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  • 2017 Volume 37 Issue 5
    Published: 15 May 2017
      
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  • Optimal Control of Gas Temperature Deviation in a 660 MW Supercritical Tangentially-fired Boiler
    GUO Anlong, FANG Qingyan, ZHAO Sinan, WU Ying, XIA Yongjun, ZHANG Cheng, CHEN Gang
    2017, 37(5): 341-348.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Aiming at the phenomenon of large gas temperature deviation between the left and right side at furnace outlet of a 660 MW supercritical tangentially-fired boiler, numerical simulation was conducted, and subsequently the results were compared with that of experiment. Results show that the simulation data agree well with experimental values, and the gas temperature deviation is found to be caused by residual rotating air flow, which can be reduced by counterclockwise adjusting the SOFA horizontal swing angle, reducing the opening of secondary air damper and increasing the opening of SOFA damper, etc. After taking above measures, the economy and safety of the boiler are improved.
  • Volatilization and Kinetic Characteristics of Arsenic During Coal Combustion
    ZOU Chan, WANG Chunbo, WANG Hefei, GUO Yongcheng, LI Xinhao
    2017, 37(5): 349-355.
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    To study the effect of different factors on arsenic volatilization, combustion experiments of seven typical coals were conducted in the temperature range of 600-1 300 ℃, while an analysis was carried out on the dynamic characteristics of arsenic during coal combustion. Results show that when the ash contents are not very different, the ratio of arsenic evaporation is greater than 0.6 for high volatile coal, and is less than 0.3 for low volatile coal at two minutes; when the volatile contents are similar, the ratio of arsenic evaporation is negatively correlated with the ash content in coal; temperature greatly affects the arsenic evaporation, and the main evaporation temperature lies in the range of 700-1 000 ℃; when the volume fraction of water vapor gets up to 10%, it would obviously affect the volatilization ratio and speed of arsenic, however, when the volume fraction goes up continuously, the effect would be gradually weakened; the impact of volatile is greater than ash on the activation energy of arsenic volatilization.
  • Modeling Analysis and Experimental Study of a Temperature-difference Type Heat Flux Meter
    GU Rongwei, GAO Jilu, DONG Jianxun, PANG Kaiyu, CHEN Xiaoli, KANG Zhuang, MENG Chenwei, WU Yuxin
    2017, 37(5): 356-360.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on temperature difference method, an ultra-fine high-temperature heat flux meter was designed to measure the heat flux on wall surface of a supercritical boiler, which is able to accurately acquire the heat flux without retrofitting the water wall. To further investigate the heat-transfer characteristics of the meter and optimize its design, modeling analysis and experimental study were conducted to analyze the effects of the thermal conducting component's thickness and hot end temperature on the sensitivity and response time of the heat flux meter via a one-dimensional transient heat-transfer model. Results show that, with the rise of the thickness of relevant thermal conducting components, both the sensitivity and response time increase, thus optimal design parameters can be obtained for the heat flux meter under the premise of optimum sensitivity and response time. Through the calibration of a black-body furnace and field tests, the calculation results are proved to agree well with actual measurements; however, the real response time is longer than calculated one, due to the external environment being not the ideal steady-state boundary condition in calibration.
  • Numerical Analysis of Heat Transfer Characteristics on Turbine Blade Surface Under the Action of Unsteady Wakes
    XUAN Liming, CHEN Liu, YANG Yujun, WANG Jiao, DAI Ren
    2017, 37(5): 361-366.
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    A simulation analysis was conducted on the unsteady flow and heat transfer of a gas turbine stage based on unsteady RANS equations and scale-adaptive turbulent model, so as to study the wake structure of upstream stator blade and analyze its influence on the heat transfer over downstream blade surface under different effects of trailing edge coolant ejection. Results show that the effects of trailing edge coolant ejection on the heat transfer over rotor blade surface mainly come from the spreading of turbulent kinetic energy wake, which increases the time-averaged Nusselt number by about 20% for the rear part of pressure surface, while its impact on suction surface can be neglected. The wake with coolant ejection enhances the intensity and scope of disturbance in downstream areas, and increases the amplitude fluctuation of downstream blade surface heat transfer. This feature becomes more obvious with the rise of momentum ratio and velocity of coolant ejection; for the momentum ratio of 1, the fluctuation in amplitude would be twice of that without trailing edge coolant ejection.
  • Effects of Impeller Twisting Law on Performance of the ORC Radial Inflow Turbine
    WANG Zhi, YIN Libing
    2017, 37(5): 367-372.
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    A 200 kW radial inflow turbine was thermodynamically and structurally designed by taking cyclohexane as the working medium, of which the internal flow was numerically studied, so as to analyze the effects of impeller twisting law on the performance of the turbine. Results show that the radial inflow turbine previously designed has good flow characteristics under transonic conditions. The twisting degree may affect the flow path profile of the impeller and the angle between the outlet gas flow and the axial direction. Meanwhile the maximum value of the wheel efficiency change may reach 2.44% under different impeller twisting laws, and the twisting law is an important factor influencing the structural design optimization of the impeller.
  • Bearing Fault Feature Extraction for a Direct Drive Wind Turbine Using Multi-scale Enveloping Spectrogram
    TENG Wei, JIANG Rui, ZHANG Yangyang, LIU Yibing, MA Zhiyong
    2017, 37(5): 373-378.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Considering the features of low rotational speed and heavy load of direct drive wind turbines, the multi-scale enveloping spectrogram (MuSEnS) is proposed for the diagnosis of actual wind turbines and for the feature extraction of faulty bearings, which is the envelop spectrum of transform results by processing the original vibration signal using complex wavelet transform. Diagnosis results show that the MuSEnS can effectively detect the weak faulty feature of bearing hidden in background noise, because it has the ability of simultaneous multi-scale decomposition and envelope demodulation. Comparing with conventional demodulation analysis, the MuSEnS is more intelligent and accurate, which can be applied to the fault diagnosis of actual wind turbines.
  • Ultrasonic Defect Recognition for Circumferential Joints of Welded Rotors Based on PSO-SVM Model
    DU Biqiang, SUN Lijiang
    2017, 37(5): 379-385.
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    An algorithm was proposed for defect recognition in circumferential joints of welded rotors based on PSO-SVM model. First, the denoised ultrasonic defect echo signals were decomposed by four layers wavelet packet and node reconstruction. Then, the form factor and crest factor were extracted from the approximate portion of node reconstructed signals, on which basis, the sample feature vector was formed in combination with the ultrasound integral value and the absolute value of variance as well as the RMS in details. Finally, the particle swarm optimization (PSO) algorithm was used to optimize the penalty factor and kernel function of support vector machine (SVM), thus completing the defect recognition. Results show that the PSO-SVM model has good recognition performance in the prediction of samples. Comparing with other commonly used SVM models, the PSO-SVM model has advantages in both recognition rate and recognition time.
  • Numerical Analysis on Heat Transfer and Pressure Drop Performance of an Asymmetric Finned Tube Heat Exchanger
    REN Zhiwen, MA Ting, ZENG Min, WANG Qiuwang
    2017, 37(5): 386-393.
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    A three-dimensional model of asymmetric finned tube heat exchanger was established on the basis of COMSOL software, so as to implement numerical study on the flow and heat transfer performance on the air side, then compare it with plain finned tube heat exchanger, and finally to further analyze the effects of inclined angle on the performance of the asymmetric finned tube heat exchanger under different Reynolds numbers. Results show that, compared with plain finned tube heat exchanger, the heat transfer factor of asymmetric heat exchanger is 13.95% higher on average when the Reynolds number varies in 3 239-9 700. The larger the Reynolds number is, the lower the friction factor would be, with an average reduction of 4.80%, and the reducing trend enhances under high Reynolds numbers. Taking MJF as the evaluation criteria and keeping other structural parameters unchanged, the MJF reaches the maximum at β=30°, when optimum comprehensive performance of the heat exchanger is obtained.
  • Research on Optimal Layout of a Fluoroplastic Heat Exchanger Based on Modularization
    XU Gang, CHEN Yuan, NIU Chenwei, MA Ying, LIU Wenyi, REN Yingjie, WANG Yi
    2017, 37(5): 394-400.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A design calculation was implemented for a fluoroplastic heat exchanger set before desulfurizer in the media gas-gas heater (MGGH) system of a 1 000 MW thermal power unit, while an optimal layout of the fluoroplastic heat exchanger was researched based on modularization in terms of gas-water crossover times. Results show that the water-side resistance is in direct proportion to the square of crossover times. The total external heat exchange area, the gas-side pressure drop, the total number of header connectors as well as the number of header connectors in the modular unit reduce with the rise of gas-water crossover times. When the number of crossover times increases from 2 to 4, the above-mentioned parameters significantly reduce, and when the number rises continually, the reducing tendency lowers gradually, i.e. optimum heat exchange performance and optimum resistance characteristics of the fluoroplastic heat exchanger as well as reasonable structure of related headers can be obtained for the crossover times of 4. Considering the thermal expansion factor, double U-shaped heat exchange modules in W-shape arrangement are recommended for the fluoroplastic heat exchanger.
  • Research and Application of the Robust Fuzzy Tree Method
    ZHANG Wenguang, ZHANG Yue
    2017, 37(5): 401-407.
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    Aiming at the problem that the noise is unavoidable and difficult to predict in actual engineering projects, a weighted fuzzy tree (W-FT) algorithm was proposed by utilizing the weighted least squares method based on local outlier factor (LOF) to replace the ordinary least squares method to learn the consequent parameters of the fuzzy rules, which were subsequently validated by two typical nonlinear examples. Meanwhile, a soft sensor model was established based on W-FT for NOx emission of boilers, and was then compared with other modeling methods. Results show that the proposed W-FT algorithm can effectively recognize the noise and outliers, and the models built on the basis of W-FT have higher prediction accuracy and stronger generalization capacity.
  • Effects of Flue Gas Velocity on the Formation of Turbulent Vortex and the Coagulation of Fine Particles
    CHEN Yawei, XIONG Yangheng, PAN Zuming, ZHOU Jianlong, ZHOU Meng
    2017, 37(5): 408-412.
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    A simulation was conducted on the collision and coagulation of particles flowing in the flue duct before electrostatic precipitator of a power plant under full load conditions using Eulerian-Lagrangian method and O'Rouekr collision model. Results show that, the higher the flue gas velocity is at the coagulator inlet, the larger the turbulent intensity and vorticity will be, which is favorable for the reduction of small particles, but in a limited degree; whereas, the higher the flue gas velocity is at the coagulator inlet, the shorter the residence time of particles will be in the coagulation zone, and the smaller the particles will be formed by collision and coagulation, which is unfavorable for the formation of large particles. Within the common range of flue gas velocity in a power plant, the increase of flue gas velocity at the coagulator inlet has a negative impact stronger than positive impact on the turbulence coagulation.
  • Moving Trajectory Simulation of Particles and Modeling of the Complex Coagulation Based on Swirl and Acoustic Wave
    LIU Dingping, LUO Weile
    2017, 37(5): 413-417.
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    To improve the probability of collision and coagulation among ultrafine particles, a tangential swirl coagulation device was developed, in which the flow field and particles moving trajectory were simulated using discrete particle model (DPM), so as to analyze the influence of swirl velocity, particle size and acoustic wave on the moving trajectory of particles. Results show that the tangential swirl has good swirling and mixing effects that benefit for the collision and coagulation of ultrafine particles; the higher the swirl velocity is, the stronger the swirling effects will be on the particles, leading to easier collision and coagulation among particles. Ultrafine particles of large sizes are subjected to large centrifugal force, which are more likely to mix with the seed particles, while those of small sizes are subjected to small centrifugal force, which are more likely to mix with the ultrafine particles of similar sizes. Acoustic wave can enhance the relative motion among particles of different sizes, which make ultrafine particles easier to collide and coagulate with the seed particles.
  • Layout Optimization of the Wind Farm in a Wind Power Station Based on Actuator Line Method
    WANG Yuanbo, LI Chun, MIAO Weipao
    2017, 37(5): 418-424.
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    Based on actuator line method, numerical simulations were conducted on the wind farm with three 5 MW wind turbines in five different aligned arrangements using OpenFOAM. By comparing the total power output, the velocity fields and velocity profiles at the hub height of wind turbines for different wind farm layouts, the effects of upstream turbine wake on the downstream wind turbine were investigated. Results show that in an aligned arrangement, the power output may be reduced by 82.72% for the wind turbine lying in the wake. Changing the relative position of wind turbines reasonably could help to optimize the wind farm layout, when the total power output may be increased by a maximum of 11.8%, even if the output of an individual wind turbine declines somewhat.