Efficient estimation of axial mixing distribution for extraction in rotating disc contactor based on simulation using mean age theory

doi:10.11949/j.issn.0438-1157.20151476

Abstract

Abstract:

In this study, on basis of verification of single-phase flow field simulation by computational fluid dynamics (CFD), the mean age theory was employed to estimate axial mixing distribution in a pilot-scale rotating disc contactor (RDC). In order to validate the mean age theory, two results of theoretical mean residence time and the simulated values by species transport model were compared. It showed that the mean age theory is capable to relatively accurately predict the axial mixing distribution in RDC within ten seconds of computional time, far shorter than two weeks by traditional species transport model, hence possesses the advantage of low computational cost. Moreover, the mean age theory is also capable to provide the spatial distribution information of axial mixing distribution, while the traditional species transport model does not. Hence, the mean age theory can provide more information for structural optimization, and is an efficient method to calculate the axial mixing distribution for extraction. Subsequent analysis on hydrodynamics in RDC showed that it is appropriately mixed flow in compartments and plug flow between compartments, which is favorable for extraction operation. Compared with the well mixing between rotors, the flow field between stators has apparent dead flow zones, which are mainly attributed to two factors of low flow velocity and cyclic vortex structure. The dead zones cause a certain flow non-idealities and are disadvantage for extraction efficiency. Hence, the structure of the stators in RDC needs to be further improved.

Key words: extraction, rotating disc contactor, CFD, mean age theory, numerical simulation, axial mixing

摘要：

在验证了CFD单相流场模拟的基础上,采用均龄理论计算了中试转盘塔内的轴向混合分布,并将计算结果和理论平均停留时间以及组分输运模型计算值进行对比。结果表明:均龄理论能准确预测转盘塔内的轴向混合信息,且其计算时间只需数十秒,远小于传统组分输运模型所需的两周时间,具有低计算量的特点;同时均龄理论克服了传统组分输运模型无法模拟轴向混合空间分布的缺陷,为萃取塔内部结构优化提供了更多信息,是一种高效的模拟方法。后续均龄理论模拟结果的分析预示着转盘塔内的流动近似呈现出级内全混、级间平推的特点,符合萃取操作的需求;而相对于转盘间良好的混合作用,静环间存在明显的流动死区,造成一定的非理想性,其结构有待于进一步的优化。

关键词: 萃取, 转盘塔, 计算流体力学, 均龄理论, 数值模拟, 轴向混合

CLC Number:

TQ021.1

CHEN Hang, SUN Ze, SONG Xingfu, YU Jianguo. Efficient estimation of axial mixing distribution for extraction in rotating disc contactor based on simulation using mean age theory[J]. CIESC Journal, 2016, 67(5): 1694-1700.

陈杭, 孙泽, 宋兴福, 于建国. 基于均龄理论高效计算萃取塔轴向混合分布[J]. 化工学报, 2016, 67(5): 1694-1700.

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