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  • 2016 Volume 36 Issue 6
    Published: 15 June 2016
      
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  • Slagging Analysis and Retrofit of a Refractory Belt in the 600 MW W-flame Boiler
    YANG Fan, ZHU Guangming, DING Changfu, DUAN Xuenong
    2016, 36(6): 421-427.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem of heavy slagging existing in the side-wall refractory belt of a 600 MW W-flame boiler, a retrofit was carried out by removing partial area of the refractory belt so as to reduce the temperature of the side wall, and thus to alleviate the slagging condition. Meanwhile, numerical simulations were conducted on the in-furnace velocity field and temperature field using CFD software under different working conditions, following which the simulation results were compared with experimental data in order to validate the accuracy of the calculation model. In addition, causes leading to slagging on the side wall of lower furnace were comprehensively analyzed based on actual operation conditions. Results show that the slagging is caused by the deviated pulverized-coal flow to side wall due to low pressure there and is aggravated by too high side-wall temperature, which could be alleviated by cutting partial area of the refractory belt to reduce the side-wall temperature.
  • Study on Heat-transfer Behavior of High-temperature Convective Heating Surfaces in a Pressurized Oxy-fuel Boiler
    GAO Zhengyang, ZHAO Hang, YANG Pengfei, MENG Xinxin, YIN Libao, LIAO Yongjin
    2016, 36(6): 428-435,460.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 300 MW coal-fired boiler as the object of study, physical properties of the boiler flue gas were studied using Aspen Plus software respectively under air, oxy-fuel and pressurized oxy-fuel combustion conditions, while the gas velocity, logarithmic mean temperature difference, heat-transfer coefficient, temperature distribution among tube coils and steam enthalpy rise in tube coils were numerically simulated for areas around the high-temperature reheater and superheater using Fluent software combined with discrete-ordinates radiation model (DOM). Results show that the heat-transfer coefficient of above heat exchangers increases in the process of changing combustion atmospheres step by step from conventional air to oxy-fuel and to pressurized oxy-fuel conditions. Compared with the air atmosphere, smaller thermal difference exists in tube coils under oxy-fuel and pressurized oxy-fuel combustion conditions, when local overheating may occur at tube bends of the heat exchanger. With the rise of gas flow rate, the heating area required for the same amount of heat exchange reduces, and the trends of heating surface variation reduces as well, under the pressurized oxy-fuel combustion conditions, in which case, some of the heat exchangers have to be moved up to the furnace top to achieve safety and stable operation of the boiler.
  • Solutions for Abnormal Vibration Faults in Boiler Water Walls
    ZHOU Hao, ZHU Guodong, HUANG Yan, WANG Hengdong, ZHOU Kang
    2016, 36(6): 436-441,460.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To overcome the abnormal vibration faults frequently occurring in boiler water walls that may affect the safety operation of the boiler, vibration characteristics of a 60 MW boiler furnace were experimentally studied and numerically simulated with Ansys software, after which vibration suppression measures were proposed and implemented, such as adding pulling bars to enhance the stiffness of rigid beams, and hanging the soot blowers to reduce the concentrated mass, etc. In addition, inherent frequencies of boiler water walls before and after retrofit, and also the vibration displacement of each measuring point under circumstance of forced vibrations, were obtained via numerical simulation. Results show that the vibration displacement can be reduced by a maximum of 84.3% and 79.2% respectively in simulated scheme and actual measurement.
  • Study on a Thermal Expansion Self-compensation System for Wetness Measurement of Moist Steam Based on Microwave Resonator
    ZHANG Shue, MENG Xiangai, HAN Zhonghe
    2016, 36(6): 442-447.
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    The effects of thermal expansion on resonant cavity sensor in the process of steam wetness measurement by microwave perturbation method were studied, after which a thermal expansion correction scheme was established for the system at working frequencies, while a dual-chamber wetness measurement system with thermal expansion self-compensation function was put forward. In the environment where resonant cavity sensor was thermally expanded, the steam wetness was measured respectively in dual-chamber and single-chamber system, and subsequently their results were analyzed and compared with focus on the action of thermal compensation. Results show that the thermal expansion self-compensation dual-chamber system can achieve high accuracy on-line measurement of steam wetness, with an error of about ±1%, and a thermal compensation capacity 40 times of the existing single-chamber measurement system, proving the frequency correction method to be effective.
  • Application of Improved VMD Method in Fault Diagnosis of Rotor Systems
    LIU Shangkun, TANG Guiji
    2016, 36(6): 448-453.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To diagnose the oil film instability of rotor systems and to solve the problem of end effect occurring in variational mode decomposition (VMD), an improved VMD method was proposed based on mutual information criterion to match the waveform and to extend the endpoints, so as to judge the instability status of the oil film by analyzing the Hilbert time-frequency spectrum of each component. Results show that the proposed method has strong decomposition capability to multi-component signals and has good inhibiting ability on the end effect, which is able to diagnose the occurrence moment and subsequent development of oil whirl. When the first-order oil whip occurs in a single disc rotor, the rotation frequency and whip frequency would become prominent in the spectrum, with simultaneous occurrence of their combination frequency components. Above research results may serve as a reference for accurate diagnosis of oil film instability.
  • Early Fault Warning of Power Plant Fans Based on MSET and the Deviation Degree
    LIU Tao, LIU Jizhen, LÜ You, CUI Chao
    2016, 36(6): 454-460.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To realize early fault warning of power plant fans, a method was proposed based on multivariate state estimation technique (MSET) and the deviation degree. Using MSET, a non-parametric model of the fan was constructed under normal operation conditions, based on which observed vectors were optimally evaluated to obtain the estimated vectors, and the difference between estimated and observed vectors is able to reflect the incipient failure. A deviation degree was introduced to quantify the difference between estimated and observed vectors, so as to capture the fault development process, and to send out early warning for relevant operators to deal with the trouble, when the average deviation has exceeded the predefined threshold set by sliding window method. The method was applied to detect the fault of an induced fan in a power plant in Changchun. Application results show that the method can help to discover abnormal status of fans promptly, and achieve the purpose of online early fault warning of fans.
  • Effects of Cu Loading Content on the Phase of Cu-ZSM-5 Catalyst and Its Performance in Fast SCR Reaction
    WANG Yongqiang, SUN Baomin, XIAO Haiping, YANG Xiaochu, WANG Yang, TIAN Sida, WEI Shuzhou
    2016, 36(6): 461-467,485.
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    Cu-ZSM-5 catalysts with different Cu loading contents were preprared by incipient-wetness impregnation method, of which the physical and chemical properties as well as their fast SCR reactivities were experimentally studied, while tests for temperture programmed desorption (TPD) of NO and NO/NO2 were conducted on these catalyst samples to analyze the NO2 content on the denitrification efficiency. Results show that element Cu disperses on the molecular sieve mainly in the form of CuO; large crystal grains of CuO would aggregate in the samples when the Cu loading content is more than 8%, and no obvious CuO crystals would be detected if the Cu loading content is less than 8%; the presence of NO2 can improve the denitrification efficiency, and Cu zeolite catalyst has good anti-sulfur performance. By using fast SCR technology, the denitrification temperature can be reduced, and among all the catalyst samples, the one with 8% Cu loading content exhibits the most excellent performance, with a denitrification efficiency up to 93%, at the temperature of 200 ℃.
  • Influence of Structural Elasticity on Aerodynamic Performance of a Wind Turbine During Pitching Step
    LIU Chong, LIU Pengyin, SHEN Xin, ZHU Xiaocheng
    2016, 36(6): 468-472,492.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Numerical simulations were conducted on aerodynamic performance of a wind turbine during pitching step, while the effects of blade asymmetry, blade elasticity and tower elasticity on aerodynamic performance of the wind turbine were analyzed, and the overshoot phenomenon of turbine aerodynamic performance occurring in pitching step was simulated. Results show that the mass imbalance of two blades is the main reason leading to the rotor torque vibration before and after pitching step, and the structural elasticity of blade structure aggravates the rotor torque oscillation during overshoot. The fluctuation of axial thrust is caused by combined action of the imbalanced rotor, the elastic blade and tower structure, etc.
  • Influence of Deformable Trailing Edge Flap on Aerodynamic Performance of the Wind Turbine Airfoil
    HAO Wenxing, YE Zhou, DING Qinwei, LI Chun
    2016, 36(6): 473-479.
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    Parametric programming was adopted on the modeling of deformable trailing edge flap (DTEF) to realize its flexible deformation and control, based on which numerical simulations were conducted to analyze the effects of DTEF on aerodynamic performance of the wind turbine airfoil and to study its flow mechanism respectively under static and dynamic conditions. Results show that under static conditions, the angle of flap affects the lift coefficient and drag coefficient obviously; with the rise of attack angle, the ability of DTEF reduces in changing the aerodynamic performance of the airfoil, and its influence on neighboring flow field weakens accordingly. Swing DTEF makes the change of lift coefficient of airfoil lags the change of flap angle, with reduced ability of DTEF on the control of lift coefficient; whereas swing DTEF makes the change of drag coefficient leads the change of flap angle, with enhanced ability of DTEF on the control of drag coefficient; these unsteady effects of flap oscillation are enhanced with the decrease of the oscillation cycle, reflecting in the variation of surface pressure coefficient of airfoil and in the development of wake vortex.
  • Optimization on Water Gas Shift Process in IGCC Power Plant
    ZHAN Zhigang, XU Qisheng, WEN Zhiyong, LI Fangyong, CHENG Mingtao, HAN Long, WANG Qinhui
    2016, 36(6): 480-485.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A novel water gas shift (WGS) process was proposed, where the heat released in WGS reaction can be utilized to heat the syngas before entering into the gas turbine, while a process model was set up for the whole integrated gasification combined cycle (IGCC) unit using Aspen Plus software, based on which the effects of pre-combustion CO2 capture on the power output, auxiliary power consumption rate and plant net efficiency of the unit were evaluated, and simultaneously the variation of two key parameters of the novel WGS process and their influences on the unit performance were analyzed. Results show that it is beneficial to decrease the auxiliary power consumption rate and increase the plant net efficiency by reducing the mole ratio of H2O/CO in syngas that entering into WGS reactor and by increasing the final heating temperature of syngas. These findings agree well with those of previous studies. By adopting the optimized operating parameters for the WGS process, the auxiliary power consumption rate and the plant net efficiency are respectively decreased by 1.3% and increased by 2.7%.
  • A Universal Energy-saving Technology in Coal-fired Power Plant: Low-temperature Coal Pre-drying
    ZHAO Shifei, XU Gang, WANG Chunlan, DONG Wei, XU Cheng, YANG Yongping
    2016, 36(6): 486-492.
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    A concept of low-temperature coal pre-drying was proposed for coal-fired power plants, while the changes in equipment configuration and auxiliary power consumption were discussed after application of the pre-drying technology. The effects of moisture content in coal on its low heating value (LHV) and on thermodynamic performance of the unit were comprehensively analyzed. Taking the low heating value of typical raw coal and the coal consumption rate of power supply as an example, their changes after application of low-temperature coal pre-drying were calculated. Results show that the LHV of coal would be increased by 1.2%-1.5% and the coal consumption rate would be reduced by 0.3-0.6 g/(kW·h), for every 1% drop of moisture content in coal, using waste heat as the drying source, without considering the energy consumption of auxiliaries, indicating remarkable energy-saving effects. Featured by simple structure and controllable investment, the low-temperature coal pre-drying technology is a very promising and effective energy-saving method, which is universally applicable to coal-fired power plants.
  • Experimental Study on Low-velocity Flow Boiling Heat Transfer in a 3×3 Rod Bundle
    ZHOU Yunlong, ZHANG Chao, LI Hongwei, YANG Di, HOU Yandong
    2016, 36(6): 493-497.
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    Taking deionized water as the working medium, experimental studies were conducted on flow boiling heater transfer in a 3×3 rod bundle at an inlet temperature of 80-100 ℃, a mass flow rate of 0-100 kg/(m2·s), and an inlet pressure of 0.1 MPa, so as to analyze the effects of mass flow rate and heat flux on the flow boiling heat-transfer coefficient, and to investigate the heat-transfer characteristics in various sub-channels. Four correlations were adopted to predict the flow boiling heat-transfer coefficient, including Liu-Winterton, Kandlikar, Gungor-Winterton and Chen, etc., and subsequently their prediction results were compared with experimental data, which were simultaneously evaluated using three statistic indicators. Results show that the predicted values of Liu-Winterton, Kandlikar, and Chen correlation are relatively lower than the experimental data, in which the error of Chen correlation is the highest, while Gungor-Winterton correlation is the most accurate one among all the four correlations.
  • Research on Aerodynamic Performance and Separating Property of Corrugated Plates for Moisture Separators
    ZHU Youjun, YANG Xiao
    2016, 36(6): 498-504.
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    Based on the model of differently-structured corrugated plates for moisture separators of nuclear power plant, numerical simulations were carried out by computational fluid dynamics (CFD) technique, so as to analyze the flow characteristics in the moisture separator, and to compare the simulation results with experimental data. Results show that the numerical simulation agrees well with the experimental measurements, proving the numerical way to be effective in simulation of relevant flow fields in moisture separators. The flow separation is found to the main cause leading to the pressure loss.