The calculation analysis and experimental study of blade fracture of a certain type of steam and static adjustable induced draft fan are carried out. Vibration signals and blade natural frequencies of fans at different speeds and openings are obtained through vibration tests and modal experiments. Performance curves of fans at different speeds are drawn according to the similarity theory, and the rotation-opening curves corresponding to the flow rate are obtained. The fan operation restricted zone is delimited by the stall line. The test results show that, when the rotation speed is constant, the amplitude of the blade passing frequency and its harmonic component increase with the stator blade opening. Combining with the modal experiment, it is found that the natural frequency of the blade and the blade passing frequency and its harmonic component coincide when the fan runs in the rotation speed range of 796~912 r/min, resulting in blade resonance. The fan should avoid running in the resonance speed range and avoid running in the speed restricted area.

With the large-scale development and grid integration of new energy sources, the fundamental control and operational mechanisms of power system have undergone significant changes to power balance and safety stability control. Low-frequency oscillation events in power systems have typically been simulated and analyzed using standard speed control system models. However, these standard models fail to reflect the regulation characteristics of the units and cannot accurately reproduce the low-frequency oscillation process. Based on the nonlinear characteristics of steam turbine valves and combined with the actual frequency control logic, a small frequency deviation compensation module and a valve flow module are introduced into the typical speed control system model to establish low-frequency oscillation model. The accuracy and effectiveness of the model are verified using actual operational data. Moreover, low-frequency oscillation evaluation indicators are established, by employing the analytic hierarchy process (AHP) and fuzzy evaluation methods, online identification and grading evaluation of low-frequency oscillations are achieved. On this basis, a phased suppression strategy for low-frequency oscillations on the prime mover side of thermal power units is proposed. The corresponding suppression measures are executed based on low-frequency oscillation evaluation results, and the low frequency oscillation model is used to carry out simulation verification. The results demonstrate the suppression strategy can effectively eliminate low-frequency oscillations on the prime mover side and improve operation safety of thermal power units.

In view of the complex variation law and strong autocorrelation of nitrogen oxides emission mass concentration of circulating fluidized bed (CFB) boiler, by using relevant variables and their historical information, ensemble learning online models of nitrogen oxides emission mass concentration are established. The ensemble learning online models include the autoregressive integrated moving average (ARIMA), random forest (RF), gradient boosting (GBDT), and eXtreme gradient boosting (XGBoost) model. The prediction results are compared and selected, among which the GBDT regressor is the best. In order to further improve the prediction effect of the model, a GBDT differential regression model is established by combining the first-order difference with the GBDT regression algorithm. The tests show that the established GBDT differential regression model has better prediction performance than the aforementioned models. The mean squared error of the predicted value is 20.2% lower than that of the simple GBDT regressor, and 46.5% lower than that of the online sequential extreme learning machine (OS-ELM) model used in the reference. The online model also fully considers avoiding the influence of the instrument purge process, and has strong practicability.

In order to provide effective repair and rust prevention treatment for hot surface pipe of utility boilers, and to ensure safe operation of the equipment, cold metal transfer (CMT) cladding process is adopted for water-cooled wall tubes. Four cladding process paths are designed, and the reliability of the numerical simulation data is verified through ANSYS numerical simulation and the CMT cladding experimental platform. Comparison based on the process developed in the simulation process shows that, design of the CMT heat source function has a higher degree of agreement in characterizing the temperature field than the conventional arc heat source. Along the material thickness direction, the change rule of the temperature gradient is consistent with the actual morphology of the specimen cross-section. In the case of the same heat input, the average temperature of the cross-melting path is 30 ℃ lower than that of the sequential melting path, the thermal effect of the cross-melting path on the substrate is smaller, and the stress is 22.0 MPa lower. Pipe deformation reduces by 0.18 mm in the cross-over reverse welding path compared with that in the sequential reverse welding path. Comprehensively considering the effects of the residual stresses and the deformations, the cross-reversed melting path is the optimal process route for CMT.

In response to significant increase in energy consumption caused by low-grade waste heat and energy waste in coal-fired power plants, a 350 MW unit is selected as the research object, the Ebsilon software is used to model and simulate different deep recovery schemes for low-grated waste heat and residue. The operating data of the unit under two schemes of “organic Rankine cycle (ORC)” and “Heater” are calculated. The energy consumption characteristics, revenue characteristics and differences are analyzed, and the mechanism and optimization plan for deep recovery of waste heat and energy are obtained. The results show that, the energy consumption characteristics of the unit improve significantly under both schemes, and the “heater” scheme has lower energy consumption. As the organic working fluid flow rate increases, the power generation of the ORC system gradually increases, but the thermoelectric efficiency of the ORC system gradually increases at first and then tends to stabilize and has a downward trend, with a range of 6.94%~7.75%. The organic working fluid flow rate has a relatively small effect on circulation efficiency of the ORC system. Both schemes are technically and economically feasible. The “ORC” scheme can bring direct electricity benefits to the power plant, while the “Heater” scheme is slightly more economical.

In order to improve the performance and efficiency of the battery in vanadium redox battery (VRB) system, a multi-stack equivalent loss circuit model is developed based on the composition and principles of VRBs, which includes electrochemical, hydrodynamic, temperature, bypass current, and vanadium batteries. Moreover, the effects of pumping loss and bypass current on vanadium batteries in the pipeline system of all-vanadium flow batteries are investigated. The relationship between pumping loss and pumping current, the bypass current model, and the equivalent circuit model of vanadium battery with multiple stacks connected in series are established, and the core mechanism of the vanadium battery taking into account the dynamic response is elaborated by transforming each model into a whole. The key factors involved in modelling of the VRB, including the pumping loss and bypass current, are discussed in detail. The influencing factors of battery performance and efficiency are also analyzed. The results show that, parameters such as the length and cross-sectional area of the pipeline affect the pipeline resistance, and the resistance of longer main and branch pipes will reduce the bypass current but increase the pumping loss current. Longer and thicker pipelines are conducive to the simultaneous reduction of both the bypass current and the pumping loss, which improves the energy efficiency of the battery. The research provides an idea for design of the manufacturer’s pipeline.

With the rapid development of renewable energy, the demand for grid-scale energy storage solutions is increasing to address the challenges posed by intermittent and variable power generation. As an integration of various mature electrothermal conversion and storage technologies, Carnot battery is gaining increasing attentions due to its scalability and independence from geographical constraints. The fundamental principles, key technologies, application prospects and current research status of Carnot battery are reviewed. The definition of high-temperature Carnot battery technology and the operational characteristics and technical challenges of related key equipment such as compressors and expanders are discussed. Additionally, practical application cases and technological prospects of Carnot battery systems based on electric heating and bidirectional cycles (such as Brayton and Rankine cycles) are analyzed, providing a reference for future research and technological development.

With the increase of wind power penetration in power systems, the inertia of the power system decreases and the frequency regulation resources are insufficient. The frequency response margin approaches the critical value, which results in great challenges to frequency security. To solve the problem, from the perspective of regulation mechanism, a wind-thermal cooperative frequency control model based on virtual inertia control of wind power is constructed. The kinetic energy of rotor is used for fast frequency regulation. Then, a load frequency controller of wind-thermal cooperative power system based on a novel active disturbance rejection control (ADRC) method is proposed and designed. This improves the anti-disturbance capability to uncertain wind power and load disturbances. The designed cascade extended state observer also solves the contradiction between high frequency noise suppression and fast response performance of conventional ADRC. The excessive regulation of wind power and thermal power units caused by frequency measurement noise can be avoided and the quality of wind-thermal coordination regulation can be improved. Finally, genetic algorithm based particle swarm optimization is used to optimize the parameters of the proposed load frequency controller. The simulation results show that, compared with the conventional ADRC and other conventional control methods, the proposed strategy can effectively improve the frequency response characteristics, and suppress the effect of measurement noise on the amplitude of system frequency response and control signal.

Aiming at the characteristics of complex and variable load and strong coupling of integrated energy system, a combined forecasting model based on variational mode decomposition (VMD), Prophet model, long- and short-term memory network (LSTM) and autoregressive integrated moving average (ARIMA) model is proposed for short-term electrical load prediction. Firstly, the electric load eigen mode functions with different center frequencies and relatively stable ones are obtained by VMD. Then, after calculating the value of zero cross rate, the modal components of each group are superimposed respectively to form the high-frequency and low-frequency timing components, and the Prophet model is used to extract the high-frequency components for timing features. Finally, the ARIMA prediction model is used to predict the low frequency component, and the LSTM neural network model is applied to predict the high frequency component. The final predicted electric load is obtained by superimposing the respective prediction results. The proposed method is applied to the actual integrated energy system, and the example analysis shows that the combined forecasting method presented above has good forecasting performance for the integrated energy system

To investigate the microstructural and mechanical properties of 1 000 MPa grade ultra-high strength steel submerged arc welding welded joints for hydroelectric engineering, the microstructure of different regions of the welded joint was characterized using scanning electron microscopy (SEM). Mechanical properties of the welded joint were determined through tensile testing, impact testing, and bending testing. The results reveals that, the weld metal of the root pass and fill passes is composed of columnar, dendritic, and equiaxed grains, with a microstructure dominated by acicular ferrite and a small amount of granular bainite. The heat-affected zone (HAZ) exhibits multiple typical regions, including a critical coarse grain zone and a coarse grain zone near the fusion line along the thickness direction. Away from the weld, fine grain zones and critical zones are observed, with a microstructure primarily consisting of granular bainite, M-A constituents, and lath martensite. The weld metal of the cap pass exhibits typical columnar grains with a microstructure primarily composed of acicular ferrite. The HAZ of the cap pass includes coarse grain, fine grain, critical, and subcritical zones. Due to the absence of subsequent welding passes, no critical coarse grain zone is formed, and the microstructure is primarily composed of lath martensite, granular bainite, and M-A constituents. The average tensile strength of the welded joint reaches 980 MPa grade, the low-temperature impact absorption energy of the weld zone and the HAZ at –40 ℃ is 118.7 J and 149.3 J (at T/4), 67.0 J and 154.0 J (at T/2), respectively. No cracks appear in the lateral bending.