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    Boiler Technology
  • Boiler Technology
    Stability Analysis on CFB System with Two Cyclones in Parallel
    HU Nan, LIU Xuemin, YANG Shi, CAO Peiqing, BAI Yang, L Junfu, YANG Hairui
    2013, 33(7): 497-501.
    Abstract ( )   Knowledge map   Save
    Non-monotonic characteristic curves of pressure drop in cyclone of a circulating fluidized bed (CFB) system were measured using transient-blowing method, while relationship between the cyclone pressure drop and solid mass flow studied under specific gas mass flow with corrected model based on cyclone pressure drop approach proposed by Chen. Meanwhile, the stability of CFB system with two cyclones in parallel was analyzed according to the law of mass conservation and constraint conditions as equality in pressure drop of all cyclones, and the least-energy principle, etc. Results show that with the rise of inlet solid mass flow, the cyclone pressure drop first decreases quickly and then increases slowly; the calculated values of cyclone pressure drop based on corrected model fit well with experimental results; when the cyclone pressure drop and circulating flow rate of CFB system are in deviation region, the CFB system will run stably in deviation flow state.
  • Boiler Technology
    Experimental Study on CO and NOx Emission of a Swirl-opposed Coal-fired Boiler
    LI Debo, SHEN Yueliang
    2013, 33(7): 502-506.
    Abstract ( )   Knowledge map   Save
    To solve the problems occurring in the swirl-opposed coal-fired boiler of a 600 MW supercritical power unit, such as high and even peak mass concentration of CO in local area of the furnace, obvious deviation of CO mass concentration between left and right side along its width direction, and great changes of CO concentration under different conditions of oxygen volume fraction, etc., corresponding countermeasures were proposed by analyzing the effect of oxygen volume fraction and overfire air volume on the CO and NOx mass concentration. Results show that the high mass concentration of CO is found to be caused by uneven air distribution, which can be improved by turning down the secondary air damper of the side air port, and the secondary and tertiary air damper of the after air port, comprehensively considering the varition tendency of CO and NOx mass concentration, the case of φ(O2)=3.0% is considered to be appropriate.
    • Turo-Generator
  • Turo-Generator
    Study on Life Prediction of Class F Insulation for Stator Coils of Large Turbo-Generators
    SHI Jinyuan
    2013, 33(7): 507-516.
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    Ageing factors and accelerated life-test methods of class F insulation for stator coils of large turbo-generators are presented, while corresponding accelerated test data of both electrical ageing and generalized thermal ageing summarized and analyzed using Weibull distribution model, and simultaneously relevant characteristic parameters of the life calculation formulae determined by reliability and non-linear regression statistics methods. Based on the life expenditure accumulation theory, an introduction is presented to a life prediction method for simultaneous electrical ageing and generalized thermal ageing of class F insulation for stator coils of turbo-generators, and to the life expenditure assignment scheme for class F insulation of water cooled stator coils. The lower life limit of class F insulation for water cooled stator coils affected mainly by electrical ageing is studied under 2 UN and 3 UN conditions. Results show that with above prediction method, the life of class F insulation for stator coils of large turbo-generators can be quantitatively predicted and assessed in the design, manufacture and service stages, thus providing a scientific basis for life determination and extension of relevant insulation in large turbo-generators.
    • Automatical Controlling and Detecting Diagnosis
  • Automatical Controlling and Detecting Diagnosis
    Mathematical Model Based on Neural Network for Supercritical Unit
    MA Liangyu, GAO Zhiyuan
    2013, 33(7): 517-522.
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    Taking a 600 MW supercritical unit as an object of study, a mathematical model was set up for the unit load and steam pressure characteristics based on neural network, which was subsequently trained with large amount of data obtained under wide-range varying load conditions. Simulation results show that the model can well fit the complex non-linear dynamic characteristics between unit load, main steam pressure and the fuel supply, feedwater flow and turbine governing valve opening with high precision and strong generalization ability, which therefore may serve as a prediction model for design of intelligent controller in supercritical units.
  • Automatical Controlling and Detecting Diagnosis
    Influence of Salt Content on Steam Wetness Measurement by Microwave Cavity
    QIAN Jiangbo, HAN Zhonghe, LI Hengfan, ZHANG Meifeng
    2013, 33(7): 523-529.
    Abstract ( )   Knowledge map   Save
    The existence of salt content in turbine exhaust may change the dielectric properties of the wet steam, and may subsequently affect the wetness measurement results. The influence of electrical conductivity on both the dielectric properties of wet steam and the wetness measurement precision were quantitatively analyzed by introducing the electrical conductivity into the pure steam complex permittivity formula and the wetness measurement formula. Results show that the real part of the complex permittivity increases with rising microwave wavelength, conductivity, wetness and temperature, whereas the imaginary part first increases and then decreases with the rise of microwave wavelength, which increases with rising conductivity, wetness and temperature; the measurement deviation of steam wetness increases with rising conductivity and wetness, and with reducing temperature and working frequency. The existance of salt content in turbine exhaust has little effect on the complex permittivity, when high precision may be achieved in the wetness measurement.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Influence of Abnormal Blade Installation Angle on Aerodynamic and Acoustic Characteristics of Axial Flow Fan Under Variable Working Conditions
    LI Chunxi, YIN Pan, YE Xuemin
    2013, 33(7): 530-538.
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    Based on Reynolds time-averaged equation and Realizable k-ε turbulent model, the internal dynamics and operating performance of an OB-84 axial flow fan with rear guide vane were numerically simulated in full flow passage by considering the effect of abnormal installation angle of single blade. Results show that the total pressure and efficiency tend to decrease with the rise of installation angle deviation Δβ, and the effect of cocurrent deviation is generally more remarkable than that of countercurrent deviation. The deviation of installation angle may cause deformation of total pressure and acoustic distribution, and with the rise of Δβ, the deformed region may be expanded from the lower pressure and higher noise region in circumferentially adjacent flow passage to the lower pressure and higher noise strips covering the circumferential downstream multi-passages. With the increase of flowrate, the influence of installation angle deviation is different on the internal dynamics and operating performance of axial flow fan.
  • Auxiliary Equipment Technology
    Experimental Study on Particle Fouling in Plate Heat Exchangers
    XU Zhiming, DONG Bing, DU Xiangyun, WANG Binglin
    2013, 33(7): 539-543.
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    Taking the solution of nano-magnesium oxide particles as the working medium, experimental study on particle fouling in plate heat exchangers was carried out so as to analyze the influence of particle concentration, particle size, flow velocity and medium temperature on the particle fouling resistance. Results show that the particle fouling in plate heat exchangers has no obvious induction period; both the scaling rate and the asymptotic fouling resistance increase with the rise of particle concentration, in a lowering gradient; the particle size has relatively obvious effect on the fouling resistance; for a fixed mass concentration of particles, the smaller the particle size is, the higher the scaling rate and fouling resistance will be; the influence of flow velocity on the fouling resistances is relatively complex; the scaling rate at a higher flow velocity is slightly greater than that at a lower flow velocity, and the asymptotic fouling resistance is smaller under the former condition than that under the latter condition; the temperature of low-temperature medium has no obvious effect on the particle fouling resistance.
    • New Energy
  • New Energy
    Experimental Study on Evaporation Characteristics of Inclined Falling Film
    NI Mingjiang, WANG Fei, XIAO Gang, ZHU Weijun, WANG Xihui, CEN Kefa
    2013, 33(7): 544-549.
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    Evaporation characteristics of inclined falling film were studied under various working conditions by adopting electric heat instead of solar energy, while the still's distillate production rate predicted using Dunkle model based on temperature distribution of the liquid film and condensing surface by dividing both the heat-absorbing and the condensing surface into evenly-spaced segments. Results show that the heat flux density, feed water flow, inclination angle, and cooling water flow are the main factors affecting the distillate production rate, which increases linearly with the rise of heat flux density; when the feed water flow is within 5.5-10.0 kg/(h·m), the distillate production rate increases linearly with the decrease of feed water flow, whereas when the feed water flow is within 0.7-5.5 kg/(h·m), the distillate production rate basically remains unchanged; In the range of inclination angle varying from 15° to 60°, the distillate production rate increases as the inclination angle increases; The still's distillate production rate would be improved when the cooling water uniformly flows through upper half of the condensing surface. The more segments the heat-absorbing and the condensing surface are divided into, the better agreement would be between the predicted values and experimental results.
  • New Energy
    Numerical Simulation on Heat Transfer Enhancement in Parabolic Trough Solar Collector of DSG Systems
    YAN Weiwei, GE Shifu, LI Yang
    2013, 33(7): 550-554.
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    To enhance the steam heat transfer in collector tubes of parabolic trough solar DSG (direct steam generator) system, and to avoid too high temperature of the tube wall, numerical simulation was carried out to study the heat transfer and flow resistance characteristics in the superheat segment of DSG systems respectively with internally ribbed tube and smooth tube, so as to analyze the influence of thread height, thread pitch and Reynolds number on the heat transfer and flow resistance characteristics, following which a comprison was performed between internally ribbed tube and smooth tube. Results show that in the internally ribbed tube, steam turbulance is enhanced, heat transfer performance is improved and tube wall temperature is reduced. The Nu of internally ribbed tube is 1.6-2.4 times of the smooth tube, and the heat transfer performance increases with rising thread height and narrowing thread pitch; the drag coefficient f of internally ribbed tube is 3.1-8.7 times of the smooth tube, which also increases with rising thread height and narrowing thread pitch.
  • New Energy
    A New Solution for Activation Energy of Coal/Biomass Co-combustion at Constant Temperatures
    WANG Chunbo, WANG Jinxing, LEI Ming
    2013, 33(7): 555-559.
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    The co-combustion characteristics of coal and biomass blends were studied on a tube furnace constant-temperature thermo-gravimetric experimental setup, during which the experiemntal results were analyzed using both conventional lnln analytics and the proposed series fitting method, and subsequently the fitting degree and relevant kinetic parameters respectively obtained by above two methods were compared as well. Results show that within the temperature range of 450-500 ℃, for sample blends with an anthracite/corncob blending ratio of 9:1, 8:2, and 7:3, the reaction activation energy calculated by lnln method is respectively 78.81 kJ/mol, 75.53 kJ/mol and 80.88 kJ/mol, which cannot reflect the actual combustion condition of the blends, while the reaction activation energy calculated by series fitting method is 38.13 kJ/mol, 24.82 kJ/mol and 20.82 kJ/mol, presenting a rule that the reaction activation energy decreases gradually with the rise of blending ratio of biomass, which fits with the experimental results. The series fitting method has a broader application scope than the lnln method, and the apparent activation energy calculated by the series fitting method at different blending ratios of biomass can better reflect the difficulty level of the co-combustion of coal/biomass blends at constant temperatures.
    • Energy System Engineering
  • Energy System Engineering
    Theoretical Study on a Waste Heat Power Generation System Driven by SOFC Based on Organic Working Medium
    YAN Zhequan, WANG Man, WANG Jiangfeng, MA Shaolin, DAI Yiping
    2013, 33(7): 560-566.
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    To make use of the advantage of organic Rankine cycle for low-temperature waste heat recovery, a waste heat power generation system driven by solid oxide fuel cell (SOFC) was proposed based on organic working medium, including an internal reforming SOFC, an after-burner, a gas turbine, compressors, pre-heaters and ORC, which can help to realize gradient utilization of energy, and improve total power generation efficiency of the system. Based on a steady-state mathematical model, an analysis platform was established for thermodynamic simulation of the system, so as to study the effects of key parameters on the system performance. Results show that the total power generation efficiency of the system may reach 65% under design conditions; with the rise of fuel flow, the net power output increases, however, the total power generation efficiency decreases; within a certain range, the increase of compressor pressure ratio is beneficial to improvement of both the net power output and total power generation efficiency; with the increase of steam/carbon molar ratio, both the net power output and the overall power generation efficiency decrease.
  • Energy System Engineering
    Study on Recovery of Waste Heat from CCHP Systems
    ZHU Jiaxian, LU Mei
    2013, 33(7): 567-571.
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    To recover the waste heat from bromine cooler of combined cooling, heat and power (CCHP) system, two solutions were put forward, to which calculation and analysis were carried out on the overall thermal utilization factor of primary energy consumption and the overall exergy efficiency. Results show that the energy utilization rates of both solutions are improved effectively; in the condition that the ratio of cold to steam (RCS) is relatively small, solution 1 with a simpler system is better than solution 2; in the condition that the RCS increases, both the overall thermal utilization factor of primary energy consumption and the overall exergy efficiency of solution 1 hardly change, while those of solution 2 increase first, decrease later on, which reach the maximum when the RCS is 3.3k.
    • Material Science
  • Material Science
    Effect of Surface Treatment on Steam Oxidation Resistance of Steel Super 304H
    MA Yunhai, ZHENG Kaiyun, LIN Fusheng, WU Zhiying
    2013, 33(7): 572-577.
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    Oxidation behaviors of steel Super 304H in water vapour atmosphere at 650 ℃/25 MPa were studied under six surface conditions, i.e. with sample surfaces respectively treated by coarse grinder, grin-ding wheel, abrasive paper grits 320, 600 and 1200, and with polished surface, during which the samples after 1 200 h oxidation were weighted using gravimetric method, while the morphology and microstructure of oxide layers analyzed by SEM and EDS, and corresponding phases characterized by XRD. Results show that the steam oxidation resistance of steel Super 304H is relatively sensitive to the surface state of samples; different surface state results in different mass variation, oxide morphology and microstructure of samples; the typical oxide films generally consist of two layers, the outer layer is mainly Fe3O4, while the inner layer mainly Cr-rich (Fe,Cr)3O4 with a small amount of Cr2O3. Protective Cr-rich oxide films are easy to form on surfaces of lower finish with strained layer, when better steam oxidation resistance is to be generated.