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Distillation columns are the preferred process to separate two or more products/components. Today, over 40,000 columns are operating worldwide. Each consumes 40% or higher of the total energy consumption or operating cost of the plant (Battisti et al., 2020; Kiss & Smith, 2020). In a typical liquefied petroleum gas plant facility (LPGPF), natural gas consisting of four components can be separated using three conventional columns and three different sequences. The first option is a direct process, in which most volatile components would be recovered and become distillate first. The second option is an indirect process, in which the heaviest component would be recovered and become the bottom product first. The third option is a distributed sequence that would be a mid-split comprising two to three distillation columns (Celenza, 2019; Shahruddin et al., 2017). Each conventional column requires a reboiler and a condenser that intensify energy consumption. Alternatively, Petlyuk columns can be utilized to minimize energy consumption.
The process of distillation involves the separation of a liquid and/or vapor mixture of two or more substances into the component fractions of desired purity by both the application and the removal of heat. Distillation separations are performed for about 95% of all fluid separations within the chemical industry, and this requires an enormous amount of energy. There are different kinds of configurations used to carry out the distillation separation, developed so as to minimize the energy consumption involved in the operation. Reduction of energy consumption provides economic benefits along with a reduction in the emissions associated with the use of fossil fuels (Kooijman & Sorensen, 2022). One such configuration is the thermally coupled distillation system. This was first proposed by Wright, and then the theoretical studies were performed by Tumbalam Gooty et al. (2023). The fully thermally coupled distillation sequence is also referred to as the Petlyuk column.
Although the Petlyuk column was introduced much earlier, half a century ago, it was not commercially implemented until now because of its operation and its design. With respect to the separation of tertiary mixtures, a fully thermally coupled distillation column (FTCDC) requires minimal energy when compared to a conventional distillation system that uses two distillation columns in various compositions of the feed (Zhu et al., 2021) . The energy saving that happens in FTCDC stems from eliminating the remixing of the intermediate component in the first column and then the reduction of mixing effect in the feed stage of the conventional distillation column design (Dünnebier & Pantelides, 1999).
The salient feature of an FTCDC lies in the use of a prefractionator through which a non-sharp split of light, medium, and heavy components into two products happens. The top product of the prefractionator contains light and medium components, while the bottom contains medium and heavy components. These products are then introduced into the main column of the unit by the thermal coupling arrangement of the top and the bottom prefractionator. In the end, the components that are present in the main column are completely separated into three distinct products. One of the major sources of separation inefficiency that is seen in a conventional multicomponent distillation is the remixing effect; for the Petlyuk column arrangement, it is the prefractionator that reduces the remixing, thus resulting in energy savings. This significant reduction in the remixing inefficiency is provided by a non-sharp split in the prefractionator. Also, this prefractionator reduces the mixing that occurs at the feed tray in a conventional distillation unit.
Because distillation columns account for the largest contribution of total energy consumption of the chemical process due to their high heat demand, there is a pressing need for an energy-efficient column design to reduce carbon-dioxide emissions. This will also help reach the climate goals of the chemical industry. The new distillation arrangements such as the dividing-wall columns (DWCs), internally heat-integrated columns, and other multi-effect columns show that there could be a potential for a high reduction of energy consumption in the distillation process.