Controllability Comparison of the Four-Product Petlyuk Dividing Wall Distillation Column Using Temperature Control Schemes

Xing Qian,Rui Liu,Yang Yuan,Shaofeng Wang,Kejin Huang,Haisheng Chen,Liang Zhang

doi:10.3390/pr8010116

Abstract

An effective process intensification strategy based on dividing walls shows promising energy-saving results for distillation processes. The three-product Petlyuk dividing wall distillation columns (DWDCs) are able to save approximately 30% energy in comparison with the traditional distillation columns. Furthermore, the four-product extended Petlyuk DWDC reduces about 50% of operation costs than conventional distillation sequences. Although researchers have extensively studied control schemes for the three-product Petlyuk DWDC, relatively little work has been done on the four-product extended Petlyuk DWDC. This paper studies feasible temperature control schemes containing temperature control scheme (TC), simplified temperature difference control scheme (STDC), and simplified double temperature difference control scheme (SDTDC) for the four-product extended Petlyuk DWDC. STDC and SDTDC are introduced so as to improve the dynamic performances with simple control schemes. All three control schemes are tested against a series of feed compositions and feed rate disturbances. Dynamic performances prove that the proposed STDC and SDTDC schemes are better at handling the inserted feed disturbances. These are very encouraging results for industrialization of the four-product extended Petlyuk DWDC in the future.

Highlights

Dividing wall distillation columns (DWDCs) are effective process intensification strategies that require significantly reduced operation costs and capital costs [1,2]
This paper proposes temperature control scheme (TC), simplified temperature difference control scheme (STDC), and simplified double temperature difference control scheme (SDTDC) for the four-product extended Petlyuk DWDC to separate a liquid alcohol mixture
In the SDTDC scheme, DTDC is adopted in the middle section and prefractionator, while TC is implemented in the main section according to whether the separation systems are adjacent component sharp splits

Summary

Introduction

Dividing wall distillation columns (DWDCs) are effective process intensification strategies that require significantly reduced operation costs and capital costs [1,2]. Though the energy saving ability of DWDC is very considerable, the controllability of the DWDC is very complicated due to excessive loop interactions and highly nonlinear behaviors. Wolff and Skogestad [5] proposed a three-point control scheme and a four-point control scheme to hold the purities of the three-product streams of the Petlyuk DWDC. A composition and temperature cascaded control structure was proposed in order to stabilize the DWDC and save the energy cost. Studied both the three-product and the four-product extended Petlyuk DWDC, and proposed feasible composition control schemes and cascade control schemes. This extended Petlyuk DWDC has extremely complicated topology structure This feature unavoidably causes highly nonlinear behaviors and excessive loop interactions, which is more difficult to operate and control than the three-product Petlyuk DWDC. Dynamic responses are compared and discussed according to the control schemes dynamic performances

Synthesis and Design

Control Schemes

Dynamic Performances and Discussions

Findings

Conclusions