化工学报 ›› 2019, Vol. 70 ›› Issue (5): 1682-1692.doi: 10.11949/j.issn.0438-1157.20190016

• 流体力学与传递现象 • 上一篇    下一篇

基于EMMS介尺度模型的双分散鼓泡流化床的模拟

佟颖1,2,Ahmad Nouman1,鲁波娜1,2,3(),王维1,2   

  1. 1. 中国科学院过程工程研究所多相复杂系统国家重点实验室,北京 100190
    2. 中国科学院大学中丹学院,北京 100049
    3. 中国科学院洁净能源创新院,辽宁 大连 116023
  • 收稿日期:2019-01-07 修回日期:2019-02-22 出版日期:2019-05-05 发布日期:2019-05-05
  • 通讯作者: 鲁波娜 E-mail:bnlu@ipe.ac.cn
  • 作者简介:鲁波娜(1979—),女,博士,副研究员,<email>bnlu@ipe.ac.cn</email>
  • 基金资助:
    国家自然科学基金项目(21576263, 21625605, 91834302);中国科学院洁净能源先导科技专项(XDA21030700);中国科学院青年创新促进会项目(2015033)

Numerical investigation of bubbling fluidized bed with binary particle mixture using EMMS mesoscale drag model

TONG Ying1,2,AHMAD Nouman1,LU Bona1,2,3(),WANG Wei1,2   

  1. 1. State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
    2. Sino-Danish College, University of Chinese Academy of Sciences, Beijing 100049, China
    3. Dalian National Laboratory for Clean Energy, Dalian 116023, Liaoning, China
  • Received:2019-01-07 Revised:2019-02-22 Published:2019-05-05 Online:2019-05-05
  • Contact: LU Bona E-mail:bnlu@ipe.ac.cn

摘要:

双分散气固鼓泡流化床中颗粒通常具有不同粒径或密度,导致产生颗粒偏析等现象,影响传递和反应行为。颗粒分离和混合与气泡运动密不可分,其中相间曳力起关键作用。最近Ahmad等提出了一种基于气泡结构的双分散介尺度曳力模型,能成功预测双分散鼓泡流化床的床层膨胀系数。本研究耦合该曳力模型与连续介质方法,模拟了两种不同的双分散鼓泡流化床,通过分析不同流化状态下的气泡运动、颗粒浓度比的轴向分布等参数,进一步检验模型的适用性。研究表明,当双分散颗粒处于完全流化状态时,耦合双分散介尺度曳力模型可合理预测不同颗粒的分离现象;而其处于过渡流化状态时,新曳力模型和传统模型均无法获得合理结果,此时调节固固曳力可改进模拟结果。

关键词: 双分散颗粒, 流化床, 介尺度, 曳力, 计算流体力学, EMMS

Abstract:

Gas-solid bubbling fluidized beds have various industrial applications. The particles involved in practical applications usually display polydisperse characteristics (having different diameter or densities), resulting in segregation phenomena and consequently influencing flow hydrodynamics and reaction performance. Particle separation and mixing are inseparable from bubble motion, where interphase drag plays a key role. Recently, Ahmad et al. proposed a bubble-based mesoscale drag considering the effect of bidisperse features which is able to predict the bed expansion of binary bubbling fluidized beds. In this study, in order to investigate the applicability of the new drag model, two bubbling fluidized beds with different binary particle mixtures are simulated using the combination of the new drag model and the continuum model. Then, the bubble motion and axial profiles of jetsam volume ratio under two different fluidization states are mainly analyzed. It is found that the new drag model can predict well the particle segregation and mixing behaviors when the binary particles are fluidized completely. However, when the binary particles are fluidized at the transition state, the new drag model shows poor predictions, and the solid-solid drag plays a notable role in improving the prediction.

Key words: binary particle mixture, fluidized bed, mesocale, drag, CFD, EMMS

中图分类号: 

  • TQ 021.1

表1

两个双分散流态化系统的物性参数"

参数

石英砂

(silica sand)

玻璃珠

(glass bead)

硅胶

(silica gel)

系统1 √ (浮料) √ (沉料)
系统2 √ (沉料) √ (浮料)
Sauter平均粒径/μm 125 500 375
球形度 1 1 1
密度/(kg·m-3) 2600 2540 600
Geldart分类 B B A-B
终端速度/(m·s-1) 0.80 4.10 1.25
最小流态化速度/(m·s-1) 0.022 0.23 0.032

图1

模拟采用的气固流化床几何构体(单位:m)"

表2

两个双分散流态化系统的操作条件"

操作参数 系统1 系统2
颗粒堆料量/kg 2.8 2.85
沉料的初始体积比 X 20 0.5 0.2
初始堆料高度/m 0.135 0.4
表观气速/(m·s-1) 0.07,0.09 0.032,0.152

表3

模拟的具体设置"

Parameter Specification
transient formulation second-order implicit
pressure-velocity coupling phase coupled SIMPLE
gradient discretization green-Gauss cell based
momentum discretization second-order upwind
volume fraction discretization quick
granular temperature algebraic
granular viscosity Syamlal-O’Brien
granular bulk viscosity Lun-et-al
frictional viscosity Schaeffer
angle of internal friction 30
frictional pressure based-ktgf
frictional modulus derived
friction packing limit 0.5
solid pressure Lun-et-al
radial distribution Ma-Ahmadi
elasticity modulus derived

gas-solid drag

binary EMMS-bubbling or Gidaspow

model

solid-solid interaction Syamlal-O’Brien symmetric model
packing limit 0.62
restitution coefficient 0.9
physical time step 0.0001 s

表4

不同网格下的全床平均气含率和某截面高度的X 2 "

网格尺寸 全床平均气含率 H=0.8对应的X 2
5 mm ×5 mm 0.8063 0.4460
3 mm ×3 mm 0.8077 0.4572
2 mm ×2 mm 0.8081 0.4610

图2

系统1的气含率分布的演化(U g=0.09 m·s-1)"

图3

系统稳定后采用不同曳力模型得到的气含率分布"

图4

系统1的固相体积分数的演化过程(U g=0.09 m·s-1)"

图5

完全流化状态下沉降颗粒体积比的轴向分布"

图6

过渡流化状态下沉降颗粒体积比的轴向分布"

图7

不同K值下的沉降颗粒体积比X 2的轴向分布(系统1:U g=0.07 m·s-1)"

图8

采用不同气固曳力模型的X 2轴向分布(系统1:U g=0.07 m·s-1,K=0.005)"

图9

不同K值下的沉降颗粒体积比X 2的轴向分布(系统2:U g=0.032 m·s-1)"

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