Development of Calculation Method for Heterogeneous Azeotropic Distilllation Based on Heat and Mass Transfer

本研究的目的是研究操作条件对非均相共沸蒸馏过程中传热传质速率的影响，并建立一种基于传热传质速率的非均相共沸蒸馏计算方法。建立了一个带有两个蒸馏器的新湿壁塔，其中进料的含油液体和含水液体在蒸馏器中分别加热，以改变进口蒸汽浓度。在全回流条件下，对乙醇-苯-水体系进行了多相共沸蒸馏实验。在富油液区得到的各组分的无因次气相扩散通量与圆管内层流传质率的理论值吻合较好。然而，从富水液体中得到的气相扩散通量的观测值比理论值大。提出了一种基于传质传热的非均相共沸蒸馏计算方法。对非均相共沸蒸馏过程的模拟表明，在塔顶和塔底，苯和水的浓度驱动力存在较大差异，同时也显示了各组分的浓度驱动力沿塔顶方向的变化。这可能导致比理论值更大的传质速率。从蒸馏实验中得到的具有代表性的浓度驱动力可能不能代表真实的浓度驱动力。这些结果表明可以用更短的精馏塔进行实验。实际上，整个两液区汽液浓度和回流流速的计算值均大于理论值，而富油两液区和富油两液区的平均扩散通量均大于理论值。

The objectives of this study are to investigate the effect of operating conditions on the heat and mass transfer rates in heterogeneous azeotropic distilllation, and to develop a new calculation method for heterogeneous azeotropic distilllation based on the heat and mass transfer rates.A new wetted-wall column with two stills is set up, where oilish and aqueous liquids of thr feed are heated separately in the stills so as to vary the inlet vapor concentrations. The experiments of heterogeous azeotropic distilllation for the ethanol-benzene-water system are carried out undet total reflux conditions with wide ranges of vapor flow rates and concentration. The dimensionless vapor-phase diffusion flux of each component obtained in an oil-rich liquid region shows good agreement with the theoretical values of the mass transfer rates with laminar flow in a circular tube. However the observed vapor phase diffusion flux obtained from an water-rich liquid show larger values than the theory.A new calculation method for heterogeneous azeotropic distilllation is developed based on heat and mass transfer. The simulation of heterogeneous azeotropic distilllation shows a large difference of concentration driving force of benzene and water between the bottom and top of the column, and also shows the variation of the concentration driving forces of those components along the column. This may cause the larger mass transfer rates than the theoretical values. The representative concentration driving force obtained from the distilllation experiments might no represents the real concentration driving force. These results indicate another experiment with a shorter distilllation column. Actually, the calculated vapor an liquid concentrations and reflux flow rates in whole two liquid regions, while the average diffusion flux in and oil-rich two liquid region are still larger than the theoretical values.