卧螺离心机内盐析流场的CFD-PBM耦合计算

doi:10.16085/j.issn.1000-6613.2018-2496

摘要/Abstract

摘要：

目前对卧螺离心机内部流场的数值模拟大多采用传统欧拉模型，考虑其内部伴有盐析等固相粒子微观行为过程的研究少有报道。本文应用计算流体力学软件Fluent，基于群体平衡模型与多相流Eulerian模型、RNG k-ε模型耦合方法，对卧螺离心机内部盐析两相流场进行三维数值模拟，通过仿真与实验相结合的方式，得到卧螺离心机内盐析流场的晶体颗粒粒径分布、组分数分布和浓度分布及其变化规律，初步揭示了卧螺离心机内伴有盐析的流场晶体颗粒分布特性。研究结果表明：卧螺离心机内盐析晶体粒径的分布随液环半径的增大而增大，螺旋叶片正壁面粒径明显较背面大，从排液端至排渣端的晶体粒径分布有整体逐渐变大的轴向粒径梯度；流道内晶体粒径随转鼓转速的增大而减小，随进口固相体积分数的增大而增大；大粒径晶体的组分数在液环外侧及螺旋叶片正面附近相对较大，而中、小粒径晶体组分数的分布规律则与之相反；盐析颗粒浓度在液环外侧较高且分布均匀，且随转鼓转速的提高而提高，PBM模型与Euler模型计算结果有一定的相似与差异。

关键词: 卧螺离心机, 盐析, 种群平衡, 粒度分布, 两相流, 数值模拟

Abstract:

At present, most of the numerical simulations of the internal flow field of the decanter centrifuge adopt the traditional Euler model, studies on the microscopic behavior of solid phase particles such as salt-out have been rarely reported. In this paper, based on the Eulerian multiphase flow model and RNG k-ε turbulence model coupled with the population balance model, the three-dimensional salt-out two-phase flow field of decanter centrifuge was numerically simulated with a computational fluid dynamics software Fluent. The distribution and change law of crystal particle size and crystal particle fraction and concentration of salting-out flow field in decanter centrifuge were obtained by the combination of simulation and experiment, and the distribution characteristics of crystal particles in the flow field with salting out in the decanter centrifuge were preliminarily revealed. The results show that the particle size of the salt-out crystal in the decanter centrifuge increases with the increase of the radius of the liquid ring. The particle size near the front wall of the spiral blade is obviously larger than that on the back side of the spiral blade, the crystal particle size distribution from the liquid discharge end to the solid discharge end has an overall axial particle size gradient which gradually becomes larger; The crystal particle size in the flow channel decreases with the increase of the drum rotational speed, and increases with the increase of the inlet solid phase volume fraction; The fraction of large size crystals is relatively large outside the liquid ring and near the front surface of the spiral blade, while the distribution law of the fraction of the medium and small size crystals is opposite; On the outside of the liquid ring, the concentration of salt out particle is higher and the distribution is uniform, and increases with the rotation speed of the drum. There are some similarities and differences between the results of PBM model and Euler model.

Key words: decanter centrifuge, salt out, population balance, particle size distribution, two-phase flow, numerical simulation

中图分类号:

TK-9

朱桂华,张傲林,巴赛,陈勇,胡志坤. 卧螺离心机内盐析流场的CFD-PBM耦合计算[J]. 化工进展, 2019, 38(9): 3947-3955.

Guihua ZHU,Aolin ZHANG,Sai BA,Yong CHEN,Zhikun HU. CFD-PBM coupled calculation on salt-out flow field in decanter centrifuge[J]. Chemical Industry and Engineering Progress, 2019, 38(9): 3947-3955.

图/表 16

图1 卧螺离心机流体域网格

图2 不同网格下螺旋叶片壁面径向晶体粒径分布

表1 入口盐析粒径组分数

分组号	平均粒径/μm	组分数
bin 0	142.5	9.1×10^-6
bin 1	127.5	4.6×10^-2
bin 2	112.5	1.0×10^-1
bin 3	97.5	1.7×10^-1
bin 4	82.5	1.9×10^-1
bin 5	67.5	2.5×10^-1
bin 6	52.5	1.8×10^-1
bin 7	37.5	5.9×10^-2
bin 8	22.5	2.8×10^-3
bin 9	7.5	3.5×10^-7

图3 卧螺离心机在x=0截面的轴向位置

图4 不同截面晶体粒径分布

图5 螺旋叶片壁面和内筒壁面晶体粒径分布斜视图

图6 当c v=1.0%时螺旋壁面径向平均粒径分布

图7 当n=3000r·min-1时螺旋壁面径向平均粒径分布

图8 流道内盐析晶体组分数分布

图9 螺旋壁面盐析颗粒组分数分布

图10 卧螺离心机盐析颗粒浓度分布

图11 不同转鼓转速下盐析浓度在径向的分布

图12 实验过程

表2 清液和沉渣中NaCl浓度实验结果

实验编号	转鼓转速/r·min^-1	清液NaCl浓度/g·L^-1	沉渣总NaCl浓度/%	沉渣析出NaCl浓度/%
1	1007	230	21.94	10.83
2	1495	191	26.39	16.18
3	2015	185	27.05	17.01
4	2502	166.5	29.20	20.57
5	2990	158	30.25	22.33
6	3217.5	157	30.37	22.46

图13 卧螺离心机内液相浓度分布

图14 不同转速下NaCl浓度的实验值与模拟值对比

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