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  • 2019 Volume 39 Issue 10
    Published: 15 October 2019
      
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  • Study on Optimization of Heating Surface Sootblowing in a Coal-fired Boiler Based on Increment Distribution
    SHI Yuanhao, LI Qiang, ZENG Jianchao, CHEN Xiaolong
    2019, 39(10): 777-783.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In view of the present unreasonable situation about the sootblowing way for boiler heating surfaces, an optimized model was established for the sootblowing by comprehensively weighing the improvement of boiler efficiency and the steam consumption caused by sootblowing, under the premise securing the safe operation of the unit. Taking the economizer of a 300 MW coal-fired power unit as an object of study, the measured data and basic thermodynamic data of its DCS system were used to calculate the contamination rate of related heating surfaces. The increment distribution for the same measuring point at different moments was obtained by analyzing the multi-group pollution rates under same working conditions, and the expected values could then be deduced according to the distribution curve. Finally, the sootblowing period was optimized to maximize the heat transfer per unit time by predicting the cleanness state of heating surfaces in the furture based on the known initial state. Results show that compared with traditional sootblowing ways, the optimized sootblowing period can not only improve the heat transfer efficiency, but also reduce unnecessary steam consumption.
  • Technical Problems Occurring in Ultra-low Load Operation of Pulverized Coal-fired Boilers and the Solutions
    MA Dafu, ZHANG Shouyu, HE Xiang, TAO li, SHI Hongfei, CHEN Duanyu
    2019, 39(10): 784-791.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An analysis was conducted on the technical problems occurring in low load (below 40% rated load) and ultra-low load (20%-30% rated load) operation of current domestic pulverized coal-fired boilers, such as poor combustion stability, low hydrodynamic safety, high pollutant emission and low unit economy, etc., following which, corresponding countermeasures were discussed. Results show that the boiler could achieve steady combustion under ultra-low load condition after taking corresponding countermeasures such as refined combustion adjustment, etc. The hydrodynamic safety of a once-through boiler is relatively high in the process above 30% rated load; with the reduction of unit load, the hydrodynamic safety of a drum boiler increases, while its economic performance drops significantly. As to the pollutant emission, more attention should be paid on the NOx concentration.
  • Study on Steam Distribution Optimization of a 600 MW Supercritical Steam Turbine at Medium and Low Load
    LIU Yonglin, HUANG Jiasi, QU Jie, YU Xiaobing, LI Yongle, WANG Wei
    2019, 39(10): 792-796.
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    Taking the 600 MW supercritical steam turbine as an object of study, a theoretical analysis was conducted on the energy saving potential of the composite regulation mode, while experimental tests were performed to determine the flow characteristics, analyze the energy consumption characteristics and to set the overlap degree of various high-pressure control valves under different sequences of operation, following which, the sequence of valve opening was optimized. Results show that after optimization, the high-pressure cylinder efficiency could be increased by 1.53%, 1.34% and 1.42%, and the corresponding heat consumption rate could be reduced by 26.0 kJ/(kW·h), 23.2 kJ/(kW·h), and 25.3 kJ/(kW·h), respectively at the medium/low loads of 500 MW, 400 MW and 330 MW.
  • Gas Excitation Study and Dynamic Stress Analysis of a Radial Turbine for ORC Cycles
    TAO Jiayin, LIU Le, WU Zhihua
    2019, 39(10): 797-803.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To continue the experimental test on a 350 kW organic Rankine cycle (ORC) unit after its blade fractured under full load condition, the nozzle and impeller of the radial turbine were specially optimized without any change to the volute, including adjusting the number and improving the profile of the nozzles and blades, and optimizing the flow path of the impeller, etc. The unsteady flow field in the radial turbine was simulated before and after optimization, while transient dynamics of the optimized impeller were analyzed at rated speed and load. Results show that in comparison with the old impeller, the new one is subject to sharply reduced excitation force of gas flow, with greatly lowered average stress and relatively small dynamic stress, which is safe enough in both static and dynamic status.
  • Simulation and Parameter Identification for Fast Valving Control of Steam Turbines
    HAN Wei, LI Wei, WU Wenjian, ZHANG Bao, SHENG Deren, CHEN Jianhong
    2019, 39(10): 804-810.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem of power oscillation caused by misoperation of steam turbine fast valving control, a turbo-generator-infinite grid coupling model was established to verify the control effect of fast valving and to identify the parameters of the control logic. Time-delay logic was set to filter the distortion signals from power transmitter, while critical clearing time (CCT) was introduced as a basis for parameter identification. Results show that the fast valving control has good effect in overspeed prevention and operation stabilization. When the delay time is set in 60-70 ms with a dead-time of 0.3 s, both the misoperation of fast valving control and the overspeed operation of unit could be avoided.
  • Experimental Research on Monitoring of Gas Flame Stability Based on Image Processing
    TIAN Zhenglin, YU Yuefeng, ZHU Xiaolei, WANG Yu, ZHANG Zhongxiao
    2019, 39(10): 811-817.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the gas combustion test platform, a large number of diffusion and premixed flame images were taken by industrial CCD camera under different conditions, following which, six characteristic variables that representing the shape, position and brightness of the gas flames were obtained by choosing and adopting appropriate image processing algorithm. Taking the six characteristic data of different kinds of flames as the training samples, the classification program was trained by support vector machine, and subsequently the real-time monitoring and stability evaluation were conducted on the combustion test platform. Results show that via the method proposed, the detection accuracy may achieve 99% for different types of flames.
  • Vibration Fault Diagnosis of Steam Turbines Based on VMD and Optimized LSSVM
    TIAN Songfeng, WEI Yan, YU Jianxiong, WANG Aonan, WANG Ziguang, XUE Zheng'ang
    2019, 39(10): 818-825.
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    To treat the vibration faults with non-stationary and multi-component features appearing in the running process of steam turbines, a new method for vibration fault diagnosis of steam turbines was proposed based on relative entropy (RE) cloud model of variational mode decomposition (VMD) and optimized least squares support vector machine (LSSVM). Firstly, the fault signal was decomposed into K modal components according to the preset scale by using the variational mode decomposition. The pseudo-components were removed according to the relative entropy of each modal component and the original signal, and subsequently optimal signal components were extracted and put into the cloud model, while the feature vectors were extracted with inverse cloud generator. Then, the improved fruit fly optimization algorithm was used to dynamically adjust the search step to find the best combination of the super-parameters that would affect the identification accuracy of LSSVM. Finally, the LSSVM with optimized input parameters of eigenvectors was used to identify the faults, and the identification results were compared with that of the LSSVM algorithm respectively based on empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) relative entropy cloud model. Results show that the proposed method is superior to traditional signal decomposition methods, which has a high recognition rate for turbine vibration faults.
  • Early Fault Warning of Auxiliary Equipment for Circulating Fluidized Bed Boilers Based on Data Mining
    ZHANG Wei, LIU Jizhen, GAO Mingming
    2019, 39(10): 826-833.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To ensure the safe operation of auxiliary equipment for circulating fluidized bed (CFB) boilers, a method of early fault warning was proposed for the auxiliary equipment based on fuzzy reasoning and moving average similarity. The fuzzy reasoning based on improved fuzzy association rule mining was used to infer the state reference values of the equipment under normal operating conditions, and the moving average similarity between the test data and reference values was used as the evaluation criterion for judging the states of auxiliary equipment, while the weights of the variables in the similarity function were determined by the analytic hierarchy process. The lowest moving average similarity in normal operating state was then taken as the fault warning threshold, which was subsequently verified by the induced draft fan of a 300 MW CFB power plant. Results show that the system can issue an early fault warning and identify the fault location when the similarity is lower than the fault warning threshold, therefore the method proposed is believed to be effective in the prediction of relevant faults.
  • Model Identification for a Wet Desulfurization System Based on Improved Differential Evolution Algorithm
    KANG Yingwei, SUN Zhibin, CHANG Jun
    2019, 39(10): 834-839.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Using the improved differential evolution algorithm (IDEA) to evaluate the model parameters, and adopting 3σ principle and Butterworth filter to process the operation data of a wet flue gas desulfurization (WFGD) system, a multi-input double-output transfer function matrix model was established for the WFGD system by taking the optimal variable set chosen through decision tree analysis as the input variables, and the slurry pH value and outlet SO2 concentration as the output variables. The model was then identified with historical data of the WFGD system. Results show that compared with traditional differential evolution algorithm (DEA), the IDEA has higher precision in model identification, with stronger adaptability and generalization ability.
  • Selection and Practice of Pretreatment Process for Zero Liquid Discharge of Desulfurization Wastewater from Coal-fired Power Plant
    ZHAGN Juan, LIU Pingyuan, JI Shunjian, HUANG Chuanmin
    2019, 39(10): 840-846.
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    To satisfy the requirements on inlet water quality by subsequent concentration reduction module, a pretreatment process of three-stage softening and two-stage separation (sedimentation pool plus tubular membrane) was proposed for the desulfurization wastewater from Xining Thermal Power Plant according to properties of the wastewater. Results show that compared with the traditional two-stage softening and one-stage separation process, the method proposed helps to reduce the dosing cost from 41 RMB to 17 RMB for every ton of water, thus achieving comprehensive application of the sludge, improving the shock resistance of the system, and providing high quality of inlet water for the subsequent concentration reduction and solidification modules.
  • Experimental Research on Straw Gasification Characteristics in a Circulated Fluidized Bed
    CHEN Yujia, WANG Qinhui, WANG Zhongxia, XIE Guilin, FANG Mengxiang, LUO Zhongyang
    2019, 39(10): 847-852.
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    To study the effects of different parameters on the gasified gas quality and relevant indicators, such as air equivalent ratio, gasification reaction temperature and fluidization velocity, etc., an experimental study was carried out on the air gasification in a small circulating fluidized bed using wheat straw as the raw material. Results show that an increase in the air equivalent ratio causes the gas calorific value and the cold gas efficiency to increase first and then decrease. At the temperature below or equal to 720℃, with the rise of gasification temperature, the calorific value of gasified gas and the efficiency of cold gas increase accordingly; however, due to the high alkali metal content in the wheat straw, agglomeration is likely to occur when the gasification temperature reaches 750℃. The increase of fluidization velocity can improve the quality of gasified gas, but its promotion effect is limited. The efficiency of cold gas is relatively high when the air equivalent ratio is 0.2, the reaction temperature is 720℃ and the fluidization rate is 1 m/s, under experimental conditions.
  • Effects of Blade Spacing and Phase Angle on the Power Characteristics of a Double-rotor Wind Turbine
    SUN Yiming, TAN Jianfeng, ZHOU Tianyi
    2019, 39(10): 853-859.
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    An analysis model was developed for the aerodynamic characteristics of a double-rotor wind turbine using N-S equations and sliding meshes, based on which, a comparison was carried out between the calculated results and experimental data for the blade surface pressure distribution and power characteristics, so as to analyze the effects of blade spacing and phase angle on the power characteristics of the wind turbine. Results show that the power output of front blade is slightly affected by the blade spacing, while that of back blade decreases with the rise of blade spacing, at a gradually improved decreasing degree. With the increase of phase angle, the power output of front blade decreases first and then increases, while that of back blade increases first and then decreases. When the phase angle comes to 30° and 75°, the total power output of the double-rotor wind turbine would reach the maximum and minimum values, respectively.
  • Effect of Hot Isostatic Pressing on Microstructures and Mechanical Properties of Mar M247 Alloy
    HE Qungong, LI Linxu, GAO Zhenhuan, YANG Gongxian, ZENG Hong, YANG Zhaohong
    2019, 39(10): 860-864.
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    The effect of hot isostatic pressing (HIP) on the microstructure and the mechanical properties of precision casting Mar M247 was investigated. Results show that the hot isostatic pressing helps to eliminate the microporosities, increase the density, improve the microstructure, and reduce the segregation of the alloy, leading to greatly improved impact property, tensile property and stress rupture property of the material. Meanwhile, the data dispersion of density and mechanical properties could be reduced for the alloy by hot isostatic pressing.