Atmospheric distillation involves the physical separation of hydrocarbon components into fractions or intermediates of a specified boiling temperature range by distillation and steam stripping. Crude is preheated to achieve partial vaporization (liquid and vapor) following which it is then fed to the atmospheric fractionator at a temperature of 340°C to 400°C.

The crude feed is then separated into several petroleum fractions within the atmospheric fractionator where several liquid side stream fractions are withdrawn from the fractionator at different sections (i.e., trays) of the fractionator. This is optimised through a series of side cut steam strippers. A naphtha and lighter stream are taken from the tower overhead, where it is condensed. The non-condensable light ends are treated and/or recovered in other refinery units. Atmospheric residue recovered at the bottom of the fractionator is fed to the Vacuum Distillation Unit (VDU).