Chaotic mixing process of fly ash in acid leaching tank intensified by rigid-flexible impeller

doi:10.11949/j.issn.0438-1157.20181179

Abstract

Abstract:

In the traditional fly ash aluminizing process, the acid immersion stirring tank adopts a rigid stirring paddle. Due to the limited pumping capacity of rigid impellers, some problems such as settlement of solid particles, deficiently of chaotic, and low efficiency of mixing in this process often occur in solid-liquid mixing processes. Thus, the rigid-flexible impeller was adopted to enhance solid-liquid chaotic mixing behavior in acid leaching process. In a fly ash-water system with a solids concentration of 30%, the chaotic mixing characteristics and energy dissipation were investigated in STRs equipped with rigid-flexible impeller. Torque sensor was employed to collect the torque time series signal. The largest Lyapunov exponents and the multi-scale entropy were compiled and calculated by Matlab to indicate the degree of chaotic mixing based on the torque time series signal. Meanwhile, the power consumption per unit volume was used to characterize the stirred reactor power characteristics. The effects of impeller types, rotation speed, flexible piece width/length, and impeller off-bottom clearance on chaotic mixing behavior were taken into consideration in the solid-liquid mixing processes. The results showed that the rigid-flexible impeller could effectively promote the chaotic mixing and reduce the accumulation of solid particles at the bottom of STRs in the fly ash-water system. Largest Lyapunov exponents of the system reached the maximum value of 0.0645 and multi-scale entropy was bigger than that of other conditions at the rotation speed of 120 r/min, the off-bottom clearance of T/4, the flexible piece length of 1.2H ₁ and width of D/8. The power consumption increases exponentially with the increase of rotation speed.

Key words: rigid-flexible impeller, coal ash, chaotic mixing, largest Lyapunov exponents, multi-scale entropy

摘要：

传统粉煤灰提铝工艺中酸浸搅拌槽均采用刚性搅拌桨。因刚性桨卷吸能力有限，导致固体颗粒易沉槽、流体混沌混合效率低。提出刚柔组合桨强化酸浸搅拌槽中固液混沌混合行为。实验基于固含率为30%的粉煤灰-自来水体系，研究了刚柔组合酸浸搅拌槽内混沌混合特性及能量耗散规律。采用扭矩传感器采集扭矩时间序列信号，借助Matlab软件编译计算混合过程中最大Lyapunov指数和多尺度熵等混沌特性参数，以单位体积功耗表征搅拌反应器的功率特性。实验考察了搅拌桨安装离底高度、柔性片长度、柔性片宽度等因素对酸浸槽内粉煤灰混沌混合的影响，对比了刚性桨与刚柔组合桨体系的能耗差异。研究结果表明：刚柔组合桨通过柔性片的作用，能增大搅拌桨的卷吸力，进而减少固体颗粒沉槽现象，促进全槽混沌混合；在最优化条件（120 r/min，搅拌桨安装离底高度为T/4，柔性片长度为1.2H ₁、柔性片宽度为D/8）下，体系最大Lyapunov指数达到最大值0.0645，各尺度下的MSE均比其他条件更大，表明刚柔组合桨能够通过柔性片的多体运动，强化体系混沌混合，均化体系能量分布；刚性桨与刚柔组合桨的单位体积功耗随着转速的增加呈现指数规律增长。

关键词: 刚柔组合桨, 粉煤灰, 混沌混合, 最大Lyapunov指数, 多尺度熵

CLC Number:

TQ 027.2

Xia XIONG, Zuohua LIU, Deyin GU, Facheng QIU, Liang WANG, Changyuan TAO, Yundong WANG. Chaotic mixing process of fly ash in acid leaching tank intensified by rigid-flexible impeller[J]. CIESC Journal, 2019, 70(5): 1693-1701.

熊黠, 刘作华, 谷德银, 邱发成, 王靓, 陶长元, 王运东. 刚柔组合桨强化粉煤灰酸浸搅拌槽内固液混沌混合[J]. 化工学报, 2019, 70(5): 1693-1701.

Figures/Tables 15

Fig.1 Schematic diagram of experimental setup

Fig.2 Impellers used in experiment

Fig.3 Schematic diagram of solid-liquid mixing in stirring tank

Table1 Mixing mediums

搅拌介质	密度/（kg/m³）	质量分数/%
粉煤灰	2400	30
自来水	998.2	70

Fig4 Effect of impeller types on LLE

Fig.5 Effect of flexible piece length on LLE

Fig.6 Effect of flexible piece width on LLE

Fig.7 Effect of impeller off-bottom clearances on LLE

Fig.8 Effect of impeller types on MSE

Fig.9 Effect of flexible piece length on MSE

Fig.10 Effect of flexible piece width on MSE

Fig.11 Effect of impeller off-bottom clearances on MSE

Fig.12 Comparison of P v at different rotation between two systems

Fig.13 Comparison of P v at different rotation between two systems

Fig.14 Time evolution of coal fly ash suspended state

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