(357c) Dynamic Intensification of Ternary Distillation Columns

Process intensification (PI) is a set of innovative design principles that transcend the traditional unit operations framework. One of the key tenets of PI is bringing multiple phenomena into closer physical proximity [1], thereby achieving smaller, safer and more efficient processes. To date, the vast majority of process intensification strategies consist of design changes, focusing on novel devices and constructs that implement the aforementioned tenet in practice. Such devices have clear advantages, in terms of, e.g., reduced transport limitations. However, tight dynamic coupling between different phenomena can also lead to control challenges, such as a reduction in the number of degrees of freedom available for control, as well as a narrower operation window compared to conventional processes [2]. Furthermore, the implementation of such new design also implies major capital expenditures.

In this paper, we will rely on a strategy for process intensification in the temporal domain, which we refer to as “dynamic process intensification (DPI).” DPI seeks to achieve improvements in process efficiency and economics by exploiting and favorably manipulating the interplay of multiple coupled phenomena occurring in a conventional or intensified process [3]. In particular, DPI relies on periodic forcing on the available manipulated variables of a column, imposing a cyclic operating regime that generates the desired product as a mixture of two or more auxiliary products, each having lower energy consumption than the desired product [4,5].

Our research is motivated by the large energy consumption of multi-component (in particular, ternary) distillation columns across the chemical and petrochemical industries. We present a conceptual framework for dynamic intensification. Then, the canonical model of a ternary distillation column separating a mixture of cyclohexane, toluene and m-xylene is used to illustrate the theoretical ideas. We demonstrate that, all other factors being equal, dynamic process intensification results in considerable energy savings compared to steady-state operation of the same column, with the added economic benefit that it requires minimal capital expenditure.

References

[1] Creative Energy. European Roadmap for Process Intensification, Technical report, Creative Energy, 2007.

[2] Schembecker, G.; Tlatlik, S. Process Synthesis for Reactive Separations, Chem. Eng. Process, 42, 179-189, 2003.

[3] Baldea, M.; Edgar, T. F. Dynamic Process Intensification, Dynamic Process Intensification, Current Opinion in Chemical Engineering, 22, 48-53, 2018

[4] Yan, L.; Edgar, T. F.; Baldea, M. Dynamic Process Intensification of Binary Distillation Based on Output Multiplicity, AIChE J, 65 (4), 1162-1172, 2019.

[5] Yan, L.; Edgar, T. F.; Baldea, M. Dynamic Process Intensification of Binary Distillation via Periodic Operation, Ind. Eng. Chem. Res., 2018. https://doi.org/10.1021/acs.iecr.8b04852.