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  • 2018 Volume 38 Issue 1
    Published: 15 January 2018
      
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  • Study on Acoustic Diode Effect and Cold Point Defect in Boiler Tube Arrays
    LIU Yuechao, JIANG Genshan, XU Weilong, KONG Qian
    2018, 38(1): 1-7.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on phononic crystal theory, numerical method was used to analyze the sound transmission characteristics through two different tube arrays by setting the tube array parameters and surrounding temperatures, and to study the sound transmission characteristics when the cold point defect lies in different areas of tube arrays. Results show that the sound transmission characteristics present unidirectional behavior within a certain range of frequencies, which is related to the transition structure between two different tube arrays. Cold point defects affect the sound transmission characteristics. The study results on sound transmission characteristics may serve as a reference for acoustic location in different tube arrays.
  • Study on Determination of Sodium Content in Coal
    SHI Huijuan, ZHANG Zhang, WANG Xin, WANG Jinsheng, LIU Taisheng
    2018, 38(1): 8-12.
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    The sodium content in 5 kinds of Xinjiang coal was determined by following three ways, such as the combined way of one-step-extraction with 600℃ low-temperature ashing, the 600℃ low-temperature ashing method and the 815℃ national standard ashing method. By comparing the determination results, the most accurate way was subsequently obtained. Results show that the combined way of one-step-extraction with 600℃ low-temperature ashing is the most accurate one, in which, ultrapure water or 0.25 mol/L hydrochloric acid can be chosen as the extraction liquid.
  • Calculation and Optimization of a Rated-Sliding Pressure Curve for Application in a Steam Turbine
    WEN Le, XUE Zhiheng, GAO Lin, YANG Xinmin
    2018, 38(1): 13-17.
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    To achieve safe, adjustable and economical operation of a power unit at partial load, an analysis was conducted on the rated-sliding pressure operation curve, while a particle swarm optimization algorithm was proposed by converting actual considerations into the constraints of position and dimension of the particles, which was then applied to optimize the rated-sliding pressure curve of a 350 MW unit. Results show that the proposed method has better convergence ability and wider universality, which can realize calculation and optimization under various restrictive conditions. The optimized rated-sliding pressure curve takes into account actual conditions of the power unit, load response capability and unit economy at low load. The average heat rate of the unit at low load has been reduced by 0.2% compared with the operating conditions before optimization.
  • Prediction on Working Clearance and Leakage Rate of Labyrinth Seals Based on Windage Heating
    XIONG Yuanjian, ZHOU Na, CAI Guohuang, ZHOU Hongyu, AI Song, ZHAO Shizhi
    2018, 38(1): 18-23.
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    Windage heating of ideal air and steam passing through labyrinth seals was respectively calculated at rotating speeds N=0 and N=3 000 r/min using CFD numerical method and different empirical correlations, based on which, actual working clearance and leakage rate of related labyrinth seals could be obtained according to the temperature difference between inlet and outlet of the seals. Results show that at same rotating speeds, the windage heating of air is more obvious than that of steam, and the temperature drop induced by throttling effect is relatively small, therefore, it is feasible to evaluate actual working clearance and leakage rate of labyrinth seals with windage heating of air for rotating machineries like gas turbine, which takes air as its working medium.
  • Application Analysis of Exhaust Gas Recirculation Technology in F-class Gas Turbines
    LÜ Xuan, GU Chunwei, LIU Jianjun
    2018, 38(1): 24-28.
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    Thermal performance of a classical F-class combined cycle unit was analyzed after the technology of exhaust gas recirculation (EGR) was applied under the recirculation ratios of none, 10%, 20% and 30%, in which case, the variation tendencies of gas turbine inlet temperature, oxygen concentration and combined cycle power output were studied. In addition, the effects of EGR on the inlet temperature and exhaust temperature of gas turbine were researched via calculation at different loads, while the benefit to adopt EGR technology in CO2 capture was evaluated. Results show that EGR helps to improve the cycle performance at partial load, which is also beneficial to CO2 capture.
  • A New Coordinated Control Method for Circulating Fluidized Bed Boilers Based on Coal-quality Correction
    HE Peng, LU Linhui, LIU Xichui, LI Yiguo
    2018, 38(1): 29-35.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the load-following capability and the coal-quality applicability of a circulating fluidized bed boiler (CFBB), a new coordinated control method was proposed based on coal-quality correction, which takes the primary air as another new control variable into the coordinated control, so as to make full use of the unburned carbon in bed, thus improving the load-following capability of the CFBB. Simultaneously, a multivariable predictive controller was designed based on augmented state space model to deal with the CFBB's characteristics, such as time-delay and strong coupling, etc. Finally, an improved strategy for online coal-quality correction was provided based on the disturbance observer. Results show that compared with conventional control scheme, the method proposed can significantly improve the load-following capability and the coal-quality applicability.
  • Design of H∞ RMPC Based on Memoryless Feedback Strategy for Superheated Steam Temperature
    HAN Pu, LIU Miao, WANG Dongfeng, JIA Hao
    2018, 38(1): 36-42.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Considering the dynamic characteristics of boiler superheated steam temperature, such as large delay, great inertia and model uncertainty behavior, etc., an H∞ robust model predictive control (HRPC) algorithm was proposed for the uncertain multi-model system based on memoryless feedback strategy, which combines the advantages of robust control and predictive control with memoryless feedback control to deduce the memoryless state feedback HRPC law using multi-step control strategy. The controller proposed was then applied to simulate the superheated steam temperature of a 600 MW power plant at different loads, and a comparison was subsequently made among the HRPC-P, conventional PID cascade control (PID-P) and the dynamic matrix cascade control (DMC-P) algorithm. Results show that both the tracking and the robust performance of HRPC-P are superior to those of PID-P and DMC-P, with fewer parameters to be optimized, which therefore may serve as a reference for application in actual engineering projects.
  • Influence of Air Leakage Distribution on the Thermodynamic Performance of a Rotary Air Heater
    BAI Delong, ZHANG Jinsong, XIE Guanyu, XING Jingwei
    2018, 38(1): 43-49.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on mechanism analysis of rotary air heaters, taking the metal element as a hypothesis fluid, which exchange heat directly with flue gas (primary and secondary air) in a micro-control volume, heat-transfer differential equations and corresponding difference equations were established for the heaters. According to the thermal design and structure parameters of a 600 MW subcritical unit, a model was set up and solved, so as to obtain the reasonable temperature distribution in the metallic heat-retaining element and working medium, and to obtain the variation law of exhaust gas temperature and outlet air temperature by changing the air leakage coefficient. Results show that the increase of air leakage rate will lead to the rise of exhaust gas heat loss, which brings negative influence on the boiler efficiency; the exhaust gas temperature of air heater shows an increasing tendency, while the primary/secondary air temperature shows a downtrend, with an increasing proportion of air leakage at hot end.
  • Theoretical Study on Wide Load Denitration of a 660 MW Supercritical Unit by Retrofitting the Feedwater Heating System
    ZHANG Guozhu, LI Bingxin, LI Yawei, LI Fei, LI Benfeng, LIU Jiping
    2018, 38(1): 50-54.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the denitration efficiency and thermodynamic performance of a 660 MW supercritical unit operating at low load, a bypass line and high/low-pressure steam regulating valves were added to its original low-load feedwater heating system including a steam ejector, so as to achieve wide load denitration of the unit. The temperature rise of No.0 high-pressure heater was calculated, while the operation mode of the steam ejector operating at high load was optimized. Results show that for the unit load greater than 30%, the No.0 high pressure heater has a large range of temperature rise to satisfy the denitration requirement. When the unit operates at high load, the thermal efficiency of the unit could be improved by reducing the pressure of high-pressure steam at inlet of the steam ejector.
  • Retrofit Schemes for Safety Operation of a 660 MW SCAL Indirect Dry Cooling Tower During Summer Period
    WANG Lanjing, LIU Kang, FU Wenfeng, LI Weihua, LI Shan
    2018, 38(1): 55-61.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The effects of cross wind speed in summer on the flow and heat transfer performance of an indirect dry cooling tower were analyzed by using the porous medium model of Fluent software, so as to find the environmental wind speed corresponding to the poorest heat transfer performance, and to retrofit the cooling tower for safety operation of the unit, in the way of adding wing walls outside the tower by considering the effects of factory buildings, based on the flow field characteristics at the wind speed. Results show that the cooling tower has the worst heat transfer performance when the cross wind speed is 12 m/s; considering the effects of factory buildings, the distribution uniformity of both the ventilation rate and the heat exchange rate is found to drop along the circumferential direction, resulting in worsened flow and heat transfer performance of the tower. After adding wing walls, the ventilation rate of draught air has been reduced by 26.57%, while the ventilation rate and heat transfer flux of the indirect dry cooling tower have been increased by 24.55% and 13.01%, respectively.
  • Effects of Air Cooling Island on the Characteristics of Bottom Boundary Layer
    WU Zhengren, LU Tingting, WANG Songling, JIN Chaoran
    2018, 38(1): 62-68.
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    A model of air cooling island was established with Gambit software by numerical method, with which, the effects of air cooling island on the local environment were analyzed using Fluent software by loading atmospheric boundary layer function through UDF and setting temperature distribution function for different temperature stratifications, so as to obtain the wind velocity and temperature at different heights in the area around the air cooling island, and to study the change trend of momentum flux and heat flux based on wind shear theory and Monin-Obukhov similarity theory. Results show that with the rise of wind velocity, the wind shear increases slightly, which reduces gradually along the flow direction. The influence of air cooling island on the momentum flux and heat flux reduces along the flow direction, while the influence on stable stratification is less than that on unstable stratification, and the influence degree on stable stratification is higher than on any other places except for the unstable stratification.
  • Experimental Study and Techno-Economic Analysis on Hydrothermal Oxidation of Sewage Sludge
    LI Weicheng, QIN Xiaogang, FANG Hui, WEN Lu, WANG Huan, YANG Huan, SUN Dengke
    2018, 38(1): 69-73.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To optimize the reaction conditions for hydrothermal oxidation of sewage sludge, and to investigate the reaction results, orthogonal experiments were conducted in a reaction vessel to study the effects of following factors on the treatment results, such as the temperature, excess air ratio and residence time, etc. Meanwhile, the solid, liquid and gas products were analyzed by thermogravimetric, elemental, COD and gas composition analysis, and the heavy metals contained in liquid and solid products were also measured. Results indicate that under optimized reaction conditions, the decomposition rate of oganic matters in the sewage sludge may reach more than 90%; the weight loss of solid residuals is less than 10%; a certain amount of COD is contained in the liquid products, which can be recovered by municipal sewage treatment; no SO2 or NOx could be detected in the exhaust gas; heavy metals are concentrated in the solid residuals. Based on techno-economic analysis, the composite cost of sewage sludge hydrothermal oxidation is found to be 130 RMB/t.
  • Experimental Study on Low-cycle Fatigue Property of 10Cr Rotor Steel
    YANG Baixun, TIAN Xiao, LI Yang, DING Lingling, WANG Meiying, XIAO Guohua, TIAN Yu, LI Yimin
    2018, 38(1): 74-79.
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    Tension and low-cycle fatigue properties were experimentally studied for domestic rotor steel 14Cr10NiMoWVNbN and same grade foreign rotor steel TOS107. Results show that the tensile properties of above two steels are similar with one another at room temperature and 600℃. The low-cycle fatigue strength of domestic rotor steel is found to be a little bit lower than that of foreign one by comparing their cyclic behavior, stress-strain behavior and strain-life behavior. According to the low-cycle fatigue properties of domestic rotor steel tested at 593℃, a fatigue design curve is worked out by converting the virtual stress and selecting appropriate safety coefficient, which can be used to predict the fatigue life of foreign rotor steel 10Cr.
  • Effects of SO2 on High-temperature Corrosion Resistance of Steel T91 Under Tension Conditions
    LIU Zhuhan, ZHOU Qulan, FU Jiapeng, NING Zhiyuan
    2018, 38(1): 80-84.
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    To study the effects of SO2 on the high-temperature corrosion resistance of steel T91 for boiler superheater, experimental tests were conducted in a high-temperature tube furnace under tension conditions respectively at 700℃ and 750℃ for 168 h, after which the samples were examined by XRD and SEM analysis. Results show that the oxide scale includes Cr-based and Fe-based two layers; under tension conditions, the gas phase SO2 does not affect the scale thickness, but has influence on the thickness ratio of the inner and outer layer, as well as on the size of surface grains; tensile stress would accelerate the migration of Cr, but not affect the migration of Ni, which could reduce the anion defect in Fe-based layer and prevent the internal migration of S element. Gas phase SO2 would affect the removal way of corrosion layer, i.e. overall fall off may easily occur to the corrosion layer.