The failure of boiler tubes in thermal power units will cause non shutdown of units and greater economic losses. Deposits in boiler tubes are an important reason for their failure, and reducing deposits in boiler tubes is of great significance to the safe and stable operation of units. It is found that the formation of deposits is related to many factors, such as overheating of furnace tubes, high heat load, poor water vapor quality, water vapor phase transition, working medium disturbance and pipe surface defects. Combined with the flexibility of units, deep peak shaving operation, environmental protection reform and other conditions, the formation mechanism and influencing factors of various types of deposits are analyzed with actual accident case pictures. The effects of overheating, salt concentration and corrosion under scale caused by deposits in furnace tubes are further discussed. The countermeasures for feedwater quality, boiler shutdown protection, unit startup steam purification, unit peak shaving, boiler tube replacement, boiler transformation and maintenance are proposed, which can effectively reduce the generation of boiler heating surface deposits and reduce the risk of boiler tube failure.

To effectively alleviate the high-temperature corrosion of the water-cooled walls on both sides of the opposed wall combustion of a 660 MW unit's boiler and the erosion caused by coal particle impingement, a solution was proposed to deflect the swirl burners near the side walls by 3.5° towards the center of the furnace. This solution was based on an understanding of the causes and mechanisms of high-temperature corrosion and considering the on-site equipment conditions. Numerical simulations were conducted to analyze the combustion in the boiler before and after the burner deflection. A comparative analysis was performed on the changes in temperature distribution, velocity field, concentration field, and particle trajectories resulting from the burner angle deflection. The proposed solution was also implemented in practical engineering. The results of the numerical simulations and engineering application demonstrated that after deflecting the burner angles, the airflow inside the furnace concentrated towards the center, resulting in a reduction of coal particle impingement near the side walls and mitigating erosion. Additionally, the temperature near the side walls decreased, leading to a decrease in reducing atmosphere and a reduced risk of high-temperature corrosion. The combustion efficiency of the boiler remained unaffected. The findings of this study can serve as a reference for preventing and managing high-temperature corrosion and water-cooled wall erosion in boilers of similar types.

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.

Combing the excellent performance of carbon dioxide thermodynamic cycle and the reutilization demands for the captured carbon dioxide, the energy storagetechnologies based on carbon dioxide thermodynamic cycle have the potential to play an important role in the future energy system which mainly consists of renewable energies. This paper presents the definition of the energy storage technology based on carbon dioxide thermodynamic cycle, and then classifies this energy storage technology into six types, which are electrothermal energy storage, compressing carbon dioxide energy storage with low, mid and highpressure gas storage, compressing carbon dioxide energy storage with low-temperature and near atmospheric temperature liquid storage, and the constant pressure gas storage energy storage. The state-of-the-art research status, advantages and disadvantages of these technologies are discussed. In general, the compressing carbon dioxide energy storage with low pressure gas storage is most mature, and there are demonstration units constructed. The compressing carbon dioxide energy storage with high pressure gas storageand the electrothermal energy storage have a good overall performance, but their costs are high. The compressing carbon dioxide energy storage with constant pressure gas storage has the highest cycle efficiency, reaching 74%~75%, and the energy storage density is up to 2 (kW·h)/m³, making it one of the most promising compressing gas energy storage technologies.

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.

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.

In view of the actual distribution of heat boundary conditions on the cooling wall of supercritical carbon dioxide (S-CO₂) coal-fired boiler, the heat transfer characteristics of supercritical CO₂ in a vertical circular tube under axial non-uniform heat flux were numerically studied by using SST k-ω low Reynolds number turbulence model. The influence of different heat flux distribution, mass flux on heat transfer performance and wall temperature distribution was analyzed. The results show that the axial non-uniform heat flux distribution has a significant effect on the heat transfer of S-CO₂. Compared with the uniform heat flux, the total heat transfer coefficient under the axial non-uniform heat flux increases by about 8%. The non-uniform distribution of axial heat flux can inhibit the heat transfer deterioration and effectively reduce the peak wall temperature. Under the condition of non-uniform heat flux, the heat transfer of S-CO₂ is mainly affected by the thickness of the gas-like film, the thermal conductivity of the gas-like film and the specific heat near the wall. The results provide theoretical guidance for the design of supercritical CO₂ boiler.

In order to explore the similarities and differences of the loss characteristics of carbon dioxide and steam in turbine cascades, the flow characteristics of the two kinds of working fluids in stator cascade and stage were studied by numerical methods. And the optimal Mach number for efficient operation of turbine stage under subsonic condition was obtained. The results show that with the increase of Mach number, the flow loss first increases and then decreases. When the Mach number is lower, the diffuser has a large range and is easy to backflow, which makes the wall boundary layer thicken and separate, and increases the overall flow loss. When the Mach number is higher, the strength of the secondary vortex in passage is larger, and the shock wave will be generated near the trailing edge of blades. The reason for the larger flow loss is the secondary flow and shock wave. Compared with steam, the dynamic viscosity of carbon dioxide is slightly higher, and its density is about twice that of steam. Under the same Mach number condition, the mainstream velocity is lower, the boundary layer is thicker, and the overall loss is larger. When the Mach number is lower than 0.30, the total-total efficiency of turbine stages with carbon dioxide is lower. While the Mach number is higher than 0.50, the efficiency of carbon dioxide is slightly higher than that of steam. When the optimal outlet Mach number of balde is about 0.60, the efficiency of both is the highest. The research results will provide a reference for further improving the design level for axial flow turbines of steam and carbon dioxide, and further understanding the loss characteristics of different medium in turbine stage.

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.

The abnormal heat transfer behavior of supercritical carbon dioxide (S-CO₂) with low mass fluxes in a horizontal tube was studied, the S-CO₂ heat transfer process in the horizontal tube under the condition of low mass fluxes was simulated with Fluent software, and the abnormal heat transfer behavior of heating and cooling conditions and the influence of heat flux on heat transfer were analyzed. The results show that when the thermal boundary conditions are P=8 MPa, G=200 kg/(m²·s) and q/G=0.2 kJ/kg, the temperature of top and bottom walls in the S-CO₂ tube decreases along the way during the flow cooling process. When the mainstream temperature of S-CO₂ reaches the pseudo critical temperature, the heat transfer coefficient of the top wall at 551.0 mm from the inlet has a sudden peak value, heat transfer enhancement occurs here. Under heating conditions, the temperature of the top wall first rises along the tube path, then drops to 395 K and then rises slowly. The temperature of the bottom wall drops briefly and then rises slowly. At the top wall 69.5 mm away from the inlet, the heat transfer coefficient has a valley value, and the heat transfer at this point deteriorates. The increase of heat flow density aggravates the deterioration of heat transfer under heating conditions, but has no obvious effect on cooling heat transfer. It can be seen that the thermal physical property distribution of the characteristic section is the main reason for the different heat transfer behaviors. Based on the low mass fluxes conditions, thermo-physical properties and buoyancy effects, a correlation equation for predicting supercritical heat transfer enhancement is constructed, which provides theoretical guidance for the design and operation optimization of supercritical fluid heat exchanger.