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The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO2Brayton cycle. In the numerical simulation of the compressor, the rapid changes in the thermophysical properties of the CO2near the critical point make it difficult to capture the condensation phenomenon. This paper investigates the influence of fluid physical properties on the condensation phenomenon. Firstly, the differences in the physical properties of CO2in the SRK EOS (equation of state), PR EOS, and SW EOS are compared. Then, the simulation of nozzles and compressors were carried out and discussed. Results show that the condensation positions predicted by the three EOSs are basically the same. Compared with SW EOS, the disparities between the maximum condensation mass fraction predicted by the PR and SRK EOSs is 5.7% and 11.5%, and that of total pressure ratio is 0.3% and 3.8%, respectively. The results show that PR EOS can be considered for numerical simulation in engineering practice. Since its physical property calculation results are closer to the actual physical properties while the physical properties change more gently, it has considerable accuracy and numerical stability.

The objective of this paper is to understand the benefits that one can achieve for large-scale supercritical CO2(S-CO2) coal-fired power plants. The aspects of energy environment and economy of 1000 MW S-CO2coal-fired power generation system and 1000 MW ultra-supercritical (USC) water-steam Rankine cycle coal-fired power generation system are analyzed and compared at the similar main vapor parameters, by adopting the neural network genetic algorithm and life cycle assessment (LCA) methodology. Multi-objective optimization of the 1000 MW S-CO2coal-fired power generation system is further carried out. The power generation efficiency, environmental impact load, and investment recovery period are adopted as the objective functions. The main vapor parameters of temperature and pressure are set as the decision variables. The results are concluded as follows. First, the total energy consumption of the S-CO2coal-fired power generation system is 10.48 MJ/kWh and the energy payback ratio is 34.37%. The performance is superior to the USC coal-fired power generation system. Second, the resource depletion index of the S-CO2coal-fired power generation system is 4.38 µPRchina,90, which is lower than that of the USC coal-fired power generation system, and the resource consumption is less. Third, the environmental impact load of the S-CO2coal-fired power generation system is 0.742 mPEchina,90, which is less than that of the USC coal-fired power generation system, 0.783 mPEchina,90. Among all environmental impact types, human toxicity potential HTP and global warming potential GWP account for the most environmental impact. Finally, the investment cost of the S-CO2coal-fired power generation system is generally less than that of the USC coal-fired power generation system because the cost of the S-CO2turbine is only half of the cost of the steam turbine. The optimal turbine inlet temperature T5becomes smaller, and the optimal turbine inlet pressure is unchanged at 622.082°C/30 MPa.

The objective of this paper is to provide the optimal choice of single-reheating or double-reheating when considering residual flue gas heat in S-CO2coal fired power system. The cascade utilization of flue gas energy includes three temperature levels, with high and low temperature ranges of flue gas heat extracted by S-CO2cycle and air preheater, respectively. Two methods are proposed to absorb residual flue gas heat Qrein middle temperature range. Both methods shall decrease CO2temperature entering the boiler T4and increase secondary air temperature Tsec air, whose maximum value is deduced based on energy conservation in air preheater. The system is analyzed incorporating thermodynamics, boiler pressure drop and energy distribution. It is shown that at a given main vapor temperature T5, the main vapor pressure P5can be adjusted to a value so that Qre is completely eliminated, which is called the main vapor pressure adjustment method. For this method, single-reheating is only available for higher main vapor temperatures. The power generation efficiency for single-reheating is obviously higher than double-reheating. If residual flue gas heat does exist, a flue gas heater FGC is integrated with S-CO2cycle, which is called the FGC method. Both single-reheating and double-reheating share similar power generation efficiency, but single-reheating creates less residual flue gas heat. We conclude that single-reheating is preferable, and the pressure adjustment method achieves obviously higher power generation efficiency than the FGC method.

ABSTRACTLignin, with its rich reserves of phenolic compounds, holds great promise as a candidate for renewable energy and valuable chemical production. However, the complex molecular structure and low reactivity of lignin have impeded progress in this research direction. Consequently, the depolymerization of lignin into high-value small-molecule chemicals has become a new area of focus. Metal and metal oxides have emerged as a promising catalyst to overcome this obstacle due to their high selectivity in depolymerizing lignin and the mild reaction conditions required. This paper reviews the properties, and products of various metal and metal oxides used for lignin depolymerization under microwave, pyrolysis, hydrogenolysis, and oxidation conditions. The research prospects and challenges of metal oxide degradation of lignin are summarized to pave the way for future applications and development of lignin depolymerization.

Novel formable porous functional biochar (LaFe/MB) was prepared for P removal.La/Fe oxide provides abundant sorption sites for P and almost no La/Fe leaching.LaFe/MB presented high compressive strength with high sorption capacity for P.