The primary distillation unit that processes crude oil (including mixtures of other hydrocarbons) at approximately atmospheric conditions. It includes apipe still for vaporising the crude oil and a fractionation tower for separating the vaporised hydrocarbon components in the crude oil into fractions with different boiling ranges. This is done by continuously vaporising and condensing the components to separate higher oiling point material. The selected boiling ranges are set by the processing scheme,the properties of the crude oil, and the product specifications.