Study On The Cascaded Total Reflux Batch Distillation With Dynamic Exchange Of Liquid Phase

A novel operation mode of cascaded total reflux batch distillation with dynamic exchange of liquid phase(CTBDEL)is proposed according to the advantage of total reflux dynamic accumulation operation. The advantages of the new-style operation mode are as follows: (1) Each column in the CTBDEL system runs independently and does not interfere with each other; (2) The total pressure drop of the system equals to the pressure drop of each column; (3) Each column runs under the total reflux state and makes full use of its separation capability; (4) The column needed can be added conveniently to the CTBDEL system according to the task. So the CTBDEL system can be use to separate the heat-sensitive mixture which requires a large number of HETP and small pressure drop, and isotope separation which requires thousands of HETP.The CTBDEL system including two columns and three columns is designed. And two mixtures difficult to separate are chose to be separated in the system, which are ethylbenzene-p-xylene system and ethanol-isopropanol alcohol system. The results of the experiment validate the operation feasibility of CTBDEL system.The essence of the CTBDEL process is the cascaded process of dynamic accumulation. However, the current study on non-reflux period of dynamic accumulation process is on the basis of oversimplified assumptive conditions. So the efficient HETP model is proposed to describe the non-reflux period of dynamic accumulation process, which consummates the dynamic accumulation model. The holdup model is setup according to the hydrodynamics of non-reflux period of dynamic accumulation process on the assumption of film flow and vertically cannular flow. The experimental setup is designed to measure the change of dynamic holdup during the course of non-reflux period and the calculation value is consistent with the experimental results, which indicates that the downflow velocity of dynamic holdup becomes smaller with the decrease of dynamic holdup in the column during the course of non-reflux period. Efficient HETP model reflects the change of Efficient HETP of distillation column in the non-reflux process according to the change of dynamic holdup. And Efficient HETP model is nearer to the truth compared to the simplied model.The CTBDEL process is made up of four periods: total reflux period, non-reflux period of filling the drum, non-reflux period of filling the column, and material interchange period between columns. The equilibrium model including efficient HETP model is established to describe the above-mentioned four processes. And the mathematical model is well solved by modified two-point implicit integration method. The simulation results are in good agreement with the experimental data of separation of ethylbenzene-p-xylene system and ethanol-isopropanol alcohol system in the CTBDEL system, which shows the accuracy of the mathematical model.