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  • 2017 Volume 37 Issue 3
    Published: 15 March 2017
      
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  • R & D of Key Technologies for a High-efficient Wide-load-range Ultra-supercritical Unit and the Engineering Schemes
    ZHANG Xiaolu, ZHANG Yong, LI Zhenzhong
    2017, 37(3): 173-178.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An introduction is presented to the operation status of domestic 1 000 MW and 600 MW ultra-supercritical units, together with an analysis on the causes leading to the efficiency reduction under varying load conditions, with focus on the effects of unit load on the efficiency of boiler, steam turbine and main auxiliaries. To solve the problem of low efficiency of main auxiliaries under varying load conditions, research and development were conducted on key technologies of the high-efficient ultra-supercritical unit over wide-load operation. On above basis, engineering schemes were proposed for the 1 000 MW high-efficient wide-load-range ultra-supercritical unit, and a comparative analysis was subsequently conducted between the high-efficient wide-load-range unit and the conventional units.
  • Combustion System Retrofit of a 600 MW Supercritical W-flame Boiler
    HAN Haiyan, LIU Pengyuan, XU Pengzhi, RUAN Jiongming
    2017, 37(3): 179-185.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A numerical simulation was conducted on the gas-solid two-phase flow in a single shutter coal separator of a 600 MW supercritical W-flame boiler, including a hot-state simulation on the in-furnace combustion, so as to obtain the simulation results on corresponding separating effect and ignition distance of the boiler at different secondary air ratios under the arch, and to compare them with experimental data. Based on above simulation results, different retrofit schemes were proposed and compared by replacing all the shutter separators with high-efficient cyclone ones, considering the combustion conditions in reasonable arrangements of over-arch secondary air nozzles and at reasonable under-arch secondary air ratios. Results show that lowest combustible matter in fly ash and balanced temperature distribution between V-type bottom of the furnace and the bottom of platen superheater would be obtained when the under-arch secondary air ratio is set to be 36%. In retrofit scheme 1, the water wall at lower part of the furnace is protected from heat-transfer deterioration by a low-temperature layer formed on the surface. The simulated boiler performance after retrofit is proved to agree well with actual test data.
  • Study on NOx Emission Characteristics of Utility Boilers Based on PLS and ε-FT
    ZHANG Wenguang, ZHANG Yue
    2017, 37(3): 186-191.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To reduce the NOx emission from utility boilers, a prediction model of NOx emission was established based on the historical data of a 600 MW coal-fired boiler by partial least squares(PLS)and ε-fuzzy tree (ε-FT). Considering the strong correlations and coupling of input variables in thermal power process, the PLS method was applied to extract important variables information and select variables from thermal data inputs of the model. Subsequently, the obtained feature matrix was used as the input of ε-FT to establish a PLS-ε-FT model of NOx emission, which was compared with other modeling methods. Results reveal that, through PLS variable selection, the variable correlations of the PLS-ε-FT model are eliminated, while the model complexity and the number of variable dimensions are decreased, thus enhancing the prediction accuracy and generalization ability of the model.
  • Prediction Model for Burnout Characteristics of Pulverized Coal at Constant Temperature Based on Proximate Analysis
    GUO Yongcheng, WANG Chunbo, LI Xinhao
    2017, 37(3): 192-198.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Combustion experiments were conducted for fourteen kinds of pulverized coal in high-temperature atmosphere on a self-made test rig, which could achieve thermal gravimetric measurement at constant temperatures. By introducing the combined parameters x1 and x2 of proximate analysis and the ratio KT1T2 of burnout time, the influence of proximate analysis and temperature on the burnout characteristics was analyzed, while the prediction model for burnout time was built. The model was then used to predict the burnout time of pulverized coal specimen at different temperatures, and the predicted results were subsequently compared with experimental data. Results show that the combined parameters x1 and x2 and the burnout time have a quadric relationship at different temperatures. For the same temperature rise, the higher the initial temperature is, the smaller the increase of early burning weight loss rate will be; the ratio KT1T2 of all pulverized coal has almost the same value at constant temperatures T1 and T2; the ratio KT1T2 is linearly related to lg T2 at constant temperature T1. The prediction model for burnout time is proved to be highly accurate.
  • Blade Model for Torsional Vibration Analysis of Turbine-Generator Shafts and the Parameter Adjustment
    ZHAO Pengcheng, GU Yujiong, CHEN Dongchao, LIN Sixuan, JIN Tiezheng, YANG Kun
    2017, 37(3): 199-206.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the LP last stage blades in a 600 MW turbine-generator set with dry friction damping shroud as an object of study, vibration characteristics of the blades were researched during torsional vibration of the shafting. Finite element model was used to calculate the inherent characteristics of the blade set, based on which, a spring-mass model of blade was set up for torsional vibration analysis of the shafting, considering the influence of the shroud on the long turbine blades, and subsequently an adjustment method was proposed for the model. Results show that the vibration of bladed disk is of the non nodal umbrella type, when torsional vibration occurs to the shafting system. The adjustment of model parameters makes the umbrella vibration calculation results consist with actual measurements, indicating improved accuracy of the model.
  • Structural Optimization on Vane-type Vortex Generator of Compressor Cascades Based on Orthogonal Experiment
    WU Yanhui, LIU Jun, PENG Wenhui, YANG Guowei, YANG Xuanzhou
    2017, 37(3): 207-212.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To greatly reduce the corner separation and improve the aerodynamic performance of a high load compressor cascade with vane-type vortex generator, structural optimization was carried out on the vortex generator. The specific way is to simulate the flow field in the generator with different geometric parameters and at different positions based on orthogonal experiment using CFD software, so as to obtain the total pressure loss coefficient and static pressure rise coefficient of the cascade at design angle of attack for different schemes. Range analysis was used to study the effects of generator geometric parameters on the cascade loss and diffusion capacity, and to analyze the influence level of different parameters on the cascade performance, and finally to find out an optimum design scheme. Results show that via the optimized vane-type vortex generator, the cascade loss can be reduced and the diffusion capacity can be improved within a wide range of attack angles.
  • Effects of Tilting Rotor on Fluid-induced Vibration Characteristics of a Labyrinth Seal
    CHEN Ciwei, ZHANG Wanfu
    2017, 37(3): 213-217.
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    Based on the three-dimensional model set up for a traditional labyrinth seal, numerical simulation was conducted on the fluid-induced force under the condition of titling rotor using computational fluid dynamics modeling method, so as to study the effects of following factors on the leakage rate and fluid-induced force, such as the deflection angle, eccentric distance, inlet pressure and rotaing speed, etc. Results show that the deflection angle and eccentric distance have less influence on the leakage rate; the inlet pressure is linearly related to the leakage rate; the deflection angle, eccentric distance, inlet pressure and the rotating speed have a linear relationship with the radial force and the tangential force, which affect more on the former one. The radial force reduces gradually with the rise of rotating speed and eccentric distance due to the tilting rotor.
  • Identification of Gas-Liquid Two-phase Flow Patterns in a Double-contact Absorber Based on Complexity Theory
    FANG Lijun, LIU Yudong, HU Yuelong
    2017, 37(3): 218-223.
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    An identification method was proposed for the gas-liquid two-phase flow patterns in a double-contact absorber based on images statistical features of gray histogram and complexity theory, containing approximate entropy, sample entropy and Lempel-Ziv complexity, where the two-phase flow images were captured by a high-speed video system. After image processing, the image gray average was selected as the statistical feature. Then, gray average time series of four typical flow regimes were established, which were analyzed by three complexity algorithms. Test results show that the results obtained by the analysis of above three complexity algorithms are very consistent; the complexity of previous four flow patterns from high to low is as follows:disorder flow, whirlpool flow, liquid-column flow and bubbly flow.
  • Application of Orthogonal Experiment in Adjustment of a Medium-speed Pulverizing System for 350 MW Unit
    LIU Wensheng, TONG Jialin, LI Wenhua, LI Ruping
    2017, 37(3): 224-228.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Orthogonal experiments were carried out on the coal pulverizer of a 1 100 t/h boiler, so as to study the effects of following factors on both the pulverized coal fineness and unit power consumption, such as the coal feed rate, primary air flow and the separator rotating speed, etc. Meanwhile, the affection degree of above 3 factors on the pulverized coal fineness and unit power consumption was determined, based on which an optimum operation mode was found for the pulverizing system. Results show that the coal feed rate and separator rotating speed greatly affect the pulverized coal fineness and unit power consumption. To ensure a safe and economic operation of the pulverizing system, the operating parameters should be adjusted after a certain period of operation. The fit curves of this study may serve as a reference for actual operation of similar pulverizing systems.
  • Modification of Meridian Plane Profile for Return Channel of a Centrifugal Compressor Based on Energy Gradient Theory
    DOU Huashu, CHEN Xing, ZHANG Binwei, LU Fuan, WEI Yikun, CHEN Xiaoping
    2017, 37(3): 229-236.
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    To improve the operating efficiency and stability of the return channel in a centrifugal compressor, the energy gradient theory was used to analyze the flow field in the compressor, so as to obtain the distribution of energy gradient K function in the return channel. According to the analysis results on energy gradient K function, an improvement way was proposed by changing the original hub inclined return channel into the shroud inclined type, based on which, numerical simulations were conducted at 5 different tilt angles. Simulation results show that the polytropic efficiency of modified model is enhanced by about 1% compared to the original model under design conditions, and the performance of whole stage has also been improved under varying conditions with discharge coefficient in the range of 0.85-1.16. The stage efficiency and pressure ratio of centrifugal compressor increase with rising tilt angles.
  • Arsenic Release from Co-firing of Coal and Biomass in Oxygen-enriched Atmosphere
    DONG Jinglan, MA Kai
    2017, 37(3): 237-241.
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    Arsenic content in the ash from coal and biomass co-firing in oxygen-enriched atmosphere was measured using AFS-933 atomic fluorescence meter by the way of wet digestion with chemical reagents. Results show that the release of arsenic is inhibited by blending biomass, and with the rise of biomass ratio, the relative enrichment factor of arsenic increases; whereas with the rise of combustion temperature and oxygen concentration, the relative enrichment factor of arsenic reduces, which have conductive effect on the release of arsenic. When different types of biomass and coal are blended, the inhibiting effect of biomass type is more obvious than the coal type on the release of arsenic.
  • Performance Research of a Thermal System Using Mining Data Instead of Measuring Point Failure Values
    LÜ Yukun, LI Jingang, SHI Jiuzhi, ZHANG Tingyu
    2017, 37(3): 242-248.
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    To solve the problem that the calculation model of a thermal system could not make a normal assessment on its performance caused by parameter failures on the measuring point, a dynamic hypersphere prediction model was established for the thermodynamic system of a certain 600 MW power unit based on its normal operation data, with which predicted values and similarity curves were obtained, while the reliability of the predicted values was verified, and the predicted values of measuring point were used as mining data to replace its failure values. Results show that the relative error of predicted values can be reduced and controlled within the allowable scope of actual engineering project, and the reliability of the failure data substitution can be improved by reasonable selection and proper supplementation of the normal historic data. This method can help to realize real-time assessment and fault diagnosis on operation performance of the thermodynamic system, in the case of random fluctuation or even individual fault of input parameters on the measuring point caused by the measurement system.
  • Fast Load Regulation of 1 000 MW Thermal Power Unit by Condensate Throttling
    LONG Dongteng, WANG Wei, LIU Jizhen
    2017, 37(3): 249-256.
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    A nonlinear model with a certain precision was established for thermal power unit and a feedback controller with multiple variables was designed to achieve coordinate control of the unit. By analyzing the static and dynamic characteristics of the condensate throttling process in a 1 000 MW unit, a transfer function between the unit load and condensate flow was obtained, and subsequently a controller was designed for the condensate channel. The dynamic characteristics of two control systems were verified at four load-up rates, while their IAE, ITAE and AGC evaluation index were compared. Results show that the scheme by condensate throttling can greatly improve the load-up rate, which is therefore beneficial for large-scale grid connection of new energy systems.