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  • 2016 Volume 36 Issue 9
    Published: 15 September 2016
      
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  • Study on Steady-state Model of Typical Oxy-fuel Air/Gas Combustion Systems
    LIU Jie, HUANG Yongli, ZENG Tiancheng, LIU Zhaohui, ZHENG Chuguang
    2016, 36(9): 677-682.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    For oxy-fuel combustion boilers aiming at reducing CO2 emission, a steady-state model was established to measure the flow rate and component of the gas in the air/gas combustion system, and subsequently to find the interrelation between the system operating parameters and the governing way of gas variables. Results show that the gas flow rate and its component calculated by the model are close to actual measurements, with both errors less than 5%. The model is therefore proved to be reasonable and effective in providing quantitative basis for the design and running of oxy-fuel combustion systems, which may also serve as a reference for relevant measurement configuration, instrument selection, quantitative governing and device manipulation of air/gas combustion systems.
  • Propagation Characteristics of High-intensity Sound in Power Plant Boilers
    JIANG Genshan, XU Weilong, KONG Qian, AN Liansuo
    2016, 36(9): 683-689.
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    Propagation characteristics of high-intensity sound with audio frequencies in power plant boilers were studied. Firstly, the mechanism of distortion and harmonic generation occurring in propagation process of high-intensity sound with pressure level of 160 dB was analyzed based on the hypothesis of simple wave theory, while the formation distance of shock waves was calculated for high-intensity sounds of different frequencies. Secondly, the strict solution of burgers equation for viscous fluid in the furnace was calculated, and the propagation characteristics of high-intensity sound were analyzed under the circumstance of nonlinear effect and dissipation effect. Finally, the propagation characteristics of high-intensity sound in the relaxation medium were discussed after solving relevant nonlinear wave equations by numerical methods. Results show that the formation distance of shock waves is inversely proportional to the sound frequency; the nonlinear effect weakens while the dissipation effect improves with the rise of sound frequency.
  • Study on Kinetic Models for Zhundong Coal Gasification
    CHEN Hongwei, MU Xinglong, WANG Yuanxin, LUO Min, ZHANG Zhiyuan
    2016, 36(9): 690-696.
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    Gasification characteristics of Zhundong coal mixed with catalyst K2CO3 and Ca(OH)2 respectively were studied in a chemical kinetic controlled regime, so as to analyze the effects of following factors on the internal and external diffusion resistance in the process of gasification, such as the amount of coal sample, the CO2 flow rate and the particle size, etc., and to obtain the fitting curves of Zhundong coal gasification at different temperatures by the homogeneous model (HM), unreacted shrinking core model (SCM) and modified volumetric model (MVM) separately, based on which the activation energy was calculated using isoconversional method, while the accuracy of the method was verified with catalytic activity index. Results show that for conversion rates of 0.2, 0.4, 0.6 and 0.8, the corresponding activation energy lies in 100.1-130.2kJ/mol, and the results calculated by above three models are 128.97kJ/mol, 140.33kJ/mol and 139.43kJ/mol accordingly, proving HM to be the most appropriate kinetic model.
  • Numerical Study on the Performance of Premixing Structure in a Gas Turbine Combustor
    HUANG Xingliang, ZHU Zhijie, YE Wen
    2016, 36(9): 697-703.
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    Numerical simulation was conducted on the fuel-air premixing and combustion process in a premixed swirl-stabilized combustor using Fluent software, so as to analyze the effects of vane parameters in the axial swirler on the premixing uniformity, flashback characteristics, total pressure loss and pollutants emission, etc., and to determine the improvement plans for the fuel injection structure. Results show that good combustion performance could be obtained when the cover degree of axial swirler is within 1.0-1.5, the angle of vane is within 40°-55° and the number of vanes is of 8-12. The premixing uniformity could be improved and the maximum combustion temperature could be lowered by following 3 measures, such as reducing the diameter of fuel injection holes, integrating the swirler with fuel injection holes and arranging the injection holes in a reasonable distribution, etc., in which case, the NOx emission would be decreased by 91%, 35% and 91% accordingly.
  • Experimental Study on Single-hole Film Cooling Effectiveness over Vibrating Plates
    GAO Yuan, GE Lishun, WANG Hongguang, HAN Tieying
    2016, 36(9): 704-710.
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    Experimental study on single-hole film cooling characteristics over vibrating plates was conducted in a high-temperature wind tunnel test setup using infrared thermography and mechanical vibration mechanism, so as to measure the film cooling effectiveness under steady-state and vibrating conditions with the blow ratio in 0.4-1.8, and to analyze the effects of amplitude (0-5mm) and frequency (0-20Hz) on the cooling effectiveness. Results show that the film cooling effectiveness is weakened by vibration, which is also affected more by amplitude than by frequency; with the rise of blow ratio, the influence of vibration reduces on film cooling effectiveness;the curves of mean effective temperature ratio respectively at varying vibration frequences and amplitudes are similar to that in steady-state conditions, and their data would be reduced by 3% and 5% accordingly in the case of X/D=5-10.
  • Individual Pitch Control Based on Different Load Measurements
    ZHOU Feng, CHEN Zhonglei, DENG Ying, TIAN De
    2016, 36(9): 711-715.
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    Individual pitch control was studied based on following 3 different load measurements, such as the blade root out-of-plane bending moment, rotating hub bending moment and fixed hub out-of-plane bending moment. Results show that the difficulty of above 3 measurement ways in implementation and maintenance is successively decreasing. Compared with controllers without load control, the controllers based on above 3 load measurements are able to cut down load fluctuations, so the load transmitted to other parts of the wind turbine would be reduced accordingly. Moreover, the load control shows no obvious influence on the power output of the wind turbine, but the pitch actuators would work more frequently.
  • Terminal Sliding Mode Control Optimization for Maximal Wind Energy Capture of DFIG Without Speed Sensors
    WU Zhongqiang, WANG Xinyi, ZHAO Xibo
    2016, 36(9): 716-725.
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    To achieve maximum wind energy capture of doubly-fed induction generators (DFIG), a Backstepping terminal sliding mode controller was designed for the complex nonlinear and strongly coupled system. The specific way is to solve the problem of large initial error by arranging the reference input signal using tracking-differentiator (TD), and then to realize speed sensorless operation using extended state observer (ESO) to estimate the flux linkage and motor speed, and reduce the ripples of flux linkage and torque, and finally to simplify the design of Backsteepping terminal sliding mode controller through observation and compensation on disturbing terms like coupling disturbance in current equations. Meanwhile, the firefly optimization algorithm (FA) is used to optimize those parameters to be set in the controller and observer. Results show that floating tracking can be achieved in the control system via the scheme, and the control accuracy is thus improved.
  • Modeling of Power Plant SCR Denitrification System Based on Improved Partial Mutual Information Method
    QIN Tianmu, LIU Jizhen, FANG Lianhang, LIU Hongyan, YANG Tingting, LÜ You
    2016, 36(9): 726-731.
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    To solve the problem of large error in calculating the regression value with conditional expectation by traditional partial mutual information (PMI) method that may produce negative effect on the selection accuracy, an improved partial mutual information (IPMI) algorithm was proposed to calculate the regression value using interpolation method, of which the effectiveness was validated by Benchmark software. The IPMI algorithm was then applied to the SCR denitrification system of a power plant. The specific way is to set up an IPMI-SVM model based on the historical data by taking the optimal variable set of IPMI as the input of support vector machine (SVM) model, and then to compare the IPMI-SVM model with traditional SVM method. Results show the IPMI-SVM model has relatively high prediction accuracy, while the IPMI method can effectively improve the generalization ability and robustness of the model and reduce the model complexity.
  • Model Improvement for Boiler NOx Emission Based on Wind Driven Optimization Algorithm
    NIU Peifeng, ZHAO Zhen, MA Yunpeng, CHEN Ke, WANG Qiuya, ZHAO Qingchong
    2016, 36(9): 732-738.
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    To accurately predict the NOx emission of power plant boilers, a unified model was established using adaptive wind driven optimization (AWDO) algorithm and extreme learning machine (ELM) by taking the 300 MW subcritical circulating fluidized bed boiler as an object of study. Prediction ability of the model was then verified with sample data obtained under different working conditions, and its prediction results were subsequently compared with that of basic ELM models and the ELM models optimized by differential evolution algorithm, particle swarm optimization and wind driven optimization, respectively. Results show that the AWDO algorithm has a strong capability in parameter optimization, and the ELM model optimized by AWDO algorithm has a higher prediction accuracy and generalization ability, which therefore is able to predict the NOx emission of power plants accurately and effectively.
  • Wind Turbine Aerodynamic Performance Optimization by Individual Pitch Control Based on Trailing Edge Separation Model
    ZHANG Yunning, YE Zhou, LI Chun
    2016, 36(9): 739-745.
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    To simulate the unsteady aerodynamic performance of a wind turbine with NREL phase VI test blade, a three-dimensional trailing edge separation prediction model was established by coupling the Kirchhoff-Helmholz trailing edge separation prediction model with 3D Du-Selig stall delay model, in consideration of the three-dimensional rotational effect and trailing edge separation phenomenon, while the influence of vortex lattice number on the calculation accuracy was analyzed using lifting surface free vortex wake method. Based on the tangential distribution of separation factor, the wind turbine aerodynamic performance was then optimized by introducing a sin wave pitch increment in half period of rotation through individual pitch control to offset the increase of attack angle resulted by the change of relative inflow velocity. Results show that when the three-dimensional trailing edge separation prediction model with two vortex lattices on the lifting surface is adopted, optimum simulation results of normal and tangential force coefficient would be obtained. In each period of rotation, the trailing edge separation factor is relatively higher between 180° and 360°, which reaches the maximum at 270°. The trailing edge separation factor is reduced by individual pitch control, and the reducing magnitude increases with the rise of pitch angle; both the shaft and flap wise torque would achieve the optimum optimization effect when the pitch angle is set at 5°.
  • Optimized Design for Thermodynamic System of Coal-fired Power Plants with CO2 Capture Based on AWPSO Algorithm
    FU Wenfeng, HOU Yanfeng, WANG Lanjing, LI Jiahua, YANG Yongping
    2016, 36(9): 746-752.
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    Taking the 1 000 MW ultra-supercritical coal-fired unit as an example, a new design scheme was proposed for the thermal system of power plant with CO2 capture, based on which a computing framework for the thermal efficiency and a parameter optimization model for the regenerative system were set up, while the adaptive weighted particle swarm optimization (AWPSO) algorithm was applied for relevant calculations. Results show that the thermal economy of the newly-designed coal-fired power unit with CO2 capture has been significantly improved, with its cycle thermal efficiency 10.7% higher than the retrofitted unit before optimization. The AWPSO algorithm is characterized by quick convergence and high stability, and its optimization results are obviously better than other methods, which therefore may be used for design optimization on thermodynamic system of coal-fired carbon-captured power units.
  • Characteristic Analysis on the Flow and Local Resistance in Large Pipe Tees
    GONG Qitao, YANG Junhong, HAN Kui, HUANG Tao, LI Jing, ZUO Pengpeng
    2016, 36(9): 753-758.
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    To reduce the effects of local resistance in pipe tees on hydraulic balancing and energy consumption of the heating supply network, the velocity and pressure field in pipe tees with diameter equal to or above 400 mm were simulated using Fluent software, so as to analyze the influence of following factors on the local resistance characteristics, such as the split ratio (q), Reynolds number (Re), diameter ratio (d) and the angle between main pipe and side branch (θ), etc. Results show that both the local resistance coefficient of main pipe to side branch ζ01 and that of main pipe to straight branch ζ02 reduce with rising Re, which basically get stabilized at Re=4.8×105. ζ01 and ζ02 increase with the rise of q in the case of d less than 0.8, which have a parabolic relationship with q in the case of d larger than or equal to 0.8. For a certain value of q, ζ01 reduces with rising d, and the reducing tendency slows down obviously in the case of d larger than 0.7. Analysis results indicate that with the rise of θ, the size of vortex, the gradient of velocity and the curving degree of streamline increase significantly in the side branch, resulting in obvious increase of ζ01, whereas the gradient of velocity slightly rises in the straight branch, resulting in slight increase of ζ02 accordingly.
  • Influence of the Sink of Insulation Materials on Design of the Insulation Layer for Horizontal Circular Heating Pipelines
    ZHAO Xu, SHEN Qie, ZHANG Ning, SUN Daming, ZOU Jiang
    2016, 36(9): 759-764.
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    Influence of the sink of insulation materials on calculation of the economic insulation thickness over horizontal circular heating pipelines was quantatively analyzed, based on which a correction method was proposed for the design of economic insulation thickness by simultaneously analyzing the heat path of the whole insulation layer. The numerical method of economic thickness was studied theorectically, and the effects of design parameters on the economic thickness was researched by varying the parameters in an acceptable range. Using the corrected numerical method of economic thickness, the insulation for heating pipelines actually operated in Huangtai Power Plant was designed. Results show that the annual insulation expense may be reduced by 0.7% after the insulation is designed by the corrected numerical method of economic thickness. The diameter of heating pipeline D0, the sink rate M and the medium temperature T0 inside the pipeline are all the main factors influencing the design of the economic insulation thickness.