The carbon dioxide (CO₂) Brayton cycle system is compact, efficient and flexible, and has a good application prospect in the third generation photothermal system and the fourth generation nuclear power system. The deterioration of CO₂ heat transfer affects the safe operation of the unit. In order to study the deterioration of CO₂ heat transfer in the vertical riser, a CO₂ heat transfer characteristic system is established for experimental research, and the CO₂ heat transfer characteristics under subcritical and supercritical conditions are compared. The influence of thermal parameters on the deterioration of CO₂ heat transfer is obtained, and the prediction correlation of CO₂ critical heat flux is established. The predicted value is in good agreement with the experimental value (error ±30%). It is found that the peak value of wall temperature is higher when CO₂ heat transfer deteriorates at subcritical pressure. Far away from the critical pressure and increasing the mass flow rate are conducive to restraining the occurrence of heat transfer deterioration.

Numerical and experimental studies are conducted on convective heat transfer performance of carbon dioxide (S-CO₂) flowing in a heated vertical helically coiled tube under supercritical pressure. The influence of flow characteristics and structural characteristics such as heat flux q, mass flow rate G, pitch P, tube inner diameter d, and spiral radius R on heat transfer are discussed, and the sensitivity of each structural parameter is studied quantitatively. A closed-loop S-CO₂ test platform was built to conduct experimental research on the convective heat transfer performance of S-CO₂ in the helically coiled tube, and the accuracy of the numerical simulation is verified based on the experimental data. Finally, the heat transfer correlation of S-CO₂ is fitted. The research has laid foundation for the thermal design method of S-CO₂ spiral-wound heat exchanger, and has certain engineering application value for the application and promotion of the spiral-wound S-CO₂ heat exchangers in nuclear power and solar thermal power generations.

For enhancing the film stiffness of supercritical CO₂ (S-CO₂) hydrodynamic dry gas seal and reducing the additional power consumption due to the installation of heater in the seal inlet line, a new structure of S-CO₂ hydrostatic-dynamic dry gas seal with the heating of the ring body at the back of the static ring is proposed. Based on the conjugate heat transfer model, the pressure and temperature distribution of dry gas seal were simulated utilizing commercial software Fluent. The steady-state performance and flow field distribution of S-CO₂ hydrodynamic seal, hydrostatic seal and hydrostatic-dynamic seal were compared and analyzed, and the flow and heat transfer characteristics and power consumption of S-CO₂ hydrostatic-dynamic dry gas seals under different heating modes and heat temperatures were discussed. The results show that the film stiffness of the hydrostatic-dynamic dry gas seal is improved more than doubled compared with the hydrodynamic dry gas seal, while the leakage rate increased significantly by 35% at the same time. The power consumption under ring heating mode is 44% lower than that under direct gas heating mode, leading to better operating economy. It provides a new idea for the structure design and auxiliary system improvement of compressor dry gas seal in S-CO₂ power generation system.

A comparative analysis between simulation and test with roughness is carried out for a supercritical carbon dioxide (S-CO₂) axial turbine with different operating conditions, focusing on the roughness impact of the turbine performance. The results show that the numerical calculation method of wall roughness is able to assess the performance of the turbine at different load conditions accurately. Compared with test result, the maximum efficiency error is 1.82 percentage point. Wall roughness degrades the overall performance of the turbine, with a maximum efficiency drop of 2.8 percentage point at Ra1.6 roughness level during the five working condition, and the turbine stage roughness has a more obvious effect on the turbine performance. In addition, the more severe of wall roughness, the greater reduction of turbine efficiency. In non-design operating conditions, the efficiency drops by 11.6 percentage point at Ra6.3 roughness level. The wall roughness exacerbates flow separation of pressure surface, causing greater friction losses and serious affecting of turbine performance. The research can provide technical support for the design and performance simulation of S-CO₂ axial turbines.

Supercritical carbon dioxide cycle has many advantages such as small turbine size, small compressor power consumption and high cycle efficiency. In order to explore the cycle configuration with the highest power generation efficiency after the power generation system of supercritical carbon dioxide cycle coupled gas turbine, four cycle layouts were proposed. The main parameters of the circulating system were optimized by genetic algorithm with the maximum circulating efficiency as the optimization objective. Among the four schemes, the gas turbine/two-turbine supercritical carbon dioxide combined cycle system has the highest cycle efficiency, which is 44.87%. And the dynamic system analysis of the scheme, with the bottom cycle input heat load as the disturbance variable, explore the dynamic response of the system after the step reduction from full load to 90% load, 80% load and 70% load respectively. The results show that the response time of parameters near the flue gas heat exchanger is faster and the response time is longer when the shadow of thermal inertia is farther away from the flue gas heat exchanger in the working medium flow. At the same position, the response time of pressure is slightly longer than that of temperature, and the drop range of parameters near the high-temperature turbine is greater than that of the low-temperature turbine.

The exhausted heat losses in the PRC and inefficiency in medium and low heat source applications are significant challenges affecting the application of supercritical carbon dioxide Brayton cycle for renewable energy sources. To achieve efficient utilization, a precooler-free power/cooling combined system with superior heat source adaptability is proposed and analyzed. Integrating with the precooling-heating coupled module and the absorption power/cooling module instead of the PRC, the waste heat from the LTR is completely recovered, moreover, multiple operating modes ensure that the system performance unaffected by ambient temperature and seasonal changes. Parametric studies indicate that the TUR2 inlet temperature, the WHE1 outflow overheat degree, and the hot end temperature difference have significant effects on the Split Ratio, energy outputs, and the coupling relations among modules. Moreover, due to the improvement of irreversibility and the decrease of exergy losses, the three-largest exergy destructions occur in the IHE, the TUR1, and the RET+GEN, which account for 56.1%, 6.9%, and 5.2% respectively. Furthermore, the optimized cases exhibit optimal η_thermal, η_exergy, c_P,total, and W_net of 84.2%, 74.1%, 9.48 dollars/GJ, and 397.4 MW respectively.

With the transformation of the power system to low-carbon, the proportion of new energy installed capacity is increasing year by year, renewable energy power generation has the characteristics of intermittent, the main power generation period and peak power consumption period are misaligned, there is an imbalance between supply and demand, and the demand for flexibility in power balance is intensified, and long-term energy storage power stations have become a magic weapon to solve the problem. According to the development of long-term energy storage technology, the technical characteristics, advantages and current bottlenecks of pumped storage, compressed air, lithium-ion batteries, flow batteries, molten salt heat storage, and hydrogen energy are analyzed, and the typical application projects of the above energy storage technologies are analyzed. Then, the typical scenario applications of energy storage are analyzed from different sides of the power supply side, the power grid side and the user side, and the application comparison of seven energy storage technologies in multiple scenarios such as energy transfer, auxiliary services, black start, and smooth new energy output is expounded. The technical parameters, battery selection, system wiring, energy management and other issues of chemical energy storage demonstration project, heat storage demonstration project and mechanical energy storage demonstration project were summarized and analyzed, and finally the future energy storage power station technology was prospected.

Driven by the “carbon peaking and carbon neutrality” goal, hydrogen blending and pure hydrogen combustion technology of gas turbines have received widespread attention. Producing “green hydrogen” from renewable energy and applying it for power generation is the development direction of the energy field in the future. However, the fluctuation of hydrogen source will inevitably cause the change of hydrogen blending ratio of hydrogen blended gas turbine fuel. Therefore, the dynamic response characteristics of the gas turbine are studied when the hydrogen blending ratio fluctuates. Taking an F-class heavy-duty gas turbine as the research object, a dynamic model is built by using the modular modeling method to analyze the response characteristics of key parameters of the unit and the safe operation of components when the hydrogen blending ratio fluctuates under different loads. The results show that when the hydrogen blending ratio fluctuates, the turbine inlet temperature (T₃) will fluctuate violently, and T₃ overtemperature will occur in the high load region, which will lead to the deterioration of the blade working environment and affect the safe operation of the unit. The larger the fluctuation of hydrogen blending ratio and the higher the power output, the more obvious T₃ overtemperature phenomenon. However, the fluctuation of hydrogen blending ratio has a relatively small impact on the compressor, and the compressor can still maintain a reasonable surge margin.

Based on a DC microgrid system coupled with photovoltaic power generation, lithium battery-supercapacitor hybrid energy storage, electrolysistank and hydrogen-burning micro gas turbine, a power allocation strategy that integrates the lithium battery state of charge (SOC) and hydrogen storage tank hydrogen state (LOH) is proposed. A PV-electrolysistank-micro gas turbine DC microgrid system model is constructed. The allocation logic of the power judgment module of the coordination control layer is designed, and three operation modes are given when the residual power exists in the DC network. The power allocation strategy is simulated and verified using MATLAB/Simulink software. The simulation results show that the power allocation strategy of DC microgrid system based on hydrogen energy storage can make the lithium battery charge state gradually converge to a reasonable storage interval and can improve the service life of lithium battery.

The optimal scheduling and economy of new energy hydrogen production systems are closely related to hydrogen production efficiency. Aiming at the problem of low hydrogen production efficiency in existing new energy hydrogen production systems, this paper proposes a control strategy for new energy hydrogen production systems based on particle swarm optimization (PSO). Firstly, based on the polymer electrolyte membrane (PEM) electrolytic cell model, the relationship between the operating point of the electrolytic cell and the hydrogen production efficiency is analyzed. Secondly, a hydrogen production system operation control method based on particle swarm optimization algorithm is proposed to improve the hydrogen production efficiency of the hydrogen production system. Furthermore, an optimal scheduling model for new energy hydrogen production systems considering the efficiency of system hydrogen production was established, and particle swarm optimization algorithm was also used to solve the optimal hydrogen production power. Finally, through simulation analysis of actual power grid operation data, it is proved that the proposed control strategy can effectively improve the hydrogen production capacity and system revenue compared to traditional startup and shutdown strategies, providing a theoretical basis for the large-scale application of hydrogen production systems in power grids.