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  • 2016 Volume 36 Issue 11
    Published: 15 November 2016
      
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  • Retrofit of an Opposed Firing Boiler to Prevent High-temperature Sulfur Corrosion
    LI Chunxi, XU Tao, LI Min, YE Xuemin
    2016, 36(11): 853-861.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem of high-temperature sulfur corrosion occurring on the side water wall of a 600 MW supercritical opposed firing boiler after low-NOx combustion retrofit, a device was added to arrange near-wall air curtain to the side wall, after which numerical simulation of the furnace combustion was carried out to examine the distribution of flue gas components near the side wall before and after the addition of near-wall air curtain, and to analyze the effects of near-wall air curtain on the in-furnace combustion and high-temperature sulfur corrosion. Results show that under the original condition without near-water air curtain, CO is mainly concentrated in the middle area of water wall with lower concentration of O2, where the simulated region of reducing atmosphere is in good agreement with actual region of sulfur corrosion observed in the boiler; in the case with near-wall air curtain, the CO concentration reduces significantly while the O2 concentration rises simultaneously in the area near the side wall, resulting in greatly improved reducing atmosphere in the area; the adoption of near-wall air curtain has negligible influence on the furnace combustion and pollutants emission.
  • Analysis on Steady-state Process of Air/Gas System for a Typical Oxy-fuel Combustion Boiler
    HUANG Yongli, LIU Jie, REN Jian, LIU Zhaohui, ZHENG Chuguang
    2016, 36(11): 862-869.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the steady-state model for air/gas combustion system of typical oxy-fuel combustion boilers, running data of the system in a 35 MW oxy-fuel combustion boiler were numerically simulated, with following problems involved in the operation process analyzed in detail, such as the air/gas distribution, oxygen injection, air leakage control and the optimization of CO2 capture and storage, etc., after which corresponding suggestions were proposed for improvement of relevant operation characteristics and process parameters. Results show that when the air leakage ratio is controlled below 3.6%, the CO2 concentration can theoretically achieve 80% in dry flue gas recirculation mode. Efficient removal of flue gas moisture is beneficial to both the system operation and the CO2 capture from the gas circulation. Different oxygen distribution modes will bring different results in combustion optimization, system safety and control adjustment.
  • Measurement of Tip Clearance Flow with Spontaneous Tip Injection Using PIV Technology
    HU Jianjun, ZHANG Duo, LI Zhixian, MA Long, KONG Xiangdong
    2016, 36(11): 870-876.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To investigate the influence of spontaneous tip injection (STI) on the turbine cascade flow, a small scale low-speed wind tunnel test rig was developed to directly measure the tip clearance flow field with spontaneous tip injection using PIV technology, so as to obtain the flow field adjacent to the injection hole at low Reynolds numbers (Re=6.46×103-3.23×104), present the interaction process between STI and tip leakage flow (TLF) under laminar and turbulence flow conditions in the tip clearance, reveal the mechanism using STI method to suppress the TLF at low Reynolds numbers (covering the transition process from laminar flow to turbulence flow), and finally to analyze the phenomenon of vortex distribution similar to the Karman vortex street (KVS) appearing in the wake of tip injection. Experimental results show that the introduction of STI may reduce the tip leakage flow in a certain degree, which however, would simultaneously intensify the complexity of the tip clearance flow.
  • Analysis of Flexible Rotor Vibration Under Coupled Action of Shaft Bend and Rotor Unbalance
    XIA Yalei, YANG Jiangang, ZHANG Xiaobin
    2016, 36(11): 877-882.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To solve the problem of unstable vibration occurring in the HP-IP rotor of a 660 MW supercritical steam turbine, a dynamic response model was set up for the system under coupled action of shaft bend and rotor unbalance using finite element method, of which the accuracy was verified with field experiments. Results show that the shaft bend caused by inconsistency between balancing and unbalance plane can not be neglected at high rotating speeds, since it may lead to the instability and increase of vibration. The balancing plane should be chosen on the unbalance plane as far as possible. High-pressure rotor is easy to have creep deformation under the effect of external force due to its high-temperature operation environment; the phenomenon is even more obvious for high-pressure rotors of large steam turbine.
  • Numerical Simulation of Ash Deposition with Adhesion of NH4HSO4 in an Air Preheater
    LUO Min, ZHAO Lingling, LI Siyu
    2016, 36(11): 883-888.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A model was built for ash deposition with adhesion of viscous liquid NH4HSO4, based on which numerical simulations were conducted to study the ash deposition process on the regenerative unit of a rotary air preheater in a 300 MW set after retrofit of its SCR denitrification system, so as to analyze the variation law of the ash deposition characteristics, such as the normal impact velocity and angle of particles, and the deposition intensity, thickness and probability, etc. Results show that the average deposition intensity in the area with NH4HSO4 adhesion is 7.3 and 4.5 times of that without NH4HSO4 respectively for the upper and lower wall; the deposition probability in the area with adhesion of NH4HSO4 is around 90%, whereas the value in areas without NH4HSO4 is lower than 35%. The average deposition intensity on the upper wall is 2 times of that on the lower wall. The distribution of deposition thickness is in the same pattern as that of deposition intensity.
  • Performance Evaluation of Power Plant Condensers After Retrofit
    CHENG Dongtao, ZOU Yang, MA Tingshan, JU Wenping
    2016, 36(11): 889-893.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To overcome the deficiency of traditional performance evaluation method for power plant condensers, a new method was proposed considering the water resistance. Based on the retrofit schemes for a certain power plant condenser, comparative analysis was conducted on the variation of water resistance before and after retrofit among various schemes, while the effects of water resistance variation were studied on the cooling water flow, circulating pump's power consumption, and then on the overall performance of the condenser, so as to find out the optimum retrofit scheme. Results show that the performance evaluation method for condensers considering water resistance is more reasonable and practicable, which therefore may serve as a reference for the decision of optimal retrofit scheme and for the follow up performance evaluation of condensers.
  • Properties of Flue Duct Evaporation Products by Desulfurization Waste Water in Coal-fired Power Plants
    MA Shuangchen, YU Weijing, JIA Shaoguang, ZHANG Runpan, CHAI Jin, HUA Jizhou
    2016, 36(11): 894-900.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Flue duct evaporation products of desulfurization waste water were analyzed by XRD, EDS and ion chromatography, while their composition and morphology were compared with that of fly ash. Results show that the evaporation products of desulfurization waste water are mainly in solid and gaseous state. The solid products include CaSO4, NaCl and Na2SO4, while the gaseous products are HCl, HF, HBr, HNO2 and HNO3. The evaporation does not have negative effect on comprehensive utilization of the fly ash, but would increase its specific resistance. In addition, gaseous products such as HCl can aggravate the corrosion of flue duct and increase the amount of desulfurization waste water discharged.
  • Performance of WO3/TiO2-ZrO2 Catalysts for High Temperature Denitrification
    LU Qiang, WANG Lei, LIN Zhuowei, MA Shuai, LI Wenyan, YANG Shaoxia, DONG Changqing
    2016, 36(11): 901-906.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    With WO3 as the active component and TiO2-ZrO2 as the carrier, WO3/TiO2-ZrO2 SCR catalysts were prepared for high-temperature (>500℃) flue gas denitrification, which were subsequently characterized by XRD. Experiments were performed to reveal the effects of TiO2-ZrO2 composition, WO3 loading and high-temperature sintering treatment on the activity of above WO3/TiO2-ZrO2 catalysts. Results indicate that the WO3/TiO2-ZrO2 catalysts are thermally stable, and their crystalline structure would not change after high-temperature treatment at 800℃, when the corresponding denitrification efficiency would decrease only a little. The two WO3/TiO2-ZrO2 catalysts with 7:3 or 0:10 mass ratio of TiO2 to ZrO2 and with 20% WO3 exhibit the best SCR performance, which could be used in high-temperature flue gas denitrification.
  • Analysis on Wave Frequency and Slow Drift Response of a Spar Platform for Offshore Floating Wind Turbines
    WANG Donghua, YE Zhou, HAO Wenxing, ZHANG Nan, LI Chun
    2016, 36(11): 907-913.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A model was established for the NREL 5 MW floating wind turbine seating on an OC3-Hywind Spar Buoy platform, with which the first- and second-order wave forces were respectively calculated using the panel method based on radiation/diffraction theory and the quadratic transfer function, while the aerodynamic load of blades was determined according to the blade element momentum theory. In addition, a comparative analysis was conducted on the first- and second-order wave force and their resulting wave frequency and slow drift response respectively under the combined wind-wave effect and wind-wave-current effect. Results show that the first-order wave force is at least one order greater in magnitude than the second-order wave force, but the response amplitude caused by them is at the same level. Wind load affects not only the slow drift response but also the wave frequency response. The wave frequency response is mainly affected by waves, while the slow drift response is basically affected by wind.
  • Application of Wind Speed Self-similarity and Fractal Dimension in Wind Field Analysis
    LI Qianqian, LI Chun, YANG Yang
    2016, 36(11): 914-919.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The fractal theory was applied to turbulent wind field analysis by studying the self-similarity and fractal dimension of the wind speed time sequence, so as to overcome the blindness in selecting the turbulent wind spectrum model from the following two aspects:the local-global relations and the fractal dimension of the wind speed time sequence. Taking the wind speed time sequence of a wind field as the sample data, different wind speed time sequence curves were obtained respectively with Kaimal, Von Karman, SMOOTH and NWTCUP turbulent wind spectrum model, and its self-similarity was then verified with Hurst exponents while the fractal dimension was calculated using box counting method. Results show that different turbulent wind spectrum models have different fractal dimensions, which can be described in a quantitative way; the internal fluctuation of wind speed time sequence is not random, but a long-term correlated process with self-similarity; the fractal dimension is related to the reference wind speed.
  • A Flue Gas Waste Heat and Moisture Recovery System for 330 MW Heat Supply Units
    WANG Jinping, DENG Yu, LI Bin, AN Liansuo, MIAO Yuwang, ZHANG Yubin, WANG Gang
    2016, 36(11): 920-926.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    For a certain 330 MW coal-fired heat supply unit, a two-stage double utilization system was designed for waste heat and moisture recovery from flue gas of the power boiler by making use of fluoroplastic heat exchanger. The unit was then retrofitted according to the design plan, for which relevant performance tests were carried out under non-heating conditions. Results show that the flue gas waste heat and moisture recovery system can not only make full use of the waste heat and reduce the water consumption of the desulfurization system, but also recover part of the moisture from the flue gas, which helps to reduce PM concentrations in the flue gas and relieve the wear and corrosion to the chimney, thus achieving effective energy-saving and emission reduction of the power plant.
  • Characteristic Study on Optimal Vacuum of a Direct Air-cooling System Under Summer Conditions
    LI Xiao'en, WANG Ningling, FENG Pengpai, YANG Zhiping
    2016, 36(11): 927-933.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Taking a 660 MW supercritical unit as an object of study, two off-design models were set up respectively for the steam turbine and air-cooling system based on its operation data obtained under summer conditions, of which their calculation accuracy was subsequently verified with the performance curves for constant dryness and the data in original calculation specifications. Moreover, the way how to determine the optimal vacuum of the condenser was analyzed under different boundary conditions, including the air temperature, the heat exchange of condenser, the load and the fan speed, etc. Results show that under summer conditions, when the load is relatively high, an overclocked operation should be kept for the fan, so as to guarantee a safe backpressure and operation for the cooling system; whereas when the load is relatively low, in case of a fixed extraction flow, the pursuit of high operation economy becomes important, since the difference between the rise of unit output and the rise of fan power consumption has a maximum value with the increase of cooling air flow.
  • Energy Utilization and Pollutants Emission in Sewage Sludge Incineration
    YUAN Yanyan, HUANG Ying, ZHANG Dong, DONG Yue, YANG Kai, XIAO Jun
    2016, 36(11): 934-940.
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    Numerical simulations were carried out on sewage sludge semi-drying incineration and blending combustion process of power generation using Aspen Plus software, during which the energy utilization and pollutants emission of 4 different sludge samples were studied. Results show that in the semi-drying incineration process, all the 4 sludge samples are required to supplement other fuels when their heating values of dry basis are lower than 11.5 MJ/kg, and as the heating value of sludge decreases, the supplements remarkably increase. The sludge samples with high content of heavy metals tend to cause air pollution and their solid residuals can hardly be recycled. In the blending combustion process, the high heating value of sludge contributes to the generation efficiency; for the same sludge samples, the generation efficiency increases with the reduction of energy ratio of sludge; lower energy ratio of sludge helps to satisfy the requirement of environmental protection, even in the case of higher content of heavy metals in the sludge; the suitable energy ratio of sludge blended to coal is suggested to be 5%-8%. When the sludge is low in heating value and high in heavy metal content, the blending combustion process is recommended, otherwise, the semi-drying incineration process is suggested.