Crude Oil Refining

What is Crude Oil?

Crude Oil is a mixture of compounds containing hydrocarbons as it found in nature formed due to the processing of decays of woods for millions of years. Compounds present in crude oil are gases, naphtha, gasoline, kerosene, diesel fuel, lubricating oils, heavy oils, and other materials.

The process of removing compounds separately and filtering out such products and other materials is called Refining.

Crude Oil refining:

The process used to refine crude oil is fractional distillation. As we discussed, crude oil consists of different mixture of compounds and they have different levels of boiling points, Fractional distillation do nothing but boil the mixture.

Fractional distillation: Fractional distillation the process of heating a mixture of different boiling points to vaporize and collected at the different levels of distillation columns.

Crude oil is taken from the specific layer of earth crust and brought to the surface through oil wells. As is difficult to process at the oil well areas, crude oil is brought to refineries through pipelines, railway or roadways and refined.

The fractional distillation process starts once the crude enters the refinery with atmospheric distillation then follow fractional distillation. The steam boiler blows heat from the bottom of the distillation column. As the temperatures rise the components of crude that boil at a different point and collected the different levels of the distillation column.

The separation efficiency is a function of the tower’s number of potential plates and the reflux ratio. Reflux is made by condensing part of the overhead vapors of the tower. Reflux ratio is the ratio of vapors condensing back to the still to vapors condensing out of the still (distillate).

The higher the reflux ratio the better the separation of the mixture.

Product of primary distillation:

Vacuum distillation:

Vacuum distillation increases the amount of middle distillates and produces the base stocks and asphalt of lubricating oil.


Residues from atmospheric distillation are the feed to the unit. Reduced pressure is applied in vacuum distillation to prevent fracturing long-chain hydrocarbons in the feed. The feed is first preheated, charged to the vacuum system radiator, and then moved to the vacuum tower in a superheated steam atmosphere.

Products obtained as side streams are vacuum gas oil (VGO), lube oil base stocks, and asphalt.