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    Boiler Technology
  • Boiler Technology
    Numerical Simulation on Near-wall Mass Transfer Characteristics of Granular Corrosion Products in Water Transcritical Zone
    WANG Chao, HOU Tianqi, LI Hongyuan, XU Hong
    2021, 41(2): 85-90. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.001
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    To investigate the deposition characteristics of typical granular corrosion products like Fe3O4 particles in transcritical region of the steam-water system in an (ultra) supercritical unit, a simulation study was carried out on the near-wall mass transfer characteristics of particles in the transcritical turbulent flow within the straight pipe based on SST k-ω model in the RANS-DPM method, while the variation of particle mass transfer with the inlet temperature, heat flux density and water mass flow rate was analyzed. Results show that the place where the highest wall temperature appears is related to the thickness of the supercritical layer; when the supercritical layer approaches to the boundary of the near-wall area, the concentration of particles in that area would reach a peak; the increase of heat flux density and mass flow rate hinders the mass transfer of particles to the near-wall area, and the transcritical phenomenon on the boundary is beneficial to the mass transfer of particles to the near-wall area.
  • Boiler Technology
    Analysis on Granulation Process and Reaction Property of the Coal Ash Oxygen Carrier Rich in Iron and Calcium
    NI Mingguo, LIN Liming, LIU Dunyu, JIN Jing, CHENG Qian, LI Wei
    2021, 41(2): 91-98. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.002
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    Based on higher oxygen release rate and better reaction performance of the coal ash rich in iron and calcium, the electronic paramagnetic resonance (EPR) spectroscopy was adopted to perform relevant tests and analyses. The high-iron high-calcium coal ash was mechanically mixed with starch, cement and ATP, respectively, and subsequently the mixtures were calcined and granulated, following which, the property of a new oxygen carrier (Ash7-ATP3) was analyzed for industrial application using a fluidized bed reactor. Results show that there are crystal defects (oxygen vacancies) in the high-iron high-calcium coal ash, which improves the oxygen release and reaction property of the coal ash itself; the samples obtained with ATP as the binder can aggregate into agglomerates, and are not easily broken. During the granulation process, when the mass fraction of ATP added is 30%, the best reaction property of Ash7-ATP3 would be obtained. The optimal reaction temperature of Ash7-ATP3 is 1 123 K, and the optimal size of reaction particles is in 0.3-<0.5 mm; the circulating oxygen release of Ash7-ATP3 is kept at about 10%. After each cycle, the mass fraction of 0.3-<0.5 mm particles is kept about 98%, indicating good wear resistance of the oxygen carrier.
    • Automatic Control
  • Automatic Control
    Design of a Sliding Mode Control Strategy for the Main Steam Pressure of Gas-fired Boilers Based on Neural Network
    WANG Sheng, ZHANG Jiayan, FENG Xugang
    2021, 41(2): 99-106. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.003
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    To solve the problem that the conventional PID control method is difficult to achieve satisfactory control effects during the main steam pressure control of gas-fired boilers due to the characteristics of non-linearity, large interference and variable model parameters of the control system, an optimized control strategy was proposed based on neural network and sliding mode control, by taking the advantages of the sliding mode controller that is not sensitive to the parameter changes and disturbance of the system. The RBF neural network was used to adjust the switching gain of the sliding mode controller to reduce its chattering at the equilibrium point, while the disturbance compensation was realized by adding a disturbance observer to the system. Results show that compared with the conventional sliding mode control and the conventional PID control, the overshoot of the control strategy proposed under different working conditions could be reduced by up to 6.62%, and the adjustment time could be reduced by up to 57.45 s, with small chattering, good following performance, high anti-interference capability and strong robustness of the control system. Application results indicate that after adopting the strategy proposed, the system chattering has been reduced by 33%, compared with the conventional sliding mode control. The fluctuation range of the main steam pressure is within -0.04-0.1 MPa, and the anti-interference ability of the control system has been significantly improved.
  • Automatic Control
    Optimization of a New Coordinated Control Strategy Based on Condensate Throttling
    ZHAO Zheng, YU Yuebo, SUN Haotian
    2021, 41(2): 107-128. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.004
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    Aiming at the nonlinear relationship between the power increment in the condensate throttling control loop and the opening of the upper deaerator water gate, a multi-loop condensate throttling control structure was proposed based on the fuzzy gain scheduling strategy. Combined with the original coordinated control system of the unit, a new coordinated scheme was designed based on condensate throttling for control optimization. The scheme was then applied to a 350 MW unit, and the model established was subsequently verified with actual operation data. Results show that the new coordinated system designed for control optimization can effectively improve the dynamic performance of the unit while ensuring safe operation of the unit, which makes up for the shortcomings of the too low response rate of the coordinated control system during initial variation of load.
    • Monitoring and Measurement
  • Monitoring and Measurement
    Fault Diagnosis of a Wind Turbine Gearbox Based on Empirical Wavelet Transform and Correlation Dimension
    YE Kehua, LI Chun, HU Xuan
    2021, 41(2): 113-120. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.005
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    Aiming at the nonlinear and instable characteristics of gearbox fault signals, a method was proposed based on empirical wavelet transform (EWT), correlation dimension (CD) and support vector machine (SVM) for fault diagnosis of the wind turbine gearbox. Firstly, EWT was used to decompose the vibration signal into several intrinsic mode functions (IMFs). Then, G-P algorithm was adopted to obtain the correlation dimensions of each group of IMFs. Finally, the correlation dimensions were taken as the input parameters of the SVM to diagnose the fault. Results show that the correlation dimension of the vibration signal is positively correlated with the embedding dimension. The correlation dimension of a normal signal is slightly different from that of a fault signal, which could be accurately identified and classified by the SVM, proving the method proposed to be effective in extracting the nonlinear characteristics of the fault, with a diagnostic accuracy up to 100%.
  • Monitoring and Measurement
    Feature Extraction for Cavitation Acoustic Emission Signals of Hydraulic Turbines Based on Optimized VMD
    LIU Zhong, LIU Zhen, ZOU Shuyun, CHEN Ying, JIANG Ying
    2021, 41(2): 121-128. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.006
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    To solve the problem that the number of decomposition modes and the penalty factor in VMD algorithm have significant influence on the decomposition result, and the above two parameters are difficult to be determined, a hybrid search optimization VMD method by grey wolf optimization (GWO) and cuckoo search (CS) algorithm was proposed, which takes the envelope entropy difference cross-correlation number as the fitness function, the minimum global fitness value as the optimization goal, to select the best combination of VMD parameters. Using the optimized VMD in characteristic analysis of acoustic emission signals under hydraulic turbine cavitation conditions, the relationship between the energy of intrinsic mode function (IMF) and the cavitation coefficient was obtained to reflect the development of turbine cavitation. Results show that:with the decrease of cavitation coefficient, the energy of major IMF increases, exhibiting the development process of cavitation in hydraulic turbines growing out of nothing and from weak to strong, proving the optimized VMD method to be effective in cavitation analysis of hydraulic turbines.
    • Engineering Thermophysics
  • Engineering Thermophysics
    Numerical Simulation on Condensation Heat Transfer Process of Wet Flue Gas
    LI Jian, ZHANG Li
    2021, 41(2): 129-172. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.007
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    To study the condensation heat transfer process of wet flue gas, the method of computational fluid dynamics (CFD) was used to simulate the heat transfer process in a wet flue gas condenser, so as to obtain the distribution of velocity field, pressure field, temperature field and heat transfer coefficient in the condenser, which was subsequently applied to a 330 MW subcritical coal-fired power unit. Results show that the simulation results are basically consistent with the actual operation data of the condenser. This may serve as a design basis for similar facilities.
  • Engineering Thermophysics
    Experimental Study and Mechanism Analysis of Acoustic-enhanced Heat Transfer
    YANG Yanfeng, JIANG Genshan, XU Weilong, JIANG Yu
    2021, 41(2): 136-143. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.008
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    To explore the mechanism of convective heat transfer of copper sphere under the action of sound wave, an experimental bench was set up to study the effect of sound waves with different sound pressure levels and sound frequencies on the convective heat transfer of the copper sphere. Combined with the action mechanism of sound flow and experimental data, the mechanism of heat transfer enhancement by sound wave was analyzed in depth. Results show that the convective heat transfer coefficient and Nusselt number of copper sphere increase nonlinearly with the increase of sound pressure level, and there exists an optimal sound frequency, when the enhancement of heat transfer is maximized. The relative Nusselt number is affected comprehensively by sound frequency and sound pressure level, which is slightly related to the diameter of copper sphere. For a given sound pressure level, the heat transfer process of sound wave enhanced copper sphere can be roughly divided into four stages:acoustic streaming control region, acoustic streaming and oscillatory flow cooperative control region, oscillatory flow control region and stable region. Finally, the empirical formula of relative Nusselt number in the first three stages is presented.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Numerical Analysis on Flow and Heat Transfer of a Low-temperature Economizer After Bypass Retrofit
    YANG Weiming, YAN Peng, DU Jingdong, WANG Zuo, ZHANG Zhiguo, QIAO Jianjun, LIANG Shuangyin
    2021, 41(2): 144-151. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.009
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    To solve the problem of blockage existing in the low-temperature economizer of a 600 MW thermal power unit, a bypass retrofit scheme was proposed for the economizer. According to the flow characteristics in parallel pipes and the fluid-solid coupling heat transfer theory, numerical simulations were conducted on the low-temperature economizer system with a bypass line added, during which, the pressure drop and heat transfer characteristics of the flue gas were obtained under different inlet flue gas velocities and bypass specifications, while the relationship between the bypass head loss and the flue gas pressure drop was fitted. Results show that keeping the bypass angle constant, as the ratio of bypass flow area increases from 20% to 40%, the improvement coefficient of flue gas fluidity would be increased by more than 20%, which would reduce with the rise of bypass angle. Meanwhile, the flue gas resistance in the system increases with the rise of the bypass head loss.
  • Auxiliary Equipment Technology
    Experimental Study on Inlet Air Flow Characteristics of Direct Air-cooling Fan Arrays Under the Action of Ambient Wind
    KONG Xinbo, LUO Zhiling, FENG Pengyuan, LI Hong, ZHOU Zhenhua, ZHANG Jinxiang
    2021, 41(2): 152-172. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.010
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    Via the platform of direct air-cooling fan arrays established, experimental tests were conducted on the inlet air flow characteristics, based on which, the volumetric flow of the fans was estimated, and subsequently the back pressure of the unit was calculated. Results show that under the action of ambient wind, the volumetric flow of fans in the first array on windward side is significantly lower than that in other arrays. The position of low flow area moves swiftly with the changes of wind direction. The volumetric flow of windward fans decreases with the increase of wind speed, and there is nearly no time delay. Maximum fluctuation of volumetric flow appears in the first array of windward fans. The accuracy of the back pressure model established is 2%-5% higher than that of traditional models. During actual operation of the unit, the back pressure of the condenser in the case with ambient wind is higher than that without ambient wind. The back pressure increases with the rise of wind speed, and the influence of ambient wind is more significant if the ambient temperature and operation load are higher.
    • Environmental Protection Technology and Equipment
  • Environmental Protection Technology and Equipment
    Effects of External Disturbances on CO2 Absorption by TiO2-MDEA Nanofluids
    YANG Liu, KONG Chengdong, ZHANG Zhongxiao, LIU Jian
    2021, 41(2): 160-166. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.011
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    TiO2-MDEA nanofluids with good dispersity were prepared by the two-step method to absorb CO2 in a bubbling reactor, so as to analyze the influence of the mass fraction and size of nanofluids on the enhancement of CO2 absorption and to study the effects of the following three external disturbances on the CO2 absorption enhanced by nanofluids, such as the gas velocity, electromagnetic stirring and ultrasonic vibration, etc. Results show that the enhancement of nanofluids on CO2 absorption is realized by preventing the bubble coalescence to increase the effective reaction area; the mass fraction and the size of nanoparticles can both influence the enhancement effect, and the optimal effect can reach 81.7%. High gas velocity would result in low enhancement effect, while the electromagnetic stirring can promote the enhancement when the mass fraction is around 0.08%. The ultrasonic vibration would significantly inhibit the enhancement of nanofluids.
    • Nuclear Technology
  • Nuclear Technology
    Design of a Core Power Controller for a Small Modular Reactor Based on LQG/LTR Method
    SHI Bo, LI Daixing, GUO Wei, ZHANG Yilin
    2021, 41(2): 167-172. https://doi.org/10.19805/j.cnk ij.c spe.2021.02.012
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    A lumped-parameter model was established for the core system of a reactor according to the principle of dynamics, which was linearizedly processed using the perturbation theory. On this basis, a core power controller was designed based on LQG/LTR method. Taking the NuScale core system of a compact small modular reactor (SMR) as an object of study, the control effects of this controller and traditional PID controller were comparatively analyzed. Results show that the core power controller designed based on LQG/LTR method has better control effect and higher anti-disturbance capability.