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    Boiler Technology
  • Boiler Technology
    Economic Analysis of an Oxygen-enriched Coal-fired Boiler at Different Modes of Flue Gas Recirculation
    DONG Jing-lan, YAN Wei-ping, MA Kai
    2012, 32(3): 177-181.
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    Taking a 300 MW oxygen-enriched coal-fired boiler as an object of study, flue gas loss and auxiliary power consumption of the boiler were calculated and compared at different modes of flue gas recirculation, while influence of flue gas recirculation mode on economy of the boiler analyzed. Results show that in the series arrangement of FGD + DCC and at the wet flue gas recirculation mode (no dehydration or desulfurization applied in the second flue gas recirculation), the flue gas loss is the lowest (5.6%) and the auxiliary power consumption is the highest(14 MW); whereas in the arrangement of only DCC and at the dry flue gas recirculation mode, the flue gas loss is the highest (7.56%) and the auxiliary power consumption is the least (13.23 MW).
  • Boiler Technology
    Heat Transfer Characteristics in a Pressurized Oxy-fuel Fluidized Bed Boiler
    WANG Chun-bo, HUO Zhi-hong, XING Xiao-na
    2012, 32(3): 182-186.
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    A model of pressurized oxy-fuel fluidized bed boiler was established, with which the in-furnace heat-transfer characteristics were studied by analyzing relevant influencing factors such as the particle size, the porosity, the bed temperature and the pressure, etc. Results show that the heat-transfer coefficient increases with reducing particle size, decreasing porosity, rising temperature and elevating pressure. However, when the pressure gets up to a certain value, the heat-transfer coefficient will tend to remain stable even if the pressure continues to be elevated.
  • Boiler Technology
    Prediction and Analysis on Tube Bank Erosion of Pulverized Coal-fired Boilers Based on Mathematical Model
    ZHOU Yun-long, CHEN Jun, XUE Guang-xin
    2012, 32(3): 187-191.
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    Based on formulas for calculation of fly ash mass concentration and flue gas velocity, a mathematical model for erosion prediction of heat surfaces was built up by taking quantities easy to get as input parameters. After acquisition of the input parameters, corresponding erosion prediction was then completed, of which the results were expressed in a function of excess air ratio and fly ash fineness. Results show that both the excess air ratio and fly ash fineness have an appreciable impact on erosion of boiler tubes, therefore controlling excess air ratio and fly ash fineness at an appropriate level can effectively reduce the erosive wear, and if combined with online measurement of input parameters, the model can also be used to monitor erosion condition of boiler convection tubes.
    • Automatical Controlling and Detecting Diagnosis
  • Automatical Controlling and Detecting Diagnosis
    Simplified Model and Characteristic Analysis of Load-Pressure Object in Heat Supply Units
    LIU Ji-zhen, WANG Qi, TIAN Liang, LIU Xin-ping
    2012, 32(3): 192-196.
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    Based on simplified nonlinear dynamic model of load-pressure object for pure condensation unit, in combination of analysis on thermodynamic system in heat-supply part of extraction steam turbine, according to the basic law of conservation of energy and mass, a differential equation model of load-throttle pressure-extraction steam flow versus boiler fuel flow-turbine governor valve’s opening-extraction control valve’s opening was constructed for heat supply units. Simulation results show that there is no significant difference between heat supply units and pure condensation units in the control characteristics of load-throttle pressure object. For heat supply units, it is recommended to take more flexible control modes to promote the load up/down rate.
  • Automatical Controlling and Detecting Diagnosis
    Study on Time Delay Estimation in Acoustic Temperature Measurement of Power Boilers
    AN Lian-suo, ZHANG Shi-ping, LI Geng-sheng, SHEN Guo-qing,FENG Qiang, DENG Zhe, XU Wei-long
    2012, 32(3): 197-203.
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    Sound field in boiler furnace was analyzed at both cold and hot state, while the time delay estimation (TDE) based on generalized cross-correlation (GCC) and related weighting functions studied theoretically. Acoustic pyrometers were installed in the boiler furnace of a domestic 300 MW unit, with which cold-and hot-state experiments were carried out using different weighting functions. Results show that the GCC-TDE method may be used for measurement of sound travel-time by acoustic technology. The GCC-TDE method weighted by PHAT can suppress sound reverberation, which may therefore help to obtain accurate TDE in cold-state reverberation conditions of boiler; whereas the method weighted by ML is suitable for measurement of sound travel-time in hot-state conditions, due to its robust anti-noise capability.
    • Engineering Thermophysics
  • Engineering Thermophysics
    Experimental and Numerical Study on Characteristics of Methane-Wet Air Reforming in a Micro-combustor
    ZHAO Liu-jie, RAN Jing-yu, ZHANG Li, WANG Fang-ming
    2012, 32(3): 204-211.
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    To study the auto-thermal reforming process of methane-wet air in a micro-combustor, a straight tube experimental system has been established with a tube diameter of 2 mm, based on which experimental tests and 3D numerical simulation are performed to analyze the conversion characteristics of the reforming, focusing on the influence of reaction temperature and feed gas ratio on the methane conversion rate and H2 yield. Study results show that at the same mass flow of methane, both the methane conversion rate and H2 yield increase with rising temperature, air-methane ratio and steam-methane ratio; the influence of air-methane ratio on methane conversion rate is greater than on H2 yield. The system with low mass flow of feed gas is more efficient than that with high mass flow in H2 yield during methane-wet air reforming. Test results agree well with that of the numerical simulation.
    • Environmental Science
  • Environmental Science
    Effect of Reduction Atmosphere on Sulfur Dioxide Capture in CFB
    LI Guang-jian, FU Pei-fang, MA Qi-lei, WANG Na, ZHOU Huai-chun
    2012, 32(3): 212-216.
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    Experimental studies were carried out in a thermo-balance reactor on the calcination characteristics of limestone for sulfur dioxide capture, while sulfur capture tests performed in a simulated rotary furnace with coal samples of different grades, so as to analyze the effect of Ca/S molar ratio, bed temperature and reaction time on the capture process. Results show that high desulfurization efficiencies can be obtained at a bed temperature of 850 ℃ and a Ca/S molar ratio of 2.3. The higher the temperature rising speed, the earlier the limestone starts to decompose, resulting in a higher decomposition speed of limestone. During desulfurization process, there exists an optimal reaction time, compared with which if actual reaction time is shorter than it, incomplete reaction will be resulted; whereas if actual reaction time is longer than it, lower desulfurization efficiency will be produced, due to partial decomposition of sulfate caused by reduction atmosphere in late stage of coal combustion. At an appropriate Ca/S molar ratio, there exists an optimal matching condition of furnace temperature with reaction atmosphere, which produces the highest desulfurization efficiency.
  • Environmental Science
    Sulfur-retention Characteristics of Different Coal Mixtures
    ZHOU Yong-gang, LI Shuai-ying, LI Pei, KONG Yan-li, ZHAO Hong
    2012, 32(3): 217-221.
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    To study the sulfur-retention characteristics of different coal mixtures, experimental tests were carried out by blending Pingshuo mid-sulfur coal with 3 typical low-sulfur coals in different proportions. Results indicate that the efficiency of sulfur-retention has relations with the molar ratio of (Ca+Mg)/S in coal and the content of (CaO+MgO) in ash. When the mid-sulfur coal of low (Ca+Mg)/S ratio is blended with a low-sulfur coal of low (Ca+Mg)/S ratio, the utilization rate of (CaO+MgO) will decrease with rising (Ca+Mg)/S ratio in the coal mixture, in which case, the sulfur removal effect mainly comes from the dilution of sulfur by the blending coal; whereas when the mid-sulfur coal of low (Ca+Mg)/S ratio is blended with a low-sulfur coal of high (Ca+Mg)/S ratio, the utilization rate of (CaO+MgO) will reach the highest at a (Ca+Mg)/S molar ratio of 0.8-1, in which case, the sulfur removal effect comes from both the sulfur dilution and sulfur retention by the blending coal.
  • Environmental Science
    Study on Reductive Decomposition of FGD Gypsums
    LU Ping, ZHANG Jing
    2012, 32(3): 222-228.
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    Using thermogravimetric analyzer, reductive decomposition characteristics of analytically pure gypsum (AG), dry FGD (flue gas desulfurization) gypsum (DG) and wet FGD gypsum (WG) were studied. Results show that the final reaction temperature, reaction atmosphere and the content of additives have significant influence on decomposition of above gypsums. With the rise of final reaction temperature in a range of 850-1 050 ℃, the total decomposition rate of above three gypsums increases, while their corresponding time necessitated for getting decomposition equilibrium decreases; whereas with the growth of CO volumetric fraction in a range of 0.5%-5%, both the total decomposition rate and the reductive decomposition rate rise, however, the rising degree gradually reduces. For analytically pure gypsum, an appropriate addition of Fe2O3 agent may help to raise not only the total decomposition rate, but also the reaction rate of reductive decomposition.
    • New Energy
  • New Energy
    Effect of Working Fluids on Performance of Solar Organic Rankine Cycles
    HAN Zhong-he, YE Yi-lin, LIU Yun
    2012, 32(3): 229-234.
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    The properties of working fluid have a significant effect on performance of solar organic Rankine cycles (ORC). Taking R600, R600a, R245fa, R236fa, R236ea, R601, R601a, RC318 and R227ea as the working fluids, cycle performance of the ORC system was studied based on the first and the second law of thermodynamics, during which the evaporating temperature, thermal efficiency, work rate and exergy efficiency were respectively calculated and compared. Results show that for a low-temperature solar ORC system, R245fa creates relatively high thermal and exergy efficiency and produces relatively low total inreversable loss, which therefore is recommended as an ideal fluid for the ORC system; secondly, working fluids R236fa and R236ea have also better properties.
    • Energy System Engineering
  • Energy System Engineering
    Development and Application of Quantitative Risk Assessment for Large Capacity Power Generating Units
    SHI Jin-yuan
    2012, 32(3): 235-241.
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    A quantitative method is presented for assessment of static and dynamic risk of components and equipment for power generating units, in which the term of risk priority number is used to quantitatively describe the risk. Calculation methods are put forward for the fault probability, fault consequences and likelihood coefficient of fault occurrence, while safety grade classification method proposed for components and equipment of power generating units, together with some application examples. This may serve as a reference for quantitative risk assessment on components and equipment of power generating units.
  • Energy System Engineering
    General Matrix Equation of Exergy Cost Distribution in Thermal System of Coal-fired Power Units
    LI Yong-hua, LIU Wei-ting
    2012, 32(3): 242-248.
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    Based on exergy cost theory, a general model for exergy cost analysis of local thermal system was established, while a general matrix equation determined for exergy cost distribution in thermal system of power units. On above basis, example calculation and analysis were performed for thermal system of a 600 MW power unit, during which the unit exergy cost of independent exergy flow was obtained. Results show that the equation with normative structure is suitable for study of different thermal systems and analysis of regularities commonly existing in thermal systems; for a specific thermal system, the unit exergy cost of independent exergy flow and the distribution regularity of unit exergy cost can be acquired simply by substituting necessary matrix elements into the equation, thus providing guidance for energy saving and consumption reduction of relevant power units; if the equation is furthermore analyzed by differential calculation, the sensitivity of alteration of some factors on unit exergy cost can also be obtained.
  • Energy System Engineering
    Influence of Gasification Parameters in a Two-stage Coal-Slurry Gasifier on Performance of the IGCC System
    LIU Yao-xin, WU Shao-hua, LI Zhen-zhong, WANG Yang, CHEN Xiao-li
    2012, 32(3): 249-254.
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    Using software ThermoFlex, a model of 200 MW IGCC system was established based on two-stage coal-slurry gasification technology, so as to study the effects of following factors on performance of the IGCC system, such as the gasification temperature, coal-slurry concentration, gasification pressure and purity of oxygen, etc. Results show that both the gross and net efficiency of power generation decrease with rising gasification temperature and pressure; higher net efficiency is to be obtained at a flow of higher purity oxgen; raising coal supply ratio (γsc) at the second stage may help to improve the system performance under same conditions of gasification temperature (or purity of oxygen, or gasification pressure). Whereas under the varying conditions of coal-slurry concentration, the designed value of carbon conversion can be achieved based on adjustment of oxygen-coal mass ratio along with the variation of γsc.
  • Energy System Engineering
    Factors Influencing CO2 Gasification of Hunyuan Coal Char and the Kinetic Characteristics
    CHEN Hong-wei, WU Liang, SUO Xin-liang, GAO Song, HAN Liang
    2012, 32(3): 255-260.
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    The effect of pyrolysis temperature, coke-forming time and gasification temperature on the CO2 gasification of Hunyuan coal char was studied, during which a dynamic model was obtained for the gasification reaction. Results show that the gasification reactivity of Hunyuan coal char decreases along with the increment of temperature. There may exist an optimal pyrolysis time at a specific temperature, which may decrease with the increment of gasification temperature. Improving the gasification temperature can remarkably increase the gasification reactivity, on which the gasification temperature has a stronger impact than the pyrolysis temperature. The gasification reactivity of coal char formed at lower pyrolysis temperatures increases obviously with rising gasification temperature. When the gasification temperature gets above 900 ℃, the gasification reactivity of coal char will have a slight change. It is recommended to use volumetric model to describe the gasification process of Hunyuan coal char, compensation effect exists among the kinetic parameters, in which the iso-kinetic temperature has been computed to be 1 199.6 ℃.