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  • 2017 Volume 37 Issue 12
    Published: 15 December 2017
      
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  • Research on Energy Conversion of a CFD Boiler Unit During Load Change Process
    MOU Ben, GAO Mingming, HONG Feng, LIU Jizhen, QIAO Jinyu
    2017, 37(12): 945-949.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The energy conversion in dynamic process of a CFB boiler unit was studied, calculated and compared quantitatively based on analysis of the energy storage features, so as to obtain the evaluation index of economical coal feed rate through comparison between the economical and actual coal feed rate, and to investigate the effects of dynamic process control. In addition, the fluctuation status of main steam pressure was used to reflect the dynamic energy balance, which was verified by two examples of load-up processes. Results show that both the study of energy conversion in the process of CFB boiler load changes and the application of evaluation index for economical coal feed rate in the control of air-coal ratio are conducive to the safe and economic operation of the CFB boiler. This may serve as a reference for the control of boiler load changes.
  • Research and Application of Wall Arrangement OFA Technology in Tangentially-fired Boilers
    KONG Hongbing, YANG Zhangning, XIE Jia, DAN Jiayu, ZHANG Shanying, HE Wei, LIU Taisheng
    2017, 37(12): 950-955.
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    A wall arrangement over fire air (OFA) technology developed by DBC was applied in a 330 MW tangentially-fired pulverized coal boiler. Based on the comparison between actual operation data and the results calculated with an improved model, the effects of wall arrangement OFA technology on following parameters were studied, such as the NOx emission, CO emission, boiler efficiency and the steam temperature deviation, etc. Results show that through reasonable air distribution, the NOx emission, CO emission and the concentration of other unburned fuel particles with OFA in wall arrangement are lower than that of conventional corner arrangement, while the boiler efficiency is kept unchanged, which has also good effects in eliminating the temperature deviation on both sides of the boiler.
  • CCSEM Investigation on Distribution Characteristics of Ca- and Fe-containing Minerals During Blend Combustion of Xinjiang High-alkali Coal
    LEI Yu, YU Pengfeng, YU Xin, WU Jianqun, ZENG Xianpeng, YU Dunxi, XU Minghou, YAO Hong
    2017, 37(12): 956-962.
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    Combustion experiments were conducted in a high-temperature drop tube furnace with a high-Si/Al coal (DNY), a high-Na/Ca/Fe coal (DNE) and their blends at various blend ratios. The particle size distribution, speciation and the symbiotic relationship of Ca- and Fe-containing particles in single and blended coal ash were characterized by the advanced computer-controlled scanning electron microscopy (CCSEM). Results show that, compared with DNE ash, the blend combustion tends to increase the particle size of Ca- and Fe-containing minerals and the complexity of association between elements. Increasing the fraction of DNY in the blends decreases the contents of Ca and Fe in aluminum-silicates, and increases the number of aluminum-silicate particles with low contents of Ca and Fe (<10%). The calculated liquidus phases also suggest that the blend combustion may apparently decrease the deposition tendency of DNE ash.
  • Flow Characteristics and Structure Optimization of a Ball-type Control Valve
    LU Jingni, TU Shan, WANG Hongjuan, DU Yang, HONG Zhenhan
    2017, 37(12): 963-968.
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    A numerical simulation model was established according to the entity of a ball-type control valve, so as to study the fluid flow in the valve under small lift conditions, and to optimize the valve structure on the basis of flow analysis. Results show that the flow pattern alters in the valve under small lift conditions, indicating in the form of high flow velocity and violent static pressure variation in the annular channel, low-speed and high static-pressure vortex area below the valve disc, as well as low-speed backflow zone near the wall of valve seat and diffuser section. The flow instability under small lift conditions can be improved by installing a 270° throttling damper in the valve chamber, increasing the diameter of inlet pipe to a certain extent, and cutting cylindrical slot on the lower surface of valve disc, etc. The lateral force imposed on valve disc drops to 0.08 times of its original after installing a 270° throttling damper, which would be reduced by about 12% once the diameter of inlet pipe is increased by 20%.
  • Nonlinear Dynamic Model of a 1 000 MW Once-through Boiler Unit and Its Closed Loop Validation
    FAN He, ZHANG Yufei, SU Zhigang, WANG Peihong
    2017, 37(12): 969-976.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The method of mechanism analysis was adopted to establish a mathematical model for the coordinated control system of an ultra-supercritical boiler unit over a wide operating range, including the coal pulverizing system, the boiler system and the turbine system, with coal quantity command, total feed water flow and opening degree of turbine valve as the inputs, and with steam enthalpy in separator, main steam pressure and unit power as the outputs. In term of parameter identification, the steady parameters were obtained by non-linear regression analysis combined with steady data; while the dynamic parameters were estimated by immune genetic algorithm (IGA) combined with operation data over a wide operating range. The mechanism model was then validated under both steady and dynamic conditions. Results show that the model owns proper and simple structure, with high accuracy, which therefore may serve as a reference for the testing of control algorithms and the design of CCS.
  • An Active Disturbance Rejection Control System for Main Steam Temperature of a CFB Boiler
    WANG Wanzhao, TAN Wen
    2017, 37(12): 977-982.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An active disturbance rejection control scheme was proposed for the main steam temperature of a circulating fluidized bed boiler based on active disturbance control theory, considering following features of the steam temperature, such as large inertia, nonlinearity and so on, which is hard to be accurately modeled due to the variation of its dynamic characteristics with working conditions. An extended state observer was designed to estimate the dynamic state uncertainty and external disturbance of the main steam temperature in real time, so as to realize an accurate control on the main steam temperature by compensating the output of the state error feedback controller with the estimator. Results show that the control scheme can solve the problem existing in the main steam temperature that its dynamic characteristics varies with boiler load, and can effectively overcome the deficiency of large inertia and nonlinearity. Compared with conventional PID control scheme, the proposed scheme significantly improves the control quality on the main steam temperature of circulating fluidized bed boilers.
  • Mechanism Modeling and Simulation for Coal Pulverizing System of MPS Medium Speed Mills
    GU Junjie, WANG Yukun
    2017, 37(12): 983-991.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To realize rapid and effective evaluation and control on the performance of an MPS medium speed coal mill, a mathematical model was built up for the grinding, drying, separation and circulation process, where the MPS medium speed mill was divided into following five parts, such as the bowl zone, grinding zone, initial separation area, classifier and the tank, etc., for which coal quality balance, heat balance and moisture balance formulas were established, and subsequently Matlab software was used to calculate and simulate the dynamic process of the MPS coal mill. Results show that under a given condition of coal mill, the simulation curves of mill output, outlet temperature and outer wall temperature agree well with actual operation conditions under the disturbance of primary air temperature, primary air flow and coal feed rate; the simulated fineness of pulverized coal corresponds with the data of actual operation for different amount of the desiccant and at different rotating speeds of the separator.
  • Evaluation on Operation Stability of a Flue Gas Desulfurization System After Ultra-low Emission Retrofit of the Coal-fired Unit
    TENG Weiming, LI Qingyi, ZHENG Chenghang, HU Daqing, FAN Haidong, LI Li, GAO Xiang
    2017, 37(12): 992-998.
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    An evaluation system was established for the desulfurization performance of a 1 000 MW coal-fired power plant after ultra-low emission retrofit, based on the consumption of material and energy, and the interrelation among the unit load, the inlet and outlet concentration of SO2, the desulfurization efficiency and the slurry pH, etc., so as to evaluate the running status, reliability and stability of the desulfurization unit in detail. Results show that the outlet concentration of SO2 is positively related to the inlet one. When the pH value of gypsum slurry is kept in 5.0-5.6, there exists a linear correlation between the outlet concentration of SO2 and the pH value. The consumption of limestone has a linear relationship with the emission rate of SO2. The relatively stable content of gypsum slurry is found to be able to meet the requirement of process design. After ultra-low emission retrofit, the water consumption reduces, the power consumption rises, the outlet concentration of SO2 drops significantly, the attainment rate reaches99.59%, and the SO2 concentration at unit outlet gets stable, indicating obvious effects of the retrofit.
  • Influence of Different Additives on Harmless Melting Treatment of Waste SCR Catalysts
    ZHOU Hao, GUO Xutao, ZHOU Mingxi
    2017, 37(12): 999-1006.
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    To study the effects of different additives on high-temperature melting treatment of waste SCR catalysts at 1 300℃, an analysis was conducted on the composition of molten slag respectively obtained by using three different additives of different mass fractions. Results show that the waste SCR denitration catalysts can be effectively stabilized by the way of high-temperature melting at 1 300℃. When the proportion of group C additives is 40% (Fe2O3 31.2%, SiO2 2.64%, CaO 5.2% and Al2O3 0.96%), the leaching toxicity of heavy metals Ni, As, Se, Cu and Mn can be reduced by 98.6%, 68.0%, 96.8%, 11.1% and 77.3%, respectively.
  • Capture Performance of an Electrostatic Precipitator for Fly Ash Particles from Boiler Flue Ducts
    WANG Weishu, WANG Xin, ZHANG Chunjie, WANG Jihong, WANG Baowen, YAO Mingyu
    2017, 37(12): 1007-1014.
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    Three-dimensional numerical simulation was carried out using standard k-ε two-equation turbulence model on a wire-plate electrostatic precipitator (ESP) installed in boiler flue duct to study the distribution of flue gas flow field, Corona electric field, particle charging and particle motion track within the ESP; besides, the effect of electric field force and turbulence action on the flue gas flow and the capturing of ash particles were analyzed. Results indicate that the gas flow distribution plates can homogenize the flow field and reduce the gas velocity at the entrance of electric field. The concentration of ash particles reduces gradually along the flow direction; the carrying capacity of ash particles increases with the rise of discharge electrode's voltage; stronger electric field force enhances the capturing of ash particles by collection plate, thus improving the dust collection efficiency. When the flue gas velocity increases, the collection efficiency of ESP decreases, due to the enhanced inertia force undertaken by ash particles under higher flue gas velocity, making the particles escape from the electrostatic precipitator more easily by overcoming the electric field force.
  • Dynamic Response and Mooring Performance of a Semi-submersible Platform for Floating Wind Turbine Considering Typhoon Sea States
    HUANG Zhiqian, LI Chun, DING Qinwei, ZHOU Hongjie, CHEN Fudong
    2017, 37(12): 1015-1022.
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    To research the dynamic response and mooring performance of a semi-submersible platform for floating wind turbine, a NREL 5 MW wind turbine model was established based on the semi-submersible platform, with which, numerical simulation was conducted on dynamic response and mooring performance of the platform under extreme sea conditions using Aqwa software by finite element method considering the combined action of random wave, wind and current load with the radiation/diffraction theory, thus obtaining the response amplitude operator (RAO), the additional mass and the rate of radiation damping changing with the wave frequency, as well as the dynamic response of the platform and the tension response of the mooring line under extreme sea conditions. Results show that the platform would have good motion performance with little dynamic response, as the wave frequency is high (above 1.6 rad/s); changes of wave directions have little effect on the heave response; severest responses of surge and pitch would happen in the wave direction of 0 degree; under typhoon sea states, both the peak of dynamic response of platform and the peak of tension response amplitude are above those without typhoon; the dynamic response of platform and the tension response of mooring line increase with worsening sea states.
  • Trailing Edge Flap Structure Parameters Optimization of a Wind Turbine and Analysis of the Control Performance
    ZHANG Wenguang, BAI Xuejian, HAN Yue
    2017, 37(12): 1023-1030.
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    To find the optimal structure parameters of trailing edge flaps (TEF) under different wind conditions, an aero-servo-elasticity wind turbine simulation platform was set up on Matlab/Simulink with secondarily developed FAST by taking the NREL 5 MW reference wind turbine as an object of study. Under 11.4 m/s steady wind condition, considering the effects of position, length, chord length ratio and angle range of TEF on load suppression and power capture of the wind turbine, an optimization scheme of TEF parameters was introduced based on orthogonal design method, and a group of optimal parameters were thus obtained. Moreover, the effects of TEF control on wind turbine dynamic properties were explored under standard turbulent wind condition. Results show that the TEF can not only significantly alleviate the fatigue load and reduce the action of pitch mechanism, but also effectively weaken the fluctuation of wind turbine power output.