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  • 2018 Volume 38 Issue 11
    Published: 15 November 2018
      
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  • Effect of Flue Gas Recirculation on Operation Parameters of a 1 000 MW Ultra-supercritical Double Reheat Boiler
    SUN Junwei, CAI Pei, HUANG Qilong, YAN Weiping, DAI Weibao, CHEN Guoqing, LI Chaofan, MA Kai
    2018, 38(11): 861-866.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The effect of flue gas recirculation on the operating parameters of a 1 000 MW ultra-supercritical double reheat boiler was investigated by recirculating the flue gas extracted from the economizer outlet or the draft fan outlet to the lower area under bottom burners in the furnace, while the influence of flue gas recirculation on the main steam temperature and reheat steam temperature was analyzed for above two flue gas recirculation schemes using standard method of boiler unit thermodynamic calculation under different conditions. Results show that both the recirculating schemes can obviously improve the reheat steam temperature; the increase of reheat steam temperature intensifies with rising amount of recirculated flue gas; the influence degree of flue gas recirculation on the reheat steam temperature enhances with reducing load; the scheme of extracting flue gas from economizer outlet has little effect on the boiler efficiency and the operation parameters of other auxiliaries, which therefore is a reasonable option for flue gas recirculation, and the optimal recirculation ratio is found to be 10%.
  • Analysis of Contamination Factor on Water Wall in a Zhundong Coal-fired Boiler Based on Fluid-Solid Coupling Simulation
    KANG Zhizhong, DING Xian
    2018, 38(11): 867-873.
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    Numerical simulations were conducted on the heat transfer and working fluid flow in the membrane wall of a supercritical pressure Zhundong coal-fired boiler according to the fluid-solid coupling heat transfer theory, while a mathematic relationship between contamination factor and slagging thickness was fitted. Results show that when the slagging thickness increases from 10 mm to 30 mm, the contamination factor would drop by 50%, and when the slagging thickness lies in 30-50 mm, the contamination factor would change slightly. With the rise of average flame temperature, the contamination factor reduces significantly. The fitting function obtained can be used in design, calculation and slagging control of power plant boilers.
  • Boiler NOx Emission Prediction Based on a Hybrid Model of CAWOA and ELM
    LAI Min, CHEN Guobin, LIU Chao, NIU Peifeng
    2018, 38(11): 874-879.
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    Considering the strong nonlinearity and coupling characteristics of input variables in combustion process of thermal power plants, an integrated model was established to predict the NOx emission based on extreme learning machine (ELM) and modified whale optimization algorithm (WOA), by using Sin chaos adaptive whale optimization algorithm (CAWOA) to search and optimize the model parameters of ELM to improve its generalization performance. In CAWOA algorithm, the Sin chaotic search strategy and adaptive inertia weight were introduced to improve the global optimization performance of WOA algorithm. The optimized ELM was finally used to predict the NOx emission of a 330 MW coal-fired boiler, and the CAWOA-ELM scheme was compared with congeneric methods. Results show that the method proposed has better regression precision and generalization capability, which therefore can accurately predict the NOx emission of power plant boilers.
  • Effect of Oxygenated Feedwater Treatment on Flow Acceleration Corrosion of a Supercritical Unit
    XIAO Zhuonan, BAI Dongxiao, XU Hong, CHEN Weipeng, LI Ke
    2018, 38(11): 880-885.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problems existing in steam-water pipeline of a power plant boiler caused by flow acceleration corrosion, such as the accelerated fouling rate, the tube wall thining and the tube burst failure, etc., a description was presented to the electrochemical corrosion process. Through real-time investigation of two different units, a comparative analysis was conducted on the Fe content in the feedwater treated respectively by all volatile method and oxygenated method, thus finding the advantages of oxygenated treatment. According to the monitoring data of a 660 MW supercritical unit, the effects of following factors on the Fe content were analyzed, such as the dissolved oxygen concentration, pH value and hydrogen conductivity, etc., so as to obtain the critical dissolved oxygen concentration, reasonable pH value and reasonable hydrogen conductivity when an oxygenated treatment is required, i.e. to obtain the suitable process control conditions for oxygenated feedwater treatment. Results show that the oxygenated feedwater treatment can effectively inhibit the flow accelerated corrosion, during which, the monitoring and control of the dissolved oxygen, pH value and hydrogen conductivity are very important.
  • Total Life Calculation for High Temperature Components of Steam Turbines and Its Engineering Verification
    SHI Jinyuan
    2018, 38(11): 886-894.
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    Total life calculation methods were proposed for high-temperature components of large steam turbines under the action of low cycle fatigue and creep, including the methods for low cycle fatigue crack initiation life, creep crack initiation life, low cycle fatigue crack propagation life and creep crack propagation life, as well as for crack initiation calendar life, crack propagation calendar life and the total life of high temperature components under the combined action of low cycle fatigue and creep. Simultaneously, an assessment method was also presented for the total life. Above methods were verified through calculation analysis on weak regions of outer surfaces in high-pressure inner cylinder of two 600 MW supercritical steam turbines. Results show that the relative error calculated for the total life of high-pressure inner cylinder of turbine 1 is 4.12%, and that of turbine 2 is -0.48%, satisfying the requirements of actual applications.
  • Research on Dynamic Characteristics and Dynamic Stress of Curvic Couplings in Heavy-duty Gas Turbines
    YUAN Shuxia, ZHANG Youyun, ZHU Yongsheng
    2018, 38(11): 895-901.
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    Combining dynamic analysis with static analysis, the dynamic stress of curvic couplings was studied in the process of working condition. First, a dynamic analysis of rotor was carried out by adopting equivalent bending stiffness model and traditional stiffness model for the contact area and the continuous region respectively. The dynamic analysis results were then taken as the displacement boundary conditions of static analysis to study the dynamic stress of curvic couplings. Results show that the bearing capacity of curvic couplings is correlated with the pressure angle, the greater the pressure angle is, the higher the bearing capacity would be. However, the pressure angle can't be too large, otherwise, the transmission efficiency would be reduced. Under the action of centrifugal force, the dynamic stress of curvic couplings changes periodically in hoop direction at different positions. The stress on teeth surface is small at bolt position, which is large at middle position, whereas the variation tendency of stress on teeth root is contrary to that on teeth surface. Under the action of torque, an obvious stress difference exists between the bearing side and non-bearing side. The rotor is no longer a cyclic symmetric structure under the action of bending force, as the running orbit of the rotor is an ellipse, and the stress distribution of the curvic teeth alters two times in a round.
  • Numerical Study on Erosion Characteristics of the Flue Gas Flowing Across Pitted Tubes
    YAN Shunlin, WANG Haoxuan
    2018, 38(11): 902-907.
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    To reduce the flue gas erosion over heat exchanger tubes in tail flue duct of a boiler, a new type of pitted tube was put forward, based on which, numerical simulations were conducted on the gas-solid two-phase flow when the flue gas flowing across the pitted tubes in aligned arrangement, so as to analyze the effects of following factors on the erosion characteristics, such as the flue gas velocity, particle size, horizontal/vertical tube spacing and the depth of pits, etc., and to compare the wear on the surface of rough and smooth tubes under same conditions. Results show that compared with smooth tubes, the wear of pitted tubes could be reduced by about 15% under same conditions, and the amount of wear increases with rising flue gas velocity, particle size and longitudinal tube spacing, as well as with reducing transverse spacing and depth of pits. For tubes with smaller transverse spacing, the erosion changes greatly with the variation of longitudinal spacing. The amount of wear caused by large particles reduces greatly with rising depth of pits.
  • Formation Characteristics of SO3 in a Pulverized Coal-fired Boiler
    XIAO Haiping, QI Cong, CHENG Qiyong, DOU Chaozong, WEI Xin, NING Xiang, RU Yu
    2018, 38(11): 908-913.
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    To study the comprehensive formation characteristics of SO3 in a boiler burning high sulfur coal, experimental tests were conducted on a one dimensional reactor, including gas phase SO3 formation process, fly ash catalytic process and V2O5 catalytic process. Results show that with the rise of reaction temperature, both the gas phase generation and the solid phase catalytic production of SO3 increase. The gas phase generation of SO3 is related to the free radicals O and OH, while Fe2O3 in fly ash and V2O5 in SCR catalysts could promote the formation of SO3 effectively. The formation of SO3 in the pulverized coal-fired furnace is mainly catalyzed by V2O5, followed by Fe2O3 in fly ash, and the gas phase generation rate of SO3 is the lowest.
  • Study on Mercury Synergistic Effect by SCR Catalyst of a 630 MW Coal-fired Ultra-low Emission Power Unit
    LI Yongsheng, XU Yueyang, XUE Jianming
    2018, 38(11): 914-918.
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    The mercury speciation and concentration in flue gas before and after selective catalytic reduction (SCR) system of a 630 MW coal-fired utility boiler were measured, while the reaction mechanism and effect of chlorine, ammonia and sulfur trioxide in flue gas on the mercury oxidation by SCR catalyst were studied. Results show that SCR has little effect on the mass concentration of total and particulate mercury. SCR catalyst promotes the oxidation of elemental mercury and has significant impacts on mercury emission characteristics. The oxidation of elemental mercury by SCR catalyst is greatly affected by the chlorine content in coal, and high chlorine-containing atmosphere obtained by burning high chlorine coal benefits the Hg0 oxidation in the SCR system. NH3 is detrimental and SO3 is promotive to the SCR catalytic oxidation of elemental mercury. Increasing the number of catalyst layers is beneficial to the SCR catalytic oxidation of elemental mercury.
  • Effect of Wettability of Mixed Alcohol Amine Absorbents on CO2 Mass Transfer Performance in Membrane Gas Absorption Process
    ZHANG Weifeng, QIU Xuefei, MA Weichun
    2018, 38(11): 919-924.
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    To investigate the influence of wettability of mixed alcohol amine absorbents on the CO2 mass transfer performance in membrane gas absorption process, the wetting properties and wetting rate of two mixed alcohol amine absorbents-MDEA (N-methyldiethanolamine)+MEA (monoethanolamine) and MDEA+TEA (triethanolamine) on the polypropylene hollow fiber membrane were determined by contact angle test and soaking test, and the mass transfer rate of CO2 under different wetting degrees was measured by absorption test. Results show that both the wetting property and wetting rate of MDEA+TEA on PP hollow fiber membrane are higher than that of MDEA+MEA at the same concentration and solute ratio. The wettability of the same mixed alcohol amine on PP hollow fiber membrane increases with rising solute ratio (w(MDEA):w(MEA)/w(TEA)). Comparative tests indicate that the decrease of CO2 mass transfer rate is caused by the wettability of mixed alcohol amine on the membrane, and the higher the wettability is, the lower the CO2 mass transfer rate would be.
  • Numerical Study on Aerodynamic Noise of an Asymmetric Airfoil with Blunt Trailing Edge
    ZHAN Zongzhou, YE Zhou, ZHANG Junwei, SONG Jianye
    2018, 38(11): 925-933.
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    To get a special airfoil for the wind turbine with high aerodynamic performance and low noise level, based on the parameterized asymmetric airfoil with blunt trailing edge, a study was conducted on the influence of trailing edge thickness and its distribution ratio on the aerodynamic performance and aerodynamic noise of the wind turbine airfoil. A noise prediction method was established using detached eddy simulation and acoustic analogy equation, and the aerodynamic noise was calculated by parametric processing of the asymmetric airfoil modified by spline function. Results show that both the lift coefficient and lift-drag ratio of the modified airfoil are greater than those of original airfoil with the increase of trailing edge thickness, while the aerodynamic performance is improved obviously. Blunt trailing edge helps to raise the aerodynamic noise of the airfoil; however, at the trailing edge thickness of 1.5% chord length and with the distribution ratio of 1:3, the increase of aerodynamic noise is relatively small.
  • Multi-objective Optimization Design of an Evaporator for Organic Rankine Cycle and the Working Fluid Selection
    HAN Zhonghe, MEI Zhongkai, LI Peng
    2018, 38(11): 934-940.
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    Taking the 130℃ geothermal water as the heat source of an organic Rankine cycle, working fluids R245fa, R123, R114, R245ca and R124 were selected as the candidate media, while a multi-objection optimization design was performed on the plate type evaporator, with focus on the length, width and spacing of plate, so as to establish a multi-objective optimization model by taking the evaporator area and evaporator pressure drop as the performance indicators, which was then solved using NSGA-Ⅱ algorithm. Results show that the total evaporator pressure drop increases and the evaporator area decreases with the rise of plate length, while the total evaporator pressure drop decreases and the evaporator area increases with the rise of plate width and plate spacing. For all the working fluids, the overall performance of evaporator is relatively good for the plate spacing of 0.002 5 m and the area of a single plate in 0.3-0.6 m2. Among all the working fluids, R245ca is found to be comprehensively optimal, followed by R245fa and R123.
  • Boiling Flow Simulation for Evaporation Section of Separated Heat Pipes in Nuclear Power Plant Containments
    SUN Haitong, YU Bin, TU Shandong
    2018, 38(11): 941-948.
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    To improve the inherent safety of nuclear power plant containments, a passive containment cooling system (PCCS) was designed by adopting separated heat pipes. The boiling flow in evaporation section of a large separated heat pipe with inner diameter of 80 mm was simulated using CFD method, while the two-phase flow was analyzed with VOF model, thus obtaining the flow pattern and finding the influence factors on the heat-transfer effectiveness in the evaporation section. Results show that the flow patterns are different in evaporator pipes with different inclined angles; the external convective heat transfer coefficient and external fluid temperature are the main factors influencing the heat transfer coefficient of evaporator pipes; the total mass flow has little effect and the inclination of evaporation section has a certain effect on the heat transfer coefficient; when the evaporation section of separated heat pipe is arranged at an angle of 50°-80°, optimal heat transfer effectiveness could be achieved.