Aiming to the performance analysis of boiler with supercritical carbon dioxide (S-CO₂) cycle, the boiler performance evaluation index system is built by taking the gas-fired boiler used in the 5 MW S-CO₂ Brayton cycle pilot unit at Xi'an Thermal Power Research Institute Co., Ltd. as the research object. The core performance indexes of S-CO₂ boiler include the fuel efficiency of boiler, the ratio of heat absorption over the input heat for each heat exchanger, the performance of air preheater, the pressure drop of working fluid system, the NO_x emission concentration, and others. The fuel consumption and excess air coefficient are calculated via the measurement of oxygen concentration. Meanwhile, the calculation method of heat loss due to exhaust gas is improved. The ratio of heat absorption over the input heat for each heat exchanger is introduced, which shows the contribution of each heat exchanger on heat absorption process. Finally, the calculation process is integrated becoming to an executable program, and it is applied in the running and monitoring procedures. An operating case showed that, for the research object, the actual condition is basically the same as that of the design parameters. The finally calculated boiler fuel efficiency is 92.05% without correction and 93.79% with correction, the later is similar as the designed value (93.53%).

A high-parameter gas turbine and supercritical carbon dioxide (S-CO₂) combined cycle model was constructed, and thermal performance analysis was carried out. The top cycle uses a high-parameter gas turbine with a combustion chamber exhaust temperature of 1 800 ℃, and the bottom cycle adopts S-CO₂ Rankine double turbine cycle, while using three-stage flue gas heating and two-stage turbine exhaust gas recovery. The parameters and thermal performance under the optimized combined cycle operating conditions are obtained by the penalty function method. The influences of the main parameters of the high-parameter gas turbine top cycle and S-CO₂ Rankine bottom cycle on the combined cycle performance is analyzed. The results show that the combined cycle thermal efficiency can reach 68.61% at the gas turbine pressure ratio of 35.5 and the combustion chamber outlet temperature of 1 800 ℃, and the efficiency of the combined cycle of the gas turbine and S-CO₂ is 2.3 percentage points higher than that of the combined cycle of the gas turbine and steam.

The combination of supercritical carbon dioxide Brayton cycle and lead cooled fast reactor is considered as one of the most ideal power cycles. The system transfers heat through the intermediate heat exchanger, and its performance affects the efficient and safe operation of the whole power generation system. Due to the significant differences in physical properties and heat mass transport properties between supercritical carbon dioxide and liquid lead bismuth eutectic, the symmetrical structure cannot match the heat transfer requirements of the working fluids on both sides. In this study, an asymmetric compact coupled heat exchanger was constructed, and the coupled heat transfer characteristics of supercritical carbon dioxide and liquid lead bismuth eutectic were studied by numerical simulation. Increasing the inlet velocity of the cold side fluid will significantly enhance the heat transfer; When the inlet velocity of LBE at the hot side is increased, the total heat transfer coefficient first decreases and then increases; When the inlet temperature of the cold and hot fluid of the heat exchanger is increased, the heat transfer coefficient of the heat exchanger first decreases and then increases, and there is an optimal value; Due to the high proportion of thermal resistance in the cold side, the similarities and differences of heat transfer characteristics of cold side supercritical carbon dioxide under buoyancy and thermal acceleration under different operating parameters are compared; It is found that in the quasi critical region, the strong buoyancy will greatly enhance the cold side heat transfer, while the acceleration effect will inhibit the heat transfer.

The effects of real gas and turbulence have a great influence on the performance of supercritical carbon dioxide (S-CO₂) dry gas seal. A typical spiral groove dry gas seal calculation model is established, and the flow equation on the end face of supercritical carbon dioxide dry gas seal is solved by CFD software to obtain the flow state of fluid between the seal slots. The influence of real gas and turbulence effects on opening force and leakage are investigated under different rotational speed. The results show that both real gas and turbulence effects make the pressure distribution of the gas film change significantly. The real gas effect improves the opening force and leakage of gas film, and the strengthening effect on the opening force becomes stronger with the increase of the rotational speed, while the effect on the leakage almost does not change with the rotational speed. At low rotational speed, the turbulence effect has a weak effect on the opening force. With the increase of rotational speed, the opening force increases sharply due to the turbulence effect, and the increase increases with the increase of rotational speed. In the high speed S-CO₂ dry gas seal, the combined effect of real gas and turbulence effect makes the opening force of gas film increase significantly, and the turbulence effect is greater than the real gas effect.

In view of the deviation between the actual heat transfer performance and the theory of printed circuit plate heat exchanger due to processing errors and deformation during service, the shape characteristics of the actual micro-channel were measured and obtained by using ultra-depth of field microscope technology. The micro-channel heat transfer with different channel shapes was numerically simulated, and the influence of channel shape on thermal performance was analyzed. According to the results of numerical simulation, a new heat transfer characteristic correlation formula was obtained, which can provide a theoretical basis for evaluating the heat transfer performance of the actual service of supercritical carbon dioxide printed circuit plate heat exchangers.

Liquid metal fast reactor/concentration solar power system coupled with supercritical carbon dioxide (S-CO₂) Brayton cycle power system will surely lead the revolutionary development in the field of energy and power in future. Due to the special properties of liquid metal and S-CO₂, the Pr number of liquid metals is low; the physical properties of S-CO₂ steep varies in the pesudocrtical region, thus its flow and heat transfer characteristics are different from those of conventional fluids, their heat transfer mechanism is relatively complex, and the conjugated heat transfer mechanism is not clear. This study summarizes the main research results of supercritical CO₂, liquid metal, conjugated heat transfer and conjugated heat exchanger at home and abroad in experiments, numerical simulation and prediction models, points out the problems in the research of CO₂, liquid metals and their conjugating heat transfer between the two fluids, the discussion can provide valuable reference for the design and safe operation of advanced power cycle and multiple working fluids coupling power systems.

Aiming at the problem of waste heat utilization of gas turbine, the technologies of intermediate cooling, intermediate reheating and split flow recompression were introduced into the supercritical carbon dioxide (S-CO₂) power cycle with heat recovery and six cycle schemes were established. Taking the cycle efficiency and the cycle net output power of the S-CO₂ cycle as the optimization objectives, the genetic algorithm was used to optimize the parameters of each scheme, and the earnings of optimization results were compared. The results show that the cycle efficiency can be improved in varying degrees by introducing one intermediate cooling, one intermediate reheat and one split flow recompression when the optimization goal is to maximize the cycle efficiency. The cycle efficiency of the sixth scheme that introduces one split flow recompression and one intermediate reheat is the highest, which reaches 43.29%. When the optimization goal is to maximize the net cycle output work, the introduction of primary intermediate cooling can increase the net output power, the introduction of primary intermediate reheating can reduce the net output power of the power cycle, and the one split recompression degenerates into no split scheme. The second scheme that introduces primary intermediate cooling has the largest net output power reaching 82 620.02 kW. When the cycle net output work is taken as the optimization objective, the economy of the six schemes is more advantageous because the waste heat utilization efficiency of gas turbine smoke exhaust is higher. The second scheme has the largest operating earnings in 20 years, which is RMB 5.065 billion.

Centrifugal compressor is one of the key components in supercritical carbon dioxide (S-CO₂) cycle system, which plays a decisive role in the efficiency and stable operation of the system. Different from the traditional air compressor, the unique physical properties of S-CO₂ working medium make the internal flow field of the compressor more complex. The loss model established based on the physical characteristics of air also needs to be modified specifically to meet the performance prediction requirements of S-CO₂ centrifugal compressor. Therefore, numerical simulation is needed to investigate the internal flow field characteristics of the compressor, so as to improve the compressor performance prediction method accordingly. Firstly, one-dimensional aerodynamic parameters of the compressor were designed, and a three-dimensional model was established based on the one-dimensional design parameters to analyze the characteristics of the internal flow field of the compressor. It was found that the shunt blade had a great influence on the internal flow field, and changes in the internal flow field of the impeller under varying working conditions would also cause changes in the outlet flow Angle. Based on this, The sliding factor and the calculated blade number of the compressor under off-design conditions were corrected, and the surface friction coefficient was improved to predict the performance of the compressor under off-design conditions. The numerical simulation results show that the prediction error of the improved model is significantly reduced, and the average efficiency error decreases from 2.03% to 0.16% under off-design conditions.

In order to effectively prevent the slagging of a supercritical 650 MW opposed firing boiler, the influence of different coal types on the flue gas temperature at the furnace outlet and the heat load of the boiler was checked by thermodynamic checking calculation, and the influence of the air distribution in the furnace and the cone-expanding angle of the burner on the flue gas dynamic field and flue temperature of the furnace was analyzed by CFD simulation. The results of the thermodynamic checking calculation showed that the boiler and the coal type were not the main reason for slagging. The variable air volume simulation showed that adjusting the ratio of internal and external secondary air could have effect on the dynamic field of flue gas. But in operation, changing the air volume did not solve the slagging problem well. The simulation results pointed out that the heat load of the water wall area could be reduced by reducing the cone-expanding angle of the burner from 45°to 30°, so as to inhibit the slagging. In the actual adjustment, after changing the cone expansion angle of the burner from 45°to 30°and adjusting the air distribution, the slagging situation of the boiler was greatly improved.The calculation results of variable SOFA wind showed that the appropriate reduction of SOFA wind proportion could reduce the flame height and the flue gas outlet temperature. The simulation of variable secondary air rotation showed that the secondary air rotation had a significant influence on the flow field and the slagging risk would significantly increase if the rotation of the burner was not arranged according to designed value. Further adjustments to SOFA wind ratio and secondary wind swirl could be considered in following adjustments.

During signal sampling process of steam turbine digital electric hydraulic control system (DEH) tests, situations that the instrument can not meet the requirements of Nyquist sampling due to the frequency of the primary components is over high may occur. To solve this problem, the envelope of the signal is calculated through Hilbert transform, and the valve closing time is calculated according to the envelope signal. However, the calculation accuracy is limited due to the time interval of the peak points. To improve the calculation accuracy, the undersampled signal is reconstructed, the primary frequency is analyzed by using fast Fourie transform (FFT), and the primary frequency of the signal is determined based on the nature of the frequency domain. On this basis, the initial phase of the AC signals is calculated using the initial value, and the undersampled signals is reconstructed according to the frequency and initial phase. The closing time is calculated according to the difference between the reconstructed and sampled signals based on Akaike information criterion (AIC). In comparison with the Hilbert transform method, the reconstruction method can improve the calculation accuracy. The reconstruction and analysis method can be used in all kinds of undersampled periodic signals, which can make up the shortcomings of hardware in DEH tests.