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  • 2016 Volume 36 Issue 8
    Published: 15 August 2016
      
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  • Numerical Analysis on Flow Instability of Supercritical CFB Boiler Water Wall Considering Metallic Heat Storage
    XIE Beibei, LONG Jun, MAO Kaiyuan, WANG Wenyu, YANG Dong, XIA Liangwei, YIN Yaning
    2016, 36(8): 589-593.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A mathematical model was established for analysis on flow instability in annular furnace of a supercritical CFB boiler considering metallic heat storage, with which the flow instability was simulated using staggered grids, so as to calculate and analyze the variation of inlet and outlet mass flow as well as tube wall temperature along with time under thermal load disturbance on the loop. Results show that once the loop was applied by 1.1, 1.2 and 1.3 times of thermal load disturbance, the inlet and outlet mass flow would fluctuate reversely along with time, both of which would finally get equivalent at the value of steady state; besides, the wall temperature would also fluctuate with time and finally get stable at a constant value, indicating that the flow condition is still stable.
  • Combustion Optimization of a Coal-fired Boiler Based on Intelligent Algorithm
    YU Tingfang, GENG Ping, HUO Erguang, CAO Mengbing
    2016, 36(8): 594-599,607.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A hybrid model was set up using Matlab artificial intelligence toolkit to optimize the combustion in a 300 MW coal-fired boiler. The specific way is to establish a BP (back propagation) neural network model for boiler combustion properties to predict the thermal efficiency and NOx emission concentration of the boiler, and then to optimize the boiler combustion with Matlab artificial intelligence toolkit based on the model by taking the thermal efficiency and NOx emission concentration as the target variables, during which the multi-objective optimization problems were transformed into single-objective optimization problems by weight coefficient method. Results show that the average relative errors of boiler thermal efficiency and NOx emission are 0.142% and 1.790% respectively, indicating good accuracy and strong generalization ability of the model. By weight coefficient method, boiler thermal efficiency and NOx emission concentration can be chosen as the key optimization objectives by selecting corresponding weight coefficients, which therefore may serve as a reference for combustion optimization of similar coal-fired boilers.
  • A Modeling Method for Heavy Duty Gas Turbines and the Parameters Estimation
    HUANG Yuzhu, JIANG Hongde
    2016, 36(8): 600-607.
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    To study the dynamic characteristics of a gas turbine, models of the gas turbine and its control system were developed based on Rowen model, while the model parameters were estimated with field data according to the laws of mass, momentum and energy conservation using basic thermodynamic formulas. Taking the GE MS 6001FA gas turbine as an object of study, specific modeling way of the gas turbine was described in detail, including its parameters estimation. Results show that the model developed can effectively reflect the dynamic characteristics conforming to actual operating rules of the gas turbine, which therefore may serve as a reference for study of similar gas turbines.
  • Numerical Study on Flow Characteristics in LEC-III Combustor Liner of a 9E Gas Turbine Under Premix Mode
    YE Wen, LIU Chuanliang, FAN Xuefei, HUANG Xingliang, WU Gexin, YANG Daogang
    2016, 36(8): 608-614,628.
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    Flow characteristics in LEC-III combustor liner of a 9E gas turbine were numerically simulated under premix mode, so as to study the velocity field, temperature field and species field in the liner. Results show that the circulation zone generated by combined action of secondary fuel nozzle and centerbody swirler can stabilize the flame in combustor liner, and the centerbody swirler is able to control the combustion range, which is very important to the flame stability in secondary combustion zone. The NO emission concentration reduces gradually with the rise of purging air flow rate, and the simulated results of NO emission are close to actual measurements, with similar variation trends observed simultaneously.
  • NOx Emission Prediction Based on Deep Boltzmann Machine Integrated with Least Square Support Vector Regression
    LI Nan, LU Gang, LI Xinli, YAN Yong
    2016, 36(8): 615-620.
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    By analyzing the relationship between flame radical images and NOx emission in combustion process, a prediction algorithm of NOx emission was proposed based on deep Boltzmann machine integrated with least square support vector regression. The specific way is to use deep Boltzmann machine to automatically learn the image features of four flame radical images (OH*, CN*, CH* and C2*), and then adopt least square support vector regression to establish the relationship between image features and NOx emission, so as to further predict the NOx emission. Results show that the predicted value of NOx emission is in good agreement with the reference data. Compared with various image-based NOx emission prediction algorithms, the proposed method has significant advantages in prediction accuracy.
  • Study on Mercury Adsorption by Fly Ash from Coal-fired Boilers of Power Plants
    FAN Baoguo, JIA Li, LI Xiaodong, LIU Jun'e, ZHENG Xianrong, JIN Yan
    2016, 36(8): 621-628.
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    To obtain the absorption characteristics of fly ash on element mercury in flue gas, a study was conducted on the fly ash from PC and CFB boilers. The absorption mechanism was further researched by analyzing the effects of following factors on the mercury adsorption by fly ash, such as the pore structure, particle size and unburned carbon content, etc. Results show that the mercury content in fly ash from CFB boiler is ten times of that from PC boiler. The higher the unburned carbon content is, the stronger the absorption capability of fly ash will be, which is also directly related to the particle size. As the particle size of fly ash rises in the range of 24.5 to 362.5 μm, the mercury content first increases and then decreases, and the peak value of about 560×10-9 appears in the range of 77.5 to 106 μm. High mesoprous content of 4-6 nm is found to be in the fly ash samples with relatively high mercury content, which is favorable for mercury adsorption, and the specific surface area plays a more important role in mercury adsorption than specific pore volume.
  • Effects of Helical Strake on Dynamic Response of the Platform for Floating Wind Turbines
    DING Qinwei, LI Chun, WANG Donghua, ZHANG Nan, YE Zhou
    2016, 36(8): 629-637,657.
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    To study the effects of helical strake on dynamic response of Spar platform for floating wind turbines, numerical models were set up for two NREL 5 MW floating wind turbines with and without helical strakes on the Spar platform, so as to analyze the influence of following factors on the dynamic response of the Spar platform under the action of wind, wave and current load, such as the number, height and pitch ratio of the strake, based on the wave radiation-diffraction theory and finite element method by orthogonal design. Results show that helical strakes could obviously inhibit the dynamic response of Spar platform, but significantly increase the F-K force and diffraction force on the platform; optimum parameter combination for the piece number, height and pitch ratio of shakes is found to be 2, 15%D and 5; both the height and pitch ratio of helical strakes as well as their interaction have significant effects on the pitch response of the platform.
  • Structural Dynamic Response of a Wind Turbine Under High-speed Strong Turbulence Inflow Conditions
    YANG Yang, LI Chun, MIAO Weipao, YE Kehua, YE Zhou
    2016, 36(8): 638-644,657.
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    To analyze the structural dynamic response of large-scale wind turbines operating under high-speed strong turbulence inflow conditions, a three-dimensional extreme turbulence flow field with an average wind speed of 25 m/s was established based on NWTCUP wind spectrum. By adding the coherent structures deduced from the scaling numerical results of Kelvin-Helmholtz instable flow to the background wind to represent an inflow condition of higher turbulence intensity, the structural dynamic response of the wind turbine respectively with coherent inflow and normal turbulence flow fields were calculated in FAST code under three off-design conditions, such as yaw to 30°, emergency shutdown and parked cases, etc. Results show that coherent structures enhance the changes of wind speed in space-time domain, with increased kinetic energy of coherent turbulence (CTKE), suitable for representing the case of higher turbulence intensity; while coherent structures promote the dynamic response of wind turbine, especially on the bending moment of tower base, with the variation range of response amplitude expanded by 1.96 times. The stimulus frequency of root bending load is the frequency of wind wheel rotation, while the response of both tower load and nacelle motion is of the first-order natural frequency of side to side vibration. Coherent structures have greater impact on the tower tip moment under off-design conditions, and the non-stationary fluctuations becomes significant during yawing, emergency shutdown and other non-steady operation periods.
  • Thermal Performance Analysis of a Coal-fired Power System Aided by Parabolic Trough Solar Collectors
    FU Li, FAN Xue, HOU Hongjuan, WANG Zhi
    2016, 36(8): 645-650.
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    Taking the EUROTROUGH-150(ET-150) parabolic trough solar collector as an example, mathematical models on heat collection and heat loss of the system were built to optimize its thermal efficiency. On above basis, a coal-fired power system aided by parabolic trough solar collectors (complementary power generation system) was researched to analyze the selection of direct normal irradiance (DNI) design values using a certain evaluation criteria in the integration mode. Results show that for collector fields with different number of loops and different latitude distributions, there exists optimal column spacing and optimal range of DNI design values to make the system annual performance optimum.
  • Analysis on Energy-saving Effect of a Raw Coal Pre-drying System Using Boiler Flue Gas
    DONG Wei, XU Gang, XU Cheng, BAI Pu, YANG Yongping, HE Xianghui
    2016, 36(8): 651-657.
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    To solve the low efficiency problem existing in power plants burning medium- and high-moisture sub-bituminous coal, a raw coal pre-drying system was proposed by using boiler flue gas. Taking a typical 600 MW sub-critical air-cooling unit as an example, the thermodynamic performance was comparitively analyzed before and after coal pre-drying under design conditions, on which basis, the influence of coal pre-drying degree on the energy-saving effect of unit was studied, while the economic benefit through coal-predrying was further explored. Results show that when the dehydration rate is 0.08 kg, i.e. the moisture content is dried from 22.6% to 15.9%, the unit coal consumption rate can be reduced by 4.0 g/(kW·h), indicating an increase of annual net income by 10 million CNY, proving remarkable economic benefit of the coal pre-drying system.
  • Research on Chemical Looping Gasification of Sewage Sludge
    CHEN Qianwen, SHEN Laihong, NIU Xin
    2016, 36(8): 658-663.
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    To improve the gasification effect of sewage sludge, experiments on chemical looping gasification (CLG) of sewage sludge were conducted in a fluidized bed using hematite as the oxygen carrier, so as to analyze the effects of O/C ratio, gasification temperature, steam content on the sludge gasification characteristics, and to study the physical and chemical properties of hematite in the process of continuous cycling. Results indicate that hematite can markedly enhance the gasification degree and carbon conversion rate of sewage sludge with increasing O/C ratio, the concentrations of CO and CH4 in the syngas decrease, whereas that of H2 firstly decreases and then increases. With the rise of gasification temperature, there is a gradual increase of CO and H2 volumetric fraction, but a gradual decrease of CO2 and CH4 volumetric fraction, with a constant improvement of carbon conversion rate. The increase of steam content would lead to the decrease of CO and CH4 volumetric fraction and to the increase of CO2 and H2 volumetric fraction in the syngas, as well as to the increase of carbon conversion rate. The hematite shows good reactivities in long-term operation periods.
  • Effects of Welding Sequence on Residual Stress Distribution in Circumferential Welded Joints with X-shape Grooves
    WAN Haibo, WANG Yanfeng, LI Qiang, TANG Bin
    2016, 36(8): 664-670.
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    Using ABAQUS software, a 2D axisymmetric sequentially coupled thermal-mechanical finite element model was developed for circumferential welds, of which the accuracy was verified with experimental data. The model was then used to calculate the residual stress in multi-pass butt welds of stainless steel cylinder formed under different welding sequences. Results show that the stress distributions formed under different welding sequences reveal essentially the same trend:the axial stress on inner wall side is of the tensile kind and that on outer wall side is of the compressive kind; whereas the hoop stress is of the tensile kind throughout the whole thickness of cylinder wall. As to the stress magnitude, welding sequence affects more on axial stresses than on hoop stresses. An optimum welding sequence is finally determined from the view of preventing stress corrosion cracking in sevice period to the greatest extent.
  • Microstructure and Mechanical Properties of Domestic Super304H Tubes During High-temperature Services
    TIAN Xiao, XU Hui, LIU Xiangliang, LI Yimin, DONG Fangqi, XIAO Guohua, YANG Baixun
    2016, 36(8): 671-676.
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    The microstructure and mechanical properties of domestic Supre304H tubes used for 600℃ ultra-supercritical boilers during high-temperature services were investigated by room-temperature tensile test, impact test, hardness test, metallographic inspection, scanning electronic microscopy and energy spectrum analysis. Results show that the strength and hardness of domestic Supre304H tubes increase with the time during high-temperature services, while their plasticity and toughness decrease. The strength, hardness and impact toughness of domestic Super304H welded joints decrease with the time during high-temperature services, which are obviously lower than the properties of base metal at same service time. After more than 30 000 hours of service, the mechanical properties of domestic Super304H tubes are still in high level with stable matrix and uhchanged sizes of grains, but the microstructure indicates aging phenomenon in the form of chain-like precipitation of M23C6 along grain boundary. In general, domestic Super304H tubes have good microstructure and mechanical properties, which are able to operate stably under the conditions designed for 600℃ ultra-supercritical units. It is suggested to strengthen the supervision on the welded joints of domestic Super304H tubes.