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    Boiler Technology
  • Boiler Technology
    Design and Optimization for Economizer of Pressurized Oxy-fuel Coal-fired Boilers
    MA Kai, YAN Wei-ping, GAO Zheng-yang, XU Jia-qing
    2013, 33(3): 165-171.
    Abstract ( )   Knowledge map   Save
    Taking the economizer of a 300 MW coal-fired boiler as an example, parameters such as the heating surface area, flue gas flow, gas-side heat-transfer coefficient and the pressure drop were calculated and analyzed respectively under conditions of atmospheric air combustion, atmospheric oxy-fuel combustion and pressurized (6 MPa) oxy-fuel combustion, after which an optimum structure was designed for the economizer according to the principle of minimum total cost of heat-exchanger per unit heat-transfer rate based on exergy-economic analysis. Results show that compared with atmospheric air combustion, the flue gas volume flow rate and convection heat-transfer coefficient reduce respectively by 28.5% and 11.5% under atmospheric oxy-fuel combustion; under the condition of pressurized oxy-fuel combustion, the flue gas volume flow rate is 98.82% lower than that of atmospheric air combustion, while both the gas-side heat-transfer coefficient and pressure drop increase and the heating surface area decreases with the rise of flue gas flow. Among all the given schemes, the flue gas velocity in optimal scheme is 1.54 m/s, when the gas-side pressure drop is 582.65 Pa, in which case the total cost of heat-exchanger per unit heat-transfer rate and the flue duct cross-section are only 60% and 7.8% of those under atmospheric air combustion.
  • Boiler Technology
    Numerical Simulation on Combustion Characteristics of Tangentially-fired Boilers at Different Air Speeds
    LI De-bo, XU Qi-sheng, SHEN Yue-liang, ZHANG Rui, WEN Zhi-yong, LIU Ya-ming
    2013, 33(3): 172-177.
    Abstract ( )   Knowledge map   Save
    The in-furnace flow field, temperature field, and the emission characteristics of CO2, CO, O2 and NO of a 220 t/h tangentially-fired boiler were studied under three different simulation conditions of air speed by Large Eddy Simulation (LES) method, of which the results were compared with actual experimental data. Results show that under the first simulation conditions, incomplete combustion may occur in the furnace, in which case, the outlet mass fraction of CO is the highest, while that of O2 is the lowest; whereas under other two simulation conditions, the results show relatively good consistency, indicating that with adequate air, the air speed will not influence much on the mass fraction of O2, CO and O2; when the excess air coefficient is relatively small or large, the outlet mass concentration of NO decreases; according to the simulation results, the maximum temperature in the furnace is 1 550 ℃ and the mean outlet temperature is 959 ℃, which are consistent with the experimental data, proving the simulation results to be accurate. With the increase of air speed and excess air coefficient, the mean in-furnace temperature and outlet temperature decrease. With the rise of air speed, both the tangential radius and the circle center do not change, but the maximum tangential air speed increases.
  • Boiler Technology
    Research on Soft-sensing of Circulation Ratio in CFB Boilers
    TIAN Liang, ZHAO Liang-yu, LIU Ji-zhen
    2013, 33(3): 178-183.
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    Circulation ratio is very important to the running condition monitoring and key parameters controlling of circulating fluidized bed (CFB) boilers, however, the value is generally very difficult to be measured directly. To solve this problem, a soft-sensing method was proposed for the circulation ratio by establishing and simplifying balance equations through mechanism analysis of chemical process in the furnace and material recirculating process in the CFB boiler according to the law of mass conservation, based on which key intermediate variables were calculated, such as the fly ash content, separator efficiency and so on, and subsequently the circulation ratio was obtained by simulation. Results show that a linear relationship exists between the circulation ratio and the density of particles in dilute region per unit load; the calculated circulation ratio is quite approximate to the design value of CFB boiler, proving the soft-sensing method to be effective and available.
    • Steam Turbine and Gas Turbine
  • Steam Turbine and Gas Turbine
    Feature Extraction of Rubbing Fault for Steam Turbines Based on Wavelet Singularity Analysis
    HU San-gao, AN Hong-wen, MA Zhi-yong, LIU Yi-bing, TENG Wei
    2013, 33(3): 184-188.
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    Aiming at the weak impact signal produced by rubbing fault of steam turbines, the location and duraction of the signal singularity were determined by conducting filtering process to the measured signal through wavelet transformation, extracting the transient impact component on a specific scale, carrying out Hilbert demodulation analysis to the impact component, enveloping the singularity of the reflection singal under the action of rubbing fault with the amplitude of transient impact singal, and conducting wavelet singularity detection to the amplitude-enveloped singal. An analysis was made to a nuclear power turbine unit using actual measurements of vibration signal. Results show that the feature extraction of slight rubbing fault can be effectively improved by detecting its abrupt information using wavelet singularity analysis.
  • Steam Turbine and Gas Turbine
    Finite Element Analysis on Collision-Vibration Characteristics of Shrouded Blades Based on ANSYS/LS-DYNA
    CHEN Zhen-nan, LU Xu-xiang, LI Lu-ping, HUANG Zhang-jun, JIN Feng-hua
    2013, 33(3): 189-193.
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    Based on 3D finite element model built up for shrouded blade using ANSYS software, and combined with explicit analysis of dynamic impact response with LS-DYNA software, relationships between collision damping effect and vibration system parameters were studied, such as the original tip gap, the phase difference and the amplitude of exciting force, etc. Results show that the collision damping among blades with zigzag shroud may effectively suppress the system vibration. The finite element analysis results agree well with relevant experimental data, proving the finite element model and method to be feasible and effective.
    • Engineering Thermophysics
  • Engineering Thermophysics
    Flow and Heat-transfer Characteristics of Finned Tube Heat Exchanger with Arc Delta Winglets
    SU Shi-chuan, LI Guang-chen, CHEN Ming-hua, ZHANG Xu, WANG Hao-dong
    2013, 33(3): 194-198.
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    3D numerical simulations were performed to investigate the flow and heat transfer coupling characteristics of finned tube heat exchangers with arc or straight delta-winglet vortex generators. Results show that when the Re is in 500-5 000, both the arc and straight delta winglets can enhance the heat transfer of heat exchanger. The enhancement effect of arc delta winglet is slightly weaker than the straight one, but its flow resistance is obviously smaller. In comparison with straight delta-winglet exchanger, the comprehensive performance of arc delta-winglet exchanger is 7.3%-11.5% and 8.2%-9.5% higher respectively in the case of aligned and staggered arrangement of heat-exchanger tube. The vortex generator can enable fluid to generate a velocity component perpendicular to the fin direction and improve the cooperativity between velocity filed and temperature field, and therefore the heat-transfer performance is enhanced.
  • Engineering Thermophysics
    Numerical Simulation on Two-phase Flow and Heat Transfer of Umbrella Vaporizers
    HE Fa-jiang, CAO Wei-wu, KUANG Jiang-hong
    2013, 33(3): 199-204.
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    Flow and temperature field in combustion chamber of a newly developed umbrella vaporizer were numerically simulated using generalized finite-rate model, which uses flue gas to impact the submerged umbrella, so as to analyze the influence of flue gas circulating rate on both the flue gas velocity and the temperature field at nozzle outlet. Numerical simulation was also performed to analyze the effect of nozzle height and liquid level on the heat transfer of gas-water two-phase flow using VOF model. Results show that optimal impact effect may be obtained when the flue gas circulating rate is 50% of the total volume generated in combustion and when the liquid level is 75 mm, in which case water drops are adequately entrained by flue gas to fill the vaporizer with enhanced heat transfer by vaporization.
    • Environmental Science
  • Environmental Science
    Efficiency Prediction of Ammonia Flue Gas Desulfurization Based on Partial Least Squares Regression
    HONG Wen-peng, CHEN Zhong
    2013, 33(3): 205-209.
    Abstract ( )   Knowledge map   Save
    Taking the main parameters affecting the ammonia flue gas desulfurization efficiency as input variables, and the desulfurization efficiency as output variables, a model for calculation of the desulfurization efficiency was built up using partial least squares regression, based on which efficiency predication was carried out for a certain power plant. Results show that the maximum relative error of desulfurization efficiency between predicted results and operation data is less than 4.0%, and the average error of the model is 0.53%, proving the calculation model to be accurate and applicable for efficiency prediction of flue gas desulfurization in actual engineering projects.
  • Environmental Science
    Factors Influencing Simultaneous CO2/SO2 Capture by Ca-based Sorbent and Evolution of the Limestone Surface Structure
    CHEN Hong-wei, ZHAO Zheng-hui, WANG Wei-li
    2013, 33(3): 210-217.
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    The process of using Ca-based sorbent to capture CO2 and SO2 sequentially was investigated on a thermo gravimetric analyzer, so as to analyze the influence of particle size, cyclic number, calcination condition and hydration on the simultaneous capture process, while the surface structure of limestone samples studied at different stages using scanning electron microscopy. Results show that the sulphation is more sensitive to particle size; the smaller the particle size is, the stronger the sulphation reaction will be. Cyclic number and calcination condition play a negative role in carbonation conversion, but affect little on sulphation. The steam hydration benefits both carbonation and sulphation. After calcination of fresh sorbent, small round projections form on the surface, and with the rise of cyclic number, these projections fuse into platy aggregates, when large pores appear. After steam hydration, many differently sized cracks and some free particles of extremely small size (<1 μm) occur on sample surface, which intensify the sorbent erosion. Sorbent with same microstructures may have different carbonation and sulphation properties, which are caused by different molar volumes of product and Gibbs free energy change of reaction.
    • New Energy
  • New Energy
    Low-temperature Ignition Characteristics of Coal/Biomass Blends
    WANG Chun-bo, WANG Jin-xing, LEI Ming
    2013, 33(3): 218-223.
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    Low-temperature ignition characteristics of coal/biomass blends were studied on a self-developed tube furnace constant-temperature thermogravimetric setup, so as to analyze the influence of the blending ratio, temperature, coal and biomass category on the ignition characteristics, while the low-temperature ignition activation energy of coal/biomass blends calculated. Results show that both the combustion rate and burnout degree increase with rising blending ratio; temperature rise helps to improve the ignition characteristics of coal/biomass blends; the effect of biomass on ignition characteristics of blends containing nonflammable coal is more obvious than that containing inflammable coal. For a specific coal, when the biomass with high moisture and high volatile content is blended, the weight loss of the blends will be accelerated at initial stage of combustion; whereas when the biomass with high ash content is blended, its promotion on coal combustion becomes weak at later stage of combustion; the activation energy reduces with rising biomass blending ratio and widening temperature range.
  • New Energy
    Fluidized Bed Combustion and Grey Correlation of Seaweed Particles
    WANG Shuang, JIANG Xiu-min, WANG Qian, JI Heng-song
    2013, 33(3): 224-227.
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    Combustion test of seaweed (Enteromorpha clathrata) particles was conducted in a fluidized bed to study the influence of bed height, bed temperature and fluidized air velocity on the mass of residual seaweed and fixed carbon, while grey correlation analysis performed on the influencing degree of each factor. Results show that bed temperature and fluidized air velocity have great influence on the mass of residual seaweed and fixed carbon, while bed height affects little. The important order of factors influencing the burnout of fixed carbon is in turn as follows: bed temperature > fluidized air velocity > bed height, indicating that bed temperature is the chief factor affecting the combustion of seaweed particles among all the factors studied.
  • New Energy
    Research on Thermal Performance of DSG Solar Trough Collectors
    CHEN Yuan-yuan, ZHU Tian-yu, LIU De-you, GE Jian
    2013, 33(3): 228-232.
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    The temperature distribution around an absorber tube in the single-phase water region, saturated region and dry steam region of a direct steam generation(DSG) solar collector was studied at steady state along circumferential direction by numerical calculations, based on which the heat loss model of collector was established, while the influence of following factors on the heat loss in different phase regions of absorber analyzed, such as the fluid temperature, mass flow-rate and working pressure, etc. Results show that fluid temperature is the key factor influencing the heat loss of collector, which rises with increasing temperature difference between fluid and ambient air; working pressure and mass flow rate of fluid have little influences on the heat loss.
    • Energy System Engineering
  • Energy System Engineering
    Thermoeconomic Analysis on a 350 MW Supercritical Direct Air-cooling Unit Based on Structural Theory
    LI Bin, DU Yan-ling, LI Lu, XIE Yi-min
    2013, 33(3): 233-238.
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    A thermoeconomic model was established for supercritical direct air-cooling unit on the basis of structural theory, of which the forming process of system production cost was analyzed by quantifying the production inter-relationship among various components and calculating the unit exergy cost of each component. Condensing components of the direct air-cooling unit were simplified and combined, while corresponding power consumption calculated approximately. According to calculation results of the unit under THA work condition, factors affecting the unit exergy cost of component product were analyzed. Results show that when the same kind of fuel is used, the lower the exergy efficiency of the component is, the higher the unit exergy cost of the product thereof will be; whereas when different kinds of fuel are used, the influence of both the fuel cost and exergy efficiency on the unit exergy cost should be considered comprehensively; it is also pointed out that the unit exergy cost of following components is relatively high, such as the No.7 low-pressure heater, feed pump, steam turbine, condensate pump, and so on; for direct air-cooling unit, the unit exergy cost of condenser is significantly higher than that of water-cooling unit; the production performance of air-cooling unit can be accurately assessed by applying the structural theory.
  • Energy System Engineering
    Thermodynamic Analysis of Combined Cooling, Heating and Power System with CO2 Transcritical Cycle
    ZHANG Xin-ming, ZHANG Chun-hui, YOU Fei
    2013, 33(3): 239-244.
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    A model of combined cooling, heating and power (CCHP) system with CO2 transcritical cycle was proposed by using the low-grade energy utilization/CCHP tri-generation technology and by taking 150 ℃ exhaust flue gas from conventional coal-fired power plant as the heat resource, based on which influences of following factors on the system performance were analyzed, such as the inlet pressure, inlet temperature of the expander, etc. Results show that the compressor’s inlet superheat degree affects little on the thermal economic coefficient of system; the coefficient of thermal performance increases with rising inlet pressure of high-pressure expander and inlet temperature of low-pressure expander, and with reducing inlet temperature of high-pressure expander, inlet pressure of low-pressure expander and evaporator temperature; a minimum irreversible loss exists in the rise of inlet pressure of high-pressure expander.