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  • 2019 Volume 39 Issue 12
    Published: 15 December 2019
      
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  • Stress Analysis and Lifetime Calculation of a Boiler Header in Flexible Operation
    PANG Liping, YI Size, DUAN Liqiang, LI Wenxue, YANG Yongping
    2019, 39(12): 953-958.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the final superheater outlet header of a supercritical boiler in flexible operation as an object of study, an analysis was conducted on the thermal stress, mechanical stress and their combined stress using Ansys finite element software, based on operation data of the unit with the load changing from 200 MW to 600 MW and finally to 180 MW, so as to analyze the distribution of above stresses in the header. The fatigue and creep life expenditure of the header during peaking process under flexible operation were evaluated according to the linear cumulative calculation method of fatigue-creep interaction. Results show that under the action of alternating thermal stress during flexible operation, the fatigue life expenditure is smaller than the creep life expenditure, and the latter one is the main factor determining the lifetime of the header.
  • Experimental Investigation on Combustion Characteristics of Coal Particles Under Low-oxygen Dilution Conditions
    ZENG Zhukai, LI Guodong, ZHANG Tingyao, JIN Ke, CHENG Shijun, ZHOU Yuegui
    2019, 39(12): 959-965.
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    In a diffusion-flamelet-based Hencken burner test setup, the flame radiation spectrums and images of bituminous coal particles were measured by the optical fiber spectrometer and CMOS camera under different combustion atmospheres (O2/N2 and O2/CO2), hot coflow temperatures (1 473-1 873 K) and oxygen volumetric fractions (5%-20%), respectively. The combustion characteristics and temperature distribution of pulverized coal particles were obtained under different combustion conditions. Results show that under O2/N2 or O2/CO2 atmosphere, the color of flame gradually changes from bright yellow to dark red while the temperature of coal particles decreases with the reduction of hot coflow temperature and oxygen volumetric fraction. The temperature fluctuation coefficient of coal particles could be reduced by 37% with the decrease of coflow oxygen volumetric fraction, indicating more uniform distribution of coal particles. Compared with that in O2/N2 atmosphere, the flame intensity of pulverized coal is weaker in O2/CO2 atmosphere, with an increased ignition standoff distance of pulverized coal, a decreased average temperature of coal particles by 24-103 K, and a maximumly reduced temperature fluctuation coefficient by 24%.
  • Combustion and Emission Characteristics of a RQL Combustor at Different Length-Height Ratios
    JIN Ming, YUAN Yiren, ZHANG Zilai, GE Bing, ZANG Shusheng
    2019, 39(12): 966-972.
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    Experimental tests were conducted in a rich/quench/lean combustor (RQL) at three different length-height ratios to study the cold-state flow field, mixing inhomogeneity, axial temperature distribution, exhaust temperature distribution and pollutants emission of the combustor under fixed inlet air and fuel flow of swirler and varied flow of quenching air. Results show that with the decrease of length-height ratio (α), the depth of the jets gets larger and the interaction between upper and lower jets gets stronger. Optimum mixing effects could be obtained for the combustor at the α of 3.75. The minimum temperature in quenching zone reduces with the rise of α. At the α of 3.75, the exhaust temperature distributes in relatively uniform pattern, but at the α of above 3.75, the distribution of exhaust temperature worsens rapidly. The NOx emission increases with the rise of α, which first increases and then decreases with reducing flow rate of quenching air at different α. The combustion efficiency of low α combustor falls quickly under high flow rates of quenching air.
  • Performance Monitoring of Indirect Air-cooled Radiators Based on Particle Swarm Optimization BP Neural Network Model
    LI Hao, LUO Yun, LI Ruidong, SU Yongjian, CHEN Xuelin, XU Yiwei, GUO Hongyuan, LI Pengzhu
    2019, 39(12): 973-980.
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    To monitor the heat transfer performance of indirect air-cooled radiators, a method was put forward for monitoring the outlet temperature of related indirect air-cooling towers. Based on heat transfer calculation and heat balance equations, an analysis was conducted on the factors influencing the outlet temperature of the indirect air-cooling towers, and subsequently a BP neural network model was established by taking the ambient temperature, wind speed, atmospheric pressure, inlet circulating water temperature of indirect air cooling tower, inlet pressure of circulating water, outlet water pressure and the shutter opening as the input variables, and outlet water temperature as the outlet variable. To avoid obtaining partial optimal solutions only, the particle swarm optimization (PSO) based on nonlinear dynamic inertia weight was used to optimize the initial weight and threshold of the BP neural network model, and then a neural network prediction model of PSO-BP was set up, which was trained and verified using the operation data of a 660 MW unit indirect air cooling system. Results show that the BP neural network model optimized by PSO algorithm has strong generalization ability, with higher prediction accuracy than the pure BP neural network model, and the mean error predicted is 0.55%.
  • Experimental Study on SO2 Dissolution Behavior During FGD Wastewater Pre-concentration with Low-temperature Flue Gas
    MA Shuangchen, FAN Zixuan, WU Kai, ZHAO Baohua, YI Zuyao, ZHANG Jinzhu, MA Caini
    2019, 39(12): 981-988.
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    To reduce the amount of SO32-/4SO2- sludge generated in the transfer of SO2 from gaseous phase into liquid phase during flue gas concentrating process, a study was carried out on the migration and conversion of SO2 in the flue gas during the concentration of desulfurization wastewater using low-temperature flue gas in the flue duct, so as to explore a preliminary scheme to control the dissolution of SO2. Results show that the SO2 dissolution could be obviously inhibited when the Cl- concentration is higher than 120 000 mg/L, and the SO42- concentration is higher than 20 000 mg/L, which could be effectively controlled at high inlet concentration of SO2, high temperatures and low pH values, and the pH value has the most obvious effect on the solubility of SO2. At the pH value of about 1.5, the SO2 hardly transfers into the liquid phase. Only 7.4% of SO2 dissolves in the desulfurization wastewater, which has been concentrated by 3 cycles after acid adjustment. The higher the concentration ratio is, the lower the efficiency of SO2 removal would be.
  • Pilot Study on the Performance of a Denitration Catalyst over a Wide Range of Temperatures
    ZHAO Rui, YU Xuehai, SHI Xiaohong, LI Yan, SU Guoping, HAN Tao
    2019, 39(12): 989-993.
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    Performance tests were conducted on a denitration catalyst over a wide range of temperatures in a pilot platform using the flue gas from an actual coal-fired power plant to study the denitration efficiency, operating temperature range and differential pressure, to calculate the ammonia slip and SO2/SO3 conversion rate, and to analyze the effects of following factors on the SO2/SO3 conversion, such as the denitration efficiency, sulfur content in coal as received basis, unit load, operating temperature, and so on. Results show that, for the denitration catalyst, when the operating temperature is 275℃ and the denitration efficiency is 88%, the ammonia slip would be less than 2.25 mg/m3, while the SO2/SO3 conversion rate less than 1%. The unit load and operating temperature exhibit more significant influence on the SO2/SO3 conversion than other factors.
  • Study on Simultaneous Desulfurization and Denitrification Based on Separated Layout of Different Absorbents
    LIU Feng, LI Haotian, ZHANG Caiduan, ZHANG Xiaoguang, WANG Lidong, LIU Pengbin, ZENG Fang
    2019, 39(12): 994-998.
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    Based on separated layout of different absorbents, an experimental study was carried out in two bubbling reactors on the simultaneous desulfurization and denitrification with MgO and NaClO2 as the absorbents respectively for the absorption region and oxidizing region, so as to analyze the effects of following factors on the desulfurization and denitrification efficiency, such as the concentration and initial pH value of NaClO2 solution, the reaction temperature and the flue gas flow rate, etc. In addition, the reaction mechanism was deduced based on an analysis of the liquid products. Results show that the removal efficiency of both SO2 and NO could reach 100%, under optimal experimental conditions, while the removal rate of NOx could achieve 65%.
  • Influence of the Angle Between Hook Plate and Wall Surface on the Removal Efficiency of a Mist Eliminator
    CHEN Hongwei, XU Jifa, LIU Tuo, ZHANG Wei, JIA Jiandong
    2019, 39(12): 999-1004.
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    Numerical simulations were conducted on the angle between hook plate and wall surface of a mist eliminator to find a balance point between its removal efficiency and the power consumption of related induced draft (ID) fan by introducing the index KpPiRe2. Results show that the removal efficiency of a mist eliminator could be significantly improved by adding a hook plate, but its collection efficiency is still low for the droplets with diameter less than 10 μm. With the rise of the angle mentioned above, both the demisting efficiency and the pressure drop increase remarkably. Based on comprehensive analysis, the angle between the hook plate and wall surface is chosen to be 50°, when the demisting efficiency is relatively high and the power consumption of related ID fan is relatively low.
  • Study on the Microscopic Features and Mercury Adsorption Behavior of Bio-char Under Fast Pyrolysis Conditions
    HUO Ruipeng, JIA Li, ZHAO Rui, QIAO Xiaolei, ZHENG Xianrong, FAN Baoguo
    2019, 39(12): 1005-1012.
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    The bio-char prepared in a drop-tube furnace was studied under fast pyrolysis conditions, while its pyrolysis properties and microscopic features were analyzed by nitrogen adsorption-desorption instrument and Fourier transform infrared spectrometer. Combined with the adsorption kinetic process, the adsorption characteristics and mechanism of elemental mercury by bio-char were further explored. Results show that the adsorption property of mercury by bio-char depends on not only the pore structures but also the surface chemical properties. Because of the particle agglomeration caused by van der Waals force and liquid bridge force during the sedimentation process, the mercury adsorption capacity of bio-char increases with the rise of pyrolysis temperature, while the BET surface area increases and the content of surface functional groups decreases. The chemical adsorption of bio-char prepared at lower pyrolysis temperatures plays a dominant role in the adsorption process, and with the rise of pyrolysis temperatures, the chemical adsorption weakens, while the physical adsorption improves.
  • NOx Emission and N Conversion Characteristics of Algae Biomass Combustion Under Non-equal Ratio Mixing Conditions
    SUN Jin, ZHAO Bingtao, SU Yaxin
    2019, 39(12): 1013-1018.
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    To investigate the NOx emission and N conversion characteristics in the combustion of algae biomass mixtures, following three kinds of algae biomass were mixed in different ratios and burned in a one-dimensional tube furnace, such as the enteromorpha, sargassum muticum and chlorella, etc. Results show that unlike the NOx emission characteristics in the combustion of a single algal biomass, the NOx emission from combustion of algae biomass mixtures exhibits a unimodal distribution at 600-800℃, and the peak value increases with the rise of combustion temperature. Both the conversion rate of NO to NOx and the unit emission of NOx reduce under mixing conditions due to the coupling effect among the three kinds of algal biomass. At 600-800℃, when above three kinds of algae biomass are mixed in the ratio of 50%:25%:25%, 25%:50%:25% and 25%:25%:50%, the NOx emission would be reduced by 22.1%-53.7%, 22.6%-45.8%, and 21.1%-48.6%, respectively, and the NOx reduction rate decreases with the rise of combustion temperature.
  • Study on a Modified Flue Gas Waste Heat Utilization System for Coal-fired Power Units
    LI Qinlun, WANG Lukai, LIU Yinhe
    2019, 39(12): 1019-1026.
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    To improve the energy efficiency of a 600 MW supercritical unit, a thermodynamic analysis was conducted on two kinds of flue gas waste heat utlization system, i.e. the bypass flue system and the heat integration system based on boiler-turbine coupling, which could improve the power supply efficiency of the unit by 0.77% and 0.85%, respectively, but there were still shortcomings in energy level matching between hot and cold working fluids in the boiler cold end heat exchangers. On this basis, a new flue gas waste heat utilization system with integrated steam-air heater (SAH) was proposed by combining the temperature matching with the heat capacity flow rate matching to optimize the cascade utilization of heat energy in the low-temperature flue gas. Results show that the power supply efficiency of the integrated SAH system could be increased by 1.10%, compared with the case unit, which is higher than the efficiency gain brought by the bypass flue system and the heat integration system based on boiler-turbine coupling. The dynamic investment payback period and net present value of the new thermal system are 2.44 years and 107.575 5 million RMB, respectively, indicating good feasibility of the system in engineering applications.
  • Experimental Study and Simulation Analysis of a Closed Brayton Cycle Under Variable Working Conditions
    ZHU Yubo, HUANG Weiguang, CUI Xiaokang, ZHANG Jingxuan
    2019, 39(12): 1027-1034.
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    Based on the test platform for MW class multi-functional closed Brayton cycles, an experimental study was carried out on the dynamic response of the system by inventory control method and bypass control method, covering the changes of system parameters, such as the pressure, temperature, flow rate and speed etc. According to Aspen HYSYS, a simulation model was established for the test platform, based on which, simulation analyses were conducted using inventory control method and bypass control method. Results show that both the inventory control method and bypass control method could effectively adjust the working conditions of the equipment in the system, making them achieve new matching points, and then further changing the working characteristics of the whole system. In the case of inventory control method, the system response is slow, due to the limitation of the charging conditions, but the operating point of the compressor remains basically unchanged. In the case of bypass control method, the system response is fast, but the operating point of the compressor changes. The simulation results agree well with the test results, proving the simulation model to be reliable, which may serve as a reference for the establishment of control strategies for similar closed Brayton cycles of power generation systems.