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    Boiler Technology
  • Boiler Technology
    Thermal Stress Analysis of Oxide Films on T23 and T91 HT Superheater Tubes of 600 MW Supercritical Boilers
    XIE Jianwen, SUN Ping, YANG Hongquan, ZHOU Keyi
    2013, 33(11): 829-832.
    Abstract ( )   Knowledge map   Save
    Taking the high-temperature (HT) superheater of a 600 MW supercritical boiler as an object of study, the effects of thickness, growth temperature and thermal expansion coefficients of steam-side oxide scale on its thermal stress were analyzed. A numerical calculation model was established for round tubes based on finite element method, with which the thermal stress variation of oxide film on steam-side surface of T23 and T91 tubes was calculated during the cooling process from growth temperature to ambient temperature at different thicknesses and growth temperatures, and subsequently the susceptible temperature ranges (STR) in which the steam-side oxide film formed respectively on T23 and T91 tubes is easy to peel off was determined according to variation laws of the thermal stress. By correlating the temperature of boiler outlet steam with the temperature of oxide scale formed on specified location in the HT superheater, a method using the boiler outlet steam temperature to identify whether the oxide scale is within the STR was proposed, and for boiler shut-down processes, the recommended value for boiler outlet steam temperature was also presented. Results show that when the tubes are cooled to be lower than certain temperatures, the stresses in the scale will approach their maximum values, which can therefore be employed to judge whether the temperature of the scale is within the STR.
  • Boiler Technology
    Experimental Study and Numerical Simulation on High-temperature Oxygen-enriched Oil-free Pulverized Coal Ignition
    LIU Guowei, DONG Peng, BIE Rushan
    2013, 33(11): 833-840.
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    An oil-free ignition method was proposed for mixture flow of high-temperature oxygen and dense phase pulverized coal, so as to study the high-temperature oxygen-enriched oil-free pulverized coal ignition process. Numerical simulation was carried out to analyze the flow field in the self-developed oil-free ignition facility. Results show that when the oxygen is heated up to 750 ℃, the mixture flow of high-temperature oxygen and pulverized coal can be ignited successfully under design conditions; it is favorable for the ignition and combustion of pulverized coal flow to raise the primary air temperature, pulverized coal density and oxygen flow rate, and to reduce the primary air velocity; the ignition starts directly ahead of the center tube nozzle, and the average temperature in the flow field is above 2 000 K, with a highest temperature above 3 000 K, which is located on both sides of the center tube axis.
  • Boiler Technology
    Experimental Study on Ash Fusion Characteristics of Zhundong Coal
    WANG Yungang, ZHAO Qinxin, MA Haidong, WANG Hao, JIANG Weiwei
    2013, 33(11): 841-846.
    Abstract ( )   Knowledge map   Save
    Experimental tests were performed to study the ash fusion characteristics of coal mixtures prepared with Zhundong coal (respectively from Shenhua and Tianchi Energy) and Jiangou coal in different blending ratios, and of mixtures prepared by blending following additives into above two kinds of Zhundong coal, such as NaCl, CaO, Al2O3 and SiO2 in different ratios. Results show that for the Jiangou-Zhundong coal mixture, the ash fusion temperature drops first and rises later with the increase of blending ratio of Zhundong coal. For the mixture of Zhundong coal added with various additives, the ash deformation temperature(DT) decreases significantly, while the ash soft temperature(ST), hemispherical temperature(HT) and flow temperature(FT) drop first and then get stable, with the increase of Na content; the influence of NaCl on the coal ash fusibility is significantly weakened when the Na content reaches a certain percentage; the influence of CaO on the coal ash fusibility is very complicated, it can both improve and reduce the ash fusion temperature of the mixture; with the rise of Al2O3 content, the ash fusion temperature of Zhundong coal first increases then decreases sharply; with the rise of SiO2 content, the ash DT of Shenhua Zhundong coal first rises then drops, and that of Tianchi Energy Zhundong coal increases gradually, while other three characteristic temperatures of the Zhundong coal reduces gradually.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Experimental Study on Aerodynamic Performance and Flow Structure of a Diffuser Cascade with Splitter Blades
    SAI Qingyi, ZHU Yuanjia, YANG Ailing, DAI Ren
    2013, 33(11): 847-852.
    Abstract ( )   Knowledge map   Save
    For diffuser cascade respectively with 45 degree turning angle and with splitter blades, aerodynamic performance of the cascade was measured under working conditions and at different attack angles, while flow structure inside the cascade studied under corresponding working conditions through PIV expe-riments. Results show that the pressure gradient from pressure surface to suction surface of large blade has been lowered substantially after small blade is added, and the load on large blade is reduced also; under design conditions, the lag angle of cascade flow can still be calculated according to Howell semi-empirical formula, however, large error will be produced if the formula is used under off-design conditions; the lag angle of cascade with splitter blades shall be obviously reduced only in the case the attack angle is small, and under other conditions, little changes will be produced; the air flow separation on large-blade surface is restrained by small blade at different attack angles; the diffuser loss of cascade reduces in the process of changing the attack angle from design condition to large values.
  • Steam Turbine and Gas Turbine
    Study on Vibration of Turbo-Generator Shaft System Based on Spin Softening
    YAO Xueshi, ZHOU Chuanrong, ZHENG Chunlong
    2013, 33(11): 853-857.
    Abstract ( )   Knowledge map   Save
    A turbo-generator shaft model was established using finite element method, with which the effects of gyroscopic moment, stress stiffening and spin softening on lateral-torsional vibration mode of the shaft system were analyzed, and subsequently corresponding dynamic equations were deduced, while the torsional, lateral and coupled lateral-torsional vibration calculated with computer programs. Results show that the torsional vibration has a certain influence on safe operation of the system; there are several forms of coupled lateral-torsional vibration; the spin softening has significant influence on the first and second backward whirl mode; the stress stiffening further increases the frequency of the third forward whirl mode; the torsional vibration frequency and critical speed can be obtained in consideration of both the effects of stress stiffening and spin softening. In comparison with beam model, the solid element model has higher simulation degrees, resulting in more accurate calculation results.
    • Automatical Controlling and Detecting Diagnosis
  • Automatical Controlling and Detecting Diagnosis
    Optimization on Internal Model PID Control for Nuclear Power Pressurizers
    LI Yongling, HUANG Yu, MA Jin, WANG Bingshu
    2013, 33(11): 858-864.
    Abstract ( )   Knowledge map   Save
    Based on the internal model control (IMC) principle and considering that the pressurizer system of nuclear power plant has the properties of large inertia, time-variation and multi-disturbances, an internal model-PID control system was developed. To tune the internal model PID controller parameters, a quantum particle swarm algorithm with high speed convergence was proposed for parameters optimization, of which the effectiveness was verified by classical test functions. Simulation results show that the internal model PID controller has better control effects than conventional PID control systems, and when the attribute of object model changes or the model is disturbed, good control effects can still be obtained by the internal model PID controller, which has higher robustness and anti-interference capability.
  • Automatical Controlling and Detecting Diagnosis
    Fault Feature Extraction from Wind Turbine Gearbox Based on Non-Gaussian Intensity
    ZHOU Yanbing, LIU Yibing, ZHAO Qiuli, LI Hong
    2013, 33(11): 865-870.
    Abstract ( )   Knowledge map   Save
    Complex vibration signals of wind turbine gearbox were studied so as to extract the fault features. The measured vibration signals were filtered and reconstructed by Gabor transformation, and then the meshing frequency and its harmonic components were inhibited, after which bispectral analysis was carried out to the reconstructed signals that mainly include sideband components, random components and inherent frequency components. Finally, the difference of non-Gaussian feature between normal gear vibration signals and pitting gear vibration signals was revealed, and subsequently the characteristic values of non-Gaussian intensity were extracted. Results show that gear faults may change the distribution of non-Gaussian components in vibration signals. The characteristic values of non-Gaussian intensity extracted from filtered signals are closely related to the gear pitting faults. The method is very simple in calculation, which therefore may be used in actual engineering projects.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Numerical Simulation on Internal Flow Field of a Two-stage Variable Vane Axial Flow Fan
    YE Xuemin, LI Xinying, LI Chunxi
    2013, 33(11): 871-877.
    Abstract ( )   Knowledge map   Save
    Numerical simulation was carried out on steady-state three-dimensional flow field in a two-state variable vane axial flow fan matched for 600 MW units using Fluent software, so as to analyze the internal flow field of its first-stage and second-stage impeller and the influence of installation angle on the performance of axial flow fan. Results show that the total outlet pressure of second-stage impeller distributes alternatively in the way of high-pressure zone and sub-high-pressure zone, presenting lower symmetry than the first-stage impeller. The total and static pressure curves on pressure and suction side of both impellers’ blades have similar distributions, and the static pressure on blades of second-stage impeller is larger than that in corresponding position of the first-stage impeller on both the pressure and suction surfaces. With the rise of installation angle, the total pressure rise coefficient of both impellers and the diffuser coefficient of the guide vane tend to increase, and the increasing range of coefficient for the second-stage impeller is greater than the first one, showing a superior performance of the second-stage impeller in both working and diffusion capability respectively of the first-stage impeller.
    • Environmental Science
  • Environmental Science
    Experimental Study on Simultaneous Activated Carbon-based Desulfurization and Denitration Under Microwave Irradiation
    ZHAO Yi, LIU Wei, ZHU Xiaoyu, ZHANG Zili, MA Shuangchen
    2013, 33(11): 878-882.
    Abstract ( )   Knowledge map   Save
    To improve the removal efficiency of simultaneous activated carbon-based desulfurization and denitration under microwave irradiation, and to reduce the energy consumption and increase the selectivity of reduction reaction, several catalysts were chosen and loaded on the activated carbon to study their influences on the simultaneous desulfurization and denitration. Results show that the greater the microwave power is, the higher the temperature of activated carbon bed and the reaction temperature will be; the adding of catalyst can improve the efficiency of simultaneous desulfurization and denitration, and different catalysts produce different effects; under the microwave power of 420 W, copper-based catalysts can promote the activated carbon-based denitration but inhibit the activated carbon-based desulfurization under microwave irradiation. As the optimal catalyst in industry application, Mn (NO3)2 can help to improve the simultaneous desulfurization and denitration efficiency up to 95%.
    • New Energy
  • New Energy
    Simulation and Optimization on Hydrogen Production by Pressurized Biomass Gasification Based on Ca-looping
    ZHAO Liang, WANG Qinhui, FAN Hongtao, FANG Mengxiang, LUO Zhongyang
    2013, 33(11): 883-898.
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    A model was developed for hydrogen production by biomass gasification based on Ca-looping, including a gasification and a combustion process. The gasification process consists of a pyrolysis and a reforming module, and the yield of each initial pyrolysis product was determined based on the results of rapid pyrolysis experiments in consideration of pressure and temperature effects. A part of char produced in secondary pyrolysis was fed into the combustor so as to achieve the calcination temperature of calcium carbonate, and the remaining char was sent to the gasifier. Calculations in reforming module and combustion process were based on Gibbs free energy minimization approach. Simulation results of the system in non-equilibrium state during pressurization process were obtained by controlling the temperature approach in restricted equilibrium state, which were subsequently verified with experimental results of gasifiers. Influences of following factors on hydrogen volume fraction and yield, carbonation reaction rate and calcination ratio of calcium carbonate were analyzed, such as the pressure, temperature, n(Ca)/n(C) and n(H2O)/n(C), etc. Results show that an optimal hydrogen output of 106.4 g/kg can be obtained, with a volume fraction reaching 94.0%, after optimization of the system.
  • New Energy
    Modal Analysis of 5 MW Wind Turbine Blades
    AN Liqiang, ZHOU Xingyin, ZHAO Hexiang, WANG Zhangqi
    2013, 33(11): 890-894.
    Abstract ( )   Knowledge map   Save
    To study the effect of ply orientation and spar structure on dynamic characteristics of large adaptive wind turbine blades, finite element models of 5 MW wind turbine blade were established using Ansys software, to which modal analysis was conducted for blades with different ply orientation and spar structures, and subsequently the first ten natural frequencies and corresponding vibration modes were obtained, while the effects of following factors on the natural frequency analyzed, such as the ply orientation, spar structure and rotating speed, etc. Results indicate that the ply orientation and spar structure of blades have a great effect on the natural frequency; in the twist-bend coupling of blades, the effects of design parameters on the modal shape of blades should be considered so as to avoid vibration failure of blades.
    • Energy System Engineering
  • Energy System Engineering
    Study on Thermal Economy of Solar-Coal Hybrid Power Generation Units
    TANG Qiang, CAO Weiwei, ZHANG Li, CUI Pengfei
    2013, 33(11): 895-901.
    Abstract ( )   Knowledge map   Save
    Three integrated modes of solar-coal hybrid power generation systems were proposed, in which the solar energy was introduced respectively at the place of boiler evaporating heating surface, extraction side of high pressure heater, and the low-pressure cylinder of steam turbine. Following evaluation indexes were defined, such as the solar thermoelectric conversion efficiency, the amount of unit coal saving and the thermal contribution rate of solar energy, etc. Taking a 300 MW power unit as an example, the thermal economy of three integrated schemes was calculated and compared using equivalent enthalpy drop method, after which the optimal integrated mode of hybrid power generation was determined, together with a preliminary analysis on its thermal economy. Results show that the thermal economic indexes, the operation safety and stability of scheme 2-1 are relatively good among the three schemes, which therefore is regarded as the optimal integrated mode. In the hybrid power generation mode, the unit cost of solar power generation is 0.63 RMB/(kW·h), being less than the cost 0.75-1.85 RMB/(kW·h) under pure solar energy power generation mode.
  • Energy System Engineering
    Study on Cycling Performance of Coal/Straw Blending Chemical Looping Combustion with Oxygen Carrier Fe2O3
    DI Haisheng, WANG Cuiping, ZHANG Jiabin, ZHANG Shujuan, HUANG Fei
    2013, 33(11): 902-906.
    Abstract ( )   Knowledge map   Save
    Multi-cycle reduction/oxidization characteristics of oxygen carrier Fe2O3 were studied during the chemical looping combustion (CLC) of coal-straw-Fe2O3 mixtures in different blending ratios, with focus on the influence of ash content brought in by solid fuel on the reaction rate of chemical looping, and on the improvement effect of straw on the chemical looping reaction. Results show that the chemical looping reaction can be improved by increasing the mass ratio of oxygen carrier Fe2O3, when the initial reaction temperature is lowered; ash content plays a negative role in influencing the cycleability of the oxygen carrier Fe2O3; the addition of straw helps to improve the CLC property of coal, which results in both improved combustion reaction rate and increased regeneration reaction rate of the oxygen carrier.
  • Energy System Engineering
    Comprehensive Analysis of Air-Flue Gas Waste Heat Recovery in Air Cooling Units
    YANG Yongping, XU Cheng, XU Gang, FANG Yaxiong, WU Ying
    2013, 33(11): 907-912.
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    Based on detailed analysis of operation characteristics of an air cooling unit, a combined air-flue gas waste heat recovery system was proposed, in which the hot air from air cooling unit is to be heated in air preheater for purposes of boiler combustion, and simultaneously, the low temperature economizer set at boiler tail is used to heat the low-pressure condensed water, thus saving the steam extracted from steam turbine. Taking a typical 600 MW subcritical direct air cooling unit as an example, the thermodynamic characteristics and energy-saving effects of its air-flue gas waste heat recovery system were analyzed. Results show that obvious economical effects can be obtained for the air-cooling unit under typical working conditions, with an increased inlet temperature of air preheater by 25 K, a reduced power supply coal consumption by 1.93 g/(kW·h), an annually economized standard coal consumption by 7 000 t, equivalent to 7 million RMB fuel cost (based on the coal price of 1 000 RMB/t with an annual running time of 5 500 hours).