Application of Dividing-Wall/Thermally Coupled Distillation Columns: Case Studies of Retrofitting and Debottlenecking a Chemical Plant

Application of Divided-Wall/Thermally Coupled Distillation Columns: Case studies of retrofitting and debottlenecking a chemical plant

Sekhar Babu Mamilla^*a, Antonio Matarredona^a, Roosen Chistoph^a Michael Schleger^a

*Corresponding author. Tel.: +31 6-53376570; e-mail: sekhar.mamilla@SABIC.com

^aSTC-Geleen, The Netherlands, T&I – Feedstocks and Olefins

Distillation is the primary separation process used in the chemical process industry. Although it is often costly and energy intensive, it remains the most commonly used separation technology in the petrochemical and refining industry. Whenever three high-purity fractions have to be separated from a hydrocarbon mixture by conventional fractionation, a direct sequence of two distillation columns are normally employed. To reduce the thermodynamic inefficiency of these systems Dividing-Wall Columns (DWC) can be employed. DWC can also be used to improve the efficiency of extractive distillation problems. The DWC offer an alternative to the conventional (extractive) distillation towers with the possibility of saving both energy and capital costs.

However, DWC is not often the best solution for the existing plants from an economic perspective due to extra investment that is required to replace the current columns.  Nonetheless, comparable energy savings and yield increase can be achieved with lower expenditure by partial or complete thermal and mass integration of the existing columns. This process intensification technique, applying the same principle as in DWC, can be used as a tool for retrofitting and/or debottlenecking the existing plants.

In general, the steam cracking plants that produce ethylene and propylene apply multiple distillation and extractive distillation columns in series to separate different hydrocarbon fractions. This paper explores the possibility of retrofitting and debottlenecking the steam cracking separation train including extractive distillations using thermally coupled distillation columns. Depending on the application, complete or partial thermal couplings can be applied to maximize the energy savings.

This study demonstrate the applicability of thermal coupling or DWC concepts for retrofitting and debottlenecking the current assets with little modification and investment, resulting in 30 - 40 % reboiler and 10 - 25% condenser duty reduction in the columns where it was applied.