The coupling of coal-fired units with molten salt electric heater systems can significantly improve their frequency regulation and peak shaving capabilities. On the basis of Modelica language, a dynamic model of the molten salt electric heater is established and the experimental verification is completed, it reveals the dynamic characteristics of the molten salt electric heater under the disturbance of molten salt flow rate and unit AGC load. A temperature control method of “feedforward+PID” regulation is proposed based on its dynamic characteristics, and the characteristics of electrical load and thermal parameter changes during AGC regulation of coal-fired units assisted by molten salt electric heaters are calculated and analyzed. The results indicate that, configuring a 10 MW molten salt electric heater can increase the AGC variable load rate of a 660 MW coal-fired unit by 340%, and the proposed control method can maintain the stability of thermal parameters of the electric heater.

An organic Rankine cycle (ORC) unit is designed through thermodynamic analysis and equipment type selection under geothermal conditions. Then, this unit is simulated to study its dynamic operating characteristics and investigate the influences of four parameters, such as heat source temperature, mass flow rate, cooling water temperature and working fluid mass flow rate, on key operating parameters and performance of the ORC unit. The results show that, the output performance of the unit is primarily affected by the cooling water temperature. An increase of 10 ℃ in the heat and cold source temperatures results in a decrease of 16% and an increase of 7% in the output power, respectively. The increased heat source temperature and mass flow rate will make the degree of superheat, evaporating pressure and shaft work increase significantly, and the system thermal efficiency decrease slightly. However, the effect of increasing heat source temperature and mass flow rate on the heat transfer of the cold side is limited, that on the hot side heat transfer is also neglectable, so the vapor superheat and evaporating pressure remains constant. Compared with the change of cold and heat source parameters, the change of working fluid mass flow rate has the lowest overshoot of parameters during dynamic operation of the unit, and the unit can reach the next steady state rapidly.

Aiming at solving the problem of complex and uneven flow field inside the coal pulverizer, a complete model of medium-speed coal pulverizer was established. The CFD software was used to solve the internal flow equation of the coal pulverizer. Moreover, DPM iteration was used to obtain particle flow parameters, and the internal flow of the medium-speed coal pulverizer and distribution characteristics of outlet air-powder at different rotation speeds of dynamic classifier were explored. The results showed that, the distribution characteristics of primary air at four pulverizer outlets were good and consistent with the test results. When the powder diameter was small, the powder mass flow deviation at four pulverizer outlets was small, and the fluctuation was not obvious with the increase of the rotation speed of the dynamic classifier. With the increase of powder diameter, the motion trajectory of powder showed a wall adherent motion, and the powder mass flow deviation at four pulverizer outlets gradually increased. Furthermore, for coal particles with large diameters, with the increase of the rotation speed of the dynamic classifier, the powder mass flow deviation at four pulverizer outlets gradually decreased.

Responding to the urgent needs of clean and efficient utilization of coal under the background of national “carbon peaking and carbon neutrality”, the pulverized coal preheating combustion technology has been developed in industrial boilers, power plant boilers and other fields. In this technology, pulverized coal is modified at high temperature in a fluidized preheating burner, then the preheated fuel enters the furnace for graded air distribution combustion, thus high efficiency and low NO_x combustion of pulverized coal is realized. Moreover, technical verification was carried out on a 60 t/h pulverized coal boiler, which adopts two preheating burners with side wall hedge arrangement, and one preheating burner is designed with thermal power of 26 MW. Using bituminous coal as raw material, the operation and NO_x emission properties of the boiler at 10%~100% operating loads were studied experimentally, and the results showed that, the boiler operated stably and well at each load, it achieved stable operation of 10% ultra-low load without any auxiliary means. The preheating burners had reasonable operating parameters and stable circulation state, which can meet the requirements of wide load operation of the boiler. The combustion efficiency of the boiler at each operating load were all above 97%, the thermal efficiency of the boiler were above 85% at 10% and 20% operating load, and above 90% at 30% and above operating load. By adjusting the air distribution, the original NO_x mass emission of the boiler at each operating load can be controlled lower than 50 mg/m³ (φ(O₂)=9%). The successful demonstration of the 60 t/h pulverized coal preheating combustion boiler provides important support for the development and application of clean, efficient and flexible combustion technology of pulverized coal.

The mathematical and physical models of different semicircular channels are established, and the accuracy of the numerical models is verified by comparing with the experimental data. The thermal and hydraulic heat transfer performance of supercritical carbon dioxide (S-CO₂) in uniform cross-section semicircular tube, diverging tube and converging tube is studied, and the influence of different channels and pressures on the thermal and hydraulic performance of S-CO₂ in a semi-circular tube with variable cross-section is calculated and analyzed. The results show that, compared with the uniform cross-section semicircular tube, the diverging tube deteriorates heat transfer, the converging tube enhances heat transfer. The overall heat transfer coefficient of converging semicircular tube with the inlet and outlet radius ratio of 1.0:0.5 increases by 39.93%, and the maximum evaluation factor PEC of flow heat transfer comprehensive performance is 1.346. When the pressure is closer to the critical pressure or the heat flux is low, the heat transfer performance is higher. Finally, the reason why the converging tube with variable cross-section can enhance heat transfer is explained from the perspective of field coordination and turbulent kinetic energy distribution. The research results can provide new ideas and theoretical guidance for the design and optimization of coolers in S-CO₂ circulation system.

In recent years, numerous incidents of harmonic resonance accidents involving new energy power stations have occurred both domestically and internationally. The frequency scanning method, characterized by its simplicity of operation and clear physical significance, has been widely employed in engineering for the assessment of system resonance. When establishing electromagnetic transient simulation models for large-scale new energy power stations and conducting frequency scans, it is common to substitute a single or multiple generators for the actual power station to reduce modeling complexity. However, the applicability of this approach in addressing high-frequency harmonic resonance issues has not been effectively revealed. To address this gap, this study takes a large-scale photovoltaic power station as an example and employs a bottom-up modeling approach to establish a detailed impedance model for the photovoltaic power station. Building upon this, a dynamic equivalent model is developed using the principle of equal power loss. The two models are then thoroughly compared and analyzed based on actual field station parameters. The research findings indicate that the series impedance of the collector lines has a minimal effect on the harmonic model. As a result, the study proposes a simplified dynamic equivalent model replacing the π-type circuit with a ground capacitor. The results demonstrate that the equivalent model established through the equal power loss method accurately reflects the harmonic resonance characteristics of the photovoltaic power station. Additionally, the model neglecting the inductance of the collector lines proves applicable for analyzing the mid-to-low frequency harmonic resonance in photovoltaic power stations.

Aiming at the lack of fault samples of power equipment, this paper proposes a dry-type air-core reactor condition assessment method based on belief rule base. By building a test platform for the electrical and temperature rise characteristics of dry-type air-core reactors under multiple working conditions, a data sample set of reactor active power and the temperature rise rate of the hottest point is obtained under different operating conditions. A reactor condition assessment model based on belief rule base and evidential reasoning is established. In order to reduce the influence of expert subjectivity on the prediction results of the state assessment model, a belief rule base optimization method is proposed, and the evidential reasoning algorithm is used to convert the input feature information of the reactor into the output state level. The evaluation model was tested by test data, and the results verified the validity and accuracy of the dry-type air-core reactor condition assessment method based on small training samples.

Flue gas flow is one of the key factors affecting the accuracy of carbon monitoring, and the complex flow field environment with uneven velocity distribution and changing with unit load is the main factor impeding the accurate measurement of flue gas flow. By taking a chimney inlet flue of a 660 MW unit in a power plant as the research object, the influence of the number of points and the layout of the process on measurement accuracy of the flowmeter with four different measurement principles was compared and analyzed based on numerical simulation results of the flue gas flow field. The results show that, the multipoint Pitot tube flowmeter has better adaptability to the complex flow field environment compared with the matrix flowmeter. When the number of measuring points is 28, the deviation of the matrix flowmeter is 1.54 times that of the multipoint Pitot tube flowmeter. The measurement accuracy of the light scintillation flowmeter is greatly affected by the elevation of the installation position, with the maximum deviation being 23.3 times the minimum deviation. This indicates that the light scintillation flowmeter has poor adaptability to complex flow field environments. The ultrasonic flowmeter can be installed obliquely and in multiple channels, with a more flexible and varied process layout, significantly improving its adaptability to complex flow fields. The dual-channel arrangement can control the deviation within ± 1.5%. The research results provide important theoretical basis and data support for the selection of flow meter equipment and process design, and have important theoretical research and engineering application value.

In 2021, China launched its national carbon market. To enhance the accuracy of carbon trading, it is essential that carbon emission data are measurable, reportable, and verifiable. Against this backdrop, online monitoring systems for flue gas have gained significant attentions as a method of quantifying carbon emissions. The basis for the effective work of continuous emission monitoring systems is the accurate measurement of flue gas flow. However, the challenge in accurately measuring flue gas flow rates is significantly heightened by the large size of power plant chimneys and the complexity of the gas flow characteristics within them. This paper focuses on analyzing the current research status of Pitot tube flowmeters and ultrasonic flowmeters in large-scale duct flow measurement, and provides a detailed introduction to gas flow measurement technologies for large-scale ducts. Additionally, it introduces an independent flow measurement method, namely the tracer gas dilution method, and discusses its current development and potential as a flow calibration method.

In electric power ancillary service market, coal-fired thermal power units are facing new opportunities and challenges in participating in frequency regulation auxiliary services. During operation of large-capacity (ultra) supercritical coal-fired unit boilers, the energy storage is limited and the AGC frequency regulation response performance are difficult to adapt to the increasing frequency regulation demand of the ancillary service market. To solve these problems, the influence of different energy states of grid and source on frequency regulation is analyzed, and a self-adaptive frequency regulation control strategy based on grid-source operation state is designed. This strategy is based on the boiler energy storage state and the grid frequency regulation demand, and can adaptively undertake the AGC frequency regulation task in the frequency regulation ancillary service market. It fully exerts the frequency regulation potential of the unit, and is beneficial to fast energy balance and parameter recovery stability of the unit itself, which realizes the grid-source goal coordination of the safe and stable operation of the unit and the improvement of the comprehensive frequency regulation performance index of the unit.