Energy, exergy and economic (3E) evaluation and conceptual design of the 1000 MW coal-fired power plants integrated with S-CO₂ Brayton cycles

The conceptual design and systematic comparison of S-CO₂ coal-fired power generation systems are performed in the viewpoint of the thermodynamic analysis and economic assessment to promote the practical application in the industry. First, the differences between the conventional steam boiler and S-CO₂ boiler are pointed out. 3 layouts of the water-cooling wall are compared in the aspect of the hydrodynamic characteristic and structural parameters to select the suitable one coupled to the S-CO₂ cycles. Based on the optimized water-cooling wall layout, the energy, exergy and economic analysis models of the integrated S-CO₂ coal-fired power systems are further developed. Finally, the mechanism of the inter-cooling thermodynamic process to improve the system performance is investigated and the distribution of the individual irreversibility is given. The systematic comparison is performed among 3 configurations of S-CO₂ coal-fired power plants with consideration of the thermo-economic performance. The conceptual design of key components is also provided. The results demonstrate that the S-CO₂ boiler is fatter due to 8 times larger mass flow rate of working fluid than the conventional steam boiler. The layout of water-cooling wall with the split flow strategy and vertical tubes is helpful in compacting the scale of the boiler for its less diameter and number of tubes, and its thermal efficiency is higher than that of other layouts. Among the 3 S-CO₂ cycle layouts studied, the S-CO₂ coal-fired power system with the inter-cooling cycle yields highest efficiency and is the most economic configuration. The thermal efficiency of the S-CO₂ coal-fired power plant composing the inter-cooling cycle is 47.69–49.09% with total thermal conductance of recuperators changed from 120 MW·K⁻¹ to 180 MW·K⁻¹ when the turbine inlet parameters are 620 °C/620 °C/30 MPa, and displays an advantage over the ultra-supercritical steam Rankine power plant. The system levelized cost of electricity is 0.0397 $·(kW·h)⁻¹ and shows great commercial potential. The detailed discussion of this study is beneficial to a comprehensive understanding of various S-CO₂ coal-fired power systems and provide a clue to establish a practical power plant for the application of coal-fired industry.