Comparison of Controllability Features of Extractive and Pressure Swing Distillations on the Example of Tetrahydrofuran Dewatering.

Jonathan Wavomba Mtogo,Péter Mizsey,Andras J Toth,Agnes Szanyi

doi:10.1021/acsomega.1c04606

Jonathan Wavomba Mtogo, Péter Mizsey + Show 2 more

Open Access

https://doi.org/10.1021/acsomega.1c04606

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Abstract

The controllability study is an integral part of chemical process design. In this work, the controllability of two special distillation techniques, extractive distillation and pressure swing distillation, designed for the separation of azeotropic mixtures is investigated with dynamic tools. The control design interface of Aspen Plus and Matlab are applied for the modeling and evaluation of the two systems. Dynamic controllability indices are determined and aggregated in a desirability function. The results are compared to obtain efficient help for process design activity. The pressure swing distillation shows significantly better controllability features than the extractive distillation. The reason can be the fact that in the case of the extractive distillation, a third compound, the extractive agent, is added to the system to carry out the separation, therefore making the system more complex. As far as the selection of manipulated variables is concerned, in the case of the extractive distillation, the reflux flows should be preferred to the reflux ratios but in the case of the pressure swing distillation, the reboiler heat loads are preferred to the reflux ratios since those are closer to the controlled compositions. Both separation systems show worse controllability features if the product purity requirement is approaching to the pure products, that is, close to 100%. Although the energy consumption of the pressure swing distillation is higher than that of the extractive distillation, it has the inherent feature that it can be automatically heat integrated due to a column operated at high pressure and, as a consequence, higher temperatures.

Highlights

Tetrahydrofuran (THF) is an excellent solvent and it is commonly utilized within the chemical industry
For the extractive distillation (ED) and pressure swing distillation (PSD) processes, we investigate the dynamics and stability by designing control strategies to effectively handle the feed rate and composition disturbances with a focus on maintaining product purity
The angular frequency is computed from the time constant, which is derived from load rejection analysis of the individual systems

Summary

INTRODUCTION

Tetrahydrofuran (THF) is an excellent solvent and it is commonly utilized within the chemical industry. An experimental work has been used to compare various entrainers for THF−water separation.[7] For the separation of an equimolar THF−water mixture, Ghuge et al.[8] simulated both extractive distillation and pressure swing distillation Their works have been on selection of the suitable process on the basis of the total annual cost (TAC). The rate of feed flow and its composition always meet disturbance in the distillation processes.[18] A good technology ought to have the capability to cope with the disturbance to a certain extent Based on their steady-state findings, various researchers have investigated the dynamic control of EDs and PSDs.[19−21] Luyben’s work detailed the dynamic control of the PSD with heat integration for separating a THF−water azeotrope.[22] These researchers have presented control structures and tuning procedures for use in Aspen Plus Dynamics for the processes.

STEADY-STATE DESIGNS

CONTROLLABILITY ANALYSIS

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES