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  • 2017 Volume 37 Issue 11
    Published: 15 November 2017
      
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  • Effects of Operation Mode on High Temperature Corrosion of the Water Wall in a Supercritical Tangential Firing Boiler
    ZOU Lei, YUE Junfeng, GUAN Shipian, ZHANG Enxian, DING Jianliang
    2017, 37(11): 861-869.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To deal with the high temperature corrosion of the water wall in a 630 MW supercritical tangential firing boiler, experimental tests were carried out for the distribution characteristics of gas components (O2, CO and H2S) near water wall, and subsequently the effects of following factors on the high temperature corrosion and NOx emission were analyzed, such as the oxygen concentration, fineness of pulverized coal, sulfur content in fuel, and the flow rate of close coupled over-fire air (CCOFA), separated over-fire air (SOFA) and circumferential air, etc. Results show that high temperature corrosion mainly occurs in areas under strong reducing atmosphere; the reducing atmosphere near water wall could be decreased by increasing the oxygen concentration and reasonably setting the air distribution along vertical direction of the furnace; the fineness of pulverized coal has little effect on the reducing atmosphere near water wall; with the rise of sulfur content in fuel, the H2S concentration increases near water wall, while the O2 and CO concentration remain basically unchanged; smaller CCOFA and proper SOFA flow rate are helpful to reduce the high temperature corrosion of water wall; the flow rate of circumferential air has great influence on the reducing atmosphere near water wall at the bottom of main burners, and it is proposed to appropriately reduce the flow rate of circumferential air in the process of operation.
  • NOx Prediction Model for Multi-coal Admixing Combustion in Boiler
    YANG Jianguo, YE Lingyun, ZHAO Min, ZHAO Hong, LI Yijin, LI Min, YU Yu, DENG Furong
    2017, 37(11): 870-875.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking into account the category and quality of the coal fired, the combination way of coal mills, the air distribution mode and the operating parameters of a 660 MW boiler, a NOx prediction model was established using support vector machine (SVM), which was used to carry out application simulation and to research the effects of following factors on the NOx concentration, such as the oxygen concentration, OFA rate, air distribution mode, coal category and the combination way of coal mills, etc. Results show that the model has good accuracy and high generalization ability as well as ideal regulation performance, which comprises information on coal category and combination way of coal mills, and therefore is of great significance for multi-coal units in improving the NOx prediction accuracy, reducing the NOx concentration, carrying out the adjustment and optimization for stable combustion, especially in guiding the coal procurement and blending, and even for purchasing of "intelligent fuel".
  • Optimization on Pulverizing System and Air Distribution Method of a Coal-fired Unit Based on Data Analysis
    LI Jianqiang, CHEN Xingxu, ZHAO Kai, WANG Anming
    2017, 37(11): 876-882.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To optimize the coal pulverizing system and air distribution mode of a 600 MW thermal power unit, data mining was carried out on following parameters by an improved Apriori algorithm for mining association rules based on the historic operating data of the system, such as the primary air flow of coal mill, the flow rate of coal feeder, the exit air pressure of coal mill, the opening of secondary air door and so on, during which optimum reference values of operation parameters were obtained under full conditions. Results show that in the medium-and low-load range, the power consumption of the pulverizing system could be decreased by reducing the running number of coal mills under the premise of ensuring the pulverized coal supply; for the same combination of coal mills, the net power generation per unit of coal has been improved remarkably after optimization, reducing effectively the power consumption of the pulverizing system; the secondary air distribution after optimization presents a constricted shape, resulting in stable combustion, high efficiency and low NOx emission of the boiler.
  • Fault Diagnosis of a Turbo-Generator Rotor Based on ALIF-HT
    TANG Guiji, PANG Bin
    2017, 37(11): 883-889.
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    Aiming at the problems that the vibration signals of turbo-generator rotor are of the multi-component and non-stationary kind, a new fault diagnosis method was proposed based on ALIF-HT by combining the novel signal decomposition method-adaptive local iterative filtering (ALIF) with the Hilbert transform (HT). The specific way is to decompose the original vibration signals of turbo-generator rotor into several signal components by ALIF, then to compute the instantaneous frequency of every component by HT to get the complete time-frequency representation of all signal components, and finally to identify the fault types according to the time-frequency characteristics. The ability of ALIF in decomposing multi-component signals was demonstrated through analysis on simulated signals and the engineering practicability of the method was verified via fault analysis of rotor oil film instability. Results show that the ALIF overcomes the mode-mixing problem existing in EMD and the ALIF-HT method has higher time-frequency accuracy than the HHT method.
  • Design of a Combined Vibration Test Rig for Shafting and Spring Vibration-isolated Foundation of Nuclear Power Half-speed Units
    LI Wangfan, WANG Xiujin, SUN Qing, JIANG Jun, WEI Qi, ZHAO Feng
    2017, 37(11): 890-894.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A design idea of combined vibration test rig for shafting and spring vibration-isolated foundation was proposed. Taking a 1 000 MW nuclear power half-speed unit as the prototype, a test rig was set up in the proportion of 1:10 based on the principles of geometric and dynamic similarity, to which, initial commissioning was carried out to verify the rationality of the design. Results show that the running speed of the test rig can reach 10 000 r/min, and the system components and monitoring parameters are all normal and controllable in the commissioning, such as the shaft vibration, bearing vibration, oil pressure and oil temperature, etc., which basically meet the safety requirements in design. There exists certain difference between peak speeds of bearing vibration and shaft vibration, and some bearing vibration peak speeds keep consistent with the modal frequencies of foundation roof, showing the effect of spring vibration-isolated foundation on the shaft vibration characteristics. The commissioning has laid a foundation for the safety and reliable operation of the test rig in the following researches and experiments.
  • Comprehensive Performance Assessment on Coordinated Control System of Thermal Power Units
    YUAN Guili, LU Siyue, FANG Fang
    2017, 37(11): 895-902.
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    A performance evaluation method based on equivalent open-loop transfer function was proposed for the multi-variable coordination control system of thermal power units. Combined with the minimum information entropy index, this method is able to solve the problem that traditional multivariable performance assessment method cannot accurately evaluate the stochastic performance of the coordinated control system when the system is disturbed by non-Gaussian noise. By transforming the deterministic index of system into the scalar form, and by combining the sub goal multiplication and division with the stochastic performance, a comprehensive index of both deterministic performance and stochastic performance is then obtained, which can be used to guide the design of the coordinated controller. Taking the comprehensive index as the objective function, an optimal control performance could be acquired through optimization of the controller parameters. The performance of the coordinated control system in the thermal power unit was monitored and evaluated in the process of operation by using the optimal index as a benchmark. Simulation results show that for the coordinated control system, the comprehensive performance and robustness of the active disturbance rejection controller is better than those of internal model PI controllers.
  • CFD-DEM Simulation on Heat Transfer Characteristics of a Spouted Fluidized Bed
    BU Changsheng, WANG Xinye, ZHANG Jubing, PIAO Guilin
    2017, 37(11): 903-911.
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    A CFD-DEM heat transfer model was established by coupling the model set up based on the mechanism of both particle-particle and particle-fluid-particle heat transfer with the computation fluid dynamics-discrete particle model (CFD-DEM), which adopts actual contact stiffness to calculate the heat transfer. The CFD-DEM heat transfer model was verified with experimental data of a typical spouted fluidized bed, and the model was then used to further study the heat transfer characteristics of the bed. Results indicate that the heat transfer coefficient of particles is greatly influenced by their flow status, and it is higher in interior cycle than in exterior cycle. The heat transfer coefficient is symmetrically distributed in the spouted fluidized bed, which is higher in fluidized region than in un-fluidized region. The highest heat transfer coefficient appears in both sides of the bed bottom and at the gas entrance, whereas, relatively low heat transfer coefficient exists in the middle region.
  • Molecular Dynamics Investigation on Nucleation and Monomeric Growth of Water Vapor
    FENG Jingyi, ZHANG Yanping, GAO Wei
    2017, 37(11): 912-917.
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    The process of water vapor condensation was simulated by molecular techniques, while the nucleation and monomeric growth of water vapor in phase change period were simulated and analyzed using non-equilibrium molecular dynamics (NEMD) method. A calculation was conducted on the steam condensation rate in the process of phase change, with a study on the effects of droplet size on the condensation rate in the initial period of nucleation and monomeric growth, and with an analysis on the influence of simulation pressure on the condensation performance. Results show that in the case of same degree of supercooling, the condensation rate decreases with the reduction of pressure. During the process of nucleation and monomeric growth, both the heat and mass transfer effectiveness are relatively good at the same pressure and temperature, which increase with the rise of droplet sizes.
  • Shape Feature and Condensation Heat Transfer of Supersonic Steam Jet in Subcooled Water
    WANG Fangnian, QIN Huan, CHEN Wei, MENG Zhaocan, CHEN Yaodong, HU Teng, SHEN Feng, CHENG Xu
    2017, 37(11): 918-924.
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    Shape features and direct contact condensation (DCC) heat transfer characteristics of supersonic steam jet in subcooled water were investigated. Two ways were proposed for shape regime identification, one is according to the three-dimensional regime map based on the exit pressure and mass flux of steam jet as well as the pool water temperature, the other is the table look-up method. Through theoretical analysis, Ma-and Ja-based dimensionless penetration length, maximum expansion ratio and new heat transfer expressions were obtained for the supersonic steam jet, and subsequently the calculation results were compared with the experimental data from literatures. Results show that the calculation values obtained with above heat transfer expressions agree well with the experimental data, and their discrepancies for penetration length and maximum expansion ratio are within ±25% and ±12%, respectively. Supersonic steam jet DCC heat transfer is able to be calculated by identifying the steam jet shape with DCC regime map and by choosing corresponding heat transfer expressions.
  • Experimental Study on Emission Characteristics of Particulate Matters from Wet Flue Gas Desulfurization System of a Coal-fired Power Plant
    CHEN Hao, LUO Zhongyang, JIANG Jianping, XU Xi, LU Mengshi, WANG Tao, FANG Mengxiang
    2017, 37(11): 925-930.
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    Particulate matters in areas before and after the wet flue gas desulphurization (WFGD) system of a 200 MW coal-fired power plant were collected at 100% and 80% boiler loads, so as to obtain the mass concentration and size distribution of particulate matters in the flue gas, and to detect the composition and content of elements involved by observing the morphology of above particulate matters. Results indicate that the mass concentration of total suspended particulate (TSP) is about 16 mg/m3 (in standard state) at the inlet of WFGD system, which is below 10 mg/m3 at the outlet, and the removal efficiency of TSP is 46.8%. The removal efficiency of particulate matters increase with the decrease of boiler load. Element calcium is found in the particulate matters at WFGD outlet, where irregular flocculation structures are formed through agglomeration and coagulation of particles. Under mist eliminator washing condition, the mass concentration of particulate matters decreases, and the content of elements Ca, S, C and O reduces obviously, when the particulate matters are mainly in round shape and dispersedly distributed.
  • Ammonia Spraying Optimization of an SCR Denitrification System Based on RBF Neural Network
    LIAO Yongjin, FAN Junhui, YANG Weijie, JI Peng, ZHANG Jing, FENG Yongxin
    2017, 37(11): 931-937.
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    To optimize the control on ammonia spraying of the selective catalytic reduction (SCR) denitrification device in a 350 MW power boiler in Guangzhou, a relationship model was established between the input and output variables based on radial basis function (RBF) neural network by taking the boiler load, flue gas flow, SCR inlet flue gas temperature, SCR inlet NOx concentration and the spraying ammonia flow as the input variables, and the SCR denitrification efficiency as the output variable, so as to realize the prediction of SCR denitrification efficiency and outlet NOx concentration. Under the premise of satisfying the requirements of NOx emission and aiming at minimizing the operating cost of the SCR system, Matlab was used to perform a simulation experiment on the model to seek a critical point among the ammonia consumption cost, power consumption cost and the NOx emission fee, thus obtaining an optimal flow of spraying ammonia. Results show that the calculated mass flow of ammonia spraying is either higher or lower than the measurements, but the operating cost of the SCR system always keeps decreasing under the premise of meeting the NOx emission standard.
  • Research on Dynamic Response of a 5 MW Wind Turbine Tower Under Seismic Conditions
    YANG Yang, LI Chun, YUAN Quanyong
    2017, 37(11): 938-944.
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    A dynamic simulation model was established for wind turbine on the basis of FAST open source software and Wolf soil-structure interaction (SSI) model under seismic conditions, with which the structural dynamic response of wind turbine was calculated under the combined action of aerodynamic loads at 5 mean wind speeds and seismic loads of 101 intensities. Results show that the aerodynamic load is nonlinearly coupled with seismic load at rated wind speed, and their coupling effect should be adequately considered during the assessment of seismic response. At a constant wind speed, the maximum bending moment of tower base remains unchanged at first, and increases linearly then. In the case of low-intensity earthquakes, the maximum bending moment at different elevations is linearly related to the height of tower; with the rise of seismic intensity, the relationship between bending moment and tower height turns to be nonlinear, and the tower top moment reaches the maximum at rated wind speed.