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  • 2019 Volume 39 Issue 8
    Published: 15 August 2019
      
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  • Exergy Analysis of a 1 000 MW Ultra-supercritical Double Reheat Boiler Unit
    CUI Xiaoning, ZHAO Zhigang, JIANG Ning, SU Sheng, XU Kai, HU Song, XIANG Jun
    2019, 39(8): 605-610.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Numerical simulations were conducted on a domestic 1 000 MW ultra-supercritical double reheat boiler system based on a unit model newly built to study the performance of the boiler, and to calculate the exergy loss and exergy efficiency of the boiler system and its components at different loads according to exergy balance equations. Results show that with the variation of unit load, all the components maintain high exergy efficiency with small fluctuation, which could satisfy the requirements of deep peak regulation under low load conditions and ensure stable operation for the unit. The exergy loss caused by combustion and heat exchange accounts for 97% of the total, which could be lowered by reducing the heat exchange temperature difference between the working medium and the high temperature flue gas.
  • Influence of Flue Gas Recirculation on the Combustion of a 1 000 MW Ultra-supercritical Double Reheat Boiler
    LI Yongsheng, CAI Pei, DAI Weibao, HUANG Qilong, SUN Junwei, YAN Weiping, HE Daoyuan
    2019, 39(8): 611-617.
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    Taking the 1 000 MW ultra-supercritical double reheat boiler as an object of study, numerical simulations and sectional calculations were conducted to analyze the effects of flue gas recirculation rate on the temperature field in the furnace, the concentration field of various gas components and the NOx generation, etc. Results show that in the case of flue gas recirculation, for every 5% increase of flue gas recirculation rate within the range of 0%-15% at BMCR load, in the area of screen bottom, the flue gas temperature would be reduced by 4.7 K, while the concentration of O2 be decreased by 4.1%, the concentration of CO be increased by 31.81%, and the concentration of NO be lowered by 6.2%; with lowering unit load, in the area of screen bottom, at the same recirculation rate of flue gas, the reducing degree of flue gas temperature rises, while the reducing degree of O2 concentration and the rising degree of CO concentration drop.
  • Study on Releasing Mechanism of Light Hydrocarbon in Rapid Pyrolysis of Superfine Pulverized Coal
    YAO Wang, LUO Lei, LIU Jiaxun, ZHANG Hai, MA Junfang, JIANG Xiumin
    2019, 39(8): 618-625.
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    To accurately understand the reaction mechanism of superfine pulverized coal during rapid pyrolysis, a series of rapid pyrolysis experiments were conducted in a drop tube furnace respectively at the temperature of 1 030℃, 1 130℃, 1 210℃ and 1 310℃, while the release amount of light hydrocarbon in the pyrolysis gas was determined using Gasmet DX4000 gas analyzer. Results illustrate that at most pyrolysis temperature with the decrease of particle size, the total release of light hydrocarbons CH4, C2(C2H2, C2H4, C2H6) and C3H8 first increases, and then reduces. Among different types of coal, it is obvious that the release of CH4, C2(C2H2, C2H4, C2H6) and C3H8 from low-rank coal is higher than that of high-rank coal. Pyrolysis atmosphere has a great influence on the release of pyrolysis products. In CO2 atmosphere, the release amount of various light hydrocarbons is significantly lower than that in N2 atmosphere.
  • Performance Degradation Analysis of a Gas Turbine After Offline Water Washing of the Compressor
    HAN Chaobing, ZHU Hongluo, HUANG Weidong, HUANG Suhua, WANG Jian
    2019, 39(8): 626-633.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To quantitatively diagnose the gas turbine performance degradation trend caused by compressor blade fouling during actual operation, a gas turbine performance degradation prediction method was proposed based on multiple nonlinear regression model. Taking the PG9351FA gas turbine as an example, performance degradation models were set up respectively for the compressor inlet air flow, compressor pressure ratio, isentropic compression efficiency and gas turbine power after offline water washing of the compressor. Results show that, the decreasing rate of gas turbine power caused by compressor blade fouling is approximately 1.7 times that of the compressor inlet air flow. Running for 2 000 hours after offline water washing under baseload condition, the compressor inlet air flow would be decreased by 3.26%, while the pressure ratio and isentropic compression efficiency be reduced by 3.04% and 2.62% respectively, leading to a comprehensive reduction of gas turbine power by 5.54%. With further rise of operation hours, the performance degradation rate gets stable.
  • Molecular Dynamics Study on Thermal Conductivity of Cu-Water Nanofluids Under Supercritical Conditions
    CHEN Li, ZHANG Yanping, GAO Wei
    2019, 39(8): 634-639.
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    The effects of following factors on the change in thermal conductivity of supercritical fluids after being added with Cu nanoparticles were studied based on equilibrium molecular dynamics, such as the system temperature, and the size and mass fraction of particles, etc. Results show that the thermal conductivity of above nanofluids increases with the rise of temperature. The rise of both the size and the mass fraction of nanoparticles would also increase the thermal conductivity of the whole system.
  • Effect of Inlet Aspect Ratio on the Flow Pattern and Performance of a Small Cyclone with Double Inlets
    ZHANG Yun, ZHAO Bingtao, WANG Dongshen
    2019, 39(8): 640-646.
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    To investigate the effects of inlet aspect ratio on the gas-phase flow, droplet trajectory and pressure drop in a small cyclone with double symmetric inlets, three cyclones with a fixed inlet area and at different inlet aspect ratios were numerically simulated by computational fluid dynamics (CFD) method. Results show that with the rise of inlet velocity, the axial velocity expands in numerical range, but does not change in magnitude, of which the distribution shape converts from M to inverted V, while the droplet trajectory gets shorter. With the increase of inlet aspect ratio, the tangential velocity rises gradually in the quasi-free vortex region, while the axial velocity keeps constant on the outer side of double peaks, and reduces gradually on the inner side. The total pressure decreases at low inlet velocity and increases at high inlet velocity with rising inlet aspect ratio. The droplet trajectory shortens with the rise of inlet aspect ratio and particle size, while the pressure drop increases with the rise of inlet velocity and aspect ratio.
  • Wind Turbine Power Curve Modelling Based on Improved Decision Tree Considering Multiple Input Variables
    LIU Lin, GUO Peng
    2019, 39(8): 647-653.
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    To improve the modelling accuracy of wind turbine power curves, a novel power curve modelling approach was proposed based on the stochastic gradient boosting regression tree (SGBRT) by analyzing the external factors affecting the wind energy capture capability using the partial mutual information (PMI) method, and by taking multiple parameters as the input variables. With actual data from the supervisory control and data acquisition (SCADA) system of a 1.5 MW wind turbine, the effectiveness and superiority of the modelling method proposed were verified. Results show that compared with existing traditional power curve modelling methods, the approach proposed based on SGBRT could more accurately predict the output power characteristics of wind turbines, with smallest forecasting errors.
  • Numerical Simulation on the Aerodynamic Noise of a Wind Turbine Airfoil Influenced by Gurney Flaps
    YE Zhou, ZHOU Wei, XU Xuehao, SONG Jianye
    2019, 39(8): 654-660.
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    To analyze the influence of Gurney flaps on the aerodynamic performance and noise characteristics of wind turbine airfoils, the LES model in Fluent software was used to study the aerodynamic performance and flow field distribution of an original airfoil and the airfoil with Gurney flaps of different heights at the angle of attack in 4°-20°, while their far-field aerodynamic noise was calculated using Acoustics modules based on FW-H sound analogy method. Results show that when the lift coefficient of airfoil is greater than 0.8, the Gurney flap could effectively increase the lift coefficient, but would also raise its drag coefficient significantly. When the flap height is less than 3% of the chord length, the stalling angle of attack would be effectively increased; when the flap height exceeds 3% of the chord length, the increase degree of lift coefficient drops, while that of drag coefficient rises, and the aerodynamic noise increases sharply thereafter. The airfoil sound radiation shows the characteristics of dipole sound field.
  • Research on High-temperature Microstructure Stability of an Iron-Nickel Based Alloy for Rotor Forgings of 700℃ Advanced Ultra-supercritical Steam Turbines
    NIE Yihong, BAI Yaguan, JIN Jiayu, WANG Baozhong
    2019, 39(8): 661-665.
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    Aging treatment and high-temperature stress-rupture tests were conducted on alloy MN1 and its modified one MN2 at 700℃ and 750℃. Results show that in alloy MN1 after being aged at 700℃, both needle-like η phase and γ″ phase grow up, while Laves phase precipitates at the grain boundary, leading to poor microstructure stability of the alloy; when the aging time reaches 5 000 h, or the temperature gets up to 750℃, the η phase would get coarsened obviously and lots of blocky Laves phases would precipitate both in the grain and at the grain boundary, resulting in relatively low stress-rupture life of alloy MN1 at 700℃. Whereas, in alloy MN2 after being aged at 700℃, fine γ' phases precipitate dispersedly in the matrix, while short rodlike phases distribute at the grain boundary, indicating that the microstructure of alloy MN2 has good stability at 750℃. The creep strength of alloy MN2 at 700℃ for 105 h is deduced to be about 127 MPa based on experimental results, which therefore could be taken as alternative material for the rotor of 700℃ advanced ultra-supercritical (A-USC) steam turbines.
  • Investigation on High-temperature Low-cycle Behaviour of Aluminized 321 Stainless Steel for Solar Thermal Power Generation
    LI Wei, ZUO Lu, XU Dongliang, CHEN Jian, PENG Zhuoyin, ZHANG Shengde
    2019, 39(8): 666-671.
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    The surface of 321 stainless steel was treated by aluminizing process, and the effect of aluminized layer on the low-cycle fatigue property and fracture mechanism of 321 stainless steel was investigated. Results demonstrate that for the same strain amplitude, the fatigue life of aluminized 321 stainless steel is obviously lower than that of as-received sample. The fatigue crack tends to originate in the Al2O3 thin film and at the interface between matrix and aluminized layer, which propagates along the grain boundary of FeAl phase. Meanwhile, the Fe3Al with DO3 structure may transform to the FeAl with B2 structure, reducing the strength of aluminized steel. Besides, the sigma phase, deposited in the process of aluminizing, further accelerates the crack propagation, resulting in reduced fatigue life of aluminized 321 stainless steel.
  • Study on Optimization Design of Reactor Coolant Pump Blade of Impeller in Nuclear Power Plant Based on Genetic Algorithm
    YE Daoxing, LAI Xide, WANG Qianglei, ZHENG Hui
    2019, 39(8): 672-678.
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    Using Kriging model, a relationship was established between the parameters of blade inlet and outlet angles and the performance of the pump, and subsequently, a multi-objective optimization was conducted on the blade parameters, while the pump performance was predicted and comparatively analyzed. Results show that β11, β 51 and β 52 are significant factors among the inlet and outlet angle parameters of the impeller blade, and their optimal combination is found to be β11=43.3°, β51=22.9° and β52=18.4°. After optimization, the impeller efficiency is respectively increased by 1.24%, 1.1% and 0.5% at the working points 0.8qV,d, 1.0qV,d and 1.2qV,d, compared with the prototype model; the pressure load on the suction surface of blade improves; at the aspect ratios of 0.5 and 0.95 on the pressure surface, the pressure load increases in the exit region of blade.
  • Numerical Analysis on Flow and Heat Transfer of Sub-cooled Boiling in the Channel of 5×5 Rod Bundles with Spacer Grids
    DU Lipeng, CHEN Xiaolong, ZHANG Pengfei, ZHANG Wenchao, JIN Guangyuan
    2019, 39(8): 679-685.
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    To numerically simulate the sub-cooled boiling in the channel of 5×5 rod bundles with spacer grids, a sub-cooled boiling model was established based on the volume of fluid (VOF) two-phase flow model, by adding appropriate mass and energy source terms into the governing equation, so as to study the heat transfer performance under conditions with and without sub-cooled boiling, and to analyze the effects of inlet velocity and inlet under-cooling degree on the heat transfer characteristics in the fuel bundles. Results show that the heat transfer effectiveness of the two-phase flow with sub-cooled boiling is better than that without sub-cooled boiling; in the case with sub-cooled boiling, the overall heat transfer coefficient in the channel would be positively correlated with the inlet velocity and negatively correlated with the inlet under-cooling degree; in local regions, the higher the degree of sub-cooled boiling, the better the effectiveness of heat transfer.
  • Design and Techno-Economic Analysis of Emergency Solutions for the Cooling System with Constant Heat Source
    DENG Yonghao, ZHANG Lixin, LIU Jingnan, GAO Ming, WAN Qian, WANG Zhixiao, YUAN Guang, WANG Lisha
    2019, 39(8): 686-692.
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    To deal with the cooling system failures caused by an emergency or a disaster that might lead to extreme accident due to cooling pool boiling resulted from heavy heat accumulation, 4 kinds of vehicle cooling solutions were designed to release the heat load from a certain constant heat source to be cooled, and the 4 schemes were subsequently compared in the aspect of space heat ratio, cost heat ratio, air heat ratio and water consumption heat ratio, etc., so as to find their fault factors. Results show that the fault factor of the solution with air cooler and evaporative cooler seriesly connected in stable temperature period is 7.43% higher than that in temperature reduction period. With the pool temperature reducing, the fault factor of the solution with two evaporative coolers in series connection without previous spray in the former cooler would drop by 10.53%. The fault factor of the only evaporative cooler solution is the lowest in the case with backflow water pre-cooling, which is believed to have the highest techno-economic effectiveness when water consumption is allowed in a certain degree. But when water consumption is not allowed, though the only air cooler solution has the highest space heat ratio, cost heat ratio and air heat ratio, it is still irreplaceable because of the zero water consumption heat ratio.