Efficient use of energy in distillation sequences

Abstract

In a growing energy consumption world, energy efficiency has become mandatory. Furthermore, the climate emergency has highlighted the necessity to replace fossil fuels with renewable energy sources. Nevertheless, the direct utilization of many of these energy sources requires, at least partially, the electrification of chemical processes. It is not uncommon the claim that distillation must be substituted by other, more efficient separation technologies. The main reason is based on the fact that distillation vaporizes a mixture in the reboiler and then liquifies a vapor stream in the condenser. However, Agrawal and Tumbalam Gooty, have shown that distillation can be much more efficient than what intuition seems to suggest. Different alternatives have been proposed to increase the energy efficiency in distillation. If we are dealing with a single separation we can consider alternatives like multi-effect distillation, and intermediate heat exchangers either in the rectifying or in the stripping section, pre-fractionations, internally heat integrated distillation columns (HIDiC) and heat pump assisted distillation (Vapor recompression, Mechanical or Thermal Vapor recompression -VRC- or bottom flashing arrangements). In multicomponent distillation, the number of alternatives increases because we can integrate the alternatives for heat integration between different columns with those of a single column and the alternatives for column sequencing inherent in multi-component distillation. In this work, we show that the systematic and simultaneous implementation of some heat integration alternatives like direct reboiler condenser heat exchange, implementation of vapor (re)compression cycles, leverage of heat in high-pressure steam utilities at lower pressure/temperatures, multiple effect distillation, etc. can eventually produce considerably reductions in energy and total annualized cost and at the same time, contribute to the electrification of chemical plants. While none of these alternatives is new, they are rarely simultaneously implemented in a distillation sequence, however, we show that there is great potential in the synergic effects of implementing simultaneously some of them.