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  • 2016 Volume 36 Issue 2
    Published: 15 February 2016
      
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  • Combustion Optimization of CFB Boilers Based on Adaptive Fuzzy Inference Method and Fruit Fly Optimization Algorithm
    ZHANG Wenguang, SUN Yazhou, LIU Jizhen, GAO Mingming, CHEN Feng
    2016, 36(2): 84-90.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the combustion efficiency and reduce the pollutant emission of circulating fluidized bed (CFB) boilers, soft measurement models were firstly established for the boiler efficiency and the emission of NOx and SO2 based on adaptive fuzzy inference method using the historical data of a domestic supercritical CFB boiler. Then, three optimization strategies were proposed based on above measurement models to optimize the adjustable parameters of the CFB boiler in a certain range using fruit fly optimization algorithm (FOA). Finally, the effectiveness of the combustion optimization method was further verified by numerical simulation. Results show that the models proposed are fast in modeling and accurate in calculation, which may serve as a reference for energy conservation and pollution reduction of CFB boilers.
  • Numerical Simulation of Sulfide Distribution on Furnace Walls with Air-staged Combustion
    QIN Ming, JIANG Wenting, WU Shaohua
    2016, 36(2): 91-98.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 600 MW ultra-supercritical boiler as an object of study, numerical simulation was conducted to study the distribution characteristics of sulfide gases around water walls in the furnace. Results show that SO2 mainly appears in the region near main burners, while H2S mainly distributes in the region between separated over fire air (SOFA) region and the main burners, where high-temperature corrosion is easy to occur due to the very low concentration of oxygen and the high-temperature atmosphere. With the rise of sulfur content in fuel, the concentration of sulfide gases is slightly increased around the water wall, but the occupation area of high-concentration sulfide gases is significantly enlarged, and high concentration of H2S even occurs in local regions of the water wall near main burners.
  • A Soft Measurement Method for Water-Coal Ratio of an Ultra-supercritical Once-through Boiler
    ZHANG Wei, LIU Jizhen
    2016, 36(2): 99-106.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 1000 MW ultra-supercritical once-through boiler as an example, two methods were proposed for soft measurement of water-coal ratio in the once-through boiler. One is to quickly calculate the water-coal ratio using basic calculation models built up based on the law of mass and energy conservation, by substitution with the boiler efficiency, coal grade and the enthalpy rise of water obtained by nonlinear least square method; the other is to dynamically estimate and predict the water-coal ratio after wave filtering with auto regressive integrated moving average (ARIMA) time series method, of which the accuracy is to be verified by error analysis. With above two methods, the water-coal ratio was respectively calculated and predicted through mechanism analysis and time series model identification. Results show that both the methods can to some extent overcome the shortcomings of traditional monitoring methods for once-through boiler of ultra-supercritical coal-fired units, such as large delay, big error, and so on.
  • Influence of Upstream/Downstream Structures on Aerodynamics of Control Valve System in Feed-water Pump Steam Turbine
    WANG Peng, HE Jin, LIU Yingzheng
    2016, 36(2): 107-112,150.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The three-dimensional steam flow in control valve system of a nozzle-governing feed-water pump steam turbine was extensively modeled at the rated condition by using computational fluid dynamics (CFD), so as to study the influence of upstream/downstream structures on internal steam flow field in the piping of control valve system when all the valves are open. In simulation, the shear stress transport (SST) model was used to solve the closure problem of classic governing equations, while the multiple reference frame (MRF) method was used to simulate the flow field around the rotor in the governing state, with focus on the pressure loss and flow distribution in different valve passages, and on the flow characteristics of superheated steam in the control valve system; meanwhile, an analysis was conducted to the complicated three-dimensional steam flow patterns in following components, such as in the multi-valve chamber, the diffuser downstream the valve exit and in the tube bends, etc. Results show that the flow capacity of control valve is mainly determined by the quantity of downstream nozzles, which is greatly influenced by the distance from the control valve to the inlet of the valve system.
  • Design and Analysis of a Centrifugal Impeller with Blade Leading Edge Located at the Impeller Eye
    GENG Wenqian, DAN Hanpan, CHEN Congcong, LI Jingyin
    2016, 36(2): 113-117.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The design of an impeller with axial admission of air flows, i.e., the impeller with blade leading edge located at the impeller eye, was presented and discussed. First, the cubic Bezier curve was applied to design the meridional flow channel. Then, the distribution of the angular momentum on surfaces of the shroud and hub was prescribed by using a piecewise polynomial function. Finally, modified formulas for the optimum ratio of D1/D2 (D0=D1) were proposed via numerical simulations for the impeller with blade leading edge at the impeller eye, and simultaneously the blade angle was analyzed. Results show that the blade angel on the shroud surface shows a monotonic increasing tendency for the impeller with axial admission of air flows, different from that with radial admission of air flows. By calculation with above modified formulas to optimize the ratio of D1/D2, the whole-pressure polytropic efficiency can be improved by 5% within the scope of working conditions.
  • Study on Prediction Model for Coal Feed Rate of a Boiler
    GU Junjie, ZHANG Yan, LIU Kang, SUN Miaoqing
    2016, 36(2): 118-122,161.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An adaptive feed-forward correction to coal quality was designed, based on which a prediction model was established for the coal feed rate of a boiler considering the power-coal coefficient via the concept of combination model. The optimal weighting factor of last 1 h to current power-coal coefficient was solved by reciprocal method, so as to predict the coal feed rate and power-coal coefficient. The model was applied to the prediction of coal feed rate in No.4 boiler of a 660 MW unit. Results show that the average prediction accuracy on coal feed rate can be improved up to 97% if the predicted value is regarded as the actual coal feed rate.
  • Measurement of Flame Temperature and Emissivity in a 330 MW CFB Boiler by FPW Method
    YANG Haojun, YANG Bin, HE Yuan, CAI Xiaoshu
    2016, 36(2): 123-129.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the principle of fast searching peak wavelength (FPW) method, a water-cooled optical fiber probe was developed to measure the flame temperature and emissivity at different positions in dilute zone of a 330 MW circulating fluidized bed (CFB) boiler, after which the data were processed by FPW method, and subsequently the flame temperature and emissivity at different positions were acquired. Results show that in FPW measurement, the maximum error of flame temperature in CFB boiler would be less than 6%, if the model of coal-fired boiler is adopted for the flame temperature measurement of CFB boiler; both the flame temperature and emissivity reduce with the rise of furnace height; compared with coal-fired boiler, the CFB boiler has a lower flame temperature, higher emissivity and stronger capability in radiation heat transfer.
  • Effects of Second Harmonic Signal on Measurement of Low-concentration Ammonia
    YU Libin, WANG Fei, ZHANG Lifang, YAN Jianhua, CEN Kefa
    2016, 36(2): 130-135.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To meet the detection requirements of ammonia slip in denitrification process of power plant, the low-concentration (10-9 magnitude) ammonia was experimentally measured at ambient temperature and pressure using tunable diode laser absorption spectroscopy by taking the NH3 absorption spectrum in ν2+ν3 band of about 2.25 μm as the detection spectrum, so as to analyze the effects of modulation voltage and frequency on the ratio of signal to noise. Results show that when the modulation voltage and frequency are set at their optimum values of respectively 0.07 V and 14.02 kHz, the second harmonic method can be used to measure the NH3 concentration of as low as 4×10-7, and the second harmonic signal thus obtained has a good linear relationship with the gas concentration, indicating that the method can be used for measurement of low-concentration ammonia in denitrification process of power plant.
  • SO2 Emission Characteristics During Constant Temperature Combustion of Pulverized Coal in High-temperature Low-oxygen Environment
    WANG Chunbo, QIAO Musen, SHAO Huan, LEI Ming
    2016, 36(2): 136-142.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An experimental study was carried out on a self-made thermogravimetric test bench at 800-1400℃, during which both the weight loss and the SO2 emission during constant temperature combustion of pulverized coal were measured in high-temperature and low-oxygen environment, so as to analyze the effects of various factors on the SO2 emission. Results show that in low-oxygen environment, the variation curve of instantaneous SO2 emission has one peak at 800℃ and 1000℃, and has two peaks at 1200℃ and 1400℃, of which the peak value increases with rising temperature. The peak morphology of instantaneous SO2 emission curve is mainly determined by temperature, but also influenced by CO2 concentration. At 1400℃, the increase of O2 concentration brings about more SO2 released in the coke burning stage; whereas in high-temperature and low-oxygen environment, the accumulative emission of SO2 increases first and decreases later on with the rise of CO2 concentration.
  • Experimental Research on ABS Formation Characteristics in SCR Denitrification Process
    MA Shuangchen, DENG Yue, WU Wenlong, ZHANG Linan, MA Jingxiang, ZHANG Xiaoni
    2016, 36(2): 143-150.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To study the effects of temperature and reactant concentrations on the formation mechanism of ammonium bisulfate (ABS), characteristic experiments were conducted on a self-developed test setup, during which the vaporating point of ABS was obtained through thermogravimetric analysis, and subsequently its decomposition temperture was acquired by calculating the Gibbs free energy for decomposition of ABS. Results show that the formation of ABS is a function of temperature and reactant concentrations, and its formation temperature lies in 220-261℃; the larger the concentration product of NH3 and H2SO4, the higher the formation temperature of ABS; for a constant excessive concentration of H2SO4, the higher the concentration of NH3, the larger the ABS precipitation amount; whereas for a constant concentration of NH3, the effect of H2SO4 concentration on ABS precipitation is not obvious. Thermogravimetric analysis indicates that the volatization and decomposition temperature of ABS are respectively 173.7℃ and 447.18℃.
  • Analysis on Static and Dynamic Characteristics of Tension Leg Platform for Offshore Floating Wind Turbines
    WU Zhongwang, YE Zhou, CHENG Xin, GAO Yuewen, LI Chun
    2016, 36(2): 151-156,161.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on Von-Mises theory, the structure strength and vibration mode of a tension leg platform (TLP) for offshore floating wind turbines (OFWTs) were studied using Ansys finite element software. Results show that tensile and compression deformations would occur at the windward and leeward side of the platform stand column, and for the areas of platform above the joint between stand column and extension leg, the deformation increases with the rise of elevation; the regions at the joint between stand column and x-direction extension leg and at the top of platform are dangerous; due to the symmetry of the platform structure and the danger of the lower order modes, the characteristics of the first- and third-order modes should be specially concerned, to prevent the platform from suffering a resonant response; both the wind wheel rotation and the wave motion would not cause resonance.
  • Functional Analysis of Cylindrical Vortex Mitigator Added at Inlet of the Residual Heat Removal System
    HOU Jianfei, XIA Yuzhuo, LIU Xichao
    2016, 36(2): 157-161.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the suction line of residual heat removal (RRA) system in CPR1000 power plant, numerical simulation and analysis were carried out by CFD technique on the original RRA suction line and the one added with cylindrical vortex mitigator, during which the difference of flow field and air entrainment was respectively compared at mid-loop level and several water levels of primary loop between the two structures. Results show that the cylindrical vortex mitigator can obviously suppress the vortex in the RRA suction line, reduce the air entrainment, and descend the critical water level of primary loop significantly, which can improve the margin of safe operation of RRA pump.
  • Aseismic Analysis and Stress Evaluation of Main Steam Safety Valve for Nuclear Power Stations
    SHEN Wei, ZHANG Qiangsheng, CHEN Tianmin, GAO Kaike
    2016, 36(2): 162-167.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Modal calculation and structural optimization were conducted to a main steam safety valve prototype for nuclear power stations using finite element software Ansys, while the stress and deformation of the valve subjected to both earthquake load and design load were calculated, so as to perform the stress evaluation and estimate the maximum gap between valve stem and related stationary part. Results show that the valve prototype can maintain structural integrity and normal operation under earthquake conditions, which is able to meet the requirement of aseismic design and would have good prospects in engineering applications.