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  • 2017 Volume 37 Issue 7
    Published: 15 July 2017
      
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  • Distribution Characteristics of Reductive Atmosphere Close to the Water Wall of an Opposed Firing Boiler
    LI Yongsheng, LIU Jianmin, CHEN Guoqing, HUANG Qilong, CAI Pei
    2017, 37(7): 513-519.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 660 MW supercritical opposed firing boiler as an object of study, experimental tests and numerical simulations were conducted to investigate the distribution characteristics of reductive atmosphere close to the side wall under different operation conditions, so as to analyze the effects of following factors on the O2, CO and H2S concentration close to the water wall, and on the NOx concentration at the inlet of SCR system, such as the unit load, operation oxygen volume, over fire air (OFA) volume and the secondary air distribution mode of burners, etc. Results show that the higher the unit load, the stronger the reductive atmosphere; high-temperature corrosion mainly occurs in the case of high unit load. The O2 concentration close to side walls can be improved by means of changing the volume of operation oxygen and OFA, but in a limited extent and with negative effect on NOx emission. Increasing the volume and reducing the swirl intensity of secondary air for burners close to side walls have no obvious effect on the reductive atmosphere.
  • Numerical Analysis on Combustion Characteristics of a MILD Oxy-fuel Burner with Strong/Weak Jets
    JIN Qiye, ZHOU Yuegui, JIN Xudong, ZHENG Tingting
    2017, 37(7): 520-524.
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    Flow and combustion characteristics of a moderate & intense low oxygen dilution (MILD) oxy-fuel burner with strong/weak jets were numerically analyzed by computational fluid dynamics (CFD) method. A finite-rate/eddy-dissipation model (FR/EDM) was used to predict the flue gas velocity, temperature field, species field and internal flue gas recirculation ratio of propane MILD oxy-fuel combustion, and the model accuracy was verified by comparison with existing experimental data. On above basis, the structure of chemical reaction zone as well as turbulence and chemical timescales of MILD oxy-fuel combustion were further analyzed. Results show that the intensive internal flue gas recirculation adequately dilutes and preheats the reactants in the main reaction zone, slows down the chemical reaction rate and further reduces the peak flame temperature, revealing that the MILD oxy-fuel burner with strong/weak jets has the features of low oxygen concentrations and moderate chemical reactions.
  • Research on Temperature Distribution Reconstruction of a Boiler Furnace Based on Acoustic Tomography
    LIU Sha, LIU Shi
    2017, 37(7): 525-532.
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    To fast and acurately obtain the temperature distribution information in real-time monitoring of a boiler furnace, an ART-NN temperature distribution reconstruction algorithm was proposed for the acoustic tomography (AT) measurement by integrating the advantages of algebraic reconstruction technique (ART) and back propagation neural network (BPNN), which was subsequently used to reconstruct a variety of typical temperature distribution models, and then the reconstruction results and robustness were analyzed. Meanwhile, to further evaluate the performance of the proposed algorithm, experimental studies were conducted. Results show that both the reconstruction quality and the robustness of ART-NN algorithm are superior to that of the Tikhonov regularization, Landweber iteration and the ART method, which therefore may serve as a reference for quality improvement of temperature distribution reconstruction of boiler furnaces.
  • Nonlinear Dynamic Response Characteristics of a Rod Fastening Rotor with Rub-Impact Faults
    HU Liang, LIU Yibing, ZHAO Li, ZHOU Chao
    2017, 37(7): 533-539.
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    Nonlinear dynamic response characteristics of a rod fastening rotor with rub-impact faults at fixed points were studied. The specific way is to model the nonlinear contact characteristics between two disks as a spring with nonlinear bending stiffness, then to derive the motion equations of the rod fastening rotor bearing system based on D'Alembert principle considering nonlinear contact characteristics, linear oil film force and rub-impact force, and finally to solve above equations by numerical integration method, so as to analyze the variation law of the displacement response of system with the rotating speed and rub-impact stiffness of disks. Results show that the nonlinear contact between disks has a great influence on the displacement response of system; the system would exhibit strong nonlinear characteristics when the rotating speed of disk rises; the rub-impact force is a main factor affecting the motion state of the rod fastening rotor bearing system, and the motion state would change when the rub-impact force is increased.
  • Simulation Study on Flow and Heat-transfer Characteristics of Gravity Heat Pipes
    ZHAN Hongren, ZHANG Haisong, LI Chunxiao, WU Zhong
    2017, 37(7): 540-545.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    By using computational fluid dynamics (CFD) software and introducing Boussinesq approximate model to the volume of fluid (VOF) model, numerical simulations were conducted on the gravity heat pipe under different heating power with water as the working medium, so as to study the flow and heat-transfer characteristics of the gravity heat pipe based on experimental, theoretical and simulation data. Results show that the wall temperature obtained by CFD simulation agrees well with that of experiment, and the CFD visualization can be used to qualitatively analyze the effects of heating power on the heat-transfer characteristics of gravity heat pipes. In the range of 10-80 W, with the increasing of heating power, the heat-transfer coefficient at evaporation section firstly increases and then decreases, while that at condensation section keeps increasing. Once the heating power exceeds a certain value, the heat-transfer performance at evaporation section deteriorates, when a dried up liquid pool could be observed through CFD visualization, indicating a heat transfer limit is already reached.
  • Fuzzy Self-tuning PID Control of Main Steam Temperature in Thermal Power Boilers Based on UMDA
    WANG Tiankun
    2017, 37(7): 546-551.
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    To solve the problem of large time delay and variable parameters in controlling the main steam temperature of thermal power boilers, a fuzzy self-tuning PID control algorithm was proposed based on univariate marginal distribution algorithm (UMDA), so as to improve the effectiveness of temperature control. For the given model of system with large time delay, fuzzy control rules were used to improve the PID controller, while parameters tuning was conducted by UMDA to achieve the optimization of the fuzzy PID controller, following which simulation and analysis were performed on the time-delay temperature control system. Results show that via the control algorithm proposed, there is basically no overshoot under normal working conditions, and the overshoot under perturbation conditions can be reduced remarkably, with obviously shortened adjustment time, indicating significant improvements on the performance of original system.
  • Nuclear Power Plant Pressurizer Control Based on Sliding Mode of Endocrine Single Neuron
    ZHAO Ming, YE Jianhua, LI Chenjing, CHEN Pengfei
    2017, 37(7): 552-557.
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    Based on the principle of biological neuroendocrine gland hormone regulation, a double layer controller containing long feedback and ultra-short feedback was designed for the nuclear power plant pressurizer with relatively complicated system. In the inner model and sliding mode compound control system, the tracking performance was realized by the internal model controller, namely the endocrine single neuron PID, while the interference of the system was eliminated by the sliding mode controller. A fuzzy controller was introduced to regulate the output gain of signal neuron PID, and a simulation model was established to control the pressure and water level of the pressurizer. Results show that the endocrine variable gain single nerve sliding mode controller has better performance than the traditional PID controller.
  • Aerodynamic Acoustic Characteristics of an Axial Flow Fan with Different Blade Tips
    YE Xuemin, ZHANG Jiankun, LI Chunxi
    2017, 37(7): 558-568.
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    Taking a two-stage variable-pitch axial flow fan as an example, the performance of the fan respectively with five differently shaped blade tips was simulated using Fluent software, so as to obtain the distribution of sound source and acoustic characteristics based on large eddy simulation and FW-H noise model. Results show that all the five blade tips in different shapes can improve the fan performance, in which, the countercurrent-flow-grooved blade tip has the highest improvement effect, followed by the double grooved blade tip, the up-step blade tip and the down-step blade tip, while the current-flow-grooved blade tip only improves the fan performance at lower flow rates. After improving the tip shape of blade, the noise level at tip region and leading edge increases apparently, due to enhanced leakage vortex at blade tip, which are the main sound sources. The tip shape has a significant effect on the amplitude of sound pressure, especially in the area closer to the noise source. The noise within the fan is mainly of the low and medium frequency rotational type, and the noise in all regions reaches its peak value at the fundamental frequency. The blade tip grooving exhibits a slightly increased effect on the sound level resulted from rising frequency, and the morphology of frequency spectrum changes appreciably.
  • Thermal Control Investigation and Engineering Practice of an SCR Denitration System in Near-zero Emission Coal-fired Units
    LI Debo, ZENG Tinghua, LIAO Yongjin, FENG Yongxin, MAO Yisheng, XIE Bin, ZHANG Guiping
    2017, 37(7): 569-576.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem existing in a certain coal-fired thermal power plant that its SCR denitrification system was unable to keep long-term stable NOx emission after near-zero emission retrofit, an investigation was conducted on the thermal control logic, and subsequently key thermal control technologies were proposed for the SCR denitrification system, which were then put into engineering application. Results show that the average NOx concentration of unit could be reduced to below 200 mg/m3 through optimization on the generation process of NOx; effective deviation adjustment could be fulfilled by introducing intelligent predictive feedforward control to the original feedforward-feedback cascade control; the emission concentration of NOx from the funnel could be reduced to below 50 mg/m3.
  • Flow Distribution Characteristics of Low-pressure High-flux Spiral Nozzles
    ZHOU Hao, GUO Wushuang, ZHU Yifan, MA Weiwei
    2017, 37(7): 577-583.
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    Experimental studies were conducted on the flow distribution characteristics of low-pressure high-flux spiral nozzles via a flow distribution testing system. To analyze the effects of nozzle size on the flow distribution characteristics, the flow rate of spiral nozzles with different heights and sizes, the position of spray surfaces at each layer, the spray angle as well as the radial volumetric flow were measured by the way of sector-shaped flasks laid in a row. Results show that at the same pressure, the greater the ratio of nozzle height to nozzle diameter is, the less the mass flow rate, the bigger the spray angle and the smaller the spray flow rate of each surface will be; whereas at different pressures, the higher the pressure is, the larger the mass flow rate, the bigger the spray angle and the larger the distance between the spray surface and nozzle center will be.
  • Study on Control Strategies for Wind Turbine Wakes
    WANG Yuanbo, LI Chun, MIAO Weipao, DING Qinwei, HAO Wenxing
    2017, 37(7): 584-589.
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    To reduce the adverse effects of wind turbine wakes, and to effectively maximize the total power output and coordinately control the aerodynamic performance of wind turbines, numerical simulations were conducted on the control strategies by 9 yaw and 9 staggered arrangements of wind turbines using OpenFOAM based on ALM and LES, so as to compare the total power output of the wind farm among above 18 wake control strageties, while the influencing mechanism of different wake control strategies on the downstream wind turbine flow was analyzed with the help of fluid field parameters. Results show that the wake severely affects the aerodynamic performance of the downstream wind turbine; both the wake control modes could optimize the global wind farm, and among all the yaw arrangements, the total power output could be impoved by a maximum of 35.3%, and among all the staggered arrangements, it could be improved by a maximum of 68.5%.
  • Performance Study on a Newly-structured Oil Cooler for Nuclear Steam Turbines
    YANG Jianfeng, WANG Qiuwang
    2017, 37(7): 590-596.
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    To overcome the deficiency of traditional segmentally-baffled shell-and-tube oil coolers, a two-layer continuous helically-baffled shell-and-tube oil cooler was proposed. The shell side streamline distribution as well as the heat-transfer and resistance characteristics were numerically investigated for shell-and-tube oil coolers respectively with segmental baffle, monolayer continuous helical baffle and two-layer continuous helical baffle using Realizable k-ε turbulence model combined with standard wall function. Results show that compared with segmental baffle, the shell-side heat-transfer coefficient of continuous helical baffle is larger, the pressure drop is lower and the comprehensive performance is obviously better, where no flow stagnation zone is found on the shell side. Moreover, the shell-side heat-transfer coefficient of two-layer continuous helical baffle is between that of the segmental baffle and monolayer continuous helical baffle, and its pressure drop is the lowest. Both the two-layer and monolayer continuous helical baffles have almost the same comprehensive performance.