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    Boiler Technology
  • Boiler Technology
    Cold-flow Model Experiment of Interconnected Fluidized Bed for Chemical Looping Combustion of Coal
    MA Jin-chen, ZHAO Hai-bo, MEI Dao-feng, GUO Lei, ZHENG Chu-guang
    2012, 32(12): 909-915.
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    Taking the configuration of "turbulent bed + fast fluidized bed" as the air reactor (AR) and a bubbling bed as the fuel reactor (FR), a coal-fueled chemical looping combustion (CLC) system was designed, where two loopseals are used to prevent gas leakage between AR and FR, and a cyclone for gas-solid separation. Cold-flow model experiments were carried out to study the pressure distribution, solids circulation rate, gas leakage rate and ash-carrier separation efficiency of the CLC system. Results show that for the interconnected fluidized bed, its AR and FR are well sealed; the solids circulation rates meet or even exceed the design requirement; the separation efficiency of secondary cyclone at the FR exit nearly reaches 100%; the mass fraction of coal ash entering into AR from FR is less than 1.55%; the coal ash separation efficiency is high. The experimental setup may operate stably and continuously for a long time in a wide range of controllable gas superficial velocities, proving it to be feasible to design and operate the interconnected fluidized bed for coal-fueled chemical looping combustion.
  • Boiler Technology
    Numerical Study on Adjustable Range of Secondary Air Swirl Intensity
    LI Bing-chen, SONG Jing-hui, SHEN Yue-liang, LI De-bo, ZHOU Shao-xiang
    2012, 32(12): 916-921.
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    Numerical simulation was conducted with software Ansys 12.0 on the flow field of power plant boiler, so as to study the effect of swirl intensity of both the internal and external secondary air on the in-furnace flow field. Results show that with the rise of swirl intensity, the central backflow zone begins to move away from the axis of burner outlet, with an elongated length and an enlarged area; when the swirl intensity rises to a certain value, no ideal central backflow zone would be formed, in which case flash phenomenon may occur; the swirl intensity of external secondary air has a higher effect on the backflow zone, with an adjustable range narrower than that of the internal secondary air; the adjustable range of internal and external secondary air is 0.58-2.74 and 0.58-1.00 respectively.
  • Boiler Technology
    Emission Characteristics of CO and NOx from Opposed Firing Boiler in a 600 MW Supercritical Unit
    HONG Rong-kun, SHEN Yue-liang, ZHAO Zhen-feng
    2012, 32(12): 922-927.
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    Emission characteristics of CO and NOx from a 600 MW supercritical boiler with burners arranged in front and back walls were studied by both field experiment and numerical simulation. Results show that the CO concentration in the flue gas is within 500-2 500 mg/m3. The turning point of NOx emission appears when the excess air coefficient α1 is within 0.86-0.90 in main burning area, higher than the designed α1 (0.80) for low NOx emission, in which case the corresponding ratio of overfire air to secondary air is about 27%-32%. NOx emission characteristics of the boiler are influenced by the design of its HT-NR3 burner for low NOx emission, indicating a negative correlation to CO emission. At the load of 600 MW and a constant total air volume, the rise of overfire air ratio from 32% to 49% would result in a significant reduction of CO concentration and combustible contents in fly ash, but an increase of NOx emission, when the influence of oxygen content on CO and NOx emission weakens obviously, which may raise the possibility of high-temperature corrosion on side walls in the main burning area.
  • Boiler Technology
    Combustion Optimization for Utility Boilers Based on Sharing LSSVM Model
    GAO Fang, ZHAI Yong-jie, ZHUO Yue, HAN Pu, LU Yuan
    2012, 32(12): 928-933.
    Abstract ( )   Knowledge map   Save
    The boiler combustion system is a complex multi-input & multi-output system. To achieve the objectives of high efficiency and low pollutant emission for the system in one model, some improvements were carried out on the standard regression algorithm ofleast squares support vector machine(LSSVM). Based on the field combustion adjustment data of a 1 000 MW ultra supercritical boiler, a sharing LSSVM model was established by taking both the boiler thermal efficiency and mass concentration of NOx emission as the output variables, with which an improved particle swarm algorithm was selected to optimize the operating conditions of the boiler. Results show that with the sharing LSSVM model, the mean prediction error for boiler thermal efficiency and mass concentration of NOx emission can reach 0.028% and 2.16% respectively, the searched parameter combination of high thermal efficiency and low NOx emission may serve as a reference for optimization of boiler operation.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Numerical Study on High-speed Heterogeneous Condensation Flow of Wet Steam
    WANG Zhi, LUO Yan, HAN Zhong-he, AN Lian-suo
    2012, 32(12): 934-940.
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    Based on sphere-cap-shaped nucleation mechanism, a numerical model of two-phase heterogeneous condensation flow of wet steam was established, with which numerical simulations were conducted on the heterogeneous condensation flow in Laval nozzle, turbine cascade and turbine stage respectively. Results show that in comparison with spontaneous condensation, the impurity particles in heterogeneous condensation flow change the condensation process, reduce the intensity of condensation shock in the Laval nozzle, alter the pressure distribution in the turbine cascade, reduce the supercooling degree of steam, and lower the thermodynamic loss of non-equilibrium. In the turbine stage, the inlet and outlet angle of heterogeneous condensation flow around rotor and stator are close to those of superheated steam flow, and its pressure before rotor blade is higher than that of superheated steam, but its degree of reaction deviates from corresponding values in superheated steam flow.
  • Steam Turbine and Gas Turbine
    Experimental Study on Film Cooling Flow Characteristics over Turbine Stator Blade at Different Setting Angles
    ZHANG Ling, DONG Hai-rui, MOU Xue-feng, WANG Wei
    2012, 32(12): 941-946.
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    Flow structures over a turbine stator blade with six rows of film cooling holes were measured at different blowing ratios and setting angles by PIV on a straight-flow low-speed wind tunnel bench, during which the flow velocity and turbulent kinetic energy were analyzed. Results show that the velocity gradient on suction surface is much higher than on pressure surface, and the velocity gradient increases with redu-cing setting angle and rising blowing ratio; the film adherence is influenced by setting angle, which reaches the best at β=70°, and the adherence on suction surface is stronger than on pressure surface; maximum turbulent kinetic energy exists on the top of bended coolant, i.e. at the boundary where mainstream mixes with jet flow; with the reduction of setting angle, the turbulent kinetic energy weakens gradually in the concentration area downstream the pressure surface, which reaches the minimum at β=70°, and with further reduction of the setting angle, the concentration area moves to the downstream region on the suction side, where the turbulent kinetic energy rises gradually.
    • Auxiliary Equipment Technology
  • Auxiliary Equipment Technology
    Effect of Abnormal Blade Incidence on Internal Entropy Generation in Axial-flow Fans
    LI Chun-xi, YIN Pan, YE Xue-min, ZHANG Lei
    2012, 32(12): 947-953.
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    The OB-84 axial-flow fan was numerically simulated at abnormal angles of blade incidence using Fluent software, while the characteristics of entropy generation in the axial-flow fan investigated and analyzed at cocurrent and reverse deviation of blade incidence based on entropy generation theory. Simulation results show that the entropy generation is mainly caused by turbulent dissipation; the entropy generation rate is relatively high in the area of moving blade and guide vane, and is relatively low around collector and diffuser; however, the total entropy generation is in the same order of amplitude respectively in regions of moving blade, guide vane and diffuser. The deviation of blade incidence influences the entropy generation of fan in different degrees; the entropy generation will be higher than normal condition inclusive of installation angle deviation Δβ=±10°, and it increases with the growth of Δβ; however, the influence of Δβ on entropy generation reduces in the case of Δβ>30°. Strip areas of high entropy generation including several flow passages will be produced along downstream of abnormal blade at cocurrent deviation, whereas only scattered high entropy generation regions will be formed at reverse deviation. At the same deviation of blade incidence, the influence of cocurrent deviation is generally higher than that of reverse deviation.
    • Environmental Science
  • Environmental Science
    Effect of Calcium Addition on Formation of Particulate Mercury in Coal Combustion Process
    GAO Zheng-yang, ZHOU Li-ming, YIN Li-Bao, ZHONG Jun,YU Hang, ZHENG Shuang-qing
    2012, 32(12): 954-959.
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    Combustion experiments on two types of coal with additions of CaO and CaCl2 were conducted in a high-temperature entrained-flow pulverized-coal reactor, during which ash samples under various combustion conditions were collected, so as to measure the mass fraction of Hg and perform EDS and XRD analysis on the fly ash. Results show that the addition of CaO may promote the formation of Hgp, but its promotion effect is weaker than CaCl2. Maximum ratio of Hgp shall be found in flue gas at a CaCl2 addition ratio of 3%, when the mass fraction of Cl in fly ash reaches the highest in the total inlet of Cl.
  • Environmental Science
    Multi-parameter Linear Regression Analysis on Cyclic CO2 Capture Behavior by Limestone
    CHEN Hong-wei, YAN Jin, Stuart Scott, WEI Ri-guang,GAO Jian-qiang, HUANG Xin-zhang
    2012, 32(12): 960-965.
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    The cyclic CO2 capture behavior of two calcium-based sorbents were tested based on thermogravimetric analysis method (TGA). Using linear regression statistic analysis, the relationship was determined between the reaction parameters (including cycle number, carbonation reaction time, calcination temperature and calcination atmosphere) and the cyclic reaction rate and conversion rate. Evaluation function F was introduced to deduce the effect of each independent parameter on the cyclic capture behavior of sorbents. Result show that the cyclic CO2 capture process by calcium-based sorbent can be accurately described under different parameter conditions through establishment of regression equations for different phases of reaction mechanism respectively. The effect of reaction time on the capture efficiency is most significant during chemical reaction control phase, and the cycle number turns to be dominant after diffusion reaction control phase is initiated.
  • Environmental Science
    Effect of Dielectric Material on NO Removal by DBD
    WANG Tao, SUN Bao-min, XIAO Hai-ping, ZENG Ju-ying, YANG Bin, RAO Su
    2012, 32(12): 966-970.
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    To study the effects of dielectric material on the removal of NO by dielectric barrier discharge (DBD), both simulation and experimental tests were carried out by taking materials with different dielectric constants as the dielectric layer, during which the relationship of E/N with either the ionization rate or the electron mean energy was analyzed based on Boltzmann equation. Results show that with the rise of dielectric constant, the field intensity increases, and accordingly resulting in promoted E/N, raised electron mean energy and improved ionization rate, in which case, more active particles will be produced. Among all the 3 materials including corundum, quartz and ceramics, the material corundum has the strongest ability to transfer charges due to its highest dielectric constant, which makes the discharge current be raised, and therefore is good for NO removal.
    • Energy System Engineering
  • Energy System Engineering
    Design and Exergy Analysis on Thermodynamic System of a 700 ℃ Ultra Supercritical Coal-fired Power Generating Set
    CAI Xiao-yan, ZHANG Yan-ping, LI Yu, HUANG Shu-hong, GAO Wei
    2012, 32(12): 971-978.
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    According to the frame structure of MC (Master Cycle) system, a thermodynamic system was designed for 1 000 MW, 700 ℃ ultra supercritical coal-fired power generating set based on MC, during which the thermodynamic parameters were determined, while a comparative thermodynamic system designed based on conventional structures. Both the thermodynamic systems were divided into 5 units, including the boiler, steam turbine, generator, condenser and pipeline, and three indexes of each unit includingthe exergy loss, exergy loss coefficient and exergy efficiency were calculated by exergy analysis method. Results show that the power generating set based on MC system has higher thermo-economy than that based on conventional system, mainly indicating in the higher thermo-economy of the steam turbine system, especially in the higher thermo-economy of the IP cylinder and of the heaters at stages 3 to 6.
  • Energy System Engineering
    An Improved Dynamic Model and Simulation of Shell Gasifiers Based on Slag Layer Method
    TANG Kai-feng, ZHANG Hui-sheng, WENG Shi-lie
    2012, 32(12): 979-983.
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    To solve the problem that conventional model of gasifier based on lumped slag layer method can’t reflect the distributed-parameter characteristics in the gasifier, a new cell-slag model was built to cover the shortage of conventional model, which takes the advantage of both the lumped slag layer method and the cell method for simulation of coal slurry gasifiers. Using the new model, numerical simulation was made on a shell gasifier, of which the results obtained at both steady and dynamic state were analyzed and compared with corresponding literature data and the simulation results based on original lumped slag layer method. Results show that the simulation results by the cell-slag method agree well with corresponding literature data, proving the new method to be feasible and superior to conventional model in simulation of distributed-parameter characteristics.
    • Nuclear Technology
  • Nuclear Technology
    Structure Optimization for Cooling Tower of an AP1000 Nuclear Power Plant
    ZHOU Lan-xin, MA Shao-shuai, GONG Xue-min, SUN Hui-liang
    2012, 32(12): 984-990.
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    Based on heat and mass transfer theory of air-water two-phase flow, a 3D numerical model was established using Fluent software for the cooling tower with 20 000 m2 spray area of an AP1000 nuclear power plant. The characteristic value of generatrix equation for a hyperbola cooling tower and its optimized throat radius were calculated, while their influences on the flow field, inlet air flow, evaporation rate and outlet water temperature studied, during which optimal structural parameters of the 210 m high tower were obtained. Results show that optimal operation performance may be achieved for the cooling tower at a radius ratio of throat to bottom in 0.6-0.7, and a characteristic value of generatrix equation in 0.17-0.18.