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  • 2018 Volume 38 Issue 7
    Published: 15 July 2018
      
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  • Conceptual Design and Thermal Analysis of a Horizontal HRSG Under Supercritical Steam Conditions
    ZHAO Zidong, YAN Weiping
    2018, 38(7): 513-518.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A double flue duct horizontal structure was proposed for the supercritical heat recovery steam generator (HRSG), of which the height was determined by comprehensively considering the heat-transfer coefficient, the flue gas resistance and the steel consumption of relevant high-pressure once-through evaporation bundles, and subsequently a thermal calculation was conducted by taking a 397 MW gas turbine as the top cycle in the combined cycle unit. Results show that the optimum flue duct width of HRSG is 11.5 m, and the height of upper and lower flue duct would better be 23 m and 21 m, respectively. When the exhaust temperature of gas turbine is same as that of the HRSG, the output of the gas-steam combined cycle under supercritical steam conditions would be 2.46% higher than that under subcritical steam conditions, with an increase in combined cycle net efficiency by 1.16 percentage points.
  • Cause Analysis and Countermeasures for Non-uniform Distribution of Gas-Solid Flows in a 330 MW CFB Boiler
    TIAN Jingyuan, ZHANG Yi, ZHANG Sihai, YANG Hairui
    2018, 38(7): 519-523.
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    To solve the problem of non-uniform distribution of gas-solid flows in a 330 MW circulating fluidized bed (CFB) boiler, an analysis was conducted on the formation mechanism and influencing factors, with focus on the relatively low primary air temperature and the large deviation of primary air temperature between both beds, after which corresponding countermeasures for 300 MW CFB boiler were put forward, such as reducing the load, increasing the primary air rate and controlling the primary air temperature deviation, etc. Results show that the problem of non-uniform gas-solid flows can be solved by taking above countermeasures.
  • Numerical Study on the Tip Leakage Reduced by Spontaneous Tip Injection Coupled with Tip Squealer
    HU Jianjun, ZHANG Xianglan, ZHANG Duo, KONG Xiangdong
    2018, 38(7): 524-530.
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    To investigate the influence of a coupled structure with passive control on the turbine cascade flow, and to further reduce the tip clearance leakage, a numerical model was set up for the blade with spontaneous tip injection coupled with tip squealer, while the jet parameters were optimized using orthogonal experiment method, after which the combination A1B1C1 was proved to be the optimum one, i.e., the clearance height, the outlet flow angle and the deviation angle were respectively 0.5 mm, 30° and 0°. On above basis, the leakage flow field with spontaneous tip injection coupled with tip squealer was analyzed in detail from the aspects of internal streamline, velocity contour and average total pressure loss coefficient. Results show that, under smaller ratios of w/h (squealer width to blade height), there exists an optimal size of squealer, i.e. w=5%h and d=1%h, when higher clearance loss and lower leakage rate would be resulted for the blade with spontaneous tip injection coupled with tip squealer, compared with the structure of only spontaneous tip injection, indicating better inhibiting effect of the coupled structure. However, with the increase of w/h, the inhibiting effect gets weakened, sometimes even becomes worse than pure spontaneous tip injection, which can be observed clearly with the decrease of d/h (squealer depth to blade height).
  • Influence of Compound Angle on Effusion Cooling Effectiveness Through Inclined Holes in Curved Wall
    ZHANG Naru, ZHANG Bo, XUE Shuangsong, JI Honghu, ZHANG Junfeng, CHENG Ming
    2018, 38(7): 531-538.
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    Numerical simulation and experimental research were conducted to investigate the distribution of flow field and film cooling effectiveness at a blowing ratio of 3.5 in the combustion chamber under the condition of curved wall, in which the compound angle of multi-inclined holes is 0°, 30° and 65°. Results show that compared with the model of 0°, the introduction of compound angle enhances the spanwise diffusion of cooling air flow, and the film has better overlapping effect between two adjacent rows of holes, resulting in increased cooling efficiency, weakened diffusion in height direction, declined involvement with high-temperature gas, and increased length of film coverage. When the compound angel is increased from 30° to 65°, the cooling efficiency improves slightly, while the discharge coefficient shows a tendency to increase first and then decrease with the rise of compound angle.
  • Effects of Local Preload on the Performance of Tilting Pad Bearings
    ZHU Jianhong, XU Yongli
    2018, 38(7): 539-544.
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    To study the effects of local preload on the performance of tilting pad bearings, a model was established for the bearing based on thermo-elasto-hydrodynamic lubrication theory, which was applied to the analysis of a five-pad tilting-pad bearing for a high-speed gas turbine. Results show that the stiffness and damping of a tilting pad bearing increase with the rise of local preload, which are affected by the location of pad pivots in different directions. For the pads in the direction with changing local preload, their maximum babbit temperature and pad pressure increase with rising local preload, while the minimum thickness of oil film decreases, and the influence on these pads would be greater than those in other directions. If local preload rises, the static equilibrium position would move away from the pad, which will move towards the pad if the local preload decreases. The lubrication oil flow reduces with rising local preload, resulting in increased power loss of the bearing.
  • Influence of Rebound Characteristics on the Separation Efficiency of an Inertia Particle Separator
    NIU Jiajia, WANG Suofang, DONG Weilin, XIE Maixiang
    2018, 38(7): 545-551.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To explore the influence of particle rebound characteristics on the separation efficiency of an engine inertia particle separator, the effects of tangential/normal restitution coefficients on the separation performance were studied using Fluent software at different scavenging ratios and inlet Mach numbers, while their comprehensive influences on the separation efficiency were analyzed. Results show that under the normal restitution coefficient of 0.5, the separation efficiency of both AC coarse dust and C-spec sand increases first and then gets stable with the rise of tangential restitution coefficient at different scavenging ratios and inlet Mach numbers. The normal restitution coefficient changes with Mach number, but is not influenced by Scavenge ratio. The critical tangential/normal restitution coefficients are affected significantly by inlet Mach number and particle diameter when the separation efficiency tends to be stable.
  • Optimization and Application of a Multiplier Coordinated Predictive Function Control Method for (Ultra) Supercritical Thermal Power Units
    HU Jiangen, SUN Yun, LI Quan, YIN Feng
    2018, 38(7): 552-557.
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    To improve the coordinated control performance of (ultra) supercritical thermal power units, a multiplier predictive function control method was proposed, while an optimal control law was designed for the multiplier predictive function with disturbance signals, and subsequently the predictive function control system and the optimized coordinated control method were applied for the control of related main and superheated steam temperatures. Taking the turbine valve instruction and coal feeding instruction as disturbance signals of the steam pressure control system, the water supply optimization instructions were obtained through calculation and then applied in the whole system after feedforward signals were superimposed; with the water supply instruction used as disturbance signal of the superheated steam temperature control system, the coal feeding orders were optimized and acted on the whole system after feedforward signals were superimposed. Results show that for the three-in-three-out supercritical unit, the method proposed can effectively solve the coupling problem in the system, and its control performance has been proved to be excellent by actual engineering applications.
  • Coordinated Predictive Control of Boiler Reheated Steam Temperature Using Tilter and Attemperator
    WANG Dongfeng, LI Ling, WANG Yuhua
    2018, 38(7): 558-563.
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    To overcome the limitation existing in current reheated steam temperature control systems, a predictive control method was proposed by coordinatedly adjusting the tilter angle and attemperator spray, based on improved control methods for boiler reheated steam temperature from aspects of control algorithm and switching logic, and subsequently the control effectiveness was compared with that of conventional predictive control and cascade PID control. Simulation results show that the method proposed can help to realize smooth swithing between tilter angle adjustment and attemperator spray regulation without any disturbance, thus improving the control performance and operation stability of the system, and lowering the switching frequency between above two ways.
  • Individual Pitch Control of a Wind Turbine Based on Fuzzy Logic ADRC
    REN Lina, LIU Su, LIU Fucai, ZHANG Lei
    2018, 38(7): 564-571.
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    Taking the variable speed variable pitch wind turbine as an object of study, which works under the condition above rated wind speeds, a fuzzy logic individual pitch control scheme was proposed based on auto disturbance rejection controller (ADRC) to reduce the influence of disturbance. For each of the state variables in the system, an auto disturbance rejection controller was designed, of which the parameters were adjusted by fuzzy logic control. The control strategy proposed was then compared with that of the PD and ADRC on the Matlab. Results show that the newly proposed control strategy can be used to observe and deal with the nonlinearity, wind speed and other unknown quantities to restrain the blade offset and achieve the goal of constant power output.
  • Effects of Contact Angles of Nanoparticles on the Boiling Heat Transfer Coefficients
    LIU Cangdan, WANG Dongmin, QUAN Xiaojun, ZHENG Ping
    2018, 38(7): 572-577.
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    To study the effects of contact angles of various nanoparticles on the boiling heat transfer coefficients, a boiling experiment was conducted using SiO2 nanofluids with different contact angles. By observing the sizes of the bubbles formed during boiling process and the morphology of the layers deposited on heated surface after boiling experiment, the effects of nanoparticles and their contact angles on the sizes of boiling bubbles and the morphology of deposited layers were studied, thus to further reveal the influence mechanism of the wettability of nanoparticles on the boiling heat transfer coefficients. Results show that the contact angles of nanoparticles would affect the stability of the bubbles formed in boiling process and the morphology of the layers deposited on heated surface, and different surface morphologies present different heat transfer effectiveness. Medium hydrophilic nanoparticles can be adsorbed on the gas-liquid interface of bubbles, producing enhanced heat transfer coefficients; whereas the medium hydrophilic nanoparticles deposited on the heated surface may increase the surface roughness, when more nucleation sites would be produced, resulting in improved heat transfer coefficients.
  • Study on CO2 Capture and Tar Removal Characteristics of a Newly Developed Ca-based Sorbent
    ZHANG Yuan, HAN Long, LIN Kang, ZHANG Hao, ZHONG Yingjie
    2018, 38(7): 578-586.
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    A CaO-based sorbent (Ca-Al-Fe) was newly developed using sol-gel method, of which the performance in tar removal and CO2 capture was examined. Results show that the Ca-Al-Fe sorbent, with main components of CaO, Ca12Al14O33 and Fe2O3, can capture the CO2 and reduce the evolution of tar species in the pyrolysis of wheat straw. The performance of Ca-Al-Fe sorbent has been significantly improved in cyclic CO2 capture, compared to ordinary CaO. After 20 cycles of "carbonation-calcination" reaction, the CO2 capture capacity and CaO conversion rate of Ca-Al-Fe sorbent are slightly reduced, from 0.42 mg/mg and 84% to 0.34 mg/mg and 67%, accordingly, while its mechanical strength is remarkably improved. Compared with those sorbents mentioned in relevant literatures, the newly developed Ca-Al-Fe sorbent has better performance in cyclic carbonation.
  • Analysis on Dynamic Seismic Response of a Wind Turbine Tower in Time-Frequency Domain Considering SSI Effects
    LIU Zhongsheng, YANG Yang, LI Chun, ZOU Jinhua
    2018, 38(7): 587-593.
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    To analyze the dynamic response of a wind turbine tower under combined wind-earthquake actions, a soil-structure interaction model was established based on Wolf method, following which a seismic load module was developed by using open source software Fast, so as to study the vibration characteristics and response amplitude of the tower in different soils. Results show that the seismic load greatly intensifies the vibration of the tower, with obviously increased amplitude of vibration at the first-and second-order natural frequency. At the fortification intensity of 8, the vibration of tower top is mainly excited by seismic load, slightly influenced by aerodynamic load. Due to different characteristics of damping and seismic response spectrum, the response amplitude and vibration characteristics are quite different for the tower in different soils. Under rated wind conditions, the lateral displacement of tower top has an increase of 316%, 242%, and 265% respectively for the tower in still clay soil, rock still soil and soft soil, compared with the condition without earthquake.
  • Numerical Calculation of Wind Loads over a Dish Solar Concentrator
    WANG Linjun, LUO Bin, ZHANG Dong, ZHANG Yuezhi, LI Yaning
    2018, 38(7): 594-600.
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    To study the variation law of wind load coefficient of a 25 kW dish solar concentrator under different working conditions, and to determine its best and worst working condition, a watershed model was built up for the concentrator using Realizable k-ε turbulence model with Fluent 14.0 software, so as to simulate the flow field around the concentrator. Results show that the resistance coefficient is proportional to the effective windward area of the dish solar concentrator, and its maximum absolute value is 1.42. At the altitude angle of 60° and the azimuth angle of 0°, the absolute value of lift coefficient reaches its maximum of 1.60. At different altitude angles (except for 90°), the lateral force coefficient, the rolling moment coefficient and the azimuth moment coefficient are approximately in sinusoidal changes with the azimuth angle, with their absolute values being 1.34, 0.18 and 0.26 respectively. The optimal avoiding condition of the dish solar concentrator lies in 90°-180°, and the worst case is 0°-0°.