OVERVIEW

Crude oil as produced in the oil field is a complex mixture of hydrocarbons ranging from methane to asphalt, with varying proportions of paraffins, naphthenes, and aromatics. The objective of crude distillation is to fractionate crude oil into light-end hydrocarbons (C ₁ ?C ₄), naphtha/gasoline, kerosene, diesel, and atmospheric resid. Some of these broad cuts can be marketed directly, while others require further processing in refinery downstream units to make them saleable.

The first processing step in the refinery, after desalting the crude, is separation of crude into a number of fractions by distillation. The distillation is carried out at a pressure slightly above atmospheric. This is necessary for the following considerations:

1. To raise the boiling point of the light-end carbons so that refinery cooling water can be used to condense some of the C ₃ and C ₄ in the overhead condenser.

2. To place the uncondensed gas under sufficient pressure to allow it to flow to the next piece of processing equipment.

3. To allow for pressure drop in the column.

Crude oil is preheated in exchangers and finally vaporized in a fired furnace until approximately the required overhead and sidestream products are vaporized. The furnace effluent is flashed into the crude column flash zone, where the vapor and liquid separate. The liquid leaving the flash zone still contains some distillate components, which are recovered by steam stripping. After steam stripping, the bottom product, also known as reduced crude, is discharged...