Vacuum Distillation – continued

The figure provided here illustrates a schematic for a vacuum tower.

Notice the top of the distillation column shown here is connected to a vacuum generation system. This keeps the vessel under the specified vacuum conditions.

In order to further distill the residuum or topped crude from the atmospheric tower at lower temperatures, reduced pressure is required to prevent thermal cracking. The process takes place in one or more vacuum distillation towers.

Heavy residual oil from atmospheric towers is heated in a furnace and introduced into a vacuum tower, as shown. Some of the incoming hot liquid, due to low pressure in the vessel, immediately flashes into vapor. As the vapor moves up along the tower, its temperature drops and side-streams are drawn out as shown.