Carnot battery (CB) is an energy storage technology with the advantages of high energy storage density and low investment cost. The single-stage heat pump of basic Carnot battery have a low coefficient of performance (COP) under high energy storage density conditions, resulting in a phenomenon of high quality but low utilization of heat. In order to solve this problem, a CB using cascaded heat pump (CHP) and supercritical organic Rankine cycle (ORC) is proposed. Through modeling and analysis, the optimal combination of CHP-CB working fluids is obtained, and the effects of waste heat source temperature, high and low temperature heat storage tank temperature, CHP intermediate temperature on system COP, energy conversion efficiency, energy storage density (E_D) and system exergy loss are discussed. The results show that under high energy density conditions, the COP of the CHP-CB is about 23.5% and 26.9% higher than that of the basic CB when the temperature of the low-temperature storage tank is 50 ℃ and 32 ℃, respeetively. When the temperature of the low-temperature storage tank is 30 ℃, the energy conversion efficiency of the CHP-CB can reach 63.11%. The E_D can reach 13.9 kW·h/m³ when the temperature difference between the high- and low-temperature storage tank is 93 ℃, and cascade heating for the heat storage working fluid can be realized.

Improving the flexibility of coal-fired power generation units is of great significance for ensuring the reliable and stable operation of the power grid. The heat and mass transfer process in the CFB boiler furnace is investigated deeply. It is found that when the load changes, the air volume entering the furnace responds rapidly, driving the change of the particle suspension density in the dilute phase zone, thus triggers the rapid change of the convective heat transfer coefficient and the total heat flux. Different from pulverized coal-fired boilers, the average furnace temperature of the CFB boiler changes little with load. During the load change process, although the heat storage capacity is large, the thermal inertia is not fully manifested, and it does not have a negative impact on the load change rate. Therefore, the load adjustment process of the CFB boiler is based on the rapid response of the heat transfer coefficient under near constant temperature conditions, which is essentially different from the load-changing mechanism of the pulverized coal-fired boiler. In addition, a considerable amount of unburned carbon in the bed material can serve as a potential fuel supply source when the load increases. When the oxygen supply is increased, the combustion rate can be rapidly improved. Combined with the heat storage of bed materials and castable, the CFB boiler can be regarded as having a built-in “energy storage” function, providing long-term energy support for load adjustment. Measures such as reducing the average bed material size, decreasing the feeding coal size, and adding powdered-coal and circulating ash can further increase the load-changing rate of the CFB boiler. The test results on a 300 MW subcritical CFB boiler unit show that the load increasing and decreasing rate can reach 4%~9%Pe/min, approaching the load-changing capability of a gas turbine unit. The research demonstrates that the CFB boiler has the potential for rapid load change in principle and will play a more crucial role in the new power system dominated by renewable energy sources.

With the continuous increase of installed capacity of new energy generation in power grid, thermal power units have to undertake more peak shaving. However, the flexibility and peak shaving capacity of current thermal power units are generally insufficient. A subcritical 300 MW coal-fired unit is retrofitted for molten salt energy storage. Six heat storage strategies and two heat release strategies are proposed and investigated. The influence of heat storage and release process on the peak shaving capacity and thermal performance of the unit under three working conditions is analyzed, the technical and economic analysis is performed in terms of the net present value. The results show the feasibility of extracting reheated steam for heat storage is higher, with a peak shaving depth of 58.9%. However, the coal consumption would increase at the same time. During the releasing heat stage, the maximum increment of power generation up to 11.3% of the rated power generation is achieved by heating the water supply to generate steam, while the higher temperature of the molten salt is required. Using high-temperature molten salt instead of low-pressure heater to preheat water supply is proved to have more advantages, while the power generation increment is relatively small. During the whole process of heat storage and release, the maximum circulating electricity efficiency can reach 0.987. The economic analysis of heat storage transformation is conducted. The dynamic investment payback period is 11.65 years, and the net present value is 49.118 million yuan. Therefore, the renovation scheme is feasible.

When multiple units are used for combined heating, the distribution of thermoelectric loads among the units significantly affects overall energy consumption. For a thermal power plant where Unit 1 and Unit 3 adopt a dual-mode coupled heat-supply method with zero output of the low-pressure cylinder and steam extraction, and Unit 2 and Unit 4 adopt a triple-mode coupled heat-supply method with high back-pressure, heat pump, and steam extraction, an off-design condition model was established using EBSILON software. The thermoelectric characteristics and energy consumption characteristics were analyzed by adjusting parameters such as main steam flow, zero output steam volume of the low-pressure cylinder, heat supply power of the heat pump, and high-back-pressure heat-supply flow rate. The operational boundaries of electrical and thermal loads and the relationship between coal consumption and thermoelectric load were fitted using the least squares method. Under the fixed boundary conditions for the entire plant’s heating load and power supply load, the optimization of thermoelectric load distribution was achieved using particle swarm optimization. The results indicate that large-capacity high back pressure heat pump units should provide heat load, and small-capacity high back pressure heat pump units should provide electric load. After optimization, the total coal consumption of the whole plant was reduced by 0.6~10.0 t/h, resulting in a degree of optimization of 0.3%~3.9%.

The distribution characteristics of the air flow field inside the natural-draft direct-air-cooling exhaust tower under low-temperature and low-load operating conditions still remain unclear. There is an urgent need to study its variation laws and propose effective measures to ensure exhaust performance and anti-freezing safety. Through the computational fluid dynamics (CFD) numerical simulation, the flow and temperature fields inside the tower at ambient temperatures of –21 ℃ and –30 ℃, and at different wind speeds are analyzed. The results indicate that, based on the symmetrical operation of steam isolation valves for sector switching of the air-cooled condenser, using louvers to regulate airflow in isolated sectors can effectively optimize the internal airflow field, ensure smooth exhaust under low-temperature conditions in winter, and significantly reduce the risk of localized freezing. Field tests verified that this measure can reduce the unit backpressure by approximately 2 kPa and improve the flue gas flow deviation.

In order to solve the technical problem that the cooling margin of the cylindrical hole is insufficient at low blowing ratios and the cold flow is separated from the wall at high blowing ratios, based on the tip-covered vortex generator (TCVG), a new type of vortex generator (VG) is proposed, which is called tile-shaped vortex generator (TVG). The conventional cylindrical hole and the cylindrical hole with TVG are numerically simulated. The results show that the film cooling efficiency of the cylindrical hole with TVG is 200% higher than that of the conventional cylindrical hole. Moreover, it solves the problem that the cold flow of the conventional cylindrical film hole will separate from the wall at high blowing ratios. With the increase of TVG width, the film cooling efficiency increases, and tends to be stable when the width reaches twice the film hole diameter. With the increase of TVG height, the suppression effect of TVG on cold flow is weakened, and there is an uncooled gap in the near-field area at high blowing ratios, and the film cooling efficiency shows a downward trend. The expansion angle of TVG has little effect on the film cooling effect, and the optimal expansion angle is 7.5°.

The optimization design of the first domestically produced full-capacity feedwater pump used for No.9 unit of the Huaneng North Power Dalat Power Plant Phase V expansion project (1×1 000 MW) is introduced. The three-dimensional structural model of the feedwater pump is established by using ANSYS Workbench software, and the thermal stress analysis of the pump body and finite-element calculation of the impeller strength are conducted. Moreover, the trial operation of the turbine-driven feedwater pump unit and optimization suggestions are provided. The feedwater pump runs under various load conditions of the unit, ensuring that the feedwater flow and pump outlet pressure meet the operational requirements, with the temperature and vibration indicators of each bearing in the steam pump unit falling within the excellent range. Based on the performance assessment test data of the feedwater pump, the calculated efficiency is 84.32%, which exceeds the guaranteed efficiency value. The successful application of this domestically produced full-capacity steam feedwater pump unit in a 1 000 MW coal-fired unit can provide experience for planned or newly constructed units and has certain reference value.

To improve the control effect of key parameters and energy conversion efficiency of ultra-supercritical coal-fired power generation units during load cycling process, 600 MW class ultra-supercritical coal-fired power generation units are taken as the research objects to carry out modeling and verification. The deviation of key thermal parameters meets the specified range of thermal power simulation standard. The spatiotemporal distribution model of internal heat storage in thermal system of coal-fired power generation units is established, and the water-fuel ratio and flue gas damper opening control logic of the feedforward internal heat storage state of the unit are proposed. The real-time heat storage state of the unit during the load cycling process is fed forward to the flow rate of feed water, coal, and flue gas damper control. The simulation results show that, when the unit load cycling rate varies from 1.0% Pe/min to 3.0%Pe/min within 40%~70% THA load range, the absolute value of the cumulative main steam temperature deviation rate decreases by 27%~31%. The average power generation standard coal consumption rate of the unit decreases by 0.37~0.65 g/(kW·h) during the transient process. The proposed control strategies improve the control accuracy of key thermal parameters and the energy conversion efficiencies of the ultra-supercritical coal-fired power generation units during load cycling transient processes.

A field test and numerical simulation study is carried out on the slagging problem of a 1 000 MW double-tangential coal-fired boiler during the co-firing of high ash melting point coal and low ash melting point coal. The test results show that as the proportion of low ash melting point coal increases, the slagging in the furnace shows a significant aggravation trend. When the proportion of low ash melting point coal is 50%, slight slagging occurs in the furnace. When the proportion increases to 67%, large-scale coking occurs on the bottom of the large screen heat transfer surface. When the proportion reaches 83%, the slagging situation deteriorates significantly, and the proportion of slag blocks in the furnace slag exceeds 40%. The numerical simulation results of slagging are in good agreement with the field operation test results. The results show that slagging is mainly concentrated in the front and rear wall areas, and the degree of slagging on each heat transfer surface increases with the proportion of low ash melting point coal. Although the addition of low ash melting point coal does not significantly change the near-wall temperature, the significant reduction of the ash melting point of the mixed coal is the fundamental reason for the deterioration of slagging. The operation mode of low ash melting point coal in the burner has a significant effect on slagging, especially when the low ash melting point coal is co-fired in layers D and C, the slagging trend is particularly obvious. It is recommended to prioritize the arrangement of low ash melting point coal in layers A and B, followed by layer F, and avoid co-firing low ash melting point coal in layers D and C.

Supercritical water coal gasification for hydrogen production is a clean and efficient power generation technology. Based on entropy generation theory, numerical investigation on the non-equilibrium condensation flow of an H₂O/CO₂ mixed working fluid in the final-stage cascade is conducted. The losses are quantified by identifying regions within the cascade where different types of losses occur and calculating the entropy generation in each region. The mechanisms behind the impact of back pressure and CO₂ mass fraction in the mixed fluid changes on various losses and entropy generation sources are analyzed. The effects of these parameters on the loss distribution are explored, including a detailed description of how shock waves influence wake losses and the entropy generation distribution within the boundary layer. The results show that wall losses, wake losses, and boundary layer losses consistently account for over 90% of the total losses under different operating conditions. The main sources of entropy generation are wall dissipation, direct dissipation, and turbulence dissipation. When the back pressure increases by 5.03 kPa, the total loss decreases by 31.73%. However, when the CO₂ mass fraction in the mixed fluid increases by 40%, the total loss increases by 4.71%. The variation in turbulent dissipation entropy generation within the wake loss is the primary cause of the total loss change and is closely linked to the velocity gradients in the flow field. This study offers significant insights for the loss analysis of the wet steam region in mixed medium steam turbines and for aerodynamic optimization.