Fractions of different boiling ranges are drawn off at different points in the tower, or, in some plants, in a series of towers, each one distilling successively heavier fractions.

• 具有不同沸点或沸腾范围的石油成份被抽到分馏塔中的不同部位，（在有些工厂里，这些成分被抽入到许多分馏塔内，每一个分馏塔将对这些成分进行连续分馏）。