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  • 2017 Volume 37 Issue 1
    Published: 15 January 2017
      
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  • Combustion Adjustment of a W-flame Boiler with Slot Burners
    WANG Ke, ZHOU Wentai, HE Xiang, SHI Hongfei
    2017, 37(1): 1-6.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problems of high carbon content in fly ash, serious overheating of platen superheaters, severe slagging on side walls, high exhaust temperatures, bias combustion on front and rear furnace walls occurring at high load condition of a W-flame boiler with slot burners, combustion optimization was performed for the boiler by adjusting the air distribution and outlet oxygen concentration, and subsequently an optimized operation mode was proposed. Results show that above problems can be effectively solved with fly ash carbon content reduced by 7.5%, exhaust temperature reduced by 8 K, boiler efficiency meeting the design requirement and with combustion economy improved remarkably, in the optimized operation mode, such as controlling the damper openings of middle secondary air, side secondary air, tertiary air and external secondary air to be at 85%, 90%, 40% and 50%, respectively, while the internal secondary air damper is kept unchanged, furnace outlet oxygen volumetric fraction kept within 3%-3.5%, and the exhaust vent reduced to 30%.
  • Application of Anti-slagging Composite Ceramic Coating in a Zhundong Coal-fired Boiler
    WANG Jinqing, YUAN Yichao, CHI Zuohe, ZHAO Kai, ZHANG Guangxue
    2017, 37(1): 7-12.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the fouling and slagging problems existing in a 670 t/h boiler burning Zhundong coal, a composite ceramic coating was sprayed onto the heating surfaces of water wall and platen superheater. Using thermal calculation method, and combined with test data of the composite ceramic coating, the optimal spraying areas were determined based on calculated heat-transfer rates for relevant water wall and superheater. Results show that one year later after the application of composite ceramic coating, the fouling and slagging situations are significantly improved in the boiler, with run time of soot blower and water consumption of desuperheater reduced by 58.2% and 75.2%, respectively; a new problem of low superheated-steam temperature appears, due to the imbalance of endothermal rate between the water wall and platen superheater, which is finally solved by adopting the optimal spraying areas, with simultaneous appropriate water consumption of the desuperheater.
  • Acoustic Propagation and TDOA Measurement in Tube Arrays of Utility Boiler
    AN Liansuo, FENG Qiang, SHEN Guoqing, JIANG Genshan, ZHANG Shiping, WANG Peng, ZHANG Haiyu
    2017, 37(1): 13-20.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A study was conducted on acoustic propagation and TDOA measurement in tube arrays of utility boiler, where the propagation characteristics were numerically compared using Fluent software under the conditions of uniform/non-uniform temperature field, and different rows of tubes in different arrangements, while the TDOA in tube arrays was measured on a self-developed test bench by Fast EEMD algorithm. Results show that acoustic band gaps exist in the tube array, which move to low frequency area in non-uniform temperature field. With the rise of tube rows, the effect of acoustic band gap becomes more obvious. Tube pitch has a certain influence on the band rejection in both sequence and stagger arrangement of tubes. Based on Fast EEMD algorithm, effective TDOA can be obtained when low frequency signals are chosen.
  • Research on Flow Field Dynamic Characteristics in a Labyrinth Seal
    MA Haoyuan, ZHANG Wanfu
    2017, 37(1): 21-25.
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    A full three-dimensional model was set up for a labyrinth seal, in which the flow field was calculated and analyzed under different working conditions using commercial CFD software Fluent, so as to study the relations of the fluid-induced force with the rotational speed, pressure ratio and the eccentricity, etc., and to obtain the dynamic coefficient and whirl coefficient of the seal that may influence the stability of the rotor. Results show that with the rise of rotational speed, pressure ratio and eccentricity, the whirl coefficient increases accordingly, and the stability of the rotor is hence reduced.
  • Effect of Partial-height Tandem Diffuser on Performance of the Centrifugal Compressor
    HUANG Yueqing, YANG Ailing, SONG Wenjie, CHEN Eryun, DAI Ren
    2017, 37(1): 26-32.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To ensure the pressure ratio of a centrifugal compressor and simultaneously broaden its stable working range, the concept of partial-height blade was introduced to the design of tandem diffuser, and subsequently the effects of relative circumference position (RCP) and relative height of forward blade (RHFB) on the performance of the centrifugal compressor and tandem diffuser were researched by numerical simulation. Based on the tandem diffuser with 30% RCP, different partial-height tandem diffusers were designed with partial-height blades used on the front row. Results show that RCP significantly affects the diffusion ability and stable working range of the diffuser, and the best performance appears as RCP ranges from 20% to 30%. Compared to the whole blade height, the surge margin of centrifugal compressor with RHFB lying in 40%-50% may be increased by 21%-25%, when the total pressure ratio and isentropic efficiency would be reduced only by 1%.
  • Pressure Drop in Plate Heat Exchanger During Condensation of Ethanol-Water Mixed Vapor
    QIAO Hongbin, WANG Shun, HU Shenhua
    2017, 37(1): 33-38.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Experimental tests were carried out in a plate heat exchanger to study the effects of outlet vapor quality on the changes of hot side pressure drop during condensation of ethanol water mixed vapor at different ethanol mass fractions (0%, 1%, 10% and 50%), different vapor pressures (70 kPa, 80 kPa and 90 kPa), and different vapor flow rates (15 m/s and 25 m/s). Based on the experimental data, the Lockhart-Martinelli model was used to calculate and correct the pressure drop. Results show that the pressure drop increases with the rise of ethanol mass fraction, which would be doubled for the mixed vapor with ethanol mass fraction of 50% as compared to pure water vapor, under same experimental conditions. Under conditions with the same ethanol concentration, vapor flow rate and outlet vapor quality, the vapor pressure has obvious effects on the pressure drop; the higher the vapor pressure is, the smaller the pressure drop will be. The error between experimental data and fitted results is within 20%.
  • Effect of Nitric Oxide in Flue Gas on Elemental Lead Adsorption over Carbonaceous Surface
    YU Yuexi, FENG Yongxin, LIAO Yongjin, YANG Weijie, GAO Zhengyang
    2017, 37(1): 39-44.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The effect of nitric oxide in flue gas on lead adsorption over carbonaceous surface was investigated by the methods of B3PW91 and B2PLYP in density functional theory of quantum chemistry. The benzene cluster with five zigzag rings was selected as the carbonaceous surface model, based on which structural optimization was carried out at different active sites, so as to obtain two configurations of NO adsoprtion on carbonaceous surface and four configurations of elematal lead adsoprtion on carbonaceous surface containing NO molecules. Meanwhile, main parameters, such as bond length, bond order, charge and adsorption energy were calculated and analyzed. Results indicate that NO molecule is more likely to be adsorpted by carbonaceous surface than elemental lead, and it competes with elemental lead for active sites on the carbonaceous surface. NO molecule could significantly enhance the adsorption of elemental lead on carbonaceous surface, and the enhancement of adsorption capacity is mainly due to further activation of ortho active sites, but not direct adsorption of elemental lead by NO molecule. Bond order exhibits a positive correlation with adsorption energy; the higher the bond order, the greater the adsorption energy of corresponding configuration. An apparent linear correlation exists between the electric charge on Pb atom and the adsorption energy; the more electric charge on Pb atom, the greater the adsoprtion energy of corresponding configuration.
  • Residual Life Evaluation of Gear Root Crack Growth in Driving Train of a Wind Turbine
    XIAO Junfeng, LI Jianlan
    2017, 37(1): 45-51.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A calculation model for the residual life of gear root crack growth in driving train of a wind turbine was established at random wind speed on the basis of the impeller aerodynamic load model, the flexible driving train model and the gear root bending stress model, based on which the crack growth rate under random loads could be analyzed by calculating the gear root bending stress at different wind speeds. An analysis was conducted on the gear root crack growth of the sun gear in a 1.5 MW wind turbine. Results show that the residual life of gear root crack growth in a wind turbine is mainly affected by the wind load. Besides, the impact caused by emergency braking during later period of the crack growth can not be ignored.
  • Study on Aerodynamic Characteristics of Low-speed Wind Turbine Airfoil in Consideration of Laminar Separation
    TANG Xinzi, HUANG Xuanqing, SUN Songfeng, PENG Ruitao
    2017, 37(1): 52-59.
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    The aerodynamic characteristics of DU93-W-210 wind turbine airfoil were studied at low Reynolds numbers (2×105-5×105) through numerical simulation and experimental tests, so as to analyze the effect of laminar separation bubble on the airfoil aerodynamic characteristics using corrected transition model at different Reynolds numbers and different angles of attack. Results show that the corrected Transition SST turbulence model predicts the lift and drag coefficients as well as the transition location well compared to experimental results at low Reynolds numbers; the lower the Reynolds number is, the more obvious the laminar separation bubble and the smaller the lift-drag ratio will be; the effect of Reynolds number on the lift-drag ratio of airfoil is evident but less obvious when stall exists, and the stall is softer at lower Reynolds numbers; at larger angles of attack, the laminar separation bubble on the upper surface of airfoil is closer to the leading edge, while that on the lower surface is closer to the trailing edge; the transition position on the lower and upper surface both moves in a linear manner before stall, and the transition position on the upper surface moves in a non-linear manner after stall.
  • Numerical Analysis on Wake Effect of Wind Turbines at Varying Wind Directions
    HU Danmei, HUO Nengmeng, YANG Guankui, ZHANG Jianping
    2017, 37(1): 60-65.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To study the wake effect of wind turbines at varying wind directions, the NREL 5 MW wind turbine model was esteblished and then a single wind turbine and two wind turbines were respectively simulated at varying wind directions under rated wind condition using Fluent software, so as to compare their power output and wake flow. Results show that when the wind direction is at 0°, namely tandem arrangement, the upstream wind turbine would have a big effect on the downstream one; when the angle of wind direction varies from 5° to 10°, the influence of upstream wind turbine on downstream wind turbine would be reduced, and the power loss of downstream wind turbine would be lowered from 7.53% to 4.24%, with obvious increase of power output simultaneously, indicating that the wake flow of a wind turbine may be affected by the change of wind directions.
  • Waste Heat Recovery from Boiler Flue Gas with Two-stage Cyclic Evaporation ORC System
    WANG Zhijun, XIONG Yuanquan
    2017, 37(1): 66-72.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    For the fact that the temperature of coal-fired boiler flue gas is low and the flue gas contains water vapor and acid vapor that may produce acid corrosion at low temperatures, a two-stage cyclic evaporation ORC system was proposed, which is more suitable for the waste heat recovery from coal-fired boiler flue gas. Taking R123 as the working medium, by referring to the flue gas parameters of a domestic coal-fired boiler, a thermodynamic model and an economic model of the two-stage cyclic evaporation ORC system were set up to calculate and analyze the performance of the boiler, which was then compared with traditional one-stage evaporation ORC system. Results show that, in terms of thermal performance, both the net work and net recovery efficiency of the two-stage cyclic evaporation ORC system are greater than the one-stage evaporation ORC system, which accordingly has larger heat-transfer area. Whereas, in terms of economic performance, the cost of the two-stage cyclic evaporation ORC system is higher in power generation, but its annual income is also higher within designed lifetime, indicating higher performance-to-price ratio of the two-stage cyclic evaporation ORC system.
  • Exhaust State Analysis and Experiment for an Indirect Air-cooling System with Compound Refrigeration Cycle During High-temperature Period
    ZHAO Bo, YANG Shanrang, CAO Shengxian, WANG Gong
    2017, 37(1): 73-78.
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    Based on the structure pattern and heat-transfer process of an indirect air-cooling system with compound refrigeration cycle (CRC-IAC), a calculation model was established for the heat-transfer process, and an orthogonal experiment was subsequently carried out on a dynamic simulation of refrigeration cycle coupled with exhaust steam. Results show that the exhaust temperture tends to be stable after the refrigeration cycle runs about 500 s, which increases with the rise of exhaust heat load and ambient air temperature, and with the reduction of face velocity. The experimental data are consistent with the simulation results of a 600 MW unit.
  • Changes of Reverted Austenite Content in Aging and Deformation Process of Steel 05Cr17Ni4Cu4Nb
    LI Xingdong, WANG Liyan, LI Yufeng
    2017, 37(1): 79-84.
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    By using rapid phase transition instrument, X-ray stress analyzer and MTS material testing machine, etc., aging tests were conducted on steel 05Cr17Ni4Cu4Nb at different temperatures, so as to measure the reverted austenite content, and to analyze the changes of reverted austenite content in the steel after being aged at 605℃ for different holding time, and under tensile deformation conditions. Results show that when the aging temperature is lower than the Ac1 of material, the content of reverted austenite would increase with the rise of aging temperature; whereas when the aging temperature is higher than the Ac1, the content of reverted austenite would reduce instead, due to the occurrence of martensite transformation in the cooling process. For the steel being aged at 605℃, the content of reverted austenite first increases and then decreases with the rise of holding time, and in the increasing process, the precipitation behavior of reverted austenite complies with JMA kinetic equation. Phase transformation of reverted austenite happens in the deformation process, and the logarithm value of the ratio of reverted austenite content before and after deformation is in good linear relationship to the true strain.