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    Boiler Technology
  • Boiler Technology
    Numerical Study on NOx Emission Characteristics of a 600 MW Opposed Firing Boiler
    LIU Yaming, LI Fangyong, XU Qisheng, FANG Qingyan
    2015, 35(5): 341-347.
    Abstract ( )   Knowledge map   Save
    NOx emission characteristics of a 600 MW ultra supercritical opposed firing boiler were numerically simulated under different ratios of over fire air (OFA) at different modes of in-service burner layers. Results show that at the rated load of 600 MW, the carbon content in fly ash linearly increases but the NO emission significantly reduces with the rise of OFA ratio; when the OFA ratio increases from 25% to 35%, the carbon content in fly ash will be raised by 1.22%, and the NO emission will be reduced by 293 mg/m3, and the optimal comprehensive index can be obtained at the OFA ratio of 30%. Both the fly ash carbon content and the NO emission produced in the ACDEF burner operation mode are lower than those in the ABCDE and BCDEF mode; compared with the BCDEF mode, the fly ash carbon content and the NO emission in ACDEF mode are respectively reduced by 0.46% and 40 mg/m3.
  • Boiler Technology
    Effect of Air Distribution Mode on Exit Flow Field of Petal Burners
    LI Huijun, JIA Baotong
    2015, 35(5): 348-353.
    Abstract ( )   Knowledge map   Save
    A physical model of petal burner was set up, of which the cold-state flow field was calculated using software Fluent at different primary and secondary air velocities, so as to analyze the distribution mode of primary and secondary air on the exit flow field. Results show that the existance of primary air reduces the recirculation zone, lowers the combustion stability, but helps to avoid the slagging problem due to its capability in adjusting the distance between recirculation zone and burner exit. At a certain velocity of primary air, with the rise of internal secondary air velocity, the axial recirculation zone increases and the combustion effect improves. By adjusting the blade angle to increase the tangential velocity of internal secondary air, the radial recirculation zone will be reduced, but the axial recirculation zone will be increased. For different coal categories, the combustion stability can be raised by appropriately choosing the velocity of primary and secondary air to increase both the axial and radial recirculation zone.
  • Boiler Technology
    Weak Leakage Signal Detection for Boiler Pressure Piping
    AN Liansuo, FENG Qiang, SHEN Guoqing, JIANG Genshan, ZHANG Shiping, WANG Peng, ZHOU Xin
    2015, 35(5): 354-360.
    Abstract ( )   Knowledge map   Save
    The method of empirical mode decomposition (EMD) combined with cross-correlation difference-Duffing oscillator (CD-EMD) was proposed for weak signal detection of initial leakage in boiler pressure piping. By adding the pneumatic sound signal of 0.6 MPa to the furnace background noise signal, weak leakage detection was numerically simulated, and the detection results were compared between EMD and wavelet transform under fixed signal to noise ratios. Detection results were also compared between EMD combined with Duffing oscillator (D-EMD) and CD-EMD by reducing the signal to noise ratios. Results show that with EMD method, the signal to be detected can be identified from the furnace background noise at -5 dB signal to noise ratio, and the effect is obviously better than wavelet transform; at -24 dB signal to noise ratio, the signal cannot be identified normally by D-EMD method due to the serious interference of initial phase; CD-EMD method can effectively overcome the misjudgment caused by initial phase, which therefore can improve the real-time property of judgement by setting the empirical threshold.
  • Boiler Technology
    The Effect of Coal Blending Ratio on Slagging/Fouling Characteristics of Zhundong Xinjiang High-alkali Coal
    CUI Yukui, ZHANG Xiang, WU Xiaojiang
    2015, 35(5): 361-365.
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    Taking two typical kinds of high-alkali and low-alkali coal in Zhundong Xinjing as an object of study, the effect of coal blending ratio on ash fusion characteristics of the coal mixture was investigated, of which the resuts were analyzed with ternary phase diagrams. Results show that the ash fusion characteristics of coal mixture changes greatly with the blending ratio due to the obvious change in chemical and mineral composition; the trends of ash fusion temperature is not linear with the blending ratio of the two coals, but mirrored by changes in the liquidus temperature from ternary systems. The ash fusion characteristics of coal mixture can be adjusted through high-temperature interaction between refractory minerals and fluxing minerals by blending the coals in different ratios, so as to change the composition of main minerals and reduce the formation of Na and K low-temperature alkali eutectics in the high-alkali coal.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Numerical Study on Effectiveness of Installing Guide Device into Exhaust Passage of a 600 MW Steam Turbine
    CAO Lihua, ZHANG Haolong, YANG Weimin, ZHANG Dao, LI Yong
    2015, 35(5): 366-372.
    Abstract ( )   Knowledge map   Save
    To analyze the causes leading to high exhaust pressure and low economic efficiency of a 600 MW steam turbine due to non-uniform flow field distribution existing at exit of the exhaust passage, numerical simulation was conducted to the exhaust passage with double back-pressure condensers, and subsequently a reasonable scheme to improve the flow field distribution was proposed by installing guide devices into the exhaust passage. Simulation results show that the problem caused by specific structure of the exhaust hood, steam exhaust from boiler feed pump turbine and the existence of low-pressure heater can be solved by reasonably installing guide devices into the exhaust passage, after which the total pressure loss coefficient will be increased by only 0.5%-2.5%, but the static pressure recovery coefficient will be increased by 6.4%-8.8%, while the uniformity coefficient will be raised by 10.4%-13.4%.
  • Steam Turbine and Gas Turbine
    Aerodynamic Design and Numerical Optimization of a Transonic Axial Flow Compressor
    REN Ping, ZHU Fang, ZHAO Lianhui
    2015, 35(5): 373-379.
    Abstract ( )   Knowledge map   Save
    Aerodynamic design and numerical optimization of a three-stage transonic axial flow compressor with inlet guide vane were described, which adopts the quasi-3D design system, including the one-dimensional mean streamline design, S2 stream surface through flow design and the blade shaping, etc., while the flow field was analyzed using Numeca software. To improve the adiabatic efficiency of compressor, the first stage transonic rotor blade was optimized under multistage conditions, using a global optimization method in combination of Genetic Algorithm (GA) with Artificial Neural Network (ANN). Results show that after numerical optimization, the adiabatic efficiency of both the transonic rotor blade and the three-stage compressor has been respectively increased by 0.87% and 0.37% at design point, with significant reduction of shock-boundary layer interaction loss at blade tip. The mass flow, total pressure ratio, adiabatic efficiency and stall margin could all satisfy the design targets.
    • Automatic Control and Detecting Diagnosis
  • Automatic Control and Detecting Diagnosis
    Vibration Monitoring by Gaussian Process Regression for Wind Turbine Towers
    GUO Peng, WANG Xueru
    2015, 35(5): 380-386.
    Abstract ( )   Knowledge map   Save
    Based on wind turbine operating theories, an analysis was conducted to the tower vibration characteristics with operation data, and it was found that the tower vibration has close relationship with some variables recorded by the supervisory control and data acquisition (SCADA) system. A vibration model describing the relation between tower vibration and relevant variables was established using Gaussian process regression method according to the characteristics of wind turbine operation data, i.e. strong randomness and high noise, which was subsequently verified. Results show that the asymmetry of rotor blade angle can be monitored and diagnosed by analyzing the tower model residual, thus proving the vibration monitoring method to be effective.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Static Characteristics of the Impeller of an Axial Flow Fan Under Rotating Stall Conditions
    ZHANG Lei, LANG Jinhua, WANG Songling
    2015, 35(5): 387-393.
    Abstract ( )   Knowledge map   Save
    Based on Realizable k-ε turbulent model, the flow field in an axial flow fan was numerically simulated under rotating stall conditions, while the static characteristics of its impeller was studied using finite element method and fluid-structure interaction theory with software Ansys. Results show that under rotating stall conditions of fan, a stall cell exists in the impeller with its propagation direction same as the rotation direction of the impeller. The equivalent stress distribution is greatly influenced by the centrifugal force, but slightly influenced by the rotating stall. The maximum equivalent stress of impeller is found to be lower than the material yield limit, proving the impeller to be safe. The aerodynamic force has important influence on the impeller total deformation. Under stall conditions, maximum total deformation appears in the area of stall cell center, which is 72.2% larger than the design condition.
  • Auxiliary Equipment Technology
    Performance and Internal Flow Characteristic of an Axial Flow Fan with Installation Deviation in Two-stage Blades
    YE Xuemin, WANG Feng, LI Chunxi
    2015, 35(5): 394-403.
    Abstract ( )   Knowledge map   Save
    Taking a two-stage variable-pitch axial fan used in a 600 MW power unit as an example, numerical simulation was carried out using Fluent to investigate the aerodynamic performance of the fan, the work capability of the impellers and the noise characteristics in the case of two blades at same circumferential position abnormally installed, of which the results were compared with those of single abnormal blade. Results show that when there are simultaneously two blades abnormally installed, the work capability of the impellers, the guide vane efficiency, and the noise and operating performance of the fan are all inferior to the case with single abnormal blade; the stall region is expanded, especially in the case of positive deviation of blades. Under small negative deviation conditions, the work capability of impellers is less than the case with same positive deviation; however, with the rise of Δβ, the work capability of impellers increases under negative deviation conditions. In the case of positive deviation, flow loss of guide vane is larger than that of negative deviation. The noise level of fan tends to increase with the rise of Δβ, and the effect of positive deviation on the abnormal impeller noise distribution is stronger than the negative deviation, and the noise of fan with single abnormal blade in the second-stage impeller is higher than that in the first-stage impeller.
    • Energy System Engineering
  • Energy System Engineering
    Comprehensive Energy-saving Evaluation of Thermal Power Plants Based on TOPSIS Gray Relational Projection and the Weight Sensitivity Analysis
    YUAN Guili, ZHANG Jianhua, WANG Tianhong, DU Juan
    2015, 35(5): 404-411.
    Abstract ( )   Knowledge map   Save
    According to the characteristics of energy-saving assessment in thermal power plant, a comprehensive gray relation projection evaluation method based on ideal point was proposed by introducing the TOPSIS, gray correlation theory and vector projection method to the unit performance evaluation. Meanwhile, the weight of evaluation index was determined by combining the Delphi with sequence synthesis technique using combination weighting method, so as to improve the scientific level and objectivity of energy-saving assessment for thermal power plant. Above methods were applied to the comprehensive evaluation of five 600 MW units, while a sensitivity analysis of the subjective weights was carried out. Results show that the indicator of both the economy and reliability is still dominant in the unit comprehensive evaluation; the model of gray relation projection evaluation based on TOPSIS is able to quantitatively evaluate the energy-saving status with high evaluation robustness, which therefore may serve as a reference for energy saving of relevant power plants.
  • Energy System Engineering
    Analysis on Dynamic Cost of Straw Direct Combustion Power Generation
    ZHAO Haoliang, ZHANG Xu, ZHAI Mingling
    2015, 35(5): 412-417.
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    Based on cost study method for thermal power plant, a monthly dynamic cost model was set up for biomass power plant, which divides the fixed annual cost according to unit capacity and load characteristics. Taking the biomass power generation system as an object of study, the maximum and minimum cost of power generation was calculated according to different straw price, while a sensitivity analysis was performed to the power generation cost. Results show that the fuel price influences most on the power generation cost of biomass power plant, followed by the depreciation expense and the house power consumption. When the fuel price is respectively reduced by 10% and 20%, the cost of power generation would drop by 5.09% and 10.17%, accordingly.
  • Energy System Engineering
    A New High-temperature High-pressure Multi-layer Structure Pipeline and the Wall Temperature Calculation
    LI Jianfeng, L Junfu, LENG Jie, CHAI Xiaojun
    2015, 35(5): 418-423.
    Abstract ( )   Knowledge map   Save
    To reduce the manufacturing cost of high-temperature high-pressure fluid pipeline, and to follow the principle of sharing the temperature and pressure load respectively, a new multi-layer structure was proposed for the pipeline, to which a thermodynamic model was established for the wall temperature calculation, so as to analyze the influence of following factors on the number of heat shields required for different sizes of inner pipe, such as the wall temperature, outer radius of heat shields, and the thermal flux, etc. Results show that when the wall temperature of inner pipe is 700 ℃, the outer pipe wall temperature will decline rapidly with rising number of heat shields, which may finally drop to 350 ℃, thus the outer pipe may be manufactured with ordinary steels, resulting in greatly reduced manufacturing cost.
    • Nuclear Technology
  • Nuclear Technology
    Research on Flow and Deposition Characteristics of Fine Particles in Rough Narrow Channels
    LIN Daping, ZHOU Tao, LI Jingjing, YANG Xu, RU Xiaolong
    2015, 35(5): 424-428.
    Abstract ( )   Knowledge map   Save
    Numerical simulation was conducted to flow characteristics of fine particles in the 1 000 mm×20 mm×20 mm narrow channel respectively with rough and smooth inner surface using Fluent software, so as to study the influence of inner surface roughness on the temperature field, and to analyze the concentration and velocity distribution in the narrow channel. Results show that fine particles will deposit on the wall when temperature gradient exists in the channel; with the rise of surface roughness, the temperature gradient near channel wall increases, which will enhance the thermophoretic and turbulent effect, and therefore promote the gathering of fine particles in the area near channel wall.