Archive

  • 2014 Volume 34 Issue 2
    Published: 15 February 2014
      
  • Select all
    |
  • Experimental Study on Inventory Overturn in a Breecheslegs CFB and the Control Strategy
    ZHOU Xinglong,CHENG Leming,CEN Kefa,XIE Jianwen,HUANG Jun,ZHOU Qi,NIE Li
    2014, 34(2): 85.
    Abstract ( )   Knowledge map   Save
    Experimental tests were conducted to study the bed material balance in a cold circulating fluidized bed (CFB) test rig with breecheslegs, during which dynamic curves of air flow rate and bed pressure were obtained under different fluidization parameters. Based on theoretical model of parallel flow, the overturn condition in breecheslegs CFB was predicted, while the effects of control system simulated. Results show that the breecheslegs furnace will work in the selfbalance zone if the fluidization air rate exceeds the critical value, in which case, the instantaneous deviation of air flow rate and bed pressure at both sides of the furnace will redress with one another and the bed material in both legs will be in dynamic balance. Bed inventory overturn occurs under the condition the total fluidization air rate being less than the critical data. The critical air flow rate decreases with rising static bed height. The method by adjusting valve opening to control the bed inventory overturn has its limitations. The most important way to control bed inventory overturn is to make the breecheslegs system operate in a selfbalance state.
  • State Prediction of Slagging on Coalfired Boilers Based on Fuzzy Cmeans Clustering and Support Vector Machine
    WANG Hongwu，SUN Baomin，ZHANG Zhenxing,XIN Jing，KANG Zhizhong
    2014, 34(2): 91.
    Abstract ( )   Knowledge map   Save
    A model of support vector machine (SVM) forecasting system was built up for state prediction of slagging on coalfired boilers based on fuzzy Cmeans clustering (FCM) data preprocessing, which takes the softening temperature, alkaliacid ratio, SiO2Al2O3 ratio, percentage of silicon content, dimensionless average furnace temperature and dimensionless diameter of actual tangential flow circle as input variables, and the slagging degree as output variable. Slagging characteristics of 10 boilers were evaluated with the optimized model. Results show that the model is able to avoid overfitting of training sample sets, and it has relatively strong generalization capability. The prediction accuracy with FCMSVM model used in this experiment is 100%, indicating high prediction accuracy of boiler slagging characteristics.
  • Numerical Simulation on 3D Cold Flow Field and Wear of a 50 MW Biomass CFB Boiler
    LI Debo,SONG Jinghui,XU Qisheng
    2014, 34(2): 97.
    Abstract ( )   Knowledge map   Save
    Threedimensional flow field in a 50 MW biomass circulating fluidized bed (CFB) boiler was simulated using Eulerian model, so as to study the gassolid twophase flow and to analyze the wear condition in the boiler. Results show that the simulated distribution of bed pressure agrees well with that of actual measurement. On both the front and back wall of CFB boiler, the solid phase is sparsely distributed in the upper part but densely distributed in the lower part, in the “S” shape. The most serious wear appears at the position of y=0.95 m, and the wear on front wall is more serious than on back wall.
  • Aerodynamic Optimization Design of Airfoils Based on Adaptive Kriging Surrogate Model
    YU Rui,ZHOU Daiwei,ZHU Xiaocheng,DU Zhaohui
    2014, 34(2): 103.
    Abstract ( )   Knowledge map   Save
    An aerodynamic optimization design for turbine airfoil was developed using adaptive Kriging surrogate model, during which the airfoil geometry parameterization was realized with Bézier function and CFD method. Searching process of the surrogate model was improved, and the airfoil geometry was modified through controlling via Bézier control points, so as to automatically achieve optimization design of the leading edge of turbine blade. Results show that that higher pressure recovery coefficient and better aerodynamic performance are obtained after aerodynamic optimization of the airfoil, which proves the optimization model to be reliable and effective.
  • Estimation on Torsional Fatigue Property of TurbineGenerator Shafts Based on Parameter Sensitivity Analysis
    2014, 34(2): 108.
    Abstract ( )   Knowledge map   Save
    Based on parameter sensitivity analysis method, the influence of various factors on torsional fatigue property index of turbinegenerator shafts was studied. Results show that the tensile strength, size factor and surface machining factor have same sensitivities to the torsional fatigue property index, of which the specific values are all 1. The larger the stress concentration coefficient, the higher the linearity of the sensitivity factor, and when the stress concentration coefficient is larger than 1.68, the sensitivity factor will be more than 1, which will become the main factor influencing the fatigue property. The notch sensitivity factor effects minimum on the fatigue strength. The estimation error of life expenditure may get up to 15.5 times because of the uncertainty of correction parameters.
  • Simplified Nonlinear Dynamic Model of Generating LoadThrottle PressureExtraction Pressure for Heating Units
    LIU Xinping,TIAN Liang,WANG Qi,LIU Jizhen
    2014, 34(2): 115.
    Abstract ( )   Knowledge map   Save
    Based on the features of extraction heating units that use adjusting butterfly valve to control extraction pressure for the regulation of heating extraction flow, and by analyzing the energy balance in extraction heating link of turbine, differential equations were constructed for simplified nonlinear dynamic model of the generating loadthrottle pressure extraction pressure versus the fuel flowopening of turbine governor valveopening of adjusting butterfly valve. On above basis, the disturbance of generating load command, extraction pressure command and mass flow of circulating water in the heating network were simulated. Simulation results show that the relations between model inputs and ouputs are in accord with actual operation conditions of heating units, which can well explain the intrinsic mechanism by controlling extraction pressure to make the extraction flow follow the heating load demand.
  • Online Measurement of 2D Temperature Field for Hightemperature Radiation Source Based on Emissivity and Radiation Intensity
    ZHU Zenghao,LIU Jiaxun,ZHOU Wu,CAI Xiaoshu
    2014, 34(2): 122.
    Abstract ( )   Knowledge map   Save
    A new system, consisting of a fiber spectrometer and a monochrome CCD camera, was developed for online measurement of hightemperature fields, with which the actual emissivity and light intensity field of hightemperature radiation source can be measured simultaneously, and subsequently the hightemperature field can be obtained through calculation. The system was used to measure the temperature field of halogen lamp filament, a hightemperature glowing object, so as to obtain corresponding temperature fields at different voltages. Moreover, a comparison was made to the highest temperature respectively measured by the proposed method and the emission spectrometry. Results show that the relative deviation between above two methods is less than 5%. The proposed method can not only make up the deficiency of emission spectrometry that is unable to get corresponding temperature fields, but also avoid the temperature field measurement errors produced by colorimetric thermometer during instantaneous changes of emissivity and bandwidth of monochromatic
    wavelength, which therefore is proved to be an effective way for temperature field measurement.
  • Study on Pollutant Emission Characteristics of Oil Shale Semicoke and Biomass Blends
    WANG Qing,XUAN Yang,WANG Xudong,LIU Hongpeng
    2014, 34(2): 128.
    Abstract ( )   Knowledge map   Save
    Experimental tests were carried out on a selfdeveloped fluidized bed reactor for oil shale semicoke and biomass blends at different mixing ratios, bed temperatures and fuel particle sizes, so as to obtain the volume fraction and formation mechanism of various gas components emitted from the combustion. Results show that the SO2 emission has a positive nonproportional relationship with the sulfur content in raw fuel blends. The formation mechanism of NOx is very complicated, which has a linear relationship with the nitrogen content, and can be represented by the conversion rate of nitrogen. The gaseous pollutants SO2 and NOx can be absorbed by both the oil shale semicoke and the fuel ash. Too small particle size of fuel blends may inhibit relevant reactions and therefore lead to incomplete combustion of the fuel blends.
  • Simulation Modelling of Coal Gasification in Pressurized Fluidized Bed
    CHEN Lifang,PIAO Guilin,ZHANG Jubing,XIE Hao,Shigekatsu MORI
    2014, 34(2): 134.
    Abstract ( )   Knowledge map   Save
    To find the optimum operating conditions and design parameters for coal gasification of largesize pressurized fluidized bed, a number of simulation models were built up, including the solid particle model, gasphase model, hydrodynamic model of bubbles and the enthalpy balance model, etc., based on which the effects of following factors on the carbon conversion rate, gas production rate and cold gas efficiency were analyzed, such as the coal feed rate, the oxygen mass and the steam flow, etc, and subsequently the optimum range of coal feed rate was determined. Results show that the carbon conversion rate is kept at a level higher than 99% in the initial stage, and for gasifiers with same bed area, their handling capacity may be increased by raising the operation pressure; the gas production rate per kilogram of coal will be increased by 34%, when the operation pressure is raised from 1.5 MPa to 2.1 MPa (raised by 40%); for an
    operation pressure of 2.1 MPa, the optimum range of coal feed rate is from 2.0 kg/(m2·s) to 2.5 kg/(m2·s); the cold gas efficiency may get up to 77% when the oxygencoal ratio is in 0.60.7; the heating value of generated gas is in direct proportion to the steamair ratio.
  • Comprehensive Optimization of Air Preheater for Boiler Flue Gas Heat Recovery
    SONG Jinghui,KAN Weimin,XU Cheng,XU Gang,SONG Xiaona
    2014, 34(2): 140.
    Abstract ( )   Knowledge map   Save
    To break through the inlet temperature limitation of lowtemperature economizer in boiler waste heat recovery system, the tail heating surfaces of boiler were comprehensively optimized, by dividing the air preheater into two stages, and installing a lowtemperature economizer between them. To make the lowtemperature economizer lie in appropriate flue gas temperature range, the outlet temperature of stage II air preheater was altered, so as to obtain optimal
    thermodynamic working conditions. Based on techniceconomic analysis, a comprehensive optimization result was finally achieved according to requirements of actual engineering practices. Results show that the standard coal consumption for power supply can be reduced by 6.7 g/(kW·h), on the basis of twostage air preheater design and reasonable setting of key operation parameters, with the optimum thermodynamic scheme. For an average annual running time of 5 500 h, the net income may reach 21 million RMB/year according to the techniceconomic analysis, indicating obvious economic benefits.
  • TechnoEconomic Analysis of a New Settlement Power Boiler System
    XU Gang,HU Yue,YANG Yongping,XU Cheng,SONG Xiaona,SONG Jinghui
    2014, 34(2): 147.
    Abstract ( )   Knowledge map   Save
    To solve the problems existing in largecapacity highparameter units caused by increased height, lengthened pipeline and increased pressure loss of boiler, a new settlement boiler design was proposed, which makes the turbine platform and the boiler superheaterreheater platform on the same plane, so as to shorten the length of the main steam pipe and the cold/hot segment of reheated steam pipe. An analysis was performed on the variation of the pressure loss, the thermal economy and the cost of power generation resulted from the changes of pipe length. Results show that via the design of settlement boiler, the pipe length can be shortened significantly. When the main steam pipe, the cold segment and hot segment of reheated steam pipe are all shortened by 120 m, the thermal efficiency of the power unit will be increased by 0.18%, while the coal consumption be reduced by 1.044 g/(kW·h), and the initial investment of pipe material be reduced by 65 million RMB. Based on annual utilization hours of 5 249 h and coal price of 600 RMB/t, the annual coal consumption would be reduced by 6 093 t, meaning the fuel cost would be lowered by 3.66 million RMB/year, and the power generation cost would be reduced by 0.002 8 RMB/(kW·h).
  • Calculation Model for Economic Back Pressure of Direct Aircooling Unit and Its Application
    GAO Jianqiang,CHEN Guanbing,XUE Nannan
    2014, 34(2): 153.
    Abstract ( )   Knowledge map   Save
    A calculation model for economic backpressure of direct aircooling unit was set up based on the process mechanism, so as to analyze the influence of back pressure change on the generator terminal power and fan power consumption. Taking a 300 MW direct aircooling unit as the object of study, the power generation benefit resulted from back pressure variation was calculated with the model at different loads, after which the variation tendency of back pressure with load was obtained. Results show that the economic back pressure of direct aircooling unit increases with rising load; the power generation benefit obtained at economic back pressure varies with load; during low load operation, greatest power generation benefit will be produced when the back pressure parameters are optimized to make the unit work at the economic pressure.
  • Numerical Simulation on Laser Fullpenetration Welding of  Mediumthickness Stainless Steel Plates
    2014, 34(2): 159.
    Abstract ( )   Knowledge map   Save
    The temperature and stress field of laser fullpenetration welding process for 16 mmthick stainless steel plates were numerically simulated using commercial software ABAQUS, during which the heat source model was described by a combination of one volume heat source and two superGaussian surface sources, respectively representing the keyhole thermal conduction and plasma/metal vapor thermal radiation. Results show that the weld joint with hourglass cross section obtained by simulation agrees well with that of experiments; the longitudinal residual stress in the plate is the largest, followed by the transverse stress, and finally the transverse throughthickness stress; longitudinal tensile stress exists mainly in the zone 25 mm away from the center line of weld, and the
    maximum value has already exceeded the yield strength; an angular distortion of 0.35° after welding is predicted, and such small distortion could be attributed to the high and dense energy input by the laser, which can fully penetrate the plate by one pass without weld groove.
  • Thermal Stress Analysis for Dissimilar Heat Surface Tubes of Boiler
    YANG Hongquan,LIU Pingyuan,LI Liren
    2014, 34(2): 165.
    Abstract ( )   Knowledge map   Save
    Aiming at the features of thermal stress existing in dissimilar heat surface tube coils, calculations were performed to the thermal expansion stress using finite element analysis, such as linearelastic smalldeformation, linearelastic largedeformation and elasticplastic largedeformation method. Above analysis results were used to evaluate the strength and fatigue life of dissimilar heatsurface tube coils, so as to widen the range of their applications. Analysis results show that the thermal stress calculated by the elasticplastic largedeformation method is closer to actual values; Application results show that the analysis method of linearelastic large deformation may help to ensure longterm operation of the boiler.