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    Boiler Technology
  • Boiler Technology
    Numerical Simulation on NOx Distribution in a 660 MW Ultra Supercritical Opposed Firing Boiler
    LI Debo, SONG Jinghui, XU Disheng, DENG Jianping, WEN Zhiyong
    2013, 33(12): 913-919.
    Abstract ( )   Knowledge map   Save
    The distribution of NOx concentration in a 660 MW ultra supercritical opposed firing boiler was numerically simulated using Ansys fluent 14.0 software, of which the results were compared with actual measurements. Results show that the simulated results agree well with actual measurements, proving the simulation method to be effective. NOx concentration in combustion zone of the first layer is higher than other two layers, which, at the combustor outlet, gets up to 0.001 rapidly; volumetric concentration of NOx reduces gradually along the furnace height, starting from the combustor in the first layer; maximum NOx concentration appears in the area near rear wall above combustion zone of the second layer.
  • Boiler Technology
    Study and Prediction on Solids Circulation Rate in Dual Circulating Fluidized Bed with Cone Air Distributor
    CHEN Hongwei, ZHANG Zhicai, LI Zhongmeng, YAN Jingbo, CUI Caiyan
    2013, 33(12): 920-925.
    Abstract ( )   Knowledge map   Save
    Experimental tests were carried out on a cold-state setup of dual circulating fluidized bed (DCFB) with cone air distributor, so as to study the effects of following factors on the solids circulation rate in the riser, such as the air velocity in riser, air velocity in gasifier, material mass and particle size, etc., of which the results were compared with that of the DCFB with horizontal air distributor. Moreover, models were built up based on three improved BP neural network algorithms to predict the solids circulation rate. Results show that the solids circulation rate increases with rising air velocity in both the riser and the gasifier, but the acceleration rate slows down when the air velocity reaches a certain value; the solids circulation rate increases linearly with rising material mass, but significantly reduces with increasing particle size; cone air distributor has advantages over horizontal air distributor, which helps to raise the solids circulation rate under same conditions; BFGS Quasi-Newton algorithm is found to have the best prediction effect, with which the maximum relative error of solids circulation rate between predicted and experimental data is 7.703 5% and the mean relative error is 3.594 3%.
  • Boiler Technology
    Study on Optimization of Flue Gas Oxygen Content for a 600 MW Coal-fired Boiler
    LI Lu, LI Yonghua, DING Yanjun, GU Lijing, ZHANG Qishi
    2013, 33(12): 926-931.
    Abstract ( )   Knowledge map   Save
    Taking a 600 MW coal-fired power unit as an example, the influence of flue gas oxygen content upon economic efficiency of the boiler was analyzed based on adjustment tests of the oxygen content, the primary air ratio, the secondary air ratio and the opening degree of overfire air damper, after which some strategies were put forward and taken for optimization of the flue gas oxygen content. Results show that for the load of 400 MW, 500 MW and 600 MW, corresponding optimum oxygen content in flue gas is respectively 3.8%, 3.2% and 2.3%, under which condition, the power generation cost, the fan power consumption rate and the NOx emission concentration are to be lowered, resulting in increased overall thermo-economic parameters of the boiler. This may serve as a reference for safety operataion, energy conservation and emission reduction of similar coal-fired boilers.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Bearing Load Identification Based on Shaft Alignment Measurements
    LI Yanyong, YANG Jiangang, DONG Chuan, PENG Bin
    2013, 33(12): 932-935.
    Abstract ( )   Knowledge map   Save
    A bearing load identification model was established using transfer matrix method based on shaft alignment measurements of a turbo-generator unit, in which the bearing elevation was first identified with alignment data, and then the bearing load was calculated with the bearing elevation. Taking a 350 MW turbo-generator unit as an example, calculations were conducted so as to analyze the difference influence of coupling sag and gap on the bearing load, as well as to analyze the load distribution under three differenet alignment conditions. Results show that the bearing elevation and load can be identified with shaft alignment measurements via this method; both the differences of coupling sag and gap are 0 under ideal alignment status; bearings No.1 and No.2 have close jacking oil pressures during low-speed turning process after maintenance, and their load distributions are basically uniform; the vibration of shafting is stable under full-load operation, in which case, abrupt unstable vibration is eliminated.
  • Steam Turbine and Gas Turbine
    Stability Analysis of Centrifugal Compressor with Vaneless Diffuser
    LIU Haiqing, GAO Chuang, ZHANG Hongwu, HUANG Weiguang
    2013, 33(12): 936-941.
    Abstract ( )   Knowledge map   Save
    Performance and stability of a centrifugal compressor with vaneless diffuser were numerically analyzed in combination with experimental data, while flow characteristics inside the vaneless diffuser compared between design point and near stall point. Results show that collapse pressure first appears at diffuser inlet in a moment when surge occurs; the inlet flow, especially the cover side flow of diffuser is the key factor that leads to instability of the compressor; backward steam injection at diffuser inlet can increase the operation stability of the diffuser.
  • Steam Turbine and Gas Turbine
    Experimental Research on Non-equilibrium Plasma-assisted Fuel Reforming
    ZHANG Yulong, LIU Qian, ZHENG Hongtao, YANG Ren, CHEN Xi, ZHANG Zhibo
    2013, 33(12): 942-946.
    Abstract ( )   Knowledge map   Save
    A series of experiments were conducted based on dielectric barrier discharge (DBD) catalytic fuel reforming test platform, so as to study the effects of following factors on the effective carbon recovery rate, methane conversion rate and product selectivity, such as the ratio of n(H2O)/n(CH4), wall temperature, residence time,input power and frequency, etc. Results show that the effective carbon recovery rate may reach 96% when the residence time is 0.29 s, which reduces linearly with rising residence time; the methane conversion rate can be promoted by increasing the residence time, the n(H2O)/n(CH4) or the input power; for a residence time of 0.59 s, the methane conversion rate is more than 20% under different operation conditions, and the selectivity of H2, C2+C3 and CO is respectively 20%, 20% and 4%, with C4+heavy hydrocarbons generated.
    • Automatical Controlling and Detecting Diagnosis
  • Automatical Controlling and Detecting Diagnosis
    Mechanism Modeling and Quantitative Feedback Control for Fuel-Water Ratio Control System of Supercritical Once-through Boilers
    GU Junjie, CAO Xiaowei, WANG Pizhou, CAO Xiaoguang
    2013, 33(12): 947-954.
    Abstract ( )   Knowledge map   Save
    Supercritical once-through boiler can be regarded as an uncertain nonlinear system, due to constant changes of its parameters under the condition of variable load operation. A simplified model for control of 600 MW supercritical unit was analyzed with the method of partially decentralized control, and the rationality of separate modeling based on the effects of dynamic characteristics of fuel quantity on the intermediate point temperature was substantially demonstrated. By taking the effect of fuel flow change on outlet temperature of water wall as the object of study, the dynamic mechanism was analyzed and a dynamic model was established, and the variation range of the model with uncertainties was determined through calculation of transfer function under three typical working conditions. Parameters of feedback controller and pre-filter in fuel-water ratio control system were calculated by applying quantitative feedback theory to the fuel-water ratio control, and in combination with the given design performance index. Results show that the intermediate point temperature of boiler can track given signals rapidly with high accuracy under various loads. The system is featured by strong robustness, good control performance and facile application.
  • Automatical Controlling and Detecting Diagnosis
    A Simplified Nonlinear Dynamic Model for Once-through Boiler Units
    QIN Zhiming, LIU Jizhen, ZHANG Luanying, GU Junjie
    2013, 33(12): 955-961.
    Abstract ( )   Knowledge map   Save
    Taking the 1 000 MW ultra supercritical power unit as an example, a simplified three-input three-output non-linear dynamic model was developed for the once-through boiler unit operating in a wide range of conditions, based on mechanism analysis and actual operation data, and by studying the dynamic characteristics of the pulverizing system, the heat-absorbing surface, the superheating surface and the steam turbine, etc., which takes the fuel flow rate, the total feed water flow and the valve opening of turbine governor as input variables, the outlet specific enthalpy of steam-water separator, the main steam pressure and the turbine power as output variables. Static parameters of the model were determined with steady-state operation data of unit, while the dynamic parameters identified using data obtained during violent fluctuation of load. Meanwhile, step response tests were performed to verify the model, of which the results were compared with actual measurements. Results show that the model can well reflect the dynamic and nonlinear characteristics of the unit, with features of simple structure, easy calculation of parameters and good reproducibility.
    • Engineering Thermophysics
  • Engineering Thermophysics
    Bubble Characteristics of Syngas During Passing Through Cistern in Gasifier
    WU Xuan, GAO Huijie, WANG Lifang, LI Haiguang, WU Wenfei
    2013, 33(12): 962-968.
    Abstract ( )   Knowledge map   Save
    Bubble characteristics of dusty gas during passing through a cistern via downcomer were numerically studied, including the process of bubble formation, bubble breaking and droplet splashing, etc., so as to analyze the influence of following factors on the bubble distribution and gas-liquid interface area, such as the gas velocity, static state liquid level and sudden expansion ratio, etc. Results show that the axial distribution of gas holdup has a turning point with the change of gas velocity. The gas holdup drops with the reduction of sudden expansion ratio in the region above liquid level, which, on the contrary, rises under same conditions in the region below liquid level. The gas-liquid interface area increases with rising gas velocity and static state liquid level, and with reducing sudden expansion ratio.
  • Engineering Thermophysics
    Study on Heat-transfer Performance of ORC Direct Contact Evaporators
    HUANG Junwei, WANG Huitao, WANG Hua, XU Jianxin, GE Zhong
    2013, 33(12): 969-973.
    Abstract ( )   Knowledge map   Save
    To analyze the heat-transfer performance of dispersed phase in continuous phase within ORC direct contact evaporator for low-temperature waste-heat power generation, the environmental-friendly refrigerant R245fa and heat-transfer oil THERMINOL66 were respectively taken as the dispersed phase and continuous phase, with which the influence of following factors on the volumetric heat-transfer coefficient of ORC direct contact evaporator was analyzed, such as the initial temperature difference, the refrigerant flow rate and the oil flow rate, etc. Results show that the volumetric heat-transfer coefficient rises first, drops later on, and finally tends to be stable, always being larger than the coefficient at initial period; for a fixed refrigerant flow rate and initial temperature difference, the flow rate of heat-transfer oil should be controlled within a narrow range so as to obtain higher volumetric heat-transfer coefficient of ORC direct contact evaporators.
    • Environmental Science
  • Environmental Science
    Numerical Prediction on Mass Fraction of Condensed Acid Solution After Flue Gas Desulfurization
    ZHAO Yi, MA Tianzhong, MENG Linghai
    2013, 33(12): 974-979.
    Abstract ( )   Knowledge map   Save
    The degree of stack corrosion can be predicted by determining the inside concentration of condensed acid solution, however, it is generally difficult to acquire such a representative sample of condensed acid solution from the stack. To solve this problem, the concentration of condensed acid solution from flue gas of a 300 MW boiler with wet flue gas desulfurization system was numerically simulated using fixed fugacity equation and matlab software, so as to analyze the effects of following factors on the concentration of condensed acid solution, such as the water vapor concentration in flue gas, wall temperature and absolute pressure of flue gas, etc. Results show that the concentration of condensed acid solution increases with reducing water vapor concentration in flue gas, rising wall temperature and with reducing absolute pressure of flue gas. The predicted values agree well with those in relevant literatures, which prove the model to be applicable in mass concentration prediction of similar condensed acid solution.
    • Material Science
  • Material Science
    Statistical Analysis on Creep Rupture Life of 2.25Cr-1Mo Steel on the Basis of Parameter Regression Models
    ZHENG Kaiyun, WU Zhiying
    2013, 33(12): 980-988.
    Abstract ( )   Knowledge map   Save
    Creep rupture lives of 2.25Cr-1Mo (T22) steel were statistically analyzed, through Manson-Haferd time-temperature parameter method, on the basis of Log-Normal, Weibull, Exponential, Gamma and Log-Logistic distribution parameter regression models, and subsequenty a comparison was made to the dependence of creep rupture time on the temperature and stress, the goodness-of-fit, and the median and 5th percentile of creep rupture time among selected models. Results show that all the distribution models except Exponential distribution are suitable for prediction of the creep rupture time, and the predited medians with the 4 models are very close, but their predictions on lower percentiles are different, expecially on scattered data, and the lower percentiles predicted with Weibull model are significantly lower than those with other models. Therefore, the creep rupture lifetime and long-term stress of 2.25Cr-1Mo steel should be comprehensively analyzed based on multiple distribution models.
    • Nuclear Technology
  • Nuclear Technology
    Matrix Algorithm for Exergy Loss Distribution in Thermal System of PWR Nuclear Power Units
    LI Yonghua, PU Liang
    2013, 33(12): 989-998.
    Abstract ( )   Knowledge map   Save
    Based on exergy analysis method and matrix algorithm, a general matrix equation of exergy loss distribution in thermal system of pressurized water reactor (PWR) nuclear power units was established, with which calculation and analysis were carried out for a 900 MW PWR nuclear power unit, and subsequently exergy loss distribution in the thermal system and relevant equipment were obtained under rated conditions. Results show that the exergy loss in nuclear reactor is the largest, accounting for 50.85% of the total nuclear exergy, followed by turbo-generator, steam generator and condenser, respectively accounting for 6.17%, 3.2% and 2.55%. Compared with traditional exergy analysis methods, the matrix algorithm has advantages in simple structure, convenient element filling of matrix, explicit physical meanings and obvious regularity. With the equation, relative calculation programs can be developed, which therefore may serve as a reference for development of energy-saving potential and for fault diagnosis in nuclear power units.