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  • 2019 Volume 39 Issue 7
    Published: 15 July 2019
      
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  • Numerical Simulation and Optimization on the Operation Parameters of a Combined Closing-to-wall Air System in a Supercritical Opposed Firing Boiler
    YANG Xigang, JIN Baosheng
    2019, 39(7): 517-523.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the combined closing-to-wall air system in a 600 MW supercritical opposed firing boiler as an object of study, numerical simulations were conducted to investigate the effects of closing-to-wall air intake mode, air rate and air velocity on the oxygen concentration in the flue gas close to the water wall, the boiler NOx emission and the unburned carbon content, etc. Results show that the reductive atmosphere around both the right and the left side wall could be effectively improved by adopting the combined closing-to-wall air system, in which case, the proportion of the area with strong tendency to form high-temperature corrosion could be reduced to be less than 20%. Considering the economic, environmental and safety operation of the unit, the simulated optimal operation conditions are as follows:the closing-to-wall air rate is 4.00%, the nozzle velocity on front and rear wall is 20 m/s, while the closing-to-wall air is taken from the overfire air system.
  • Interaction in Blended Coal Combustion Process: Effects of Coal Blend Way and Air Distribution Mode on Ignition and Burnout Characteristics of the Blended Coal
    CHEN Xinke, MA Qilei, FANG Qingyan, TAN Peng, MA Lun, LI Wei, ZHANG Cheng, CHEN Gang
    2019, 39(7): 524-530.
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    Taking the test furnace with double primary air nozzles as an object of study, numerical simulations were conducted to study the effects of coal blend way and air distribution mode on the ignition and burnout characteristics of the blended coal, and to reveal the inhibition mechanism of oxygen competition on the burnout rate, following which, optimal regulation methods were proposed. Results show that the coal blend way is an important factor that affects the ignition characteristics of the blended coal. In the out-furnace blend way, the ignition characteristics of low-volatile coal could be improved by blending in high-volatile coal, indicating that the coal blend way has significant influence on the burnout characteristics of low-volatile coal; whereas, in the in-furnace blend way, the oxygen competition could be inhibited between the low-and the high-volatile coal, while the burnout rate of low-volatile coal could be improved. Reasonable adjustment of secondary air distribution could further improve the burnout rate of both the low-volatile coal and the coal mixture.
  • Prediction of Carbon Content in Boiler Fly Ash Based on Quantum and Iterative Chaos Vortex Search Algorithm
    LI Xia, NIU Peifeng, LIU Jianping, LI Guoqiang
    2019, 39(7): 531-540.
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    To accurately predict the carbon content in boiler fly ash, an improved vortex search (I-VS) algorithm was proposed based on Bloch coordinates and iterative chaos mapping, following which, a performance comparison was conducted among the original vortex search (VS) algorithm, I-VS algorithm, particle swarm optimization (PSO) algorithm, sine cosine algorithm (SCA) and salp swarm algorithm (SSA). Based on the operation data of a 300 MW circulating fluidized bed boiler, the I-VS algorithm was used to optimize the extreme learning machine with parallel layer perception (PELM) to form the I-VS-PELM model for prediction of carbon content in fly ash. The prediction results of I-VS-PELM were then compared with those of PELM, PSO-PELM, SCA-PELM, SSA-PELM and VS-PELM. Results show that, compared with other models, the I-VS-PELM model has not only higher prediction precision, but also better generalization ability, which could then be used to effectively predict the carbon content in boiler fly ash.
  • Modeling of Steam Turbine Control Stage Under Variable Conditions Based on Operation Data
    YU Jianxi, LIU Pei, LIU Shaojie, LI Zheng
    2019, 39(7): 541-547.
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    By neglecting the reaction degree of steam turbine control stage, an algorithm was proposed for estimating the pressure and temperature after control valve, which laid a foundation for establishing a mathematical model of the control stage under variable conditions using actual operating data of the turbine. For the 330 MW steam turbine of a power plant, according to the opening and closing state of the valve, a dominant factor model was established and verified for the control stage in the sequential valve operation mode based on the method proposed, and subsequently, the flow rate and efficiency characteristics of the control stage were calculated within the full condition range. Results show that the model can accurately calculate the pressure and temperature after the control stage, which proves the proposed method to be reliabile.
  • Endwall Modification Design Based on Flow Control over the Trailing Edge Region
    ZHANG Xuyang
    2019, 39(7): 548-553.
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    Based on numerical simulation results of the Langston cascade, an analysis was conducted on the flow characteristics around the trailing edge of the original model, and subsequently a new type of endwall model was established and optimized, while a comparative evaluation was carried out on the flow phenomena of the new and the original model, with an in-depth discussion on the flow mechanism of the two models. Results show that the new type of endwall can inhibit the generation of twin vortices and tail vortex, eliminate the endwall sink point, make the static pressure distribution on the endwall more uniform, ease the accumulation of low-energy fluid in the trailing edge region, reduce the dead zone at the trailing edge, which all improve the fluid flow effectively. Simultaneously, the total pressure loss factor and entropy increment decrease obviously in the trailing edge region.
  • Aerodynamic Design Optimization of a Highly Loaded Axial-flow Fan Based on Curvature Control Technique
    LI Jieling, CHEN Huanlong, LIU Yang, WANG Junli, YANG Xianqing
    2019, 39(7): 554-561.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Aiming at the features of high adverse pressure gradient, high viscous shear and compressible transonic flow in a highly loaded fan stage, an aerodynamic design optimization was conducted on the fan stage based on geometric curvature control technique. Through reasonablly adjusting the geometric curvature distribution, a new aerodynamic structure was obtained for the fan under design conditions. Results show that after optimization, the total pressure ratio of fan stage achieves 2.490, the adiabatic efficiency gets above 87%, and the mass flow rate reaches 25.8 kg/s, indicating a wider scope of operation with high efficiency. The geometric curvature of blade passage has important driving and adjusting effects on the mainstream and the flow in boundary layer in terms of dynamics.
  • Application Simulation of a Configuration Predictive Controller in pH Value Control of Desulfurization Systems
    HUA Wei, CUI Xiaobo, SHUAI Yunfeng, HUANG Zhijun
    2019, 39(7): 562-567.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To further improve the control quality upon desulfurization systems of thermal power units, a generalized predictive controller was used to replace the traditional primary PID controller for pH value cascade control of the desulfurization systems. Meanwhile, a configuration predictive control method was proposed by simplifying the algorithm and fitting the functions, based on which, a new pH value control system was designed through DCS configuration. Results show that the configuration predictive controller is superior to traditional cascade controller in terms of adjustment time, overshoot and dynamic deviation, which can significantly improve the adjustment accuracy and reduce the adjustment time on pH values. Compared with conventional generalized predictive controller, the configuration predictive controller has basically the same control performance.
  • Optimization of Load Reducing Control for Large-scale Wind Turbines Considering Fatigue Damage Evaluation
    GAO Feng, DENG Xingxing, WU Xiaojiang, YANG Xiyun
    2019, 39(7): 568-575.
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    In view of the increasingly serious problem of fatigue load in large-scale wind turbines, a study was conducted on the optimized strategy of load reduction control. Firstly, FAST and Matlab were combined to build a control model for the 5 MW wind turbine developed by NREL. Then an optimized scheme about advanced pitch control below the rated wind speed was designed, and the optimal advanced pitching range was selected according to the comprehensive evaluation of fatigue damage and power generation. Meanwhile, combined with the power and load control objectives, the PI parameters of the individual pitch controller were optimized in each wind speed segment above the rated wind speed, and then the variable gain scheduling function of the individual pitch controller was fitted. Finally, the load feedback loop was added to further reduce the peak load of the flapwise bending moment at blade root based on the variable gain PI individual pitch strategy. Simulation results show that, the advanced pitching strategy could effectively weaken the load and power fluctuation around the rated wind speed, while the variable gain PI individual pitch controller, added with load feedback, could significantly reduce the blade fatigue damage compared with the collective pitch controller.
  • Sludge Wet Air Oxidation Experiments in a Continuous Hot Test Bed
    YANG Huan, CHEN Yang, QIN Xiaogang, WANG Huan, WEN Lu, FANG Hui, SUN Dengke
    2019, 39(7): 576-584.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To verify the industrial feasibility, robustness and safety of a sludge wet air oxidation (WAO) process, a continuous hot test bed was built to research the sludge wet treatment effectiveness under typical conditions, including analyzing the compositions and properties of the reaction products in solid, liquid and gas phase, and conducting kinetic calculations for relevant reaction processes. Results show that the test bed is able to run steadily for more than 100 h under typical reaction conditions, and the degradation rate of organic matters in solid phase reaches 78.62%. The contents of original and leached heavy metal in residue meet relevant emission standards. In liquid phase, the COD, ammonia state nitrogen, total nitrogen and total phosphor are out of specifications, which need to be retreated in related waste water treatment plants. No SO2 or NOx is detected in the exhaust gas. The sludge WAO process includes the fast-reaction phase and slow-reaction phase, both of which are under the control of chemical reaction kinetics.
  • R/S Analysis on Hurst Exponent of Wind Speed Time Series
    XU Zifei, ZOU Jinhua, LI Chun, YUAN Quanyong
    2019, 39(7): 585-590.
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    Aiming at the nonlinear characteristics of wind speed time series featured by both determinacy and randomness, a study was conducted on the precision of R/S analysis for time series with different durations, while corresponding Hurst exponents of measured wind speed time series were researched based on R/S theory. Results show that for long time series, the CRS method has higher precision in the case of low Hurst exponent, whereas the Lo method is more accurate in the case of high Hurst exponent. For short time series, the CRS method is more accurate in the case of low Hurst exponent, whereas the V/S method is more precise in the case of high Hurst exponent. The wind speed time series has the characteristics of "1/f fluctuation" with long-term correlation. The long time series of wind speed is featured by both long-term correlation and strong short-term correlation, while the short time series of wind speed is featured by strong long-term correlation, in conformity to the strong short-term correlation of long time series.
  • Parameter Analysis of an AA-CAES System Coupled with Solar Auxiliary Heating
    LI Peng, AN Peng, HAN Zhonghe, MEI Zhongkai, JIA Xiaoqiang
    2019, 39(7): 591-597.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the performance of an advanced adiabatic compressed air energy storage (AA-CAES) system, a solar auxiliary heating subsystem was coupled to the original system, and subsequently, a study was conducted on the performance of the newly coupled system. Results show that at a fixed number of compressor stages, the temperature of cold and hot tanks increases slowly with the rising number of turbine stages, while at a fixed number of turbine stages, the temperature of cold and hot tanks decreases with the rising number of compressor stages. When the number of compressor stages is equal to that of turbine stages, the energy storage efficiency, the energy storage density and the coupled energy storage efficiency of the system would be higher than the case the two numbers are not equal. With the enhancement of heat exchanger effectiveness, the temperature of cold and hot tanks, the expansion work and the compression work increase, while the energy storage efficiency and the coupled energy storage efficiency of the system increase first and then decrease.
  • Effects of Thermal Storage Capacity on the Primary Frequency Regulation of a Nuclear Island
    DING Zhenyu, YU Dahai, YU Xiuyue, SU Yi, CHEN Wei, XU Zhenhua, LIU Jianhua
    2019, 39(7): 598-604.
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    To analyze the effects of thermal storage capacity on the primary frequency regulation of a nuclear island, a theoretical analysis was conducted on the steam generator (SG) heat storage, reactor coolant pump (RCP) heat storage and the temperature effect on the heat storage of a domestic M310 pressurized water reactor. On above basis, a heat storage calculation model was set up for the nuclear island by establishing an integral energy conservation equation for the primary circuit, secondary circuit and the nuclear island based on the principle of energy conservation, and subsequently the heat storage coefficient and time constant of the SG and RCP were calculated and verified with a matched simulator. It has been found that the model calculations are just slightly different from the simulation results, which satisfy the requirements of engineering calculations. Due to the existence of temperature effect, the nuclear power unit has a strong self-stability, indicating in the form of strong thermal storage capacity, which is completely able to meet the energy demand of primary frequency regulation.