The configuration of a column is defined by the number of column sections, the position of the feed charge and the points from which products are withdrawn. There are four main types of column configurations. The conventional column is more commonly known as the regular column. It has been around for many centuries, and as far as the author is aware, it is the one used exclusively in current industrial practice. Unconventional columns were proposed by Robinson and Gilliland in 1950. These include the inverted, middle vessel and multivessel columns. The diferent column configurations are defined below:
Middle vessel column: the feed may be charged to a vessel located between two column sections and the products may be withdrawn simultaneously from the reflux drum (lightest first) and the reboiler drum (heaviest first), as shown in Figure c.
Multivessel column: comprises more than one column section ; the feed may be distributed among the reflux drum, side vessels and reboiler drum, and the products may either be collected in these vessels or be withdrawn into accumulators, as shown in Figure d. This column is also referred to as a multi-effect column since multiple products are produced simultaneously.