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    Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    A Method to Calculate Contact Speed of Neighboring Shrouds or Lacings of Long Blades
    CHEN De-xiang, XU Zi-li, CAO Shou-hong, FAN Xiao-ping, WU Qi-lin
    2012, 32(9): 661-665.
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    To determin the contact speed of neighboring shrouds or lacings for long blades of steam turbines, a method is proposed to use the normal contact force to characterize the relations of relevant contact surfaces, based on which the critical speed (i.e. contact speed) is calculated when the normal force changes from zero to positive. The normal contact force is obtained by 3D contact finite element analysis. To achieve better convergence of the analysis, previous analysis results are taken as initial values of the next analysis. The method has been applied to calculate the contact speeds of related shroud and lacing of a last stage blade in a 200 MW unit working at 3 000 r/min. Results show that the error of contact speed can be reduced to be less than 11.7 r/min after 7 times iterations; the normal contact force of both the shroud and lacing increases with rising rotational speed, which will reach the highest at working speed.
  • Steam Turbine and Gas Turbine
    Numerical Analysis on Unsteady Flow in Blade Tip Clearance of Steam Turbines
    CAO Li-hua, ZHANG Dong-xue, HU Peng-fei, LI Yong
    2012, 32(9): 666-671.
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    Taking the blade tip clearance in high-pressure stage of steam turbine as an object of study, numerical simulation was performed on unsteady leakage flow in the clearance using k-ω sst turbulence model and PISO algorithm, so as to analyze the incidence, trajectory and intensity of the leakage vortex. Results show that the tip leakage flow is of the cyclic and unsteady type; the incidence, trajectory and intensity of the leakage vortex vary with the time and tip clearance height; the effect of tip leakage flow on main stream exhibits a regular variation, from weak to strong, and then from strong to weak; the strength and incidence of the leakage vortex reach their maximums at T/4; and at T/2, the tail-edge shedding vortex of stator blade mix with the leakage vortex in the front of suction surface of rotor blade, creating a new vortex system, while the leakage vortex in the rear of suction surface of rotor blade mix with the separation vortex at its boundary, leaving the suction surface of rotor blade.
    • Boiler Technology
  • Boiler Technology
    The Way to Study Hydrodynamic and Heat-transfer Characteristics of Water Wall Tubes in a Power Plant Boiler
    YU Gu-ying, ZHANG Fu-xiang, YANG Yong, YU Meng, ZHU Cai-guang
    2012, 32(9): 672-677.
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    Ways to study the hydrodynamic and heat-transfer characteristics of water wall tubes in a power plant boiler are being discussed, using a segment of electric heating tube and real radiant water wall tubes, to which a comparison and analysis have been carried out. Experimental results are finally given, concerning the hydrodynamic and heat-transfer characteristics of the spiral water wall tubes in a 1 000 MW ultra supercritical-pressure tower-type once-through boiler, respectively tested in a real furnace and a hydrodynamic test rig. This may serve as a reference for design of water wall systems for similar power plant boilers.
  • Boiler Technology
    Structural Optimization of a Multistage Inertia Pulverized Coal Concentrator
    ZHANG Ya-qing, LI Na, ZHOU Qu-lan, TIAN Ming-quan, SHEN Ji-zhao
    2012, 32(9): 678-681.
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    A multistage inertia pulverized coal concentrator was tested and simulated based on orthogonal experiment theory and numerical simulation method, during which the influence of structural parameters of the coal concentrator on the rich/lean ratio of pulverized coal was studied, and hence an optimized structure was obtained by orthogonal design. Results show that compared with the concentrator designed based on empirical data, the optimized concentrator has a higher separation efficiency, which therefore may serve as a reference for research and development of inertial pulverized coal concentrators.
  • Boiler Technology
    A New Method to Evaluate the Slagging Behavior of Coal Ash
    WEN Xiao-qiang, LIU Yan-chen, GUAN Xiao-hui
    2012, 32(9): 682-687.
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    To solve the problem that the prediction accuracy of coal ash slagging behavior is generally low by single index, a model has been built up for the prediction purpose based on partial least squares (PLS) method and cross-validation theory, which includes four input variables, such as the softening temperature, base-acid ratio, percentage of silicon content and silica-alumina ratio, and one output variable, i.e. the slagging rate. A new concept of isotropic and anisotropic index is proposed, according to which the influence of each index on the slagging behavior is qualitatively analyzed, and subsequently an evaluation criterion is obtained combined with relevant fitting equations. Measurement results show that the proposed PLS model is much more accurate in prediction than that of single index, proving the model to be reasonable and feasible.
    • Engineering Thermophysics
  • Engineering Thermophysics
    Study on Heat Transfer over a Cylinder in Pulsating Flows with Different Vibration Parameters
    ZHENG You-qu, LI Guo-neng, HU Gui-lin, ZHANG Zhi-guo
    2012, 32(9): 688-693.
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    To study the influence of vibration parameters on heat transfer over a cylinder with uniform heat flux in laminar pulsating airflows, an experimental study was carried out on a test rig, with a Reynolds number of 171, under conditions of f=15, 30, 45, 59 Hz, prms=45~286 Pa. Results show that the heat transfer can be enhanced obviously in pulsating airflows with low pulsating frequency and large pressure amplitude. The relative Nusselt number increases with rising pressure amplitude and reducing pulsating frequency, which may get up to 2.55. In the case of Re=171, the empirical formula for heat transfer enhancement is Nur=0.268 4+0.586 7prms0.388 3/f0.317 0, with the correlation coefficient R=0.994 1, indicating a nonlinear relationship between the vibration parameters and heat transfer enhancement.
  • Engineering Thermophysics
    Experimental Study on Spray Characteristics of a Gas-outside Liquid-inside Atomizer
    LIU Ding-ping, YU Hai-long
    2012, 32(9): 693-697.
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    On the design basis of a gas-outside liquid-inside atomizer with built-in Rafael air nozzle, an experimental setup has been built up to study the liquid atomization in multi-phase flows, analyze the influence of gas-liquid mass ratio on the atomized particle size distribution, Sauter mean diameter and spray cone angle, etc., and therefore deduce the formula between the liquid-air pressure ratio and the air-liquid mass ratio, with which the critical air-liquid mass ratio is found to be 0.057. Results show that the liquid-air pressure ratio increases with reducing air-liquid mass ratio; when the air-liquid mass ratio is 0.057, the corresponding liquid-air pressure ratio is 0.92; the air flow coefficient has an inverse relationship with the air-liquid mass ratio. The atomization effect under single-phase condition is far below the two-phase condition, which increases with rising liquid pressure; however the enhancement of liquid pressure weakens gradually on the atomization performance.
    • New Energy
  • New Energy
    3D Flow Field Numerical Simulation on Aerodynamic Characteristics of New Double-rotor Wind Turbines
    ZHOU Yun-long, YANG Cheng-zhi, LI Lü-wan
    2012, 32(9): 698-704.
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    Based on Simplic algorithm and SST k-ω turbulence model, using numerical simulation software Fluent 6.3, the 3D aerodynamic flow field of a new type of small double-rotor wind turbines has been studied and compared with that of single-rotor wind turbines in same size. Results show that compared with single-rotor wind turbine, the turbulence intensity of new double-rotor wind turbine strengthens along with the increase of blade number of rear rotor, and its operation stability reduces to a certain extent; however, the rear rotor with a reasonable number of blades has little influence on the front rotor, which can capture the air leakage of the front rotor effectively, and therefore enables the wind turbine to simultaneously have a larger windward area and maintain a higher rotating speed, and subsequently helps it to achieve two grade utility of wind energy, improve the power generation efficiency and raise the wind power utilization coefficient.
    • Energy System Engineering
  • Energy System Engineering
    Simulation on the Thermodynamic System of a 300 MW Coal-fired Power Plant
    ZHANG Chao, ZHAO Hai-bo, JIN Bo, ZHENG Chu-guang
    2012, 32(9): 705-711.
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    Based on the modeling and simulating principles of process systems engineering, a steady-state thermodynamic system has been developed for simulation of a 300 MW pulverized coal-fired power plant, of which the basic principles and modeling approaches are described in detail. By varying the input parameters, loads and environmental conditions, operation performance of the power plant is simulated under different working conditions. Results show that the relative error of performance data between simulation and performance test is less than 2%. The thermodynamic parameters of mass and energy flow (including mass flow rate, temperature, pressure, specific enthalpy, specific entropy, etc.) and the main equipment running parameters (including isentropic efficiency of steam turbine and pump, terminal temperature difference of heater, heat conduction coefficient, etc.), which are obtained during simulation, may serve as a reference for actual operation and optimization, exergy analysis and thermo-economic analysis of coal-fired power plants.
  • Energy System Engineering
    Economic Analysis of the Power Station with Pressurized Oxy-fuel Combustion and CO2 Capture
    YAN Wei-ping, DONG Jing-lan, REN Hai-feng
    2012, 32(9): 712-717.
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    Taking the 300 MW sub-critical turbine-generator unit as an object of study, an economic calculation was carried out for the unit with 6-8 MPa pressurized oxy-fuel combustion, of which the result was compared with that of the atmospheric oxy-fuel combustion. Results show that under pressurized oxy-fuel combustion condition, the gross unit power output reaches 320 MW due to the increased systematic pressure, the recovered latent heat in flue gas steam, which is to be used to heat low-temperature condensate, and the increased turbine output resulted from reduced steam extraction; the power consumption of air separation unit rises greatly, accounting for about 26% of the gross power, and that of the purification and compression unit reduces sharply, accounting for about 0.2% of the gross power; considering other auxiliary power consumptions, the overall net efficiency of unit with 6-8 MPa pressurized oxy-fuel combustion may be improved by 4.5%, compared with that of the atmospheric oxy-fuel combustion, indicating obvious economical effect in the application of carbon capture and storage technology.
  • Energy System Engineering
    Calculation and Analysis of the Water Cycle System for IGCC Gasifiers
    WU Nu-bin, LIU Jian-bin, JIAN Lang, REN Xi-qing, XU Hong
    2012, 32(9): 718-722.
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    Taking the gasifier in an integrated gasification combined cycle (IGCC) unit as an example, calculation and analysis were carried out based on newly built mathematical models, so as to balance the water flow, heat distribution and pressure distribution in the water cycle system of complicatedly structured IGCC gasifiers. Results show that high rates of water circulation enable sufficient water to flow through the heat surfaces, among which heat-transfer deterioration is avoided. The high pressure drop, occurring in the three tube banks on upper part of the gasifier at target flow, may be reduced by optimizing the structural arrangement, simplifying the steam-water flow path and preventing the steam-water mixture from flowing downward along the tubes, and accordingly the unit efficiency is raised and the operation cost is reduced.
    • Material Science
  • Material Science
    An Investigation on Crack Growth Behavior of a Turbine Rotor After Long-period Operation
    SHI Ke-xian, LIN Fu-sheng
    2012, 32(9): 723-727.
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    Dissection tests were carried out on a HP-IP 30Cr1Mo1V steel rotor for the subcritical pressure turbine, which had been operated for about 16 years, during which the initiation and propagation of the creep and creep-fatigue cracks were studied at 538 ℃ using D.C. electrical potential technique, so as to analyze the influence of initial stress intensity factor on initiation time and propagation rate of the creep cracks, while a comparison made on the crack property of specimens respectively taken at high and low temperature sections. The effect of hold time on growth behavior of creep-fatigue cracks was also investigated, and the correlations between crack growth and time or cycle was simultaneously analyzed under different conditions. Results show that for creep-fatigue cracks, the initiation time may be reduced and the propagation rate may be raised by the effect of fatigue; the growth behavior of creep-fatigue cracks is cycle-dependent at short hold time, which becomes time-dependent at long hold time.
  • Material Science
    An Approach for Long-term Creep-rupture Strength Prediction of Steel TH347H
    DANG Ying-ying, PENG Zhi-fang, PENG Fang-fang
    2012, 32(9): 728-732.
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    On the basis of a multi-region Larson-Miller parameter method newly proposed, long term creep rupture strengths (600-750 ℃, 5×103~2×105 h) were successfully predicted for steel TP347H by using the data from tests lasting up to only 5×103 h at 700 ℃ and 750 ℃. Results show that in the plot of stress vs. rupture life, a set of creep rupture data can be divided into several data sets according to the specific value of σ/σTS, so that the value C is unique in each individual data set; by using the C value in LMP corresponding to the lower-stress longer-time region, long-term creep rupture strengths have been assessed for the steel, of which the predicted results agree well with that of actual measurements. Compared with conventional single region LMP method, the proposed approach may not only avoid overestimation of creep rupture strength, but also shorten the time needed for creep rupture tests. This may serve as a reference for prediction of long-term creep-rupture life of similar steels.
  • Material Science
    A Discussion on Exfoliation Behavior of Duplex Scales Based on Ecocide Hypothesis
    XU Hong
    2012, 32(9): 733-740.
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    Based on Ecocide Hypothesis, theories about the exfoliation of duplex scales on high-temperature heating surfaces of boiler are elaborated. The exfoliation is found to be caused by both internal and external factors, which are mainly the voids existing at the interface between inner and outer layer of scale, and the stresses lying in the scale. Furthermore, the internal and external causes that affect the formation of the voids are respectively chromium content in steel and steam conditions. In superheated steam, oxygen content bears pronounced correlation with chromate content. The cation conductivity of superheated steam could serve as the characteristic index of the chromia evaporation from scale. The inner layer would continue to increase in thickness after exfoliation of outer layer, but it is hard to flake off then. In this case, supercritical units that have suffered thorough exfoliation would be relatively safe, without a worry about peeling off of oxide scales for a long period of time.