110th Anniversary: Thermal Coupling via Heat Transfer: A Potential Route to Simple Distillation Configurations with Lower Heat Duty

Abstract

Numerous configurations are available for the separation of a multicomponent mixture by distillation; each of which has different energy requirements. We classify heat integration (a valuable method of reducing energy requirements) within distillation into two categories: conventional thermal coupling with mass exchange between columns (TCM) and thermal coupling via heat transfer without mass exchange (TCH). The sharp split distillation configurations, with the lowest number of distillation sections and transfer streams, provide simple distillation configurations but are known to have heat duties that are much higher than the fully thermally coupled (FTC) or Petlyuk configuration. However, for a mixture with four or more components, FTC, having the maximum number of column sections, is a complex configuration to build and operate. Through specific examples of four and five component distillations, we present, for the first time, sharp split configurations, using only one TCH and no TCM, which have a lower heat duty than the corresponding FTC containing only TCM, without requiring substantial pressure changes in the system.

A Simple Criterion for Feasibility of Heat Integration between Distillation Streams Based on Relative Volatilities

“…As first shown in our prior work, this demonstrates that, for certain feed mixtures, TCH can enable simple configurations to outperform the conventional FTC , even when all columns are operated at the same pressure. The HI model, which incorporates the aforementioned TCH calculations, yields the same value of 208 kmol/h for the minimum vapor duty, with the same TCH [ C , BCD ] being predicted.…”

“…50 Yet, as shown in example 1 (Figure 5c), non-FTC configurations can achieve a lower heat duty when TCH is employed. 2,26,40,51,52 Even without pressure changes, TCH can enable FTC to further reduce its heat duty. 53,54 For a subset of TCH, we have empirically observed through numerous case studies that their implementation within configurations could result in the same heat duty as the conventional FTC, but never lower.…”

“…As argued above, heat integration opportunities can substantially alter the total heat duty of a configuration. More specifically, in a prior work, we showed that a simple heat integration can reduce the heat duty of an easy-to-operate configuration below that of a fully thermally coupled (FTC) configuration where all intercolumn transfer streams are present and thermally coupled. Hence, it is imperative that heat integration opportunities be analyzed during this process synthesis stage.…”

“…As such, prior work in the literature has been limited in the automated screening of distillation configurations while exploring the potential for heat integration. Our prior work 2 classified heat integration opportunities in distillation as follows. Thermal coupling via mass transfer (TCM) is the transfer of heat between two locations through mass exchange, while thermal coupling via heat transfer (TCH) is the direct transfer of heat between two locations without mass exchange.…”

“…Our prior work classified heat integration opportunities in distillation as follows. Thermal coupling via mass transfer (TCM) is the transfer of heat between two locations through mass exchange, while thermal coupling via heat transfer (TCH) is the direct transfer of heat between two locations without mass exchange.…”