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  • 2016 Volume 36 Issue 5
    Published: 15 May 2016
      
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  • Operating Parameters Optimization for Low NOx Combustion of Coal-fired Boilers
    LI Jianqiang, WANG Anming, PAN Wenkai, CHEN Xingxu, ZHAO Kai
    2016, 36(5): 337-342,403.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To satisfy the low-NOx combustion adjustment requirement of a 300 MW unit, a soft measurement model of secondary air and a clustering model of oxygen content in the flue gas were built up based on the NOx formation rules and data analysis method by filtering the data in original database of the power plant to reduce the number of operating parameters, after which various parameters in the simplified database were optimized using Aprior algorithm improved with particle swarm optimization, so as to achieve the reduction of NOx emission. Results show that all the optimized parameters are in accordance with the combustion adjustment test, such as the oxygen content in flue gas, combination mode of coal mills, and opening degree of both the secondary air damper and SOFA air damper, etc., indicating that the NOx concentration can be effectively reduced at the inlet of SCR facility on the premise of ensuring the thermal efficiency of boiler.
  • Ignition Characteristics of High-temperature Oxygen Generator in a W-flame Boiler
    YAN Gaocheng, QI Xin, REN Ting, LIU Shi
    2016, 36(5): 343-351.
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    To solve the problem of large oil consumption in cold start-up process of W-flame anthracite-fired boilers, a new ignition technology was proposed with the use of high-temperature oxygen. The specific way is to heat the oxygen to a high temperature with little oil, and then use the high-temperature oxygen to ignite the stream of pulverized anthracite. Hot-state experiments and numerical simulations were implemented to validate the feasibility and effectiveness of the proposed technology. Results show that oxygen can be safely heated to 1450℃ using a high-temperature oxygen generator. In a pure oxygen environment, fuel oil would burn out instantaneously. At the outlet of high-temperature oxygen generator, both the temperature and oxygen mass fraction are uniformly distributed. When the ignition heat power is 700 kW, the flame temperature of pulverized anthracite stream would get up to 1250℃, with the flame length being more than 8 meters.
  • Effect of Shaft Seal Leakage on IP First-stage Steam Cooling Performance of an Ultra-supercritical HIP Combined Steam Turbine
    ZHONG Gangyun, LI Jun, HUO Wenhao, FAN Xiaoping
    2016, 36(5): 352-359.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The effect of shaft seal leakage on intermediate-pressure (IP) first-stage steam cooling performance of an ultra-supercritical high & intermediate pressure (HIP) combined steam turbine was numerically investigated by coupled flow-field calculation and conjugated heat-transfer method, while the steam cooling characteristics were analyzed and compared respectively under no steam cooling, steam cooling and leakage steam cooling conditions. Results show that turbine stage efficiency at first stage of IP cylinder decreases with the rise of shaft leakage flow rate; for a shaft leakage flow rate of 9.68 kg/s, the turbine stage efficiency would be decreased by 0.68% in comparison with the zero leakage case; the cooling mechanism of leakage steam on the first-stage components is same as that of the cooling steam, and their cooling effects are different due to their different flow rates and temperatures; compared with the steam cooling condition, the cooling effect on blade root by steam mixture from both shaft leakage and coolant flow weakens with the rise of leakage flow rate, resulting in increased temperature but reduced temperture gradient at blade root.
  • Unsteady Aerodynamic Study on Last-stage Long Blades of a Steam Turbine Low-pressure Cylinder
    YANG Rui, YANG Jiandao
    2016, 36(5): 360-364.
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    Taking the last two-stage blades of a steam turbine low-pressure cylinder as the objects of study, the aerodynamic flow around the blades was analyzed using non-linear harmonic method, after which the distribution of unsteady aerodynamic loads on the blade surfaces was acquired. Results show that the method proposed can well capture the phenomenon of unsteady flow, such as strong unsteady flow in the diffuser of last-stage stator blade, no obvious unsteady flow in the area of blade tip, etc. The calculation results may serve as a reference for dynamic response analysis of last-stage long blades.
  • Predictive Sliding Mode Control on Bed Temperature of CFB Boilers
    ZHU Hongxia, SHEN Jiong, LI Yiguo
    2016, 36(5): 365-371.
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    To tackle the uncertainties caused by variations of load, coal and environmental conditions as well as by model simplification, a predictive sliding mode control strategy, which is easily understandable and applicable in practice, was proposed for the thermal processes with large inertia or time delay. Firstly, a predictive model without output delay was established to estimate the process output by using a second-order plus dead-time (SOPDT) model obtained in nominal case. Secondly, a reasonable sliding function and a sliding mode control law with adaptively estimated uncertain upper bound were designed to asymptotically stabilize the closed-loop system with uncertainties and disturbances. On the basis above, numerical simulations were conducted on bed temperature of a circulating fluidized bed (CFB) boiler. Results show that the control strategy proposed is fast in bed temperature regulation with small overshoot and strong anti-disturbance capability.
  • Study on Dynamic Load Response of an Ultra Supercritical Unit Caused by Condensate Throttling
    GU Junjie, WANG Peng, HOU Yafei
    2016, 36(5): 372-377,388.
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    Based on conservation equations of mass and energy in the low-pressure heating system of an ultra supercritical unit, a relationship model of condensate flow and unit load was established by studying the dynamic relations between above two variables, to which a numerical simulation was conducted according to the heat balance diagram and structural parameters of a 1000 MW ultra supercritical unit, so as to provide theoretical basis for the control of condensate throttling and unit load in thermal power plants. Results show that the transfer function of condensate flow and unit load can be regulated by changing the condensate flow under rated conditions; the gain coefficient of transfer function increases and the time constant reduces with the rise of unit load under different working conditions.
  • Study on Power Control of Nuclear Reactors
    LIU Wenjie, YE Jianhua
    2016, 36(5): 378-382.
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    A mathematical model of nuclear reactor was built based on numerical simulation, and subsequently PID and fuzzy-PID controls were simulated with the model, while advantages and disadvantages of the two control methods were analyzed. By integrating the two control strategies, a compound control mode was proposed for the nuclear reactor, in which case, the control can be switched between the above two methods. Results show that through integration of the two methods, the effects of power control are significantly optimized and improved in the aspects of response time, overshoot and robustness, etc.
  • Decoupling Control on Electric Power and Average Refrigerant Temperature of Nuclear Power Stations Based on Optimal Hankel-norm Approximation
    QIAN Hong, FANG Zhenlu, YANG Zukui, ZHOU Lei
    2016, 36(5): 383-388.
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    Based on the objective model obtained using least-square method, a complete decoupler of diagonal matrix was designed according to coupling features of the electric power and average refrigerant temperature in a nuclear power station, to which the model order was reduced on the basis of optimal Hankel-norm approximation, and the model thus obtained was subsequently verified with Matlab/Simulink. Results show that the PID control system of order-reduced diagonal matrix is faster in response with lower overshoot in power control, compared with the simple PID control system.
  • Numerical Simulation on Erosion Properties of Finned Tubes
    ZHONG Lei, ZHAO Lingling, CHU Mo
    2016, 36(5): 389-394.
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    Three-dimensional numerical simulations were conducted on gas-solid two-phase flow respectively around the rectangle finned tube, spiral finned tube, single H-type finned tube and double H-type finned tube, so as to comparatively analyze the erosion properties of the base tube and fins. Results show that the erosion at base tube of the spiral finned one is more serious than other three tubes, due to the higher flow velocity around it; for single H-type and double H-type finned tubes, the particle concentration near the root of fin is relatively high, however, the existence of axial velocity helps to reduce the collision angle between particles and the base tube, and therefore alleviate the erosion degree at the root; the double H-type finned tube has not only good rigidity, but also better abrasive resistance for both the base tube and the fins.
  • Numerical Analysis on Pressure Fluctuation of an Axial Flow Fan with Abnormal Installation Angles of a Single Blade
    YE Xuemin, DING Xueliang, LI Chunxi
    2016, 36(5): 395-403.
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    Taking the OB-84 variable-pitch axial-flow fan as an object of study, an unsteady calculation was conducted on the internal dynamics and fan performance under different deviation degrees of a single blade, so as to obtain the time-domain and time-frequency characteristics, and the distribution of time-averaged static pressure and equivalent stress. Simulation results show that both the pressure signal and pressure fluctuation energy at each monitoring point exhibit unusual features with abnormal installation angles of blade, especially the most obvious changes at impeller outlet. The impacts of abnormal blade installation on time-domain and time-frequency characteristics are enhanced with rising deviation degrees, resulting in increased intensity of pressure fluctuations. The approximate entropy at each monitoring point changes obviously with large deviation degrees, indicating good characterization ability on the abnormal blade installation. Remarkable changes are found in the distribution and values of time-averaged static pressure, but the equivalent stress only varies obviously in values.
  • NOx Reduction Optimization Based on Distance Learning Particle Swarm Algorithm
    LI Qingwei, CHEN Huifeng, YAO Guihuan
    2016, 36(5): 404-410.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To reduce the NOx emission of coal-fired power plants by combustion optimization, a prediction model was established using ensembled support vector machine based on the 3 formation mechanisms of NOx introduced, which was subsequently optimized by particle swarm algorithm. To overcome the premature problem of particle swarms, an improved distance learning particle swarm algorithm was proposed. The new method was applied to optimize the NOx emission of a power plant, and was then compared with other methods. Results show that the ensembled support vector machine can effectively improve the accuracy of prediction results, while the new method is able to further lower the NOx emission and makes the search results be more stable.
  • Tube to Tubesheet Welding Technology of Nickel-based Alloy 690
    SUN Guohui, ZOU Dijing, XIE Yanwu
    2016, 36(5): 411-415.
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    Tube to tubesheet welding technology of nickel-based alloy 690 was experimentally studied for the steam generator of AP1000 nuclear power stations. Using the process of all-position automatic inert-gas tungsten-arc welding, qualified weld joints were obtained in the single-layer single-pass self-fusion way with 95%Ar+5%H2 as the shielding gas, and by separately setting welding parameters for different sections of each weld. Meanwhile, macroscopic and microscopic inspections were also carried out to the tube to tubesheet joints welded with different compositions of shielding gas and different heat inputs. Results show that for same welding parameters, different shielding gas would result in different sizes of effective throat. The risk of root crack would increase with the rise of welding heat inputs.
  • Performance Study of Silver-Indium-Cadmium Absorber Rods
    LI Jiwei, XUE Jingjing, LIU Jiazheng, HAN Jiqing, ZHU Libing, ZHENG Xuejun, DANG Yu
    2016, 36(5): 416-420.
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    To satisfy the design requirements of control rod used in nuclear power plants, a structurally-modified large-grain silver-indium-cadium absorber rod was manufactured, of which the chemical composition, grain size, physical properties, mechanical properties and thermal creep properties were tested, so as to analyze the effects of grain size and center hole on the performance of the absorber rod. Results show that the chemical composition of absorber rod can satisfy the requirements of ASTM standards, and the physical properties are consistent with that of the reference material; the thermal conductivity and thermal creep properties could be improved by increasing the grain size, when the strength would be lowered; the mechanical properties are not affected by the center hole. It is expected that the absorber rod can be used in nuclear power plants for long life-time services.