefficients on the system's performance is investigated. Exergy analysis of the system is performed based on the second law of thermodynamics. The results show that the proposed system has 11-13% higher efficiency than the steam Rankine cycle system. The addition of a thermophotovoltaic device mainly reduces the exergy loss of the boiler due to the temperature difference between the combustion flue gas and the steam. Increasing the emitter area improves the system efficiency, and a system with Si cells is more efficient than a system with GaSb cells. Increasing the heat transfer coefficient of the air heat exchanger and the outlet flue gas temperature to generate a higher flame temperature is crucial to improving the performance of the combined system. The addition of a thermophotovoltaic device does not reduce the exergy loss during combustion. Thus, further energy cascade utilization should consider the efficient conversion of high-order chemical energy of a fuel. This study contributes to the theory of photo-thermal energy cascade conversion and provides new insights into improving the performance of the steam Rankine cycle.