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  • 2016 Volume 36 Issue 7
    Published: 15 July 2016
      
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  • Mechanism Analysis on Combustion Characteristics of a 600 MW Boiler Retrofitted with Dual-scale Low Nitrogen Technology
    SUN Lingfang, REN He, LANG Kun, TANG Hong, HOU Bo
    2016, 36(7): 505-512.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Combining the thermodynamic calculation in sections for large capacity boilers with simplified dynamic model of full-furnace pressure and temperature, and based on the law of energy conversation and the theory of radiation heat transfer, mechanism models of furnace temperature were set up for three zones of a 600 MW boiler before and after dual-scale low nitrogen retrofit, with which combustion characteristics in vertical space of the furnace was simulated using Simulink software. In addition, the temperature field and velocity field in horizontal space of the furnace were also simulated using Fluent software, while the mechanism of dual-scale low nitrogen combustion retrofit was analyzed comprehensively. Results show that the flow of primary air is in opposite direction to the secondary air due to the bias of primary air flow after retrofit, thus making the swirl region expanded in horizontal direction and shortened in vertical direction, resulting in increased combustion efficiency and lowered NOx emission in partial areas, but simultaneously increased inertia of combustion process and reduced adaptability to uploading conditions.
  • Effects of SOFA Ratio on NOx Generation Characteristics in a Supercritical Tower Boiler
    LI Jianning, XIONG Xianwei, SHI Hongfei
    2016, 36(7): 513-518.
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    Taking a 670 MW supercritical tower boiler under BMCR condition as the benchmark model, numerical simulations were implemented on staged combustion of the eight-corner single-tangential firing boiler, so as to study the generation, distribution and emission characteristics of NOx at different SOFA ratios, and to compare the simulation data with actual measurements. Results show that when the SOFA ratio is raised from 0.040 to 0.207, the peak temperature in furnace would be reduced by 80 K, and the outlet NOx concentration would be reduced from 535 mg/m3 to 373 mg/m3, indicating obvious effects of SOFA ratio on the NOx emission. By comprehensively considering the oxygen and temperature factors, it is recommended to keep the SOFA ratio no more than 0.2 in actual operation.
  • Research on Cell Models for Thermodynamic Calculation of Double Reheaters
    LI Delong, ZHANG Zhongxiao, YU Juan, FAN Haojie, DONG Jiancong, GAO Haotian
    2016, 36(7): 519-524.
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    A concept of cell models was proposed for thermodynamic calculation of double reheaters, while the cell dividing principles and schemes were described, including the calculation procedure and equations, etc. With the models, thermodynamic calculation and analysis were conducted on the double reheaters. Based on the dividing principles, high-temperature superheaters were divided into four cells (Ⅰ, Ⅱ, Ⅲ and Ⅳ) according the direction of flue gas and steam flow, while the primary and secondary high-temperature reheater were uniformly divided into three cells (Ⅰ, Ⅱ and Ⅲ) according to the arrangement relationship between superheaters and reheaters. Calculations were then conducted on each of the cells under different working conditions in the sequence of flue gas and steam flow. Results show that the calculated main steam temperature is around 610℃ and the outlet steam temperatures of reheaters are both above 600℃, with an error within 0.6% under BMCR condition, compared with the design value, which could be controlled by adjusting the flow rate of desuperheating water under all the conditions. This model is proved to be applicable for thermodynamic calculation of double reheaters, simply and easily.
  • 3D Simulation on Flow Field at Condenser Water Side of a 1000 MW Unit
    ZHOU Lanxin, ZHANG Na
    2016, 36(7): 525-529,550.
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    Taking a 1000 MW unit as an example, numerical simulations were conducted on flow characteristics at its condenser water side using Fluent software. Results show that the large vortex produced by circulating water in the water chamber of high- and low-pressure condenser and the impact of circulating water on the tube plate would lead to the increase of resistance loss and the non-uniform distribution of water velocity in tube bundle areas; the phenomenon of water swirl can be significantly reduced by adding guiding plates and convex buckles in the water chamber, where the water velocity would become uniform and smooth, the impingement on baffle plate would be weakened, and the water would flow into the tube bundle along the direction of convex buckles, resulting in increased average water velocity by 0.033 m/s and raised overall heat-transfer coefficient by 28 W/(m2·K), indicating obvious improvement of heat-transfer effect at water side of the condensers.
  • Experimental Study on Heat Transfer Enhancement of Corrugated Plate by Staggered Perforations
    LI Pengcheng, SUN Zhijian, HUANG Hao, TANG Zhou, HU Yacai
    2016, 36(7): 530-534.
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    Transient test method was used to study the heat transfer performance of corrugated plate with staggered perforations in different arrangements (15°, 30° and 45°), and to compare the value of Nu/Nuo* at equal pumping power. Results show that compared with corrugated plates without perforations, the average Nu of the plate with staggered perforations in above three arrangements is increased by 17.1%, 24.8% and 34.9% respectively, with an increase of friction factor f by 24.7%, 33.1% and 38.4% accordingly. Compared with the arrangements of 15° and 30°, the value of Nu/Nuo* in the case of 45° is correspondingly increased by 53.3% and 67.8%, indicating that the heat transfer performance of corrugated plate reaches the maximum in the arrangement of 45°.
  • Research on CO2 Capture Performance of PZ/AEEA Blends
    ZHAN Zhigang, ZHOU Xuping, XU Qisheng, LI Fangyong, YU Yuexi, FANG Mengxiang, LIU Fei, WANG Tao, LUO Zhongyang
    2016, 36(7): 535-540.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Mass-transfer properties of piperazine (PZ)/2-(2-aminoethylamino) ethanol (AEEA) blends in different mixing ratios for CO2 capture were investigated in a wetted-wall column, so as to study the effects of mixing ratio and CO2 loading on overall mass-transfer coefficient of the blends. Meanwhile, continuous CO2 absorption performance of PZ/AEEA blends in different mixing ratios were analyzed in a bubbling reactor at different temperatures. Results show that PZ/AEEA blends have better performance than 30% MEA in mass-transfer properties, absorption capacity and absorption rate. CO2 loading affects the mass-transfer properties of PZ/AEEA blends, approximately linearly dependent; while temperature significantly influences the CO2 absorption of PZ/AEEA blends. However, the mixing ratio has less effect on both the CO2 absorption and mass-transfer properties of PZ/AEEA blends.
  • Analysis of Carbon Capture Process by Ammonia Based on Technical Economics
    HAN Zhonghe, BAI Yakai
    2016, 36(7): 541-550.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To reasonably evaluate the operation performance of a coal-fired power plant adopting the ammonia-based carbon capture process, a technical economic model was set up based on the simulation model of carbon capture system and the variable condition model of power plant, so as to analyze the effects of following parameters on operation performance of the unit, such as the ammonia concentration, lean solvent loading, chilled temperature, desorber pressure, ammonia slip rate and carbon capture rate, etc., and subsequently to determine the optimal variables of the carbon capture system. Results show that the optimal values of ammonia concentration, lean solvent loading and chilled temperature are respectively 11%, 0.36 and 15℃, when the power generation efficiency would be increased by 0.7127%, and the coal consumption rate, power generation cost and carbon capture cost would be reduced by 6.9594 g/(kW·h), 0.011 CNY/(kW·h) and 16.7563 CNY/t accordingly, compared to the original power unit.
  • High-temperature Steam Gasification of Forestry Wastes for Production of Clean Gas
    NIU Yonghong, HAN Fengtao, CHEN Yisheng, WANG Li, GUO Ning
    2016, 36(7): 551-555,588.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An experimental platform for steam gasification of biomass was built based on downdraft gasifier, which makes use of pine sawdust briquette to produce hydrogen-rich gas, so as to analyze the gas composition, hydrogen yield, gas yield, gas calorific value and coal gas efficiency at different temperatures. Results show that the high-temperature steam can effectively promote the forward reaction of steam reforming. When the gasification temperature rises from 700℃ to 900℃, the H2 volume fraction, the hydrogen yield, the gas yield and the cold gas efficiency would be increased by 50%, 2.5 times, 70% and 37%, respectively. The steam reforming reaction can be accelerated towards the generation of H2 by high specific enthalpy contained in the high temperature steam involved in the reaction. The rise of gasification temperature helps to boost the forward reaction for more output of gas product. The gas produced in high-temperature steam gasification of forestry wastes, like pine sawdust, etc., is of high grade, which is able to burn stably in the experiment and therefore is theoretically considered to be available in commercial process.
  • Resonance Analysis of a Hydraulic-driven Floor-type Wind Turbine Unit with Long Transmission Pipeline
    AI Chao, LIU Yanjiao, YE Zhuangzhuang, KONG Xiangdong
    2016, 36(7): 556-562.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To investigate the stable operation conditions of a hydraulic-driven floor-type wind turbine system with long transmission pipeline, the effects of its system parameters on the system resonance were explored, based on which a mathematical model was established for the main drive system, and subsequently the resonance excitation sources were studied from the aspects of energy input, hydraulic components and load output etc., while factors influencing the pressure ratio of the system were analyzed, thus the influence of various parameters on the system resonance were determined. Results illustrate that the parameters, such as the tube diameter, tube length and oil viscosity, have a great influence on the amplitude of pressure ratio, while the movement viscosity and volume modulus also affect the operating frequency of the system; the system resonance frequency exhibits in the form of odd multiples of the fundamental frequency.
  • Optical Analysis and Simulation of a Linear Fresnel Solar Collector
    SONG Jinghui, MA Jishuai, ZHAN Zhigang, DAI Yanjun
    2016, 36(7): 563-568.
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    The optical efficiency and concentrating property of a linear Fresnel solar collector were calculated mathematically and simulated optically. Based on the principles of geometrical optics, mathematical models of relative optical losses (cosine loss, shading & blocking loss, etc.) in the collector mirror field were established so as to calculate related optical efficiency corresponding to each energy loss). Meanwhile, geometrical models of the collector were created using software TracePro to simulate the transmission of ray incident to the mirror field in model space by ray tracing method, including the absorption, reflecting and scattering of ray on the model surface, thus the optical efficiency and concentration ratio of the collector could be calculated by tracing the radiation flux of the ray. Results show that the optical efficiency obtained respectively by methamatical and geometrical model agrees well with one another. The detail and integral analysis on factors influencing the optical performance of linear Fresnel solar collectors may serve as a reference for the design of similar collectors, which may be used in combination or be mutually complementary with each other.
  • Sensitivity Analysis on Supply Cost of Farmer Straw for Power Generation
    ZHAI Mingling, ZHANG Xu, CHENG Fei, ZHAO Haoliang, SU Xing
    2016, 36(7): 569-574,588.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In the collection process of farmer straw for power generation, there are in total following four supply modes:manpower collection + active delivery, machinery collection + active delivery, manpower collection + waiting for delivery, and machinery collection + waiting for delivery. Corresponding models were established for cost calculation of farmer straw in above supply modes, while single factor analysis was conducted for different key sensitive factors. Results show that the mode of manpower collection has lower cost than machinery collection, which however is greatly affected by the labor price, and when the labor price is more than 18 CNY/h, the mode of manpower collection + active delivery costs the maximum. When the arable area is larger than 0.667 hm2, the cost of all supply modes would basically keep constant. The mode of manpower collection is more affected by conveying distance than machinery collection, the shorter the stubble is, the higher the influence will be. Machinery collection is found to be the most suitable mode for the condition of high crop yields.
  • Calculation Method for Optimum Back Pressure of Direct Air-cooling Unit and Its Application
    ZHAI Yongjie, MI Lu, LIU Jinlong
    2016, 36(7): 575-582.
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    By analyzing the main factors that affect the back pressure of a direct air-cooling unit, and based on its historical data, a calculation model was set up for optimum back-pressure of the unit using support vector machine and particle swarm algorithm, so as to study the relations of back pressure with both the generator power and the power consumption of air-cooling fan. Taking a 300 MW direct air-cooling unit as the object of study, the optimum back pressure corresponding to different loads and ambient temperatures was calculated with the model, while a scheme for optimization of the back pressure was designed in DCS, and the optimized back pressure was then put into the adjusting logic of back pressure to regulate the controller. Results show that the optimum back pressure of direct air-cooling unit increases with the rise of load and ambient temperature. The application of optimum back pressure can help to increase the unit economy under the premise of ensuring safe and stable operation of the unit.
  • Effect of Heat Treatment Process on Microstructure and Properties of Martensite Stainless Steel X39CrMo17-1
    HUANG Weihao, REN Xiao, HE Long
    2016, 36(7): 583-588.
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    In the localization of martensitic stainless steel X39CrMo17-1 for valve internal parts, it was found that the mechanical properties were not up to standard. Comparative studies on X39CrMo17-1 steel were conducted in terms of different quenching and tempering processes by OM, SEM and room-temperature mechanical property tests. Results show that the microstructure and mechanical properties of X39CrMo17-1 steel can not be improved obviously when it is previously quenched at 1060℃ for different holding time or at higher quenching temperatures, and is then tempered at 750℃ for 3 hrs. A further microstructure analysis suggests that the steel is with the characteristics of hypereutectoid steel closed to eutectoid point. Consequently, it should be quenched and tempered at relatively low temperatures accordingly. The mechanical properties of martensitic stainless steel X39CrMo17-1 can be remarkably improved after being subjected to the optimized quenching and tempering process 1040℃/1 h+650℃/4.5 h, when an optimum coupling of plastic, strength and impact toughness can be reached, due to uniform distribution and dispersion of carbides in the form of tiny particles in X39CrMo17-1 steel.