The operating parameters of coal mills directly affect the safety and combustion performance of coal-fired units. Therefore, it is of great significance to carry out real-time monitoring of CO volume fraction at the outlet of coal mills and accordingly have safety early warning based on the monitored data. In this work, the measurement accuracy and detection limit of wavelength modulation direct absorption spectroscopy(WM-DAS) method were verified based on tunable diode laser absorption spectroscopy(TDLAS) and Herriott multi-pass cell. The experimental results showed that the measured CO volume fraction agree very well with the preset values in the range of 1 to 10 μL/L, and the detection limit can be as low as 5.2×10^–3 μL/L(300 s), which suggests the extremely high measurement sensitivity and accuracy of this method. Subsequently, based on this prototype experiment, an on-line monitoring system for the trace CO volume fraction was developed. Then, combined with the high-fidelity pretreatment technology of fuel gas based on the principle of constant-flow dilution, an on-line monitoring system for trace CO volume fraction was developed and applied to the outlet of coal mill of thermal power unit. The on-line CO monitoring and safety warning at the outlet of 5 coal mills of a single thermal power unit were realized by using multi-point alternating measurement strategy. With the monitored CO volume fraction and temperature of the coal mill outlet, the temperature of the primary air is adjusted to improve the boiler efficiency while ensuring safe operation of coal mill.

In order to improve the cooling performance of cooling tower, this study takes a 300 MW unit cooling tower in the north as an example, establishes a 3D numerical calculation model of cooling tower, compares the effect of non-equal packing in two and three zones on the outlet tower water temperature, determines the optimal radius dividing point, and cooperates with non-uniform water distribution for optimization, analyzes the effect of different optimization schemes on the air flow rate, tower water temperature and ventilation volume in the outlet tower. The results show that the cooling performance is improved with the exit tower water temperature of 31.798 ℃and 31.696 ℃ under the non-equally spaced packing in the second and third divisions, respectively. The coupling optimization of non-equally spaced packing with non-uniform water distribution significantly improves the uniformity of aerodynamic and temperature fields. With the increase of water distribution in the inner zone, the outlet water temperature and ventilation volume both show a trend of first increase and then decrease, and the optimal water distribution in the inner zone is 50%, and the outlet tower water temperature is 31.36 ℃ and ventilation volume is 7 122.8 kg/s. Compared with 26 mm and 30 mm equidistant packing arrangement, after collaborative optimization, the water temperature of the tower is reduced by 0.768 ℃ and 0.83 ℃, respectively, and the cooling performance is significantly improved.

In the context of energy transition driven by "carbon peak and carbon neutrality", an adaptive PID control algorithm in frequency domain is proposed to solve the quality problem of steam turbine back pressure regulation caused by frequent change of operating conditions in flexible air-cooled thermal power units. Considering the practicality and accuracy of the variable working condition model, on the basis of the site operation data, the improved particle swarm optimization (PSO) algorithm is used to identify the dynamic system of multiple working conditions of the air cooling unit. Then, based on the nominal model of the controlled object operated under multiple working conditions, the transfer function configuration mode adaptive method is employed to calculate and optimize the parameters of PID controller in real time, thus to adapt to the change of model parameters of the controlled object under flexible operation and overcome the control quality problems caused by PID controller structure and fixed parameters. The simulation results show that, the adaptive PID controller in frequency domain can well track the variation of model parameters under different load conditions, which makes the back pressure control keep good control quality.

In order to avoid disrepair and overrepair, improve the reliability and availability of gas turbine, reduce operation and maintenance cost, and ensure its safe, stable, green and efficient operation, a novel approach is proposed for fault diagnosis of gas turbine in power plants under transient operating condition with variable geometry compressor. The mathematical relationship of the influence of the compressor inlet guide vane position on compressor flow and efficiency characteristics is deduced. A high-precision thermodynamic model for the purpose of performance analysis and gas-path fault diagnosis is established. Moreover, the gas path fault diagnosis strategy of power plant gas turbine, which is suitable for transient and variable conditions and includes variable geometry, is proposed. Through actual operation test, it is verified that the proposed method has high diagnostic accuracy and good real-time performance, and the fault identification under transient and variable conditions is realized.

In view of the frequent failure of power generation equipment under the background of frequent deep peak regulation, flexible operation, energy saving and consumption reduction of thermal power units, a coal mill fault warning method based on multiple state estimation-analytic hierarchy process is proposed. Firstly, based on the characteristic parameters of coal mill Spearman correlation analysis for dimension reduction, equidistant sampling method is used to extract some samples from a large number of coal mill history data memory matrix, after normalization, memory matrix is formed. Then, multi-state estimation algorithm is adopted to calculate the corresponding memory estimated vector according to the memory matrix and the observation vector. The characteristic parameters are given different weights by using analytic hierarchy process (AHP), and the fusion similarity between the observed vector and the estimated vector is calculated, and the fault warning of coal mill is carried out based on the adaptive threshold method. Finally, the actual fault data of a roller medium speed coal mill is taken as an example to verify the effectiveness of the method. The results show that, this method has less misalarm rate and false alarm rate for coal mill fault warning, which can reduce the actual fault probability of coal mill to a certain extent.

Frequency conversion condensate pump is easy to produce structural resonance because of insufficient support stiffness of vertical structure and increased working frequency range. According to the problem of excessive vibration in two resonance zones of a 350 MW vertical variable-frequency condensate pump, this paper introduces the principle and influencing factors of structural resonance, the judgment method of vibration fault and the treatment process. Theoretical calculation and actual treatment results show that, when there is unbalance on the shafting, dynamic balancing can effectively reduce the vibration amplitude in the resonance area of the condensate pump. However, when there are multiple resonance zones at the same time and the counterweight schemes corresponding to different resonance zones are contradictory, the dynamic balance mode cannot be considered at the same time. The angle of the counterweight determines the dynamic balance effect. Due to the limitation of the reserved counterweight angle, the rapid change of the vibration phase near the resonance point, inaccurate measurement and other factors, it is difficult to achieve on-site fine dynamic balance. Increasing the support to improve the system stiffness can change the natural frequency of the structure and reduce the vibration amplitude in the resonance area, which is an effective measure to solve the resonance problem. The vibration reduction effect of radial support is better than that of axial support.

The effects of different heat transfer fluid (HTF) parameters on charging and mechanical performance of the thermal energy storage (TES) tank using phase change material (PCM) capsules are studied by employing the fluid-solid coupling calculation. The results show that, with the inlet HTF flow velocity increased from 0.000 7 m/s to 0.000 9 m/s, the total heat storage quantity is basically unchanged, the average charging power increases from 5.33 MW to 6.79 MW, and the peak maximum mechanical stress (MMS) of the tank wall decreases. When the initial cold HTF temperature decreases from 610 K to 530 K, the total heat storage quantity increases, the average charging power increases from 5.29 MW to 6.81 MW, but the peak MMS of the tank wall also increases. With the initial hot HTF temperature increases from 730 K to 810 K, the total heat storage quantity increases obviously, the average charging power increases from 3.81 MW to 7.97 MW, but the peak MMS also increases to 159.6 MPa. Hence, to improve the charging performance of the TES tank, on the premise of ensuring the structural safety of steel wall of the TES tank, the inlet HTF flow velocity and initial hot HTF temperature should be increased properly, and the initial cold HTF temperature should be reduced properly.

The main-auxiliary combined indirect dry cooling system has attracted attention from the industry in recent years, while few scholars at home and abroad have conducted studies on its flow and heat transfer performances. In order to investigate the transport characteristics of the main-auxiliary combined indirect dry cooling system under different configurations, this paper establishes six physical models of the combined indirect dry cooling systems with the double-layer/single-layer main and auxiliary radiators. And then the cooling performances are analyzed and compared using the commercial software FLUENT. The results show that, the construction has obviously higher impacts on the auxiliary cooling system than the main one, meanwhile the air mass flow rate presents larger difference than the heat rejection; In absence of wind, the main-auxiliary combined cooling system with double-layer heat exchanger arrangement, has better cooling performance than that with the single layer heat exchanger arrangement, and case A possesses the best cooling performance; Under crosswind effects, case C has highest cooling capability of the auxiliary cooling system, while the behavior of its main cooling system should also be considered before the engineering selection. This research may provide some theoretical guidelines for the engineering design and application of the main-auxiliary combined natural draft dry cooling system.

As the proportion of new energy power generation continues to increase, the stability of grid frequency is severely challenged, and the role of conventional thermal power units in grid frequency regulation has become increasingly prominent. However, the adjustment rate and accuracy of some thermal power units are difficult to meet the demand of grid load fluctuations. Therefore, a response performance optimization strategy for flywheel-thermal power system automatic generation control based on load forecasting was proposed. Firstly, the load is predicted, using the tree-based pipeline optimization tool TPOT library to automatically machine learning to match and train the load regression prediction model, and the automatic generation control day-ahead planned value is introduced into the training data to reduce the prediction error. Then, according to the load prediction value and the current flywheel system, with the optimization goal of minimizing the regulation rate of thermal power units, the flywheel energy storage system is acted firstly in load distribution, and the state of charge of the flywheel is adjusted meanwhile. Finally, a simulation experiment is carried out based on the actual operation data of a power plant in Hubei, and the experimental results prove that the proposed method can effectively improve the frequency modulation performance of thermal power units.

Under the background of auxiliary heat supply of ejector, in order to study the characteristics of ejector under variable working conditions, the calculation methods of ejector at home and abroad are investigated, the ejector calculation model is established and coupled with the high back pressure unit. Moreover, the effects of working steam, ejected steam, ejector back pressure, and ejector opening on the performance of the ejector under variable working conditions are obtained. The results show that, when the working fluid pressure of the ejector changes from 0.25 MPa to 0.45 MPa, the mass flow of the working fluid first increases and then decreases, and the ejector has the best performance at the design working steam pressure. The critical back pressure increases with the steam injection pressure. The pressure of the mixed fluid after injection will not only affect the work of the ejector but also the work of the condenser. Compared with the back pumping unit, the minimum cooling flow of the low pressure cylinder of the high back pressure coupling injector unit can be reduced by 140 t/h and the power supply range can be increased by 43 MW.