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  • 2018 Volume 38 Issue 8
    Published: 15 August 2018
      
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  • Numerical Simulation on the Effects of Near-wall Air Distribution on the High-temperature Corrosion of a 300 MW Tangentially-fired Boiler
    WAN Zhongping, LIU Jichang, MAO Xiaofei, FANG Qingyan, ZHANG Cheng, CHEN Gang
    2018, 38(8): 601-609.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem of serious high-temperature corrosion in partial water wall areas of a 300 MW tangentially-fired boiler after application of low NOx combustion technology, some retrofits were conducted on the near-wall air distribution, so as to numerically study the effects of near-wall air curtain on the high-temperature corrosion characteristics under four cases of near-wall air parameters. Simulation results show that:among the four cases with all the near-wall air nozzles on, in the process of gradually increasing the near-wall air flow rate, case 2 has the best comprehensive effect, which can effectively alleviate the high-temperature corrosion with lower outlet content of unburned carbon in fly ash and lower NOx emission; the high-temperature corrosion could be further alleviated by switching off the near-wall air nozzles with airflows opposite to the main stream, and by increasing the velocity of the remaining near-wall airflows, when better combustion effect may be obtained.
  • Comparative Study Between Chinese and American Boiler Performance Test Codes
    CHANG Yongqiang, LIU Xuemin, QI Guoli, LI Debiao, MENG Yong, GUAN Jian
    2018, 38(8): 610-616.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A comparative study was conducted on the Chinese standard GB/T 10180-2017 "Thermal performance test code for industrial boilers", Chinese standard GB/T 10184-2015 "Performance test code for utility boilers" and the American standard ASME-PTC4 "Performance test code for fired steam generators". Results show that for the calculation methods, the test principles of the Chinese and American standards are the same, based on the energy balance that the energy entering the system boundary is equal to that leaving the system boundary. In ASME PTC4 and GB/T 10184, the energy input to the system is classified into two kinds:energy input from fuel (heating value of fuel) and energy input from other sources, while in GB/T 10180, the energy input is defined as the total energy added to the system (heating value of fuel and energy input from other sources). Therefore, the boiler efficiency in both ASME PTC4 and GB/T 10184 essentially refers to fuel efficiency, whereas in GB/T 10180, it refers to gross efficiency. For uncertainty analysis, ASME PTC4 describes the assessment method of test uncertainty in detail, while Chinese standards are lack of uncertainty analysis and assessment method. By comparison of Chinese standards and ASME PTC4, it can be found that in the performance test for utility boilers, the two standards are getting closer and closer, while in the performance test for industrial boilers, great differences still exist.
  • Study on Time Delay Estimation in Boiler Acoustic Temperature Measurement Based on Second Correlation PHAT-β Algorithm
    SHEN Guoqing, YANG Jiedong, CHEN Dong, LIU Weilong, ZHANG Shiping, AN Liansuo
    2018, 38(8): 617-623.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To overcome the deficiency that pseudo peaks generally exist in traditional cold-state time delay estimation due to the presence of reverberation, a new algorithm of time delay estimation was proposed based on second correlation and phase transform weighting (PHAT-β), so as to improve the accuracy of time delay estimation in acoustic temperature measurement of power plant boilers. The algorithm proposed was then used for temperature measurement of a test furnace and a 300 MW power unit, and the measurement data were subsequently compared with that of traditional method. Results show that the PHAT-β algorithm based on second correlation can accurately measure the time of flight of the acoustic wave, and can suppress the reverberation more efficiently, having a relatively good applicability in boiler environment with strong noise. The new algorithm provides a feasible approach for optimization of time delay estimation in temperature measurement, which may serve as a reference for other monitoring means based on time delay estimation.
  • Study on Coupling Algorithm of Sensor Fault Diagnosis Based on WEE and EEMD
    SHI Licheng, ZHAO Xiao, ZHAO Qunfei, WANG Yuzhang
    2018, 38(8): 624-632.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on sample sets and label data established for all classes of sensor faults, the fault signals of various sensors were detected by using wavelet energy entropy (WEE) combined with K nearest neighbor (KNN) classifier and ensemble empirical mode decomposition (EEMD) combined with sparse representation classifier (SRC). Through optimization and integration of above methods, a coupling algorithm combining WEE with EEMD was proposed for the detection of gas turbine sensor faults, which was validated with the trial data of a certain gas turbine. Results show that the algorithm proposed has high detection accuracy, fast analysis speed and good robustness, with analysis results more reliable than the single detection method, which therefore has broad prospects in engineering applications.
  • Study on Heat Transfer Performance of a Co-rotating Cavity with Pre-swirl Inflow of Steam and Air
    HU Weixue, WANG Suofang, MAO Shasha
    2018, 38(8): 633-639.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To investigate the effects of different cooling mediums on the heat transfer performance of a gas turbine co-rotating cavity with pre-swirl inflow, a numerical analysis was conducted on the heat transfer process of the co-rotating disc cooled by air and steam in the pre-swirl system, so as to compare the heat transfer effectiveness of the two cooling ways at different rotational Reynolds numbers, non-dimensional mass flow rates and at different total inlet temperatures. Results show that the effectiveness of both air and steam cooling on the rotating disc with pre-swirl inflow is better than that without pre-swirl inflow under the same non-dimensional mass flow rate. The heat transfer performance of co-rotating cavity with steam cooling is superior to that with air cooling, under different non-dimensional mass flow rates. The average Nusselt number of steam cooling is 22% higher than air cooling at the same rotational Reynolds number ranging from 5.5×106 to 7.2×106. For both the mediums, the cooling effect of rotating disc at low rotational Reynolds number is slightly better than at high rotational Reynolds number. At different total inlet temperatures, the effectiveness of steam cooling is always better than air cooling, but the superiority weakens with the rise of total inlet temperature. The average Nusselt number of co-rotating cavity reduces with the increase of total inlet temperature.
  • Condenser Performance Calculation Considering the Influence of Vacuum Pump Under Off-design Conditions
    QU Binbin, ZHANG Li, WANG Fuhua
    2018, 38(8): 640-644.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the low-pressure condenser of a 600 MW power unit as an example, the flow condition on shell side of the condenser and the condenser performance changing with the pumping pressure were numerically simulated, while the suction capacity of the water-ring vacuum pump was calculated under off-design conditions. Based on actual conditions of combined operation of the vacuum pump and the condenser, the working point and pressure of the condenser were determined considering the influence of the vacuum pump under off-design conditions. Results show that the condenser working pressure increases with the rise of the temperature of water working in the pump. To evaluate the performance of the condenser accurately, it is suggested that the change of the temperature of water working in vacuum pump should be taken into account according to actual conditions of the unit.
  • Application of an Economizer System with Feedwater Redistribution in a Utility Boiler
    CHONG Pei'an, DING Shifa, LI Jianning
    2018, 38(8): 645-649.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To put the SCR system into safety operation at low load of a utility boiler, a retrofit scheme was proposed by adopting the economizer system with feedwater redistribution, where a part of low-temperature feedwater is bypassed directly to the downcomer, and a part of hot water is recirculated from the economizer outlet to the inlet. Results show that the economizer system with feedwater redistribution can help to improve the inlet tempemperature of working medium in the economizer, reduce the heat-transfer temperature difference, reduce the quantity of heat transfer, and improve the flue gas temperature at economizer outlet, i.e. improve the flue gas temperature at SCR inlet, thus achieving safety operation of the SCR facility during low load operation of the boiler. After retrofit, the boiler is now able to operate safely and stably, and the NOx emission is reduced accordingly due to the SCR unit coming into use.
  • Research on Applicability and Pollutant Emission Characteristics of a LLT-ESP
    LIU Hanxiao, YAO Yuping, LI Jianguo, HE Yuzhong, CHEN Zhaomei
    2018, 38(8): 650-657.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An analysis was conducted on the dust/SO3 ratio of nearly 200 kinds of domestic coal, while a study was carried out on the effectiveness improvement and pollutant emission characteristics of a low-low temperature electrostatic precipitator (LLT-ESP) based on improved testing technologies. Results show that the dust/SO3 ratio of most kinds of domestic coal is above 100, in which case, no risk of low temperature corrosion would occur in the application of LLT-ESPs. The LLT-ESP technology can greatly reduce the specific resistance and improve the average particle size of fly ash, increase the electric field corona and breakdown voltage, and reduce the mass flow rate and velocity of flue gas, thus greatly improving the efficiency of the ESP, with an increase in dust removal efficiency by 0.01-0.17 percentage point, a reduction in PM2.5 emission and SO3 emission by 48.3% and 96.6%, respectively, and with a significant increase in mass fraction of sulfur element and sulfuric acid root in fly ash.
  • Research on the Influence of Tuned Mass Damper on the Stability of a Floating Wind Turbine
    HUANG Zhiqian, HAO Wenxing, LI Chun, YE Zhou
    2018, 38(8): 658-664.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the NREL 5 MW floating wind turbine with ITI Barge platform as an object of study, by equipping a tuned mass damper (TMD) in the nacelle, the control effects of TMD on the tower top displacement and platform sway characteristics were researched under environmental loads. Results show that TMD does not have an obvious effect on the control over back-and-forth displacement of the tower top, but it does have a remarkable influence on the lateral displacement, with a reduction in maximum value by 66%, and an increase in stability by 38%. Under the control of TMD, significant decline can be obtained for the floating wind turbine in platform sway and roll, with a reduction in maximum values of sway and roll by 29% and 45%, respectively, resulting in an increase in stability by 18% and 41% accordingly.
  • Study on Aeroelastic Modeling and Active Control Simulation of Smart Wind Turbine Blades
    ZHANG Wenguang, LIU Ruijie, WANG Yifeng
    2018, 38(8): 665-673.
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    To study the aeroelastic characteristics of smart blades on a large-scale wind turbine and the effects of trailing edge flaps (TEFs) on the deformation and fatigue load of blades, taking NREL 5 MW reference wind turbine with TEFs as an object of study, a multimodal flapwise aeroelastic model of smart blade was established considering the factors of rotation, gravity, damping and aeroelastic coupling of the flexible blades, and subsequently the results were compared with that of FAST. Furthermore, a TEF active controller was designed based on the least mean square (LMS) algorithm, and a control simulation was conducted for the blade tip deflection under turbulent wind condition. Results show that the accuracy of the aeroelastic model is relatively high, and the TEF active control method can effectively reduce the fluctuation of blade tip deflection and the fatigue load of related blades.
  • Study on Maintenance Method for Transmission System of a Wind Turbine
    XIE Lubing, RUI Xiaoming, LIN Yuxi, HUO Mingqing
    2018, 38(8): 674-681.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To study the maintenance method for wind turbines, the planned and opportunistic preventive maintenance models were respectively established by simplifying the wind turbine as a series system, and taking the minimum maintenance cost, maximum availability and comprehensively considering both the minimum maintenance cost and maximum availability of the single-cycle system as the objectives. Subsequently, the weight coefficients were introduced to compare the two preventive maintenance models to find the most satisfactory decision for the wind turbine transmission system. Results show that when the minimum maintenance cost is sought, the comprehensive model would be closer to the one based on minimum maintenance cost, and when the system availability is more concerned, the comprehensive model would be closer to the one based on maximum availability. Compared with the planned preventive maintenance method, the opportunistic maintenance strategy can further reduce the maintenance cost and improve the availability of the single-cycle system.
  • Study on Low-cycle Fatigue Property of Rotor Steel FB2 for High-efficiency Ultra-supercritical Steam Turbine Units
    DING Lingling, YANG Baixun, TIAN Xiao, LI Yimin
    2018, 38(8): 682-688.
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    Microstructures and tensile properties of FB2 rotor steel for high-efficiency ultra-supercritical steam turbine units were researched at the reheat temperature of 620℃, while its low-cycle fatigue properties were comparatively analyzed at both room temperature and 620℃ using axial loading constant-amplitude low-cycle fatigue method, based on which, the relationship between the plastic strain energy/amplitude and the cycle number was obtained for the rotor steel FB2. Results illustrate that the microstructure of FB2 steel is of the fully-tempered martensitic kind, with large sizes of BN inclusions. The tensile properties of FB2 are found to be uniform in different orientations, with Rp0.2 at room temperature exceeding 700 MPa, which meets the requirements of COST522 project. Cyclic softening could be observed under low cycle condition, and the relationship between cyclic strain and life conforms to the Manson-Coffin model. The relationship between plastic strain energy/amplitude and fatigue life of FB2 exhibits the linear characteristics in double logarithmic coordinates, which can be used in estimation of low-cycle fatigue life of FB2 steel.