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    Boiler Technology
  • Boiler Technology
    Effects of Burner Operation Mode on Performance of the Boiler Under Low Load Conditions
    ZHONG Lijin, DENG Jian, SUN Weijie, YUAN Li, FANG Qingyan,TAN Peng, ZHANG Cheng, CHEN Gang
    2015, 35(9): 693-698.
    Abstract ( )   Knowledge map   Save
    Taking a 700 MW utility boiler as an object of study, which has been retrofitted for low-NOx emission, experimental tests and numerical simulation were conducted at 300 MW low load to investigate the effects of following 3 burner operation modes on the performance and coal consumption of the boiler, such as putting the burners respectively in CDEF 4 layers, DEF upper 3 layers and CDE middle 3 layers into operation. Results show that at the low load of 300 MW, the operation mode of burners has a significant effect on the reheat steam temperature and unit coal consumption. In the DEF operation mode, the flue gas temperature at entrance of platen superheater is significantly improved, the heat transfer of reheater is enhanced, resulting in greatly increased reheat steam temperature, improved turbine efficiency and reduced unit coal consumption for power generation and supply. Under the load conditions of 300 MW or below, the DEF operation mode is recommended, so as to improve the comprehensive efficiency of the unit.
  • Boiler Technology
    Study on Steam Temperature Characteristics of a 600 MW Subcritical Boiler After Low-NOx Retrofit
    XIAO Kun, ZHANG Jianwen, WANG Zhendong
    2015, 35(9): 699-703.
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    Taking a 600 MW subcritical boiler as an example, the static and dynamic characteristics of steam temperature were analyzed after low-NOx retrofit. Results show that great changes have taken place in the boiler after low-NOx retrofit, such as the in-furnace temperature field, the heating surface slagging and the boiler operation mode, which would significantly affect the steam temperature characteristics. Under high load conditions, the boiler steam temperature is mainly subjected to the combined effects of both furnace outlet gas temperature rise and drop respectively caused by air staging combustion and alleviated heating surface slagging; whereas under low load conditions, the steam tempeature is mainly influenced by the lowered furnace flame center due to air staging combustion and by the outlet oxygen concentration. During unloading process of boiler, the rapid decline of reheat steam temperture is caused by both the lowering of furnace flame center and the dropping of exhaust steam temperature in high-pressure cylinder of steam turbines.
  • Boiler Technology
    Retrofit on Low-NOx Combustion of a 350 MW Pulverized Coal-fired Boiler and the Parameters Optimization
    CHENG Huaizhi, WEN Lei, SONG Zhengchang
    2015, 35(9): 704-708.
    Abstract ( )   Knowledge map   Save
    An analysis was performed to the retrofit schemes for low-NOx combustion of a 350 MW pulverized coal-fired boiler, while numerical simulations were conducted to study the gas velocity field, in-furnace temperature field and the NOx emission under different working conditions, following which the simulation results were compared with actual measurements. Results show that the NOx emission may be reduced by extending and regulating the secondary air cone of swirl burner; to facilitate the NOx reduction, enhance the flue gas temperature control at furnace outlet and to relieve the coking status, it is recommended to change the structure of over fire air (OFA) nozzle and increase the OFA flow rate, so as to keep the main combustion zone in the reduction atmosphere. The simulation results are proved to agree well with acutal measurements.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Optimization on Initial Pressure of a Steam Turbine Based on Improved Krill Herd Algorithm
    NIU Peifeng, YANG Xiao, MA Yunpeng, LU Qing, LIN Peng
    2015, 35(9): 709-714.
    Abstract ( )   Knowledge map   Save
    To obtain the optimal main steam pressure of a steam turbine under variable working conditions, a heat rate prediction model was established using operating data of the turbine by echo state networks (ESNs), with which the optimal initial steam pressure was searched in the range of permitted pressure by taking use of the global searching ability of improved krill herd algorithm (I-KH), and the optimized turbine sliding pressure operation curve was compared with the design curve. Results show that the unit heat rate reduces at various loads after optimization, which could be effectively lowered if the turbine runs according to the optimized sliding pressure operation curve.
  • Steam Turbine and Gas Turbine
    Effects of Backing Plate Profile on Leakage Flow and Temperature Distribution of the Brush Seal
    JIANG Shengke, WANG Yan, KONG Xianglin, WANG Yuci, LI Jun
    2015, 35(9): 715-721.
    Abstract ( )   Knowledge map   Save
    The effects of 5 different backing plate profiles on leakage flow and temperature distribution of the brush seal were numerically studied by solving relevant Reynolds-Averaged Navier-Stokes (RANS) equations and energy equations based on Non-Darcian porous model. Results show that the leakage rates of brush seal obtained by numerical simulation agree well with those by experimental tests, proving the simulation method to be effective; it would not be beneficial to the reduction of leakage rate if the backing plate is slotted, and the leakage rate may even be significantly increased when the slot is connected with a downstream cavity. For all the 5 backing plate profiles, the highest temperature is found to be on the contact surface between bristle pack and rotor shaft, and the slotted structure of backing plate does not help to reduce the temperature on tip of the bristle pack.
  • Steam Turbine and Gas Turbine
    Numerical Analysis of Film Cooling on Vibrating Flat Plates
    GE Lishun, WANG Hongguang, SHEN Jiahuan
    2015, 35(9): 722-727.
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    The single-hole film cooling process on a vibrating flat plate was numerical studied, so as to compare the curves of adiabatic film cooling effectiveness in the downstream of jet hole centerline obtained at different vibration frequencies, amplitudes and different blow ratios λ, and to analyze the distribution of relative static pressure around the jet hole. Results show that vibration weakens the effectiveness of film cooling. In the case of λ=1.0, the adiabatic film cooling effectiveness at different amplitudes and frequencies of vibration (FCEV) is larger than that at steady state (FECS), and if x/D>10, the difference between above two states will become more obvious. Under same vibration conditions, and for λ<0.6, the FCEV will be larger than the FECS in the case of x/D<5, and the FCEV will be smaller than FECS in the case of x/D>5. The FCEV will always be smaller than the FECS under the condition of λ>0.6. The distribution of relative static pressure around jet hole appears periodic changes under vibration conditions.
  • Steam Turbine and Gas Turbine
    Numerical Study on Flow and Heat Transfer in a Vibrating Channel with Rib Turbulators
    SONG Ping, SHEN Jiahuan, WANG Hongguang
    2015, 35(9): 728-732.
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    The two-dimensional flow field and heat transfer characteristics of a rectangular vibrating channel with rib turbulators were numerically investigated using the dynamic meshing and UDF programming technology via CFD Fluent software, so as to analyze the effects of inlet velocity, vibration amplitude and vibration frequency on the flow field and heat transfer characteristics under same vibration conditions. Results show that under same vibration conditions, and with the rise of Re, the enhancement of heat transfer weakens, the fluctuation of inlet pressure increases, and the phase of pressure peak advances compared with the stationary case. At same vibration intensities, the higher the vibration amplitude is, the poorer the enhancement of heat transfer will be, resulting in reduced growth rate of heat transfer; however, when the amplitude gets up to the critical value, the effect of vibration amplitude would affect little on the heat transfer; the fluctuation of inlet pressure intensifies with the rise of vibration amplitude. Generally, the vibration enhances the heat transfer, but in some regions, it may also inhibit the heat transfer as the Re and vibration amplitude increase.
    • Automatic Control and Measurement Technology
  • Automatic Control and Measurement Technology
    Nonlinear General Predictive Control and Optimization of Superheat Steam Temperatures
    WANG Songhe, DING Weiming, WANG Wei
    2015, 35(9): 733-739.
    Abstract ( )   Knowledge map   Save
    Aiming at the strong inertia, time-dependent and nonlinear characteristics of boiler superheat steam temperature, an online adaptive nonlinear general predictive control (GPC) algorithm was proposed based on feed-forward compensation of neural network. The mixed model of high-order inertia link plus neural network compensation was used for prediction purpose, instead of the traditional CARIMA model, with which the control law of nonlinear GPC was derived, so as to obtain the optimum estimate-length and control-length under typical conditions through simulation experiments, and to find the nonlinear relationship between these lengths and boiler load. Results show that the control algorithm proposed has a good track capability to some nonlinear controlled objects. During unloading test of boiler, the shortcomings caused by time-independent object parameters and structure can be overcome effectively, which may serve as a reference for actual engineering projects.
  • Automatic Control and Measurement Technology
    Static Modelling and Analysis on Load Change Capability of Condensate Throttling
    WANG Wei, LIU Jizhen, ZENG Deliang, NIU Yuguang
    2015, 35(9): 740-745.
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    Using steam-water distribution equation, the variations of extraction flow caused by condensate throttling were calculated for each stage of unit, based on which two boundary models were set up for the relationship between turbine power output and condensate water flow, so as to determine the range of load change by condensate throttling. On the basis of analyzing the water temperature change in deaerator, the maintain time of condensate throttling under present water storage was obtained, which was subsequently verified by a 600 MW unit. Results show that condensate throttling would double the rate of load change in power plants; moreover, the load change capability would be stronger when the unit load is higher, in the case of same throttling rate.
  • Automatic Control and Measurement Technology
    Experimental Study on Acoustic Measurement of Flue Gas Flow in Power Boilers
    SHEN Guoqing, HE Shourong, AN Liansuo, FAN Peng
    2015, 35(9): 746-751.
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    Cold simulation was performed to acoustic measurement of flue gas flow in power boilers, during which the gas flow rate was measured based on time-difference method by taking audible sound wave as the signal source and using flow field simulation of Fluent to find the optimum arrangement of loudspeakers. The sound travel-time was estimated respectively by direct cross-correlation algorithm and the generalized cross-correlation algorithm weighted by PHAT. To validate the simulation results, vortex shedding flowmeter was adopted to directly measure the gas flow rate in the flue duct. Results show that the data obtained by acoustic method agree well with actual measurements by vortex shedding flowmeter, and the sweep signal of 6 000-8 000 Hz is proved to be ideal. The algorithm weighted by PHAT is superior to that based on direct cross-correlation in terms of accuracy and sensitivity. The acoustic measurement of flue gas flow can reach a high accuracy, which therefore may serve as a reference for online monitoring of flue gas flow in power boilers.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Performance and Static Analysis of an Axial Fan After Blade Trimming
    YE Xuemin, DING Xueliang, LI Chunxi
    2015, 35(9): 752-759.
    Abstract ( )   Knowledge map   Save
    Taking the OB-84 variable-pitch axial fan as an object of study, the fan performance was simulated using Fluent software in the case of constant tip clearance at installation angles of 29°, 32° and 35°, and with the blade respectively trimmed by 5%, 10% and 15%, so as to analyze the effects of installation angle and trimming rate on the fan performance, noise, blade static analysis and the economy, etc. Results show that both the full pressure and the efficiency reduce with increasing trimming rate and decreasing installation angle when qV≥35 m3/s, with more remarkable decrease in the side of large volume flow; the unstable region could be diminished or even eliminated either by raising the trimming rate or by reducing the installation angle when qV<35 m3/s, in which case the fan operation condition is to be improved, the noise level would be reduced, and all the results of static strength test could meet relevant requirements. For above two methods, the effect of blade trimming is more evident. In the mode of β=29° and Δ=10%, optimum fan economy could be ensured, which is applicable for different schemes.
    • Energy System Engineering
  • Energy System Engineering
    Numerical Simulation on High-pressure Dense-phase Pneumatic Conveying of Pulverized Coal in Vertical Elbow
    PEI Yu, XIONG Yuanquan, ZHOU Haijun
    2015, 35(9): 760-767.
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    Based on existing wall surface model and particle kinetics, a new model of multiphase flow was set up for high-pressure dense-phase pneumatic conveying of pulverized coal in an integrated pipe (vertical pipe, elbow and horizontal pipe connected together) with nitrogen as the carrying medium, by adequately considering the impact of friction stress on the gas-solid two-phase flow. The model was used to simulate the flow characteristics of gas-solid two-phase flow in an integrated pipe, so as analyze the effects of supplementary air flow on the solid-phase velocity, concentration and distribution of turbulent kinetic energy as well as the elbow pressure drop. Results show that the error of elbow pressure drop between simulation results and experimental data is reduced to be less than 20%, verifying the correctness of the model; with the rise of supplementary air flow, the elbow pressure drop increases first and decreases later on, resulting in increased superficial gas velocity, reduced accumulation of pulverized coal on outer side of elbow surface, increased low density area, and increased solid-phase turbulent kinetic energy and granular temperature; when the supplementary air flow gets up to 1.0 m3/h, both the solid-phase turbulent kinetic energy and the granular temperature reduce.
    • Nuclear Technology
  • Nuclear Technology
    Stress Analysis for Magnetic Isolation Shims in CRDM of Nuclear Power Plants
    QU Dazhuang, LI Chen, QIAN Hao, ZHU Bao, ZHAN Yanglie, JING Yi, LIU Gang
    2015, 35(9): 768-772.
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    Considering the elastic supports provided by lift poles, and based on the theory of plates and shells in elastic mechanics, a stress analysis model was set up for the magnetic isolation shim placed on elastic foundation with axisymmetrical bending and subjected to impact load from lift plunger in control rod drive mechanism (CRDM) of nuclear power plant, with which corresponding analytical solutions were obtained by means of power series and matrix transfer technology, and subsequently the anlaytical results were compared with numerical calculations. Results show that the analytical results agree well with those of finite element calculation. Bending tensile stress caused by impact fatigue occurs in the shim at the side contacting with lift pole. The maximum equivalent stress, which is mainly of the radial tensile kind, appears in the one-third radial width from inner side of the shim. This is the main reason leading to fatigue carcking of the shim after the action of impact load from lift plunger for a certain period of operation.
  • Nuclear Technology
    Exergy Analysis for Thermal System in Conventional Island ofNuclear Power Units
    ZHANG Lele, ZHANG Yanping, GAO Wei, HUANG Shuhong, LI Shen, MEI Xiaoyan, CHEN Yunliang
    2015, 35(9): 773-780.
    Abstract ( )   Knowledge map   Save
    Taking the conventional island of a nuclear power unit as the object of study, the exergy loss and exergy efficiency of thermal equipment or processes in the thermal system were calculated by exergy analysis method. Based on the work process of steam turbine and the heat-transfer of the heaters, factors influencing the exergy loss and efficiency of the steam turbine and heaters were analyzed, while the distribution law of exergy economic index thus obtained was illustrated. Results show that in the thermal system of conventional island, the largest exergy loss is in the turbo-generator unit, and the low-pressure cylinder has the energy-saving potential. The design of steam turbine last-stage blade has relatively great effects on thermal economy of the nuclear power unit and the energy-saving potential can be deeply explored by optimizing the cold end system of the nuclear power unit.