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1.
A comprehensive investigation was carried out to study hydrodynamics aspects of secondary air injection in circulating fluidized beds. This article presents modeling and results of computational fluid dynamics simulations of gas-solid flow in the riser section of a laboratory-scale (ID = 0.23 m, height = 7.6 m) circulating fluidized bed with a radial secondary air injector. The gas-solid flow model is based on the two-fluid (Eulerian-Eulerian) approach, where both gas and solids phases are treated as interpenetrating continua. A granular kinetic theory model is used to describe the solids phase stresses. The simulation results are compared with measured pressure drop and axial particle velocity profiles; reasonable agreement is obtained. Qualitatively, excellent agreement is obtained in predicting the increase in solids volume fraction below secondary air ports, the accumulation of solids around the center of the riser due to momentum of secondary air jets, and the absence of the solids down-flow near the wall above the secondary air injection ports, which are the prominent features of secondary air injection observed in the experiments. 相似文献
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EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS 总被引:3,自引:0,他引:3
Yong Kang Pyung S. Song Jong S. Yun Yi Y. Jeong Sang D. Kim 《Chemical Engineering Communications》2000,177(1):31-47
Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m3 and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.
It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations. 相似文献
It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations. 相似文献
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YONG KANG PYUNG S. SONG JONG S. YUN YI Y. JEONG SANG D. KIM 《Chemical Engineering Communications》2013,200(1):31-47
Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m3 and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed. It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations. 相似文献
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采用稳态吸附方法,测定了示踪剂在下行式流化床反应器中的轴向浓度分布,并与理论分布进行拟合,利用Marquardt法,求取了不同操作条件下的轴向扩散系数与气固传质系数,藉以揭示并流下行循环流化床反应器中的气固传质特性.基于实验结果,通过因次分析与线性回归,得到了轴向扩散系数Ea及传质系数KFa与操作条件的经验关联式:Pe1≡(Luf)/Ea=0.226Re0.499PΘ-0.302Pe2≡uf/(KFa.L)=0.000185Re0.618pΘ-0.983Θ≡Gs/(ufρp)=us(1-ε)/(ugε)关联式与实验数据拟合较好. 相似文献
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在直径为φ260mm 的循环流化床中,采用工业 FCC(Y—7)催化剂,于气速1.45~4.71m/s 范围内测量了颗粒循环速率及循环床沿轴向的压力分布。根据轴向压力分布的分段特性,确定了循环床底部加速段的长度。引入了粒子团聚度系数 C 的概念,用所提出的模型对加速段内颗粒的加速规律进行了模拟计算。计算结果与实验数据吻合较好,并得出最合适的 C_(z)关系式为:C_(z)=C_(n)exp(-bZ) 相似文献
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气固流化床流型特性及其识别的复杂性研究 总被引:4,自引:0,他引:4
运用复杂性C2、涨落复杂性Cf及Lempel-Ziv复杂性C(n)等复杂性参数对气固流化床压力脉动信号进行分析,研究它们随流化床操作气速增大历经不同流型的变化趋势并将结果作了比较,进一步探讨了流化床流型特性的内在规律性,研究结果表明,在起始流化致鼓泡态转变的过程中,气-固体系会进行一种所谓的“重构”现象,并证实了气泡的存在是影响压力脉动信号复杂性的重要因素,同时实验显示复杂性参数能明确地指示固定床,鼓泡流化及湍动流化等不同流型之间的转变过程,为流型识别提供了新思路。 相似文献
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低密度循环流化床反应器床层截面平均颗粒速度的变化规律 总被引:4,自引:0,他引:4
本文在高8m,内径186mm 的循环流化床中采用 FCC 颗粒,利用 TSI 光纤激光多普勒测速仪测定了局部颗粒速度的径向分布,并获得了床层截面平均颗粒速度。实验结果表明:截面平均颗粒速度随操作气速的增大而增大,随固体循环速率的增大而略有减小。由实验数据回归得到了计算本实验条件下低密度速度的经验关联式。论文还从基本流体力学理论出发,在考虑颗粒加速运动的条件下,建立了一维气、固两相流模型,可以用于预测床层截面平均颗粒速度和空隙率的变化规律,模型计算结果和实验数据吻合较好。 相似文献
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引 言流化床换热器具有防、除垢和强化传热等优点 ,在化工、食品、海水淡化、废水处理等领域具有广阔的应用前景[1].目前 ,流化床换热器历经散式流化床、内循环流化床 ,已发展到外循环流化床换热器[2 ],它要求在较稀的颗粒浓度 (颗粒浓度小于 5% )、较高的流速 ( 1~ 3m·s- 1)下操作 .流化床换热器中液体流动及颗粒运动状态的研究对流化床换热器的设计和操作具有重要意义 ,但人们对循环流化床换热器中颗粒运动情况的研究还很缺乏 .考虑到循环流化床换热器中的每根换热管都可作为一个独立的循环流化床对待[3].本文试图建立一滑移速度模型… 相似文献
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Solids circulation rate and solids holdup are experimentally investigated in a liquid-solid circulating fluidized bed that covers a wide range in solid and liquid flow rates, particle size, and density. The drift-flux model, which is extensively used to describe the flow behavior of gas-liquid systems, is modified in the present work and for the first time applied to the experimental data of a liquid-solid circulating fluidized bed. The distribution parameter Co is evaluated using the drift-flux model from the present experimental data and also from the data available in the literature. It is found from the analysis that the value of the distribution parameter lies in the range of 0.78 to 0.99, which is a reverse trend to the liquid-gas system. The weighted average drift velocity (usj) is well correlated to the terminal velocity of the particle. The solid holdup predicted using this model agrees with the experimental results. 相似文献
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PREDICTION OF SOLIDS CIRCULATION RATE IN THE RISER OF AN INTERNALLY CIRCULATING FLUIDIZED BED (ICFB)
A predictive mathematical model based on pressure drop in the riser of an Internally Circulating Fluidized Bed (ICFB) is developed to predict solids circulation rate (Gs). The values of Gs predicted using the model agree well with the experimental data. The model also predicts well Gs at higher operating temperatures in the riser of an ICFB. 相似文献
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PREDICTION OF SOLIDS CIRCULATION RATE IN THE RISER OF AN INTERNALLY CIRCULATING FLUIDIZED BED (ICFB)
A predictive mathematical model based on pressure drop in the riser of an Internally Circulating Fluidized Bed (ICFB) is developed to predict solids circulation rate (Gs). The values of Gs predicted using the model agree well with the experimental data. The model also predicts well Gs at higher operating temperatures in the riser of an ICFB. 相似文献
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进行了DGS循环流化炉的冷态试验和燃烧试验,考察了炉内物料在流化状态下,给料量、风量、温度及压力之间的关系,为下一步煤的流化气化工作打下基础。 相似文献
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料位高度是气、固流化床内重要的基本参数之一。虽然有压降法、测温法、电容法和回波法等可用于料位的测量,但是这些方法作为工业应用都不能令人满意。本文根据流化床内部特性提出了利用流化床内压力波动信号和料面附近的平均压力降测量流化床料位高度的新方法。实验表明,这种方法原理简单,测量精度高。不仅能测量流化床内料位的平均高度。而且还能得到料位的瞬时高度和波动范围;且测量结果不受流化床的几何尺寸、床内物料的特性及流化状态等因素的影响,从而为工业流化床提供了一种料位在线测量的新方法。 相似文献
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本文采用床层压力脉动测试技术,通过凝聚函数法进行分析,对流化床气泡上升过程的变化规律进行了研究。表明气-固流化床浓相段沿床高可划分为三个区域,即初始气泡生成聚并区,气泡相对稳定区和气泡崩破区。并对操作条件,颗粒物性及床层结构因素,对于划分区域的影响进行了探索 相似文献
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流化床射流深度的研究 总被引:2,自引:0,他引:2
综述了近三十年来流化床中垂直向上射流、水平射流射流深度的研究状况,结合笔者在多环隙气速、混合物组分射流深度的一系列研究结果,详细论述了射流深度的测试方法、影响因素(射流气速、固体颗粒物性、床层操作压力、环隙气量、放大效应),同时对诸多射流深度关联式进行了分析,指出了应注意的问题.探讨了射流深度的研究方向. 相似文献
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非流化移动床内颗粒的流动为柱塞流,颗粒间无相对运动,竖管传热主要靠颗粒间导热。由于导热热阻大,在管壁周围的颗粒吸热后不易传出,而在其周围形成一个热边界层,阻止了传热。利用在竖管上加上的扰流圈,使近壁处颗粒发生扰动,而使热颗粒传出,冷颗粒得以进入管壁周围,从而起到强化传热的作用。强化后的平均传热系数可增加20%左右。平均传热系数值可达220W/(m ̄2·K)。 相似文献