Archive

  • 2016 Volume 36 Issue 12
    Published: 15 December 2016
      
  • Select all
    |
  • Influence of CO2 Effect on Coal Char Combustion in Oxygen-enriched Environment
    JIN Xudong, ZHOU Yuegui, JIN Qiye, ZHENG Tingting
    2016, 36(12): 941-944.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An analysis was conducted to the influence of O2 concentration, CO2 chemical effect and thermal effect on the coal char combustion rate in oxygen-enriched environment containing a certain amount of CO2 with Ar gas to control the surface temperature of the coal char particles, based on a continuous-film model considering the coal char surface C-O2/C-CO2 reactions and the gas phase CO-O2 reaction. Results show that when the volumetric fraction of O2 rises from 21% to 26.5% in the oxygen-enriched environment, the surface temperature of char particles would be increased by 154 K, resulting in increased burning rate, and shortened ignition and burnout time. O2 concentration plays the most important role in influencing the coal char combustion rate, followed by CO2 chemical effect, and then by thermal effect, with relative contributions of 56.4%, 25.7% and 17.9%, respectively.
  • Effects of Combustion Temperature on the Ash Melting Properties of Zhundong Coal
    ZHOU Wentai, HE Xiang, WEI Zengtao, CHEN Duanyu, SHI Hongfei, MA Dafu
    2016, 36(12): 945-950.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Ash fouling properties of Zhundong coal were studied in a test rig at combustion temperatures of 950℃, 1 150℃ and 1 350℃, and with the oxygen concentration set as 2.0%-2.5%, 4.0%-4.5% and 6.5%-7.0%, respectively. The fly ash collected from relevant contamination segments was then examined by combustible test, SEM analysis and X-ray fluorescence spectrometer analysis, etc. Results show that with the rise of combustion temperature, the sintering behavior on surface of coal particles tends to increase, which inhibits the diffusion of oxygen into coal particles, leading to increased combustible content in fly ash. In the temperature range of 950-1 150℃, element Na releases quickly in a certain form, but element K does not. The lower the combustion temperature is, the lower the ash melting temperature and the stronger the clinkering property will be, however, this is not the main cause of ash deposition in the furnace. The variation of oxygen concentration at furnace outlet affects little on the composition of fly ash and the release of alkali metal.
  • Relationship Between Swelling Behavior and Physical/Chemical Properties of Coal Particles During Pyrolysis
    ZHANG Shengcheng, HE Rong
    2016, 36(12): 951-957.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To investigate the coal particle swelling behavior during pyrolysis, a numerical model was developed by using the fractal pore model to generate the coal particle pore structure, and then to describe the chemical reactions, gas diffusion and the swelling and contraction behavior of coal particles during pyrolysis. Based on fitted curves with model results, a differential equation was obtained to describe the coal particle swelling, which was validated by comparing with predicted results of other researchers, and was then used to study the effects of following factors on the swelling, such as the functional group content, particle porosity and specific surface, etc., and finally a comprehensive parameter X was defined to characterize the swelling ability of coal particles in consideration of above factors. Results show that both the maximum coal particle swelling ratio and the char swelling ratio increase with rising functional group content, and with reducing porosity and specific surface area. The larger the X is, the greater the swelling of coal particles will be during pyrolysis.
  • Finite Element Strength Analysis of a Cracked HP Inner Cylinder with Shrink Ring for Supercritical Steam Turbine and the Countermeasures
    DENG Zhicheng, SHI Jinyuan
    2016, 36(12): 958-962.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    An introduction is presented to the finite element method for the strength analysis of HP inner cylinder with shrink rings in a certain type of supercritical steam turbine, based on which strength analysis and calculation of a cracked HP inner cylinder with shrink rings were conducted respectively at rated load working condition and following transient working conditions, such as in the cold start, warm start, hot start and very hot start process, etc., so as to obtain the temperature and stress distribution in the cylinder, and subsequently propose countermeasures for operation optimization of the steam turbine. Results show that the excessive stress occuring under transient working conditions is found to be one of the main causes leading to the cracking, which could be avoided by extending the rated load operation time, reducing the start-stop frequency of unit, lowering the heating rate of main steam during start-up period from 29% load to 56% load, especially for the load lying in 53%-56%.
  • Whole Stage Optimization Design of a Centrifugal Compressor Based on Genetic Algorithm
    CHENG Chao, QIN Guoliang
    2016, 36(12): 963-969.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A whole stage physical loss model of centrifugal compressor was founded, while a genetic algorithm procedure was programmed for optimization of the whole stage performance parameters. To verify the reliability of the physical loss model and to study the feasibility using CHC genetic algorithm to optimize the whole stage performance parameters, numerical simulations were carried out on the whole stage performance before and after optimization. Results show that compared with the performance before optimization, the whole stage performance has been improved after optimization, with more reasonable inner flow field obtained in the stage, where flow separations are avoided and flow loss is reduced.
  • Calculation Method and Experimental Study of Particle Voidage in Particle Curtain Heat Exchanger
    LI Heng, CHEN Donglin, CHENG Songqing, WU Xiuzhen, YE Tuo, WEN Cong, XIONG Ying
    2016, 36(12): 970-975.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A calculation formula of particle voidage was deduced using energy conservation principle and Ergun formula based on particle curtain working conditions and operation parameters, while the effects of various working conditions on the voidage were studied according to the experimental data of a particle curtain heat exchanger. Results show that the voidage in particle curtain first decreases and then increases along the descending direction, which increases with rising inlet velocity and initial curtain thickness, and with reducing particle size and mass flow rate. Both the inlet gas velocity and initial curtain thickness affects more on the voidage than the particle size and mass flow rate.
  • CO2 Compression and Purification Experiment Based on Oxy-fuel Combustion
    LI Yanbing, ZHAO Rui, CHEN Yinbiao, HUANG Weijun
    2016, 36(12): 976-981.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Using the carbon capture technology based on oxy-fuel combustion, CO2 compression and purification experiments were conducted on a 300 t/a first self-developed test platform at different CO2 concentrations to find the optimal operation parameters. Results show that when the volumetric fraction of CO2 is 80%, the optimum liquefaction temperature and pressure would be -30℃ and 3.0 MPa, respectively, in which case the CO2 liquefaction rate would be up to 81.86%, with power consumption low to 1 273 kJ/kg and the final CO2 purity up to 99%. The platform can be used to simultaneously remove NOx, SO2 and other pollutants.
  • Experimental Study of Ozone Generation Characteristics During DBD Process
    ZHU Yanqun, LIN Fawei, YUAN Dingkun, MA Qiang, WANG Zhihua, ZHOU Junhu, CEN Kefa
    2016, 36(12): 982-986.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A tube type dielectric barrier discharge (DBD) chamber was used to carry out the discharge tests using a high-frequency high-voltage plasma power source, so as to study the effects of following factors on the ozone generation, such as the discharge voltage, gas flow rate and oxygen concentration, etc. Results show that the ozone concentration first increases and then decreases with rising discharge voltage, due to the accelerated decomposition of ozone with rising temperature. With the rise of gas flow rate, the ozone concentration reduces, which reaches the maximum value of 138 g/m3 at the oxygen flow rate of 1 L/min, while the power consumption of zone generation first decreases and then increases. The presence of nitrogen helps to promote the breakdown voltage, where the oxygen is more easily ionized with the rise of its concentration, thus the ozone concentration is increased and the power consumption is lowered.
  • Prediction of Mercury Emission from Coal-fired Flue Gas Based on Gaussian Process Regression
    ZHONG Mei, ZHAO Bingtao, HUANG Shuo
    2016, 36(12): 987-992.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    By selecting the parameters which significantly influence the mercury emission from coal-fired flue gas, the concentration of elemental, oxidized and particulate mercury in flue gas was predicted using Gaussian process regression, a new random process method, while the effects of covariance function and train-test sample ratio on the simulation accuracy were respectively studied. Results show that the squared exponential covariance function is better than rational quadratic and Matern covariance function; the predicted accuracy increases with the rise of train-test sample ratio; Gaussian process regression is superior to traditional modeling methods of nonlinear regression, and displays good generalization ability, which therefore has strong applicability in prediction of mercury speciation in coal-fired flue gas.
  • Influence of Wind Speed on the Performance of Wind Turbine Blades
    HU Bin, LIU Shuang
    2016, 36(12): 993-999.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the three-dimensional mathematical model of wind turbine blade, a simulation analysis was carried out on the turbine flow field using CFD software Fluent, while a stress analysis of the blade was performed with Static Structural module, in which case fluid-solid coupling was realized in the Workbench platform. The method proposed was used to study the flow field and stress distribution of wind turbine blades at different wind speeds. Results show that the calculated values agree well with actual measurements in literature[14], and the maximum error is less than 5%, proving the calculation method and mathematical model to be correct. With the rise of wind speed, the velocity on impeller surface also increases, and the pressure distribution becomes obviously non-uniform. When the wind speed rises from 5 m/s to 12.5 m/s, the maximum deformation of blade would be increased by 0.91 m, and the blade deformation is nonlinearly related to the wind speed. The vibration of blade is mainly in the wave form.
  • Analysis on Environmental Load of Wind, PV and Coal-fired Power Generation Based on Life Cycle Assessment
    JIA Yalei, WANG Jixuan, HAN Zhonghe, PANG Yongchao, AN Peng
    2016, 36(12): 1000-1009.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Life cycle assessment systems of wind, PV and coal-fired power generation were established based on life cycle assessment theory, so as to compare and analyze their environmental load produced at different stages. Results show that in the construction state of a power plant, the carbon footprint of coal-fired power generation is 1.94 g/(kW·h), which is the lowest in the three power generation ways, and the carbon footprint of wind power generation is 9.42 g/(kW·h), which is the highest. Whereas in the operation stage of a power plant, the carbon footprint of PV power generation is almost zero, and that of wind and coal-fired power generation is respectively 0.2 g/(kW·h) and 83.3 g/(kW·h), indicating that coal-fired power generation produces the highest carbon footprint. The ratios of carbon footprint in construction stage for wind and PV power generation are relatively high, which are 99.4% and 99.78%, respectively; while the ratio of carbon footprint in operation stage for coal-fired power generation has the highest value of 96.13%. Results also indicate that coal-fired power generation has the greatest influence on global warming in a whole life cycle with a standard equivalent of 3.63×10-5, while wind power generation has the least influence with a standard equivalent of 7.9×10-7; whereas PV power generation has the biggest impact on environmental acidification with a standard equivalent of 6.7×10-6, and wind power generation has the smallest impact with a standard equivalent of 1.6×10-7. The emission of solid waste is almost zero in both wind and PV power generation.
  • Performance Analysis of a Full-flow Geothermal Power Generation System and Its Application in Dual-stage Systems
    ZHAO Jun, YU Yuefeng
    2016, 36(12): 1010-1016.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A model of full-flow geothermal power generation system was set up to analyze the optimal dryness of its inlet working medium according to the relationship between screw expander efficiency and expansion ratio, based on which a study was made on the generating performance of the full-flow geothermal power generation system with saturated water of 90-150℃ as the heat source, in comparison with ORC system. Results show that there exists an optimal inlet dryness of screw expander when the system net power reaches the maximum; when the temperature of heat source lies in 90-130℃, the system shows a relatively good performance, whereas when the temperature lies in 130-150℃, the system shows no significant advantages. It is suitable for the system to take the steam with a certain degree of dryness as its heat source, due to reduced exergy loss of throttling. For the heat source at 130-150℃, the second-stage full-flow geothermal power generation system exhibits an excellent effect on recycling the waste heat from the first-stage ORC system in a dual-stage system.
  • Experiments on the Relationship Between Cavitation Status and Acoustic Emission Signal Features for a Francis Turbine Model
    LIU Zhong, ZOU Shuyun, CHEN Ying, LI Zhipeng
    2016, 36(12): 1017-1022.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To obtain the features of acoustic emission signals and their variation laws under the condition of hydraulic turbine cavitation, a series of cavitation experiments were conducted for a Francis turbine model, during which the acoustic emission signals were collected at typical measuring points under different cavitation conditions, while following features were extracted in a conventional analysis way, such as the event count, hit count, frequency center and the root mean square value of voltages, etc., so as to analyze the effects of cavitation coefficient on above features. Results show that with the decrease of turbine cavitation coefficient, the cavitation state changes from none to incipient, and further to fully-developed status; correspondingly, the features of acoustic emission signals vary in an obvious regularity; as a whole, the event count decreases gradually, while other three features increase, and their variation amplitudes depend on the stage in a cavitation process.