With the increasing proportion of new energy connected to the grid, the issue of frequency safety in the power system and mastering the regulation ability of the units have become more important. At present, in power system simulation, thermal power unit models suitable for electromechanical transient and medium-long term dynamics mainly adopt the simplified model of drum boilers and the single reheater turbine model recommended by IEEE. If a similar model is also used for the once-through boiler unit, the simulation results of the main steam pressure will deviate significantly from the actual situation due to the dynamic of thermal storage coefficient and the deviation of control system, which leads to a misjudgement of the unit’s regulation ability. By using thermodynamic modeling methods, a supercritical once-through boiler unit model suitable for multi-time scale dynamic simulation is proposed. By establishing a moving boundary model of the water wall and a dynamic heat flow model of the superheater, the heat storage capacity of the once-through boiler can be reflected more accurately. By incorporating feedwater control and superheat control, the control system is more in line with the actual unit. The high simulation accuracy of the model is verified using power plant operation data. Compared with the existing power simulation models, the simulation accuracy of the main steam pressure has been improved significantly. Therefore, the model can describe the dynamics of supercritical once-through boiler units more accurately in primary and secondary frequency regulation and peak shaving, which is helpful for simulating the frequency process of power systems.

Based on the computational particle fluid dynamics (CPFD) numerical simulation method, the study takes the 660 MW supercritical circulating fluidized bed (CFB) boiler in Pingshuo, Shanxi as the research object. A full-loop model of the furnace is established and numerically simulated. On the basis of the parameters of the actual furnace, the material distribution characteristics of six cyclone separators are investigated. By altering the ratio of primary to secondary air, the uniformity of primary air, and the uniformity of secondary air, the effect of operational parameter changes on the gas-solid flow field within the furnace and the material distribution at the cyclone separator inlets is analyzed. The results indicate that the distribution characteristics of particles within the furnace lead to a distribution feature of particle mass flow rate at the cyclone separator inlets, which is “high on both sides and low in the middle”. When the total air volume is constant, a larger ratio of primary to secondary air can reduce the deviation in particle mass flow rate at the cyclone separator inlets. The uniformity of air distribution for both primary and secondary air in the furnace also affects the particle mass flow rate distribution at the cyclone separator inlets. The deviations in particle mass flow rate at the inlets of the six cyclone separators reach their minimum when the wind speed deviation at the middle air distribution plate is 10% and the deviation in the middle secondary air volume is 5%, respectively.

Nowadays, circulating fluidized bed (CFB) coal-fired boilers face challenges in the process of deep peak regulation, such as high CO emission concentrations and the lack of theoretical guidance for collaborative emission reduction of multiple pollutants including NO_x and SO₂. Taking a 150 t/h CFB coal-fired boiler as the research object, a model for quickly predicting mass concentrations of CO, NO_x and SO₂ emitted from the furnace is established based on the long short-term memory (LSTM) neural network, the Attention mechanism and the XGBoost algorithm. Moreover, an online emission reduction strategy is proposed by coupling with the particle swarm optimization (PSO) algorithm. 36 298 operational data points from the coal-fired boiler throughout 2023 are selected as training samples. A correlation analysis is conducted between the boiler inspection data and pollutant emission mass concentrations to determine the input parameters for the prediction model. The fitness function and boundary function are determined with the prediction model coupled with the PSO algorithm. Through the calculation of emission reduction optimization model, an online emission reduction optimization strategy for CO, NO_x and SO₂ mass concentrations of CFB boilers in different load ranges is proposed, and the feasibility of the algorithm in practical boiler tuning applications is evaluated.

Improving the heat transfer efficiency between liquid lead-bismuth eutectic (LBE) and supercritical carbon dioxide (S-CO₂) is of great significance for advancing the development of advanced nuclear energy systems. The heat transfer performance of printed circuit heat exchangers (PCHE) with different channel structures (straight shaped, wing-shaped, S-shaped and Z-shaped) is investigated through numerical simulation. The results show that the thermal resistance on cold side of the heat exchanger is significantly higher than that on the hot side, with the average heat transfer coefficient of the hot side in straight-channel PCHE being 26.2 times that of the cold side. Under the condition of a fixed hot-side channel structure, the effects of different cold-side channel structures on PCHE heat transfer performance are explored. The results indicate that, compared with straight channels, the heat transfer of Z-shaped, S-shaped and wing-shaped channels increases by 23.3%, 22.2%, and 10.6%, respectively, while the specific pumping power improves by 1.48 times, 1.68 times, and 1.44 times, respectively. In addition, the dynamic performance of different PCHE designs when the cold-side flow rate increases by 20% is compared, revealing that the straight-channel PCHE has the shortest rebalancing time. The pressure drop loss is more significant than the improvement in heat transfer. These findings provide theoretical guidance for optimizing the design of LBE/S-CO₂ heat exchangers and contribute to enhancing the thermal efficiency of next-generation nuclear energy systems.

Circulating fluidized bed (CFB) boilers are characterized by high thermal inertia and strong heat storage capacity, enabling banked fire and near-zero output peak shaving. However, there is limited experimental research on banked fire and peak regulation in large-scale CFB units, with a lack of studies on key parameter variations and control strategies during this process. In this study, a banked fire and peak regulation test was conducted on a supercritical 350 MW CFB boiler to investigate the evolution of critical parameters during shutdown and propose optimization strategies for boiler feedwater flow rate and integrated turbine valve position control. These optimizations aim to maximize the peak shaving duration while ensuring operational safety. Experimental results demonstrate that the optimized supercritical CFB unit achieved 85 minutes of shutdown peak regulation with a load of 5~8 MW. Throughout the test, the boiler maintained dry operation, while the main and reheat steam temperatures decreased from 566.0 ℃ and 553.0 ℃ to 482.0 ℃ and 472.0 ℃, with average cooling rates of 0.99 ℃/min and 0.95 ℃/min, respectively. The average bed temperature declined from 875.8 ℃ to 730.9 ℃ at a rate of 1.70 ℃/min. During the test, the maximum exhaust temperature of the high-pressure cylinder reached 380.0 ℃, with the steam temperature at the regulating stage exceeding that of the cylinder inner wall. The wall temperature deviation at the outlet of the boiler water-cooled walls and mid-partition walls gradually decreased, peaking at 97.5 ℃. These findings confirm the feasibility of hour-level shutdown peak regulation in supercritical CFB units and provide a reference for engineering applications of similar units.

With the continuously increasing proportion of installed capacity from new energy sources, higher flexibility demands are imposed on coal-fired power generation units, including supercritical circulating fluidized bed (CFB) boilers. By taking a 350 MW supercritical CFB boiler as the research object, the computational particle fluid dynamics (CPFD) method was employed to simulate the furnace response characteristics under variable load conditions, focusing on parameters such as furnace temperature, near-wall particle concentration, and average heat flux density on heating surfaces. The effects of combustion and circulation interventions on the rate of load change were also explored. The results indicate that, during load ramp-up operation, the response rate of average heat flux density in low load range (30%~50% of the unit rated load) decreases by about 38% compared with that in high load range (above 50% of the rated load). Focusing only on the high load range, the heat flux density responds faster during load ramp-down, with the rate of change about 31% higher than that during ramp-up. Under varying load amplitudes, the particle suspension concentration and convective heat transfer intensity inside the furnace can respond rapidly, while temperature changes lag slightly, indicating that CFB boilers rely more on variations in the heat transfer coefficient for rapid thermal regulation. Through combustion interventions, such as substituting 40% of the original coal feedstock with fine coal particles sized several hundred microns, the change in furnace temperature can be effectively accelerated, with the response rate of average heat flux density during ramp-up in the high load range increasing by about 43%, and by nearly 16% in the low load range. Additionally, implementing circulation interventions, such as adding a certain amount of fine bed material during ramp-up, can rapidly increase the particle suspension concentration in a short time and thus effectively improve the response rate of the heat transfer coefficient on the heating surface. If hot fine material is further added (for example, through a hot circulating ash storage and return system), the response rate of the average heat flux density during ramp-up in the high load range can be improved by approximately 31%, and by about 13% in the low load range. The study elucidates the internal response mechanisms of CFB boilers under variable loading conditions, confirms the feasibility of improving load change rates through circulation and combustion interventions, and provides a reference for further tapping the flexibility potential of supercritical CFB boilers and improving their variable load capability.

Butterfly valves are widely used in industrial field, and under certain working conditions, strong unstable flow will occur in the butterfly valve and cause vibration in pipeline system. By taking the connecting pipe of the medium and low pressure cylinder of a 600 MW heating unit as the research object, the mechanism of unstable flow in the butterfly valve and the vibration of the connecting pipe was revealed through the combination of field measurement and steady numerical simulation. Then, based on the flow pattern optimization, a new type of butterfly valve with valve plate and diversion structure was designed, and the unsteady numerical simulation of the maximum vibration condition of the original butterfly valve and the optimized butterfly valve was carried out. The results show that, after adding the flow-guiding structure to the valve plate, most of the main steam flow moves along the middle of the steam inlet pipe of the low-pressure cylinder. This can effectively weaken the exciting force generated by unstable flow and suppress the vibration of the connecting pipe. The new butterfly valve proposed can be applied to suppress the vibration of the pipeline system with small opening of the butterfly valve.

With the rapid expansion of new energy power generation capacity in China, the insufficient load regulation capability of coal-fired power plants has become increasingly evident. In order to explore the start-stop peak regulation capability of supercritical circulating fluidized bed (CFB) power units, a 350 MW supercritical CFB unit was taken as the research object, and experimental studies on banked-fire hot standby and rapid start-stop operations were conducted. The experimental results demonstrated that the supercritical CFB unit can rapidly reduce its load to near zero (with an average load change rate of about 10%Pe/min) during bank firing, and then maintain hot standby for 108 minutes. After banked firing, the boiler quickly switched to wet-state operation, with the main steam pressure decreasing rapidly at a rate of 0.13 MPa/min. By reasonably controlling the feedwater flow, the working fluid temperature and wall temperature of the water-cooled walls and water-cooled panels were kept stable. The heat released from the combustion of residual carbon caused the bed temperature to decrease slowly during banked firing, which also provided favorable conditions for re-ignition. During the load lift phase, the unit could be quickly started, with NO_x emission mass concentration reaching an instantaneous peak of 101 mg/m³, while the hourly average was stable below 50 mg/m³. Throughout the entire experimental period, SO₂ emission mass concentration was consistently below 35 mg/m³, and pollutant emissions met the ultra-low-emission requirements. All parameters of the steam turbine and generator remained within normal ranges during the hot standby and startup/shutdown. The rapid decline in main steam pressure and the low superheat of the main steam temperature were the main factors limiting the duration of banked firing in this experiment. The relevant research work provides a reference for the start-stop peak regulation of higher-parameter supercritical and ultra-supercritical CFB units.

With the proposal of “double carbon target”, the pace of low-carbon transformation of power system has been further accelerated. The flue gas waste heat utilization systems have been widely applied in thermal power units. As the core equipment of the flue gas waste heat utilization system, the flue gas cooler has a high failure rate in actual operation due to factors such as limited space in the flue gas layout, high flue dust concentration, and ammonium bisulfate deposition. This not only reduces the recovery of flue gas waste heat, but also increases system resistance, resulting in an increase in fan power consumption and even affecting the unit’s load capacity and environmental emission. On the basis of extensive researches on the operation of more than 250 sets of flue gas coolers in the thermal power industry, typical faults commonly found in flue gas coolers, such as leakage, boiler ash deposition, bottom flue ash deposition, and low-temperature flue gas corrosion, are summarized. The causes of the above typical faults and their coupling relationships are analyzed in depth. Moreover, the targeted preventive measures are proposed to provide guidance for transformation and operation/ maintenance of flue gas coolers.

A novel power generation system integrating an organic Rankine cycle (ORC) with an air-cooled coal-fired power plant is proposed to achieve cascaded utilization of steam energy and enhance output power capability. Based on the efficient thermoelectric conversion characteristics of the ORC system at low and medium temperatures, the steam expanding to a certain level in the coal-fired unit is extracted to drive the ORC system for higher output power. This coupling scheme can achieve the multiple purposes of increasing output power, recovering exhaust steam waste heat and preventing air cooler icing in winter. Focusing on a 600 MW coal-fired power plant, thermodynamic performance evaluation has been carried out. The results show that, when the extraction flow rate is 160 kg/s, the thermal efficiency of the system at 50% THA, 75% THA and 100% THA loads increases by 3.48, 1.72 and 1.08 percentage points, respectively. The exergy efficiency increases by 3.38, 1.68 and 1.05 percentage points, and the coal consumption rate decreases by 27.72, 12.88 and 7.92 g/(kW·h), respectively. The heat recovery rate reaches 64.57%, 25.64% and 15.40%, respectively. This approach not only improves the performance of existing air-cooled coal-fired power plants, but also reduces coal consumption, and the research results can provide a way to improve the overall performance of power plants.