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  • 2016 Volume 36 Issue 1
    Published: 15 January 2016
      
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  • Experimental and Numerical Investigation on Optimization of Tertiary Air Flow Characteristics in a W-flame Boiler
    WANG Tuwei, MA Lun, FANG Qingyan, LE Fangyuan, ZHANG Cheng, YAO Bin, CHEN Gang
    2016, 36(1): 1-6.
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    Taking the 300 MW W-flame boiler with direct flow split burner as an object of study, a 1:1 scale cold model of wind box was set up to experimentally and numerically study the tertiary air flow characteristics, so as to find the causes leading to the reduction of the tertiary air incidence angle, and to obtain necessary information for structural optimization of the wind box. Results show that the internal structure of tertiary wind box is the main factor that affects the incidence angle of tertiary air flow, and the volumetric flow of tertiary air has basically no effect on the incidence angle. When large wind box is adopted, the incidence angle of tertiary air would greatly become smaller due to the abrupt shrinkage of nozzle flow area and to the squeezing action at turning point of top and bottom surface near the nozzle in the wind box, which could be improved by adding air deflectors in the vertical direction; whereas when small wind box is used, the phenomenon of incidence angle reduction could be eliminated by keeping the flow area of tertiary air nozzle to be same as that of the air chamber, so as to achieve the designed valve of incidence angle of tertiary air.
  • Prediction of Ash Fusion Temperatures Based on Melting Behavior of Mineral Components in Coal Ash
    WANG Chunbo, YANG Chengjun, CHEN Liang
    2016, 36(1): 7-15.
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    To analyze the coal ash fusion properties and predict the ash fusion temperatures (AFTs), a mineral composition model of coal ash at high temperatures in weak reducing atmosphere was established by solving linear programming problems with mass balance equations as the constraint conditions and the minimum of total changes in the Gibbs free energy of chemical reactions as the objective function. Based on above mineral composition model, the fusion point of each mineral (fpi) was introduced to build the function relationship (f) between mineral compositions and AFTs, and the corrected values (φi) were thus obtained via linear-regression analysis, and subsequently the AFTs was predicted by iterative method. Results show that the mineral composition simulated by the model has a good similarity with the XRD patterns and Fact Sage phase spectrums, and the change of minerals also plays a significant role in reflecting ash fusion characteristics, explaining and predicting the changing trends of AFTs as well as determining major minerals in the coal ash. The absolute error of predicted values lies in the range from -80 K to 80 K.
  • Research and Design on the Coordinate Control System of a Once-through Boiler Unit
    QIN Zhiming, ZHANG Luanying, GU Junjie
    2016, 36(1): 16-21,29.
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    Taking the 1 000 MW ultra supercritical once-through boiler unit as an object of study, a nonlinear model was built up for the coordinate control system (CCS) through mechanism analysis, which was linearized based on small deviation method, while corresponding multivariable decoupling controller was designed to achieve full decoupling of the input and output variables, thus the three-input-three-output coordinated control system was finally established and verified under disturbance of coal quality and specific enthalpy of feed water during load-up and load-down process. Results show that the CCS proposed has good control performance.
  • Parameters Tuning and Optimization for Variable-gain PI Controller of Wind Turbine Based on Immune Genetic Algorithm
    GAO Feng, WANG Wei, YANG Xiyun
    2016, 36(1): 22-29.
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    Aiming at the difficulties that the controller parameter of wind turbine are hard to be calculated and adjusted during the process of design and optimization, a linear model of wind turbine suitable for parameter adjustment was proposed through the model linearization of Bladed software, to which the PI controller parameters were adjusted based on the immune genetic algorithm, and subsequently a complete set of adjustment and optimization method for variable-gain PI controller parameters was established via calculation on the parameters of general and variable-gain PI controllers according to statistical probability of wind speed in wind farm and identification parameters of Bladed software. Results show that the method proposed is able to adjust and optimize relevant parameters, which may serve as a reference for design and optimization of variable-gain PI controller for wind turbines.
  • Research on Steady Speed Control of Hydraulic Wind Turbines Based on Dynamic Surface Control
    AI Chao, YAN Guishan, KONG Xiangdong, DONG Yanwu
    2016, 36(1): 30-35,64.
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    To achieve steady speed control of hydraulic governing system in hydraulic wind turbines, mathematical models were built up for the wind speed and wind turbine characteristics, while state equations were established for key parameters in the fixed displacement pump-variable displacement motor hydraulic governing system. A steady speed control method based on dynamic surface control was proposed, of which the control law was derived and analyzed, so as to realize multi-closed-loop control of the motor speed using dynamic surface control principles. The proposed conrol method was verified on the basis of a 30 kVA hydraulic wind turbine platform. Simulation and experimental results show that the control method based on dynamic surface control has good control effect, with good inhibiting functions on time-varying behavior and uncertainty of wind input, achieving steady speed control of the wind turbine.
  • Fast Measurement of Flame Temperature in Pulverized Coal-fired Boiler Based on Peak Wavelength Method
    YANG Haojun, YANG Bin, GUI Xinyang, CAI Xiaoshu
    2016, 36(1): 36-41.
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    Based on Wien's displacement law and Planck's law, a fast measurement technique, the method of peak wavelength, was presented for directly determining the flame temperature of pulverized coal-fired boiler according to the relative spectrum of coal flame measured by fiber optic spectrometer, so as to study the effects of flame emissivity function on the temperature measurement. Taking two boilers respectively of 300 MW and 350 MW as objects of study, specific formulae of peak wavelength were proposed for measurement of the flame temperature. Results show that the peak wavelength method can be used for fast measurement of the non-gray flame like the flame in pulverized coal-fired boiler, with maximum measurement error less than 1.60%.
  • Fault Diagnosis on Lubrication State of Journal Bearings Based on EMD and Grey Relational Degree
    LU Xuxiang, SU Yiming, WU Jiateng, LI Luping
    2016, 36(1): 42-47.
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    A comprehensive fault diagnosis method was proposed for lubrication state of journal bearings based on empirical mode decomposition (EMD) and weighted grey relational degree, since a mapping relation exists between the energy distribution in different frequency bands of acoustic emission and the lubrication state. First, the acoustic emission signals were decomposed into a finite number of stationary intrinsic mode functions based on EMD algorithm, then false components contained in the IMF was eliminated using the correlation coefficient method, and finally the first 10-order IMF components containing main fault information were chosen to calculate the energy ratio and to construct the characteristic vector. Results show that the weighted grey relational analysis has good classification effect on recognition of small samples, which can be used to calculate the grey incidence of different acoustic emission signals, so as to perform fault diagnosis on lubrication state of journal bearings effectively.
  • Inlet Flue Gas Temperature Reduction of SCR Denitrification Systems and the Application in a 1100 t/h Tower Once-through Boiler
    SUN Shaopeng, TIAN Xin, NING Yuqin, GUO Dong, ZHOU Chongbo
    2016, 36(1): 48-52.
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    To solve the problem of too high inlet flue gas temperature existing in the denitrification system of tower once-through boilers, a high-temperature flue gas heat exchanger was designed to reduce the inlet temperature down to the optimum operation range of relevant catalysts, while the heat in flue gas was recycled. A retrofit scheme was proposed for the flue gas heat exchanger system, and its operation effect was evaluated. Results show that the method proposed has helped to solve the problem of too high inlet flue gas temperature of the SCR denitrification system; at rated load, the denitrification efficiency can be increased by 1.4%; in the case of load fluctuation, the heat exchanger may help to stabilize the inlet temperature of SCR denitrification system; with the application of high-temperature flue gas heat exchanger, both the exhaust flue gas temperature and the outlet air temperature of boiler can be reduced.
  • Removal Efficiency of Different WESPs in Coal-fired Power Plants with Near-zero Emissions
    ZHAO Lei, ZHOU Hongguang
    2016, 36(1): 53-58.
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    Using a traditional particle collector and a Dekati DPI small particle collector, flue gas particles were sampled from the inlet and outlet of two differently-structured wet electrostatic precipitators (WESPs) in two 300 MW coal-fired units with near-zero emissions, to which the overal and grade removal efficiency were measured, while the particle size distribution was analyzed. Results show that both the wire-plate and wire-pipe WESP have an outstanding paricle removal efficiency, and the near-zero emission standard of flue gas particles can be achieved using either the wire-plate or wire-pipe WESP, i.e. the particle emission could be controlled under 5 mg/m3. Compared with the wire-pipe WESP, the wire-plate one has a higher particle removal efficiency in the range of particle sizes larger than 10 μm and smaller than 1 μm.
  • Numerical Study on Performance of Serrated Baffles with Hooks
    HONG Wenpeng, LEI Jianqi
    2016, 36(1): 59-64.
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    Numerical simulation was conducted to gas-liquid two-phase flow in serrated baffles of a wet flue gas desulfurization system using Fluent software, during which the demisting efficiency of serrated baffles with hooks was obtained for different droplet sizes at different air speeds, and subsequently a comparison of demisting performance was made for serrated baffles with five differently-sized hooks. Results show that the demisting efficiency can be effectively improved by adding hooks at the outside of flow turning point; the hook length directly affects the baffling performance over gas flow; the longer the hook is, the higher the demisting efficiency and pressure drop will be. Wider hooks will cause the demisting efficiency and pressure drop to reduce a little bit.
  • Comparison of Dynamic Response Between Stationary and Floating Wind Turbines
    DING Qinwei, LI Chun, ZHOU Guolong, YE Zhou
    2016, 36(1): 65-73.
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    Considering wave loads, the dynamic responses of stationary and floating wind turbine platforms and relevant flexible components were studied by taking the measured data of NREL as the source of turbulent wind field and the NREL 5 MW wind turbine as a prototype. Results show that the movements of above platforms are mainly in surge, pitch and yaw directions; the in-plane moment and out-of-plane force at blade root of floating wind turbines are bigger than that of stationary wind turbines; for floating wind turbines, the shear force in surge direction of tower top and tower base and the pitching moment of tower base are three times as much as that of stationary wind turbines; the acceleration at tower top of floating wind turbines presents the characteristics of high frequency and large span.
  • Three-dimensional Numerical Investigation on Fracture Toughness Testing of SA335 P11 Alloy Steel for PWR Main Steam Piping
    ZHANG Xu, DOU Yikang, LIANG Bingbing
    2016, 36(1): 74-78.
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    Using commercial software ABAUQS, a detailed three-dimensional finite element analysis was conducted to the loading process before breaking of SA335 P11 alloy steel for PWR main steam piping during fracture toughness test, so as to numerically analyze the toughness of standard CT specimens with and without side grooves, and to obtain the distribution and variation law of the plastic zone, stress field and local J integrals around the crack front. Meanwhile, a fracture toughness test was carried out to P11 alloy steel specimens with side grooves, and the load-displacement curves agreed well with those of finite element analysis, proving the numerical method to be effective. Based on both the finite element analysis and experimental tests, it has been found that for testing of ductile metals, the specimen with plane-sided structure is hard to get cracking, and the structure with side groove is believed to be a better choice, as it keeps providing high level of constraints around crack front, which makes the distribution of plastic zone dimension, local J integrals and the opening stress become more uniform, and therefore helps to optimize relevant test procedures.
  • Shakedown Analysis of the J-weld Between RPV Closure Head and CRDM Penetration Based on Elastoplastic Constitutive Model
    GAO Yongjian, HE Yinbiao, CAO Ming
    2016, 36(1): 79-83.
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    Finite element models were set up for the J-weld between reactor pressure vessel (RPV) closure head and control rod drive mechanism (CRDM) penetration, and subsequently a shakedown analysis was conducted on the J-weld according to ASME B&PVC-III-1-NB-3228.4 using Chaboche nonlinear kinematic hardening model based on stress-strain curves. Results show that the plastic shakedown analysis could reduce the conservatism of analysis effectively, and the shakedown requirements that could not be satisfied under elastic material assumption could be alternatively guaranteed by the plastic shakedown analysis.