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    Boiler Technology
  • Boiler Technology
    Analysis of Thermal Deviation in L-type Platen Superheaters of a 135 MW CFB Boiler
    JIN Xin, MA Youfu, Lü Junfu
    2020, 40(3): 177-184. https://doi.org/10.19805/j.cnki.jcspe.2020.03.001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A study was conducted on the generation mechanism of thermal deviation in the L-type platen superheaters of a 135 MW CFB boiler. By establishing a prediction model of thermal deviation and based on the self-developed software, the thermal deviations in the same platen and among different platens were calculated and analyzed. Results show that when Z-type arrangement is adopted for the steam lead-in pipe and lead-out pipe in the same platen, the header effect and the non-uniform lengths and structures of inner and outer tubes in the tube bundle could balance out their effects on the flow distribution, i.e. the thermal deviation in the same platen is mainly caused by the non-uniform structure and the non-uniform heat flux distribution. When Z-type arrangement is also adopted for the inlet header of lead-in pipes and the outlet header of lead-out pipes, the flow distribution among platens is obviously non-uniform due to the header effect, which contributes a lot to the thermal deviation among platens. In practical applications, it is suggested making full use of the header effect on the flow distribution in the same platen and among different platens, i.e., making the flow distribution of working fluids in the tubes balance the heat flux distribution outside the tubes, thus achieving a well control on the thermal deviation in L-type platen superheaters.
  • Boiler Technology
    Experimental Study on Combustion Characteristics of Zhundong Coal
    HANG Yixuan, JIN Jing, YANG Haoran, ZHANG Ruipu, ZHU Yizhou, LIU Zhongyi
    2020, 40(3): 185-190. https://doi.org/10.19805/j.cnki.jcspe.2020.03.002
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    To investigate the difference in combustion characteristics between low-ash high-alkali Zhundong coal and the reference coal, a thermogravimetric analysis was conducted on the two kinds of coal to study the effects of mass fraction of ash and alkali metal sodium on the combustion and kinetic characteristics of the coal samples. Results show that, according to the amount of converted ash, Zhundong coal has lower ash content, higher calorific value and slightly higher content of alkali metal Na. When the content of alkali metal sodium is the same, compared with the high-ash reference coal, the low-ash Zhundong coal has higher maximum burning rate, higher average burning rate and higher comprehensive combustion index, resulting in more rapid and intense combustion process, better combustion characteristics and lower activation energy of Zhundong coal. When the amount of converted ash is the same, Zhundong coal with high content of alkali metal sodium has higher maximum burning rate, larger comprehensive combustion index and lower activation energy. The properties of ultra-low or low ash content and high alkali metal content of Zhundong coal are important factors affecting the burning rate, among which, the low ash and ultra-low ash content have more obvious impacts.
  • Boiler Technology
    Study on Combustion Process and Sodium Transformation Behavior in a Swirl Burner Purely Burning High Sodium Zhundong Coal
    KANG Zhizhong, DING Xian
    2020, 40(3): 191-198. https://doi.org/10.19805/j.cnki.jcspe.2020.03.003
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    CHEMKIN software was used to simplify the reaction mechanism of sodium in flue gas, and then the simplified 32-step elemental reactions and CFD software were combined to simulate and analyze a swirl burner designed for purely burning Zhundong (ZD) coal. Results show that there is an elliptic stable recirculation zone with 3 m long axis and 1.5 m short axis in the operation of the swirl burner. The petal-shaped flame exhibits the feature of "wind wrapping fire", and there exists a stable flame area after the recirculation zone. In the combustion process of ZD coal, the space distribution and volumetric fraction of various sodium-containing substances differ significantly; in the flame zone, sodium mainly presents in the form of Na (30%), Na2SO4 (25%), NaCl (20%) and NaOH (10%), while at the outlet of combustion chamber, sodium mainly appears in the form of Na2SO4 (43%), NaCl (30%) and Na2Cl2 (24%). The sodium transformation could be roughly divided into three stages:sodium release process (0.28-0.37 s), rapid reaction process (<0.37-0.95 s), and Na2SO4 generation process (>0.95 s).
  • Boiler Technology
    Effect of Temperature on Ash Deposition Characteristics of Waste Coke from Coal Chemical Industry
    YANG Wenhai, LUO Junwei, ZHU Tao, HU Yueyi, CHE Defu
    2020, 40(3): 199-205. https://doi.org/10.19805/j.cnki.jcspe.2020.03.004
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    To find the influence mechanism of flue gas temperature and wall temperature on the ash deposition characteristics in the process burning pyrolysis waste coke, experiments were carried out in a high-temperature drop-tube furnace to analyze the physicochemical properties of the deposited ash respectively in the initial and sintered layer. Results show that flue gas temperature has a greater effect on the property of the deposited ash in sintered layer than in initial layer, while wall temperature has an opposite effect. With the decrease of flue gas temperature, the fusion and adhesion degree of deposited ash reduce gradually, resulting in easy removal of the deposited ash; whereas, the decrease in wall temperature could alleviate the fusion of deposited ash in initial layer, thus weakening the capture of large ash particles, thereby reducing the ash deposition to some extent. In addition, alkali metal elements mainly exist in the initial layer rather than in sintered layer by the way of heterogeneous condensation. The existence of high contents of calcium and iron is the main causes leading to severer ash deposition on the heating surface during waste coke combustion.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Calculation and Analysis of a Low-pressure Cylinder Under Small Flow Conditions and the Corresponding Retrofit Measures
    LI Mingyu, WEI Cunhai, LIU Wangkou, XU Jiamin
    2020, 40(3): 206-212. https://doi.org/10.19805/j.cnki.jcspe.2020.03.005
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    Numerical calculations were conducted on the thermal parameters, flow field, last-stage rotor blade strength and dynamic stress of the low-pressure cylinder in a 350 MW supercritical steam turbine unit under small flow conditions, while an analysis was carried out on the interstage thermal parameters and exhaust parameters, so as to obtain the variation law of the rotor blade strength and dynamic stress. In addition, operation risks of the low-pressure cylinder were analyzed under small flow conditions, following which, corresponding retrofit measures were proposed. Results show that with the continuous decrease in the inlet steam flow of the low-pressure cylinder, the phenomena of vortex and back flows begin to appear in the low-pressure long blade areas, while the blasting heat of the low-pressure cylinder grows, the temperature of the rotor blade rises, the allowable stress reduces and the dynamic stress increases. To ensure safe operation of the low-pressure cylinder under small flow conditions, it is suggested adopting the following measures, such as increasing the number of temperature monitoring points, reducing the temperature in exhaust areas by water spray, and so on.
  • Steam Turbine and Gas Turbine
    Nonlinear Dynamic Characteristics of a Rod Rotor with Rub-Impact Faults Under Bending-Torsion Coupling
    LI Ao, ZHAO Li, ZHOU Chuandi, LIU Yibing
    2020, 40(3): 213-219. https://doi.org/10.19805/j.cnki.jcspe.2020.03.006
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    To study the nonlinear dynamic characteristics of a rod rotor with rub-impact faults under bending-torsion coupling, a model was established for the double-disc rod rotor supported by sliding bearings at both ends, and subsequently the nonlinear dynamic differential equations of the system obtained based on the D'Alembert principle were then solved using fourth-order Runge-Kutta method. Results show that the nonlinear dynamic characteristics of the system intensify with the increase of rotational speed, when the influence of torsional vibration could not be neglected, while the rub-impact force gradually becomes the main factor influencing the nonlinear dynamic characteristics of the rotor.
  • Steam Turbine and Gas Turbine
    Effects of Root Geometry and Inflow Conditions on Endwall Heat Transfer Performance of the Blade
    ZHU Peiyuan, TAO Zhi, SONG Liming, LI Jun
    2020, 40(3): 220-226. https://doi.org/10.19805/j.cnki.jcspe.2020.03.007
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    A numerical model was established for the endwall heat transfer of a typical Pack-B gas turbine blade. Upon numerical validation, the effects of root fillet geometry and inflow conditions on endwall heat transfer performance of the blade were researched. Results show that with the rise of root fillet radius, the heat transfer at the leading edge reduces, but that at the trailing edge enhances. As the minimum root fillet angle of blade increases, the heat transfer in endwall area at the leading edge rises slightly, while that at the trailing edge weakens to some extent. When the inflow turbulence intensity is 1%, due to the significant change of secondary flow structures near the endwall, the heat transfer at the leading edge and in the middle area of endwall would be obviously higher than that with turbulence intensities of 4%, 6% and 10%, but the heat transfer in other regions enhances with growing turbulence intensity. With the rise of inflow Reynolds number, the heat transfer on the whole endwall intensifies.
    • Automatic Control
  • Automatic Control
    A Data Extraction Method for the Modeling of Superheated Steam Temperature Systems Using Kullback-Leibler Divergence
    YANG Wei, HONG Feng, YU Haoyang, SHEN Zhongli
    2020, 40(3): 227-231. https://doi.org/10.19805/j.cnki.jcspe.2020.03.008
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    A data extraction method was proposed for the modeling of superheated steam temperature systems based on Kullback-Leibler divergence (KLD), which uses operation data to construct the KLD sequence, and then the KLD sequence is linearly segmented. The data for modeling are finally extracted according to the segmented results. The simulation and field operation data of a large-scale thermal power unit were applied to verify the data extraction method for the modeling of its superheated steam temperature system. Results show that better modeling effect could be achieved by the way proposed, proving the data extraction method to be effective.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Simulation on Gas-Solid Heat Transfer Characteristics of a Bottom Ash Cooler in the Cross-flow Moving Bed
    YANG Yu, LIN Shunhong, TIAN Ye, BAI Jisong, JI Xuanyu, XU Ming, LU Xiaofeng
    2020, 40(3): 232-238. https://doi.org/10.19805/j.cnki.jcspe.2020.03.009
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    A bottom ash cooler was proposed for the cross-flow moving bed to recover and utilize the waste heat in the high-temperature bottom ash discharged from a circulating fluidized bed boiler, for which, a mathematical model was compiled by the Fortran language to investigate the gas-solid heat transfer characteristics, and to analyze the effects of inlet gas velocity, ash drop velocity and ash particle size on the bottom ash cooling and reusing efficiency. Results indicate that a higher inlet gas velocity is beneficial for the rapid cooling of bottom ash, but it would increase the energy consumption of the system and decrease the reuse efficiency of waste heat in bottom ash. A higher ash drop velocity extends the cooling process of bottom ash and slightly elevates the energy consumption, but the handling capacity of the system rises simultaneously, when the reuse efficiency of waste heat in bottom ash firstly increases and then decreases. The decrease of ash particle size has little effect on the gas-solid heat transfer capacity, however, it sharply increases the energy consumption. In addition, in the bottom ash cooler of cross-flow moving bed, the temperature of heated flue gas could reach 800℃, and the reuse efficiency of waste heat in bottom ash is about 40%, indicating higher performance of the cooler in bottom ash cooling and reusing.
  • Auxiliary Equipment Technology
    Aeroacoustics and Performance of an Axial-flow Fan with Serrated Trailing Edge Blades
    YE Xuemin, ZHANG Ruixing, ZHANG Chao, LI Chunxi
    2020, 40(3): 239-246. https://doi.org/10.19805/j.cnki.jcspe.2020.03.010
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    Taking the variable-pitch axial-flow fan of OB-84 type as an object of study, large eddy simulation and FW-H acoustic model were used to study the areoacoustics and performance of the fan with serrated trailing edge blades, during which, the effects of serrated edges with different lengths on the following parameters were researched, such as the noise, pressure fluctuation and performance of the fan, while the internal flow field and noise reduction mechanism were analyzed. Results show that the serrated trailing edge could significantly reduce both the noise in the middle and low frequency bands and the intensity of airflow pressure fluctuation in the flow passage; the longer the serration is, the more obvious the effects will be. The serrated trailing edge enhances the flow mixing in the wake region and changes the shedding structure at the trailing edge, leading to the formation of a two-layered comb-like flow-oriented vortex, thereby reducing the noise of the fan. Models A, B and C could improve the efficiency of the fan at design or lower flow rates. Model A presents the most obvious improvement on the fan performance among the three models, whereas at higher flow rates, the fan performance is lower than that of the original for all the three models.
    • System Engineering
  • System Engineering
    Exergy Analysis and Optimization of Steam Extraction-High Back Pressure Combined Heating for Dual Cogeneration Units
    LIANG Zhanwei, ZHANG Lei, XU Yatao, ZHANG Junjie, JING Changcai, WANG Shunsen
    2020, 40(3): 247-255. https://doi.org/10.19805/j.cnki.jcspe.2020.03.011
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    To optimize the operation condition of heat and power cogeneration units, a simulation model was set up based on the self-developed thermal power integration scheme (TPIS) software for the thermal power system, while an exergy analysis model was established for the cogeneration unit, so as to study the variation law of following parameters with the main steam flow, such as the heating exergy efficiency, the exergy efficiency of equivalent electricity consumption and the total exergy efficiency of the thermal power plant, thus obtaining the optimal operating conditions respectively for the mode of steam extraction heating, steam extraction-high back pressure combined heating, and extracting steam cascade utilization-high back pressure combined heating by means of exergy analysis. Results show that the optimal operation interval of extracting steam cascade utilization-high back pressure combined heating is larger than other two heating modes, and heating capacity of steam extraction-high back pressure combined heating is the highest. This may serve as a reference for energy consumption evaluation and operation optimization of heat and power cogeneration units.
  • System Engineering
    Sliding Pressure Curve Optimization for Flexible Operation of Thermal Power Units
    DONG Zhulin, NIU Yuguang, DONG Enfu, ZHOU Guiping, LUO Huanhuan, ZHANG Guobin
    2020, 40(3): 256-264. https://doi.org/10.19805/j.cnki.jcspe.2020.03.012
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    To ensure the quick response to load commands during peak shaving of a unit and to reduce the pressure fluctuation of the main steam, the effects of initial pressure changes on the safety, stability, economy and response speed of the unit were analyzed, including the requirements on above characteristics in different load ranges. A heat rate prediction model was established based on least squares support vector machine (LSSVM) combined with chaotic particle swarm optimization (CPSO) algorithm to determine the optimal initial pressure for each typical load of a 660 MW unit. In addition, a new sliding pressure strategy was proposed by combining the performance test optimization curve with the article optimization curve, i.e., adopting the article optimization curve in dynamic regulation period, and then switching to the performance test optimization curve in stable operation condition. For simulation and verification purposes, the new sliding pressure strategy was subsequently added to the coordinated control system to generate pressure setting values of the main steam. Results show that the new sliding pressure strategy could not only improve the response speed of load variation in dynamic regulation, but also maintain the economy of the unit in stable operation condition.