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  • 2018 Volume 38 Issue 12
    Published: 15 December 2018
      
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  • Optimization Analysis and Energy Saving Strategy for Startup Process of a 660 MW Supercritical Boiler
    LIU Wanyu, YANG Dong, WAN Li, LIU Dan, DANG Long, ZHAO Guangxun, ZHOU Haike
    2018, 38(12): 949-956.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A computing program HDBS was developed by establishing and solving the models for furnace combustion and heat transfer process to simulate the cold startup behavior of a supercritical once-through boiler from ignition to minimum startup load, and subsequently the minimum safety flow was determined, while the energy saving and security strategy were proposed. Results show that the program could well simulate the cold startup process and is able to provide optimal starting curves for the boiler in the process from ignition to minimum startup load, which therefore may be used for actual engineering calculations. Adopting a 20%BMCR startup flow can meet the safety startup requirements of the boiler, when the startup time could be greatly shortened, compared with the current scheme of 37%BMCR startup flow, resulting in reduced fuel and water consumption in the startup period. This is meaningful to the energy saving, emission reduction and grid connection of the power plant.
  • Study of the Low NOx Combustion Technology for Biomass-fired Grate Boilers
    LUO Yonghao, ZHANG Min, DENG Ruiqu, CAO Yang
    2018, 38(12): 957-964.
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    To solve the problems of high NOx and high CO emissions existing in current biomass-fired grate boilers in China, experimental studies were conducted on the pyrolysis characteristics of large fuel particles and the NO conversion behavior during heterogeneous reactions with char by setting up models for both mass combustion and NOx formation, so as to obtain kinetic parameters of above models, and to compare the unit furance experimental data with calculation results. According to the structural features of domestic boilers, an improvement scheme was proposed by adopting the "zigzag" arch combined with air-staged combustion technology. Results show that the "chimney flow" behavior in current open furnaces is found to be the main reason leading to the high concentraions of NOx and CO in flue gas. After improvement, various gas components are well mixed in the reduction zone, and the residence time of the gas mixture is also extended, thus obtaining a clear inhibition effect on NOx concentration and a complete oxidization of CO.
  • Analysis on Factors Influencing the Low-cycle Fatigue Life of a Boiler Drum
    LI Jun, ZHANG Yang
    2018, 38(12): 965-971.
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    Based on calculation models for boiler stress and life loss, the effects of following factors on the life loss of a boiler drum were studied in the processes of cold startup and peak load regulation, such as the drum structure, material properties and heating rate, etc., while corresponding study results were vasualized. Results show that the use of a small diameter thick wall drum could significantly reduce the life loss of boiler drum during cold startup and peaking period, and the material with high thermal diffusivity and low expansion coefficient could also help to reduce the life loss during cold startup process. Although adopting low heating rate could obviously reduce the life loss of boiler drum in cold startup process, the cost of fuel would be apparently increased, so it is necessary to minimize the total cost and select an optimal heating rate for the cold startup process.
  • Study on Optimal Blending Ratio of Lignite Based on Expert Confidence
    ZHANG Yifa, ZHOU Wentai
    2018, 38(12): 972-976.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To find the optimal blending ratio of lignite for 1 000 MW bituminous coal-fired units, a series of co-firing tests were carried out, following which, a multi-dimensional assessment was conducted from the aspects of unit economy, unit security and environmental protection based on the expert confidence theory and the depth profile analysis, during the process, the multi-dimensional assessment was transferred into single-dimensional assessment. Results show that the optimal blending ratio of lignite is found to be 20%, different from traditional analysis results that high lignite blending ratio is preferred.
  • Calculation Program Development for Physical Properties of Water and Steam
    LAN Wenhong, YU Xinguo
    2018, 38(12): 977-982.
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    A calculation program was developed for the physical properties of water and steam based on IAPWS-IF97 formulations and related complementary equations, in which, the calculation domain was divided into five large regions and several sub-regions for iterative calculation, covering from 0 MPa to 100 MPa, and 273.15 K to 2 273.15 K, while a new regional discriminating algorithm was proposed based on simulated annealing algorithm (SA algorithm). The calculation steps and program structures were specially designed with much smaller sizes, making the calculation faster and more accurate. Besides, the feedback calculation algorithm was adopted in the program for the first time, which could compare numerical solution with analytical solution to guarantee the calculation accuracy. Results show that, the program developed covers wider ranges of pressure and temperature than mainstream computing programs, with significantly higher calculation speed. Under same conditions, the newly developed program helps to improve the calculation speed by 43.01% and 26.29%, reduce the resource occupancy by 20.33% and 56.43%, and decrease the occupation space by 47.02% and 13.02% respectively, compared with the calculation programs XSteam and IAPWS-IF97.
  • Effects of Stabilizer Structure on the Instability of Lean Premixed Flame
    DUAN Runze, ZHAO Ruolin, LIU Liansheng, TIAN Liang, WANG Xingyi
    2018, 38(12): 983-987.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Experimental studies were conducted on the instable phenomena of lean premixed flame in three different burners respectively with tangential swirl flame stabilizer, radial swirl flame stabilizer and porous medium flame stabilizer, with focus on an analysis of their extinction limits, flame structure and flame instability in the lean premixed combustor. Results show that the porous medium flame stabilizer has the optimal extinction limit, flame stability and flame closure, followed by the radial and tangential swirl flame stabilizers.
  • Factors Influencing the Atomization Characteristics of Hollow Cone Pressure Swirl Nozzles
    WU Zhengren, ZHEN Meng, LIU Mei, WANG Songling, LIU Qiusheng
    2018, 38(12): 988-995.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A model of pressure swirl nozzle was established using numerical simulation method, and the effects of spray pressure, spray height and tilt angle on the atomization characteristics were analyzed, such as the droplet velocity, droplet diameter and DPM concentration, etc. Results show that with the rise of spray pressure, the droplet Sauter mean diameter reduces, while the droplet flux increases. The droplet velocity at 2.0 MPa is higher than that at 1.5 MPa and 1.0 MPa. The average axial velocity of droplet increases with rising spray height. When the tilt angle of spray is increased from 0° to 40°, the average droplet velocity reduces, in which case, the DPM concentration on the right side of calculation domain basically remains stable, but that on the left side reduces significantly. The droplet flux is inversely proportional to the size of spray area, which reduces with the rise of spray height.
  • Numerical Comparison and Investigation of Condensation Heat-transfer Performance in ACC Base Tubes with Lee Model and VOF Method
    YANG Tingting, YANG Jinghua
    2018, 38(12): 996-1003.
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    To compare the condensation heat-transfer performance in flat, oval and round base tubes of air-cooled condensers (ACCs) widely used in power plants, a 1:4 scale model was set up based on actual base tubes of a 600 MW air-cooling unit to simulate the two-phase flow and condensation heat-transfer performance in the tubes with Lee model and VOF method, thus obtaining the condensation heat-transfer coefficient, Nusselt number and volume fraction of the two phase fluids. Results show that the round tube with an inclined angle of 30° has the optimal in-tube condensation performance; the condensation heat-transfer performance in ACC base tubes is considerably influenced by both the temperature of saturated steam and the axial velocity at the tube inlet, which is slightly affected by the subcooling degree of the tube wall. The two-phase flows in above three tubes are all of the falling film kind, and the thickness of condensate film over the tube wall depends on the tube type, the inlet velocity of steam and the subcooling degree of the tube wall.
  • Heat Transfer Calculation for Wet Flue Gas Condensation Process and its Engineering Application
    LIU Jiangning, LEI Chengyong
    2018, 38(12): 1004-1007.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    By analyzing the effects of dimensionless factor Ln on the surface heat transfer coefficient during condensation process based on the principle of heat and mass transfer in the boundary layer of vertical wall film condensation, a number of condensation heat-transfer tests were conducted on the process of wet flue gas passing through the heat exchangers with multi-row tube bundles, and subsequently an Nu formula was fitted for the heat-transfer process using above experimental data. On this basis, a flue gas condensing heat exchanger was developed for large power plant boilers, which was successfully applied to a 1 000 MW power unit. Results show that the actual performance parameters of the flue gas condenser developed agree well with its design values, and the formula fitted may be used in engineering designs of similar flue gas condensers.
  • NO Adsorption Properties of Ordered Mesoporous Carbons with Different Pore Diameters
    CAO Feifei, GAO Xiang, NI Mingjiang, CEN Kefa
    2018, 38(12): 1008-1015.
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    To study the NO adsorption properties of carbonaceous materials with different pore diameters, ordered mesoporous carbons (OMCs) with 8 kinds of pore diameters were synthesized through solvent evaporation-induced self-assembly (EISA) method, so as to test its NO adsorption properties using intraparticle diffusion model and TPD method. Results show that when the mass ratio of F127 to resol is 2/5, the ordered mesoporous structure would not occur, and the NO adsorption capacity would be relatively small. When the mass ratio gets up to 8/5, and the average pore size of OMC rises from 2.6 nm to 4.8 nm, the NO adsorption capacity and the NO desorption amount during TPD would be increased by 40% and 180%, respectively. Among the 3 stages of NO adsorption divided by intraparticle diffusion model, the slow adsorption stage mainly produces the difference in NO adsorption capacity. With the further increase of the mass ratio of F127 to resol, the NO adsorption capacity reduces, probably caused by the destruction of ordered mesoporous structures during removal of F127.
  • Research on Bend-Twist Coupling Properties of Twisted Composite Blades for Large Wind Turbines Based on Aeroelastic Tailoring
    LIU Yuhang, WANG Yuanbo, LI Chun, SUN Rui, HAO Wenxing
    2018, 38(12): 1016-1021.
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    To obtain excellent bend-twist coupling properties of wind turbine blades, a three-dimensional finite element shell model was established for the blade of a 5 MW wind turbine based on aeroelastic tailoring by ply stacking of composite laminates. The CFD method was used to analyze the aerodynamic load on the blade surface, and the effect of ply structure on the overall performance of related twisted blades was analyzed by the node displacement method. Results show that the symmetrical ply structure helps to achieve the bend-twist coupling of blades. Under the action of aerodynamic load, both the bend deformation and twist deformation appear, and the bend-twist coupling deformation increases along spanwise direction of blades, which is nonlinearly related to the position of cross sections. The bend-twist coupling coefficient increases firstly and then decreases with growing offset angle of blade skin, i.e. the bend-twist coupling performance varies with the offset angle, and there exists an optimal solution.
  • Research on Reliability Model for Creep-Fatigue Life Prediction of P92 Steel Based on Strain Energy Density
    JI Dongmei, GUO Hengchao, REN Jianxing, SUN Quan, DAI Chen, ZHU Quanjun
    2018, 38(12): 1022-1029.
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    Based on the self-developed model for creep-fatigue life prediction, a relationship between strain energy density and fatigue life under actual working conditions was derived at different reliabilities by taking the stress and strain energy density as random variables, and subsequently creep-fatigue tests were carried out for P92 steel at 600℃ to verify the reliability model of creep-fatigue life prediction with experimental data and to calculate the average creep-fatigue life under different experimental conditions. Results show that the creep-fatigue life of P92 steel would be 43% of the average one when the reliability is 99%.