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  • 2014 Volume 34 Issue 12
    Published: 15 December 2014
      
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  • Numerical Simulation on Combustion Characteristics in a Tangentiallyfired Boiler with Variable Volumes of SOFA
    LI Debo,XU Qisheng,SHEN Yueliang,DENG Jianhua,LIU Yaming,WEN Zhiyong
    2014, 34(12): 921.
    Abstract ( )   Knowledge map   Save
    To reduce the NOx emission from a 660 MW tangentiallyfired boiler, a low NOx retrofit was carried out by adding separated overfire air (SOFA) to the boiler, after which numerical simulation was conducted to the combustion characteristics using Ansys Fluent 14.0 software, and subsequently a comparison was made between the simulation results and actual measurements. Meanwhile, the infurnace velocity distribution, temperature field, species field and NOx concentration distribution were studied, and the NOxconcentration distribution in combustion zone and along furnace height were analyzed at different volumes of SOFA. Results show that after the low NOxretrofit by adding SOFA to the boiler, uniform temperature distribution and ideal tangential firing are achieved without flame adhering to the wall. When the damper opening of SOFA varies from 30% to 100%, the maximum temperature in combustion zone reduces from 1 803 K to 1 684 K, with a reduction of 119 K; the maximum NOx concentration in combustion zone reduces from 388 mg/m3 to 259 mg/m3, with a reduction of 129 mg/m3; the NOx concentration at furnace exit reduces from 487.9 mg/m3 to 307.4 mg/m3, with a reduction of 180.5 mg/m3, indicating that the NOx concentration at furnace exit can be effectively reduced by changing the damper opening of SOFA.
  • Numerical Simulation on Flow Characteristics of Different Density Particles in a Fluidized Bed
    LI Bin,ZHOU Zunkai,YAO Lu,JIAO Mingyue,SONG Xiaolong
    2014, 34(12): 932.
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    Numerical simulation was conducted on the flow characteristics of different density particles in a fluidized bed, whose density is randomly generated and obeys normal distribution, with selfdeveloped program combining computational fluid dynamics and the discrete element method, during which the fluidization process of different density particles at different superficial gas velocities, the gas velocity field, the particle velocity, the distribution of volume fraction along bed height and the segregation rates were obtained. Results show that separation phenomenon appears in different density particles at relatively low superficial gas velocities; the larger the density difference is, the more obvious the separation phenomenon will be, which weakens with the rise of superficial gas velocity. The velocity of small density particles is greater than that of large ones, and the larger the density difference is, the greater the velocity difference will be.
  • Coupled Torsional Vibration Analysis of ShaftLast Stage Blade System in Large TurboGenerator Units Using CMS Method with Nested Substructures
    XU Zili,DOU Baitong,FAN Xiaoping,FANG Yu,WANG Jianlu,CAO Shouhong
    2014, 34(12): 938.
    Abstract ( )   Knowledge map   Save
    To solve the problem of multidegree of freedom and hard achievement in calculating the torsional vibration of coupled shaftlast stage blade
     system in large turbogenerator units with threedimensional finite element method, major equations based on component mode synthesis (CMS) method with nested substructures were derived, while the thinking and principles of order reduction were given. Torsional vibration characteristics of a coupled system of rotor, laststage and second laststage disks and blades of a 1 000 MW turbogenerator unit were calculated and analyzed by the proposed method,
      of which the calculated results were compared with the torsional vibration modes of the entire shaft without considering the effect of actual structure of the laststage and second laststage disks and blades. Results show that some important natural modes would be neglected if the actual diskblade structure is not considered, bringing hidden dangers to the safety of the rotor and blades. The degree of freedom of the entire system is about 150 million by 3D finite element method, which is only 0.07％ of the original one after order reduction. The CMS method with nested substructure can be used to analyze the torsional vibration of a coupled system consisting of rotor, laststage and second laststage disks and blades of large turbogenerator units.
  • Performance Contrast Between LMD and EMD in Fault Diagnosis of Turbine Rotors
    XIANG Ling,YAN Xiaoan
    2014, 34(12): 945.
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    A comparative study was conducted to the performance between local mean decomposition (LMD) and empirical mode decomposition (EMD) in diagnosis of simulation and experimental fault signals of turbine rotors, after which the end effect evaluation indexes and fault diagnosis method for rotor imbalance, oil whirl and rubbing phenomenon were put forward based on LMD. Meanwhile, the signal decomposition results based on EMD and LMD were compared and analyzed. Results show that by the method of LMD to decompose the rotor fault signals, the level of mode mixing is lower than that of EMD. Also, LMD has a stronger capability in inhibiting end effect and a higher precision in fault diagnosis, compared with EMD algorithm, which therefore can be effectively applied in fault diagnosis of turbine rotors.
  • Wind Turbine Fault Diagnosis Based on Adaptive Highfrequency Harmonics LMD
    WU Yingjie,LIU Changliang,FAN Degong
    2014, 34(12): 952.
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    To solve the mode mixing problem of local mean decomposition (LMD) in actual applications, an adaptive highfrequency harmonics LMD was proposed. The effect of abnormal events on the envelope function and mean function was analyzed, and the adaptive highfrequency harmonics were constructed and added into the signal to deal with the mode mixing problem by changing the distribution of extreme points of the original signal. Simulation comparison was made to signals containing typical abnormal events between adaptive highfrequency harmonics LMD (AHLMD) and ensemble LMD (ELMD), illustrating the effectiveness and superiority of AHLMD, which was subsequently applied to fault diagnosis for the drive train system of a wind turbine. Results show that the mode mixing situation can be improved significantly and the shaft unbalance characteristics can be extracted successfully via the method, which therefore may serve as a reference for fault diagnosis of wind turbines.
  • Study on Simultaneous Wet Flue Gas Desulfurization and Denitration Based on (NH2)2CO/NaClO2 Solutions
    BAO Jingjing,WANG Jianhang,LIU Hang,YANG Linjun,YANG Hongmin,PENG Fei
    2014, 34(12): 959.
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    Simultaneous flue gas desulfurization and denitration based on (NH2)2CO/NaClO2 solutions were experimentally investigated in consideration of actual operation conditions of relevant power plants, during which the main influence factors and optimal technological conditions were investigated, and the reaction mechanism of simultaneous desulfurization and denitration by (NH2)2CO/NaClO2 solutions was analyzed. Results show that pure (NH2)2CO solution can effectively absorb SO2, but its denitration effect is poor due to the insolubility of NO. However, the removal of NO can be improved by adding NaClO2 into the (NH2)2CO solution. The growth of either liquidtogas ratio or mass fraction of NaClO2 is beneficial to the simultaneous desulfurization and denitration by (NH2)2CO/NaClO2 solutions, in which the effect of NaClO2 mass fraction on denitration efficiency is more significant than that of desulfurization efficiency. In addition, the removal efficiency of SO2 and NO is negatively related to the superficial gas velocity and the initial concentration of NO. The desulfurization efficiency of (NH2)2CO solution is slightly affected by the addition of NaClO2. The SO2-3 converted from SO2 after being absorbed is oxidized into SO2-4 mainly by O2 in flue gas soluble in water; whereas, the NO, which is insoluble in water, is oxidized into NO2 or NO-2 by NaClO2 firstly, and then absorbed by (NH2)2CO solution. NOx in flue gas is finally discharged in the form of N2.
  • Experimental Research on SO3 Removal
    CHEN Xiaolu,ZHAO Qinxin,BAO Yingqun,WANG Yungang,LI Yuxin
    2014, 34(12): 966.
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    The effect of temperature on SO2/SO3 conversion rate under the action of SCR catalyst was studied on a selfdeveloped experimental setup, in which case, the absorption capability of Cabased and Mgbased sorbents to SO3 was investigated, and simultaneously the samples were analyzed using scanning electron microscopy before and after adsorption experiment, so as to analyze the factors influencing the SO3 adsorption by Cabased and Mgbased sorbents and the removal mechanism. Results show that the SO2/SO3 conversion rate increases with rising reaction temperature, and the increasing tendency slows down when the temperature gets up to 300 ℃. The conversion rate has a good linear relationship with the temperature in the reaction scope. The adsorption capability of the four sorbents tested to SO3 are ranked from high to low as follows: Mg(OH)2, Ca(OH)2, MgO and CaO.
  • Reliability Design and Verification of Large Capacity Thermal Power Units
    SHI Jinyuan
    2014, 34(12): 972.
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    Models for availability calculation of thermal power units were established, while calculation methods proposed for corresponding equivalent availability factor and equivalent forced outage rate, together with reliability verification methods suggested for design values of the equivalent availability factor. Statistical results for correction factor of forced outage rate and derating factor of thermal power units were given, simultaneously with a calculation example and verifaction practice shown for the equivalent availability factor, based on 45year operation data of nine 1 000 MW ultrasupercritical power units in four thermal power plants. Results show that the relative error of equivalent availability factor is between -0.55% and 3.37%. These reliability design methods may be used in quantitative calculation of the equivalent availability factor and forced outage rate, which therefore may serve as a reference for reliability design and improvement of large thermal power units.
  • Research on Formation Mechanism of Low Frequency Noise in a Heat Recovery Steam Generator
    TANG Hongyun，JIANG Weikang，ZHONG Zhenmao，ZHAO Yingjiu
    2014, 34(12): 978.
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    To investigate the formation mechanism of low frequency noise in a heat recovery steam generator (HRSG), numerical simulation was carried out to analyze the nonstationary flow field and aeroacoustic noise in the heat exchanger tube array using large eddy simulation (LES) method combined with Ffowcs WilliamsHawkings (FWH) equation. Features of vortex noise were studied respectively for sing tube, finnedtube and tube array, and the results were compared with that of actual measurements. Results show that the low frequency noise of HRSG mainly comes from the vortex shedding in the heat exchanger tube array. The vortex noise of single tube has obvious characteristic frequency, and the spiral fin reduces both the characteristic frequency and total sound level of finned tube. For tube arrays, the vortex noise is of the narrowband type with a certain bandwidth, due to enhanced interaction of flow fields between the tubes.
  • Influence of Syngas Sensible Heat Recovery on Performances of IGCC Power Plant Based on Coal Water Slurry Gasification
    DENG Guangyi,HAN Long,FAN Yongchun,MA Xuesong,ZHENG Yun,WU Jiakai
    2014, 34(12): 985.
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    400 MW IGCC power plant models were developed based on GETexaco and EGas coal water slurry gasification technologies by using Thermoflex thermodynamic system software. Five schemes for syngas sensible heat recovery were set up to study the influence of following factors on the IGCC performance, such as the gasifier type, the configuration of syngas cooler and the syngas temperature at cooler exit, etc. Results show that comparing with GETexaco technology, EGas gasification process has lower steam turbine output and net power output, but higher power supply efficiency and lower house power consumption rate under sensible heat recovery conditions; comparing with GETexaco quench method, the installation of radiant and convective syngas coolers helps to promote the steam yield during syngas sensible heat recovery process, thus elevating the steam turbine output, net power output and power supply efficiency of the IGCC unit; decreasing the syngas temperature at cooler exit is beneficial to improve the plant performance.
  • Optimization of a Novel Combined Cycle System Using LNG Cold Energy and Lowtemperature Solar Energy
    RAO Wenji,ZHAO Liangju,ZHANG Mogeng,MO Yili
    2014, 34(12): 990.
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    Parameter optimization analysis and exergy analysis were conducted for a novel combined cycle system using LNG cold energy and lowtemperature solar energy. Taking R143a as the working fluid, the effects of four independent variables, such as the evaporative temperature, turbine inlet and condensing temperature, and LNG vaporizing pressure, were studied on the cycle system efficiency, exergy efficiency and heat transfer area per unit work, etc. Results show that both the system efficiency and exergy efficiency increase first and decrease later on with the rise of evaporative temperature, which also increase with the rise of turbine inlet temperature and LNG vaporizing pressure; the higher the condensing temperature, the lower the cycle system efficiency and exergy efficiency; the change of the area of heat exchanger per unit net work with these variables is opposite with that of system efficiency and exergy efficiency. Optimum cycle performance can be obtained at the evaporative temperature of 298.15 K, turbine inlet temperature of 353.15 K, condensing temperature of 213.15 K and the LNG vaporizing pressure of 3 MPa, in which case, the heat exchanger exergy loss accounts for 80% of the total cycle exergy loss, and the pump exergy loss is the minimum among all the components.
  • Comparative Study of Strengthened Layer on Blade Surface by 3D Laser Cladding and Alloy Sheet Brazing
    YAO Jianhua,PAN Shiming,YANG Longxing,DONG Gang
    2014, 34(12): 997.
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    To overcome the weakness of poor adhesion between stellite alloy layer and substrate during brazing process, diode laser was adopt to clad the special cobaltbased alloy on the inlet edge of turbine blade. The crosssectional structure, microhardness distribution and bonding strength of inlet edge respectively reinforced by stellite alloy brazing and laser cladding were studied. Results show that metallurgical bonding is achieved between laser cladding layer and substrate, and the bonding area does not break in the tensile test due to an average tensile strength is 699 MPa; the laser cladding layer has a homogeneous structure without any defects, and the microhardness shows a gradient distribution from cladding layer to the substrate. Whereas in the brazing specimen, gas pores are found in the brazing layer, which is uneven in thickness, different in hardness from brazing layer to substrate, with a minimum tensile strength of only 206 MPa. The bonding strength between laser cladding layer and substrate is at least twice higher than that between alloy brazing layer and substrate.