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    Boiler Technology
  • Boiler Technology
    Analysis of Asymmetric Flow and Nonlinear Characteristics in an Opposed Wall-fired Boiler
    CHEN Kai, YANG Mo
    2021, 41(4): 257-262. https://doi.org/10.19805/j.cnki.jcspe.2021.04.001
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    To study the asymmetric flow in a furnace, the cold flow field was simulated by a two-dimensional model with symmetric geometric structure and physical boundary conditions, which was abstracted from an opposed wall-fired boiler. The symmetry of flow field was compared under various Reynolds numbers, and the nonlinear characteristic of special solution was analyzed by using phase diagram and frequency spectrum. Results show that even if the geometric structure and physical boundary conditions are symmetric, asymmetric flow still exists. With the increase of Reynolds numbers, the asymmetry of flow field increases gradually, fluid velocity oscillates over time, and even appears chaotic flow. There are three kinds of special solutions with different properties: steady solution, periodic oscillatory solution and aperiodic oscillatory solution. The phase diagram of steady solution is a fixed point, and no other fundamental frequency appears in the spectrum; the phase diagram of periodic oscillation solution is a folded limit cycle, and a fundamental frequency appears in the spectrum; the phase diagram of aperiodic oscillatory solution is irregular but limited to a certain region, and the spectrum diagram transforms from discrete to continuous.
  • Boiler Technology
    Study on Oscillation Characteristics of Coal Particles Under Strong Acoustic Waves
    YANG Yanfeng, JIANG Genshan, YU Miao
    2021, 41(4): 263-271. https://doi.org/10.19805/j.cnki.jcspe.2021.04.002
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    Considering the Stokes force as the main force of the particles, the dynamic governor equation of coal particles under the action of strong acoustic waves was established, and the calculation formula of the particle entrainment coefficient was given. The effects of particle position, flue gas temperature, particle density, particle size, acoustic frequency and sound pressure level on the motion characteristics and entrainment coefficient of coal particles before the formation of shock wave were investigated by numerical calculation. Results show that particles at different distances from the acoustic source in a strong acoustic field have different oscillation periods and amplitudes, presenting rich oscillation characteristics. Near the acoustic source, the particles are mainly affected by the fundamental wave, showing a sinusoidal oscillation, when they are far away from the sound source and close to the shock wave formation position, the particles are mainly controlled by the fundamental wave, the second and third harmonics, showing irregular oscillation behaviours. The entrainment coefficient is negatively correlated with particle position, particle mass and acoustic frequency, but positively correlated with flue gas temperature.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Thermal Performance Optimization Analysis of Gas-Steam Combined Cycle Unit Based on the Inlet Gas Temperature Adjustment
    FAN Xuefei, JIANG Jun, LIU Wangkou, ZHU Zhijie, WANG Siyuan
    2021, 41(4): 272-277. https://doi.org/10.19805/j.cnki.jcspe.2021.04.003
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    Taking the GE S109FA gas-steam combined cycle unit as the research object, a comprehensive optimization scheme based on the inlet gas temperature adjustment for the thermal performance of the unit was proposed. The low-pressure steam of the waste heat boiler and the exhaust gas of the tail flue gas were used to cool and heat the inlet gas of the compressor. The corresponding thermodynamic design parameters were given, and the thermodynamic calculation before and after inlet gas cooling or heating was carried out by using the thermodynamic calculation software GT Pro. Results show that reducing the inlet gas temperature can increase the combined cycle generation power by 4.73%-6.10% under the basic load. Under different partial loads, when the inlet gas temperature is heated from 15 ℃ to 35 ℃, the gas turbine load rate can be increased by 8%-14%, and the combined cycle power generation efficiency can be increased by about 0.88%, so as to meet the requirements of thermal performance optimization of the unit under different atmospheric temperature and load conditions.
  • Steam Turbine and Gas Turbine
    Study on Gas Turbine Inlet Air Heating Technology Based on Waste Heat Utilization
    GUO Laijia, HAN Chaobing, LU Bingguang, ZHANG Hanxian, HUANG Suhua, WANG Jian
    2021, 41(4): 278-285. https://doi.org/10.19805/j.cnki.jcspe.2021.04.004
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    To analyze the influence of compressor inlet air temperature on gas turbine thermal efficiency under partial load, a technical scheme of gas turbine inlet air heating system based on waste heat utilization was proposed. The principle of using waste heat utilization technology to improve the economy of combined cycle unit was explained, and the energy saved by gas turbine inlet air heating system in and out of service under partial load was evaluated. In addition, heat exchanger design was optimized. Results show that the compressor inlet air temperature can be raised by 7.2-8.0 K via waste heat utilization technology under gas turbine partial load, and then, gas turbine thermal efficiency is increased by 0.19%-0.26%, heat recovery steam generator(HRSG) exhaust flue gas temperature is reduced by 5.5-6.7 K and the equivalent efficiency of HRSG is increased by 0.8%-1.1%. Finally, the combined cycle thermal efficiency is increased by 0.42%-0.46%. Through rational design of heat exchanger structure parameters, the air intake resistance of the compressor is increased by only about 41 Pa under the premise of satisfying the heat transfer,which ensures the safe and economic operation of the unit.
  • Steam Turbine and Gas Turbine
    Detection Method of Combustion Instability Based on PCA-MEA-WNN Model
    HUANG Wei, LI Changwei, XI Jianzhong
    2021, 41(4): 286-293. https://doi.org/10.19805/j.cnki.jcspe.2021.04.005
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    To detect the abnormality of the combustion chamber pressure and monitor its real-time pressure change trend, a model based on the combination of principal component analysis (PCA), mind evolutionary algorithm (MEA) and wavelet neural network (WNN) was proposed. PCA was used to clean and preprocess original data from the power plant firstly, then optimal solution was obtained from WNN optimized by MEA, and performance evaluation index of the model was established. Combined with the deviation of the metrical prediction from the observed value, the warning threshold was set through the sliding window method to achieve the purpose of overrun alarm. The model was verified by a gas-steam combined cycle generator set simulation platform,and simulated in an actual operation of the thermal power plant. Results show that PCA-MEA-WNN algorithm can detect combustion instability in time and give an early warning. It has more accurate prediction results, generalization ability and higher fitting degree. The error is reduced significantly, which is helpful for the actual operation analysis of the combustion chamber.
    • Engineering Thermophysics
  • Engineering Thermophysics
    Flow Transition and Bifurcation of Laminar Wake in Elliptical Tube Bundles
    LI Yirong, YANG Mo, ZHANG Zheng
    2021, 41(4): 294-300. https://doi.org/10.19805/j.cnki.jcspe.2021.04.006
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    The finite volume method(FVM) was used to simulate the air flowing across elliptical tube bundles at different dimensionless tube spacings, so as to analyze the flow change process of the wake and the corresponding bifurcation phenomenon. Results show that keeping the initial boundary conditions unchanged, when dimensionless tube spacing varies from 0.5-3.5, as the Reynolds number increases to the corresponding critical value, the occurrence of Hopf bifurcation makes the wake from stable symmetrical flow to unstable state. When the tube spacing is small, the fork bifurcation occurs, and the deviation of the tube flow would aggravate the instability of the flow state. With further increase of the Reynolds number, the stable deviation in the wake quickly transits to unstable deviation, and the system changes from quasi-periodic state into chaos. When the tube spacing is large, the appearance of in-phase and reverse-phase flow increases the regularity of wake disturbance. The tube flow will oscillate up and down with the rear wake, and the system will not be bifurcated with tuning fork. The flow state will eventually enter a quasi-periodic state.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Numerical Analysis of Bionic Blades Applied in Centrifugal Fan
    WU Changle, CHEN Eryun, YANG Ailing, LI Guoping
    2021, 41(4): 301-308. https://doi.org/10.19805/j.cnki.jcspe.2021.04.007
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    In order to study the influence of bionic blades on the aerodynamic characteristics, flow and sound fields of centrifugal fan, three types of bionic structures including corrugated leading edge, serrated trailing edge and surface pits were applied on centrifugal fan blades, and the flow and noise radiation for each structure were numerically calculated. Results show that for the structure of surface pits, it suppresses the separation flow on the suction surface of blades and improves the total pressure and efficiency of the fan, however, the pressure pulsation near the wall of the volute increases, and finally the noise of the fan goes up by 0.85 dB; for the structure of serrated trailing edge, the power capacity of the fan is decreased, but the high efficiency can still be maintained, at the same time the flow in the impeller is improved and the pressure pulsation is significantly weakened, finally the total sound pressure level is reduced by an average of 5.04 dB; for the structure of corrugated leading edge, the aerodynamic performance of the fan is slightly improved compared with the prototype, and the whole noise reduction is 3.14 dB.
    • New Energy
  • New Energy
    Minute-scale Ultra-short-term Wind Speed Prediction Based on Improved HHT
    ZENG Namei, HUO Zhihong, XU Chang, DENG Zhiwen, JIN Zhijie
    2021, 41(4): 309-315. https://doi.org/10.19805/j.cnki.jcspe.2021.04.008
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    To solve the problem that minute-scale wind speed was difficult to predict due to its stronger randomicity and nonlinearity, a minute-scale ultra-short-term wind speed prediction model was established based on improved Hilbert-Huang transform (HHT). HHT was applied to decompose the original wind velocity data. The spectrum of each intrinsic mode function (IMF) was analyzed through Hilbert transform (HT). According to the spectrum characteristics of each component, different neural network models were built to predict wind speed. Weighted coefficients of each component were calculated through the weight floating interval model and the mathematical analytic model. Two groups of wind speed prediction values were obtained by summarizing each component results according to the weighted values. Final prediction results were obtained by optimizing such combination. The availability of the established model was verified by the actual operation data in a wind farm. Results show that compared with the original HHT combined prediction model, the method is better and can effectively improve the accuracy of wind speed prediction.
  • New Energy
    Identification and Cleaning of Wind Power Data Methods Based on Control Principle of Wind Turbine Generator System
    MEI Yong, LI Xiao, HU Zaichun, YAO Hui, LIU Da
    2021, 41(4): 316-322. https://doi.org/10.19805/j.cnki.jcspe.2021.04.009
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    In view of difficulties encountered in abnormal data recognition and cleaning on wind power curve fitting for the variable-speed variable-pitch wind turbine, an effective algorithm based on control principle was proposed. Starting from wind turbine control principle, a data pretreatment of wind power scatters was adopted by active power and generator speed signals, and then the power limiting data was recognized by analyzing the time series distribution of power data. Finally, wind speed tip speed ratio scatters and wind power scatters were cleaned by the quartile method, while screening for power scatters was completed, the operation status of the unit under different wind speeds was identified. Results show that the algorithm developed has a good cleaning effect on wind power scatters with different morphological characteristics, which is of high execution efficiency.
  • New Energy
    Analysis on Vibration Signal Decomposition Methods of Wind Turbine Gearbox
    HU Xuan, LI Chun, YE Kehua
    2021, 41(4): 323-329. https://doi.org/10.19805/j.cnki.jcspe.2021.04.010
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    Based on the significant non-linearity and non-stationarity of the vibration signal of the wind turbine gearbox, ensemble empirical mode decomposition (EEMD), intrinsic time scale decomposition (ITD) and empirical wavelet transform (EWT) decomposition methods were used to process gearbox signals respectively, and the component information entropy of each method was obtained and the feature vector was formed as input parameters of support vector machine (SVM) for fault identification and classification. Results show that EWT can better extract the impact components in the vibration signal; ITD has the highest and the most stable accuracy among the three decomposition methods, which is most conducive to the fault diagnosis of wind turbine gearbox.
    • System Engineering
  • System Engineering
    Research on Optimal Scheduling of Multi-source Cooling, Heating and Power Cogeneration Systems for Public Buildings and Institutions
    GU Wenbo, LI Yutong, CHEN Yiming, XIE Sijia, MA Tao
    2021, 41(4): 330-330. https://doi.org/10.19805/j.cnki.jcspe.2021.04.011
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    To resolve the issues on optimizing the scheduling of multi-source cooling, heating and power cogeneration systems in large public buildings and institutions, a multi-objective optimization study was carried out in consideration of the economical, environmental-friendly and energy saving effects. First, numerical models were established for all the equipment in a multi-source cooling, heating and power cogeneration system, for which, corresponding constraints were set. Then, based on the optimal index of satisfaction, a scheduling strategy was proposed for the multi-energy system on a typical day in summer, while the effects of different irradiation on the optimal value of each index were analyzed. Results show that for multi-source cooling, heating and power cogeneration systems, the optimal scheduling strategy based on the optimal index of satisfaction can comprehensively satisfy the economy, environmental protection and energy saving requirements, although it can not achieve the optimal values of all the indexes simultaneously. The optimal value of each individual index reduces while that of satisfaction index increases as the proportion of renewable energy rises in the multi-energy system.
    • Material Research
  • Material Research
    Effects of Postweld Heat-treatment and Long-time Thermal Exposure on the Microstructure of HT700 Alloy Friction-welded Joints
    LI Boshuai, ZHU Ming, LU Jintao, XU Yaxin, DANG Yingying, ZHANG Huihui
    2021, 41(4): 337-344. https://doi.org/10.19805/j.cnki.jcspe.2021.04.012
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    HT700 alloy joints were welded by inertial friction method under the spindle speed of 1 500 r/min and the friction pressure of 300 MPa, following which, heat treatment and long-time thermal exposure tests were conducted on the welded joints, so as to study the effects of heat treatment process and long-time thermal exposure on the microstructure of the nickel-iron-based superalloy friction-welded joints. In addition, the microhardness of the welded joints was tested. Results show that the microstructure is symetrically distributed about the centerline of the welded joint, which, after heat treatment and long-time thermal exposure, can be divided into three regions, i.e. the weld center zone, heat affected zone and base metal zone. The average hardness of weld joints is the highest, which appears when the heat treatment process is 1 140 ℃×20 min + 1 020 ℃×1 h (water quenching) + 650 ℃×16 h + 820 ℃×4 h. Long time aging at 750 ℃ will lead to coarsening of the M23C6 as well as merging and growing of the γ', resulting in lowered microhardness of the welded joint. However, no harmful phase precipates in the process of high-temperature exposure, indicating good thermal stability of the HT700 alloy friction-welded joints.