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  • 2019 Volume 39 Issue 1
    Published: 15 January 2019
      
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  • Visualized Research on Bubbling Characteristics in an Internally Circulating Fluidized Bed with Uneven Air Distribution
    LIU Dianfu, SUN Yongchun, ZHOU Chaoqun
    2019, 39(1): 1-6.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The bubbling characteristics in an internally circulating fluidized bed were visualizedly researched by digital image analysis, such as the shape, the movement track and the rising velocity of bubbles, as well as their size changes along bed height, etc. Results show that only in the high-velocity zone, a lot of bubbles moving upward are found to be produced in the internally circulating fluidized bed. The bubbles gradually expand along horizontal orientation and their sizes increase in the process moving upard along bed height. When the bubble moves upward, it may shift transversely, and the shift offset increases with the rise of air velocity in the high-velocity zone. The bubble's rising velocity changes greatly along bed height. Above results may serve as a reference for the design and operation of internally circulating fluidized beds.
  • Analysis on the Combustion Characteristics of Pulverized Coal Under O2/CO2 Atmosphere
    YING Zhi, ZHENG Xiaoyuan, CUI Guomin
    2019, 39(1): 7-12.
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    In the process of oxy-fuel combustion, the effects of atmosphere, oxygen concentration and coal type on the coal combustion characteristics were investigated using thermogravimetric analysis, while the combustion kinetics was studied for different temperature zones. Results show that the ignition of lignite and anthracite is of the heterogeneous kind, and that of the bituminous coal presents hetero-homogeneous features. Compared with air, the ignition temperature increases and the burnout time extends for pulverized coal in O2/CO2 atmosphere with the same O2 concentration. Under O2/CO2 atmosphere, both the ignition temperature and burnout temperature decrease while the burnout time shortens as the oxygen concentration rises. The coal type has significant effect on the ignition and burnout of coal under same atmosphere. In terms of combustion characteristic index S, increasing the oxygen concentration would improve the burnout rate of pulverized coal. In the low-temperature zone, the reaction order of pulverized coal is 0.3, while in the high-temperature zone, the reaction order lies in 1-2.5.
  • Simulation and Analysis on Boundary Layer Flow in Supercritical Units with Accelerated Corrosion
    XIAO Zhuonan, BAI Dongxiao, WANG Chao, HE Lijuan, CHEN Weipeng, XU Hong
    2019, 39(1): 13-16.
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    To solve the problems of water leakage and tube burst failures occurring in supercritical units at high pressures caused mainly by flow accelerated corrosion (FAC), an analysis was conducted from both micro and macro views to simulate the flow accelerated corrosion using Fluent software, and to study the effects of following factors on the flow accelerated corrosion, such as the temperature, flow rate, tube shape and boundary layer flow characteristics, etc. Results show that at 150℃, the Fe2+ concentration is relatively high in boundary layer, with smaller thickness of boundary layer, and severer corrosion in that place, indicating that flow accelerated corrosion is easy to occur at 150℃. The corrosion rate increases with rising flow rate. Flow accelerated corrosion appears more easily in tee tube compared with straight tube, and the severest corrosion generally occurs in the place where flow direction changes.
  • Modeling of a Load Control System for 350 MW Supercritical CFB Unit
    YAN Guodong, HONG Feng, GAO Mingming, CHEN Feng
    2019, 39(1): 17-24.
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    Taking a 350 MW supercritical CFB unit as an object of study, a model of load control system was established for the unit by studying the dynamic process of its coal feeding system, furnace heat release, steam-water system and steam turbine system based on mechanism analysis, and subsequently the identification of model parameters and the determination of partial unknown functions were realized by steady-state recognition, regression analysis and particle swarm optimization. Using actual operation data of the power plant, the model accuracy was verified and the model step tests were carried out on the Simulink simulation platform. Results show that the model output agrees well with actual output, indicating that the model can accurately reflect the operation characteristics of the unit, which is able to meet the design requirements of various control algorithms, thus providing a theoretical basis for the design of load control systems for supercritical CFB units.
  • DMD Analysis on Unsteady Flow Field in a Transonic Compressor Rotor
    LIU Zhenxiong, ZHU Xiaocheng, DU Zhaohui
    2019, 39(1): 25-32.
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    A dynamic mode decomposition (DMD) analysis was performed to investigate the unsteady flow field in the tip region of a transonic axial compressor rotor. Based on the spatial and temporal information as well as the spatial coherent structure in the tip region captured with DMD technology, and taking the results calculated for the unsteady flow field under low mass flow condition as the basic data, the DMD cloud map and characteristic frequency of streamwise velocity and radial velocity at 99% span were acquired, and subsequently the capability of DMD method was evaluated in analyzing the unsteady flow in the tip region of axial compressor rotor blade. Results show that DMD can obtain the frequency of the unsteady flow field in the tip region of blade, and the frequency of the second DMD mode is equal to the blade tip frequency under low mass flow condition; the frequency of other higher order modes is just multiples of the operating frequency. Among the first four DMD modes, the first mode is similar to homogenous flow field. The flow field oscillation is mainly caused under low-frequency mode; higher order modes are only supplementary information of field details. Within a period of oscillation, the unsteady flow field experiences alterative changes from positive velocity to negotive velocity in the tip region of blade.
  • A Kinetics Study on NOx Emission of an Axially-staged Gas Turbine Combustor
    QIAN Wenkai, ZHU Min, LI Suhui, DING Sheng, CUI Pihuan, LIU Xiangshan
    2019, 39(1): 33-40.
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    A chemical reactor network (CRN) model was established for the axially-staged combustor to study the effects of following key staging parameters on the NOx emission under typical operating conditions of advanced gas turbines, such as the fuel split, residence time split and flow rate split between the two stages. Results show that under constant exit temperature of combustor, the NOx emission could be reduced significantly when running the second stage hotter than the first one, by splitting more fuels to the second stage, and/or by shortening the residence time in the second stage through adjusting the layout of the second stage nozzles. In addition, poor mixing of the first-stage combustion products with the second stage mixture of fuel and air would remarkably affact the NOx emission reduction of the staged combustion system.
  • Simulation on Aerodynamic Performance of a Variable-pitch Axial Flow Fan with Circumferentially Skewed Blades
    LI Chunxi, FAN Fuwei, LIU Hongkai, YE Xuemin
    2019, 39(1): 41-49.
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    To improve the aerodynamic and acoustic performance of an axial flow fan, a comparative study was conducted on the aerodynamic performance and internal dynamics of an OB-84 single-stage variable-pitch axial flow fan with rear guide vanes before and after blade skewing, using Fluent software and Ansys finite element analysis, while the static structure features were investigated and the noise was predicted. Simulated results show that the total pressure rise is improved by the skewed blades and the promotion is apparent on the side of large flow rate; the best forward-skewed angle is 3.0° at the design point, in which case, the total pressure rise and the efficiency would be increased by 3% and 0.16%, respectively. The skewed blade improves the axial velocity, delays the emergence of separation flow in the region of blade root, raises the working ability in the middle and lower part of blades, and lessens the pressure difference between the suction surface and pressure surface in the tip region, leading to the effective reduction of tip leakage flow. The skewed blade has little influence on reducing the sound power level, but has a significant impact on the reduction of high-noise area, and thereby the fan noise is weakened.
  • Prediction Model for SCR Denitrification System Based on Mutual Information and Multiscale Wavelet Kernel Partial Least Squares
    DONG Ze, YAN Laiqing
    2019, 39(1): 50-58.
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    A prediction model was proposed for NOx emission of a selective catalytic reduction (SCR) denitrification system with features of complicated reaction process, non-linearity, large time-delay and strong disturbance under varying working conditions, based on the mutual information and multiscale wavelet kernel partial least squares (MWKPLS). Firstly, the time-delay of each input variable was estimated by mutual information estimator, and the phase space of model samples was reconstructed. Then, by introducing the multi-scale kernel and Morlet-parent wavelet kernel with strong ability to characterize the data trend, an MWKPLS modeling method was proposed based on the KPLS. For the optimization of model parameters, the fuzzy C-means clustering was used to divide samples into required number of scales, and 10-folds cross-validation and grid search were used to determine the wavelet scale. Based on simulation of benchmark datasets, the MWKPLS algorithm proposed was verified with field data of an SCR denitrification system. Results show that compared with other modeling methods, the MWKPLS has the features of strong generalization and anti-noise performance.
  • Experimental Study on De-NOx Characteristics of an SCR System for Coal-fired Units
    GAO Lisha, WANG Jixuan, GAO Xudong, GAO Yanfeng
    2019, 39(1): 59-64.
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    Numerical simulations and experimental tests were conducted on the selective catalytic reduction (SCR) system of a 1 000 MW ultra-supercritical unit to study its de-NOx performance, including a steam consumption model of liquid ammonia evaporator established for the de-NOx system, with focus on the effects of denitration efficiency on the NH3 mass flow and steam flow, inlet concentration of NO on the denitration efficiency, as well as NH3/NOx molar ratio, oxygen concentration and reaction temperature on the denitration efficiency and SO2/SO3 conversion rate. Results show that the temperature window is 360-370℃, and the optimal reaction temperature is 367℃. When the denitration efficiency is 80%, the NH3 mass flow and the steam mass flow would be 446 kg/h and 275 kg/h, respectively. The denitration efficiency increases with the rise of inlet concentration of NO. When NH3/NOx molar ratio is 1, the denitration efficiency would be 95.3%, and to ensure the denitration efficiency and ammonia escape rate, the NH3/NOx molar ratio should be controlled within 1-1.2. The denitration efficiency reduces and the SO2/SO3 conversion rate increases with rising oxygen concentration.
  • Study of Actuator Disc Method Based on Improved Turbulence Model
    REN Huilai, ZHANG Xiaodong, KANG Shun
    2019, 39(1): 65-71.
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    To solve the problem of overestimation of wake velocity in the actuator disc model, the source term in momentum equation was modified to accurately reflect the effect of wind turbine rotor on the incoming flow. The turbulence model was corrected by adding new source terms to the turbulence kinetic energy equation and the turbulence dissipation rate equation in the standard k-ε turbulence model, to make the formation and dissipation of turbulent kinetic energy coordinated with each other. The parameter C4ε in the dissipation rate equation was corrected from a constant to a certain distribution along radial direction. The wind tunnel experimental data were chosen to verify the simulation results and the wake flow field was analyzed under different arrangement conditions. Results show that under tandem arrangement, both the velocity loss and the turbulence intensity in the wake increase, which reduce with rising spacing. The influence of staggered arrangement on the turbulence intensity is greater than that on the velocity. Under staggered arrangement, an asymmetric profile of turbulence intensity occurs in the wake; the maximum deviation occurs in the case of 1D spacing, and the asymmetric phenomenon can still be observed even the spacing gets up to 4D.
  • Control and Parameter Optimization of the MTMD System for Floating Wind Turbines
    HUANG Zhiqian, DING Qinwei, LI Chun
    2019, 39(1): 72-78.
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    Taking the ITI Barge floating wind turbine as an object of study, a system of multiple tuned mass damper (MTMD) was established by configuring several tuned mass dampers (TMDs) with different parameters for the cabin and tower of wind turbine. Based on multi island genetic algorithm (MIGA), the parameters of MTMD system were optimized, and subsequently the stability of wind turbine was comparatively studied under the conditions without control, with ordinary MTMD control and with optimized MTMD control. Results show that MTMD has an obvious inhibition effect on the longitudinal displacement of tower and the rolling angle of platform, both of which reduce with rising mass of TMDs for the cabin and tower, and with the reduction of TMD damping. After the optimization of MTMD parameters, the stability of floating wind turbine is further enhanced, with the stability of longitudinal displacement at tower top and of platform roll angle improved by 80.4% and 83.8%, respectively.
  • Performance Analysis of an Organic Rankine Cycle Considering Evaporator Pressure Drop
    LI Peng, MEI Zhongkai, HAN Zhonghe, JIA Xiaoqiang
    2019, 39(1): 79-84.
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    Taking the ORC system with R245fa as working fluid driven by geothermal heat source as an object of study, the effect of evaporator pressure drop on the system performance was investigated. Results show that at a given evaporation temperature, both the thermal efficiency and the exergy efficiency of the system decrease and the pressure loss power increases with the rise of evaporator pressure drop, while the evaporation cost first decreases rapidly and then tends to be stable, indicating that there exists an optimal range of pressure drop where higher efficiency and less evaporator cost can be obtained simultaneously. The evaporator pressure drop decreases and the evaporator cost increases with the rise of evaporation temperature, and there exists an optimum range of evaporation temperature, where both higher efficiency and less evaporator cost can be achieved. With the rise of geothermal water temperature, the pressure drop of evaporator increases with rising increase rate. The evaporator cost reduces with decreasing size, and the decrease rate rises gradually.