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  • 2018 Volume 38 Issue 9
    Published: 15 September 2018
      
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  • Effects of Different Additives on Slagging and Fouling Characteristics of Zhundong Coal
    HE Xiang, SHI Hongfei, ZHOU Wentai, MA Dafu, JIN Jing
    2018, 38(9): 689-694.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Slagging and fouling characteristics of Zhundong coal with 3 different additives were studied in a 0.4 MW test rig. Results show that there exists only slagging phenomenon in the furnace and on the front screen of serpentine tube, mainly in the form of low-melting-point compound salts containing Fe and Ca, etc., while Na doesn't dominate the slagging process. The melting point of Zhundong coal ash is about 1 100℃ under test conditions. Fouling phenomenon occurs on the heating surface, mainly in the pattern of condensation deposition of Na2SO4 and CaSO4 at the flue gas temperature of 800℃. When Zhundong coal slag is used as an additive, the inhibiting effect on slagging and fouling is not obvious; whereas when kaolin clay is used as an additive, the slagging layer would be thicker, but looser, and therfore is easy to remove, showing an obvious effect in reducing slagging severity; when the General Temple coal is taken as an additive, it can obviously weaken the fouling severity.
  • Effects of Combined Type Primary Air Pipe on Operation Performance of the Boiler
    YAN Shunlin, HAN Wei, WANG Haoxuan, ZHANG Yongsheng, LIU Yang
    2018, 38(9): 695-705.
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    To solve the problem of unstable combustion in low load operation of a boiler due to low concentration of pulverized coal, a retrofit scheme was put forward by adopting the design of combined type primary air pipe. Based on the comprehensive model of pulverized coal combustion and the model of pollutant emission, numerical simulations were conducted on the combustion status and NOx emission of a 660 MW boiler respectively under 40% THA and 30% THA condition before and after retrofit using Fluent software, so as to comparatively analyze the effects of combined type primary air pipe on the aerodynamic field, ignition condition and NOx emission of the boiler. Results show that when the combined primary air pipe is adopted, the aerodynamic field would be slightly influenced, as long as the nozzle of the burner is properly transformed; the overall temperature in the furnace, especially in the burner area, would be improved, resulting in increased combustion stability of the boiler; the NOx emission at furnace outlet would be reduced greatly in low load operation, in which case safety and economical operation would be obtained for the boiler.
  • Soft Sensor Modelling of Steam Turbine Heat Rate Based on CPSO-LSSVM
    WANG Lili, CHEN Guobin, LI Yilong, LIU Chao, NIU Peifeng
    2018, 38(9): 706-712.
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    To accurately predict the heat rate of steam turbines, a soft-sensing model was proposed based on least square support vector machine (LSSVM) modified by chaos particle swarm optimization (CPSO). The specific way is to use the variable space chaos searching strategy and the particle cross mirror image processing strategy to improve the global search ability of particle swarm optimization (PSO). Then a CPSO algorithm was developed to find the optimal parameters of LSSVM to improve the regression accuracy and generalization ability of the model. Finally, a CPSO-LSSVM model of heat rate was established for a 600 MW steam turbine based on its operation data. Simulation results show that the CPSO-LSSVM model has a higher accuracy in prediction and stronger capability in parameter optimization and generation, which may help to accurately and effectively predict the heat rate of steam turbines.
  • Variation of Structural Strength and Clearance in HP Cylinder Balance Piston Area of an Ultra-supercritical Steam Turbine Unit in Start/Stop and Operation Process
    SU Hu, WU Shifang, CHEN Yongzhao, WANG Weizhe
    2018, 38(9): 713-718.
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    Based on history data of a power unit, the temperature field, stress field and displacement field in its HP cylinder balance piston area were analyzed in the process of start, stop and steady state operation, considering the elastic-plastic mechanics and creep behavior using ABAQUS finite element method, with focus on the varation tendency of the temperature, stress and radial clearance by taking two key points as the objects of study. Results show that the stress and radial clearance change greatly in start period, but vary slightly in steady state operation and stop period. Moreover, the minimum clearance appears in the central area of balance piston during start period, where no rubbing phenomenon would be observed, which therefore can be used as a preset margin for the balance piston area, and may serve as a reference for relevant designs.
  • Effect of Longitudinal Vortex Generator on Impingement Cooling over Leading Edge of a Gas Turbine Blade
    LIU Liangliang, ZHU Xiaocheng, LIU Hao, DU Zhaohui
    2018, 38(9): 719-724.
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    The flow and heat transfer on leading edge of a gas turbine blade were investigated by using 3-D numerical method. A pair of delta-winglet vortex generators (VGP) was installed in the jet cavity to study the effects of following factors on the impingement heat transfer, such as the attack angle of VGP, the spacing between two VGPs and the distance between the VGP and the jet nozzle. In addition, the mechanism of heat transfer enhancement by longitudinal vortex generator was discussed in detail. Results show that the cross flow velocity in front of the jet nozzle decreases in case the delta-winglet VGP is placed on the top wall, when both the jet penetration and the turbulent kinetic energy improve accordingly in the jet cavity, resulting in significantly increased peak value of heat transfer and enlarged area of heat transfer region. However, the effects of VGP geometry parameters on the heat transfer are not significant at a lower cross-flow Reynolds number.
  • Experimental Study on the Conversion of NOx to Nitrous Acid at High Pressures
    YU Shuaishuai, LIU Dunyu, CHEN Jun
    2018, 38(9): 725-731.
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    To solve the problem that direct detection can not be realized for the nitrous acid (HONO) converted from NOx during flue gas resource recovery using pressuring and cooling technologies, the differential optical absorption spectroscopy (DOAS) was used to measure the HONO concentration, while gas phase and liquid phase experiments were conducted to find the mass balance law of molecular nitrogen. Results show that the conversion rate of NO increases with the rise of reaction pressure in gas phase experiments, while the conversion rate of NO to HONO reduces slightly in liquid phase experiments. The relative error in mass balance of nitrogen related species is less than 10% in both gas and liquid phase. At the end of experiments in N2 sweeping period, with the increase of pressure, the amount of HONO from desorption of solutions decreases slightly.
  • Low-temperature SCR Denitrification Performance of a Cu-based Catalyst Modified by MnOx-CeO2
    SUN Jiaxing, ZHANG Zhiyue, ZHI Jingtao, LIU Hao, YANG Hongmin
    2018, 38(9): 732-739.
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    Several CuO-MnOx-CeO2/γ-Al2O3 catalysts were prepared using sol-gel method by loading different proportions of transition metal oxide MnOx-CeO2 onto the Cu-based catalyst CuO/γ-Al2O3, and their low-temperature SCR denitrification performances were subsequently tested in a catalytic reaction efficiency evaluation system under simulated flue gas condition by the way of temperature programmed method. In addition, the catalysts were also characterized by means of BET, XRD and SEM techniques, so as to analyze the mechanism of these catalysts in the low-temperature SCR reaction. Results show that the denitrification efficiency of catalyst 6% CuO-5% MnOx-10% CeO2/γ-Al2O3 could be kept above 80% at 100-200℃; SO2 and H2O have an inhibiting effect on NOx conversion, while O2 is necessitated in SCR reaction.
  • Analysis on Anti-ice Performance of Offshore Wind Turbines with Ice Breaking Cone
    XU Zifei, YE Kehua, LI Chun, YANG Yang
    2018, 38(9): 740-746.
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    To reduce the ice damage to the structure of an offshore wind turbine, an ice breading cone was installed at the boundary between wind turbine and sea level. Based on Matlock and Ralston methods, a calculation model was established for the collision load between the ice and the tower base, and subsequently a dynamic simulation model was set up for the wind turbine under real-time coupling of turbulent wind and ice load on the basis of exploiting an ice load computing module and integrating the module with open source FAST software. Results show that under the condition without ice breaking cone, the maximum value, average value and standard deviation of shear force on the tower base increase with the rise of ice thickness and velocity, in which, ice thickness has great influence on the average and maximum value, while standard deviation is more sensitive to ice velocity. Whereas for the offshore wind turbine with ice breaking cone, the maximum and average value of shear force on the tower base would reduce by 67.8% and 41.6% respectively, when the standard deviation would first reduce significantly and then get stabilized, thus greatly lowering the fatigue load of turbine tower.
  • Influence of Heave Plate on the Dynamic Response of a Floating Wind Turbine Platform
    YU Wan, DING Qinwei, LI Chun, HAO Wenxing, ZHOU Hongjie, ZHANG Kai
    2018, 38(9): 747-754.
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    A model of floating wind turbine was established based on Classic Spar platform and Cell Spar platform to study the dynamic response of the two Spar platforms under the excitation of wind flow load, and to investigate the influence of heave plate and its parameters on the dynamic response of Cell Spar platform. Results show that compared with Classic Spar platform, the amplitude response operator in frequency domain of Cell Spar platform is significantly smaller in each degree-of-freedom, with corresponding higher peak frequency. Under the same equivalent diameter, the dynamic response of Cell Spar platform in each degree-of-freedom is the smallest when round heave plates are attached. The dynamic response of Cell Spar platform in each degree-of-freedom first drops and then gradually gets stable with the rise of plate thickness. With growing number of heave plates, both the surge response and pitch response of Cell Spar platform gradually increase, while the heave response decreases little by little. Changing the air permeability of heave plate has no obvious effect on the surge response of Cell Spar platform, but it plays an important role in influencing the heave and pitch response.
  • A Flue Gas Waste Heat and Water Recovery System Based on Mechanical Vapor Recompression
    YAN Min, LI Yuzhong, MA Chunyuan
    2018, 38(9): 755-762.
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    A flue gas waste heat and water recovery system was proposed based on mechanical vapor recompression (MVR), of which, the recovery mechanism was analyzed using flue gas temperature-humidity chart, while the methods to calculate the recovered heat/water and to evaluate the system performance were provided. Taking a 300 MW coal-fired unit as an example, the recovered heat and water were computed, the system performance was optimized, and the technical economy of the unit was analyzed. Results show that for a 300 MW coal-fired unit, about 81.4 t/h of water could be recovered in the case that the flue gas temperature drops from 50℃ to 30℃, when zero water consumption could be realized theoretically for the FGD process. The waste heat that could be recovered is 65.2 MW, which turns out to be 67.6 MW of power output after mechanical vapor recompression, when the system performance factor is 21.5. Regarding economic performance, the additional investment for the system proposed is approximately 86.50 million RMB; considering the heat for flue gas reheating, the static payback period is 3.87 years, with a net income of 12.231 million RMB per year, indicating significant effects of the system in energy saving, water saving and economic benefits.
  • Characteristic Analysis of an S-CO2 Recompression Brayton Cycle
    WANG Bingbing, QIAO Jiafei
    2018, 38(9): 763-767.
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    To study the performance of an S-CO2 recompression Brayton cycle, a mash model was established, based on which, the effects of following key parameters on the cycle efficiency were analyzed, such as the inlet temperature and pressure of both the main compressor and turbine, the efficiency of corresponding equipment, and so on, while the influencing mechanism was explored and the optimal working point was designed. Results show that the cycle efficiency increases monotonically with rising inlet temperature and pressure of the turbine, and with reducing inlet temperature and pressure of the main compressor. There exists an optimal inlet pressure of the main compressor that makes the cycle efficiency reach the maximum. The cycle efficiency is related to the efficiency of corresponding equipment in the cycle loop, among which, the turbine isentropic efficiency and the high-temperature recuperator efficiency affect the most.
  • Research of Influencing Factors on Fracture Toughness Test Results of Forging Alloy 25Cr2Ni4MoV
    TIAN Genqi, SHI Kexian, WAN Haibo, WANG Yanfeng
    2018, 38(9): 768-772.
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    Through fracture toughness tests of alloy 25Cr2Ni4MoV conducted by single sample unloading compliance method, the influence of following factors on the test results was investigated, such as the initial crack length, specimen size, test parameters and the data processing method, etc. Results show that both the fracture toughness measured and the maximum load applied in the test reduce with the rise of initial crack length. The fracture toughness obtained with CT25 (25 mm thick) specimen is higher than with CT38 (38 mm thick) specimen. At low loading rate (<1.5 MPa·m0.5·s-1), the measured data of fracture toughness is slightly affected by the loading rate, which would reduce when the loading rate is further increased; the longer the holding time is, the smaller the measured data of fracture toughness would be. The main differences between GB/T 21143-2014 and ASTM E1820-2016 lie in such data processing methods as the blunting line, valid data judgment and the curvilinear equation, etc., and the values calculated with the former standard would be lower than that with the latter one.