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  • 2014 Volume 34 Issue 7
    Published: 15 July 2014
      
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  • Hydrodynamic Safety Analysis for Retrofit of a Supercritical Tshaped Constantpressure Operating Boiler
    LU Qiliang,YANG Dong,SHEN Yanrong,LU Ye
    2014, 34(7): 501.
    Abstract ( )   Knowledge map   Save
    A mathematical model for predicting the flow rate and wall temperature of a supercritical oncethrough boiler was established according to mass conservation, momentum conservation and energy conservation equations observed by the circuit and node, with which the flow rate and wall temperature of a 500 MW supercritical Tshaped constantpressure operating boiler were calculated at different loads with and without OFA, while its hydrodynamic safety analyzed. Results show that the flow distribution differs only in the water wall at lower radiation area II before and after addition of OFA, with a flow deviation less than ±10.9%, and an outlet temperature difference of working medium less than 15.4 K; the midwall temperature rises with reducing load under constantpressure operating conditions; all the tube wall temperatures at both the midpoint and other places are within the allowable range of tube material at various loads, therefore the boiler is considered to be safe after retrofit.
  • Study on Heattransfer Characteristics of a 200 MW Oxyfuel Coalfired Boiler
    WANG Peng,LIU Zhaohui，LIAO Haiyan,LI Yanbing,ZHU Haiyue,LI Xiangyu,CHEN Yinbiao
    2014, 34(7): 507.
    Abstract ( )   Knowledge map   Save
    Amendments were made to the heattransfer calculation method for conventional air combustion to make it applicable to oxyfuel combustion mode. Moreover, parameter optimization and modification were conducted to the weighted sum of gray gases (WSGG) model, so as to obtain the variation law of gas emissivity with the flue gas temperature, effective thickness of radiation layer and with the pressure ratio. Taking the database of American National Institute of Standards and Technology (NIST) as the criteria, physical parameters such as heat conductivity, kinematic viscosity and Prandtl number of gas components under oxyfuel combustion mode were fitted, and the method for convective heattransfer calculation was improved by calculation steps of first single components then their mixtures, which subsequently was used to a 200 MW oxyfuel coalfired boiler. Results show that the error between fitted physical parameters and actual measurements of CO2 in flue gas is less than 0.61% under oxyfuel combustion mode; main parameters such as the heat absorption of various heating surfaces and the outlet gas temperatures under oxyfuel combustion mode with both 26% oxygen concentration in dry recycle condition and 29% oxygen concentration in wet recycle condition agree well with those under corresponding air combustion mode, indicating that the compatibility can basically be reached between above two combustion modes for the same boiler.
  • Online Soft Sensing of Coal Moisture for Utility Boilers
    LI Feng,LUO Jia,ZHAO Zheng,GAO Shan,ZENG Deliang
    2014, 34(7): 512.
    Abstract ( )   Knowledge map   Save
    A soft sensing model of coal moisture was established for utility boilers according to operation mechanism of relevant directfired MPS mediumspeed mill, based on energy and mass balance of matter at the mill inlet and outlet. Using the model, online measurement of coal moisture was carried out, of which the results were compared with that of proximate analysis. Moreover, data fusion was performed to the calculated moisture of multiple mills. Results show that the data calculated with the soft sensing model agree well with that of the proximate analysis, and the accuracy and reliability of the soft sensing method may further be improved by data fusion.
  • Industrial Experimental Study on Combustion of Oil Shale Semicoke in a CFB Boiler
    YAN Junwei,JIANG Xiumin,HAN Xiangxin,LIU Jianguo
    2014, 34(7): 518.
    Abstract ( )   Knowledge map   Save
    An industrial experiment was carried out to the combustion of oil shale semicoke in a 65 t/h circulating fluidized bed (CFB) boiler, so as to study the combustion characteristics, combustion efficiency and pollutant emission of the boiler. Results show that at a certain value of fuel feed rate, the boiler can operate steadily; parameters such as the main steam temperature, pressure, mass flow rate and the bed temperature in main combustion chamber are basically constant; the boiler is free of any sign of instable combustion, and its combustion efficiency is above 95%; all the gaseous pollutant emission can meet the requirements of GB 13223—2003 Emission Standard of Air Pollutants for Thermal Power Plants. The CFB technology enables clean and efficient treatment of the oil shale semicoke with high ash content and low heat value, thus achieving 100% utilization of oil shale resources.
  • Modelling on AirFlue Gas System of Fluidizedbed Boilers Based on Signal Flow Graphs
    ZHANG Yue，HAN Pu，CHEN Wenying
    2014, 34(7): 524.
    Abstract ( )   Knowledge map   Save
    During mechanism modelling process, the concept of signal flow graph was introduced to describe the system to be analyzed, while relevant devices and connections in the system simplified into nodes and branches, and an algorithm description made with the nodes and branches. Taking a 130 t/h fluidized bed boiler as an object of study, a mechanism model was built up for the airflue gas system based on the proposed method, with which online simulations were performed. Results show that the effects of primary air flow disturbance on major parameters of the system agree well with actual characteristics of fluidizedbed boilers, indicating that the model can reflect the parameter variation trend of airflue gas systems in fluidizedbed boilers.
  • Study on Time Delay Estimation in Acoustic Pyrometry Under Reverberation and High Noise Environments
    SHEN Guoqing,ZHANG Shiping,AN Liansuo
    2014, 34(7): 529.
    Abstract ( )   Knowledge map   Save
    To solve the problems of reverberation and high background noise respectively occurring in cold and hot surroundings of power plant boilers, both numerical simulation and experimental study were carried out on measurement of the acoustic transmitting time under corresponding conditions. Results show that under reverberation environments, the reverberation impact can be eliminated by prefiltering relevant signals with Butterworth filter and by performing time delay estimation based on PHAT weighted crosscorrelation algorithm; whereas under high noise environments, the noise impact can be alleviated by crosscorrelation algorithm based on Butterworth filter and ML weighting function.
  • Experimental Study and Improvement on Dust Removal Efficiency of ElectrostaticFabric Integrated Precipitators
    SUN Chaofan,WU Sike,QIAN Wei,YU Xinglu,LOU Bo,LONG Xinfeng
    2014, 34(7): 534.
    Abstract ( )   Knowledge map   Save
    The effects of voltage, flue gas temperature and inlet concentration on dust removal efficiency of an electrostaticfabric integrated precipitator were studied using selfdeveloped experimental facilities, so as to analyze the change rule of the dust removal efficiency and the size distribution of trapped particles. Results show that the
    total removal efficiency increases with rising working voltage, which reduces obviously when the flue gas temperature is higher than 130 ℃; the removal efficiency of
    electrostatic precipitator reduces greatly when the inlet dust concentration gets up to 14.7 g/m3; particles larger than PM10 are mainly collected by electrostatic
    precipitator, while those smaller than PM10 are removed by bag filter. In actual operation process, both the total dust removal efficiency and PM2.5 capture rate may be improved by appropriately raising the working voltage and reducing the inlet dust concentration.
  • Internal Dynamics of a Variablepitch Axial Flow Fan During Nonsynchronous Adjustment of Single Blade on the First or Secondstage Impelle
    YE Xuemin，LI Xinying，LI Chunxi
    2014, 34(7): 541.
    Abstract ( )   Knowledge map   Save
    Threedimensional steady numerical simulation was carried out to a twostage variablepitch axial flow fan, so as to study the effects of nonsynchronous adjustment of single blade fixed on the first or secondstage impeller on the flow field around the fan, single impeller and the abnormal blade. Results show that the full pressure and efficiency of fan show little change when the blade installation angle deviates slightly; the fan performance deteriorates obviously with the increase of deviation degree Δβy; in the case the abnormal blade is on the firststage impeller, the overall fan performance, the total pressure rise capability of singlestage impeller, the work capability of abnormal blade itself, and the guide blade efficiency will all be inferior to those in the case the abnormal blade is on the secondstage impeller, especially with negative deviation of installation angles, except Δβy=12°; for positive deviations of abnormal blade, the entropy generation rate and streamlines of both the first and secondstage impeller present similar distributions, with high entropy generation region and detached eddy forming in the trailing edge on suction side of abnormal blade, which expand with growing Δβy; in the case of negative deviation, when the abnormal blade is on the firststage impeller, high loss region will occur on the pressure side of abnormal blade, whereas when the abnormal blade is on the secondstage impeller, detached eddy will generate in the trailing edge on suction side of adjacent blades.
  • Effects of Guide Plate Installed at Fan Outlet on Performance of the Aircooled Unit
    CHENG Youliang,DING Liyuan,HU Hongkuan
    2014, 34(7): 551.
    Abstract ( )   Knowledge map   Save
    Based on typical structure of a 600 MW direct aircooled condenser, physical models were established for the aircooled unit with guide plates installed at the fan outlet, with which numerical simulations were performed to the flow field inside the aircooled unit with and without guide plates, so as to analyze the effects of guide plate number and shape on its internal aerodynamic flow field and heattransfer characteristics. Results show that the flow field of cooling air can be uniformly distributed by installing a certain number and shape of guide plates at fan outlet, which may help to reduce local high temperatures on tube bundle surface, and therefore to improve the heattransfer effect of aircooled condenser. adding eight pieces of guide plate will produce the best effect, and among arched, rectangular and cambered guide plate, the arched one is proved to be the most effective.
  • Heattransfer and Hydrodynamic Coupling Steady Model of DSG Parabolic Trough Collectors
    GUO Su,LIU Deyou,XU Chang,WANG Pei
    2014, 34(7): 556.
    Abstract ( )   Knowledge map   Save
    A heattransfer and hydrodynamic coupling (HHC) steady model of direct steam generation (DSG) trough collector was built up based on its heattransfer and hydrodynamic characteristics, with which steadystate characteristics of the DSG collector were numerically simulated, so as to obtain the variation law of its outlet parameters under different conditions of DNI, fluid mass flow, inlet fluid temperature and inlet fluid pressure, etc. The simulation results were compared with those experimental data from the literature and with calculation data in other literatures. Results show that for normal operation of the DSG collector, its outlet fluid should be kept in dry steam region, with the outlet temperature being within a reasonable range; the DNI should be larger than threshold value with a reasonable margin left; the fluid mass flow should be set in a certain range, and the available range is relatively narrow; the inlet fluid temperature and pressure should be able to meet operation requirements in a wide range. The proposed model is proved to be effective and accurate by comparison between experimental data and calculation results.
  • Effect of Oxygen Ratio on Properties of Sawdust Gasification Tar in a Fluidized Bed
    QIN Yuhong,FENG Jie,LI Wenying
    2014, 34(7): 564.
    Abstract ( )   Knowledge map   Save
    Pinus sawdust gasification experiments were carried out in a spout fluidized bed at 900 °C, during which the tar properties were analyzed under different oxygen ratios using gel permeation chromatography coupled with a photodiode array detector (GPCPDA) and gas chromatographymass spectrometry (GCMS) analytical techniques. Results show that at relatively high gasification temperatures, the tar yield drops with rising oxygen ratio, but not all of the tar will crack into gas; both the relative molecular mass of tar and its distribution remain unchanged; structural features of main compounds in the tar also keep unchanged, but their relative contents change at high temperatures; the gasified tar primarily consists of aromatic compounds with or without sidechains and of small oxygencontaining polar molecular compounds.
  • Study on Heating Mode of a Large Heat and Power Cogeneration Unit Based on Equivalent Extraction Pressure
    GE Zhihua,CHEN Yuyong,LI Peifeng,HE Jianren,YANG Yongping
    2014, 34(7): 569.
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    An analysis model was established for a large heat and power cogeneration unit with single effect lithium bromide absorption heat pump (AHP) under variable working conditions, which reveals the change rules of AHP thermodynamic coefficient with the saturation steam pressure of AHP driving heat source, under different backwater temperature and temperature rise conditions. The concept of equivalent extraction pressure (EEP) was proposed for selection of heating mode from two options. Taking a 300 MW direct aircooling unit as an example, calculation and analysis were carried out under variable working conditions. Results show that with the increase of backwater temperature and temperature rise in the heatsupply network, the AHP thermodynamic coefficient reduces; for heating units of 300 MW and above to be retrofitted, the AHP heating mode is more energy saving, as the extraction pressure of turbine's medium and lowpressure cylinder is higher than corresponding equivalent extraction pressure.
  • Effects of Heat Wave Movement on Performance of a Reverse Flow Catalytic Reactor
    CHEN Geng，CHI Yong
    2014, 34(7): 576.
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    Numerical simulations were carried out to operation characteristics of a reverse flow catalytic reactor, during which the effects of heat wave movement on both performance and extinction limit of the reactor were studied by taking heat wave creeping range as the reference parameters. Results show that for a constant heat wave creeping range and inlet methane concentration, but at different inlet gas velocities, the temperature distributions inside the reactor are essentially similar; the higher the inlet gas velocity is, the narrower the temperature plateau and the higher the maximum temperature will be. The minimum methane concentration required to maintain autothermal operation of the reactor grows with the rise of heat wave creeping range, and the growth rate increases gradually. The extinction limit may be lowed by substituting part of the catalyst section with inert packing, and the minimum methane concentration will be about 570710 mg/m3 when the inert portion accounts for 20 to 40 percent. Under same working conditions, the heat wave creeping range tends to reduce with the rise of inert portion.
  • Study on Critical Rotating Speed of  a Fivepad Tiltingpad BearingRotor System
    PAN Guomin,PU Qiqi,ZHANG Jiangtao
    2014, 34(7): 582.
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    Based on the model of bearingrotor system for conventional island pump of CAP1400 nuclear power plant, a tiltingpad journal bearing was designed, of which the critical rotating speed was calculated with dynamic parameters of the bearing oil film under different support conditions, while its vibration characteristics studied through hotstate online test for the feed pump. Results show that both the stiffness and damping coefficient of the tiltingpad bearing change with the rotating speed; the critical rotating speed under rigid supporting is greater than under elastic supporting, and the increase of water film stiffness under "wet" condition makes the critical rotating speed greater than under "dry" condition, which is far greater than actual rotating speed. All the amplitude and velocity of relevant vertical, horizontal and axial vibration measured in the test meet relevant national standards.