Crude Furnace

ATMOSPHERIC DISTILLATION. CRUDE OIL DISTILLATION (FRACTIONATION). The first step in the refining process is the separation of crude oil into various fractions or straight-run cuts by distillation in atmospheric and vacuum towers. The main fractions or "cuts" obtained have specific boiling-point ranges and can be classified in order of decreasing volatility into gases, light distillates, middle distillates, gas oils, and residuum.
At the refinery, the desalted crude feedstock is preheated using recovered process heat. The feedstock then flows to a direct-fired crude charge heater where it is fed into the vertical distillation column just above the bottom, at pressures slightly above atmospheric and at temperatures ranging from 650° to 700° F (heating crude oil above these temperatures may cause undesirable thermal cracking). All but the heaviest fractions flash into vapor. As the hot vapor rises in the tower, its temperature is reduced. Heavy fuel oil or asphalt residue is taken from the bottom. At successively higher points on the tower, the various major products including lubricating oil, heating oil, kerosene, gasoline, and uncondensed gases (which condense at lower temperatures) are drawn off.
ATMOSPHERIC DISTILLATION PROCESS
Feedstock From Process Typical products . . . . . . To
Crude Desalting Separation Gases . . . . . . . . . . . . . Atmospheric distillation tower
      Naphtas. . . . . . . . . . . . Reforming or treating
Kerosene or distillates . . Treating
Gas oil . . . . . . . . . . . . . Catalytic cracking
Residual . . . . . . . . . . .  Vacuum tower or visbreaker