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    Boiler Technology
  • Boiler Technology
    Numerical Simulation on an 800 MW Swirl-opposed Firing Boiler Retrofitted for Low NOx Emission
    DUAN Er-peng, SUN Bao-min, GUO Yong-hong, BAI Tao, XIN Jing
    2012, 32(11): 825-829.
    Abstract ( )   Knowledge map   Save
    According to the problem of high NOx emission existing in an 800 MW supercritical boiler, retrofit schemes with three air distribution modes were designed, based on which the in-furnace combustion, heat transfer and NOx emission were numerically simulated using CFD method, while the temperature field, NOx concentration distribution and CO concentration distribution analyzed. Results show that the calculated results agree well with actual measurements. In the modes of staged-air combustion, the temperature reduces in primary combustion zone, where the CO concentration rises and the NOx emission drops significantly. Over-fire air may have unfavorable influence on the burn-off rate and outlet gas temperature, which will reduce the security and efficiency of the unit. The results of comprehensive comparison and analysis on the burn-off rate and outlet gas temperature prove the retrofit scheme with air distribution mode three to be the most optimal one.
  • Boiler Technology
    Influence of Structural Parameters on Fouling of Throttle Orifice in Boiler Water Walls
    YU Lan-lan, ZHOU Ke-yi, TANG Yan
    2012, 32(11): 830-835.
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    To solve the fouling problems occurring in throttle orifice for ultra supercritical boiler water walls, numerical calculation models were set up to analyze the fouling causes and the influence of structural parameters on the fouling degree. A relational model between the structural parameters and fouling degree was established based on a large amount of calculation and using BP artificial neural network, with which optimal structural parameters were obtained by using genetic algorithms for minimum fouling of the orifice. Results show that the precipitation and deposition of magnetic oxide iron caused by sudden pressure drop near the orifice plate are found to be the main reasons of orifice fouling; the influence of following structural parameters on the maximum pressure drop amplitude and throttling effect may be different around the orifice plate: such as the inlet angle, outlet angle, pore diameter and length of the orifice, etc.; the shorter the orifice length, the better the performance effect; the outlet angle hardly affects the orifice fouling, but the inlet angle and pore diameter play an important role in influencing the fouling degree; the optimal parameters of orifice plate are determined to be 9.54 mm for the pore diameter and 35° for the inlet angle.
  • Boiler Technology
    Study on Combustion and Deposition Characteristics of Coal Particles in a Cyclone Burner
    RAN Jing-yu, LIU Li-juan, LI Chai-zuo
    2012, 32(11): 836-840.
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    Combustion and deposition characteristics of coal particles in a cyclone burner were studied by numerical simulation and experiments. Results show that the burner can realize high-temperature combustion (above 1 700 K) at different loads, with high combustion efficiency and slag captured rate. Particles mainly deposit on the front wall, evenly distributed on both the upper and lower part. Smaller particles can follow well with the airflow, and are hard to deposit. Almost all the particles larger than 60 μm can deposit and burn on the front wall. To get uniform distribution of coal particles on inner wall of the burner, and prevent them from jamming in the low-temperature region, it is recommended to apply an appropriate excess air coefficient and a primary air ratio within 0.30-0.35.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Numerical Simulation on Aerodynamic Performance of Low-pressure Exhaust Hood for Steam Turbines
    ZHU You-jun, WANG Hong-tao, ZHU Xiao-cheng, DU Zhao-hui
    2012, 32(11): 841-846.
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    Based on the effects of aerodynamic performance of low-pressure exhaust hood on the steam turbine efficiency, numerical simulations were carried out on a small-scale test model of low-pressure exhaust hood to obtain the wall pressure distribution of guide ring at diffuser inlet and the velocity distribution of characteristic plane at diffuser outlet, during which the calculated results were compared and verified with actual measurements. Moreover the performance of diffuser and volute was analyzed by numerical simulation method. Results show that the vortex structure is very complicated between the diffuser and volute, and the passage vortex is found to be the main cause leading to the reduced diffusion capacity and energy loss in the exhaust hood.
  • Steam Turbine and Gas Turbine
    Analysis and Study on Moisture Loss in Steam Turbines
    GAO De-wei
    2012, 32(11): 847-852.
    Abstract ( )   Knowledge map   Save
    An analysis has been carried out on water erosion features of the last stage blade in an extraction condensing turbine unit, based on which the original empirical formula for calculation of moisture loss is proved to be insufficient. Moisture loss generally comes from following two aspects: the preliminary water droplet and the secondary water droplet. When the steam moisture is higher than a certain value, the loss by secondary water droplet will be greater than that by the preliminary one. Meanwhile, the preliminary water droplet formed by nucleation condensation will also cause water erosion on the blades. The moisture loss may be reduced by using outer-edge inner-surface dewetting boards, with which the unit efficiency will correspondingly be raised and the service life of blades can be elongated.
    • Automatical Controlling and Detecting Diagnosis
  • Automatical Controlling and Detecting Diagnosis
    Analysis of Furnace Pressure Based on Multi-scale Correlation and Mechanism Modeling
    TIAN Liang, LIU Xin-ping, WANG Qi, LIU Ji-zhen
    2012, 32(11): 853-858.
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    Using wavelet analysis ideas for reference, simple filter banks were designed to decompose the signals into frequency components with different scales. Correlation analysis was made among components of different signals, and the correlation characteristics among frequency components with different scales were compared to roughly determine the influencing factors and types of signals. Boiler furnace pressures were analyzed using multi-scale correlation method, during which significant positive correlation was found between the low/medium-frequency components of furnace pressure and the medium/high-frequency components of fuel and air flow. A simplified dynamic model was then built up between the flow of fuel/forced-draft air/induced-draft air and the furnace temperature and pressure. Mechanism analysis results show that bandpass filter characteristics exist between the pressure signal and combustion efficiency; the furnace pressure can reflect the change of combustion intensity in a wide range of load and frequency.
    • New Energy
  • New Energy
    Effects of Catalyst Particle Size and Mass on Catalytic Crackingof Biomass Pyrolysis Tar
    LI Yong-ling, WU Zhan-song
    2012, 32(11): 859-864.
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    According to the effects of catalytic cracking conditions on the treatment of biomass pyrolysis tar, the process of tar catalytic cracking under the action of catalyst was studied on the fixed-bed test rig by taking the tar from stalk pyrolysis as the raw material, so as to analyze the influence of catalyst particle size, mass and other parameters on the tar conversion effect and the catalytic cracking product. Results show that the decrease in catalyst particle size or the increase in catalyst mass can facilitate the conversion of gases from large molecular size with high heating values into small molecular size with low heating values, so that the catalytic cracking of tar is promoted, the gas yield is improved and the gas heating value is reduced.
  • New Energy
    Effects of Pyrolysis Temperature on Characteristics of Biomass Char
    LU Xu-ao, RAN Xu, ZHENG Xiao-long, YAN Wei-ping
    2012, 32(11): 865-870.
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    Mechanism-based pyrolysis experiments were carried out on rice husk and straw, during which physicochemical properties of the char were studied using TG, SEM, EDX and XDR, such as the pore structure, slagging characteristics, migration of chlorine and sulfur, and crystalline phase of the inorganic compound, etc. Results show that the pore structure of biomass char changes a lot at 500-800 ℃. When the pyrolysis temperature gets up to 1 000 ℃, the convex side of rice husk char will appear in melting state, while the straw char in melting and bounding condition. Most remaining of chlorine and sulfur will precipitate from the char at 800-1 000 ℃. The phase changes greatly and amorphous inorganic compound appears at a final pyrolysis temperature of 1 000 ℃ in the process of rice husk and straw pyrolysis.
    • Energy System Engineering
  • Energy System Engineering
    Numerical Simulation on Fixed-bed Sintering of Fly Ash from Municipal Solid Waste Incinerators
    DU Hui-jie, WANG Heng, SONG Guang-dong, WANG Hu, CHANG Zheng-ze
    2012, 32(11): 871-877.
    Abstract ( )   Knowledge map   Save
    To achieve sintering harmless treatment of fly ash from a municipal solid waste incinerator (MSWI), numerical models were set up for the in-furnace gas flow, heat and mass transfer as well as the combustion process. The sintering process was numerically simulated using Fluent software under design conditions, during which the gas flow and pressure distribution were calculated using porous media model, while the material combustion process described using shrinking core model, following which the gas velocity field, gas and material temperature field as well as the gas composition distribution were obtained. Results show that in the area 0.2 m away from the tuyere, the speed of blowing air gets stable and becomes evenly distributed; the material combustion mainly happens in the zone 0.3-0.55 m above the center line of tuyere; when the material falls down the center section of tuyere, the combustion process is already completed; for a coal mixing ratio of 12%, pellet diameter of 16mm and an excess air coefficient of 1.2, the material temperature may reach 1 138-1 400 K, which can fully meet the requirement of sintering harmless treatment of MWSI fly ash.
  • Energy System Engineering
    Thermogravimetric Experiment on Co-firing Characteristics of Coal with Municipal Sewage Sludge
    TANG Zi-jun, CEN Chao-ping, FANG Ping
    2012, 32(11): 878-884.
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    Combustion characteristic experiments were respectively performed for one coal sample(C), two municipal sewage sludge samples (S1, S2) and their mixtures using thermogravimetric analysis. Results show that the sludge weight loss mainly results from the separation and combustion of volatile components. Raising the heating rate may help to speed up the sludge disposal, but may decrease both the total weight loss rate and the quantity reduction effect. The co-firing performance of sludge with coal generally expresses the joint action of both the fuels; with the increase of sludge ratio, ignition temperature of the mixture reduces gradually; the comprehensive combustion performance index reaches the maximum at a sludge ratio of 25%. Besides, the kinetic parameters obtained by using the Freeman-Carroll differentiation prove the sludge to be more active at low temperatures, while the coal behaves in an opposite way. Based on analysis of combustion characteristics and chemical kinetics of sludge at different blending ratios, the combustion treatment is believed to be more suitable for sludge S2.
  • Energy System Engineering
    Experimental Study on Gasification of Jinjie Coal Char with CO2 Under Compound Catalytic Action of CaO and Fe(NO3)3
    CHEN Hong-wei, SUO Xin-liang, CHEN Long, YU Wei-feng, HUANG Xue-li
    2012, 32(11): 885-890.
    Abstract ( )   Knowledge map   Save
    The gasification characteristics of Jinjie coal char with CO2 under compound catalytic action of CaO and Fe(NO3)3 were studied under isothermal and ordinary pressure conditions on a fixed-bed experimental system. Results show that the optimal mass addition of compound catalyst is1%Ca+2%Fe, in which case, the gasification time can be reduced by 103 min and 18 min respectively as compared with that of raw coal char and single-component catalyst, and the catalytic intensity coefficient will be 5.71, 1.65 and 2.04 times of raw coal char, single-component catalyst CaO and single-component catalyst Fe(NO3)3, with a reduction of gasification temperature by 100 K, and a reduction of gasification temperature lying between single-component catalysts CaO and Fe(NO3)3; the activity of partial Ca(NO3)2 produced under the compound catalytic action is different from that of CaO, that is, the catalytic intensity of Ca has a certain relationship with the form of its precursor; the activation energy of coal char with addition of single-component catalyst is basically the same as that of raw coal char. Addition proportions of compound catalyst influence the increase degree of activation energy of coal char, and the minimum increase degree 15.4% is to be obtained at the optimal addition proportion.
    • Material Science
  • Material Science
    Experimental Study on High Temperature Corrosion of FiveSuperheater Materials for Power Plant Boilers
    CHENG Ding-nan, ZHANG Zhi-xiang, BIAN Bao, DENG Xiang,JIANG Wei-wei, ZHAO Qin-xin
    2012, 32(11): 891-897.
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    Taking following 5 materials for ultra supercritical boiler superheater as the objects of study, such as Tempaloy AA-1, Super 304H, TP347HFG, Tempaloy A-3 and HR3C, experimental tests were carried out in a laboratory vacuum oven to study their corrosion resistance respectively to high-temperature gas and gas-liquid (molten salt) two-phase flows. A new index was proposed to evaluate the corrosion rate by adding up the thickness of corrosion layer and the migration depth of corrosive elements, based on which high-temperature corrosion resistance was obtained for above 5 materials. Results show that all the 5 materials have a strong resistance to high-temperature corrosion in gas atmosphere, and their corrosion resistances in gas-liquid atmosphere are in following increasing order: Tempaloy A-3, TP347HFG, Super 304H, Tempaloy AA-1 and HR3C. The corrosion sustained by superheater materials is mainly of the gas-liquid two-phase kind.
  • Material Science
    Effect of Microstructure Evolution on Property of P92 Steel During High-temperature Creep-Rupture Tests
    JIANG Jun, ZHU Li-hui, WANG Yan-feng
    2012, 32(11): 898-902.
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    The microstructure of domestic P92 steel was investigated by SEM and TEM during creep-rupture tests at 600 ℃, while the effect of microstructure evolution on its mechanical property analyzed. Results show that during the creep-rupture tests, the hardness of P92 steel reduces before 1 429 h due to the coarsening of M23C6, and increases later on resulting from the precipitation of a large amount of Laves phase. With the coarsening of Laves phase, the hardness reduces again after test duration of 6 063 h, when MX still keeps fine and has excellent precipitation strengthening effect. During the whole process of creep-rupture test, the strengthening of dislocation and solid solution weakens due to both the recovery and recrystallization of lath martensite and the precipitation of Mo and W from the matrix.
  • Material Science
    Effect of Surface State on Steam Oxidation Rate of Steel TP347H
    ZHANG Bo, QI An-fang, JIN Yong-qiang, WANG Jian-yong,ZHENG Zi-jie, ZHENG Kai-yun
    2012, 32(11): 903-908.
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    Steam oxidation tests were carried out at 650 ℃ for 2 000 hours in steam oxidation furnace for TP347H specimens with surfaces respectively treated by grinding, shot blasting, fine grain + acid pickling, grinding + acid pickling and 15% cold deforming + acid pickling, so as to analyze the influence of the surface state on the oxidation rate, during which the surface morphology and composition of oxidized specimens were observed and studied using SEM and EDS, while the oxidation film analyzed using XRD, and the oxidation rate calculated by weight loss and thickness method. Results show that the oxidation films formed on above five specimens have basically similar morphology, but their oxidation rates are different, which are found to be in following increasing order: grinding, shot blasting, fine grain + acid pickling, grinding + acid pickling and 15% cold deforming + acid pickling specimen.