针对气固节涌床，在实验基础上，基于欧拉?欧拉双流体模型结合颗粒动力学理论，考虑Geldart A类颗粒聚团对气固间曳力的影响，采用修正后的Gidaspow曳力模型对气固节涌床进行数值模拟。结果表明，通过与实验结果及经验公式进行对比，修正的模型可准确合理地模拟流化床内节涌特性。表观气速0.09 m/s≤Ug≤0.39 m/s时，床层内部压力脉动标准偏差随表观气速增加而增加，流型由鼓泡转变为节涌直至节涌程度最大，床内气固流动主要受轴对称栓运动特性影响，床内压降、床层膨胀比、气栓平均上升速度、最大轴对称栓长度随表观气速增加而增加，最大轴对称栓产生位置随表观气速增加而降低；Ug>0.39 m/s后，床内压力脉动标准偏差随表观气速增加而降低，节涌程度降低至向湍动流态化流型转变，床内气固流动主要受壁面栓运动特性影响，增加表观气速，节涌床内压降变化幅度较小，气栓平均上升速度增加幅度加大，床层膨胀比及最大轴对称栓长度降低，最大轴对称栓产生的位置略有升高。
In this work, the hydrodynamic characteristics in slugging fluidized beds were simulated by using computational fluid dynamics (CFD) code. Considering the existence of cohesive inter-particle forces which could result in larger effective particle sizes and hence reduced fluid?particle drag forces in Geldart A particles, based on the theory of gas-cluster model and the experimental data, an effective mean particle cluster diameter was used to modify the Gidaspow drag force model. Based on the Eulerian?Eulerian two-fluid model which was integrated with the kinetic theory for solid particle, the numerical simulation of the gas?solid fluidized bed after modifying the drag model showed that the modified drag model can accurately and reasonably simulate the slugging characteristics of fluidized bed through the comparison of experimental results and empirical formulas. In the range of superficial gas velocity Ug=0.09~0.39 m/s, the standard deviation of the differential pressure fluctuation inside the bed increased with the increase of Ug, which corresponded to the change of flow pattern from bubbling to slugging until to the maximum stage of slugging. The gas?solid flow in the bed was mainly affected by the motion characteristics of the axial slug. The pressure drop, the expansion ratio of the bed, the average rising speed of the slug, and the maximum length of axial slug increased with the increase of Ug, and the position of the maximum axial slug decreased as Ug increased. When Ug exceeded 0.39 m/s, the standard deviation of the differential pressure fluctuation inside the bed decreased with the increase of Ug, which corresponded to the change of flow pattern from the weakening of slugging until to the turbulent. The gas?solid flow in the bed was mainly affected by the motion characteristics of the wall slug. The pressure drop, the expansion ratio of the bed, the average rising speed of the slug, and the maximum length of axial slug decreased with the increase of Ug, and the position of the maximum axial slug increased slightly as the Ug increased.
[1]Guana Y, Yaob X, Wub G, et al.CFD Investigation of Slugging Behavior in a Gas-Solids Fluidized Bed[J].Chemical Industry & Chemical Engineering Quarterly, 2017, 23(4):529-536 [2]Grace J R.Reflections on Turbulent Fluidization and Dense Suspension Upflow[J].Powder Technology, 2000, 113(3):242-248 [3]金涌，祝京旭，汪展文，等.流态化工程原理 [M]. 清华大学出版社，2002 [4]Jin Y, Zhu J X, Wang Z W, et al.Fluidization Engineering Principles[M]. Tsinghua University Press, 2002. [5]Baeyens J, Geldart D.An Investigation into Slugging Fluidized Beds[J].Chemical Engineering Science, 1974, 29(1):255-265 [6]Stewart P S B, Davidson J F.Slug Flow in Fluidized Beds[J].Powder Technology, 1967, 1(2):61-80 [7]Weber J M, Mei J S.Bubbling Fluidized Bed Characterization Using Electrical Capacitance Volume Tomography (ECVT)[J].Powder Technology, 2013, 242(4):40-50 [8]杨富军, 王嘉骏, 顾雪萍, 等.类颗粒节涌流态化的实验和数值模拟[J].过程工程学报, 2005, 5(6):597-600 [9]Yang F J, Wang J J, Gu X P, et al.Experiment and Numerical Simulation on Slug Fluidization of Geldart D Particles[J].The Chinese Journal of Process Engineering, 2005, 5(6):597-600 [10]Hosseini S H, Zhong W, Esfahany M N, et al.CFD Simulation of the Bubbling and Slugging Gas-Solid Fluidized Beds[J].Journal of Fluids Engineering, 2010, 132(4):041301-1 [11] Ramirez E, Finney C E A, Pannala S, et al.Computational Study of the Bubbling-to-Slugging Transition in a Laboratory-Scale Fluidized Bed[J]. Chemical Engineering Journal, 2017, 308:544-556. [12]Wang J W.A Review of Eulerian Simulation of Geldart A Particles in Gas-Fluidized Beds[J].Industrial & Engineering Chemistry Research, 2009, 48(12):5567-5577 [13]Zimmermann S, Taghipour F.CFD Modeling of the Hydrodynamics and Reaction Kinetics of FCC Fluidized-Bed Reactors[J].Industrial & Engineering Chemistry Research, 2005, 44(26):9818-9827 [14] 时瑶, 王德武, 赵斌, 等.旋流筛板式气固挡板流化床内压力脉动特性[J]. 过程工程学报. 2018, DOI: 10.12034/j.issn.1009-606X. [15]Shi Y, Wang D W, Zhao B, et al.Pressure Fluctuations in a Gas-Solids Fluidized Bed with Rotating Sieve Tray Type Baffles[J]. The Chinese Journal of Process Engineering, 2018, DOI: 10.12034/j.issn.1009-606X. [16]Mckeen T, Pugsley T.Simulation and Experimental Validation of a Freely Bubbling Bed of FCC Catalyst[J].Powder Technology, 2003, 129(1-3):139-152 [17] Liu X X, Zhu C Q, Geng S J, et al.Two-fluid Modeling of Geldart A Particles in Gas-Solid Micro-Fluidized Beds[J]. Particuology, 2015, 21:118-127. [18]LettieriP, Newton D, Yates J G.Homogeneous Bed Expansion of FCC Catalysts,Influence of Temperature on the Parameters of the Richardson-Zaki Equation[J].Powder Technology, 2002, 123(2):221-231 [19]Gao J S, Chang J, Lan X Y, et al.CFD Modeling of Mass Transfer and Stripping Efficiency in FCCU Strippers[J].AIChE Journal, 2008, 54(5):1164-1177 [20]Geldart D.Expansion of Gas Fluidized Beds[J].Industrial & Engineering Chemistry Research, 2004, 43(18):5802-5809 [21]Hosseini S H, Zhong W, Esfahany M N, et al.CFD Simulation of the Bubbling and Slugging Gas-Solid Fluidized Beds[J].Journal of Fluids Engineering, 2010, 132(4):041301-1 [22]Baker C G J, Geldart D.An Investigation into the Slugging Characteristics of Large Particles[J].Powder Technology, 1978, 19(2):177-187 [23] Kehoe P W K, Davidson J F.Continuously Slugging Fluidized Beds [A]. Institution of Chemical Engineers Symposium Series, Chemeca’70[C]. Sydney: Butterworths, 1970, 97-116.
