What is atmospheric distillation and what products does it yield?

Atmospheric distillation (crude distillation unit, CDU) is the primary separation process in a refinery. Crude oil is heated to about 350-400C and fed to a fractionating column operating at near-atmospheric pressure. Products from top to bottom: LPG (C3-C4, <30C), light naphtha (C5-C6, 30-90C), heavy naphtha (C6-C12, 90-180C), kerosene (C10-C16, 180-250C), diesel/gas oil (C14-C20, 250-350C), and atmospheric residue (>350C, sent to vacuum unit). Separation is based on boiling point differences. Typical capacity: 100,000-400,000 barrels per day. CDU is the first major processing unit; all other refinery processes receive feeds from CDU cuts.