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    Boiler Technology
  • Boiler Technology
    Numerical Simulation on Combustion Characteristics of a 660 MW Tangentially-fired Boiler After Low-NOx Retrofit Under Different Coal Mill Combinations
    LI Debo, XU Qisheng, SHEN Yueliang, LIU Yaming, WEN Zhiyong
    2015, 35(2): 89-95.
    Abstract ( )   Knowledge map   Save
    Numerical simulations were conducted to combustion characteristics of a 660 MW tangentially-fired boiler after low-NOx retrofit under different coal mill combinations using Ansys Fluent 14.0 software, so as to study the in-furnace velocity field, temperature field, species field andpollutants emission, and to compare the simulation results with experimental data. Results show that uniform temperature distribution can be obtained in the furnace after the addition of SOFA air, without flame adhering to the wall; in the combustion zone, the temperature rises gradually along the height of boiler furnace under different coal mill combinations; in the area between CCOFA and SOFA nozzles, the temperature drops first, then rises, and finally reduces again; in the area above SOFA nozzles, the average temperature profile in furnace cross section is basically the same under different coal mill combinations, which reduces along with the furnace height; in the area between CCOFA and SOFA nozzles, the NOx concentration reduces along the furnace height under different coal mill combinations, whereas in the area above SOFA nozzles, the NOx concentration rises first and drops later on, but the variation is relatively moderate; maximum NOx concentration occurs in the ABCEF mode of coal mill combination at furnace outlet, which is 382.2 mg/m3, while minimum NOx concentration occurs in the ABCDE mode of coal mill combination at furnace outlet, which is 307.4 mg/m3.
  • Boiler Technology
    A Coupling Method of Direct and Inverse Heat Conduction Problems for Transient Temperature Calculation of a Boiler Drum
    LI Bin, CHEN Feng, SHI Liangxiao
    2015, 35(2): 96-102.
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    A coupling method of direct and inverse heat conduction problems was proposed for transient temperature calculation of a pressurized boiler drum, of which the locally heated outer surface is divided into two regions, namely heated and unheated area. For the unheated area, the inverse method is used to determine the temperature field by circumferentially arranging thermocouples to measure the outside surface temperature of the drum, and for the heated area, the direct method is adopted to solve the temperature field; whereas at the junction of above two areas, the temperatures determined by the inverse method are used as known boundary conditions to calculate the temperature field of heated area by the direct method. By this way the coupling solution of direct and inverse heat conduction problems is realized, and the whole temperature distribution of the drum is obtained. A comparison was made to the drum temperature distribution during cold startup of the boiler respectively obtained by Ansys software and the coupling method. Results show that the coupling method of direct and inversion heat conduction problems has high precision and strong adaptability under complicated boundary conditions, which therefore may be used in actual engineering projects.
  • Boiler Technology
    Characteristic Analysis on Recirculation Zone of a Petal-shaped Swirl Burner Based on Cold-state Conditions
    LI Huijun, JIA Baotong, JIAO Yingzhi, WEI Gang
    2015, 35(2): 103-107.
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    Based on physical models set up for a petal-shaped swirl burner, numerical simulations were performed to the outlet flow field using Fluent software at different tangential velocities of inner secondary air, so as to analyze the characteristics of the recirculation zone and compare the simulation results with cold-state experimental data. Results show that the petal-shaped swirl burner is able to form both axial and radial recirculation zones in the valley behind petal peak, where the radial convective heat transfer has a good effect on combustion stabilization, thus improving its adaptability to low-quality coal; within a certain range, the greater the tangential velocity is, the faster the axial recirculation zone will be formed, but too high tangential velocity will lead to the reduction of radial recirculation zone.
  • Boiler Technology
    Experimental Study on Ash Deposition Characteristics of High Sodium Coals from Xinjiang
    NIE Li, BAI Wengang, RAN Shenming, ZHOU Qi, ZHANG Xiuchang, CHE Defu
    2015, 35(2): 108-112.
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    The effects of flue gas and outer wall temperature on the ash deposition characteristics of heating surface tubes during the combustion of three different coals were experimentally investigated on a 3 MW pulverized-coal combustion test rig, including two high sodium coals from Xinjiang and one non-high-sodium coal. Results indicate that the flue gas and outer wall temperature can significantly impact the ash deposition characteristics of the test section, which is closely related to the melting point of all kinds of sodium compounds in flue gas. When the flue gas temperature is 520 ℃ (lower than the lowest melting point of various sodium compounds in flue gas), the ratio of the heat transfer coefficient Rh almost does not change with time, which is approximately equal to 1. When the flue gas temperature is higher than 650 ℃, the Rh of the test section reduces gradually with the extension of time, and the higher the flue gas temperature is, the faster the Rh falls.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Numerical Study on Conjugate Heat Transfer Performance of Steam-cooled Blades
    DU Changhe, LI Liang, FENG Zhenping
    2015, 35(2): 113-118.
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    To evaluate the steam cooling effect upon turbine blades, a thermo-fluid-solid coupling simulation was carried out to a Mark II blade, so as to study the influence of different turbulence models on the calculation results by comparing with the experimental data. Cooling effects were also compared among different mediums, such as the air, superheat steam and wet steam, while the influence of cooling steam flux, inlet turbulence intensity and blade surface roughness on the steam cooling effects was studied. Results show that the SST transition turbulence model has superior accuracy than other turbulence models in the evaluation of heat transfer characteristics. Compared with air cooling, superheated steam cooling has higher efficiency with lower wall temperature of blades. Wet steam cooling gains higher cooling efficiency and lower blade wall temperature than superheated steam cooling, and with the rise of steam wetness, the wet steam cooling efficiency increases, and the blade wall temperature decreases. The cooling efficiency may be improved by raising the cooling steam flux, in which case the temperature rise of cooling steam decreases. When the turbulence intensity of cooling steam is less than 3%, the cooling efficiency will increase with the rise of inlet turbulence intensity. The increase of blade surface roughness may lead to a significant rise of the cooling efficiency.
  • Steam Turbine and Gas Turbine
    Orthogonal Simulation on Cooling Efficiency of Turbine Cascade Endwall
    ZHANG Ling, ZHU Jian, GUO Dafei, HAN Jianing
    2015, 35(2): 119-125.
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    Four rows of cylindrical film cooling holes were cut on the turbine cascade endwall, respectively in the regions of 21%, 51% and 81% axial chord length, and in the 9% upstream region of leading edge. The endwall film cooling effectiveness was analyzed using CFD method under different conditions of blowing ratio, axial angle and radial angle, based on which optimal arrangement of above cooling holes was obtained via orthogonal algorithm. Results show that the blowing ratio has greatest influence on the cooling effectiveness, followed by radial angle and axial angle; highest cooling effectiveness may be reached when the blowing ratio is 2.0, axial angle is 30° and radial angle is 45° (the first and third rows of cooling hole form a 45° angle to the negative direction of axis y, while the second and fourth rows of hole form a 45°angle to the positive direction of axis y), which is seemed as the optimum scheme under combined action of above three factors.
    • Automatic Control and Measurement Technology
  • Automatic Control and Measurement Technology
    Control on Maximum Power Point Tracking of Hydraulic Wind Turbines
    AI Chao, KONG Xiangdong, YAN Guishan, LIAO Lihui
    2015, 35(2): 126-133.
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    Aiming at the issues of wind energy utilization, modeling and analysis were conducted to a wind turbine and its closed circuit hydraulic main transmission system, and subsequently a control method was proposed for the maximum power point tracking (MPPT) based on variable step size, with which the operating range of wind turbine was determined according to wind turbine speed and power generation, the given power was adjusted real-timely in accordance with the operating range, thus the MPPT was achieved by indirectly controlling the wind turbine speed for the control of power generation. Above simulation and experimental studies were carried out on a 30 kVA hydraulic wind turbine experiental platform. Results show that the method of MPPT control based on variable step size is very effective, since the system pressure and power generation can accurately follow the change of the wind speed.
  • Automatic Control and Measurement Technology
    Influence of Coupled Fluid-Solid Heat Transfer on the Sensor of Steam Wetness Measurement
    QIAN Jiangbo, YAN Xiaozhe, HAN Zhonghe, LI Hengfan
    2015, 35(2): 134-140.
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    The temperature field and thermal deformation of resonant cavity were calculated using coupled fluid-solid analysis under different steam parameters and flow velocities, while the influence of cavity thermal deformation on the resonant frequency was analyzed according to the average value of node deformation on the effective cavity surface. Results show that with the rise of steam temperature and flow velocity, the average temperature and thermal deformation of resonant cavity, and the offset value of resonant frequency increase. The effect of cavity thermal deformation on the wetness measurement may be reduced by improving the material and structure of the resonant cavity and the specific measurement way.
  • Automatic Control and Measurement Technology
    Online Filtration Efficiency Measurement of Oil Mist Filter Based on Long Optical Path Extinction
    YIN Pengfei, CHEN Jun, YANG Huinan, LIU Lili, CAI Xiaoshu
    2015, 35(2): 141-146.
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    To measure the filtration efficiency of oil mist filter, a long optical path extinction method for low concentration particles was developed based on the measurement of oil mist particle size and concentration before and after filtration, for which simulation oil mist generator and folding optical path measuring head were designed. The optical path was calibrated as 2 000 mm, and the oil mist particle size distribution and concentration were retrieved by particle extinction spectrum. In the experiment, the average particle size D32 and volume fraction of filtered oil mist were respectively 0.28 μm and 1.5×10-8, according to which the filtration efficiency was calculated as 93.15%. Results show that the measuring apparatus based on long optical path extinction is suitable for measurement of size and concentration distribution of fine particles (like oil mist particles), which may be used in performance testing and evaluation of high efficient filters.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Layout Optimization of Guide Plates in a 90 Degree Elbow with Rectangular Cross Section
    YU Fei, LIU Ming, LI Weidong, YAN Junjie
    2015, 35(2): 147-152.
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    A series of 3D numerical simulation were conducted to 90 degree elbows with rectangular cross section before and after installation of guide plates based on computational fluid dynamics (CFD) software Fluent using Realizable k-ε turbulence models, after which optimal layout schemes were proposed for elbows with 1.0≤R/b≤1.5 by quantitatively analyzing the effects of following factors on the flow field uniformity of several reference sections after the turning point, such as the start/end position and central angle of guide plate, and the way that the channel was divided by guide plate. Results show that the optimal layout of guide plate is as follows: the central angle θ≥60°, placed at back position (β=0°) and the channel partitioning way meeting the conditions of b1/b2=0.4-0.5.
  • Auxiliary Equipment Technology
    Study on Dynamic Characteristics of an SCAL Indirect Air-cooled Tower
    LI Lan, MA Huan, SI Fengqi, ZHANG Yifa, ZHU Kangping
    2015, 35(2): 153-159.
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    Taking the large SCAL indirect air-cooled tower in a 600 MW unit as an object of study, a mathematical model was established for dynamic characteristics of the tower, which was solved using Euler algorithm, so as to analyze the dynamic response of enthalpy-temperature channel to the disturbance of following factors, such as the inlet water temperature and flow rate of circulating water, the environmental temperature and the wind speed, etc. The calculated dynamic characteristics were compared with actual operation data. Results show that the dynamic characteristics obtained with above model agree well with actual measurements, with an error less than 3%, which therefore may serve as a reference for operation control of indirect air-cooling systems.
    • New Energy
  • New Energy
    Analytical Method for Combustible Content in Eucalypt Biomass Ash
    LI Li, SONG Jinghui, LI Fangyong, ZHANG Renchao
    2015, 35(2): 160-165.
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    The analytical method for combustible content in eucalypt biomass ash was studied by simultaneously using thermogravimetry, differential scanning calorimetry and Fourier transform infrared spectroscopy (TG-DSC-FTIR). Results show that the eucalypt biomass ash contains a variety of metal compounds, in which slow oxidization, carbonate decomposition and alkali chloride evaporation may occur during the heating process to high temperatures in air, and accordingly, the measurement accuracy of combustible content may be affected. The combustion temperature of combustibles in eucalypt biomass ash is about 350-550 ℃. To eliminate the negative effect of above factors, low concentration sulphuric acid may be used to wash out the carbonate and alkali chloride from the ash, and the slow oxidation of metal compounds may also be inhibited by controlling the heating rate to be below 10 K/min, thus obtaining accurate measurement of combustible content in the fly ash.
    • Energy System Engineering
  • Energy System Engineering
    Performance Analysis of an SOFC-GT Hybrid System Fueled with Biomass
    GENG Xiaoru, Lü Xiaojing, WENG Yiwu
    2015, 35(2): 166-172.
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    Taking biogas as the fuel, a simulation model was set up for solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid systems, with which the effects of air and fuel flow rate on performance of the hybrid system were analyzed using characteristic parameters of the fuel cell and characteristic curves of the compressor and turbine. Results show that the maximum power generating efficiency of the hybrid system may get up to 61.55%, in which case, the lifetime and reliability would drop suddenly. The system power generating efficiency may get up to 55.31% under design conditions. For a constant fuel flow rate, with the air flow rate ranging from 0.084 0 kg/s to 0.179 9 kg/s, the power generating efficiency varies in the range of 61.55%-51.43%; whereas for a constant air flow rate, to prevent the compressor from surging, the fuel flow rate should be controlled within 0.062 3-0.048 6 kg/s, in which case the system power output would change from 124.9 kW to 187.3 kW.