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  • 2019 Volume 39 Issue 9
    Published: 15 September 2019
      
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  • Study on Adjustment of Fuel Particle Size for Oxy-fuel Combustion with High O2 Concentration in a CFB Boiler
    YAN Yong, DUAN Lunbo, DUAN Yuanqiang
    2019, 39(9): 693-699.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Numerical models were established for bed material concentration and heat transfer in the furnace of a 1 000 t/h circulating fluidized bed (CFB) boiler according to the gas-solid two-phase flow and heat transfer characteristics to study the variation behavior of the material concentration and heat transfer respectively in conventional air, 21%φ(O2)/79%φ(CO2) and 30%φ(O2)/70%φ(CO2) atmosphere, and subsequently the way to adjust the bed material concentration was proposed by optimizing the particle size of the bed material, thus further improving the in-furnace heat transfer effectiveness. Results show that when the combustion atmosphere is switched from air to 21%φ(O2)/79%φ(CO2), the material concentration distribution and heat transfer coefficient would keep almost unchanged along the height of the furnace; when the combustion atmosphere is switched from air to 30%φ(O2)/70%φ(CO2), the bed material concentration would decrease in the dilute phase due to the reduction of fluidized velocity, which would further lead to the decrease of the heat transfer coefficient. It is available to operate existing CFB boilers in 30%φ(O2)/70%φ(CO2) atmosphere by only optimizing the particle size of bed material without adding extra heating surfaces.
  • Experimental Study on Deviation Adjustment of Reheat Steam Temperatures Under Deep Peak Shaving Conditions
    ZHOU Wentai, WANG Ke, Lü Weizhi
    2019, 39(9): 700-704.
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    To eliminate the deviation of reheat steam temperature on both sides of a boiler during low load operation, the causes leading to the temperature deviation were analyzed by measuring the burner nozzle temperature and pulverized coal density. Results show that the deviation of reheat steam temperature at low load is mainly caused by the uneven distribution of coal powder at mill exit, which produces unbalanced combustion among the burners, and further affects the flame center height around the left and right side walls. At low loads, it is difficult to reduce the difference of ignition distance for all the burners by strengthening the ignition, but it is possible to achieve the consistency by weakening the ignition of partial burners. However, the latter way may result in lowered combustion stability, which needs to be evaluated according to specific furnace conditions in actual application. The fundamental method to solve the problem is to install a coal powder distributor at exit of the coal mill.
  • Damage Assessment of an Ultra-supercritical Steam Turbine Valve Based on R5 Procedures
    ZHOU Jue, CAI Zhenwei, WANG Weizhe
    2019, 39(9): 705-710.
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    Finite element calculations were carried out on an ultra-supercritical steam turbine valve to obtain the distribution of its temperature and Mises stress in startup, stable operation and shutdown processes using Abaqus software, while the results taken from characteristic positions were adopted to implement the damage and life assessment under the interaction of fatigue and creep by applying the damage assessment process in R5 procedures. Results show that the valve has remarkable creep behavior in operation period; great local stress appears in some areas of the valve, and the Mises stress varies greatly in different stages; the single cycle damage at most dangerous position of the valve is 0.014 07, securing the safe operation of the valve for 70 cycles.
  • Effect of Surface Roughness on Heat Transfer Characteristics of Heavy Duty Gas Turbine Airfoils
    HE Lei, HUANG Qihe, ZHAO Lianhui, ZHU Xiaocheng, DU Chaohui
    2019, 39(9): 711-716.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the profile of the first-stage stator blade in a heavy duty gas turbine as an object of study, the effect of surface roughness on heat transfer characteristics of the blade airfoil was researched using the equivalent sand-grain roughness model of commercial software CFX. Results show that the variation of roughness affects little on the time-mean flow field near the airfoil, but under a typical surface roughness of turbine blade, the heat transfer coefficient would be increased by 36.6% and 33.4% respectively on the pressure side and suction side, compared with a smooth surface, indicating enhanced heat transfer effectiveness. Small-scale surface roughness has little effect on the heat transfer of a leading edge, but when the roughness hs gets up to 51 μm, the average heat transfer coefficient would drop by 15%, compared with a smooth surface. According to the one-dimensional model of heat conduction, when the heat transfer coefficient is increased by 30%, the average temperature of the blade metal would be increased by 17 K, resulting in significantly reduced life of the blade.
  • Early Fault Warning for Auxiliary Equipment of Power Plants Based on Multivariate State Estimation and Adaptive Threshold
    NIU Yuguang, LI Xiaobin, ZHANG Jiahui
    2019, 39(9): 717-724.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To effectively identify the faults occurring in the operation of auxiliary equipment, the multivariate state estimation technique was applied for the fault warning of related auxiliaries. The historical state matrix of these auxiliaries was divided into three categories according to the power level of the unit, while typical states were selected to establish submodels based on isometric sampling. For input observation vectors, corresponding estimation vectors were given, and the deviation between them was reflected by a similarity function. Based on interval estimation, the adaptive threshold of similarity degree was designed. Numerical simulations were finally conducted with the data obtained before coal clogging in the medium speed mill of a 350 MW thermoelectric unit. Results show that the model is able to send an early warning 264 s before coal mill tripping, indicating that the method has a high efficiency in fault detection, which helps to reduce the false alarm rate, compared with traditional fixed threshold methods.
  • Research on the Factors Influencing the Angle Scattering Method Measurement of Ultra-low Emission Dust
    DENG Jie, YU Tianze, YANG Bin, CAI Xiaoshu
    2019, 39(9): 725-730.
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    To solve the problem of inaccurate measurement for dust concentration by angle scattering method under ultra-low emission conditions, a simulation model of dust angle scattering was built based on Mie scattering theory. Considering the features of ultra-low emission dust particles, simulated calculations were conducted under different parameters to analyze the effects of following factors on the angle scattering measurement of ultra-low emission dust, such as the laser wavelength, detection angle, relative refractive index, particle size and particle concentration, etc. Results show that the particle size, dust concentration and refractive index have a great influence on the selection of key parameters for the measurement system. The incident wavelength and the detection angle should be determined according to the properties of ultra-low emission particles.
  • Research on Noise Reduction Characteristics of a Slotted Structure at Leading Edge of the Diffuser Blade
    XIAO Pengfei, YANG Ailing, CHEN Eryun
    2019, 39(9): 731-739.
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    The large eddy simulation technology and FW-H method were used to numerically simulate the unsteady turbulent flow field and its far-field radiation noise in a centrifugal blower, so as to analyze the influence law and mechanism of the parameters of slot at leading edge of diffuser blade on the noise features of the blower. Results show that the diffuser with slotted structure could suppress or delay the separation of boundary layer on the surface of diffuser blade, which makes the flow become more uniform and thereby suppresses the origination of flow noise. The noise features of a centrifugal blower are related to the geometrical parameters of the slot at leading edge of the blade. In the case of relative slot length L/C=0.3 and relative slot height h/H=0.1, the total sound pressure level of all measuring points could be reduced by up to 20 dB. It can be seen that the model with fixed relative slot height and variable relative slot length has better noise reduction effectiveness than that with fixed relative slot length and variable relative slot height.
  • Experiment Study on Cement-based Solidification of High-salt Desulfurization Wastewater
    MA Shuangchen, XIANG Yajun, CHEN Jianing, WAN Zhongcheng, ZHANG Jingrui, CHAI Jin
    2019, 39(9): 740-746.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Orthogonal experiments were carried out to determine the optimal mass ratio of various components in the solidified wastewater, and to study the effects of different water samples on the properties of the blocks. Taking the concentrated desulfurization wastewater as the blending medium, the chloride ion binding ability of the solidified desulfurization wastewater was researched. Results show that the optimal mass ratio of the solidified body is as follows:cement:fly ash:high-salt brine:sand=0.97:0.17:0.60:0.98; the Friedel's salt formed by the reaction of Cl- in water with C3A in cement could increase the compressive strength of the blocks; the sulfate in concentrated FGD wastewater reduces the Cl- binding capacity and increases the Cl- leaching rate of the blocks; solidified blocks with high content of free Cl- could be taken as the non-reinforced materials or road stones, etc.
  • Quantum Chemistry Study on the Adsorption of Mercury in Coal-fired Flue Gas by Metal Ion-loaded Biochar
    YAO Yuxing, JIA Li, QIAO Xiaolei, ZHENG Xianrong, FAN Baoguo, JIN Yan
    2019, 39(9): 747-751.
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    A saturated cluster model was established for the washing biochar (WB) loaded with metal ions, based on which, the adsorption process of Hg0 on the surface of modified WB was studied using density functional theory. Results show that metal ions could be stably loaded on the surface of WB; the adsorption of Hg0 on the surface of modified WB is found to be the chemical kind according to the results of adsorption energy and Mulliken charge, and the metal ions could improve the adsorption capacity of WB for elemental mercury.
  • Study on Combustion Characteristics of RDF-Coal Mixtures in a CFB Boiler
    ZHAO Pengbo, LI Nan, YUAN Ye, XIAO Ping, GAO Hongpei, SUN Xianbin, ZHANG Wei
    2019, 39(9): 752-757.
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    Combustion characteristics of refuse derived fuel (RDF) coupled with coal were studied in a 1 MW circulating fluidized bed (CFB) test bench. Results show that, the SO2 emission of RDF-coal mixture 1 is 234.06 mg/m3, while that of Huolinhe lignite is 273.81 mg/m3, indicating that the addition of RDF helps to reduce the emssion of SO2. When RDF-coal mixtures are burned, the NOx emission increases with the rise of RDF blending ratio, and for mixture 3, the NOx emission reaches 350 mg/m3. The N2O emission of mixture 1 decreases with the rise of temperature. The dioxin emission of both mixture 1 and mixture 2 is lower than that specified in relevant national emission standards.
  • Flutter Modeling and Active Control Simulation of Smart Wind Turbine Blades
    ZHANG Wenguang, WANG Yuanyuan, LIU Ruijie, SHEN Yangzhi
    2019, 39(9): 758-764.
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    Taking the NREL 5 MW reference wind turbine with trailing edge flaps as an object of study, an improved aeroelastic model was established for the smart blade considering the unsteady aerodynamics, aerodynamic damping and bend-twist coupling, of which the simulation results were compared with that of FAST platform. Based on the adaptive PID of RBF neural network, an active controller was designed for the trailing edge flap to control the deflection of blade tips under standard turbulent wind conditions. Results show that the accuracy of the improved aeroelastic model is relatively high; the active controller for the trailing edge flap can effectively reduce the fluctuation of the blade tip deflection.
  • Wind Tunnel Experimental Study on the Influence of Sand Accumulation on the Output Characteristics of PV Modules
    ZHAO Mingzhi, SUN Hao, MIAO Yiming
    2019, 39(9): 765-769.
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    Wind tunnel experiments were conducted to study the effects of sand accumulation on the output characteristics of solar photovoltaic (PV) modules at different sand concentrations and wind speeds, so as to plot the output characteristic curves at different dip angles, and to compare the power generation efficiency with and without sand accumulation. Results show that at low wind speeds, the power output of all the components at different angles changes slightly between the case with and without sand accumulation, showing a reduction degree below 5%; whereas at high wind speeds, the power output changes significantly between the case with and without sand accumulation, showing a reduction degree in 5%-10%. At installation angles of 30° and 60°, the power output of solar PV modules in pure sand environment presents obvious turning features.
  • Effects of Low-temperature Aluminized Coating on Oxidation Behavior of P92 Steel in Saturated Steam at 650℃
    ZHOU Yongli, LU Jintao, DANG Yingying, YANG Zhen, HUANG Jinyang, YUAN Yong, GU Yuefeng, ZHAO Qinxin
    2019, 39(9): 770-776.
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    An aluminized coating was prepared for P92 steel using low-temperature pack cementation process at service temperatures, while a study was carried out on the oxidation behavior of P92 steel and the aluminized coating in saturated steam at 650℃ by the way of oxidation weight gain, scanning electron microscope and X-ray diffraction analysis. Results show that P92 steel has poor steam oxidation resistance and its oxidation kinetics follow the parabolic law in the first 350 h; the double-layered oxide scales consist of Fe3O4+Fe2O3 outer loose layer and FeCr2O4 inner layer formed during exposure, and the outer loose layer peels off severely after oxidation for 700 h. As for aluminized P92, however, its steam oxidation resistance could be improved significantly due to the formation of a protective Al2O3 film on the surface. The major degradation of aluminized coating is not the consumption of aluminum to grow Al2O3 due to its slow growing-rate, but the inward diffusion of aluminum into the substrate to form AIN phase and the outward diffusion of Fe into the coating to form Fe3Al, thus decreasing the concentration gradient of aluminum from the top surface to the base metal.