外加电场对静电流化床中颗粒运动与床层粘壁的调控机制

doi:10.11949/0438-1157.20210414

化工学报 ›› 2021, Vol. 72 ›› Issue (9): 4544-4552.DOI: 10.11949/0438-1157.20210414

外加电场对静电流化床中颗粒运动与床层粘壁的调控机制

黄正梁^1,³(),张鹏^1,³,杨遥^1,³,任聪静⁴(),王靖岱^1,²,阳永荣^1,²

^1.浙江大学化学工程与生物工程学院，浙江杭州 310027
^2.浙江大学化学工程联合国家重点实验室，浙江杭州 310027
^3.浙江省化工高效制造技术重点实验室，浙江杭州 310027
^4.浙大宁波理工学院，浙江宁波 315100

收稿日期:2021-03-24 修回日期:2021-06-18 出版日期:2021-09-05 发布日期:2021-09-05
通讯作者: 任聪静
作者简介:黄正梁（1982—），男，博士，高级实验师，huangzhengl@zju.edu.cn
基金资助:
国家自然科学基金项目(21808197);国家自然科学基金创新研究群体项目(61621002)

Effects of external DC/AC electric fields on particle motions and wall sticking in fluidized bed with electrostatics

Zhengliang HUANG^1,³(),Peng ZHANG^1,³,Yao YANG^1,³,Congjing REN⁴(),Jingdai WANG^1,²,Yongrong YANG^1,²

^1.College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, Zhejiang, China
^2.State Key Laboratory of Chemical Engineering, Zhejiang University, Hangzhou 310027, Zhejiang, China
^3.Zhejiang Provincial Key Laboratory of Advanced Chemical Engineering Manufacture Technology, Zhejiang University, Hangzhou 310027, Zhejiang, China
^4.Ningbotech University, Ningbo 315100, Zhejiang, China

Received:2021-03-24 Revised:2021-06-18 Online:2021-09-05 Published:2021-09-05
Contact: Congjing REN

摘要/Abstract

摘要：

对流化床反应器中的颗粒运动行为进行调控可达到强化反应器性能的目的。通过冷模实验研究了直流/交流电场对静电流化床中颗粒运动的影响规律与影响机制，建立了通过外加电场调控静电流化床中床层粘壁的方法。结果表明，在低场强条件下，库仑力主导外加直流电场对颗粒运动的影响，由床层壁面指向床层中心的外加直流电场使得颗粒运动强度和轴向颗粒运动分率降低，而由床层中心指向床层壁面的外加直流电场则作用相反；在高场强条件下，极化力主导外加直流电场对颗粒运动的影响，使得颗粒运动强度减弱。在外加交流电场中，无库仑力存在时，极化力仍在高电场强度下使得颗粒运动强度减弱，但当库仑力存在时，电场强度和方向的周期性改变使得颗粒发生周期性摆动，颗粒运动强度增强。在本文的实验条件下，外加交流电场是一种控制床层粘壁的良好方法。2.5 kV/cm、50 Hz的正弦交流电场使得床层粘壁下降76%。研究结果可为聚烯烃流化床反应器的安全运行和过程强化提供指导。

关键词: 外加电场, 静电, 流化床, 颗粒运动, 粘壁, 多相流, 反应工程

Abstract:

Regulating the particle motions in fluidized bed reactor can realize the enhancement of the reactor performance. Effects of external DC/AC (direct current/alter current) electric fields on particle motions in the fluidized bed with electrostatics were investigated by cold model experiments, and the method of regulating the wall sticking by the external electric field was established. The results showed that the Coulombic force dominated effects of external DC electric fields on particle motions at lower field strength. DC electric fields from the reactor wall to the center weakened the intensity of particle motions and the fraction of axial particle motions, while DC electric fields with opposite directions led to totally opposite results. At higher field strength, polarization forces dominated effects of external DC electric fields on particle motions and it always weakened the intensity of particle motions. Under external AC electric fields, polarization forces still led to the decrease of particle motions without the existing of Coulombic force. However, when the Coulombic force exists, the periodic change of the electric field strength and direction would make the particles oscillate periodically, which increased the intensity of particle motions. Besides, under the experimental operations in this work, external AC electric field can be used to reduce the wall sticking well. The sinusoidal AC electric field of 2.5 kV / cm and 50 Hz could reduce the adhesion of the bed by 76%. The research results can provide guidance for the safe operation and process enhancement of polyolefin fluidized bed reactors.

Key words: external electric fields, electrostatic, fluidized bed, particle motion, wall sticking, multiphase flow, reaction engineering

中图分类号:

TQ 051.13

黄正梁, 张鹏, 杨遥, 任聪静, 王靖岱, 阳永荣. 外加电场对静电流化床中颗粒运动与床层粘壁的调控机制[J]. 化工学报, 2021, 72(9): 4544-4552.

Zhengliang HUANG, Peng ZHANG, Yao YANG, Congjing REN, Jingdai WANG, Yongrong YANG. Effects of external DC/AC electric fields on particle motions and wall sticking in fluidized bed with electrostatics[J]. CIESC Journal, 2021, 72(9): 4544-4552.

图/表 11

图1 外加电场静电流化床冷模实验装置简图

Fig.1 Schematic diagram of the external electric field enhanced gas-solid fluidized bed

图2 无外加电场流化床中粘壁颗粒的粒径分布

Fig.2 Particle size distribution of wall sheeting in the fluidized bed without electric fields

图3 不同轴向高度声能量随外加直流电场强度的变化

Fig.3 Variations of acoustic energies with the field strength under effects of DC electric field with different directions

图4 不同方向外加直流电场作用下床层H=200 mm处压力脉动标准差

Fig.4 Variations of the standard deviation of pressure fluctuations with the field strength under effects of DC electric field with different directions (H=200 mm)

图5 库仑力作用下的颗粒迁移

Fig.5 Particles migration under the effects of Coulombic forces

表1 声信号5尺度小波分解对应的频率范围

Table 1 The frequency range of various levels after 5 scales wavelet decomposition

Scale	f/kHz
d₁	125—250
d₂	62.5—125
d₃	31.3—62.5
d₄	15.6—31.3
d₅	7.81—15.6
a₅	0—7.81

图6 不同位置颗粒-壁面碰撞摩擦能量分率比随外加直流电场强度的变化

Fig.6 Variations of Dc/Df with the field strength of DC electric field at different axial positions

图7 不同轴向声能量随外加交流电场强度的变化

Fig.7 Variations of acoustic energy with the field strength of AC electric field at different axial positions

图8 消除静电后外加交流电场对压力脉动标准差与声能量的影响

Fig.8 Variation of standard deviations of pressure fluctuations and the acoustic energy at different heights with the field strength when electrostatics were eliminated

图9 不同位置Dc/Df随外加交流电场强度的变化

Fig.9 Variations of Dc/Df with the field strength of AC electric field at different axial positions

图10 不同方式外加电场作用下床层粘壁量(Ws)随电场强度的变化

Fig.10 Variations of Ws with the field strengths in the fluidized bed with different electric fields supplied

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外加电场对静电流化床中颗粒运动与床层粘壁的调控机制

Effects of external DC/AC electric fields on particle motions and wall sticking in fluidized bed with electrostatics

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