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  • 2014 Volume 34 Issue 4
    Published: 15 April 2014
      
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  • Distribution of Pressure Drop and Particle Concentration in a Horizontal Circulating Fluidized Bed Boiler
    XIANG Jie,LI Qinghai,ZHANG Yanguo,MENG Aihong
    2014, 34(4): 253.
    Abstract ( )   Knowledge map   Save
    To study the gassolid flow characteristics in a horizontal circulating fluidized bed (HCFB), the effects of bed material diameter and superficial gas velocity on the profile of pressure drop and particle concentration were analyzed by taking three glass beads (dp=87 μm, 170 μm, and 211 μm) as the test material on a HFCB coldstate test setup with cyclone separator using differential pressure sensors and a fiber optic probe. Results indicate that the pressure drop mainly occurs in the primary chamber, accounting for approximately 90% of the total pressure drop. However, the pressure changes little in the secondary and burnout chamber. In the primary chamber, the axial profiles of both pressure drop and particle concentration are characterized by an exponential curve and the lateral particle concentration distributes in an annuluscore structure. The particle concentration is severely asymmetrical in the secondary chamber, dilute at the left and dense at the right, which always remains low in the burnout chamber. The superficial gas velocity has to reach at least 1.25 m/s, 1.50 m/s, and 2.00 m/s respectively for the three glass beads to obtain a state of circulating fluidization.
  • Numerical Simulation on an Optimized Swirl Burner with LowNOx  Emission
    LI Yonghua,ZHOU Binxuan,ZHENG Pingan
    2014, 34(4): 260.
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    An optimization retrofit was made to the structure of a DBCOPCCI swirl burner, to which numerical simulation was carried out before and after the retrofit using Fluent software, so as to analyze corresponding velocity field, temperature field and NOx concentration distribution. Results show that a central recirculation zone appears in the velocity field after retrofit, and the recirculation zone increases both in length and width while reduces significantly in velocity values. The temperature drops entirely after retrofit, and the maximum temperature drop gets up to 200 K, especially, the temperature drops obviously at the expansion cone of burner outlet. The NOx concentration reduces significantly, and the maximum drop of NOx  concentration turns out to be 1×106. The performance of the optimized swirl burner is proved to be better than before.
  • Influence of Mill Separator Outlet Temperature on Properties of Zhundong and Local Coal
    CHENG Zhihai,JI Mingbin,HE Xiang,LIU Hailong,JIN Xin
    2014, 34(4): 267.
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    Experimental tests were carried out to the pulverizing system of a 330 MW heating unit at different mill separator outlet temperatures, so as to study the outside moisture, coal fineness and size distribution of Zhundong and local pulverized coal. Results show that the R90 value of local coal is 5% higher than Zhundong coal under various conditions. With the rise of separator outlet temperature, the R90 value of Zhundong coal reduces from 23.5% to 21%, but the local coal remains unchanged; the particle size of Zhundong coal less than 90 μm gets smaller, but the changing tendency slows down at the temperature above 75 ℃; although the particle size distribution of local coal keeps unchanged, the particles less than 75 μm becomes coarser.
  • Research on Boiler Combustion Enhancement by Sound Field
    WANG Yingzhou,HAN Pu
    2014, 34(4): 271.
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    An ultrasonic generator was installed in the boiler combustion facility, so as to generate resonance among coarse and nonflammable coal particles, and to find the optimum resonance frequency. Combustion tests were subsequently performed under different conditions with and without ultrasonic actions, and the burnout rate of pulverized coal was then calculated through analysis of the ash content. Results show that the burnout rate may be raised by 9.016 3% under the condition with ultrasonic action, due to the enhanced diffusion of oxygen around coal particles, enlarged contact area between oxygen and coal particles, lowered caking probability of coal, and therefore resulting in guaranteed coal combustion, reduced boiler coking probability, and finally improved overall boiler performance.
  • Study on Heattransfer Behavior of Highpressure Inlet Valve for Large Steam Turbines During Cold Startup Process
    CHEN Yongzhao，HUANG Wei，WANG Yuxiang，LIU Liping，XIN Jianhua
    2014, 34(4): 275.
    Abstract ( )   Knowledge map   Save
    Heattransfer behaviors of steam turbine highpressure inlet valve during cold startup process were studied by data analysis and finite element simulation, while features of both the condensation and singlephase convective heat transfer analyzed with insitu test data. Based on empirical formulas for calculation of heattransfer coefficient, and for the purpose of successive approximation, a new method of stepbystep approach was put forward and applied to an actual example, and subsequently the calculation result was compared with that of empirical formulas. The applicability of above heattransfer coefficients was studied for design of different valves during startup process. Results show that the stepbystep approach has higher calculation accuracy and agrees better with actual conditions, by which the calculated heattransfer coefficients can be applied in a certain range.
  • Effects of Geometrical Parameters on Sealing Performance of Turbine Rim Seals
    KONG Xianglin,TAO Jiayin,FENG Zengguo,LI Jun
    2014, 34(4): 280.
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    Effects of geometrical parameters on sealing performance of turbine axial rim seals were numerically studied using 3D ReynoldsAveraged NavierStokes (RANS) equation and SST turbulent model based on the CFD software AnsysCFX. A comparison was made to the sealing performance of axial rim seals between simulated results and experimental data, while an analysis performed to the influence of axial rotorstator space and seal gap on the mainstream ingress and sealing efficiency. Results show that the sealing efficiency obtained by numerical simulation agrees well with that by experiment, proving the numerical method to be reliable; the asymmetric distribution of external mainstream pressure may lead to ingress and egress at different circumferential locations; as to the axial rim seals, the mainstream ingress reduces and the sealing efficiency increases with rising rotorstator space and reducing seal gap.
  • Analysis and Comparison of Lowfrequency Vibration in Tiltingpad Journal Bearing Under Different Load Cases
    2014, 34(4): 286.
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    To solve the problem of lowfrequency vibration in titlingpad journal bearing for large rotating machineries, a numerical simulation was carried out by joint solution of bearing lubrication equations and pad dynamic equations, so as to analyze the fault features of oil whirl and pad fluttering, with an introduction to examples of above two kinds of faults occurring in a turbogenerator unit. Results show that both the oil whirl and pad fluttering may lead to lowfrequency vibration in the tiltingpad journal bearing, and under both the cases, the vibration is of the lowfrequency kind, and the amplitude increases with rising rotating speed, so above two faults are easy to be confused. Oil whirl fault is easy to occur in light load cases while pad fluttering fault is easy to happen in heavy load cases. Both the shaft vibration and bearing vibration are large in the case of oil whirl, and in the case of pad fluttering, the shaft vibration is small, but the pad vibration is large.
  • Influence of Blade Surface Superhydrophilic and Superhydrophobic Property on Formation of Secondary Droplets
    ZHOU Wu,CAI Xiaoshu,JI Xiao
    2014, 34(4): 292.
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    To reduce the erosion damage of lowpressure turbine blades by water impact, considering the formation mechanism of secondary water droplets, a suggestion was proposed to take superhydrophilic and superhydrophobic treatment to relevant blade surfaces, based on which a test platform was set up to simulate the process of water film fragmentation on the superhydrophilic and superhydrophobic surfaces, and the process of formation of secondary droplets in the steam turbine. The particle size and velocity of water droplets were measured using single frame single exposure imaging method, and subsequently the influence of surface hydrophilicity and hydrophobicity of simulation blades on formation of droplets was analyzed. Results show that, compared with ordinary and superhydrophobic surface, smallsized droplets are easy to generate on the superhydrophilic blade surface, which will be carried over by main steam flow, and therefore producing slight water droplet impact damage; superhydrophilic treatment to stationary blade may help to reduce the water droplet impact damage.
  • Study on CFB Boiler Combustion Control Based on Multivariable IMC Decoupling Strategy
    ZHONG Liangmin,LIU Jizhen,ZHANG Heng,WANG Ruiqi
    2014, 34(4): 298.
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    To improve the automatic control quality of CFB boiler combustion system, a general decoupling control structure was proposed for the system based on analysis of the interaction between main steam pressure and bed temperature in the adjustment process. Taking the primary air flow and the coal feed rate as adjustment variables, the decoupling of this strongly coupled twoinput twooutput (TITO) system was achieved through the use of compensated multivariable decoupling internal model control (IMC) strategy. Design process of the decoupling controller was described in detail, while an improved filter designed to effectively offset the slow or dominant pole during the process to speed up response. Parameter tuning index based on overshoot and settling time of response was developed on the basis of comprehensive ISE index. By applying the suboptimal model reduction to the controller and verifying its robustness in the case of input/output disturbance and model mismatch, the decoupling strategy is proved to be effective.
  • Study on Turbine Speed Governing System Based on Selfadaptive Inverse Control
    WANG Wanzhao,WANG Jie
    2014, 34(4): 307.
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    For the turbine speed governing system generally with features of time lag, nonlinearity, obvious variation of dynamic characteristics with working conditions and being hard to be modeled, a selfadaptive inverse control scheme was proposed by adopting the selfadaptive inverse control theory in combination with the neural network technology. Using RBF network online identification, the plant model, inverse model and disturbance canceller were obtained, so as to respectively control both the reference and the disturbance signal, and make them simultaneously achieve best control effects. Simulation results to a 200 MW unit show that compared with PID control method for turbine speed governing system, this scheme can well adapt to the change of plant characteristics, effectively overcome the plant inertia and nonlinearity, significantly inhibit external disturbances, and thus obviously improve the control quality of the turbine speed governing system.
  • Wind Turbine Fault Classification Based on BP Neural Network and Feature Selection Algorithm
    TONG Chao,GUO Peng
    2014, 34(4): 313.
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    To reduce the maintenance cost of wind farms, a condition monitoring method was proposed for wind turbines based on BP neural network combined with ReliefF feature selection algorithm, with which blade angle asymmetrical faults were analyzed using wind farm operation data. Results show that the proposed method can effectively distinguish the asymmetrical faults with high accuracy.
  • Feature Analysis and Stability Prediction of Flame Combustion Based on RAGAPPC Model
    BAI Xiang,LIU Shi
    2014, 34(4): 318.
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    A realcoded accelerating genetic algorithm projection pursuit classification (RAGAPPC) model was used to analyze the five flame features that may affect the flame stability in the time and frequency domain, after which the optimal projection direction reflecting the highdimension data structure was obtained and the materiality level of the five features was determined. An evaluation model of flame stability was then proposed based on the relationship between projection value and sample number, to which the function was given and the errors were analyzed, and subsequently the model was applied to the prediction of measured samples. Results show that the intensity mean has the least contribution but the flicker frequency has the largest contribution to the flame stability. The results agree well with classical combustion theory, which is proved to be applicable in actual stability evaluation of flame combustion.
  • Flue Gas Hg0 Removal by KMnO4 Solution and Its Mass TransferReaction Kinetic Study
    SHI Zhou,WU Jiang,HE Ping,DAI Xuewei,ZHANG Shuaibo,WU Yu
    2014, 34(4): 324.
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    To explore the reaction mechanism between Hg0 and KMnO4, experimental tests were carried out on a bubble reactor, during which the effects of following factors on the removal efficiency of Hg0 in simulated flue gas were analyzed, such as the initial KMnO4 concentration, the pH value and the reaction temperature, etc., while relevant mass transferreaction kinetic parameters calculated. Results show that the removal efficiency of Hg0 increases with rising initial KMnO4 concentration, reducing pH value and reducing reaction temperature; the reaction between Hg0 and KMnO4 is of the complex gasliquid mass transfer kind; both the E and KG/kL increase with the rise of initial KMnO4 concentration, indicating an enhanced effect of chemical reaction on mass transfer process and a weakened liquid membrane resistance, and therefore resulting in improved Hg0 removal efficiency; the removal efficiency of Hg0 reduces with rising reaction temperature, due to the lowered KG/kL coefficient and increased liquid membrane resistance, which are unfavorable to the reaction process.
  • Low Cycle Fatigue and Fracture Properties of Domestic P92 Heatresistant Steels
    ZHANG Zhen,HU Zhengfei,FAN Likun,WANG Bin
    2014, 34(4): 330.
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    Experimental tests were conducted to study the low cycle fatigue behaviors of domestic P92 at both room temperature and 600 ℃ with total strain controlled, during which the fracture morphology was analyzed by scanning electron microscopy (SEM). Results show that the P92 steel is featured by cyclic softening, and the improvement of strain amplitude and temperature is the main cause leading to reduction of its uniaxial fatigue life. All fatigue cracks at both the temperatures originate from the surface and extend in the stripe mechanism. The lower fatigue life at higher temperature is closely related to the oxidative damage, crack expansion rate and plastic deformation.