Archive

  • 2019 Volume 39 Issue 2
    Published: 15 February 2019
      
  • Select all
    |
  • Numerical Simulation on Particle Mixing Characteristics in a Fluidized Bed Under Different Intake Modes
    LI Bin, TENG Zhaoyu, ZHANG Shangbin, WANG Youtian, BA Xingyuan, LIU Zhe
    2019, 39(2): 85-91.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To analyze the movement mechanism of particles in a fluidized bed under different intake modes from micro perspectives, numerical simulations were conducted on the motion state in the fluidized bed using computational fluid dynamics and discrete element method, while the Gidaspow drag force model was adopted to achieve the coupling of gas-solid two phases. The mixing state of the particles was qualitatively and quantitatively analyzed by the Lacey mixing index, and the influence of velocity parameters on the mixing characteristics was discussed. Results show that the particle mixing effectiveness in the spouted fluidized bed is affected by the velocity of both the spout and background gas; the final mixing state with spout gas is better than that with uniform gas intake; introducing the background gas in the presence of spout gas will make the dead zone become smaller, and the larger the background gas velocity is, the smaller the dead zone will be. In particular simulation conditions, there exists an optimal background gas velocity, when the particles are mixed most adequately in the bed.
  • Experimental Study on NOx Emission Characteristics of Shanxi Anthracite Under Air-staged Combustion Conditions
    HAN Jiachen, WANG Yongqiang, ZHOU Chaoyang, CHENG Shijun, Jin Ke, BAI Nuomin, ZHOU Yuegui
    2019, 39(2): 92-97.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    NOx emission characteristics of Shanxi anthracite were tested in a 20 kW one-dimensional self-sustaining furnace system under different air-staged combustion conditions. Results show that the self-built test system helps to realize the self-sustaining combustion of pulverized coal and is able to effectively simulate the whole process from pulverized coal flow to coal combustion and NOx formation in the furnace. Under single-staged combustion conditions, the NOx reduction efficiency increases with the deepening of air staging, and the maximum reduction efficiency may get up to 51.7%. With the deepening of air staging, the best postion of burnout air nozzles move upward. The NOx reduction efficiency in multi-air-staged combustion condition is greatly higher than the single-air-staged condition by appropriately arranging the burnout air nozzles and reasonably selecting the burnout air ratio, which may reach 60%.
  • Numerical Simulation on Optimization of Air Distribution Mode for a 200 MW Oxy-fuel Combustion Boiler
    WANG Peng, CHEN Yinbiao, LIAO Haiyan, LI Yanbing, GUO Junjun
    2019, 39(2): 98-103.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 200 MW tangentially-fired boiler as an object of study, numerical simulations were conducted on the pulverized coal combustion process respectively in pure air and oxy-fuel environment, by the computational fluid dynamics (CFD) combined with improved radiation model and chemical reaction mechanism. Based on analysis of the in-furnace combustion and heat transfer characteristics, the oxy-fuel combustion condition was optimized. Results show that high concentrations of CO tend to appear in dry flue gas recycling; the total radiative heat transfer in oxy-fuel combustion with 28.5% and 27.1% concentration of oxygen respectively under dry and wet flue gas recycling mode is nearly the same as that in pure air combustion; increasing the momentum of secondary air (SA) can effectively reduce the concentration of CO in the hopper area, and the utilization of SA deflection technology can effectively weaken the reducing atmosphere near the wall.
  • Numerical Simulation on Flow Characteristics in a Pulverized Coal MILD Gasifier
    XING Wenzhao, LEI Fulin, XIAO Yunhan
    2019, 39(2): 104-109.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the operating characteristics of a MILD coal gasifier, the effects of following parameters on the flow field, the reflux ratio, and the average residence time were numerically studied, such as the nozzle location, nozzle diameter (jet velocity) and coal particle size, etc. Results show that the flow field distribution in a MILD gasifier is mainly affected by the secondary jet location and the air jet velocity, among which the location of secondary jet shows greater influence. Keeping the primary and secondary air jet velocity constant, as the distance between the secondary jet nozzle and the central line of the furnace increases, both the reflux ratio and the particle average residence time would increase firstly and then decrease. With the rise of jet velocity, the reflux ratio increases, while the particle average residence time reduces; whereas with the reduction of mean diameter of pulverized coal, the reflux ratio changes slightly, but the particle average residence time increases significantly.
  • Diagnosis of Sliding Bearing Lubrication State Based on Information Entropy Distance of Acoustic Emission Signal
    TAN Haoyu, LU Xuxiang, ZHANG Hao, LI Kunlin, JIANG Yadi
    2019, 39(2): 110-115.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To effectively evaluate the lubricated state of a sliding bearing and prevent serious accidents caused by sliding bearing faults, a diagnosis method was proposed for the lubrication state of a sliding bearing based on information entropy and information entropy distance. The dry friction state, boundary friction state and liquid friction state of the sliding bearing were simulated on a 300 MW turbo-generator test rig, and subsequently acoustic emission signals of different friction states were obtained, which were then analyzed to identify the lubrication state using the information entropy distance method, so as to guarantee the operation performance and safety of the sliding bearing. Results show that the information entropy distance diagnosis method with wavelet space feature spectrum entropy is more accurate than that without wavelet space feature spectrum entropy.
  • Numerical Analysis of Flow and Heat Transfer Characteristics in a Pitted Tube
    YAN Shunlin, YU Xingbao, HAN Jian, CAO Baoxin, ZHANG Sha
    2019, 39(2): 116-122.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The influence of structural parameters on the fluid flow and heat transfer characteristics in a pitted tube was studied using three-dimensional numerical simulation, while criterion formulae were fitted respectively for the heat transfer and resistance characteristics by multiple linear regression method. Results show that the periodic convex hull on the inner wall of tube has a good disturbance effect on the boundary layer near the wall, which improves the synergy between fluid velocity field and temperature field, thus enhancing the heat transfer effectiveness. Compared with smooth tubes, the Nusselt number (Nu) and friction resistance coefficient of a pitted tube could be respectively increased by 16%-40% and 15%-53%, while the comprehensive performance evaluation criterion (CPEC) lies in 1.05-2.5. Compared with smooth tube heat exchangers, the relative heat transfer area of a pitted tube heat exchanger could be reduced by 10%-35%, when the heat transfer and fluid power consumption remain unchanged; the relative heat exchange capacity could be improved by 1.08-1.36 times, when the volume of heat exchanger and the fluid power consumption keep constant, in which case, the economical efficiency of the heat exchanger could be improved significantly.
  • Experimental Investigation on the Operation Performance of an Air-Liquid Ejector
    XUE Kangkang, CHONG Daotong, CHEN Weixiong
    2019, 39(2): 123-127.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The operation performance of an air-liquid ejector was experimentally studied under different conditions. Results show that under the critical mode, the entrainment ratio decreases slightly with the increase of liquid-air ratio in the primary fluid, and when the liquid-air ratio varies from 0 kg/min to 0.2 kg/min, the entrainment ratio would be reduced by 5.9%-8.7% accordingly; whereas under the sub-critical mode, the entrainment ratio reduces significantly with the rise of liquid-air ratio, resulting in lowered entrainment performance of the ejector, and when the liquid-air ratio varies from 0 kg/min to 0.2 kg/min, the entrainment ratio would be reduced by 16.9%-29.3% accordingly. At the same time, both the critical back pressure and the critical pressure ratio decrease with the rise of liquid-air ratio, resulting in poor pressure-lifting performance; when the liquid-air ratio varies from 0 kg/min to 0.2 kg/min, the critical back pressure and the critical pressure ratio would be reduced by 0.006-0.010 MPa and 0.041-0.065, respectively.
  • Effects of Periodically Fluctuated Inlet Concentration of Reactants on Operation Performance of a Reverse Flow Catalytic Reactor
    DU Tianzi, CHEN Geng, ZHU Yingying
    2019, 39(2): 128-134.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A numerical simulation was conducted on the operation performance of a reverse flow catalytic reactor with inlet concentration of reactants periodically fluctuated. Taking methane and propane as the model reactants, the effects of following factors on the operation performance of the reactor were studied, such as the fluctuation cycle of reactant concentration, the switching period of flow direction, the superficial velocity and the addition of supplimental fuel, etc. Results show that when the fluctuation cycle of reactant concentration equals to the switching period of flow direction, resonance response would occur in the reactor, indicating in the increase of maximum temperature, decrease of average temperature, and increase of bed temperature fluctuating amplitude, resulting in reduced thermal stability of the reactor. Above resonance phenomenon and temperature oscillation could be inhibited by increasing the superficial velocity or adding supplemental fuel to compensate the instantaneous fluctuation of inlet concentration of relevant reactants.
  • Experimental Research on Evaporation Characteristics of Desulfurization Wastewater by Flue Evaporation Treatment
    BAI Yanwu, LIU Pingyuan, LU Qiliang, ZHANG Juan, ZHAO Liang, CHEN Wei, YANG Linjun
    2019, 39(2): 135-141.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A series of experiments were conducted in a PDA and a hot-state coal-fired test system to study the atomization properties of different two-fluid nozzles, and to analyze the effects of following factors on the evaporation characteristics of desulfurization wastewater, such as the flue gas temperature, flue gas humidity, chloride concentration, and the wastewater temperature, etc. Results show that different nozzles have different atomizing characteristics, and the nozzles with higher precision have better atomizing effects, resulting in fewer droplets of large sizes and shorter evaporation time. Flue gas temperature has the greatest influence on the evaporation of desulfurization wastewater, and the increase of flue gas temperature would accelerate the wastewater evaporation, but the evaporation time of large droplets is still to be long. To let the desulfurization wastewater completely evaporate before entering the electrostatic precipitator, (with residence time ≤0.75 s), the flue gas temperature should be above 130 ℃. The increase of flue gas humidity has a certain inhibitory effect on the evaporation of desulfurization wastewater. The concentration of chloride and the temperature of desulfurization wastewater have little influence on the evaporation of desulfurization wastewater. After the evaporation of desulfurization wastewater, about 90%-95% chloride ions are evaporated into the form of inorganic salt particles, which will be removed by dust collector.
  • Experimental Study on the Combination Mode of Perforated Plates for Wide-angle Electrostatic-bag Precipitators
    ZHOU Hao, ZHAO Menghao, ZHAO Kai, MA Weichen
    2019, 39(2): 142-147.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the dust removal efficiency and internal flow field distribution of wide-angle electrostatic-bag precipitators, simulation tests were conducted on the combination mode of perforated plates with different porosities. Results show that the relative velocity of inlet cross section was reduced from 84% to 21%, while the relative velocity deviation of measured cross-section met relevant standard requirements; the flow field distribution in an electrostatic-bag precipitator could be adjusted by adopting the combination of different non-uniformly perforated plates, thus to elongate the service life of the bag filter, reduce the maintenance cost and improve the dust removal efficiency of the composite precipitator.
  • Numerical Simulation on the Erosion of SCR Denitration Catalysts by Flue Gas Fly Ash
    CHEN Hongwei, XU Jifa, WANG Guangtao, ZHAO Baoning
    2019, 39(2): 148-154.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Numerical simulations were conducted to study and analyze the wear law of SCR denitration catalysts in various areas at different flue gas flow rates and incident angles using CFD software, and subsequently the annual wear of the catalysts was predicted. Results show that the wear rate at the end face of catalyst is much higher than that of the wall. At different flue gas flow rates, the wear rate exhibits the same variation law along the direction of the channel, which is relatively small in the middle region and large in the vicinity of the cross section. At different incident angles, the wear rate of front surface is proportional to the incident angle within 0.04 m away from the inlet, and is inversely proportional to the incident angle beyond 0.04 m; the wear rate of back surface decreases rapidly near the inlet along the direction of the channel, which then increases gradually up to the outlet. At different incident angles, the wear rate of end face reduces with the rise of incident angle. When the denitration system operates under design conditions, the annual wear of the catalyst is negligible, but when the flue gas flow rate gets up to 11 m/s, the wall surface of the catalyst would be worn through within one year, therefore in actual operation process, the flue gas flow rate should be reduced and the incident angle should be reasonably determined.
  • Optimal Design of a Closed Brayton Cycle System Based on He-N2 Working Fluid
    CAO Ting, HUANG Weiguang, ZHANG Jingxuan
    2019, 39(2): 155-162.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on optimization and analysis of a closed Brayton cycle system with He-N2 as the working fluid, performance parameters of various components in the system were obtained under the condition when highest system efficiency is reached. On above basis, a preliminary design was carred out for the components including turbomachineries and heat exchangers. Taking the costs of turbomachineries and heat exchangers as the reference data for the cycle with pure helium working medium, relative costs of these components were calculated at different mole fractions of helium by using approximate relations between the equipment cost and their geometric parameters. According to the weight ratio of the costs of turbomachineries and heat exchangers, the relative total costs of the Brayton cycle with different molar ratios of helium were then obtained. Results show that when the mole fraction of helium gas lies in 50%-60%, there exists a minimum value of relative total cost, 12% lower than the pure helium case, which provides a better choice of working medium for closed Brayton cycle systems.
  • A Novel Creep-Fatigue Life Prediction Model for X12CrMoWVNbN10-1-1 Steel Based on Cyclic Strain Energy Density
    DAI Chen, JI Dongmei, CHEN Jiajia, WU Zhenmao, REN Jianxing, ZHU Quanjun
    2019, 39(2): 163-168.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Load-controlled creep-fatigue (CF) tests were conducted for X12CrMoWVNbN10-1-1 steel at 620 ℃ to verify the creep-fatigue life prediction model based on strain energy density, while an analysis was carried out on the creep strain, the elastic strain and the plastic strain characteristics of the steel. Results show that the process of X12CrMoWVNbN10-1-1 steel under CF load condition consists of three stages. The strain energy density at stable stage is inversely proportional to the total strain energy density dissipated by X12CrMoWVNbN10-1-1 steel, and the total strain energy density under different test conditions is proportional to the fatigue life, therefore the expression of the strain energy density at stable stage could be chosen to predict the fatigue life. The model obtained from the load-controlled CF test of X12CrMoWVNbN10-1-1 steel with short holding time may be used to predict the fatigue life of the steel with long holding time, indicating that the life prediction model based on strain energy density is also applicable to X12CrMoWVNbN10-1-1 steel.