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  • 2016 Volume 36 Issue 3
    Published: 15 March 2016
      
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  • Experimental Study on Lateral Dispersion Coefficient of Solid Particles in a CFB Boiler
    HU Nan, GUO Zhaojun, YANG Hairui, LÜ Junfu, PEI Yufeng
    2016, 36(3): 168-171,206.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The effect of gas velocity on lateral dispersion coefficient in dense zone of a 300 MW single-furnace CFB boiler was investigated in a 1:10 scale test setup by taking hot solids as the tracer particles. A new correlation of dispersion coefficient was fitted through the data from current study and former investigation, with which the lateral dispersion coefficient of solid particles in large CFB boilers was predicted. Results show that the dispersion ability weakens and the lateral dispersion coefficient reduces with the rise of gas velocity. For CFB boiler of different sizes, the lateral dispersion coefficient in dense zone lies in 0.06-0.4 m2/s under various working conditions.
  • Numerical Simulation of Oxy-fuel Combustion Characteristics in a 300 MW Coal-fired Boiler
    GE Xueli, WU Xiaojiang, ZHANG Jianwen, FAN Haojie, ZHANG Zhongxiao
    2016, 36(3): 172-177.
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    Taking the 300 MW coal-fired boiler as an object of study, the models for reaction mechanism, physical parameters and heat transfer of the combustion process were revised, so as to comparatively investigate the temperature field in the furnace and the carbon content in the pulverized coal by numerical method respectively under air and oxy-fuel combustion conditions. Results show that the reaction mechanism and physical parameters have significant influence on the oxy-fuel combustion, when the ignition of pulverized coal is delayed, and the shape of the flame is narrowed and elongated. With the rise of oxygen concentration, the residence time of coal particles in the furnace reduces while the burnout rate increases. Compared to air combustion conditions, the peak temperature of flue gas and coal particles decreases, the heat-transfer capability reduces and the height of flame center moves upward under oxy-fuel combustion conditions. When the oxygen concentration increases from 26% to 29%, the oxy-fuel combustion has a good agreement with the air combustion in trends of temperature variation. The capacity of heat transfer calculated by numerical simulation is 4%-11% lower than that by thermal calculation.
  • SVM Time Series Prediction Model for Active Control of Thermoacoustic Instability
    ZHOU Hao, DING Fang, HUANG Yan
    2016, 36(3): 178-184.
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    To overcome the time delay problem of present thermoacoustic active control system, a method of fuzzily predicting the time series of thermoacoustic instability was proposed using support vector machine (SVM). In the self-developed Rijke tube thermoacoustic instability test bench, the experiments of speaker disturbance were conducted to capture the dynamic pressure sequence under thermoacoustic oscillation, and to build the input and output datasets using phase space reconstruction theory, following which a prediction model was established by SVM and verified with test datasets, and the effects of embedding dimension and time delay on prediction accuracy of the model were qualitatively analyzed. Results show that via the model, high prediction accuracy can be achieved, and the coefficient of determination can get up to 0.95 even if the time delay is large, indicating high degree of fitting, proving the time series prediction method to be effective.
  • Analysis on Contact Status and Vibration Characteristics of Last Stage Rotor Blades in Ultra-supercritical Steam Turbines
    CHEN Haiyan, ZHANG Yanchun, FAN Wei
    2016, 36(3): 185-190.
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    For the structure of damping lacing wire and interlocked shroud generally used in the last stage rotor blades of ultra-supercritical steam turbines, a 3D nonlinear contact model was established, based on which numerical simulation was conducted on the strength and vibration of a certain homemade blade using finite element method, so as to analyze the torsional deformation of blades under different mounting clearance between of lacing wire to lacing wire and shroud to shroud, and to obtain the variation law of their contact status with rotating speed, and the effects of above nonlinear contact on the vibration characteristics according to the design value of clearance. Results illustrate that the nonlinear contact of lacing wire to lacing wire and shroud to shroud has significant effects on torsional deformation and dynamic frequencies of the blade. The stiffness and dynamic frequencies of the blade can be altered by changing the structure of lacing wire and shroud as well as their mounting clearance.
  • Experimental Study on Upstream Endwall Film Cooling at Leading Edge of Gas Turbine Blades
    JIANG Wencheng, ZHAO Zhijun, LI Shuyuan
    2016, 36(3): 191-195,226.
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    To study the upstream endwall film cooling effectiveness at leading edge of gas turbine blades, experimental tests were conducted in a low-speed high-temperature wind tunnel test rig using infrared thermal imaging technology, so as to obtain the temperature distribution around endwall film holes at different blowing ratios and Reynolds numbers. Results show that both the film cooling effectiveness and the film cooling range increase with the rise of blowing ratio. The leading edge cooling range on suction surface would be larger than on pressure surface when the blowing ratio is more than 1.2. The endwall film cooling effectiveness of main stream at high Reynolds numbers would be better than at low Reynolds numbers.
  • Error and Range in Measurement of Inhalable Particle Sizes by Acoustic Entrainment Method
    YANG Xufeng, FAN Fengxian
    2016, 36(3): 196-200.
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    Based on the dynamic model for particles subjected to both the Strokes force and unsteady force in a horizontal standing wave acoustic field, the error and range in measurement of particle sizes by acoustic entrainment method were numerically studied. Results show that for a specified size of particles, there exists an optimal acoustic frequency corresponding to zero error of particle size measurement; when the acoustic frequency is lower or higher than the optimal one, the measured value would be accordingly larger or smaller than the true value. As the particle density increases, the measurement error decreases rapidly, and finally the error approaches to zero. Both the upper limit and lower limit of the measurement range reduce with the increase of acoustic frequency, resulting in decreased range of particle size measurement. As the acoustic intensity increases, the upper limit of the measurement range increases but the lower limit keeps constant, thus the measurement range increases.
  • Ultrasonic Measurement of Pulverized-coal Concentration in Power Plant Pipelines
    LI Yongming, SU Mingxu, ZHOU Jianming, YUAN Anli, CAI Xiaoshu
    2016, 36(3): 201-206.
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    An ultrasonic method including a one-piece ultrasonic probe with 31 kHz center frequency was proposed for measurement of pulverized-coal concentration in power plant pipelines. Based on the model of acoustic scattering theory, the relationship between ultrasonic attenuation coefficient and pulverized-coal concentration was fitted by numerical simulation. The method was applied to measure the pulverized-coal concentration in different depths of the conveying pipeline in a power plant. Corresponding acoustic attenuation values were acquired by analyzing the oneline measurements of ultrasonic signals, then the pulverized-coal concentration was obtained based on analysis of the relationship between the ultrasonic attenuation coefficients and the pulverized-coal concentration. Results show that there exists a linear relationship between the ultrasonic attenuation coefficient and the pulverized-coal concentration; the volumetric concentration of pulverized coal in the test section of pipeline lies in 0.09%-0.14%. Therefore the proposed method may serve as a reference for online measurement of pulverized-coal concentration in power plant pipelines.
  • Soft-sensing of Primary Air Flow in a Coal Mill Based on LSSVM
    YANG Yaoquan, ZHANG Xinsheng
    2016, 36(3): 207-212,217.
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    To solve the problem that the off-line soft-sensing model for primary air flow in coal mill of a power unit can not satisfy the requirement of variable load operation, a dynamic soft-sensing model based on LSSVM was proposed, which is able to adaptively modify the model parameters by taking the total prediction error as a threshold to update the model parameters in real time without any manual work according to the load variation. Two optimal parameters of LSSVM model were obtained by grid search and PSO algorithm. The model was trained with actual operation data of a power plant, and was then used to dynamically predict the primary air flow. Results show that the LSSVM soft-sensing model is reasonable and accurate (maximal error less than 1.5%), with good real-time performance, which is able to realize real-time prediction of the primary air flow, and therefore may serve as a reference for on-line monitoring of the primary air flow in coal mills.
  • Prediction on Mean Residence Time of Ash Particles Rolling Down the Surface of a Rotary Ash Cooler
    JIA Jiandong, LIU Hantao, SU Tiexiong, ZHANG Peihua, MA Liqiang, FAN Zeming
    2016, 36(3): 213-217.
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    Using the particle trajectory model and considering the slag fall time, a mathematical model was established for the mean residence time of ash particles rolling down the surface of a rotary ash cooler, which was compared and verified with previous models and experimental data. The model was used to analyze the effects of following factors on the pgun, such as the drum diameter, the roller speed, the roller angle, and the ratio of slag bed height to drum diameter h0/R, etc. Results show that the model is more accurate and the pgun can be improved by increasing the drum diameter, the roller speed and the roller angle, and by reducing the value of h0/R, in which the drum diameter and roller speed have great influence.
  • Effect of Relative Circumferential Position Between Abnormal Blades on Performance of a Variable-pitch Axial-flow Fan
    YE Xuemin, WANG Feng, DING Xueliang, LI Chunxi
    2016, 36(3): 218-226.
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    Taking a two-stage variable-pitch axial-flow fan as an example, a 3D steady numerical simulation was performed to study the effect of 4 relative circumferential positions between abnormal blades located separately in two impellers on the fan performance and internal flow dynamics. Results show that for smaller deviation of blade installation angle Δβ, the full pressure under abnormal cases is approximately same as under normal case, while the efficiency declines slightly. With the increase of Δβ, the regular distributions of total pressure and turbulence energy on impeller exit sections are disturbed notably, and the intensity of turbulence energy is generally augmented, resulting in deteriorated distribution of full pressure and reduced efficiency, especially in low flowrate regions. Generally, the fan performance and flow characteristics are affected mostly by relative circumferential position between abnormal blades F1 and S2, followed by that between abnormal blades F1 and S1, and minimally by that between abnormal blades F1 and S3.
  • Experimental Study on SO2 Removal with Renewable Organic Amines
    XU Hongjian, JIN Jizhao, SUN Yaping, WANG Meixia, PAN Weiguo
    2016, 36(3): 227-235.
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    Absorption experiments were performed in a bubbling system to study the effects of four different organic amines on the wet flue gas desulfurization, while desorption experiments were conducted in an oil-bath heating device to analyze the desorption effects of the four organic amines. Results show that the desulfurization rate of above organic amines declines with the variation of time following the order below:piperazine> ethylenediamine> DEA> MDEA; whereas their desorption rate at same desorption temperatures increases with the variation of time, showing the desorption performance from strong to weak as follows:MDEA> ethylenediamine> DEA> piperazine. Through calculation with thermodynamic parameters, it is found that the Gibbs free energy of MDEA for absorption of SO2 is less than that of limestone, indicating that MDEA is a better desulfurizing agent, with stronger capability in SO2 absorption than limestone.
  • Design of Reactor Core Simulator for ACME Integral Test Facility
    LI Yuquan, CHANG Huajian, YE Zishen, CHEN Lian, WANG Han
    2016, 36(3): 236-241.
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    To experimentally test the passive core cooling system of CAP1400 nuclear power unit, an integral test facility, called ACME, was designed and constructed as a 1/3 height scale model of CAP1400, based on which thermal hydrualic scaling analysis was conducted on the reactor core, so as to determine the similarity criteria for design of the core simulator matching the integral test facility, and to find the optimal design specifications and geometric arrangement of the heater rods contained in the ACME core simulator, by comparing different design schemes and comprehensively considering relevant manufacturing processes and engineering constraints. To support the heater rods against dynamic load induced by turbulent flow during test operation, support plates with quatrefoil supporting holes were designed and installed, where drain holes were also punched, and the dimension of drain holes was determined through resistance calculation, so as to meet the requirements of flow resistance similarity. Results show that the design of ACME core simulator has been successfully verified in processes of manufacturing, assembling, pressure drop calibration and test operation, indicating that the design of reactor core simulator can meet the requirements of integral effect test.
  • Experimental Study on Pressure Drop Characteristics of Fuel Assembly Nozzles
    LI Jiwei, GAN Fujun, ZHENG Yixiong, ZHANG Chaozhu, ZHU Libing, GU Hanyang
    2016, 36(3): 242-246.
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    To measure the pressure drop in top and bottom nozzles of CAP1400 fuel assembly, experimental tests were conducted, after which the coefficient of resistance and the uncertainty of measurement were obtained through data processing with the appropriate method proposed, while a comparison and an analysis were performed between above test results and the data of reference test pieces. Results show that the frictional pressure drop of test specimen can be ignored; the relative expanded uncertainty of resistance coefficent for both the CAP1400 and the reference top and bottom nozzles are all lower than 1.5%; the resistance coefficient of CAP1400 top nozzle is 9% lower than that of the top reference test piece, while the resistance coefficient of CAP1400 bottom nozzle is 2.4% lower than that of the bottom reference test piece.
  • Study on Hardfacing Process of Reactor Vessel Internals with Cobalt Alloys
    LI Yanbao, GUO Baochao, JIN Weifang
    2016, 36(3): 247-251.
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    To study the hardfacing process of reactor vessel internals with cobalt alloys, the cobalt-base alloy Stellite 6 was deposited on the surface of 304H stainless steel by gas tungsten arc welding (GTAW) process using different welding parameters, after which a series of tests were conducted on the deposited metal to analyze its chemical composition, cross-section microhardness, Rockwell hardness, intergranular corrosion and the microstructure, etc. Results show that both the electrical parameters and the weld thermal cycle have obvious effects on the chemical composition, hardness and microstructure of the deposited metal; under the welding parameters of preheat temperature at 176℃, welding current in 145-190 A and welding speed in 8-12 cm/min, the acceptance rate of deposited weld gets up to 97%; the risk of cracking of the deposited metal can be further prevented by depositing a 3 mm transition layer on the surface of stainless steel 304H with welding wire ER308L, prior to the final hardfacing process with cobalt-base alloy Stellite 6 at the preheat and interpass temperature of 400℃.