Retrofitting internal heat integration to a distillation column

The objective of this research was to develop a method of internal heat integration that could be retrofitted to an existing tray column. Hitherto, all designs for heat-integrated distillation columns (RIDiC) have relied on heat transfer through a heat-conducting wall separating a high-pressure rectifying section from a (concentric) lower-pressure stripping section. This method gives rise to major problems in scale-up, which have impeded its adoption in any industrial plant.

We have developed a method in which heat is transferred at each tray, or selected trays, to or from a circulating refrigerant mixture whose temperature glide in evaporation and condensation approximately matches the temperature profile in the rectification and stripping sections of the column respectively. Refrigerant vapour generated by absorption of heat and creation of internal reflux in the rectifying section is compressed externally, and the high-pressure vapour circulated through heat exchangers in the rectifying section, where it condenses and causes internal reboiling. The distillation column and its controls remain unchanged save for the installation of on-tray heat exchangers; the refrigerant circulation system is also self-contained and may be controlled independently.