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  • 2017 Volume 37 Issue 2
    Published: 15 February 2017
      
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  • Heat-transfer Performance of Vertical Water Wall in an Ultra-supercritical Pressure Boiler with High Efficiency and Wide Regulation Load at Low Mass Flux
    WANG Siyang, WANG Wenyu, SHEN Zhi, NIE Xin, YANG Dong, SONG Baojun, JIA Peiying
    2017, 37(2): 85-90.
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    Heat-transfer performance of an internally ribbed tube was experimentally studied at low mass flux under the condition of p=21-29.8 MPa, G=600-1 100 kg/(m2·s) and q=330-793 kW/m2, following which relative heat-transfer correlations were derived by sorting out the experimental data in the near and super critical pressure region. Results show that in the near critical pressure region, where the capacity to restrain the DNB of rifled tube is weakened, heat-transfer performance in the subcritical part behaves better than that in the supercritical part; heat-transfer deterioration can be delayed by increasing the mass flux and lowering the heat flux. In the supercritical pressure region, the lower the pressure is, the stronger the heat-transfer enhancement would be in the large specific heat region; keeping all other parameters constant, the influence of thermal physical properties of supercritical water on the heat-transfer process would be significantly affected by both the mass flux and heat flux; continuously increasing the heat flux while keeping the mass flux unchanged, heat-transfer reduction would take the place of heat-transfer improvement in the large specific heat region.
  • DEM Simulation on Mixing Characteristics of Particles in Double Jets Fluidized Bed
    ZHANG Junqiang, JI Lü, LI Bin, CHEN Haisheng, BIAN Yuming
    2017, 37(2): 91-97.
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    Combining the discrete element method (DEM) with computational fluid dynamics, and based on Fortran language programming, a gas-solid coupling model was established according to Newton third law to reveal the motion mechanism of particles in the fluidized bed from the micro-level. The mixing degree of particles in different characteristic regions of the bed was quantitatively analyzed using Lacey mixing index, while factors infuencing the mixing characteristics were studied, during which the axial and radial mixing sequence diagram of particles, the gas and particle velocity distribution, as well as the particle mixing index in the entire bed and at different regions of the bed were obtained. Results show that under the action of air jets, the particles get mixed and segregated, and finally achieve dynamic equilibrium. The axial mixing of particles is faster than radial mixing at the same superficial gas velocity. The scale of fountain area increases with rising superficial gas velocity, while the radial diffusion capacity improves, and the axial diffusion capacity lowers.
  • Effects of Alkali Salts on the Fouling Properties of Coal Ash in Weak Reducing Atmosphere
    CHEN Hongwei, ZHANG Zhiyuan, HE Junpeng, LIANG Zhanwei, YANG Xin
    2017, 37(2): 98-104.
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    To study the fouling properties of coal ash, sintering experiments were carried out in weak reducing atmosphere by converting alkali salt additives into equivalent weight of alkali oxides, and then adding them into different kinds of coal ash. Results show that Tianchi Energy coal has strong tendency of fouling due to high content of Na element in the coal ash; alkali salt additives can obviously promote the sintering of coal ash and reduce its initial fouling temperature; the fouling properties of coal ash are determined by the combined effect of alkali salt additives and the inherent minerals; Na-based compounds have stronger effect on the fouling properties of coal ash than K-based compounds at low temperatures, while K-based compounds have stronger effect at high temperatures.
  • Optimized Design of a Plate Stiffener for Steam Turbine Exhaust Hood
    CHEN Taowen, ZHU Yanqun, DING Xinghua
    2017, 37(2): 105-110.
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    An optimization was conducted to the design of a plate stiffener located in the lower area of steam turbine exhaust hood using Latin hypercube experiment design, cubic response surface model and Hooke-Jeeves direct search technique. Based on numerical investigation of a large number of samples, the influence of different geometric parameters of the stiffener was studied on the aerodynamic performance of the exhaust hood, which was examined under variable conditions after optimization. Results show that both the distance between the stiffener and the meridian plane X as well as the dip angle of the stiffener θ have large influence on the aerodynamic performance of the exhaust hood, while the distance between the stiffener bottom and the hood outlet Y as well as the length of the stiffener L have little influence. The static pressure recovery coefficient can be improved effectively by arranging the stiffener appropriately, when the outlet non-uniformity would be reduced; however, this may lead to a certain loss of the total pressure.
  • Large Eddy Simulation on the Effects of Inlet Pressure on the Premixed Combustion Instability and NOx Emission
    SHI Li, FU Zhongguang, SHEN Yazhou, WANG Ruixin
    2017, 37(2): 111-118.
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    Effects of inlet pressure on the combustion instability and NOx formation characteristics of premixed flame were studied using a three-dimensional full compressible large eddy simulation (LES) approach. Results show that, due to the instability of inner shear layers, two spiral-shaped precession vortex cores would form at different inlet pressures on the boundary of center recirculation zone in the combustion chamber, where instable combustion is easy to occur at higher inlet pressures. High inlet pressure helps to improve the temperature in combustion chamber and raise the mole concentration of reactants, which would result in high concentration of NOx emission.
  • Thermal-Stress Analysis of Rolling Bearing Failure at High-speed End of a Wind Turbine Gearbox
    TAN Bowen, QIU Yingning, LI Dan, FENG Yanhui
    2017, 37(2): 119-125.
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    A thermal resistance network model was established for the high-speed end bearing of a wind turbine gearbox, based on which dynamic thermal characteristics of the bearing were studied at varying wind speeds and loads. Ansys Workbench finite element method was used for three dimensional thermal-stress coupling analysis to simulate the temperature, deformation and thermal-stress characteristics of the bearing under fault conditions. Results show that the wind speed, the contact thermal resistance between inner ring and roller element of bearing as well as the convective thermal resistance of oil would significantly influence the bearing temperature. In the case of normal bearing operation, the maximum deformation occurs at the contact surface between inner ring and roller element, while the maximum stress occurs at the edge of outer surface of outer ring. When bonded and wear failures appear to the bearing, its temperature distribution, heat flux and thermal stress would change in different degrees.
  • Attenuation Characteristics of Acoustic Waves in Boiler Flue Gas Containing Solid Particles
    JIANG Genshan, XU Weilong, AN Liansuo
    2017, 37(2): 126-133.
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    Numerical simulation was conducted on the attenuation mechanism of audio waves in the furnace of power plant boiler, based on which a formula of sound attenuation coefficient in the gas medium containing solid particles was built, so as to analyze the effects of following factors on the attenuation coefficient, such as the acoustic frequency, particle concentration, particle size and flue gas temperature, etc. Moreover, attenuation characteristics of acoustic waves in the furnace of fluidized bed boiler containing solid particles of higher volumetric fractions were also studied based on multi-body multiple scattering theory, and subsequently corresponding attenuation coefficients were corrected. Results show that for general coal-fired boilers, the sound attenuation coefficient increases with rising flue gas temperature, particle concentration and sound frequency, and with reducing particle size; whereas for fluidized bed boilers, the acoustic attenuation mainly originates from the thermal diffusion on the surface of medium particles.
  • Modeling and Parameter Analysis of Carbon Capture Process with Ca-based Sorbents
    HU Yue, XU Gang, DUAN Dongwei, GAO Yachi, ZHANG Kai, YANG Yongping
    2017, 37(2): 134-139.
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    In terms of the CO2 capture in natural gas combined cycle (NGCC) power plant, a way of CO2 capture by Ca-based calcination and carbonation was studied. Based on the mathematic model built in Matlab, the effects of following factors on the CO2 capture ratio were analyzed, such as the carbonation temperature, sorbent inventory, sorbent circulation flow rate and the sorbent make-up rate, etc. Results show that, to obtain 90% capture ratio of CO2 (rcc), the carbonation temperature in NGCC power plant would be 594℃, which is lower than that in coal-fired power plant (650℃), due to the low mole fraction of CO2 in NGCC power plant. With the rise of cycle number, the absorbing capability of sorbent decreases obviously. For a fixed F0, rcc increases significantly and then levels off with the increase of WCaO and FR, whereas for the same WCaO, rcc increases with the rise of F0 and FR, however, when FR gets up to a certain value, rcc reduces instead, due to the insufficient inventory of CaO in carbonator, leading to that partial of the CaO entering into the carbonator can't achieve the maximum conversion.
  • Heat Storage Mechanism and Coal Consumption Calculation of a 1 000 MW Power Unit Under Transient Conditions
    YANG Zhiping, SONG Yang, GUO Xiyan, SUN Weipeng, FENG Tingyou
    2017, 37(2): 140-147.
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    Models to calculate the coal consumption and heat storage rate of the working medium and metallic materials of a 1 000 MW power unit under trainent conditions were established, based on which, calculation and analysis were performed on the transient test process of the unit, so as to obtain the curves of standard coal consumption rate for power generation corresponding to the heat storage rate and under the heat storage effect during the test, analyze the distributions of heat storage on various heating surfaces at different loads, and to compare the test results with field data. Results show that the total heat storage rate of the unit varies in the same trend with that of metallic materials, and the latter is 1.5-2.0 times of the working medium. Water walls share the largest proportion in the heat storage of working medium, while superheaters share the least. Affected by heat storage, the standard coal consumption rate is at most increased by 3.48 g/(kW·h) during loading up period and decreased by 3.2 g/(kW·h) during loading down period.
  • Exergy Analysis and System Optimization of a Flue Gas Pre-dried Lignite-fired Power System Based on Fan Mill Dryer and Open Pulverizing System
    HAN Xiaoqu, LIU Ming, YAN Junjie, CHONG Daotong, LIU Jiping, XIAO Feng
    2017, 37(2): 148-155.
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    An exergy analysis model was developed for the flue gas pre-dried lignite-fired power system (FPLPS) based on fan mill dryer and open pulverizing system, so as to explore its energy-saving mechanism from the perspective of the second law of thermodynamics, and to perform exergy analysis for the subsystems and main components of a 600 MW supercritical unit. Results indicate that the efficiency of the plant with FPLPS is relatively 3.42% higher than that with conventional lignite-fired power system (CLPS). The improvement of plant efficiency originates from the replacement of high-grade chemical energy by lower-grade flue gas as the heat source for moisture evaporation, during which the exergy destruction is reduced accordingly. Moreover, the dryer exhaust gas is separated from the coal powder in the open pulverizing system, which prevents the evaporated moisture from recycling in the furnace, thus raising the combustion temperature, reducing the inefficiency of the combustion process and increasing the boiler efficiency. However, the dryer exergy efficiency is only 20.20% due to high irreversibility. The retrofitting option by extracting cold flue gas from economizer outlet is estimated to increase the plant efficiency relatively by 0.33%, benefiting from a reduction of the exergy destruction in the mixing of drying agents.
  • Corrosive Behaviors of Austenitic Stainless Steels for Boiler in Simulated Coal Ash and High Sulfur Flue Gas
    LI Yan, LU Jintao, YANG Zhen, ZHU Ming, GU Yuefeng
    2017, 37(2): 156-162.
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    High-temperature corrosive behaviors of three austenitic stainless steels Super304H, TP347HFG and HR3C used for boiler were studied by experimental tests at 650℃ in simulated coal ash and flue gas environment containing high sulfur content. Weight changes of the tested samples were measured by discontinuous weighing method, while morphologies, compositions and phases of the corrosion products were analyzed using SEM, EDS and XRD, respectively. Results indicate that corrosion damage was found in all the tested alloys, and the damage level of HR3C was in a light level compared to TP347HFG and Super304H. Two-layer oxides formed on the surface of TP347HFG and Super304H, with outer layer of Fe2O3 and inner layer of Cr2O3 plus a large amount of inner sulfide, where serious spalling was observed. A Cr-rich (Cr, Fe)2O3 layer was found on the surface of HR3C due to its high Cr content, where no obvious spalling was observed.
  • Uncertainty Analysis on Calculation of Probabilistic Fracture Mechanics for Reactor Pressure Vessels
    WANG Donghui, LI Kai, ZHANG Jing
    2017, 37(2): 163-166.
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    To evaluate the effects of input parameters on the calculation results of reactor vessel failure probability under specific operation conditions, a calculation model for probabilistic fracture mechanics of reactor pressure vessel(RPV) was established for sensitivity analysis on main parameters applied in the calculation, so as to study the influence of various factors on the RPV failure probability, such as the defect type and shape, irradiation embrittlement degree, material chemical composition and warm pre-stressing, etc., and to analyze the sensitivity of each parameter. Results show that reliable input parameters are the prerequisite to ensure the reliability and validity of analysis results for probabilistic fracture mechanics. In addition, the material chemical composition and defect depth are key factors influencing the calculation results.
  • Research on the Effects Caused by Newly Installed Baffles at Secondary Side of a PRHR HX Based on Scaled Experiment
    LU Daogang, ZHANG Yuhao, WANG Zhongyi, CAO Qiong, FU Xiaoliang, YANG Yanhua
    2017, 37(2): 167-172.
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    To reduce the thermal stratification extent in the in-containment refueling water storage tank (IRWST) during the operation of passive residual heat removal heat exchanger (PRHR HX), a scale-down test facility was set up to analyze the separation effect, where the baffles were newly installed at secondary side along verticle tube bundle of the PRHR HX, and subsequently, the temperature distributions, flow characteristics and the PRHR HX heat-transfer effects were evaluated by experiments. Results show that the baffles can change the natural convection characteristics, increase the heat-transfer potential of cold fluid in the lower region, and reduce the stratification phenomenon in IRWST. The two design plans respectively with four and eight baffles can reduce the thermal stratification extent by 32.3% and 37.3%, accordingly. However, the maximum velocity of the flowing up fluid is also reduced, leading to the decrease of the heat-transfer coefficient. As a result, different factors should be taken into consideration to develop the optimal design.