In this study, an improved CO₂ separation and purification system is proposed based on in-depth analyses of cryogenic separation and distillation theory as well as the phase transition characteristics of gas mixtures containing CO₂. Multi-stage compression, refrigeration, and separation are adopted to separate the majority of the CO₂ from the gas mixture with relatively low energy penalty and high purity. Subsequently, the separated crude liquid CO₂ is distilled under high pressure and near ambient temperature conditions so that low energy penalty purification is achieved. Simulation results indicate that the specific energy consumption for CO₂ capture is only 0.425 MJ/kgCO₂ with 99.9% CO₂ purity for the product. Techno-economic analysis shows that the total plant investment is relatively low. Given its technical maturity and great potential in large-scale production, compared to conventional MEA and Selexol^TM absorption methods, the cost of CO₂ capture of the proposed system is reduced by 57.2% and 45.9%, respectively. The result of this study can serve as a novel approach to recovering CO₂ from high CO₂ concentration gas mixtures.

Compressed air energy storage (CAES) is a commercial, utility-scale technology that provides long-duration energy storage with fast ramp rates and good part-load operation. It is a promising storage technology for balancing the large-scale penetration of renewable energies, such as wind and solar power, into electric grids. This study proposes a CAES-CC system, which is based on a conventional CAES combined with a steam turbine cycle by waste heat boiler. Simulation and thermodynamic analysis are carried out on the proposed CAES-CC system. The electricity and heating rates of the proposed CAES-CC system are lower than those of the conventional CAES by 0.127 kWh/kWh and 0.338 kWh/kWh, respectively, because the CAES-CC system recycles high-temperature turbine-exhausting air. The overall efficiency of the CAES-CC system is improved by approximately 10% compared with that of the conventional CAES. In the CAES-CC system, compressing intercooler heat can keep the steam turbine on hot standby, thus improving the flexibility of CAES-CC. This study brought about a new method for improving the efficiency of CAES and provided new thoughts for integrating CAES with other electricity-generating modes.

In this paper, the exergoeconomic analysis was conducted to an existing ultra-supercritical coal-fired power plant in China to understand the cost-formation process, to evaluate the economic performance of each component and to find possible solutions for more cost-effective designs. The total revenue requirement (TRR) and the specific exergy costing (SPECO) methods were applied for economic analysis and exergy costing, respectively. Quantitative balances of exergy and exergetic costs as well as necessary auxiliary equations for both individual component and the overall system were established. The results show that the exergoeconomic factors of the furnace and heat exchangers at low temperature levels, including air preheater and low-pressure feedwater preheaters, are rather small; while those of other components are relatively large. Moving more heat absorption into furnace to use the effective radiation heat transfer, increasing the air preheating temperature and adding more low pressure feedwater preheaters can be promising solutions for future design.