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  • 2018 Volume 38 Issue 10
    Published: 15 October 2018
      
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  • High-temperature Corrosion Tests for the Water Wall of a 1 000 MW Ultra Supercritical Coal-fired Boiler with Double Reheat Cycles
    YUE Junfeng, ZOU Lei, ZHANG Enxian, GUAN Shipian, DING Jianliang, KONG Junjun, JIA Tao
    2018, 38(10): 773-781.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    According to the features of the burner applied in a 1 000 MW ultra supercritical coal-fired boiler with double reheat cycles, experimental tests were carried out to measure the water wall temperature and the distribution characteristics of gas components near the water wall, so as to analyze the effects of following factors on the high-temperature corrosion over the water wall, such as the oxygen concentration, fineness of pulverized coal, sulfur content in fuel, primary air flow rate, offset angels of air-grade part (AGP), AGP air flow rate, and the air flow rate in the concentric firing system (CFS), etc. Results show that the reductive atmosphere near the water wall could be reduced effectively by increasing the oxygen concentration and reducing the fineness of pulverized coal. With the rise of sulfur content in fuel, both the CO concentration and H2S concentration increase near the water wall. Decreasing AGP air flow rate and increasing CFS air flow rate are helpful to reduce the high-temperature corrosion. The offset angels of AGP have little influence on the reductive atmosphere near the water wall. Decreasing primary air flow rate will deepen the high-temperature corrosion. In the same furnace reducing atmosphere, a 1 000 MW ultra supercritical boiler with double reheat cycles would withstand higher risk of high-temperature corrosion on the water wall than those with single reheat cycle.
  • NOx Emission Optimization of a Boiler Based on Improved Flower Pollination Algorithm and Extreme Learning Machine
    NIU Peifeng, LI Jinbai, LIU Nan, LI Guoqiang, WANG Rongyan
    2018, 38(10): 782-787.
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    To reduce the NOx emission of a utility boiler, an improved flower pollination algorithm was proposed by modifying the switch probability and local search of the basic flower pollination algorithm. The improved flower pollination algorithm and extreme learning machine were then adopted to build a characteristic model of NOx emission using the historical data of a 330 MW coal fired boiler. Based on the model, the adjustable parameters of a coal-fired boiler were modified in a certain range to optimize its NOx emission with the improved flower pollination algorithm. Results show that the NOx emission model proposed has higher prediction accuracy compared with BP neural network model and basic extreme learning machine model; besides, the NOx emission optimized by improved flower pollination algorithm is significantly lower than that by the original algorithm. This may serve as a reference for reducing NOx emission of similar coal-fired boilers.
  • Effects of Double-U Combustion Mode on the Characteristics of Furnace Combustion
    LÜ Hongkun, TONG Jialin, QI Xiaojuan, LI Jian, CAI Jiecong
    2018, 38(10): 788-793.
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    Numerical simulations were conducted to study the combustion characteristics in the furnace of a 2 045 t/h opposed firing boiler adopting double-U combustion mode, such as the average flue gas temperature and the reductive atmosphere near water wall, the average NO concentration, the burnout rate and the flue gas temperature deviation at furnace arch exit, as well as the amount of bottom ash, etc. Results show that compared with traditional combustion modes, the double-U mode, realized through optimizing the angle of same layer burner blades and the distribution of coal flows, could help to reduce the flue gas temperature near water wall by about 100 K, while the deviation factor of flue gas temperature at furnace arch exit remains unchanged. Under the mode of double-U combustion, the area containing high concentration of CO reduces from 40% to 10%, resulting in lower risk of high-temperature corrosion in that area; the burnout rate reduces at arch exit, while the amount of bottom ash increases slightly. In actual practice, comparing with baseline test, the volume fraction of CO in high reduction atmosphere reduces by about 40%.
  • Effect of Inner Surface HT ZST Nano-ceramic Coating on the Performance of a Large Coal-fired Boiler
    ZHANG Jianhui, TAI Zhaoshan, WANG Bohai, ZHAN Mingxiu, WANG Jinqing, CHI Zuohe
    2018, 38(10): 794-799.
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    To solve the problems of heat surface fouling, slagging, high-temperature corrosion and erosion that affect the operation safety and economic benefit of a large coal-fired boiler, a retrofit scheme was proposed by applying ZST nano-ceramic coating to the pipes and lining of relevant heating surfaces. Based on profile image analysis, a contact angle measurement system was designed using high temperature hanging drop method to test the influence of nano-ceramic coating on the adhesion properties of coal ash. For a 530 MW coal-fired boiler, hot state operation data and cold state inspection results were respectively compared before and after the application of nano-ceramic coating. Results show that the ceramic coating can reduce the adhesion of coal ash on the base metal, helping to improve the slagging resistance of steel. The boiler efficiency could be increased by 0.21% compared with that without coating. The problems of fouling and slagging in the furnace are alleviated and the frequency of soot blowing is reduced by 70% after the spraying of ceramic materials. High temperature corrosion and erosion caused by flue gas on the heating surface are effectively blocked in the presence of ceramic coating, resulting in enhanced heat transfer performance of furnace, lowered outlet flue gas temperature by 1.5 K and reduced NOx emission.
  • Design Point Optimization of a 1 000 MW High-efficiency Wide-load-range Ultra-supercritical Unit
    HE Haiyu, FAN Shiwang, PENG Zeying
    2018, 38(10): 800-806.
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    To improve the full load economy of a 1 000 MW ultra-supercritical unit, the opening point of its overload valve was reduced to 850-950 MW. Simultaneously, a No.0 high-pressure heater and a bypass regulating system for the high-pressure heater were added on the basis of its original regenerative system. The No.0 high-pressure heater would be put into operation at low load, whereas the overload valve and the high-pressure heater bypass system would be put into use at high load. Moreover, the steam parameters and unit economy were compared before and after optimization, while the generating capacity was demonstrated, and the overall economy of various schemes was compared at different load rates. Results show that the main steam pressure increases and the heat rate reduces under part-load conditions after optimization of the unit. The economy of unit could be further improved by putting No.0 high-pressure heater into operation. The generating capacity could be increased by running the overload valve and the high-pressure heater bypass system, thus to satisfy the requirements of rated and maximum power output of unit. The overall economy of unit is greatly influenced by the load rate, which therefore should be considered in the selection of optimization schemes.
  • Finite Element Analysis of Fatigue Crack Growth Between Last Disc and Blade of a Large Capacity Steam Turbine
    YAN Shangjun, LI Luping, FENG Jiang, CHEN Pengfei, LI Kunlin
    2018, 38(10): 807-814.
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    An analysis was conducted on the fatigue crack growth between last disc and blade of a domestic 600 MW steam turbine using software ABAQUS, so as to study the stress distribution in that area and the crack propagation in the rim with maximum stress. Considering the effect of fluctuating steam load on the rim fatigue crack, the growth law of fatigue crack in the rim with maximum stress was simulated respectively at the rated speed of 3 000 r/min and the overspeed of 3 300 r/min, thus to find the relationship between the number of crack growth cycles and the length of end surface cracks, and to compare the crack length under two working conditions after 1±106 cycles. Results show that the crack tends to grow more easily under overspeed condition, and the propagation rate is also higher than that under rated condition.
  • Rotor Vibration Analysis Under the Coupled Effect of Shaft Bend and Mass Unbalance
    XIA Yalei, ZHANG Wentao, LU Yibing, YANG Jiangang
    2018, 38(10): 815-819.
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    To reduce the vibration of a unit caused by shaft bend and mass unbalance, dynamic equations were set up for the generator rotor, so as to study the amplitude-frequency and phase-frequency response when the angle between unbalance plane and bend plane is 0°, 90° and 180° respectively. The coupled model was then used to analyze the abnormal vibration of the generator rotor in a 600 MW unit. Results show that the vibration is significantly influenced by the angle between unbalance plane and bend plane, and the "negative critical speed" phenomenon would occur when the angle is 180°, i.e. the vibration reaches the minimum at the point of critical speed. The vibration response in acceleration process of generator rotor obtained based on the coupled model established agrees well with that of actual variations.
  • Fault Diagnosis of Wind Turbines Based on Improved Multiblock Kernel Principal Component Analysis
    JIA Ziwen, GU Yujiong
    2018, 38(10): 820-828.
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    To overcome the difficulty in fault diagnosis of wind turbines due to their complex operation conditions and data information structure, an improved multiblock kernel principal component analysis (MBKPCA) method was proposed based on factor analysis, so as to establish an association mechanism among the unit data, variables and operating conditions by deeply mining the operation data. Through corresponding analysis, the relationship between unit variables and the data was defined, while the number of MBKPCA sub-blocks and their actual meanings were determined. Finally, the factor analysis was adopted to find out the correlation between the data of various sub-blocks and the process of corresponding motions, thus improving the diagnostic accuracy of MBKPCA. Results show that the improved MBKPCA method can help to make fault diagnosis timely and accurately for wind turbines, which may be applied in actual engineering projects.
  • Multi-objective Optimization of an Organic Rankine Cycle Based on MOGWO Algorithm
    HAN Zhonghe, MEI Zhongkai, LI Peng
    2018, 38(10): 829-835.
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    To improve the overall performance of an organic Rankine cycle, a multi-objective optimization model was established from the perspectives of thermoeconomics and exergoeconomics by taking the total investment per unit power output and the cost per unit exergy of the system as the performance indicators. For the 423.15 K low temperature flue gas waste heat source, the R245fa, R123, R114, R245ca, R601, cyclohexane, butane, and R236ea were chosen as the candidate working fluids. The model established was solved using the multi-objective gray wolf algorithm (MOGWO), while the effects of evaporation temperature and condensation temperature on the turbine efficiency were analyzed with a one-dimensional radial-inflow turbine efficiency prediction model. Results show that, for all the working fluids, the turbine efficiency reduces with the rise of evaporation temperature, but increases with the rise of condensation temperature. Among the working mediums selected, R601 is the optimal working fluid.
  • Effects of Reynolds Number on Stall Characteristics of an Airfoil with Flaps
    CHEN Fudong, HAO Wenxing, LI Chun, MIAO Weipao, YANG Yang, DING Qinwei
    2018, 38(10): 836-842.
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    Taking the airfoil NREL S809 as an object of study, numerical simulations were conducted to investigate the effects of flap angles on the aerodynamic performance of the airfoil at different Reynolds numbers, while the aerodynamic parameters of unsteady flow field were analyzed with power spectrum. Results show that the optimal flap angles are approximately linear with respect to the angles of attack at different Reynolds numbers. The fluid has stronger attaching ability to the airfoil surface at higher Reynolds numbers, making the optimal flap angles get smaller at corresponding angles of attack. The flap at high Reynolds numbers has stronger ability to reduce the fluctuation amplitude of aerodynamic parameters than that at low Reynolds numbers.
  • Study on the Integration of Supercritical Carbon Dioxide Cycle with Coal-fired Boiler
    ZHENG Kaiyun, HUANG Zhiqiang
    2018, 38(10): 843-848.
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    To solve the problems existing in the integration of recompression supercritical carbon dioxide cycle with coal-fired boiler, such as high temperature of working fluid flowing into the boiler, narrow heating window and large mass flow rate, etc., a partial cooling cycle was proposed, along with the scheme of working fluid split flow to cool the tail flue gas, and the modified air preheating method, to which, a thermodynamic analysis was conducted in detail. Results show that compared with the recompression cycle, the partial cooling cycle integrated with boiler can significantly reduce the temperature of working fluid flowing into the boiler, enlarge the heating window and reduce the mass flow rate. The tail flue gas of boiler could be cooled down by working fluid bypass flow, thus to control the exhaust gas temperature and ensure the boiler efficiency. When the working fluid is split from the main compressor exit, the cycle efficiency would decrease with the increase of split fraction, and when the working fluid is split from the entrance of high temperature recuperator, the cycle efficiency would first remain unchanged with the increase of split fraction and then reduce gradually once the split ratio exceeds the critical value. Both the air preheating designs proposed could raise the preheating temperature of secondary air, and reduce the temperature of working fluid entering the boiler.
  • Study on Taking Backpressure BFPT Exhaust of 350 MW Supercritical Unit as Industrial Heat Source
    YU Yan, JIN Yibo, YANG Hongxia, CAI Xiaoyan
    2018, 38(10): 849-854.
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    To satisfy the heating requirement on a 350 MW supercritical unit, a novel scheme was proposed to take its backpressure BFPT exhaust as the source of industrial heat supply. An introduction was presented to the arrangement of related thermodynamic system in the noval scheme, while a comparison of economy was made between conventional and the proposed heat supply mode based on detailed calculation. In addition, a feasibility study was performed for the noval scheme in engineering application. Results show that by the way of taking backpressure BFPT exhaust as the heat source, high economy of unit would be resulted, without requiring additional equipment and with high operation flexibility, which therefore may serve as a reference for industrial heat supply of steam turbines.
  • Study on Microstructure, Hardness and Impact Energy Absorption of Alloy 617B with High Content of C/(Al, Ti) After Being Aged at 750 ℃
    SHI Zhenbin, LAI Xianhong, XIANG Changhong, YANG Xiaochuan, YANG Huachun, PENG Zhifang, CHEN Fangyu
    2018, 38(10): 855-860.
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    Hardness and Charpy energy absorption of two 617B alloys with different contents of C, Al and Ti were investigated after being aged at 750℃ for 5 000, 7 500 and 10 000 hours, respectively. The microstructures were observed by OM, SEM and TEM, while their phase parameters were determined with the use of SEM/TEM-EDS+MPST(multiphase separation technology). Results show that compared with high Al/Ti-containing alloy B, the impact value of high C-containing alloy A is relatively samller with M23C6 phase continuously distributed along the finer grain boundaries after solution heat treatment. After being aged for 5 000-10 000 hours, alloy A with a relatively low volume fraction of γ' phase basically keeps its hardness unchanged due to the existence of multiphase microstructure of very fine M23C6 and γ' particles distributed throughout the grain interiors; whereas alloy B with a relatively high volume fraction of γ' phase has a significantly reduced hardness due to the lack of multiphase miscrostructure of M23C6 and γ' particles in the vicinity of grain boundaries. With the rise of aging time, the amount of M6C phase increases slightly on the grain boundary of alloy A, while that of γ' phase increases evidently on the boundary of alloy B, resulting in obviously reduced energy absorption of alloy B. In brief, the precipitates scattered along the grain boundary influence the grain size and then determine the impact energy absorption of the alloy. In addition, the multiphase microstructure of M23C6 and γ' particles distributed throughout the grain interiors helps to keep the alloy hardness unchanged. It is evident that the contents of C, Al and Ti play a decisive role in the orignation and development of above phenomena.