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    Boiler Technology
  • Boiler Technology
    Wobble Mechanism of Pressure Drop in Furnace of a Large Scale CFB Boiler
    LI Jin-jing, L Jun-fu, GONG Peng, MI Zi-de, ZHANG Qing-feng
    2013, 33(4): 245-249.
    Abstract ( )   Knowledge map   Save
    To study the mechanism of pressure drop wobble occurring under specific working conditions in furnace of a large scale CFB boiler that adopts the design of single riser and parallel cyclones, a mass balance model was built up for the main loop of CFB boiler. Based on the data collected from industrial tests, the rates and directions of lateral mass flow in the CFB riser were analyzed qualitatively. Results show that the wobble of bed inventory is mainly due to lateral mass transfer caused by the unbalance of gas-solid flow at both sides of the furnace. The mass transfer between furnace and loopseal delays the process of pressure drop wobble.
  • Boiler Technology
    Analysis and Calculation of Heat Storage in Supercritical Once-through Boilers
    QIN Zhi-ming, LIU Ji-zhen, ZHANG Luan-ying, GU Jun-jie
    2013, 33(4): 250-255.
    Abstract ( )   Knowledge map   Save
    By dividing the evaporating surface of supercritical once-through boiler into cold-water, density-change and overheat-steam three sections according to thermal properties of water and steam, a lumped-parameter model was built up for the evaporating surface, separator and superheater through mechanism analysis and model simplification, with which the heat storage coefficient of boiler was calculated under different loading conditions based on design data of boiler structure. Application results to a 1 000 MW supercritical unit show that the heat storage of working medium in boiler water wall varies more greatly along with the pressure at subcritical pressure than at supercritical pressure; the heat storage capacity of metal material is much higher than working medium; the superheater collects about 70% heat of the whole boiler; the heat storage coefficient of supercritical boiler reduces with rising pressure.
  • Boiler Technology
    Slagging Characteristics of Coal Ash with Different Alkali/Acid Ratios on Corundum-based Refractory Liner
    CHEN Dong-lin, DU Yang, ZOU Chan, CAI Yang
    2013, 33(4): 256-260.
    Abstract ( )   Knowledge map   Save
    Slagging characteristics of two kinds of coal ash with different alkali/acid ratios were studied on corundum-based refractory liner in Muffle furnace in air at 1 350 ℃ for 40 h, after which the slag morphology and composition were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). Results show that the coal ash with higher alkali metal content has lower viscosity, stronger liquidity and therefore may severely erode the refractory liner; elements in melting ash infiltrate into the liner, distributing in a reducing atomic percentage along the liner depth; the little Cr2O3 contained in refractory liner may penetrate into coal ash and subsequently form there (Al0.9Cr0.1)2O3 with high melting point and high viscosity, which helps to prevent the liner from erosion by coal ash.
  • Boiler Technology
    Investigation on NOx Formation Characteristics Under Air-staged Combustion
    SUN Bao-min, WANG Ding-hui, DUAN Er-peng, GUO Yong-hong,CAO Wei-hua, ZHANG Shou-heng
    2013, 33(4): 261-266.
    Abstract ( )   Knowledge map   Save
    NOx formation characteristics were studied under air-staged combustion by numerical simulation, during which the NOx formation rate around the burner and in the whole furnace was analyzed, so as to obtain the NOx formation characteristics at different over-fire air rates. Results show that NOx is mainly generated at the initial stage of combustion; NOx reduction will occur when the fuel and O2 are mixed insufficiently; seen from the whole furnace, the formation rate of fuel NOx is significantly higher than that of thermal NOx; fuel NOx is formed in both the main combustion zone and the burn-out zone, while thermal NOx produced almost only in the main combustion zone where the temperature is extremely high; moreover, the sensitivity of thermal NOx to the O2 volume fraction is weaker than that of fuel NOx; the major control factors on NOx formation rate in the main combustion zone and burn-out zone are respectively the O2 volume fraction and the coke combustion rate; with the rise of over-fire air rate, both the NOx formation rate and NOx formation region reduce in the main combustion zone, with an increased reduction region and a decreased mass concentration of NOx emission.
  • Boiler Technology
    Study on NOx Emission from CFB Boilers Based on Support Vector Machine and Fruit Fly Optimization Algorithm
    NIU Pei-feng, MA Hong-bo, LI Guo-qiang, MA Yun-fei, CHEN Gui-lin, ZHANG Xian-chen
    2013, 33(4): 267-271.
    Abstract ( )   Knowledge map   Save
    To control the NOx emission from circulating fluidized bed (CFB) boilers, a model was established based on test data of a 300 MW thermal power plant using support vector machine (SVM). To overcome the deficiency of SVM regression prediction in artificial determination of relevant parameters, the fruit fly optimization algorithm (FOA) was applied to optimize the SVM parameters. Prediction performance of the FOA-SVM model was then verified with sample data under different experimental conditions, of which the prediction results were compared with those optimized by particle swarm optimization (PSO), genetic algorithm (GA) and gravitation search algorithm (GSA). Results show that the FOA-SVM model has stronger genralization capability, higher prediction accuracy and shorter training time, which may therefore predict the mass concentration of NOx emission quickly and accurately.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Steam Enthalpy Calculation Model for Wet Steam Region of Steam Turbines
    ZHANG Le-le, ZHANG Yan-ping, HUANG Shu-hong, GAO Wei
    2013, 33(4): 272-277.
    Abstract ( )   Knowledge map   Save
    To accurately determine the extraction and exhaust enthalpy in wet steam region of steam turbines, a new calculation model is proposed based on the concept of stage indicative relative internal efficiency and the method of both energy balance and curve extrapolation, with which calculations were performed for steam turbine under various conditions. Results show that this model demands little on initial iterative values by energy balance method, and has a good adaptability under various conditions, of which the calculation precision for both the regenerative extraction enthalpy in wet steam region and the exhaust enthalpy of low-pressure casing is higher than that of other existing models.
  • Steam Turbine and Gas Turbine
    Application of Morphological Filtering in Denoising of Acoustic Emission Signals for Sliding Bearing
    LU Xu-xiang, LIU Yu-jia, LI Lu-ping, CHEN Zhen-nan, HUANG Zhang-jun
    2013, 33(4): 278-284.
    Abstract ( )   Knowledge map   Save
    To overcome the deficiency of sudden noise interference and huge computation contained in acoustic emission signals for condition monitoring of sliding bearings, a morphological filter was used to denoise the signals. Real-time morphology filtering was carried out with optimized filter for acoustic emission signals of sliding bearing obtained during field testing of a 310 MW turbine-generator set, based on which time-domain characteristic parameters were real-timely calculated for No.4 sliding bearing in the process of speed increasing, such as the root mean square value VRMS, peak value Vc and kurtosis factor Fk, etc. Denoising effect of the optimized morphological filter was finally compared with that of wavelet filtering. Results show that the optimized morphological filter with reasonably selected structure elements can well denoise acoustic emission signals, retain their original characteristics, and produce better filtering effect than wavelet filter. The real-time characteristic parameters obtained by morphological filtering help to diagnose lubrication faults of sliding bearings rapidly and accurately, which therefore may serve as a reference for actual condition monitoring of sliding bearing with acoustic emission signals.
    • Automatical Controlling and Detecting Diagnosis
  • Automatical Controlling and Detecting Diagnosis
    PID Parameter Optimization for Main Steam Temperature Control System Based on Immune Vaccine Algorithm
    YUAN Gui-li, XUE Yan-guang, LIU Ji-zhen, ZHANG Jian
    2013, 33(4): 285-289.
    Abstract ( )   Knowledge map   Save
    To improve the thermal efficiency of main steam temperature control system, an adaptive immune vaccine algorithm (AIVA) was proposed based on adaptive genetic algorithm (AGA) by introducing the immune memory cell, vaccine extraction operator and vaccine vaccination operator according to immune principles, of which the convergence was subsequently proved. The algorithm was then used to optimize the PID parameters of main steam temperature control system, and the corresponding results were compared with that of the adaptive immune genetic algorithm (AIGA). Results show that the convergence of AIVA is more stable than AIGA, and the control effect on PID parameters generated by AIVA is also better than that by AIGA due to both its shorter adjustment time to step response and its more stable transition process, which prove this algorithm to be effective.
    • Environmental Science
  • Environmental Science
    Efficiency Prediction of Ammonia Flue Gas Desulfurization Based on Adaptive PSO-BP Model
    HONG Wen-peng, CHEN Zhong
    2013, 33(4): 290-295.
    Abstract ( )   Knowledge map   Save
    To improve the prediction accuracy of ammonia flue gas desulfurization(FGD) efficiency, a BP neural network model was established by taking 8 main operation parameters as the input variables, following which a new PSO-BP model was set up based on particle swarm optimization(PSO) algorithm via optimization on the weight of the previously-established BP network model. The new PSO-BP model was verified with 20 sets of operation data from a desulfurization system of power plant. Results show that network local minimum can be avoided by using PSO algorithm to optimize the weight and threshold of BP neural network, thus the generalization capability of network can be improved, and subsequently high accuracy can be obtained in predicting ammonia FGD efficiency by using PSO-BP model.
  • Environmental Science
    Experimental Study on NO Reduction by Biomass Char Reburning
    WANG Qin-chao, LU Ping, HUANG Zhen, QI Hai-ming, LI Chen-liang
    2013, 33(4): 296-302.
    Abstract ( )   Knowledge map   Save
    Nitric oxide (NO) removal characteristics were studied in an entrained flow reactor at an initial NO volume fraction of 1×10-4-3×10-4 by reburning various kinds of biomass, such as the mixture of wood chips char and sawdust (WCC), rice straw (RS), mulberry branch char (MBC) and bamboo char (BMC), etc., during which the influence of following factors on the NO removal was analyzed, like the category and particle size of reburning fuel, reaction temperature (t2) and lingering time (τ) in the reburning zone, and so on. Results indicat that among all the four kinds of biomass tested, the strongest reduction effect can be obtained by reburning WCC with a highest NO removal efficiency of 63.4%, followed by RS and BMC, and MBC has nearly no effect on NO reduction; the smaller the particle size, the higher the NO removal efficiency; NO removal efficiency decreases with reducing initial NO volume fraction, how-ever, when the initial NO volume fraction drops below 1×10-4, the removal efficiency by RS rises instead; NO removal efficiency increases with rising temperature in reburning zone within the range of t2=950-1 250 ℃, which reduces with shortening τ in the range of τ=0.4-0.8 s, and at τ=0.4 s, the efficiency will be less than 10%. To guarantee a reasonable NO removal efficiency, it is recommended that the reaction temperature and lingering time in the reburing zone of WCC be set at 1 150 ℃ and 0.8 s, respectively.
    • Energy System Engineering
  • Energy System Engineering
    Analysis on Energy Consumption and Thermal Cost of Seawater Desalination System in Thermal Power Units
    CHEN Hai-ping, LAN Jun-jie, ZHANG Cai, ZHONG Ya-juan
    2013, 33(4): 303-308.
    Abstract ( )   Knowledge map   Save
    Taking a 600 MW subcritical thermal power unit and its seawater desalination system as an object of study, the energy consumption characteristics were investigated based on basic thermodynamic principles, while a power-water heat consumption allocation model and a seawater desalination thermal cost calculation model established based on mass unit, and a sensitivity analysis carried out by taking the unit load, water generation ratio and coal price as the sensitive elements. Results show that for a fixed amount of steam extraction, the seawater desalination cost increases with reducing unit load; for a fixed unit load, the seawater desalination cost decreases slightly with rising amount of steam extraction; the total cost of water production by seawater desalination increases significantly with growing unit price of standard coal; the water generation ratio has a relatively great influence on the thermal cost of seawater desalination, which reduces significantly with the rise of water generation ratio at different loads.
  • Energy System Engineering
    Economic Analysis on Ejector Cold-Power Cogeneration System with Low-temperature Heat Sources
    ZHANG Xin-ming, DING Chong-an, HONG Guang, YOU Fei
    2013, 33(4): 309-315.
    Abstract ( )   Knowledge map   Save
    A thermodynamic model was established for the low-temperature heat-source ejector cold-power cogeneration system, based on which the system economy was analyzed by taking the ratio Rap of total heat-exchanger area to available output and the ratio Rvp of expander inlet specific volume to available output as the target functions, and by selecting five organics as the working fluid. Results show that for a power-cold ratio r=0.5, there exists an optimal condensation temperature tc=30 ℃ and an optimal refrigeration evaporation temperature te=8 ℃, when R600 is the optimum working fluid. The low-temperature heat-source ejector cold-power cogeneration system applies to occasions where the power-cold ratio is relatively low.
    • Nuclear Technology
  • Nuclear Technology
    Numerical Analysis on Thermal-Hydraulic Behavior of Supercritical Fluid in 7-rod Bundles
    WANG Lei, GU Han-yang
    2013, 33(4): 316-321.
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    Based on heat-transfer data of supercritical freon in 7-rod bundles, numerical analysis on thermal-hydraulic behavior of the supercritical fluid was carried out in three typical cases using ω-type turbulence models SST and RSO, and ε-type turbulence models RNG and SSG. Results show that the ω-type turbulence models treated by low-Reynolds number modeling method can qualitatively reveal the heat-transfer deterioration phenomenon in the near-wall region, while the wall function method can not. Due to the asymmetry of thermal boundary condition and the influence of strong buoyance in 7-rod bundles, the mass flux distributes non-uniformly in different channels, and the heat-transfer characteristics between the central and surrounding rod have significant difference. To accurately predict the heat-transfer characteristics of supercritical fluid in the rod bundles, especially the typical heat-transfer deterioration phenomenon, emphases should be laid on improving the treatment methods for near-wall area of turbulence models.
  • Nuclear Technology
    Performance Optimization for 2D Diffuser of a 1 100 MW Nuclear Power Turbo-Generator Based on CFD Method
    HU Lei, ZHANG Xiao-hu, HU Jian-bo, YUAN Jian-hua, YUAN Yi-chao
    2013, 33(4): 322-329.
    Abstract ( )   Knowledge map   Save
    A 2D numerical model was established for the diffuser of a 1 100 MW nuclear power turbo-generator using CFD commercial software, so as to study the flow characteristics and performance parameters of the preliminarily designed diffuser under design conditions. Simultaneously, profiles of the both side planes were parameterized and analyzed according to the cubic Bezier curve, during which a group of profiles with excellent flow properties were obtained. Results show that for different types of profile, the main parameters play opposite roles in influencing the flow properties. Compared with the preliminary diffuser, the outlet velocity distribution of optimized diffuser has been improved greatly, with a reduction of total pressure loss coefficient by 83.92% and an increase of static pressure recover coefficient by 20.83%.