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  • 2014 Volume 34 Issue 5
    Published: 15 May 2014
      
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  • Research Process on Mercury Oxidation and Capture with Fly Ash of Coalfired Power Plant
    YANG Jianping,ZHAO Yongchun,ZHANG Junying,ZHENG Chuguang
    2014, 34(5): 337.
    Abstract ( )   Knowledge map   Save
    Current research process on mercury oxidation and capture with fly ash of coalfired power plant is summarized, including a brief introduction to the enrichment pattern of mercury in fly ash, with focus on the influence of fly ash intrinsic characteristics (such as unburned carbon content, composition and microstructure of petrography, some active inorganic components, etc.) on the mercury removal with fly ash, as well as the influence of flue gas components (conventional components, HCl, SOx, NOx and Br, etc.) on the mercury oxidation and capture. Meanwhile, a new approach is proposed for mercury removal with magnetosphere fractions present in fly ash.
  • Experimental Study on Particle Concentration Distribution in a 1 060 t/h CFB Boiler
    CHANG Weiming,MA Suxia,LUO Dingling,ZHANG Jianchun，LIU Jianhua
    2014, 34(5): 346.
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    Experimental tests were carried out to a 1 060 t/h circulating fluidized bed (CFB) boiler with breechesleg under different operation conditions, after which the curves of infurnace pressure distribution and the particle concentration distribution in the dilute region were obtained at different loads. Meanwhile, the impact of air velocity and pressure drop on the particle concentration distribution was analyzed, and subsequently the variation laws of particle concentration distribution, respectively with air velocity and furnace height, and with pressure drop and furnace height, were obtained. Results show that at a steady pressure drop, the air velocity is directly proportional to the average infurnace particle concentration; whereas at a steady air velocity, the pressure drop is directly proportional to the average particle concentration in a certain range; when the bed pressure rises to a critical value, the pressure drop is inversely proportional to the average particle concentration in the furnace.
  • Experimental Study on Heattransfer Coefficient in Furnace of Hightemperature CFB Boilers
    SUN Xianbin,LIU Haifeng,WANG Haitao,SHI Zhenghai,GAO Hongpei,JIN Senwang
    2014, 34(5): 351.
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    To measure the infurnace heattransfer coefficient of hightemperature CFB boilers, experiments were carried out on a 1 MW hotstate CFB boiler's test facility, during which the heattransfer coefficient was measured and the influence of bed temperature and solid suspension density on the heattransfer characteristics was analyzed. A correlation model of heattransfer coefficient associated with the bed temperature and solid suspension density was then obtained through regression analysis of the test data. Results show that the infurnace heattransfer coefficient increases with the rise of bed temperature and solid suspension density; the error of infurnace heattransfer coefficient between calculated results and actual measurements is less than 7%, indicating high precision of the correlation model, which therefore may be used in design of hightemperature CFB boilers.
  • Isothermal Thermogravimetric Analysis of Mixed Coals and Synchronous Testing of NO Emission
    WANG Chunbo,LI Chao
    2014, 34(5): 355.
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    Isothermal thermogravimetric analysis was carried out to individual and mixed coals on a selfdeveloped test rig, while the NO emission simultaneously measured. Results show that when Indonesian lignite is mixed, the overall average weight loss rate of coal mixtures will be increased, and the burnout time will be shortened; the higher the rank of parent coal is, the more obvious the effect will be. The average rate of weight loss both in whole process and at initial stage has a linear correlation with the mixing ratio. The accumulated NO emission from combustion of mixed coals is less than the weighted value of that from various individual coals. Mutual restraint exists in the process of nitrogen release from Tashan bituminous coal and Indonesian lignite, resulting in great difference of accumulated NO emission between experimental data and weighted value of Tashan coal mixtures.
  • Determination of Inertia Coefficient for Calculation of Turbine Rotor Temperatures
    YANG Yu
    2014, 34(5): 361.
    Abstract ( )   Knowledge map   Save
    A method was proposed for determination of relevant inertial coefficients through patternbased direct search algorithm using finite element calculation results, which takes the average temperature of turbine rotor in cold, hot and extremely hot start process calculated by finite element method as standard values, and subsequently determines the number of parallel inertia links, and the time constant and weighting coefficients of each inertia link by optimized search algorithm. A comparison was made to the calculated rotor bulk temperature in warm start process between finite element method and inertia link algorithm, so as to verify the calculation accuracy and availability of the proposed method. Resuts show that the constant and coefficient obtained by the proposed method can satisfy the precision requirement of actural engineering projects, which therefore may serve as a reference for safety operation of turbine rotors in thermal stress control and optimization at variable operation modes.
  • Creep Strength Analysis for Highpressure Inner Casing of Ultrasupercritical Units
    YU Chao,WANG Weizhe,ZHANG Junhui,LIU Yingzheng
    2014, 34(5): 365.
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    Based on 3D model for inner casing of an ultrasupercritical unit built up with commercial finite element software ABAQUS, numerical studies were carried out to its hightemperature creep strength, while calculation and analysis performed simultaneously. Results show that the maximum stress of inner casing is lower than the yield strength of the material at corresponding temperatures under steady state conditions, indicating that the inner casing has not reached its yield state; creep strain main occurs in the area of steam inlet and balance piston; multiaxial effect significantly influences the result of creep assessment, and more accurate results can be obtained by using multiaxial creep strain to assess the creep strength; stress relaxation due to bolt creep behavior decreases the bolt tightening force, and 2×105 hours later, it further affects its sealing performance at the highpressure inner casing split.
  • Study on Characteristic Calculation of Aircooled Turbines
    WEI Ming,WANG Yonghong,SONG Huafen
    2014, 34(5): 371.
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    For the features of high cooling air flow and transonic working condition of modern gas turbines, an improvement was made to the turbine throughflow model, based on which relevant equations were derived for characteristic calculation of the aircooled turbines, while its application scope was extended. By combining the throughflow model with a loss model, and based on the proposed characteristic calculation equations, a set of calculation software suitable for the characteristic calculation of aircooled turbines was designed with Matlab under variable working conditions, which was verified by a number of turbines. Results show that the characteristic calculation method has relatively high precision.
  • Identification of Main Steam Temperature System Based on Improved Harmony Search Algorithm and Field Data
    WANG Dongfeng,HUANG Jinshan
    2014, 34(5): 376.
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    For model identification of main steam temperature system with field data, an improved harmony search (HS) algorithm was proposed in combination with particle swarm optimization (PSO). Empirical mode decomposition was used for filtering of noised data. Discretesimularity method was chosen for computer implementation and numerical calculation after analyzing and comparing the commonly used identification strategies. The proposed method was finally applied for model identification of the main steam temperature system in a circulating fluidized bed. Results show that the obtained model has a high indentification precision, which can reflect the dynamic and static characteristics of actual main steam temperature systems; with fast convergence speed, the improved HS algorithm exhibits better stablility and higher global optimization capability, compared with PSO method.
  • Numerical Simulation on Heat Transfer and Flow Resistance Characteristics of Htype Finned Tube Bundles
    SUN Zhongping,WU Xin,WANG Yaou
    2014, 34(5): 382.
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    Based on analyses of Htype fin efficiency and the fluid properties and temperature difference between outer wall of the tubes and base of the fins, numerical simulation was performed to study the effects of structure parameters on the heat transfer characteristics, flow resistance characteristics and comprehensive performance of the Htype finned tube bundles. Results show that the Nusselt number decreases first and increases later on with the increase of fin pitch and fin thickness, which also increases with rising slit width, rising longitudinal tube pitch, and reducing transverse tube pitch; there is a proportional relationship at lower Reynolds numbers and an inverse relationship at higher Reynolds numbers between Nusselt number and fin height. Euler number increases with rising fin thickness, fin height and longitudinal tube pitch, and with reducing fin pitch, slit width and transverse tube pitch. The integrated factor j/f rises with the increase of fin height and slit width, and with the reduction of fin thickness, transverse and longitudinal tube pitch, which drops first and rises later on with the increase of fin pitch.
  • Pressure Drop of GasLiquid Twophase Flow in Rectangular Microchannels
    SUN Ke,LIU Bo,LU Kun,WU Yu
    2014, 34(5): 390.
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    Taking nitrogen as the gasphase medium and the liquid with different surface tensions (pure water, 0.01% SDS solution, ethanol) as the liquidphase medium, a visualized experiment was carried out to study the pressure drop of gasliquid twophase flow in rectangular microchannels of different sizes (200 μm×200 μm, 400 μm×400 μm, 800 μm×800 μm), during which the twophase frictional pressure gradient was measured and compared with those predicted by homogeneous flow model, separated flow model and flow patternbased phenomenological models. Results show that the pressure gradient is highly dependent on the surface tension, channel size and twophase flow velocity; the flow patternbased models provide the best prediction of twophase pressure drop in the microchannels.
  • Effects of Phase Between Two Abnormal Blades on Performance of the Axial Flow Fan
    YE Xuemin,LI Chunxi,YIN Pan,LI Xinying
    2014, 34(5): 396.
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    Taking an OB84 type adjustable blade axial flow fan as the object of study, a 3D numerical simulation was carried out using Fluent software to investigate the operating performance, full pressure, entropy generation rate and noise distribution of two abnormal blades with positive deviation of installation angles at different phases. Simulation results show that the phase and installation deviation of abnormal blades have different effects on operation performance and internal dynamic characteristics of the fan; in the case with abnormal blades, the full pressure and efficiency are usually lower than those in normal case, and the maximum sound level varies in the opposite direction; under same installation deviations, the full pressure and efficiency tend to reduce with rising interval distance of abnormal blades; the phase and installation deviation have consistent effects on the full pressure, entropy generation rate and acoustic source power level distribution; with the rise of installation deviation, the abnormal blades will induce adjacent high pressure region, high entropy generation rate region and high noise region evolved into ribbons covering circumferential downstream flow passages, therefore resulting in severely deviated operation performance of the fan.
  • Flow and Heattransfer Characteristics in Buoyancy Driven "Natural Draft Cooling Tower" Under Crosswind Conditions
    ZHAO Wensheng,TANG Xuefeng,LI Weihua
    2014, 34(5): 404.
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    Based on the condenser model and principle of "natural draft cooling tower installed in chimney", a simplified porous medium model and a buoyancybased natural convection heattransfer model were set up, with which flow field in the tower and heat exchange capacity in each condensing unit were simulated and analyzed at different wind speeds using Fluent software, and subsequently improvement solutions to reduce the influence of crosswind were put forward. Results show that the flow field will be even and symmetric if there is no crosswind, in which case, the air flow at each air intake will be uniform and the duty of each condenser will be homogeneous; if there is crosswind, the air flow at each air intake will be quite different, and the duty of each condenser will be uneven, due to the circularcylinder flow at air intakes and the "wind cover" phenomenon at air outlets; when the wind speed is larger than 4 m/s, the duty of each condenser will be obviously different, the larger the wind speed is, the severer the phenomenon will be. For the purpose of reducing the influence of crosswind, it is feasible to install guide plates at air intakes.
  • ThermalEconomic Analysis on Introduction of Residual Heat into Thermal System of Power Plants
    LIU Hao,ZHOU Shaoxiang,HU Sangao,LIANG Shuangyin
    2014, 34(5): 411.
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    To accurately calculate the amount of energy saving by introducing residual heat into thermal system of power plants, operating characteristics of relevant turbine stages affected by residual heat application were studied under variable working conditions, and subsequently a new way for calculation of the internal power increment was proposed based on equivalent entropy drop method. Combining with the fluid transport properties, an estimate method for calculating the power increment of circulating pump and condensate pump caused by residual heat application was proposed. Taking a 1 000 MW supercritical unit as an example, the extraction parameters, internal power and auxiliary power were analyzed under the introduction of residual heat into different heaters of the thermal system. Results show that the introduction of residual heat into thermal system makes relevant turbine stages work in variable operation conditions, with an actual internal power increment less than the calculated result by equivalent enthalpy drop method; the higher the temperature level of residual heat is, the better the energy saving effect will be, whereas the smaller the heattransfer temperature difference of the lowtemperature economizer is, the higher the investment will be.