工业聚乙烯流化床的气固流动特性数值模拟

刘信瑀; 张海涛; 马宏方; 李涛

doi:10.14135/j.cnki.1006-3080.20210731001

工业聚乙烯流化床的气固流动特性数值模拟

doi: 10.14135/j.cnki.1006-3080.20210731001

华东理工大学大型工业反应器工程教育部工程研究中心, 上海 200237

详细信息

作者简介:
刘信瑀（1998—），男，浙江台州人，硕士生，主要研究方向为多相流模拟。E-mail：798588739@qq.com

通讯作者:
李　涛， E-mail：tli@ecust.edu.cn

中图分类号: TQ021.1
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- 文章访问数: 257
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- PDF下载量: 58
- 被引次数: 0
出版历程
- 收稿日期: 2021-07-31
- 网络出版日期: 2021-11-09
- 刊出日期: 2022-12-28

Numerical Simulation of Gas-Solid Flow Characteristics in Industrial Polyethylene Fluidized Bed

Engineering Research Center of Large Scale Reactor Engineering and Technology of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China

摘要

摘要: 采用计算颗粒流体力学（CPFD）的数值模拟方法，对工业级聚乙烯流化床内的气固流动特性进行了冷态模拟，并利用Matlab的图像处理功能将图像的像素点与模拟网格进行对应来计算流化床内的气泡大小。从流化床流动结构、颗粒、气泡3个角度，研究了不同气速、不同初始物料量对工业级聚乙烯流化床的气固流动特性的影响。结果表明：从颗粒的轴径向分布情况可以看出，工业流化床内部的边壁效应明显较弱，密相区整体呈现较为均匀的颗粒分布；气速对于流化床气固流动的影响较大，当气速为0.46 m/s时，流化床内密相区的颗粒分布最为均匀，整体的流动较好；初始床层高度主要影响流化后密相区的高度，对于床层膨胀率的影响较小。
- 两相流 /
- 流化床 /
- 数值模拟 /
- CPFD /
- 图像处理
Abstract: Based on computational particle fluid dynamics (CPFD), an industrial grade polyethylene fluidized bed model in cold state was established to simulate the gas-solid flow characteristics in fluidized bed, and the image processing function of MATLAB was used to calculate the bubble size in the fluidized bed by matching the image pixels with the simulated grid. The effects of gas velocity and initial material quantity on the gas-solid flow characteristics of industrial grade polyethylene fluidized bed were studied from the perspectives of fluidized bed flow structure, particles and bubble. The results show that compared with the equipment in pilot and experimental stages, the side-wall effect in the industrial fluidized bed is obviously weak, and the dense-phase zone presents a more uniform particle distribution. The gas velocity has a great influence on the gas-solid flow in the fluidized bed. Under the operating condition of 0.46 m/s gas velocity, the particle distribution in the dense-phase zone is the most uniform, and the bulk flow becomes steady. The initial bed height mainly affects the height of the dense phase zone after fluidization, but has little effect on the bed expansion rate.
- two-phase flow /
- fluidized-bed /
- numerical simulation /
- CPFD /
- image processing

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图 1 流化床几何结构

Figure 1. Geometry of the fluidized bed

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图 2 流化床的网格划分

Figure 2. Meshing generation of fluidized bed

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图 3 不同网格尺度轴向固含率的分布

Figure 3. Distribution of axial solid holdup at different grid scales

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图 4 图像数字化

Figure 4. Image digitization

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图 5 针对气泡的Matlab图像处理过程

Figure 5. Process of Matlab image processing for bubbles

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图 6 流化床内部颗粒随时间分布变化情况

Figure 6. Particle distribution varying with time in the fluidized bed

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图 7 各气速下流化床内的流线图

Figure 7. Flow diagram in the fluidized bed at various gas velocities

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图 8 气速对聚乙烯颗粒轴向分布的影响

Figure 8. Effect of gas velocity on polyethylene particle axial distribution

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图 9 气速对聚乙烯颗粒径向分布的影响

Figure 9. Effect of gas velocity on polyethylene particle radial distribution

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图 10 气速对气泡平均直径轴向分布的影响

Figure 10. Effect of gas velocity on axial distribution of average bubbles diameter

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图 11 初始床层高度对轴向固含率的影响

Figure 11. Effect of initial bed height on axial solid holdup

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表 1 气相的组成

Table 1. Composition of gas phase

Gas composition	Mole fraction
H₂	0.065
C₂H₄	0.350
C₄H₈	0.140
N₂	0.445

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表 2 聚乙烯颗粒的组成

Table 2. Composition of polyethylene particles

Particle size distribution/μm	Mass fraction/%	Average diameter/μm
840	40.2	831
420~840	31.5	600
250~420	12.3	322
150~250	6.5	190
104~150	3.8	120
74~104	1.8	89

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表 3 模拟参数及计算条件

Table 3. Simulation parameters and calculation conditions

Operating temperature/K	Operating pressure/MPa	Mean particle diameter/μm	Particles density/(kg·m⁻³)	Maximum allowable volume fraction of particles	Initial apparent density of bed particles/(kg·m⁻³)	Initial bed height/m	Normal recovery coefficient of particle-wall collision
361	2.3	580	920	0.6	480	8	0.9

Gas density/ (kg·m⁻³)	Gas viscosity/ (Pa·s)	Gas velocity/ (m·s⁻¹)	Drag force model	Turbulence model	Time step/s	Time average calculation start time/s	Simulated time/s
22	1.507×10⁻⁵	0.46	Gidaspow	LES*	0.001	20	40
$*$—Large eddy simulation model

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表 4 不同初始床层高度的膨胀率

Table 4. Expansion rates at different initial bed heights

Initial bed height/m	Height of dense zone/m	Bed expansion rate
4	6.539	1.635
6	10.412	1.735
8	13.860	1.733

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