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  • 2019 Volume 39 Issue 11
    Published: 15 November 2019
      
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  • Influence of Burner Design on Thermal Deviation of Tower Boiler Heating Surfaces
    XIAO Kun, XIN Nana, ZHANG Jianwen
    2019, 39(11): 865-869.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 1 000 MW ultra supercritical tower boiler as an example, the influence of burner design on thermal deviation of the heating surfaces was studied by means of numerical simulation, and subsequently the simulation results were compared with actural operation data of the boiler. Results show that the thermal deviation of heating surfaces presents the saddle distribution due to the flue gas ring formed in the furnace caused by tangential firing, where both the flue gas temperature and velocity are high. Changing the installation angle of burner would affect the position and size of the flue gas ring, and then further affect the distribution of the thermal deviation. The effect of installation angle of burner could be reduced by adopting the blowback type of pulverized coal burner and reducing the angle of the bias air. Reversely and horizontally swinging the separated overfire air could effectively reduce the thermal deviation on the flue gas side.
  • Research and Application of the Wide-range De-NOx Technology with Flue Gas Reheating Device
    ZHU Zhifu, SONG Guohui, ZHU Jingquan, WANG Hongming, DING Jiyu, Lü Weizhi, MENG Yongjie, TAO Li
    2019, 39(11): 870-875.
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    To accurately put the De-NOx system into normal operation during deep peak regulation of a 300 MW subcritical unit at low load, a wide-load De-NOx technology was proposed by directly heating the flue gas with reheating device. Results show that this technology can greatly improve the flue gas temperature by 10-30 K at the inlet of selective catalytic reduction (SCR) system, which ensures a normal operation of the SCR system at low load during peak regulation process. On the other hand, during start-up process, the flue gas reheating burner can greatly shorten the operation time of the SCR, thus meeting the needs of grid connection and putting the SCR into normal operation.
  • Design and Optimization of an S-CO2 Turbine Based on Gauss Process Regression
    SHI Dongbo, LIU Tianyuan, XIE Yonghui, ZHANG Di
    2019, 39(11): 876-883.
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    To solve the problem of poor accuracy and long period of design and optimization for a supercritical carbon dioxide (S-CO2) turbine using traditional design method, a fast thermodynamic design method was established for the radial inflow turbine based on one-dimensional flow theory. A design-optimization method was also proposed based on Gauss process regression, which combines the high precision three-dimensional aerodynamic analysis with the thermodynamic design to evaluate the real efficiency of the turbine aerodynamic design, verify the accuracy of the design results in simulated annealing process, and to demonstrate the effectiveness of the design and optimization for the S-CO2 turbine with calculation examples. Results show that via the method proposed, the isentropic efficiency of the turbine could be increased from the original 83.68% to the optimal 91.20%; an optimal design result would require 120 cycles of aerodynamic analysis by traditional method based on simulated annealing optimization, however, by the method proposed, only 24 cycles are requred, which greatly shortens the time of design and optimization, and therefore may serve as a reference in engineering applications.
  • Characteristic Analysis and Structure Optimization of the Plate-Fin Heat Exchanger in a Gas Turbine
    CUI Na, SUN Wenchao, TAN Chunqing, WANG Jianwen
    2019, 39(11): 884-892.
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    A multi-objective analysis and optimization model was established for the plate-fin heat exchanger in a micro gas turbine, based on the coupling relationship between the structural parameters of the heat exchanger and the performance of the gas turbine. On that basis, the effects of key exchanger parameters on the performance of both the heat exchanger itself and the gas turbine were analyzed under two operating conditions (constant heat absorption in the combustion chamber and constant power output of the gas turbine). Results show that the main factor influencing the power output and heat absorption is the pressure loss but not the effectiveness of the heat exchanger. The variation trend of all parameters in above two operating modes keeps consistent (except for the heat absorption and power output). After optimization of the fin structure, the turbine power output is increased by 6.8%, and the heat absorption of combustion chamber is decreased by 5.1%. Compared with the original parameters, the optimized fin thickness, fin spacing and corrugation angle decrease, while the fin height increases, thus ensuring a small pressure loss of the heat exchanger. At the same time, it is found that there is no significant difference in the results when minimum entransy dissipation and minimum entropy production are taken as the optimization objectives.
  • Numerical Simulation and Mechanism Analysis of Heat Transfer to Supercritical Water in Semi-circumferentially Heated Ribbed Tubes
    QU Mofeng, LI Juan, DONG Le, ZHOU Xihong, YANG Dong
    2019, 39(11): 893-899.
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    To study the law and mechanism of heat transfer to working fluids flowing in water wall tubes of 700℃ efficient ultra supercritical boiler and ultra-supercritical circulating fluidized bed (CFB) boiler, the SST k-ω turbulence model was used to simulate the heat transfer to supercritical water flowing in a vertical upflow four-head internally ribbed tube with a length of 2 m and a hydraulic diameter of 19 mm in the region of large specific heat capacity under semi-circumferential heating conditions. Results show that the inner wall temperature and heat flux in the ribbed tube exibits in the feature of parabolic distribution under semi-circumferentially heating conditions. In the local region with little change in heat flux (φ=0°-90°), the inner wall temperature reaches the maximum at the intersection of rib root and leeward side wall, and reaches the minimum at the intersection of rib crest and windward side wall; however, the heat flux of inner wall shows an opposite trend, which is caused by the swirling action of internal ribs. The circumferential distribution of heat flux on the inner wall is not the only factor affecting the heat transfer characteristics of supercritical water. When the phenomenon of heat transfer enhancement occurs in the supercritical water, it is mainly due to the high share of specific heat in the boundary layer, which is independent of the magnitude of the turbulent kinetic energy.
  • Experimental Investigation on Condensation Oscillation Characteristics of Unstable Steam Jet
    YUE Xiaoyu, WANG Lutao, CHONG Daotong, ZHAO Quanbin, CHEN Weixiong, YAN Junjie
    2019, 39(11): 900-905.
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    The pressure oscillation caused by condensation of unstable steam jet submerged in subcooled water was investigated experimentally. Results show that there are three typical flow patterns in the condensation process at different mass flow rates of steam jet and different temperatures of subcooled water, i.e. chugging (C), hemispherical bubble oscillation (HBO) and periodic bubble oscillation (PBO). The frequency of pressure oscillation increases with the rise of steam mass flow, which first increases and then decreases with rising temperature of subcooled water, and the maximum value appears in the transition area from chugging/HBO to PBO. The intensity of pressure oscillation in chugging/HBO region reduces and that in PBO region increases with the rise of steam mass flow. Moreover, the intensity of pressure oscillation increases with rising temperature of subcooled water under all the three flow patterns.
  • Experimental Study of the Direct Non-aqueous Gas Stripping Process for CO2 Capture Using Nanoparticle Suspensions
    YU Wei, LIU Fei, WANG Tao, XIONG Yili, Yann LE MOULLEC, FANG Mengxiang
    2019, 39(11): 906-911.
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    To reduce the energy consumption for solvent regeneration in chemisorptions, a nanofluid-based direct non-aqueous gas stripping process was proposed for CO2 capture. Nanofluid solvents were prepared based on SiO2, TiO2 and γ-Al2O3 nanoparticles and monoethanolamine (MEA) solution, with pentane, hexane, and cyclohexane as the carrier gases, to study the CO2 desorption ability in the direct non-aqueous gas stripping process, and to analyze the regeneration rate, cycle load and related energy consumption. Results show that the nanofluid solvents prepared above are relatively stable. Compared with conventional stripping processes, optimum regeneration effects could be obtained with pentane as the carrier gas, when the regeneration energy could be lowered by more than 40%.
  • Research on Selective Removal of SO3 by Modified Absorbents
    YANG Jiangyi, LU Qiang, QU Yanchao, LIU Dingjia, CUI Minshu, LI Wenyan, YANG Yongping
    2019, 39(11): 912-918.
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    To avoid simultaneous removal of SO3 and SO2 by alkaline absorbents commonly used to control SO3 concentration, the highly efficient absorbent NaHSO3 was modified to improve its selectivity for SO3 removal, following which, corresponding experimental results were kinetically analyzed. Results show that the absorbent NaHSO3 modified by NaHCO3 has the best selective removal effect on SO3. When the mass ratio of NaHSO3 to NaHCO3 is 10:1, the removal efficiency on SO3 would achieve 91% with a selectivity of 100% after continuous reaction for 1 h at the temperature of 300℃ and the space velocity of 60 000 h-1. Intraparticle diffusion is not the only factor controlling the removal process, and chemisorption might be the main way for NaHCO3 modified absorbent NaHSO3 in SO3 removal.
  • DFT Study on Adsorption Mechanism of Trace Element Mercury by Active SiO2 in Fly Ash
    DONG Jinglan, GENG Xiao, LIU Yanfeng, GAO Zhengyang
    2019, 39(11): 919-925.
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    To study the enrichment characteristics of trace element mercury in fly ash, the adsorption mechanism of elemental mercury Hg0 and oxidized mercury HgCl by active SiO2 in fly ash was studied by density functional theory (DFT). The adsorption configuration was studied through energy calculation, AIM theory analysis and Mayer bond analysis, while the interaction type was analyzed using localized molecular orbital (LMO) map. Results show that the adsorption energy of elemental mercury Hg0 by active defect of amorphous SiO2 is less than 50 kJ/mol, proving the adsorption to be the weak physical kind; whereas the adsorption energy of oxidized mercury HgCl by active defect of amorphous SiO2 is greatly larger than 50 kJ/mol, indicating a typical chemical adsorption, and the interaction between HgCl and SiO2 is covalent.
  • Probabilistic Short-term Interval Forecast of Wind Power Based on EEMD and SOA-KELM Model
    YANG Xiyun, KANG Ning, YANG Yuwei, SU Jie
    2019, 39(11): 926-933.
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    To optimize the wind power prediction intervals (PIs), a probabilistic PIs model was built based on ensemble empirical mode decomposition (EEMD) and kernel extreme learning machine (KELM) modified by seeker optimization algorithm (SOA). Firstly, EEMD technique is adopted to decompose the original wind power series into a number of subsequences based on time-frequency analysis of nonstationary wind power. For each subsequence, a KELM interval prediction submodel is established based on lower-upper bound estimation method, while SOA is used to optimize the output weights of KELM submodels, aiming to improve the prediction performance of the model proposed. Finally, a comparison was conducted between the model proposed and other five PSO-optimized models using real power data. Results show that the EEMD-SOA-KELM model is globally converged with higher convergence rate, which is reliable and effective in interval predictions.
  • Modal Analysis of Offshore Wind Turbines
    CHENG Youliang, LI Shuailing, ZHOU Bin, QU Jiangman
    2019, 39(11): 934-939.
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    To obtain the natural frequencies of a 1.5 MW wind turbine without prestressing force, a natural vibration analysis was conducted on the simplified coupled structure of its tower and pile foundation using finite element method, and subsequently the natural frequencies of the coupled system without prestressing force were obtained, while the low-order vibration patterns and corresponding modal shape curves were output, which were then compared with the external excitation frequencies, i.e. rated 1P, 3P and 6P of the wind turbine based on Campbell diagram, to estimate whether resonance occurs under external excitation conditions, and to find the critical speed and safety zone of the wind turbine. Finally, modal analysis results were obtained for the whole wind turbine. Results show that compound movements of swing and brandishing appear in the vibration mode of the whole machine based on the mode of the coupled structure entity of the tower and pile foundation, and the natural frequencies of the whole machine are close to the static characteristic frequencies of the entity.
  • Characteristic Study on Noise Reduction Mechanism for Leading Edge Blades with Root-planed Wave Teeth
    ZHANG Guang, CHEN Eryun, YANG Ailing, CHEN Yuan
    2019, 39(11): 940-946.
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    To reduce the pressure pulsation and self-noise of a blade, a hybrid method combining LES and FW-H was used to numerically simulate the blade with the Reynolds number of 2×105 at an attack angle of 5°, so as to study the mechanism of noise reduction and analyze the transient flow field and sound field characteristics of the leading edge blade with root-planed wave teeth. Results show that the root-planed wave teeth accelerate the fluid flow at the leading edge of blade, which can better regulate the flow field and reduce the separation vortex, while the thickness of the wake vortex becomes smaller, and the large-scale vortex breaks into small-scale vortexes in the progress of extrusion and stretching, when the vortex structure gets more compact. The leading edge structure of root-planed wave teeth reduces the pressure pulsation on the blade surface, which has good effects on noise reduction, exhibiting broadband characteristics at low and medium frequencies, with a reduction in total sound pressure level by up to 9 dB.
  • Effects of Total Cycle Period and Hold Time on the Creep-Fatigue Crack Growth Behavior of P91 Steel
    LIU Changjun, YAN Achen, TAN Jianping, QIN Jingfang, ZHANG Jing, WANG Donghui
    2019, 39(11): 947-952.
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    Creep-fatigue crack growth tests were carried out at 620℃ to study the effects of total cycle period on the crack initiation time, and to analyze the crack growth behavior under various time durations. Results show that in a single-logarithm coordinate, the crack initiation time shows a linear relationship with the total cycle period. When the total cycle period is less than 20 s, the number of cycles for crack initiation does not change with the total cycle period. When the crack growth rate characterized by ΔK, the crack growth rate increases with the rise of hold time, but decreases first and then increases with the rise of ΔK, while that characterized by (Ct)avg can correlate well the crack growth rates under different time durations.