Crude oil is heated in a furnace to provide the heat required as per crude oil quality. The heated crude oil is separated into different fractions like LPG gases, Naphtha, kerosene, and diesel in a distillation tower called crude column. Lighter fractions move up and heavier down in the column with the lightest (LPG Gas) at the top and the heaviest (Reduced or residue) at the bottom. This separation in the crude column is carried out at pressure near to atmosphere.
For further recovery of valuable products from the residue crude (crude column bottom) is processed in Vacuum Distillation Column. Residue crude is first heated in a furnace and then flashed in a Vacuum Distillation tower under vacuum conditions. Vacuum conditions help to lower the boiling point of the reduced oil and separate into fractions (light vacuum gas oil, heavy vacuum gas oil, and residue) without thermal cracking of the oil.
Vacuum gas oil fractions are sent to the hydrocracking unit for the production of Diesel and other valuable products. Vacuum residue is converted in to fuel oil or bitumen as per oil refinery design.