Atmospheric Distillation Unit and Vacuum Distillation Unit

Distillation of crude oil is carried out in two steps, first in an Atmospheric Distillation Unit (ADU) and further processing of the residue from ADU in the Vacuum Distillation Unit (VDU). Atmospheric distillation is carried out to fractionate crude oil into a number of fractions such as lighter gases (C1-C4), Naphtha, Kerosene, Gasoline, Diesel, and Fuel Oil. The residue from the atmospheric tower contains heavy hydrocarbons having boiling points >450oC. The ADU temperature is limited due to the concerns over thermal cracking. Thus, the residue from the bottoms of the Atmospheric Distillation unit can be processed into another distillation column operated under vacuum called a Vacuum Distillation unit (VDU) for further separating of remaining heavy hydrocarbon residues into gas oils and asphalt. The Distillation process (VDU) requires products that can withstand extremely high temperatures and pressures. The VDU can vaporize these components at a temperature lower than that at which thermal cracking will occur.