Division BAT 29: In order to use energy efficiently when using distillation, BAT is to use one or a combination of the techniques given below.
United Kingdom
| Technique | Description | Applicability | |
|---|---|---|---|
| a. | Distillation optimisation | For each distillation column, the number of trays, reflux ratio, feed location and, for extractive distillations, the solvents to feed ratio are optimised | Applicability to existing units may be restricted by design, space availability and/or operational constraints |
| b. | Recovery of heat from column overhead gaseous stream | Reuse condensation heat from the toluene and the xylene distillation column to supply heat elsewhere in the installation | |
| c. | Single extractive distillation column | In a conventional extractive distillation system, the separation would require a sequence of two separation steps (i.e. main distillation column with side column or stripper). In a single extractive distillation column, the separation of the solvent is carried out in a smaller distillation column that is incorporated into the column shell of the first column | Only applicable to new plants or major plant upgrades. Applicability may be restricted for smaller capacity units as operability may be constrained by combining a number of operations into one piece of equipment |
| d. | Distillation column with a dividing wall | In a conventional distillation system, the separation of a three-component mixture into its pure fractions requires a direct sequence of at least two distillation columns (or main columns with side columns). With a dividing wall column, separation can be carried out in just one piece of apparatus | |
| e. | Thermally coupled distillation | If distillation is carried out in two columns, energy flows in both columns can be coupled. The steam from the top of the first column is fed to a heat exchanger at the base of the second column | Only applicable to new plants or major plant upgrades. Applicability depends on the set-up of the distillation columns and process conditions, e.g. working pressure |