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  • 2019 Volume 39 Issue 4
    Published: 15 April 2019
      
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  • Effects of SOFA Velocity Bias Setting on the Flue Gas Temperature Deviation of a 660 MW Tangentially-fired Tower-type Boiler
    LIU Jichang, FANG Qingyan, MA Lun, YU Pengfeng, ZHANG Cheng, CHEN Gang
    2019, 39(4): 257-266.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    By analyzing the characteristics and formation mechanism of the flue gas temperature deviation in a tower-type boiler, a flue gas temperature deviation control strategy was proposed based on SOFA velocity bias setting, and subsequently the combustion processes in a 660 MW supercritical tangentially-fired tower-type boiler were numerically simulated respectively in the basic case(case 1) and four SOFA velocity bias setting cases. Results show that the simulated data agree well with actual measurements for the volume fractions of O2, CO, and CO2, the mass concentration of NOx and the burnout rate of fly ash in case 1. The flue gas temperature on left side is higher than that on right side in the basic case, due to the combined action of the flue gas rotation, the layout of platen heating surfaces and the traction of induced draft fan. The deviation of flue gas temperature would be aggravated when the right SOFA velocity is higher than the left, and vice versa. In cases that the left SOFA velocity is higher, the deviation of flue gas temperature decreases first and then increases with the rise of left SOFA velocity; the optimum condition occurs in case 4, at the ratio of left to right SOFA velocity of 1.30, when the deviation of flue gas temperature is the smallest.
  • Effects of Pulverized-coal Fineness on the Combustion Behavior in a Tangentially-fired Boiler
    ZHAO Sinan
    2019, 39(4): 267-272.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The effects of pulverized-coal fineness on the ignition, combustion and burnout characteristics in a 630 MW tangentially-fired boiler were numerically simulated, while field tests were performed to measure the boiler efficiency, the power consumption of pulverizing system and the coal consumption for power supply under different conditions of pulverized-coal fineness. Results show that with the coarsening of pulverized-coal particles, the rising position of flue gas temperature moves back gradually along the direction of primary-air jet, i.e. the ignition distance increases; the combustion rate decreases gradually in the initial stage; the temperature in ash-hopper zone increases, and that in main combustion zone decreases obviously, but the position of combustion center remains basically unchanged. The residence time and burnout rate of pulverized coal mainly depend on the fineness of coal particles coming from the burner in the bottom layer. When the pulverized coal is relatively coarse, the boiler efficiency would drop obviously, with reduced power consumption of pulverizing system and increased coal consumption for power supply. The discharge rate of boiler slag would drop when the pulverized coal is relatively fine in the lower mill.
  • Fuzzy Model-based H2/H∞ Load Tracking Control of a Boiler-Turbine System
    LU Zhuye, WANG Dongfeng, WANG Biao
    2019, 39(4): 273-279.
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    Aiming at the nonlinear characteristics of a boiler-turbine coordinated control system for thermal power units, which generally experiences various uncertainties and disturbances in field operation, a design method of T-S fuzzy load tracking controller was proposed under the constraints of mixed H2/H∞ performance index. Targeting the mixed H2/H∞ tracking performance, the method uses the parallel distributed compensation method to design fuzzy state feedback gain and error integral gain controllers for the T-S fuzzy model of the system, and adopts Lyapunov function to analyze the stability of the closed-loop system to obtain linear matrix inequalities (LMI) satisfying the H2/H∞ tracking performance. On above basis, simulation tests were conducted on the T-S fuzzy model of Bell-Åström boiler-turbine system at different loads, while a comparison was made among the T-S fuzzy model, mismatched T-S model and local linear model of the controlled system. Results show that the control method designed has good control performance and shows good robustness in the control of mismatched T-S model.
  • Effect of Turbine DEH Proportional Differential Feedforward Control on Stability of the Power System
    QI Jiangyong, JIN Ge, YANG Tao, HAN Xuewen
    2019, 39(4): 280-285.
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    Considering that the time delay will deteriorate the damping in a turbine speed control system, the proportional feedforward mode was changed into the proportional differential feedforward mode in the speed controller. Through mathematical derivation and frequency domain analysis, the mechanical damping coefficient characterizing the damping characteristics of the speed regulation system was analyzed, while a single-machine infinite power grid model of a steam turbine unit with time delay and other non-linear components was established using Matlab/Simulink to perform numerical simulations by adding small frequency disturbance to the unit. Results show that the damping on the turbine side could be improved significantly by adding a differential link into the conventional proportional feedforward control system. The electric power overshoot is smaller in the proportional differential feedforward mode, with shorter time to achieve stability of the power system.
  • Study on Yaw Control Strategy for Wind Turbines Based on the Target of Comprehensive Economic Efficiency
    CHEN Si, GUO Peng
    2019, 39(4): 286-292.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on power generation simulation of a yaw system and fatigue life quantitative analysis of the yaw bearing, a yaw control reboot tracing wind strategy model was established, which takes comprehensive economic benefits of the wind turbine in a life cycle as the target, the start and stop control of the yaw system as the strategy, thus to reasonably balance the relationship between the power generation and the yaw frequency. To find the optimal control strategy, the hybrid particle swarm optimization-genetic algorithm (PSO-GA) was adopted to optimize the control model. Results show that the model proposed can achieve the expected optimization goals, which may serve as a reference for improving the comprehensive economic benefits of wind turbines.
  • Fault Diagnosis of Rolling Bearings Based on AE Signals and LMD Under Low Speed Conditions
    LIN Jianggang, HU Zhengxin, LI Jing, ZHAI Yimeng, DENG Aidong
    2019, 39(4): 293-298.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To realize the fault diagnosis of rolling bearings under low speed conditions, and to solve the problems existing in acoustic emission (AE) analysis, such as huge volume of waveform flow data and high computational complexity, etc., which are unfavorable to real-time analysis, a time-frequency analysis method of local mean decomposition (LMD) was proposed based on the entropy characteristics of AE signal timing information. Firstly, the method adopts framing preprocessing method and extracts information entropy feature frame by frame to establish timing feature sequence. Secondly, the LMD method is used to decompose the time-series feature sequences. Finally, the Hilbert envelope curve of the first-order modal instantaneous amplitude is calculated. Theoretical analysis and experimental results show that the features extracted by the proposed method have strong ability in identification of inner ring crack faults at low speeds. It is an effective way to identify the faults in rolling bearings under low speed conditions.
  • Study on the Flow Characteristics in Packed Beds with Sand Particles
    LI Liangxing, WANG Huasheng, WANG Kailin, ZHANG Shuangbao
    2019, 39(4): 299-304.
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    To reduce the uncertainties in quantification of debris bed coolability in a severe accident of nuclear power plant, packed beds with sand particles in two size ranges were used to simulate the debris bed and perform single-/two-phase flow tests. Based on the pressure drops measured in the single-phase flow tests and the effective diameter of sand particles calculated with Ergun equation, the air-water two-phase flow tests were performed while the corresponding pressure drops were measured, so as to verify the analysis model for the two-phase flow in the debris bed. Results show that for the packed beds with smaller sand particles, the measured two-phase flow pressure drops show gradual increasing tendency with rising air Renolds number, and the prediction of Lipinski model is closer to actual measurements at lower air Renolds number, while the Reed model becomes more accuracy at higher air Renolds number. Whereas for the packed beds with coarse sand particles, the interficial drag is believed to have a great effect on the two-phase flow resistance, and the two-phase flow pressure drops reduce first and then increase with rising air Renolds number.
  • Experimental Study on Steam Condensation in Horizontal Enhanced Condensation Channels
    WEN Jianjun
    2019, 39(4): 305-312.
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    To investigate the heat transfer characteristics of steam condensation in horizontal enhanced condensation channels (HECCs) and horizontal circular channels (HCCs), the condensation process of steam-nitrogen mixture in HECC and HCC were studied experimentally, while the effects of following factors on the heat transfer characteristics of steam condensation were analyzed, such as the steam pressure, the cooling water flow rate and the non-condensable gas concentration, etc., so as to obtain the variation law of the condensation heat transfer coefficient, the condensate mass flow rate and the steam-side pressure loss. Results show that compared with HCC, the enhancement factors of average condensation heat transfer coefficients in horizontal multi-head spiral channels (HMHSCs) and horizontal multi-start straight channels (HMSSCs) are 2.35 and 1.45, the enhancement factors of average condensate mass flow rate are 1.25 and 1.12, and the enhancement factors of average steam-side pressure loss are 1.29 and 1.16, respectively. That is to say, HECC can effectively enhance the condensation heat transfer characteristics, however, the average steam-side pressure loss increases accordingly.
  • Study on Demisting Efficiency and Pressure Loss of a Mist Eliminator with Freely-rotating Threads
    XIANG Xiaodong, ZHONG Jie, SHI Ge, ZHANG Xueyou
    2019, 39(4): 313-318.
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    To study the performance of a mist eliminator with freely-rotating threads, the effects of the number and speed of rotating threads on the demisting efficiency and pressure loss were researched. Experimental results show that the demisting efficiency increases exponentially with the number of rotating threads, which may reach 95% when the number of threads is 100 and the rotating speed exceeds 900 r/min. The demisting efficiency would be in approximately linear relationship with the rotating speed, when the latter is less than 900 r/min. The increase of demisting efficiency would slow down when the rotating speed gets above 900 r/min, due to the inhabitation effect of the accelerated thread impact fragmentation and the fall-off of water droplets from the threads caused by the excessively high rotary speed. The pressure loss is in linear relationship with the increase of the number of freely-rotating threads, which shows a 4.42 power relation with the rotating speed, indicating that the increase of rotating speed would lead to the remarkable rise of pressure loss.
  • Synergistic Removal of Mercury by Low-Low Temperature ESP for Ultra-low Emission Coal-fired Power Plants
    ZHAO Yi, HAN Lipeng
    2019, 39(4): 319-323.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    By adjusting the flue gas temperature of low-low temperature economizer in a 660 MW ultra-low emission coal-fired power plant, the mercury content in coal and the mercury concentration of different species in flue gas at inlet and outlet of the electrostatic precipitator (ESP) were measured, so as to study the variation characteristics of mercury speciation in the flue gas under different working conditions. Results show that the flue gas temperature in low-low temperature economizer would affect the distribution of mercury speciation, and when the flue gas temperature drops, the elemental mercury turns into oxidized mercury and particulate mercury. The low-low temperature ESP has a synergistic effect on the removal of both gaseous elemental mercury and oxidized mercury. When the outlet flue gas temperature of low-low temperature economizer is 90℃, the shares of elemental mercury and particulate mercury are the highest at the inlet of low-low temperature ESP, while the mass concentrations of elemental mercury and oxidized mercury are the lowest in the outlet flue gas, indicating an optimal effect of low-low temperature ESP on the removal of mercury, with a removal efficiency reaching 84.4%. The mass concentrations of gaseous elemental mercury and oxidized mercury in the outlet flue gas of low-low temperature ESP are higher than other working conditions when the low-low temperature economizer is out of service.
  • Analysis of Key Factors Affecting the Evaporation of Wastewater Droplets
    CHEN Hongwei, WANG Guangtao, WANG Zhaoyang, XU Jifa, LIU Xiaodong
    2019, 39(4): 324-330.
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    To study the evaporation laws of desulfurization wastewater in power plant, numerical simulations were conducted on the evaporation of atomized droplets injected into the rear flue of a boiler, so as to analyze the effects of operation parameters on the total evaporation time of the droplets, and finally to obtain the relationship between the flue gas temperature and the optimum mass flow rate through nozzles by fitting method. Results show that the evaporation time would be the shortest when the gas velocity through rear flue is 10 m/s and the initial velocity of atomized droplets is 5 m/s. At the optimum mass flow rate determined previously, the atomized droplets could be evaporated completely before entering the electrostatic precipitator (ESP), when the flue gas temperature is higher than the acid dew point. The mass flow rate of nozzle injection is linearly proportional to the evaporation time, which is negatively correlated with the temperature of the flue gas before entering the ESP.
  • Analysis and Optimization on Thermal Performance of a 60 MW Supercritical CO2 Recompression Closed Brayton Cycle
    ZHAO Feng, CHEN Yunliang, SHI Jinyuan
    2019, 39(4): 331-337.
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    A mathematical model was established for the 60 MW supercritical CO2 recompression closed Brayton cycle to study the effects of various cycle parameters on the cycle efficiency and cycle power using Matlab language. The cycle parameters were then optimized, after which, optimal parameters were finally presented for the 60 MW supercritical CO2 recompression closed Brayton cycle. Results show that the cycle efficiency and cycle power increase linearly with the rise of turbine inlet temperature; however, the cycle efficiency varies non-monotonically with the split ratio, turbine inlet pressure, and main compressor outlet temperature and pressure, due to the highly non-linear change of carbon dioxide properties near critical point and the constraints of pinch point.
  • Configuration and Operation Optimization of the Micro Gas Turbine Units in a CCHP System
    WANG Zhiguang, HUANG Zhipeng, WANG Yuzhang, WENG Shilie
    2019, 39(4): 338-344.
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    Planning and optimal design were conducted on a combined cooling, heating and power (CCHP) system with micro gas turbine (MGT) as the key equipment based on particle swarm optimization algorithm (PSOA), while configuration of the MGT was optimized by taking the system economy, environmental protection and energy saving as the optimization objectives, so as to analyze the effects of unit configuration and operation strategy on the planning, design and performance of the CCHP system. Meanwhile, a comparative analysis was carried out on the performance of the system respectively in series, parallel and series-parallel operation mode. Results show that the performance of the CCHP system could be greatly increased in the series-parallel operation mode, when the load range of the system is extended, and the start-stop frequency is reduced, which therefore is able to guarantee cooling, heating and power supply in the case of large fluctuations in load.