Hydrodynamic of mesoscale flow structure in dense phase fluidized bed

doi:10.11949/0438-1157.20211427

Abstract

Abstract:

Three kinds of particles, including sand, sand and fine silica powder mixed particles, are used in the experiment. Time series signals of solid holdup measured by optical fiber probe are statistically analyzed. A method of decoupling complex optical fiber signals was established. The threshold of bubble phase is determined by traversing method, and its accuracy is verified. Variation of the bubble threshold of different particles in radial direction is analyzed, and it is found that addition of fine particles helps to improve the fluidization quality. The threshold of bubble phase decrease with increasing superficial gas velocity. The criterion of particle agglomerate identification in the dense-phase bed is proposed. The characterization of mesoscale flow structure is realized, and a software for decoupling optical fiber signals is written. Mesoscale flow structures of sand and its mixed particles are analyzed. The fractions of bubble phase, emulsion phase and particle agglomerate are obtained. The result shows that addition of a small amount (5%,mass fraction) of fine particles can reduce the formation of agglomerate and significantly improve the fluidization quality. Addition of 10% fine particles will weaken the improvement of fluidization quality. An analysis of hydrodynamics of bubbles reveals that with addition of 10% fine particles, the chord length of bubbles increases and the frequency and rising velocity of bubbles decreases. An analysis of hydrodynamics of agglomerate reveals that the effect of superficial gas velocity on agglomerate velocity is weaken as the content of fine particles increases. With the increase of fine powder, the chord length of agglomerates decreases slightly. When the content of silica powder is 5%, the frequency of particle agglomeration is small and the radial distribution is uniform. When the content of silica powder is 10%, the frequency of agglomerates increases, indicating that adding too much fine powder will promote the formation of agglomerates.

Key words: dense phase fluidized bed, mesoscale, bubble, agglomerate, hydrodynamics characteristics

摘要：

在一套流化床冷模实验装置中对黄沙颗粒和黄沙-硅微粉（20 μm）混合颗粒进行实验。测量固含率时间序列信号并进行统计分析，提出并建立复杂光纤脉动信号的解耦方法，实现稠密气固流中介尺度流动结构的准确识别。基于统计矩一致性原理提出气泡阈值的计算方法，通过遍历法确定气泡阈值。对气泡阈值变化规律进行分析，发现加入细颗粒有助于改善流化质量，随表观气速的增加，气泡阈值减小。对气泡、乳化和聚团三相的相分率进行统计，发现在黄沙颗粒中加入少量（5%，质量分数）细颗粒能够显著改善流化质量，细颗粒添加量过多时（10%），对流化质量的改善将减弱。对气泡的流体力学特性进行分析，发现加入10%硅微粉后，气泡弦长增大，频率降低，速度略有降低。对颗粒聚团流体力学特性进行分析，发现随硅微粉含量增加，表观气速对聚团速度的影响减弱，聚团弦长略有减小。加入5%硅微粉后，颗粒聚团的出现频率较小且径向上分布均一。加入10%硅微粉后，聚团频率有所增大，说明加入过多硅微粉会促进聚团的形成。

关键词: 密相流化床, 介尺度, 气泡, 颗粒聚团, 流体力学特性

CLC Number:

TQ 051

Li NIU, Mengxi LIU, Haibei WANG. Hydrodynamic of mesoscale flow structure in dense phase fluidized bed[J]. CIESC Journal, 2022, 73(6): 2622-2635.

牛犁, 刘梦溪, 王海北. 密相流化床中介尺度流动结构的流体力学特性研究[J]. 化工学报, 2022, 73(6): 2622-2635.

Figures/Tables 18

Fig.1 The schematic drawing of the experiment process

Table 1 Physical properties of particles

颗粒种类	平均粒径/μm	堆积密度/(kg/m³)	颗粒密度/(kg/m³)
黄沙	385	1587	2486
硅微粉	20	—	2649

Table 2 Physical properties of mixed particles

颗粒种类	颗粒粒径d_p/μm	颗粒密度ρ_p/(kg/m³)	起始流化固含率
黄沙	385	2486	0.67
黄沙+硅微粉 (5%,质量分数)	364	2495	0.60
黄沙+硅微粉 (10%,质量分数)	347	2503	0.55

Fig.2 Distribution of particle size of materials

Fig.3 Steps of optical fiber signal decoupling

Fig.4 Radial distribution of the threshold of the bubble phase in various superficial gas velocities

Fig.5 Bubble identification

Fig.6 Schematic diagram of the identification of the agglomerate

Fig.7 Particle clustering identification

Fig.8 Schematic diagram of agglomerates measurement by probe

Fig.9 Schematic diagram for solving the probability density of the agglomerate chord length

Fig.10 Volume fraction of three phases in radical directions（h=512 mm）

Fig.11 Radial distribution of bubble velocity（h=512 mm）

Fig.12 Radial distribution of bubble frequency（h=512 mm）

Fig.13 Radial distribution of bubble size（h=512 mm）

Fig.14 Radial distribution of velocity of particle agglomerates for various superficial gas velocities（h=512 mm）

Fig.15 Radial distribution of frequency of particle agglomerates for various superficial gas velocities（h=512 mm）

Fig.16 Radial distribution of chord length of particle agglomerates for various superficial gas velocities（h=512 mm）

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