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  • 2017 Volume 37 Issue 4
    Published: 15 April 2017
      
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  • Temperature Distribution of Vertical Tube Water Wall in an Ultra-supercritical Once-through Boiler
    HE Honghao, LI Wenjun, ZENG Jun, XIE Guohong, PENG Min, DUAN Xuenong, YANG Yi
    2017, 37(4): 257-260.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the 660 MW ultra-supercritical once-through boiler burning high sodium coal as an example, the temperature distribution of its vertical tube water wall was experimentally investigated under different working conditions. Results show that the uniformity of wall temperature distribution can be improved by raising the blending ratio of high sodium coal, thus lowering the heat load in the combustion zone. At supercritical pressure but low load, the deviation of temperarture distribution increases, and one of the reasons is that the throttle orifice could not adjust the flow rate of working fluid as designed. The uniformity of wall temperature distribution can be improved to a certain degree by reasonably adjusting the boiler operation mode.
  • Analysis and Technical Retrofit on Low Reheat Steam Temperature of a 660 MW Ultra-supercritical Boiler
    DANG Lijun, YANG Hui, YING Wenzhong, WANG Zhenhao, FAN Shangdong, LIU Canhua, LIU Mingqi
    2017, 37(4): 261-266.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem of low steam temperature existing in a 660 MW ultra-supercritical boiler, especially the obviously lower reheat steam temperature occurring when the boiler was operated under medium and low load, combustion adjustment tests were conducted, while technical retrofits were carried out on both the burners and the heating surfaces. Results show that above problems are mainly caused by the insufficient heating surface area of reheater, which may be overcome by enlarging the heating surface. The retrofit by expending the heating surface has helped to solve the problem of low reheat steam temperature. This may serve as a reference for technical retrofit of similar boilers.
  • Experimental Study on Combustion Characteristics of the Design Coal for a CFB Boiler
    SUN Baomin, ZHAO Lizheng
    2017, 37(4): 267-272.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To investigate the effects of bed temperature and limestone on the combustion stability and pollutant emission of a CFB boiler, combustion tests were conducted in a 3 MW CFB boiler combustion test bed at different loads and different primary to secondary air ratios burning the design coal. Results show that the ignition temperature of design coal is 436℃ and stable operation can be kept in the test bed when the bed temperature is 780℃. Limestone can improve the desulfurization efficiency, but would decrease the combustion efficiency. If the coal feed is interrupted for ten minutes, normal operation could still be recovered automatically after the coal feed continues again. The self-desulfurization efficiency of design coal gets up to 38%, while its desulfurization efficiency lies in 88.2%-95.1% for the Ca/S mole ratio of 3.7 in the case of bed temperature fluctuation. The load and primary air ratio effects more on NOx generation than other factors, and the NOx emission can drop down to 100 mg/m3 through reasonable adjustments on the load and primary air ratio.
  • Fault Diagnosis of a Wind Turbine Rolling Bearing Based on Variational Mode Decomposition and Condition Identification
    LIU Changliang, YAN Xiao
    2017, 37(4): 273-278.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Aiming at the problem that the classification performance of a wind turbine on its rolling bearing fault was reduced by the variation of operating conditions, the fuzzy C means clustering was used to identify the operating conditions, so as to perform fault diagnosis under corresponding sub conditions. To extract the characteristics of the vibration signal of rolling bearing more accurately, a method of feature extraction was proposed based on the variational mode decomposition (VMD), AR model and the singular value decomposition, in which, VMD was used to decompose the vibration signal of rolling bearing into several modes, then the singular value of AR model parameters, residual variance and modal matrix of each model were taken as the feature vector. Finally, the Euclidean distance discriminant function was established to identify the status and fault types of rolling bearing. Results show that the method could extract the fault feature information of rolling bearing and diagnose the fault type correctly, which has strong adaptability to the change of operating conditions.
  • 3D Simulation and Structure Optimization on the Condenser Water-side Rubber Ball Cleaning System of a 1 000 MW Unit
    FU Wenfeng, ZHANG Na, LIU Kang, WANG Lanjing, ZHOU Lanxin
    2017, 37(4): 279-284.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking the condenser in a 1 000 MW unit as an object of study, the water chamber flow field and rubber ball trajectories were simulated with the help of software Fluent during operation of the rubber ball cleaning system. Simulation results show that the rubber ball trajectories change a lot in the water chamber and the rubber balls agglomerate partly in the tube bundle, which causes blocked water flow and inefficient cleaning effect. The distribution of rubber balls becomes uniform in the tube bundle when curved buckles are added on the inlet tube sheet. When the thickness of curved buckles is 0.15 m, the total heat-transfer coefficient of condenser would be increased by 4.4%.
  • Effects of Blade Erosion on Performance Degradation of a Variable-pitch Axial Flow Fan
    YE Xuemin, ZHANG Dan, LI Chunxi
    2017, 37(4): 285-292.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A 3D numerical simulation was conducted on a single-stage axial flow fan using Fluent software to investigate the particle trajectories, the particle mass concentration on pressure surface and the wear regularity at different installation angles of blade, and to examine the effect of blade wear on the fan performance. Results show that, with the rise of blade angle, the particle trajectories tend to be complicated with the features of increasingly frequent bounce between two blades, and the number of particles impacting the trailing edge increases, with high concentration area extending to the trailing edge, resulting in severe wear of the edge. After operation for a period of time, the total pressure of fan keeps basically unchanged, but the efficiency reduces significantly, and the decline of efficiency would be gradually lowered with the rise of blade angle.
  • NOx Emission Reduction of a Boiler Based on Ameliorated Chicken Swarm Optimization
    LI Xia, NIU Peifeng, MA Yunpeng, CHEN Ke, WANG Qiuya
    2017, 37(4): 293-300.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To reduce the NOx emission of a boiler, an ameliorated chicken swarm optimization (A-CSO) algorithm was proposed by respectively modifying the foraging behaviors of hens and chicks in the original chicken swarm optimization algorithm to overcome the shortcomings of lower convergent speed and premature convergence, of which the performance was proved to be better than the particle swarm optimization algorithm, gravitational search algorithm, krill swarm algorithm and the original chicken swarm optimization algorithm through test function verification. Meanwhile, a prediction model was established for boiler NOx emission on the basis of A-CSO algorithm and fast-learning network, so as to optimize the adjustable parameters in boiler operation and obtain the way of boiler combustion optimization. Results indicate that the NOx emission in all cases is significantly lowered after optimization, and the relative decline rates are superior to that in the literature. Considering the influence of unburned carbon in the fly ash from boiler combustion, it is proposed to appropriately adjust the optimized oxygen content and primary air flow to achieve high efficiency and low NOx emission of the boiler.
  • Experimental Study on Isothermal SNCR Process of NOx Removal
    LIN Yuping, WANG Zhizhou, LIANG Ling, SUN Zhiao, QIAN Jun, ZHAO Jianxin, NIU Yanqing, HUI Shien
    2017, 37(4): 301-306.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To optimize the NOx removal system by selective non-catalytic reduction (SNCR) and to control the NOx emission in power plants, an isothermal SNCR experimental setup was established to study the effects of following factors on the SNCR process, such as the reaction temperature, mixing time and O2 concentration, etc. Results show that, in the temperature range of 973-1 373 K, with the rise of reaction temperature, the NOx removal efficiency first increases and then decreases, and the optimum denitrification temperature is 1 173 K, when the removal efficiency could reach 92.9%. The efficiency of NOx removal can be effectively improved by reducing the mixing time, especially when the temperature is higher than 1 203 K. The efficiency of NOx removal increases with rising O2 concentration at the temperature lower than 1 148 K, while decreases at the temperature higher than 1 148 K.
  • Study on Heat-transfer Characteristics of a Parabolic Trough Solar Collector
    WANG Xiuyan, HAN Lu
    2017, 37(4): 307-312.
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    To study the heat-transfer characteristics of a parabolic trough solar collector (PTC), a mathematical heat-transfer model was established under the circumferentially non-uniform heat flux boundary conditions, which simplifies the heat flux of absorber into rectangular distribution, considering the circumferential heat conduction of tube walls. The reliability of the model was validated with Dudley experimental data in the literature, while main factors influencing the heat-transfer characteristics were studied, and the circumferential distribution of temperature on absorber surface was analyzed by Fluent simulation. Results show that the mathematical model is reliable in calculating the heat-transfer performance of PTC. The fluid temperature and mass flow rate as well as solar radiation intensity are the main factors influencing the heat-transfer characteristics and circumferential wall temperature distribution of PTC.
  • Design and Performance Analysis of a Two-stage Tower-type Solar Cavity Receiver
    WANG Ting, PANG Liping, YANG Yongping
    2017, 37(4): 313-320.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A new type of two-stage tower-type solar cavity receiver was designed, and calculation models for its radiation, convection and flow were established under the Gaussian heat flux, so as to determine the piping layout and geometries in the receiver I and receiver Ⅱ, and to obtain the heat flux distribution in different positions. Main parameters concerning the working fluid temperature, steam quality, pressure drop and wall temperature distribution along typical pipes were specified according to the heat transfer and flow characteristics of the two-phase flow. Meanwhile, a series of systematic design processes were developed and an analysis was conducted on thermal performance of the two receivers. Results show that this type of two-stage cavity receiver can minimize the size of receiver I, while raise the average heat flux, reduce the mean temperature, and subsequently increase the thermal efficiency of the two receivers; besides, the multiple pass layout of coiled pipe header can make a more uniform distribution of the outlet parameters, preventing severe problems like overheating.
  • Techno-Economic Comparison of Three Processes for Boiler Waste Heat Recovery
    MA Youfu, YANG Lijuan, LÜ Junfu
    2017, 37(4): 321-328.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 600 MW ultra-supercritical coal-fired power unit as an object of study, the thermal economy and techno-economic performance of following three processes for the boiler waste heat recovery were calculated and compared, such as the process of conventional low-temperature economizer, prepositive low-temperature economizer and that of bypass flue, etc. Results show that, in the case of waste heat recovery with exhaust flue gas temperature being reduced from 122℃ to 90℃, for above three processes, the net standard coal consumption rate of unit can be reduced by 1.51 g/(kW·h), 1.71 g/(kW·h) and 2.81 g/(kW·h), respectively, with capital costs of 11.25, 19.40 and 16.85 million CNY, and dynamic investment payoff periods of 4.42, 8.66 and 3.29 years, accordingly. The prepositive low-temperature economizer process has the worst techno-economic performance, which has little improvement on net power supply efficiency, due to an obvious increase in equipment investment caused by the use of heat medium water air preheater. Among the three processes, the bypass flue one shows the highest thermal economy and best techno-economic performance, which is therefore recommended to be further studied for future application.
  • Simulation Study of an Absorption Heat Transformer
    PENG Shuo, ZHOU Xian, WANG Baomin
    2017, 37(4): 329-334.
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    Based on the principle of absorption heat transformer (AHT), a mathematical model was established for the key process, while a calculation program was developed for the cycle simulation, so as to analyze the effects of evaporation, generation, condensation and absorption temperature on the main performance evaluation indexes of AHT, such as the coefficient of performance ηCOP, the circulation ratio R, the temperature enhancement ability ΔT, and the deflection ratio ΔX, etc. Results show that, for a given absorption temperature, the circulation ratio reduces with rising evaporation temperature, while the ηCOP of system first increases sharply and then reduces slowly; for a given absorption temperature, the circulation ratio increases with rising condensation temperature, while the ηCOP of system first decreases slowly and then decreases rapidly; for a given evaporation temperature, the circulation ratio increases with rising absorption temperature, while the ηCOP of system first increases slowly and then decreases rapidly.
  • Study on Structural Failure Mode of Reactor Pressure Vessel Under Severe Core Meltdown Accident
    ZHU Jianwei, MAO Jianfeng, LI Yuebing, BAO Shiyi, GAO Zengliang
    2017, 37(4): 335-340.
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    To evaluate the structural integrity of a reactor pressure vessel (RPV) bearing complicated and dangerous loads under severe core meltdown accident, various analyses were conducted, including an analysis on the stress distribution across the RPV wall using finite element method, and a study on the failure mode with a multi-layered failure model proposed, suggesting that the RPV wall could be divided into five layers from inner to outer wall along its thickness, namely, molten layer, high-temperature creep dominated layer, compressed plastic dominated layer, elastic layer, and tensile plastic layer, etc. Meanwhile, factors influencing the plastic failure and high-temperature creep failure of RPV were analyzed, during which load conditions of both the failures were obtained. Results show that the internal pressure is the main factor affecting the RPV plastic failure. With the rise of internal pressure, the elastic layer in RPV wall gradually reduces, and when the elastic layer disappears, the corresponding internal pressure is considered as the load condition of plastic failure. Whereas, under creep conditions, once the internal pressure gets up to a certain value, the plastic layer, the creep strain and the plastic strain on RPV wall cross section increases rapidly, and the RPV promptly reaches its limit state, when the corresponding internal pressure is considered as the load condition of high-temperature creep failure.