Archive

  • Select all
    |
    Boiler Technology
  • Boiler Technology
    Effect of O2 Volumetric Fraction in Primary Oxidant on Ignition Standoff Distance of Oxy-coal Combustion
    XU Yangyang, ZHOU Yuegui, JIN Xudong, GU Guangjin
    2013, 33(9): 665-670.
    Abstract ( )   Knowledge map   Save
    Numerical simulation was carried out to a 40 kW coaxial jet oxy-coal combustion facility, so as to analyze the effect of O2 volumetric fraction in primary oxidant on the ignition standoff distance under given overall O2 volumetric fraction and excess oxidant ratio, and to study the ignition mechanism and flame stability of the oxy-coal combustion under low O2 volumetric fractions in primary oxidant. Results show that the ignition standoff distance of oxy-coal combustion is found to be small with an attached flame for an O2 volumetric fraction of 20.9% in primary oxidant, an overall O2 volumetric fraction of 40% and an excess oxidant ratio of 1.15. However, the ignition is delayed with an increased standoff distance and a detached flame when the O2 volumetric fraction in primary oxidant drops to 14.6%, 10.0% and 5.5%, respectively. Higher preheat temperature of secondary oxidant is helpful to the formation of stable flames under low O2 volumetric fraction in primary oxidant for oxy-coal combustion system.
  • Boiler Technology
    Effect of Supercritical Boiler SOFA on Heat Absorption Deviation of the High-temperature Heating Surfaces
    LI Shutian, CHEN Li
    2013, 33(9): 671-676.
    Abstract ( )   Knowledge map   Save
    To solve the problems of steam side oxidation and overtemperature tube burst concerning superheater and reheater of a 600 MW supercritical boiler, experimental tests were carried out to study the influence of separated overfire air (SOFA) on heat absorption deviation of the high-temperature heating surfaces, under conditions of the SOFA nozzle being arranged respectively at tangent and reverse tangent angle of 15°, so as to analyze the effect of flue gas temperature distribution at furnace outlet and in horizontal flue duct on the steam temperature distribution in the superheater and reheater. Results show that it obviously helps to reduce the tangential circle diameter of upper furnace and minimize the heat absorption deviation in horizontal flue duct, when the SOFA nozzle is arranged at a reverse tangent angle. Uniform tube wall temperature distribution can be obtained in the high-temperature superheater by reasonable arrangement of air distribution, in which case the peak temperature at left side of final stage superheater is to be reduced by about 10 K.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Effect of Oil Film Thickness of Elliptic Sliding Bearing on Steam Turbine Vibration
    ZHANG Aiping, XIE Meina, LIN Shengqiang
    2013, 33(9): 677-681.
    Abstract ( )   Knowledge map   Save
    To meet the high requirements of steam turbine on stability of sliding bearing, the effect of oil film thickness of elliptic sliding bearing on the steam turbine vibration was analyzed using Ansys software. The specific way is to firstly import the physical model established by UG software into icem software for meshing, then to calculate the oil film pressure distribution under different oil film thicknesses with CFX module in the Ansys, and finally to study the oil film property and its influence on the bearing vibration amplitude with Mechanical module, so as to realize multi-physics coupling simulation with Ansys software. Results show that there exists a reasonable range of oil film thickness, in which the turbine vibration amplitude can be controlled within allowable limits. The elliptic sliding bearing has a higher stability than cylindrical bearing under same working conditions.
    • Nuclear Technology
  • Nuclear Technology
    Influence of Foundation on Dynamic Characteristics of the Shafting in Large-scale Nuclear Power Half-speed Units
    SUN Qing, YIN Xuejun, LI Wangfan, WANG Xiujin, WANG Weiqiang, GU Chaohong
    2013, 33(9): 682-687.
    Abstract ( )   Knowledge map   Save
    To quantitatively study the influence of foundation on dynamic characteristics of the shafting in turbine-generator set, numerical calculations were carried out to the support dynamic stiffness of different bearing seats for a1 000 MW nuclear power half-speed unit, under conditions respectively with conventional foundation and spring foundation, by taking the foundation and bearing seat as the boundary of support dynamic stiffness, based on which an analysis was performed to the main dynamic characteristics, such as the critical speed of shafting, the unbalance response of journal and the logarithm decrement of shafting, etc. Results show that the critical speed of rotors and the unbalance response of journals are very close in value under above two foundation conditions, with both instability speeds of shafting greater than 2 000 r/min. The critical speed of rotor in horizontal mode declines and that in vertical mode rises, in the case spring foundation is adopted, under which condition the support stiffness can be optimized to a degree equivalent to conventional foundations via appropriate designs.
  • Nuclear Technology
    Experimental Study and Numerical Simulation on Local Resistance of Steam Generator Nozzles
    QU Shixiang, GU Hanyang
    2013, 33(9): 688-693.
    Abstract ( )   Knowledge map   Save
    An experimental study was performed to investigate the local resistance of inlet and outlet nozzles in primary side of a scaled steam generator model, while corresponding flow fields analyzed using Fluent software with SST model based on the structural grid for test models of the inlet and outlet nozzles. Results show that the simulated coefficients of local resistance at both inlet and outlet nozzles have good agreements with the experimental data, and their relative error is less than 5%. The coefficient of local resistance around inlet nozzle increases significantly with rising angle between the inlet tube and cylinder axis, therefore nozzles with small angles between inlet tube and cylinder axis are suggested as long as the installation standard is satisfied. The velocity and pressure field at inlet area of baffle plate are not evenly distributed, which will lead to nonuniform mass flow among tubes of steam generator. The balance of pressure drop between both the outlet tubes of outlet nozzle has great effect on the mass flow distribution.
  • Nuclear Technology
    Study on Density Wave Instability in a Medium-pressure Heated Channel
    CHEN Lei, YAN Changqi, WANG Jianjun
    2013, 33(9): 694-697.
    Abstract ( )   Knowledge map   Save
    The density wave instability in a medium-pressure heated channel was studied using RELAP5/Mod3.4 software, while the sensitivity of the number of nodes investigated based on the prediction results. The influence of following factors on the density wave instability was analyzed, such as the inlet mass flow of single phase water, inlet/outlet length, inlet/outlet local resistance factor and the inlet degree of supercooling, etc., after which the boundary of flow stability was determined based on the supercooling number and phase change number. Results show that it is necessary to perform a node sensitivity analysis before studying the density wave instability using RELAP5 software. The flow stability in heated channel increases with rising inlet mass flow of single phase water, rising inlet local resistance factor, reducing inlet/outlet length and reducing outlet local resistance factor. The boundary of flow stability can be described using both the supercooling number and phase change number.
  • Nuclear Technology
    Research on Thermophoretic Deposition of Micro Droplets in Narrow Rectangular Channels
    LIN Daping, ZHOU Tao, RU Xiaolong
    2013, 33(9): 698-701.
    Abstract ( )   Knowledge map   Save
    Thermophoretic deposition of micro droplets entrained by air flow in a narrow rectangular channel was simulated using Fluent software, during which the mass concentration and velocity distribution of the droplets were obtained. Results show that when temperature gradient exists in the channel, the micro droplets will deposit on the channel wall, and with the rise of temperature gradient, the deposition effect will be intensified, therefore the micro droplets may be removed by raising the temperature gradient.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Effect of Abnormal Blade Reverse Deviation on Performance of the Axial Fan
    YE Xuemin, LI Chunxi, YIN Pan
    2013, 33(9): 702-710.
    Abstract ( )   Knowledge map   Save
    Taking the OB-84 variable pitch axial fan as an example, numerical simulation was carried out to study its performance curves using Fluent software under abnormal reverse deviation of two blades, so as to analyze the influence of deviation degree Δβ and phase of the two blades on the distribution of total pressure, entropy generation rate and acoustic source power level. Results show that under the reverse deviation of blade installation angle, the full pressure and efficiency are distinctly drifted from normal values, and the maximum value of acoustic power level tends to be raised under various flow coefficients. With the rise of Δβ, the fan performance is deteriorated obviously, which is closely related to the phase between abnormal blades. The internal flow characteristics on typical cross sections are remarkably influenced by the phase variation and Δβ. The additive effect of both abnormal blades with alternating phases on internal flow characteristics is clearly protruded, and the independent effect of blades with abnormal phases tends to be basically symmetrical on the internal flow distribution following and adjacent to the abnormal blades.
  • Auxiliary Equipment Technology
    Off-design Operation Optimization for Closed Circulating Water System of Thermal Power Plants
    ZHENG Shan, ZHANG Ruishan, LIU Ming, CHONG Daotong, YAN Junjie
    2013, 33(9): 711-716.
    Abstract ( )   Knowledge map   Save
    Taking the closed circulating water system of a 600 MW power unit as an example, an optimized operation mode was proposed based on the load of steam turbine, the ambient temperature and the relative environment humidity, while a variation law obtained about how the inlet/outlet water temperature of cooling tower in the closed circulating water system (i.e. the outlet/inlet temperature of condenser) change with the unit load, ambient temperature and relative environment humidity by coupling variable conditions of the cooling tower, condenser and turbine.. Results show that with the rise of circulating water flow, the inlet temperature of cooling tower reduces, but the outlet temperature of cooling tower increases, under a certain environmental condition and load; both the inlet/outlet temperature of cooling tower increase with rising ambient temperature, relative environment humidity and unit load.
  • Auxiliary Equipment Technology
    Study on Flow Characteristics and Separation Efficiency of a Gypsum Cyclone with Central Solid Rod
    AN Liansuo, YANG Yang, LIU Chunyang, FENG Lei
    2013, 33(9): 717-721.
    Abstract ( )   Knowledge map   Save
    To eliminate the air core phenomenon formed in gypsum cyclone of a WFGD (wet flue gas desulfurization) system, numerical simulation was carried out on the process of air core development using Fluent software, while an analysis performed to the influence of cylindrical/cone-shaped central solid rod on the velocity field in the cyclone, and a comparison made to the separation efficiency of cyclone with different structures. Results show that the air flows spirally in the core; with the insertion of solid cone rod, the air core phenomenon is eliminated, the tangential velocity is slightly affected, the lingering time of gypsum slurry is elongated in the cyclone, resulting in an increased separation efficiency of coarse particles.
    • Environmental Science
  • Environmental Science
    Effects of Particle Size on Element Mass Fraction Distribution in Fly Ash of Coal-fired Power Plants
    GAO Zhengyang, ZHENG Shuangqing, ZHONG Jun, YIN Libao, CHEN Chuanmin
    2013, 33(9): 722-727.
    Abstract ( )   Knowledge map   Save
    Scanning electron microscopy, X-ray diffraction analysis, electron probe analysis and ion chromatography analysis were carried out to fly ash samples with different particle sizes from coal-fired power plants, so as to study the variation law of element mass fraction with the particle size of fly ash, and to analyze the influence of excess air coefficient on the distribution of element mass fraction. Above results were subsequently compared with the experimental data of a drop tube furnace. Results show that the mass fraction distribution of Na, S, Ca, and Cl changes basically in a negative correlation with the variation of particle size, whereas that of Al, Si, Ka and Fe changes in a positive correlation; the variation law of mass fraction distribution with excess air coefficient is obvious for particle sizes in 25-45 μm, which is not obvious for particle sizes greater than 45-75 μm; in the range of 200-350 ℃, the heating temperature has no effect on the mass fraction distribution of elements Cl and S in fly ash.
  • Environmental Science
    Effect of Metallic Oxides on Adsorption of SO2 on Activated Carbon
    LIU Shaojun, CAO Feifei, GAO Xiang
    2013, 33(9): 728-732.
    Abstract ( )   Knowledge map   Save
    Effect of metallic oxides on adsorption of SO2 on activated carbon was studied at 150 ℃ using thermogravimetric method. Physical-chemical structure changes of metallic oxide-loaded coconut shell-based activated carbon were characterized by N2 adsorption and X-ray photoelectron spectroscopy (XPS). Results show that there is delay of SO2 adsorption due to the diffusion of SO2 from gas phase into pores. Both the distribution of active sites for SO2 adsorption and the equilibrium absorption capacity change significantly after the activated carbon being loaded with metallic oxides. The distribution of active sites in Ce- and Zr-loaded active carbon is relatively uniform, which is helpful to the enhancement of SO2 adsorption; while most active sites in Fe-, Co- and Ni-loaded active carbon are located on the outside surface, resulting in a low utilization rate of internal pores and therefore a reduced capability in SO2 adsorption.
  • Environmental Science
    Determination of Optimal Initial Operation Pressure of a Thermal Power Unit Under Given Load
    HU Yong, LIU Jizhen, ZENG Deliang, PENG Can, LI Yazhe
    2013, 33(9): 733-738.
    Abstract ( )   Knowledge map   Save
    To overcome the deficiency of traditional pressure calculation method in iterative optimization, an optimized calculation method for main steam pressure of turbine under given load was proposed, with which optimal operation values of the main steam pressure were obtained at different loads, based on variable condition theory of steam turbine and particle swarm optimization (PSO) algorithm, and simultaneously an analysis was performed by taking a 1 000 MW steam turbine as an example. Results show that the newly proposed method may help to optimize the operation pressure under given load, and to obtain optimal sliding pressure operation mode and initial operation pressure of the unit, namely, for a load above 80%, keeping the unit to operate at a constant pressure of 25 MPa, whereas, for a load below 80%, adopting the sliding pressure operation mode with two valves fully open. The thermal economy of unit at two-valve fully-open sliding pressure operation mode is obviously higher than that of three-valve fully-open sliding pressure operation mode in the low load region.
    • Energy System Engineering
  • Energy System Engineering
    Morphological Characteristics of Steam-side Oxidation Scales on 10CrMo910 Steel Tubes
    XIE Guosheng, LONG Huiguo, LONG Yi, CHEN Hongdong, MOU Shenzhou
    2013, 33(9): 739-744.
    Abstract ( )   Knowledge map   Save
    Steam-side oxidation scales formed on inner surface of super-heater and re-heater tubes made of 10CrMo910 steel in a power plant were investigated by metallurgic inspection, scanning electron microscope-energy dispersive X-ray (SEM-EDX) spectrometer, and X-ray diffraction analysis. Results show that the steam-side oxidation scale normally consists of two layers: the inner layer is a heterogeneous oxidation film rich in Cr and pores, whereas the outer layer contains porous and fine particles identified as Fe3O4 and Fe2O3; internal oxidation exists at the interface between base metal and inner layer, resulting in compact bonding of the interface; the oxidation at interface between inner and outer layer is not obvious, where firm adhesion is formed and a small number of oxide particles are left after decomposition; both the inner and outer oxidation layer are composed of nanometer or micro particles, and the thermal stress caused by mismatch of thermal expansion coefficients are relaxed by pores lying in the oxidation particles. The steam-side oxidation film of 10CrMo910 steel tube is difficult to peel, and its growing thickness may cause the heating surface steel tube to work at overheating temperatures.