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  • 2014 Volume 34 Issue 3
    Published: 15 March 2014
      
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  • Experimental Study on NOx Emission of a 1 000 MW Ultra Supercritical Tower Type Boiler
    ZOU Lei,LIANG Shaohua,YUE Junfeng,XU Yiran,ZHANG Enxian
    2014, 34(3): 169.
    Abstract ( )   Knowledge map   Save
    A series of experiments on combustion optimization and adjustment were conducted for a 1 000 MW ultra supercritical tower type boiler, so as to analyze the effects of following factors on the boiler combustion and NOx emission, such as the oxygen volumetric fraction at economizer outlet, unit load, secondary air distribution mode, flow rate of close coupled overfire air (CCOFA), flow rate of separated overfire air (SOFA), and the combination mode of coal mills, etc. Results show that the oxygen volumetric fraction and unit load have great influence on both the boiler efficiency and NOx emission. With the rise of oxygen volumetric fraction, the mass concentration of NOx emission increases significantly; whereas with the reduction of unit load, the NOx emission drops first and rises later on, while the boiler efficiency increases first and decreases later on. Not only the boiler efficiency may be improved, but also the NOx emission may be reduced, by reasonably setting the distribution mode of secondary air, the flow rate of CCOFA and SOFA, and the combination mode of coal mills.
  • Numerical Simulation on Effects of OFA Rate on Infurnace Combustion of Boilers
    SONG Jinghui,LI Bingchen,LI Debo,ZHOU Shaoxiang
    2014, 34(3): 176.
    Abstract ( )   Knowledge map   Save
    Numerical simulation was carried out to the infurnace combustion of an opposite firing boiler, so as to analyze the effect of overfire air (OFA) rate on both the infurnace temperature field and the NOx concentration, on the basis of actual boiler working conditions. Results show that from the point of view of boiler safety, the proportion of OFA rate to total secondary air volume should not be more than 0.30, which, from the point of view of NOx concentration, should be kept above 0.23. Comprehensively considering both the boiler safety and NOx concentration, the proportion of OFA rate to total secondary air volume should be controlled within 0.23-0.30.
  • Influence of Lignite Dryness on Heat Transfer and Operation Economy of Power Boilers
    GAO Zhengyang,LI Jinda,FAN Yuanzhou,CHEN Songtao,WU Peixin
    2014, 34(3): 182.
    Abstract ( )   Knowledge map   Save
    Taking a 300 MW lignitefired unit as an object of study, the influence of lignite dryness on furnace combustion and heattransfer characteristics of the boiler was analyzed through calculation respectively with lignite moisture content of 34.1%, 30.0%, 25.0%, 20.0% and 18.0%, so as to study the variation of boiler thermal economy before and after lignite drying. Results show that with the rise of dryness, the theoretical combustion temperature of lignite has been respectively increased by 50.19 K, 101.51 K, 134.82 K and 148.13 K, compared with the original lignite with moisture content of 34.1%, and the highest temperature rise reaches 8.18%, resulting in enhanced infurnace combustion, increased heat radiation, lowered flue gas velocity, reduced convective and radiant heattransfer coefficient of heating surface, increased convective heat transfer per unit of fuel, lowered exhaust gas temperature, and finally increased boiler efficiency and operation economy.
  • Numerical Simulation on Rotating Characteristics of Particles in Fluidized Bed
    LI Bin,SONG Xiaolong
    2014, 34(3): 189.
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    Rotating characteristics of particles in fluidized bed were numerically simulated with selfdeveloped program using discrete element method and computational fluid dynamics, so as to obtain the gas velocity field, particle velocity field and the distribution of particle average volume fraction and particle average rotating speed, and to analyze the effect of particle rotation on the particle  average velocity, bed expansion height, average void fraction, and the factors influencing the particle rotating speed. Simulation results show that the particle rotation not only influences the particle movement, but also has some impacts on the flow field. The average rotating speed of particles has relationship with not only the collision frequency but also the collision strength, and the average rotating speed of highdensity particles is less than that of the lowdensity particles, while the average rotating speed of smallsized particles is higher than that of the largesized particles.
  • Optimized Operation of SAICSiemens Ultrasupercritical1 000 MW Steam Turbines
    SUN Yongping,TONG Xiaozhong,BAO Jinsong,QIN Pan
    2014, 34(3): 196.
    Abstract ( )   Knowledge map   Save
    To improve the operation performance of SAICSiemens ultrasupercritical 1 000 MW steam turbines, performance tests were carried out to the HP/IP/LP turbine casing so as to obtain their flow efficiency, based on which operation optimization was studied for the unit. The throttling loss of highpressure control valve was reduced by comparing the sliding pressure operation modes and optimizing the sliding pressure operation curves at turbine inlet end. The coldend effect was maximized by developing an SIS platformbased coldend optimization management system to guide operators to determine optimal operation mode of coldend equipment, like circulating water pump, according to comparing and sorting results of related benefitcost model. To solve the temperature deviation problem existing in two pipes at stage 6, insulation covers was added to external wall of the pipes to increase the inside steam temperature by 10 K, eliminating the hidden trouble of internal water accumulation. Application results to a 1 000 MW steam turbine indicate that the implementation of above optimization and improvement measures has to some extent helped to improve the operation safety and economical efficiency of the unit.
  • A Modeling Method for Heavy Gas Turbines Considering Variablegeometry Characteristics
    FU Yunpeng，HUANG Yikun，ZHANG Huisheng，SU Ming
    2014, 34(3): 200.
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    Based on traditional simulation model of gas turbines, by comparing and analyzing the gas turbine performance between calculation results and experimental measurements, the effects of angle change of adjustable inlet guide vane (IGV) on the gas turbine performance were quantitatively obtained, and thus an improved simulation mode of heavy gas turbines was constructed considering the effects of IGV angle change on the gas turbine perfomrance. Results show that the steady state simulation results agree well with experimental data, exactly indicating the relationship between running parameters and the power of gas turbine, therefore the model may be used to the analysis of relevant dynamic characteristics and to the design of corresponding control systems of gas turbines.
  • Effects of Mainspan Supporting Characteristics on Vibration of the Threebearing Structure
    SU Yinping,ZENG Qingmeng,FU Xingjun
    2014, 34(3): 205.
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    A finite element model was set up for the shafting of a 1 000 MW unit, based on which verification tests were carried out to study the vibration characteristics of its threebearing supporting structure. Results show that the supporting characteristics at both ends of the generator have great effects on vibration of the threebearing supporting structure. Many factors should be considered during field balancing. When determinating the form and axial position of an imbalance, the mainspan supporting characteristics should be taken into consideration. In case that the imbalance form is determined directly according to the harmonic component method, repeated dynamic balancing may be ineffective, and even divergent vibration may be caused during vibration treatment.
  • Fractionalorder PIλDμ Control of Boiler Steam Temperature Based on Mixed H2/H∞ Optimization
    WANG Dongfeng,WANG Song
    2014, 34(3): 210.
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    To improve the accuracy of parameter tuning in fractionalorder control system, an optimized method was proposed for parameter determination of fractionalorder PIλDμ controller. By simultaneously considering the tracking accuracy, antiinterference capability and robustness, the H2 performance index was minimized via particle swarm optimization (PSO) algorithm with constraints of H∞ performance index, and then the parameters of optimized PIλDμ controller were obtained based on mixed H2/H∞ optimization, which was subsequently applied to steam temperature control of a circulating fluidized bed boiler. Results show that the optimized PIλDμ controller has good setpoint tracking and antiinterference capability and strong robustness.
  • Study on Multiscale Simulation of Flow Characteristics in Direct Aircooling Systems
    HU Hemin,DU Xiaoze,YANG Lijun,YANG Yongping
    2014, 34(3): 216.
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    To analyze the complicated flow characteristics in direct aircooling system of a large thermal power unit, a multiscale synchronous simulation method was proposed. The specific way is to set up a lowdimensional proper orthogonal decomposition (POD) model for smallscale aircooled condenser (ACC) unit, so as to solve the variables such as air velocity, turbulent kinetic energy and turbulent dissipation rate, and then to simulate the flow and transfer characteristics in largescale region, with the preserving smallscale transfer information from reduced order solution based on POD as boundary conditions, on the transscale interfaces between aircooled condenser and largescale aircooled island. Taking the multiscale physical model as an example, which consists of a twodimensional aircooled condenser and an aircooled island, the proposed method was verified. Results show that the multiscale simulation method can help to achieve transscale coupling of air flow characteristics in the air cooling system and reveal the interaction mechanism of turbulent vortices with different scales; compared with traditional numerical simulation, the method saves computation time and resources significantly, and the simulation precision is relatively high. 
  • Visualization of Flow Patterns and Calculation of Pressure Drops in Parallel Rectangular Microchannels
    ZHOU Yunlong,CHEN Yuxiu,LIU Xu
    2014, 34(3): 222.
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    Experimental studies were conducted to parallel rectangular microchannels with hydraulic diameter of 177.8 μm and length of  3 mm, in which the airwater twophase flow was visualized using high speed camera, where a number of typical flow patterns were observed. Total pressure drop in the parallel rectangular microchannel was predicted respectively with separated and homogenous flow model, of which their mean absolute error (MAE) was compared with that of actual measurements. Results show that the homogenous flow model has better effects than the separated flow model in prediction of total pressure drop, and the MAE calculated with Dukler correlations based on the homogenous flow model is the minimum, indicating a good prediction effect.
  • Effects of Firststage Guide Vane Improvement on  Performance of Twostage Variable Vane Axial Flow Fan
    YE Xuemin,LI Xinying,LI Chunxi
    2014, 34(3): 228.
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    3D numerical simulation was carried out to a twostage variable vane axial flow fan using Fluent software, so as to study the effects of the firststage guide vane structure on aerodynamic performance of the fan, such as longshort composite guide vane or single long guide vane, etc., and to compare the fan performance when the short vane is placed at different axial and circumferential positions and has different lengths. Results show that both the singlestage diffusion performance and the overall aerodynamic performance of the longshort composite guide vane are superior to those of the single long guide vane. When the short vane is located at inlet of the firststage guide vane in the intermediate pitch between two adjacent long vanes, both the full pressure and efficiency of fan shall reach the optimum, especially the efficiency will be significantly higher than at other places. In addition, the length of short guide vane also has significant effects on the fan performance. Increasing or decreasing the length of short guide vane will cause deterioration of the fan performance and result in notable irreversible loss, when the length of the short guide vane is 320 mm.
  • Experimental Research on Fishhook Effect in Gypsum Cyclone of Wet Flue Gas Desulfurization
    AN Liansuo,YANG Yang,LIU Chunyang,SHEN Guoqing
    2014, 34(3): 236.
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    To solve the problem of fishhook phenomenon in gypsum cyclone, experimental tests were carried out to study the separation efficiency of different sized particles in gypsum slurry at following ratios of underflow to overflow diameter, such as 0.500, 0.625, 0.667, 0.714, 0.750, 0.833 and 1.000, etc., so as to analyze the influence of above ratios on the fishhook effect, and the influence of inlet pressure and air core on the separation efficiency at the ratio of 0.625. Results show that the percentage of fine particles in underflow can be reduced and high separation efficiency of coarse particles can be obtained when both the ratio of underflow to overflow diameter and the inlet pressure are appropriate. The fishhook phenomenon may also be reduced by inserting a central solid rod to eliminate the air core; however, this may lead to lowered separation efficiency of medium sized particles.
  • Formation Mechanism of Creepweak Zones During Creep Process of P91 Weld Metal
    ZHANG Yan,WANG Yanfeng
    2014, 34(3): 241.
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    Microstructure, hardness and chemical composition of P91 steel weld metal were studied in aswelded state and after creeprupture test, while the gradient of carbon activity in white bands of fracture surface simulated using ThermoCalc software. Results show that significant depletion of alloying elements can be found at interbead boundary in aswelded state, featured by low hardness, carbide dissolution, low carbon mass fraction and recrystallization to ferrite grains, where creep cracks are easy to form. The carbon activity at interbead boundary is far above the surrounding matrix, and with the depletion of alloying elements up to the measured level, the carbon element in white bands will deplete to the mass fraction less than 0.01 %, when the carbides dissolve completely. The recrystallization of martensite to low hardness ferrite at interbead boundary during creep process will make its creep property greatly reduced.
  • Hightemperature Mechanical Properties of C276 Alloy Weld Joint
    MA Yan,LU Chenlin,XU Yanze,LI Xin
    2014, 34(3): 248.
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    Hightemperature tensile properties of C276 alloy joints formed by electron beam welding were measured in the temperature range from 500 ℃ to 650 ℃, while microstructure analysis performed for relevant specimens treated at 600 ℃ for 300 h. Results show that the hightemperature strength of above joints reduces with rising test temperature, and their yield strength is higher than or close to the base metal, but the highest fracture strength is only 70% of the base metal, with an elongation percentage far below the base metal. After isothermal treatment at 600 ℃ for 300 h, both the yield and fracture strength are enhanced significantly, but the percentage of elongation rises little. The microhardness in fusion zone of weld joint is higher than base metal, which is further hardened by the isothermal treatment. The fine lamellar structure formed in the fusion zone is found to be the main factor of hardness enhancement. After isothermal treatment, precipitants are also observed in the fusion zone, which have precipitation strengthening effects.