Abstract: For multiphase mass transfer processes in distillation columns, computational fluid dynamics can be used not only to simulate the flow phenomena, but also to study the heat and mass transfer processes and their interactions with the flow. Based on previous work on gas-liquid flow simulation in distillation trays, this work applied the multiphase flow solver of the OpenFOAM platform. The energy and species transport equations were considered to construct the heat and mass transfer models for the distillation system. The ideal system of cyclohexane-n-heptane and the non-ideal system of ethanol-water distillation were simulated respectively. The distribution of the gas-liquid two-phase flow, component and temperature on the column trays were analyzed. For the ideal system, the ideal solution mass transfer model can provide accurate predictions for the temperature and concentration fields on the trays. However, for non-ideal systems, it was necessary to introduce the activity coefficient model on the basis of the ideal model. To this end, the effects of two activity coefficient models, UNIQUAC and NRTL, were introduced and compared. In the current simulation framework, the activity coefficient models were able to improve the simulation accuracy of temperature and concentration field. The overall trends predicted by the two models were generally consistent with the results in the literature, and the UNIQUAC model agreed better with the literature. In addition, the comparative analysis of gas-liquid two-phase flow field and concentration field distribution showed that the circulating flow of liquid phase can enhance the local mass transfer efficiency of the column tray, resulting in higher efficiency at the liquid inlet and the weir than the tray center. However, the gas-liquid renewal in the circulating region renewed ly, which led to a reduction in the overall mass transfer efficiency of the column tray. This study can be used for the design and optimization of distillation columns, and it is also valuable for simulations of heat and mass transfer in other gas-liquid two-phase flow systems.

Key words: gas-liquid two-phase flow, distillation, hot state simulation, heat and mass transfer, OpenFOAM

摘要： 对于精馏塔内的多相传质过程，计算流体力学(Computational Fluid Dynamics, CFD)不仅可用于模拟流动现象，而且可以用于研究传热传质过程及其与流动的相互作用规律。基于之前精馏塔板气液流动模拟的研究工作，本研究应用OpenFOAM平台的多相流求解器，考虑了能量方程与组分输运方程，构建了精馏体系的传热传质模型，分别对环己烷-正庚烷理想体系与乙醇-水非理想体系进行了模拟，并分析了塔板上气液两相流动、组分浓度及温度等参数的分布规律。对于理想体系，理想溶液传质模型能够较准确地预测多层塔板上的温度及浓度场；对于非理想体系，需要在理想溶液传质模型的基础上引入活度系数模型，为此对比了UNIQUAC与NRTL两种活度系数模型的效果。在当前模拟框架下，引入活度系数模型有助于提升非理想体系温度场与浓度场的模拟精度，两种活度系数模型预测的整体趋势与文献结果基本一致，但在数值上UNIQUAC模型与文献结果吻合更好。此外，气液两相流场与浓度场分布的对比分析表明，液相的循环流动能够提升塔板的局部传质效率，导致液相入口与塔板堰处的效率高于塔板中心，但是循环区域内气液两相无法及时更新，将导致塔板整体传质效率下降。以上研究有望用于精馏塔板的设计与优化，为提高精馏塔传质效率、降低精馏能耗提供指导，对于其他气液两相流的CFD传热传质模拟也具有参考价值。

关键词: 气液两相流, 精馏, 热态模拟, 传热与传质, OpenFOAM