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  • 2014 Volume 34 Issue 10
    Published: 15 October 2014
      
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  • Measurement of Solid Flux Distribution near Water Wall of a 330 MW CFB Boiler
    ZHOU Xinglong,XIE Jianwen,GAO Shengbin,FAN Yongsheng,CHENG Leming,CEN Kefa
    2014, 34(10): 753.
    Abstract ( )   Knowledge map   Save
    To study the solid flux distribution near water wall of a 330 MW subcritical CFB boiler, local solid flux in the furnace was measured by watercooled suction sampling probe through holes cut on the wall. Results show that the net solid flux is basically independent of the suction velocity, when the suction sampling method is used for CFB boilers. Particles distribute in obvious coreannulus structure in the dilute zone of furnace, and downward solid flow with relatively high flux forms near the water wall. The thickness of annular downflow layer is about 0.10.18 m at measuring holes of both level 5 and level 6, which increases with rising superficial gas velocity. The location of antiwear beams, supended panels and output windows has a significant impact on the structure of solid coreannulus flow.
  • Research on Limestone Control of Circulating Fluidized Bed Boiler
    GAO Mingming,YUE Guangxi,LEI Xiujian,LIU Jizhen,ZHANG Wenguang,CHEN Feng
    2014, 34(10): 759.
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    For the instable and time delay process of infurnace desulfurization in circulating fluidized bed(CFB) boiler, a specific "active limestone" state monitoring model was set up to simulate the desulfurization process, while a method for optimization of the n(Ca)/n(S) was suggested according to the balance of "active limestone", and simultaneously a SO2emission prediction model was proposed based on the coal feed rate, air flow rate and infurnace active limestone mass, with which simulation tests were carried out to a 600 MW supercritical CFB boiler using actual operation data. Simulation results prove the prediction model to be effective, and the optimization of n(Ca)/n(S) based on the model helps to improve the stability of SO2 emission.
  • Hybrid Modeling of Boiler Combustion System Based on Numerical Simulation and Experimental Data
    NIU Yuguang,SHA Chao,KANG Junjie
    2014, 34(10): 765.
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    Based on training samples of a numerical simulation model established for boiler combustion system, a least squaresupport vector machine (LSSVM) model was set up, which was subsequently corrected with experimental data and updated with realtime operation data. On above basis, a hybrid modeling method was finally put forward for boiler combustion system. Results show that the hybrid modeling method could effectively improve the prediction precision and calculation speed of original LSSVM model, and by correcting and updating the model respectively with experimental data and realtime operation data, the model precision could be further improved, thus laying a good foundation for optimization of boiler combustion systems.
  • A Method for Online Reliability Monitoring of Large Power Generation Units and Its Application
    SHI Jinyuan
    2014, 34(10): 771.
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    Four parameters for online reliability monitoring of power generation units were presented, such as the equivalent availability factor with planed outage hours deducted, the reliability growth factor, the percentage of unplanned outage hours of major facilities, and the reliability influence factor in the power station. These parameters were used to monitor the reliability of single and multiple power units in the station, to which calculation methods were given, and subsequently corresponding maintenance measures were proposed for relevant equipment, together with an application example described. Based on the online monitoring parameters of multiple power units, the outage frequency, the maintenance grade, and the outage interval of planned maintenance could be reasonably arranged and optimized. Results show that via the online reliability monitoring and maintenance optimization, the reliability growth of related power units is promoted, ensuring that the reliability of multiple power units in the power station is under control.
  • Study on Widelyranged Poweradjustable Control for Wind Turbine Generation Systems
    LIU Jizhen,HU Yang,LIN Zhongwei
    2014, 34(10): 778.
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    To deeply manage the load from both the mechanical side and electrical side of wind turbine generation system (WTGS), operation characteristics of variable speed variable pitch WTGS was analyzed, based on which a combined adjustment method composed of pitch control and generator control was proposed for limited power tracking, under the condition below rated wind speed, while the decoupling coordinated control strategy was put forward for variable speed variable pitch mode with multiple degree of freedom. Considering the compatibility of limited power tracking and maximum power tracking, an integrated control strategy was established for WTGS to widely adjust the output power over full range of wind speed. Meanwhile, PID gain scheduling technique was used for process control design over full operating range, where a kind of nonlinear measure index was applied to reduced the number of partioned operation points and the TS fuzzy logic was adopted to define the gain scheduling algorithm. Simulation tests were finally carried out to a 2 MW WTGS based on the nonlinear model. Results show that the power setpoint could be well tracked by the widelyranged poweradjustable control system, which enables the WTGS to have comprehensive management ability on load.
  • PSObased Individual Pitch Control for Wind Turbines Without Load Sensor
    GAO Feng,GUO Peng
    2014, 34(10): 784.
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    An individual pitch control (IPC) approach for wind turbines without load sensor was proposed based on loads pridicted by blade element theory. To make the load calculation more accurate, corrections were made to the measured wind speed and the hub wind speed affected by wind shear and tower shadow. The pitch angle was then controlled by partical swarm optimization (PSO) according to previous load prediction, and the realtime control was achieved by selecting the objective function and setting relevant parameters in optimization search. Simulations were made to a 1.5 MW variable pitch wind turbine by Bladed software. Results show that the proposed individual pitch control strategy helps to not only guarantee power control objectives, but also realize load control purposes, which can simultaneously reduce both the load imbalance of wind wheel and the fatigue load of wind turbines.
  • Measurement of Average Gas Velocity in a Short Duct Based on Flow Rectification with Screen Grid
    ZHAO Yonggang,SUN Baomin,LIU Zhiqiang,YANG Dinghua,GUAN Qingliang,ZHANG Ruiqing
    2014, 34(10): 790.
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    A measurement method was proposed for average gas velocity in a short duct by dividing the section to be measured into several units with a screen grid for flow rectification, where pressure tapping holes are distributed, and the pressure taps are to be led to a large vessel for acquisition of the average pressure. Numerical simulation was carried out to the flow rectification effected by a screen grid with cross section of 800 mm×500 mm. Results show that the screen grid is very effective in regulating the originally disordered flow in branch duct of large wind box. The velocity distribution tends to be uniform with reducing arrayed pitch of screen grid, while the rectifying effect is not closely associated with relative location of the screen grid. The thickness of screen grid plays a determining role in influencing the rectifying effect, and the influence becomes gradually weakened when the thickness is over 200 mm. Under the condition that the pitch, location and thickness of screen grid are ideal, the average pressure of each subsection will be in good linear relation with the average gas velocity in each branch duct.
  • Numerical Simulation of Falling Liquid Film Based on Lattice Boltzmann Method
    JIA Xiaodong,LIU Yongwen,LI Long,SU Ming
    2014, 34(10): 796.
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    A twophase ShanChen model with adjustable surface tension was proposed by improving the original lattice Boltzmann model, based on which falling film flow was simulated under 2dimensional conditions respectively under Reynolds numbers of 5, 10 and 20, so as to further study the flow characteristics of film with inlet disturbance, analyze the influence of external disturbance and surface tension on the steadystate wave motion, and to summarize the tendency of steadystate film development. Results show that the flow morphology acquired through numerical calculation is in good agreement with experimental data, demonstrating that the ShanChen model is capable of reflecting the physical process of falling film flow.
  • LBM Simulation on Droplet Deformation and Breakup Under the Action of Mass Force
    ZHAO Yin,YANG Fan,GUO Xueyan,DAI Ren
    2014, 34(10): 801.
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    The motion, deformation and breakup of droplets were simulated based on pseudopotential model using twophase Boltzmann method, during which the required surface tension coefficient was obtained according to YoungLaplace law, while the isotropy of surface tension of droplets in the model was verified. Meanwhile, the motion and deformation of droplets were simulated under different Bond and Ohnesorge numbers. Results show that the deformation of droplets intensifies with the rise of Bond number, until droplet breakup; whereas with the rise of Ohnesorge number, the droplet tends to keep its original shape, in which process, droplet breakup is inhibited.
  • Experimental Study on Running Condition of the Catalyst in a Domestic SCR Denitrification System
    LI Debo,LIAO Yongjin,XU Qisheng,ZENG Tinghua
    2014, 34(10): 808.
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    Experimental studies were conducted to running conditions of the catalyst in an SCR denitrification system, during which a device for measurement of catalyst activity was developed, while the causes leading to catalyst deactivation were analyzed by means of advanced instruments. Results show that the catalyst deactivation is mainly caused by both the wear of catalyst resulting in lost active components and the fly ash deposition, and among all the factors in surface deposition, alkali metals and CaSO4 play the major role.
  • Simulation of the Effect of Alkali Metals on Homogeneous Mercury Oxidation by Chemical Kinetics Coupled with Fluid Dynamics
    SHI Xiaofang，DIAO Yongfa，YU Wanxuan
    2014, 34(10): 814.
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    Considering the features of high chlorine and high alkali metal content in biomass, a Hg/C/H/O/N/S/Cl/K/Na model was established for the cocombustion process of biomass and coal. Based on kinetic calculation and sensitivity analysis, the homogeneous mercury oxidation under different concentration of Cl2 was analyzed by applying Chemkin 4.1 and Fluent 6.3 software to realize the coupling of chemical kinetics and fluid dynamics, so as to subsequently study the effect of alkali metals on homogeneous mercury oxidation. Results show that the Hg oxidation activity is limited by temperature. Hg oxidation mainly occurs at the temperature around 800 K, when the Hg chlorination activity is the strongest, and the K chlorination activity is the weakest, in which case the generation of HgCl2 is promoted. Additionally, in the case that alkali metal exists, the reaction between alkali metal and Cl2 would inhibit Hg oxidation, and the reaction between alkali metal and SO2 would promote Hg oxidation.
  • Research on PM10 Emission Characteristics During Combustion of Different Coals
    CHEN Jian,LIANG Xiujin,MENG Ying,WANG Qunying,YING Guangwei,Yoshihiko Ninomiya
    2014, 34(10): 821.
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    The influence of coal rank, particle size, temperature and residence time on PM10 emission was studied through combustion tests with 4 typical types of coal in a drop tube furnace (DTF). Results show that anthracite generally has low PM10 emission, and bituminous coal has high PM1+ emission, whereas two types of lignite have high PM1- emission with inconsistent PM1+ emission trends. The effect of particle size varies greatly with the coal rank; with the rise of particle size, the PM10 emission of bituminous coal increases, and the PM10 emission of high rank lignite increases first and decreases later on, while low rank lignite almost has no change in PM10emission. With the rise of temperature, the PM10emission rises first and reduces later on, in the case the highest temperature is above the ash fusion point. With the elongation of residence time in high temperature zone, fine PM10 particles have a tendency to agglomerate into large ones.
  • Precipitation Behavior of σ Phase in S30432 Steel During Creep Rupture Test at 700 ℃ and the Effect on Material Property
    TANG Bo，ZHU Lihui, WANG Qijiang
    2014, 34(10): 827.
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    The precipitates in S30432 steel during creep rupture test at 700 ℃ were studied by means of ThermoCalc software, transmission electron microscopy and scanning electron microscopy, with emphasis on the precipitation behavior of σ phase and the effect on the creep ductility. Results show that Curich phase, MX phase and M23C6 carbide form in S30432 steel during creep rupture test at 700 ℃, and blocky σ phase begins to precipitate at grain boundary after testing for 4 363 h. The blocky σ phase increases both in number and size with the rise of creep rupture time. The rapid decrease of creep ductility after creep rupture test from 4 363 h to 6 234 h is mostly ascribed to the blocky σ phase at grain boundaries, since it plays an important role in the formation of cavities and in the development of intergranular cracks.
  • Property Analysis for Three Zirconium Alloys of Nuclear Power Stations
    MA Linsheng,WANG Kuaishe,YUE Qiang,PENG Sheng
    2014, 34(10): 833.
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    Taking three typical zirconium alloys Zr4, M5 and Zirlo respectively in ZrSn, ZrNb and ZrSnNb series as objects of study, systematic comparison and analysis were performed to the difference among these alloys in the aspect of second phase particles, mechanical properties, hydride orientation and corrosion resistance, etc., while an evaluation was carried out to their application status. On the basis of current analysis, it is suggested that the material design method should be used in the development of new zirconium alloys with high properties.